WO2024251828A1 - Procédé de production d'un matériau biocéramique - Google Patents

Procédé de production d'un matériau biocéramique Download PDF

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Publication number
WO2024251828A1
WO2024251828A1 PCT/EP2024/065488 EP2024065488W WO2024251828A1 WO 2024251828 A1 WO2024251828 A1 WO 2024251828A1 EP 2024065488 W EP2024065488 W EP 2024065488W WO 2024251828 A1 WO2024251828 A1 WO 2024251828A1
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calcium carbonate
sintering
ceramic body
carbon dioxide
applications
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Inventor
Fabrizio ORLANDO
Gabriela MELO RODRIGUEZ
Franck Baradel
Laura DE MIGUEL
Joachim Schoelkopf
Quentin COURRIER
Gregory HERIN
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Omya International AG
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Omya International AG
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/447—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on phosphates, e.g. hydroxyapatite
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
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    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
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    • C04B2235/442—Carbonates
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    • C04B2235/444—Halide containing anions, e.g. bromide, iodate, chlorite
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    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
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    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
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    • C04B2235/963—Surface properties, e.g. surface roughness

Definitions

  • the present invention relates to a method for manufacturing a ceramic body from a composition comprising surface-reacted calcium carbonate, a ceramic body obtainable from said method, and the use of said ceramic body.
  • Bioceramic materials based on calcium phosphates are widely used in medical and dental applications. Hydroxyapatite is one of the most commonly used bioceramic materials because of its excellent biocompatibility properties with the main mineral phase of bone and teeth in structure and chemical composition. Such synthetic bone substitute or scaffold materials typically focus on porous ceramics, which provide an increased surface area that encourages osseointegration, involving cell colonization and revascularisation.
  • Bioceramic materials are typically produced from powders by compacting the powder into so-called “green bodies” which are eventually sintered to obtain the final ceramic.
  • hydroxyapatite typically requires the addition of a binder in order to provide sufficient compactability for forming a green body.
  • the high temperatures applied during sintering can lead to a conversion of the hydroxyapatite.
  • EP3628342 A1 discloses two-phase composites comprising a matrix phase comprising a sintered calcium phosphate component and a discontinuous phase within said matrix phase comprising a plurality of elongated carbonate inclusions.
  • US20040099998 A1 relates to a method for manufacturing a sintered compact, comprising the steps of: molding a green compact by compacting hydroxyapatite powder; and sintering the green compact in an oxygen-containing atmosphere, in which the partial pressure of oxygen is higher than that in an atmospheric air, at a temperature in the range of 925 to 1300°C to obtain a sintered compact.
  • WO2022162023 A1 describes the production of carrier particles with secondary internal structures comprising inter alia the steps of (a) combining carrier material with a template material, wherein the carrier material forms a primary structure around the template material, (b) transforming the template material, and (c) removing the transformed template material. Thereby, hollow carrier particle are formed.
  • said document does not disclose a ceramic body which is obtained from forming surface-reacted calcium carbonate into a green body and sintering said green body.
  • a method for making an implant is described in W09605038 A1 , which involves the steps of forming a mixture of calcium phosphate and a polymer binder, and selectively fusing the polymer binder to form an implant. Therefore, there is a continuous need in the art for alternative methods for producing bioceramic materials, and in particular, for methods that allow a control of the total porosity and pore size distribution within the bioceramic.
  • the method provides the possibility to control the mineralogical composition formed after sintering. Furthermore, it would be desirable that the method enables an easy formation of a green body and does not necessarily require the presence of a binder.
  • a method for manufacturing a ceramic body comprising the following steps: a) providing a mineral composition comprising surface-reacted calcium carbonate, wherein the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more HsO + ion donors, wherein the carbon dioxide is formed in situ by the HaO + ion donors treatment and/or is supplied from an external source, b) forming the mineral composition of step a) into a green body, and c) sintering the green body formed in step b) to form a ceramic body.
  • a ceramic body obtainable by a method according to the present invention is provided.
  • a ceramic body according to the present invention in medical applications, biomedical implant applications, bone replacement applications, pharmaceutical applications, wicking applications, tableware applications, tile applications, brick applications, sanitary ware applications, fluid treatment, analytical applications, heterogenic catalyst applications, or cell culture applications is provided.
  • the mineral composition comprises the surface-reacted calcium carbonate in an amount of at least 10 wt.-%, preferably at least 20 wt.-%, more preferably at least 50 wt.-%, even more preferably at least 80 wt.-%, based on the total weight of the mineral composition, and most preferably the mineral composition consists of surface-reacted calcium carbonate.
  • the surface-reacted calcium carbonate is in form of particles having a volume determined median particle size cfeo from 1 to 75 pm, preferably from 2 to 50 pm, more preferably from 3 to 40 pm, even more preferably from 4 to 30 pm, and most preferably from 5 to 15 pm, and/or a volume determined top cut particle size da from 2 to 150 pm, preferably from 4 to 100 pm, more preferably from 6 to 80 pm, even more preferably from 8 to 60 pm, and most preferably from 10 to 30 pm, and/or a specific surface area in the range from 15 to 200 m 2 /g, preferably from 27 to 180 m 2 /g, more preferably from 30 m 2 /g to 160 m 2 /g, even more preferably from 45 m 2 /g to 150 m 2 /g, and most preferably from 48 m 2 /g to 140 m 2 /g, measured using nitrogen and the BET method according to ISO 9277:2010.
  • the sintering step c) is carried out in an atmosphere comprising at least 50 vol.-% carbon dioxide, preferably at least 80 vol.-% carbon dioxide, more preferably at least 90 vol.-%, even more preferably at least 95 vol.-%, and most preferably in an atmosphere consisting of carbon dioxide, or the sintering step c) is carried out in an atmosphere comprising carbon dioxide and water, preferably in an atmosphere having a CO2/H2O volume ratio from 99.9:0.1 to 1 :1 , or the sintering step c) is carried out in an inert atmosphere, preferably consisting of helium, nitrogen, argon, or mixtures thereof.
  • the sintering step c) comprises the steps of c1) sintering the green body formed in step b) in an air atmosphere, and c2) sintering the sintered green body obtained in step c1) in an atmosphere comprising at least 50 vol.-% carbon dioxide, preferably at least 80 vol.-% carbon dioxide, more preferably at least 90 vol.-%, even more preferably at least 95 vol.-% , and most preferably in an atmosphere consisting of carbon dioxide, or in an atmosphere comprising carbon dioxide and water, preferably in an atmosphere having a CO2/H2O volume ratio from 99.9:0.1 to 1 :1 .
  • the sintering step c) is carried out at a temperature of at least 850°C, preferably from 900°C to 1400°C, more preferably from 950 to 1300°C, and most preferably from 1000 to 1200°C, and/or the sintering step c) is carried out for at least 30 min, preferably at least 1 h, more preferably at least 2 h, even more preferably at least 3 h, and most preferably at least 5 h.
  • the mineral composition of step a) further comprises a porogen and/or a porogen is added before and/or during step b), preferably the mineral composition comprises the porogen in an amount from 1 to 80 wt.-%, more preferably in an amount from 5 to 70 wt.-%, even more preferably in an amount from 10 to 65 wt.-%, and most preferably in an amount from 15 to 60 wt.-%, based on the total weight of the mineral composition.
  • the porogen is in form of spheres, granules, fibers, beads, or mixtures thereof, and preferably the porogen is in form of spheres having a volume determined median particle size dso from 5 to 500 pm, preferably from 10 to 400 pm, and most preferably from 20 to 300 pm.
  • the porogen is selected from the group consisting of organic polymers, polysaccharides, inorganic salts, waxes, naphthalene, or mixtures thereof, preferably consisting of polyethylene, polypropylene, sodium hydroxide, cellulose, starch, paraffin wax, or mixtures thereof, and most preferably the porogen is polyethylene and/or cellulose.
  • the mineral composition of step a) is compacted and/or sieved before step b) and/or a lubricant is added before and/or during step b).
  • the green body formed in step b) is a tablet, a granule, a shaped catalyst body, an implant, a flat substrate, a disc, a part of a watch housing, or a workpiece.
  • the method does not comprise a step of adding a binding agent to the composition provided in step a).
  • the mineral composition of step a) comprises a binding agent and/or a binding agent is added before and/or during step b), preferably the binding agent is selected from the group consisting of polyvinyl alcohol, methyl cellulose, polyvinyl butyral, polyethylene glycol (PEG), ethylene-vinyl acetate copolymers, polylactic acid (PLA), poly-DL- lactide (PDLLA), polyglycolic acid (PGA), poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), polyurethane (PU), poly(methyl methacrylate) (PMMA), polydioxanone (PDO), polyhydroxyalkanoates (PHA), polypropylene fumarate) (PPF), polyether ether ketone (PEEK) and their copolymers, and mixtures thereof.
  • the binding agent is selected from the group consisting of polyvinyl alcohol, methyl cellulose, polyvinyl butyral, polyethylene glycol (PEG),
  • the ceramic body comprises at least one water-insoluble calcium salt selected from tricalcium phosphate, tetracalcium phosphate, and/or apatitic calcium phosphate, preferably selected from the group consisting of hydroxylapatite, substituted hydroxylapatite, octacalcium phosphate, and mixtures thereof, more preferably selected from the group consisting of hydroxylapatite, fluoroapatite, carboxyapatite, and mixtures thereof, and most preferably hydroxylapatite, calcium oxide, and optionally calcium carbonate, preferably calcite.
  • apatitic calcium phosphate preferably selected from the group consisting of hydroxylapatite, substituted hydroxylapatite, octacalcium phosphate, and mixtures thereof, more preferably selected from the group consisting of hydroxylapatite, fluoroapatite, carboxyapatite, and mixtures thereof, and most preferably hydroxylapatite, calcium oxide, and optionally
  • the ceramic body is non-porous having a porosity of less than 20%, preferably less than 15%, more preferably less than 10%, and most preferably less than 5 %, determined by mercury porosimetry measurement, and/or a bulk density of at least 2.5 g/cm 3 , preferably at least 2.6 g/cm 3 , more preferably at least 2.7 g/cm 3 , and most preferably at least 2.8 g/cm 3 .
  • the ceramic body is porous having a porosity of at least 20%, preferably at least 30%, more preferably at least 40%, still more preferably at least 50%, even more preferably at least 60%, and most preferably at least 70%, determined by mercury porosimetry measurement.
  • an “acid” is defined as Bnansted-Lowry acid, that is to say, it is an HaO + ion provider.
  • the term “free acid” refers only to those acids being in the fully protonated form (e.g., H2SO4).
  • An “acidic salt” is defined as an HaO + ion-provider, e.g., a hydrogencontaining salt, which is partially neutralised by an electropositive element.
  • a “salt” is defined as an electrically neutral ionic compound formed from anions and cations.
  • a “partially crystalline salt” is defined as a salt that, on XRD analysis, presents an essentially discrete diffraction pattern.
  • pK a is the symbol representing the acid dissociation constant associated with a given ionisable hydrogen in a given acid, and is indicative of the natural degree of dissociation of this hydrogen from this acid at equilibrium in water at a given temperature.
  • Such pK a values may be found in reference textbooks such as Harris, D. C. “Quantitative Chemical Analysis: 3 rd Edition”, 1991 , W.H. Freeman & Co. (USA), ISBN 0-7167-2170-8.
  • a “dry” material e.g., dry surface-reacted calcium carbonate
  • dry material may be defined by its total moisture content which, unless specified otherwise, is less than or equal to 5.0 wt.-%, preferably less than or equal to 1 .0 wt.-%, more preferably less than or equal to 0.5 wt.-%, even more preferably less than or equal to 0.2 wt.-%, and most preferably between 0.03 and 0.07 wt.-%, based on the total weight of the dried material.
  • total moisture content refers to the percentage of moisture (i.e. water) which may be desorbed from a sample upon heating to 220 °C.
  • Natural ground calcium carbonate in the meaning of the present invention is a calcium carbonate obtained from natural sources, such as limestone, marble, or chalk, and processed through a wet and/or dry treatment such as grinding, screening and/or fractionating, for example, by a cyclone or classifier.
  • Precipitated calcium carbonate in the meaning of the present invention is a synthesised material, obtained by precipitation following reaction of carbon dioxide and lime in an aqueous, semi-dry or humid environment or by precipitation of a calcium and carbonate ion source in water.
  • PCC may be in the vateritic, calcitic or aragonitic crystal form. PCCs are described, for example, in EP2447213 A1 , EP2524898 A1 , EP2371766 A1 , EP1712597 A1 , EP1712523 A1 , or WO2013142473 A1.
  • surface-reacted in the meaning of the present application shall be used to indicate that a material has been subjected to a process comprising partial dissolution of said material upon treatment with an HaO + ion donor (e.g., by use of water-soluble free acids and/or acidic salts) in aqueous environment followed by a crystallization process which may occur in the absence or presence of further crystallization additives.
  • an HaO + ion donor e.g., by use of water-soluble free acids and/or acidic salts
  • H 3 O + ion donor in the context of the present invention is a Bnansted acid and/or an acid salt, i.e. a salt containing an acidic hydrogen.
  • volume-based median particle size dso was evaluated using a Malvern Mastersizer 2000 or 3000 Laser Diffraction System.
  • the dso or dgs value measured using a Malvern Mastersizer 2000 or 3000 Laser Diffraction System, indicates a diameter value such that 50 % or 98 % by volume, respectively, of the particles have a diameter of less than this value.
  • the raw data obtained by the measurement are analysed using the Mie theory, with a particle refractive index of 1 .57 and an absorption index of 0.005.
  • the “particle size” of particulate materials, other than surface-reacted calcium carbonate and calcium phosphate, herein is described by its weight-based distribution of particle sizes dx.
  • the value dx represents the diameter relative to which x % by weight of the particles have diameters less than dx.
  • the d2o value is the particle size at which 20 wt.-% of all particles are smaller than that particle size.
  • the dso value is thus the weight median particle size, i.e. 50 wt.-% of all particles are smaller than this particle size.
  • the particle size is specified as weight median particle size d5o(wt) unless indicated otherwise.
  • Particle sizes were determined by using a SedigraphTM 5100 instrument or SedigraphTM 5120 instrument of Micromeritics Instrument Corporation. The method and the instrument are known to the skilled person and are commonly used to determine the particle size of fillers and pigments. The measurements were carried out in an aqueous solution of 0.1 wt.-% Na4P2O?.
  • the term “pore” is to be understood as describing the space that is found between and/or within particles, i.e. that is formed by the particles as they pack together under nearest neighbor contact (inter-particle pores), such as in a powder or a compact and/or the void space within porous particles (intra-particle pores), and that allows the passage of liquids under pressure when saturated by the liquid and/or supports absorption of surface wetting liquids.
  • the specific pore volume is measured using a mercury intrusion porosimetry measurement using a Micromeritics Autopore V 9620 mercury porosimeter having a maximum applied pressure of mercury 414 MPa (60 000 psi), equivalent to a Laplace throat diameter of 0.004 pm ( ⁇ nm).
  • the equilibration time used at each pressure step is 20 seconds.
  • the sample material is sealed in a 3 cm 3 chamber powder penetrometer for analysis.
  • the data are corrected for mercury compression, penetrometer expansion and sample material compression using the software Pore-Comp (Gane, P.A.C., Kettle, J.P., Matthews, G.P. and Ridgway, C.J., "Void Space Structure of Compressible Polymer Spheres and Consolidated Calcium Carbonate Paper-Coating Formulations", Industrial and Engineering Chemistry Research, 35(5), 1996, p. 1753-1764.).
  • the total pore volume seen in the cumulative intrusion data can be separated into two regions with the intrusion data from 214 pm down to about 1 - 4 pm showing the coarse packing of the sample between any agglomerate structures contributing strongly. Below these diameters lies the fine interparticle packing of the particles themselves. If they also have intra-particle pores, then this region appears bimodal, and by taking the specific pore volume intruded by mercury into pores finer than the modal turning point, i.e. finer than the bimodal point of inflection, we thus define the specific intra- particle pore volume. The sum of these three regions gives the total overall pore volume of the powder, but depends strongly on the original sample compaction/settling of the powder at the coarse pore end of the distribution.
  • the “specific surface area” (expressed in m 2 /g) of a material as used throughout the present document can be determined by the Brunauer Emmett Teller (BET) method with nitrogen as adsorbing gas and by use of an ASAP 2460 instrument from Micromeritics. The method is well known to the skilled person and defined in ISO 9277:2010. Samples are conditioned at 120°C under vacuum for a period of 60 min prior to measurement. The total surface area (in m 2 ) of said material can be obtained by multiplication of the specific surface area (in m 2 /g) and the mass (in g) of the material.
  • BET Brunauer Emmett Teller
  • a “solution” as referred to herein is understood to be a single phase mixture of a specific solvent and a specific solute, for example a single phase mixture of a water-soluble salt and water.
  • the term “dissolved” as used herein thus refers to the physical state of a solute in a solution.
  • a “suspension” or “slurry” in the meaning of the present invention comprises undissolved solids and water, and optionally further additives, and usually contains large amounts of solids and, thus, is more viscous and can be of higher density than the liquid from which it is formed.
  • aqueous suspension refers to a system, wherein the liquid phase comprises, preferably consists of, water. However, said term does not exclude that the liquid phase of the aqueous suspension comprises minor amounts of at least one water-miscible organic solvent selected from the group comprising methanol, ethanol, acetone, acetonitrile, tetrahydrofuran and mixtures thereof.
  • the liquid phase of the aqueous suspension comprises the at least one water-miscible organic solvent in an amount of from 0.1 to 40.0 wt.-% preferably from 0.1 to 30.0 wt.-%, more preferably from 0.1 to 20.0 wt.-% and most preferably from 0.1 to 10.0 wt.-%, based on the total weight of the liquid phase of the aqueous suspension.
  • the liquid phase of the aqueous suspension consists of water.
  • viscosity or “Brookfield viscosity” refers to Brookfield viscosity.
  • the Brookfield viscosity is for this purpose measured by a Brookfield DV-II+ Pro viscometer at 25 °C ⁇ 1 °C at 100 rpm using an appropriate spindle of the Brookfield RV-spindle set and is specified in mPa s. Based on his technical knowledge, the skilled person will select a spindle from the Brookfield RV-spindle set which is suitable for the viscosity range to be measured.
  • the spindle number 3 may be used, for a viscosity range between 400 and 1 600 mPa s the spindle number 4 may be used, for a viscosity range between 800 and 3200 mPa s the spindle number 5 may be used, for a viscosity range between 1 000 and 2 000 000 mPa s the spindle number 6 may be used, and for a viscosity range between 4 000 and 8 000 000 mPa s the spindle number 7 may be used.
  • a method for manufacturing a ceramic body comprising the steps of: a) providing a mineral composition comprising surface- reacted calcium carbonate, b) forming the mineral composition of step a) into a green body, and c) sintering the green body formed in step b) to form a ceramic body.
  • the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more HsO + ion donors, wherein the carbon dioxide is formed in situ by the HsO + ion donors treatment and/or is supplied from an external source.
  • a mineral composition comprising surface-reacted calcium carbonate
  • the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more HsO + ion donors, wherein the carbon dioxide is formed in situ by the HsO + ion donors treatment and/or is supplied from an external source.
  • the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more HsO + ion donors, wherein the carbon dioxide is formed in situ by the HaO + ion donors treatment and/or is supplied from an external source.
  • a HsO + ion donor in the context of the present invention is a Bnansted acid and/or an acid salt.
  • the surface-reacted calcium carbonate is obtained by a process comprising the steps of: (a) providing a suspension of natural or precipitated calcium carbonate, (b) adding at least one acid having a pK a value of 0 or less at 20°C or having a pK a value from 0 to 2.5 at 20°C to the suspension of step (a), and (c) treating the suspension of step (a) with carbon dioxide before, during or after step (b).
  • the surface-reacted calcium carbonate is obtained by a process comprising the steps of: (A) providing a natural or precipitated calcium carbonate, (B) providing at least one water-soluble acid, (C) providing gaseous CO2, (D) contacting said natural or precipitated calcium carbonate of step (A) with the at least one acid of step (B) and with the CO2 of step (C), characterised in that: (i) the at least one acid of step B) has a pK a of greater than 2.5 and less than or equal to 7 at 20°C, associated with the ionisation of its first available hydrogen, and a corresponding anion is formed on loss of this first available hydrogen capable of forming a water-soluble calcium salt, and (ii) following contacting the at least one acid with natural or precipitated calcium carbonate, at least one water-soluble salt, which in the case of a hydrogen-containing salt has a pK a of greater than 7 at 20°C, associated with the ionisation of the first available hydrogen, and the salt ani
  • Natural ground calcium carbonate preferably is selected from calcium carbonate containing minerals selected from the group comprising marble, chalk, limestone and mixtures thereof. Natural calcium carbonate may comprise further naturally occurring components such as alumino silicate etc.
  • the grinding of natural ground calcium carbonate may be a dry or wet grinding step and may be carried out with any conventional grinding device, for example, under conditions such that comminution predominantly results from impacts with a secondary body, i.e. in one or more of: a ball mill, a rod mill, a vibrating mill, a roll crusher, a centrifugal impact mill, a vertical bead mill, an attrition mill, a pin mill, a hammer mill, a pulveriser, a shredder, a de-clumper, a knife cutter, or other such equipment known to the skilled man.
  • a secondary body i.e. in one or more of: a ball mill, a rod mill, a vibrating mill, a roll crusher, a centrifugal impact mill, a vertical bead mill, an attrition mill, a pin mill, a hammer mill, a pulveriser, a shredder, a de-clumper, a knife cutter, or other
  • the grinding step may be performed under conditions such that autogenous grinding takes place and/or by horizontal ball milling, and/or other such processes known to the skilled man.
  • the wet processed ground calcium carbonate containing mineral material thus obtained may be washed and dewatered by well-known processes, e.g. by flocculation, filtration or forced evaporation prior to drying.
  • the subsequent step of drying (if necessary) may be carried out in a single step such as spray drying, or in at least two steps. It is also common that such a mineral material undergoes a beneficiation step (such as a flotation, bleaching or magnetic separation step) to remove impurities.
  • Precipitated calcium carbonate in the meaning of the present invention is a synthesized material, generally obtained by precipitation following reaction of carbon dioxide and calcium hydroxide in an aqueous environment or by precipitation of calcium and carbonate ions, for example CaCh and Na2COs, out of solution. Further possible ways of producing PCC are the lime soda process, or the Solvay process in which PCC is a by-product of ammonia production. Precipitated calcium carbonate exists in three primary crystalline forms: calcite, aragonite and vaterite, and there are many different polymorphs (crystal habits) for each of these crystalline forms.
  • Calcite has a trigonal structure with typical crystal habits such as scalenohedral (S-PCC), rhombohedral (R- PCC), hexagonal prismatic, pinacoidal, colloidal (C-PCC), cubic, and prismatic (P-PCC).
  • Aragonite is an orthorhombic structure with typical crystal habits of twinned hexagonal prismatic crystals, as well as a diverse assortment of thin elongated prismatic, curved bladed, steep pyramidal, chisel shaped crystals, branching tree, and coral or worm-like form.
  • Vaterite belongs to the hexagonal crystal system.
  • the obtained PCC slurry can be mechanically dewatered and dried.
  • the precipitated calcium carbonate is precipitated calcium carbonate, preferably comprising aragonitic, vateritic or calcitic mineralogical crystal forms or mixtures thereof.
  • Precipitated calcium carbonate may be ground prior to the treatment with carbon dioxide and at least one HaO + ion donor by the same means as used for grinding natural calcium carbonate as described above.
  • the natural or precipitated calcium carbonate is in form of particles having a weight median particle size cfeo of 0.05 to 10.0 pm, preferably 0.2 to 5.0 pm, more preferably 0.4 to 3.0 pm, most preferably 0.6 to 1 .2 pm, especially 0.7 pm.
  • the natural or precipitated calcium carbonate is in form of particles having a top cut particle size da of 0.15 to 55 pm, preferably 1 to 40 pm, more preferably 2 to 25 pm, most preferably 3 to 15 pm, especially 4 pm.
  • the natural and/or precipitated calcium carbonate may be used dry or suspended in water.
  • a corresponding slurry has a content of natural or precipitated calcium carbonate within the range of 1 wt.-% to 90 wt.-%, more preferably 3 wt.-% to 60 wt.-%, even more preferably 5 wt.-% to 40 wt.-%, and most preferably 10 wt.-% to 25 wt.-% based on the weight of the slurry.
  • the one or more HaO + ion donor used for the preparation of surface reacted calcium carbonate may be any strong acid, medium-strong acid, or weak acid, or mixtures thereof, generating HsO + ions under the preparation conditions.
  • the at least one HsO + ion donor can also be an acidic salt, generating HsO + ions under the preparation conditions.
  • the at least one HsO + ion donor is a strong acid having a pK a of 0 or less at 20°C.
  • the at least one HsO + ion donor is a medium-strong acid having a pK a value from 0 to 2.5 at 20°C. If the pK a at 20°C is 0 or less, the acid is preferably selected from sulphuric acid, hydrochloric acid, or mixtures thereof. If the pK a at 20°C is from 0 to 2.5, the HaO + ion donor is preferably selected from H2SO3, H3 O4, oxalic acid, or mixtures thereof.
  • the at least one HsO + ion donor can also be an acidic salt, for example, HSO4 or H2 O4; being at least partially neutralized by a corresponding cation such as Li + , Na + or K + , or HPC 2- , being at least partially neutralised by a corresponding cation such as Li + , Na + , K + , Mg 2+ or Ca 2+ .
  • the at least one HsO + ion donor can also be a mixture of one or more acids and one or more acidic salts.
  • the at least one HsO + ion donor is a weak acid having a pK a value of greater than 2.5 and less than or equal to 7, when measured at 20°C, associated with the ionisation of the first available hydrogen, and having a corresponding anion, which is capable of forming water-soluble calcium salts.
  • at least one water-soluble salt which in the case of a hydrogen-containing salt has a pK a of greater than 7, when measured at 20°C, associated with the ionisation of the first available hydrogen, and the salt anion of which is capable of forming waterinsoluble calcium salts, is additionally provided.
  • the weak acid has a pK a value from greater than 2.5 to 5 at 20°C, and more preferably the weak acid is selected from the group consisting of acetic acid, formic acid, propanoic acid, citric acid, and mixtures thereof.
  • Exemplary cations of said water-soluble salt are selected from the group consisting of potassium, sodium, lithium and mixtures thereof. In a more preferred embodiment, said cation is sodium or potassium.
  • Exemplary anions of said water-soluble salt are selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, oxalate, silicate, mixtures thereof and hydrates thereof.
  • said anion is selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, mixtures thereof and hydrates thereof. In a most preferred embodiment, said anion is selected from the group consisting of dihydrogen phosphate, monohydrogen phosphate, mixtures thereof and hydrates thereof.
  • Water-soluble salt addition may be performed dropwise or in one step. In the case of drop wise addition, this addition preferably takes place within a time period of 10 minutes. It is more preferred to add said salt in one step.
  • the at least one HsO + ion donor is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid, and mixtures thereof.
  • the at least one HsO + ion donor is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, oxalic acid, H2PO4; being at least partially neutralised by a corresponding cation such as Li + , Na + or K + , HPC 2- , being at least partially neutralised by a corresponding cation such as Li + , Na + , K + , Mg 2+ , or Ca 2+ and mixtures thereof, more preferably the at least one acid is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, oxalic acid, or mixtures thereof, and most preferably, the at least one HsO + ion donor is phosphoric acid.
  • the one or more HaO + ion donor can be added to the suspension as a concentrated solution or a more diluted solution.
  • the molar ratio of the HaO + ion donor to the natural or precipitated calcium carbonate is from 0.01 to 4, more preferably from 0.02 to 2, even more preferably 0.05 to 1 and most preferably 0.1 to 0.58.
  • the natural or precipitated calcium carbonate is treated with carbon dioxide. If a strong acid such as sulphuric acid or hydrochloric acid is used for the HaO + ion donor treatment of the natural or precipitated calcium carbonate, the carbon dioxide is automatically formed. Alternatively or additionally, the carbon dioxide can be supplied from an external source.
  • HsO + ion donor treatment and treatment with carbon dioxide can be carried out simultaneously which is the case when a strong or medium-strong acid is used. It is also possible to carry out HsO + ion donor treatment first, e.g. with a medium strong acid having a pK a in the range of 0 to 2.5 at 20°C, wherein carbon dioxide is formed in situ, and thus, the carbon dioxide treatment will automatically be carried out simultaneously with the HaO + ion donor treatment, followed by the additional treatment with carbon dioxide supplied from an external source.
  • the HaO + ion donor treatment step and/or the carbon dioxide treatment step are repeated at least once, more preferably several times.
  • the at least one HaO + ion donor is added over a time period of at least about 5 min, preferably at least about 10 min, typically from about 10 to about 20 min, more preferably about 30 min, even more preferably about 45 min, and sometimes about 1 h or more.
  • the pH of the aqueous suspension measured at 20°C, naturally reaches a value of greater than 6.0, preferably greater than 6.5, more preferably greater than 7.0, even more preferably greater than 7.5, thereby preparing the surface-reacted natural or precipitated calcium carbonate as an aqueous suspension having a pH of greater than 6.0, preferably greater than 6.5, more preferably greater than 7.0, even more preferably greater than 7.5.
  • the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate (GNCC) with carbon dioxide and one or more HsO + ion donors, wherein the carbon dioxide is formed in situ by the HaO + ion donors treatment.
  • GNCC natural ground calcium carbonate
  • the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate (GNCC) with carbon dioxide and phosphoric acid, wherein the carbon dioxide is formed in situ by the phosphoric acid treatment.
  • GNCC natural ground calcium carbonate
  • surface-reacted precipitated calcium carbonate is obtained.
  • surface-reacted precipitated calcium carbonate is obtained by contacting precipitated calcium carbonate with HsO + ions and with anions being solubilized in an aqueous medium and being capable of forming water-insoluble calcium salts, in an aqueous medium to form a slurry of surface-reacted precipitated calcium carbonate, wherein said surface-reacted precipitated calcium carbonate comprises an insoluble, at least partially crystalline calcium salt of said anion formed on the surface of at least part of the precipitated calcium carbonate.
  • Said solubilized calcium ions correspond to an excess of solubilized calcium ions relative to the solubilized calcium ions naturally generated on dissolution of precipitated calcium carbonate by HsO + ions, where said HsO + ions are provided solely in the form of a counterion to the anion, i.e. via the addition of the anion in the form of an acid or non-calcium acid salt, and in absence of any further calcium ion or calcium ion generating source.
  • Said excess solubilized calcium ions are preferably provided by the addition of a soluble neutral or acid calcium salt, or by the addition of an acid or a neutral or acid non-calcium salt which generates a soluble neutral or acid calcium salt in situ.
  • Said HsO + ions may be provided by the addition of an acid or an acid salt of said anion, or the addition of an acid or an acid salt which simultaneously serves to provide all or part of said excess solubilized calcium ions.
  • the natural or precipitated calcium carbonate is reacted with the one or more HsO + ion donors and/or the carbon dioxide in the presence of at least one compound selected from the group consisting of silicate, silica, aluminium hydroxide, earth alkali aluminate such as sodium or potassium aluminate, magnesium oxide, or mixtures thereof.
  • the at least one silicate is selected from an aluminium silicate, a calcium silicate, or an earth alkali metal silicate.
  • the silicate and/or silica and/or aluminium hydroxide and/or earth alkali aluminate and/or magnesium oxide components can be added to the aqueous suspension of natural or precipitated calcium carbonate while the reaction of natural or precipitated calcium carbonate with the one or more HsO + ion donors and carbon dioxide has already started. Further details about the preparation of the surface-reacted natural or precipitated calcium carbonate in the presence of at least one silicate and/or silica and/or aluminium hydroxide and/or earth alkali aluminate component(s) are disclosed in WO 2004/083316 A1 , the content of this reference herewith being included in the present application.
  • the surface-reacted calcium carbonate can be kept in suspension, optionally further stabilised by a dispersant.
  • a dispersant Conventional dispersants known to the skilled person can be used.
  • a preferred dispersant is comprised of polyacrylic acids and/or carboxymethylcellu loses.
  • the aqueous suspension described above can be dried, thereby obtaining the solid (i.e. dry or containing as little water that it is not in a fluid form) surface-reacted natural or precipitated calcium carbonate in the form of granules or a powder.
  • the surface-reacted calcium carbonate has a specific surface area of from 15 m 2 /g to 200 m 2 /g, preferably from 27 m 2 /g to 180 m 2 /g, more preferably from 30 m 2 /g to 160 m 2 /g, even more preferably from 45 m 2 /g to 150 m 2 /g, most preferably from 48 m 2 /g to 140 m 2 /g, measured using nitrogen and the BET method.
  • the surface-reacted calcium carbonate has a specific surface area of from 75 m 2 /g to 100 m 2 /g, measured using nitrogen and the BET method.
  • the BET specific surface area in the meaning of the present invention is defined as the total surface area of the particles divided by the mass of the particles. As used therein the specific surface area is measured by adsorption using the BET isotherm (ISO 9277:2010) and is specified in m 2 /g.
  • the surface-reacted calcium carbonate particles have a volume median grain diameter cfeo (vol) of from 1 to 75 pm, preferably from 2 to 50 pm, more preferably 3 to 40 pm, even more preferably from 4 to 30 pm, and most preferably from 5 to 15 pm.
  • the surface-reacted calcium carbonate particles have a grain diameter daa (vol) of from 2 to 150 pm, preferably from 4 to 100 pm, more preferably 6 to 80 pm, even more preferably from 8 to 60 pm, and most preferably from 10 to 30 pm.
  • the value d x represents the diameter relative to which x % of the particles have diameters less than d x .
  • the daa value is also designated as “top cut”.
  • the d x values may be given in volume or weight percent.
  • the c/50 (wt) value is thus the weight median particle size, i.e. 50 wt.-% of all grains are smaller than this particle size
  • the c/50 (vol) value is the volume median particle size, i.e. 50 vol.-% of all grains are smaller than this particle size.
  • volume median grain diameter c/50 was evaluated using a Malvern Mastersizer 2000 or 3000 Laser Diffraction System.
  • the raw data obtained by the measurement are analysed using the Mie theory, with a particle refractive index of 1 .57 and an absorption index of
  • the weight median grain diameter is determined by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field.
  • the measurement is made with a SedigraphTM 5100 or 5120, Micromeritics Instrument Corporation.
  • the method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments.
  • the measurement is carried out in an aqueous solution of 0.1 wt.-% Na4P2O?.
  • the samples were dispersed using a high speed stirrer and sonicated.
  • the processes and instruments are known to the skilled person and are commonly used to determine grain size of fillers and pigments.
  • the specific pore volume is measured using a mercury intrusion porosimetry measurement using a Micromeritics Autopore V 9620 mercury porosimeter having a maximum applied pressure of mercury 414 MPa (60 000 psi), equivalent to a Laplace throat diameter of 0.004 pm ( ⁇ nm).
  • the equilibration time used at each pressure step is 20 seconds.
  • the sample material is sealed in a 5 cm 3 chamber powder penetrometer for analysis.
  • the data are corrected for mercury compression, penetrometer expansion and sample material compression using the software Pore-Comp (Gane,
  • the total pore volume seen in the cumulative intrusion data can be separated into two regions with the intrusion data from 214 pm down to about 1 - 4 pm showing the coarse packing of the sample between any agglomerate structures contributing strongly. Below these diameters lies the fine interparticle packing of the particles themselves. If they also have intraparticle pores, then this region appears bi modal, and by taking the specific pore volume intruded by mercury into pores finer than the modal turning point, i.e. finer than the bi-modal point of inflection, the specific intraparticle pore volume is defined. The sum of these three regions gives the total overall pore volume of the powder, but depends strongly on the original sample compaction/settling of the powder at the coarse pore end of the distribution.
  • the surface-reacted calcium carbonate has an intra-particle intruded specific pore volume in the range from 0.1 to 2.3 cm 3 /g, more preferably from 0.2 to 2.0 cm 3 /g, especially preferably from 0.4 to 1 .8 cm 3 /g and most preferably from 0.6 to 1 .6 cm 3 /g, calculated from mercury porosimetry measurement.
  • the intra-particle pore size of the surface-reacted calcium carbonate preferably is in a range of from 0.004 to 1 .6 pm, more preferably in a range of from 0.004 to 1 .3 pm, especially preferably from 0.004 to 1 .15 pm and most preferably of 0.004 to 1 .0 pm, determined by mercury porosimetry measurement.
  • the composition comprises the surface-reacted calcium carbonate in an amount of at least 10 wt.-%, preferably at least 20 wt.-%, more preferably at least 50 wt.-%, even more preferably at least 80 wt.-%, based on the total weight of the composition.
  • the composition consists of surface-reacted calcium carbonate.
  • the surface-reacted calcium carbonate is in form of particles having a volume determined median particle size cfeo from 1 to 75 pm, preferably from 2 to 50 pm, more preferably from 3 to 40 pm, even more preferably from 4 to 30 pm, and most preferably from 5 to 15 pm.
  • the volume determined median particle size cfeo was evaluated using a Malvern Mastersizer 3000 Laser Diffraction System.
  • the surface-reacted calcium carbonate is in form of particles having a volume determined top cut particle size daa from 2 to 150 pm, preferably from 4 to 100 pm, more preferably from 6 to 80 pm, even more preferably from 8 to 60 pm, and most preferably from 10 to 30 pm.
  • the volume determined top cut particle size daa was evaluated using a Malvern Mastersizer 3000 Laser Diffraction System.
  • the surface-reacted calcium carbonate is in form of particles having a specific surface area in the range from 15 to 200 m 2 /g, preferably from 27 to 180 m 2 /g, more preferably from 30 m 2 /g to 160 m 2 /g, even more preferably from 45 m 2 /g to 150 m 2 /g, and most preferably from 48 m 2 /g to 140 m 2 /g, measured using nitrogen and the BET method according to ISO 9277:2010.
  • the mineral composition is provided in dry form, preferably in form of a powder or in form of particles, beads, granules, needles, ribbons, or flakes, and most preferably in form of a powder or in form of granules.
  • step b) the mineral composition of step a) is formed into a green body.
  • a “green body” in the meaning of the present invention is an unsintered, cohesive body comprising surface-reacted calcium carbonate.
  • the term “compaction” refers to a process by which fine powders are pressed into a compacted form such as beads, granules, needles, ribbons or flakes. This can be achieved, e.g., by means of a roller compacter, wherein powder is forced between two counter rotating rolls and pressed into the compacted form.
  • a roller compacter e.g., a roller compacter
  • suitable compacting equipment are briquetters or pellet mills.
  • compression refers to a process by which fine or compacted powder or other compacted forms are compressed into a green body.
  • the composition may be formed into a green body by any method known in the art.
  • the green body is formed by powder compression.
  • the composition of step a) may be provided in dry form, preferably in form of a powder or in form of particles, beads, granules, needles, ribbons, or flakes, and most preferably in form of a powder or in form of granules.
  • the powder compression comprises three basic steps: (1) filling a mold or die with powder, (2) compressing the powder to a specific size and shape, and (3) ejecting the compressed body from the mold or die.
  • Suitable compressing equipment is known to the skilled person and may involve specialized mechanical, hydraulic, hydraulic-mechanical, pneumatic or direct electrically driven powder presses.
  • a tablet press may be used.
  • the pressure may be applied uniaxially or isostatically.
  • the powder In the uniaxial compression process, the powder may be axially pressed between rigid punch faces and die walls.
  • isostatical compression process equal pressure is applied in all directions on a powder, which means that the die wall friction is significantly reduced or eliminated entirely.
  • isostatic compression typically involves the use of elastomeric molds rather than rigid dies. For example, the powder is loaded into the flexible mold, the mold is sealed and the pressure is applied in a pressure vessel via a liquid. Isostatic compression may be performed “cold” or “hot”.
  • Cold isostatic pressing may be used to compress powders at ambient temperatures
  • hot isostatic pressing may be used to fully consolidate green bodies at elevated temperatures by solid-state diffusion.
  • the HIP process may apply high pressure (e.g. 50 to 200 MPa) and high temperature (e.g. 400 to 2000°C) to the exterior surface of green bodies via an inert gas (e.g., argon or nitrogen).
  • the elevated temperature and pressure may cause sub-surface voids to be eliminated through a combination of plastic flow and diffusion. Accordingly, the HIP process may be especially preferred for preparing a non-porous green body.
  • method step b) is carried out by powder compression, preferably by uniaxial powder compression.
  • the powder compression is carried out at a compression force from 0.1 to 100 kN/cm, preferably from 0.5 to 50 kN/cm, more preferably from 1 to 25 kN/cm, and most preferably from 1 to 10 kN/cm.
  • the mineral composition of step a) can be formed into a green body by other forming methods such as injection molding, extrusion, die pressing, slip casting, tape casting, or 3D- printing.
  • a binding agent may be required.
  • 3D-printing refers to the construction of a three-dimensional object from a CAD or digital 3D model, wherein material is deposited, joined or solidified under computer control and is typically added together layer by layer.
  • Suitable 3D-printing technologies for the production of ceramic materials based on mineral compositions are known to the skilled person, and may be selected, for example, from material jetting, binder jetting, material extrusion, stereolithography, digital light processing, multiphoton polymerization, inkjet printing, direct ink writing, powder bed printing, selective laser sintering, selective laser melting, laminated object manufacturing, or fused deposition modelling.
  • the mineral composition provided in step a) comprises a binding agent.
  • a binding agent may be added before and/or during method step b).
  • Suitable binding agents are known to the skilled person, and may be, for example, selected from polyolefins, polyvinyl alcohol, polyvinyl pyrrolidone, gelatine, cellulose ethers, polyoxazolines, polyvinylacetamides, partially hydrolyzed polyvinyl acetate/vinyl alcohol, polyacrylic acid, polyacrylamide, polyalkylene oxide, sulfonated or phosphated polyesters and polystyrenes, casein, zein, albumin, chitin, chitosan, dextran, pectin, collagen derivatives, collodian, agar-agar, arrowroot, guar, carrageenan, starch, tragacanth, xanthan, rhamsan, poly(styrene-co-butadiene), polyurethane latex, polyester latex, styrene-butadiene latex, styrene-acrylate latex, polyvin
  • the binder is selected from the group consisting of starch, polyvinyl alcohol, styrene-butadiene latex, styrene-acrylate latex, polyvinyl acetate latex, polyolefins, ethylene acrylate, microfibrillated cellulose, microcrystalline cellulose, nanocellulose, cellulose, methyl cellulose, carboxymethylcellulose, bio-based latex, polyvinyl butyral, polyethylene glycol (PEG), ethylene-vinyl acetate copolymers, polylactic acid (PLA), poly-DL-lactide (PDLLA), polyglycolic acid (PGA), poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), polyurethane (PU), poly(methyl methacrylate) (PMMA), polydioxanone (PDO), polyhydroxyalkanoates (PHA), polypropylene fumarate) (PPF), polyether ether ketone (PEE
  • the binding agent may be present in an amount from 0.1 to 10 wt.-%, based on the total weight of the mineral composition, preferably from 0.2 to 8 wt.-%, more preferably from 0.4 to 6 wt.-%, and most preferably from 0.5 to 5 wt.-%.
  • the method does not comprise a step of adding a binding agent to the composition provided in step a).
  • the green body may be shaped in any possible form.
  • the green body formed in step b) is a tablet, a granule, an implant, a flat substrate, a disc, a part of a watch housing, or a workpiece.
  • the obtained green body may be further shaped into a desired shape or form, as necessary.
  • the green body may be shaped by subjecting it to a predetermined machine working such as cutting, grinding, or polishing.
  • the mineral composition of step a) is compacted before the composition is formed into the green body.
  • Compaction may improve the flowability of the mineral composition of step a), which may facilitate the powder compression and increase the packing uniformity of the green body.
  • Suitable compaction methods are known to the skilled person and may comprise tumbling agglomeration, press agglomeration, roller compaction, wet granulation, spray drying, or fluidized-bed spray granulation.
  • the compaction is carried out by means of a roller compactor, preferably at a compaction pressure in the range from 2 to 20 bar.
  • roller compacting refers to a process in which fine powders are forced between two counter rotating rolls and pressed into a solid compact or ribbon.
  • the roller compacting can be carried out with any suitable roller compactor known to the skilled person.
  • roller compacting is carried out with a Fitzpatrick® Chilsonator IR220 roller compactor of the Fitzpatrick Company, USA.
  • the roller compacting is carried out at a roller compaction force from 2 to 20 kN/cm, preferably from 4 to 15 kN/cm, more preferably from 4 to 10 kN/cm, and most preferably from 4 to 7 kN/cm.
  • the granulated composition may be sieved in order to remove fines.
  • the mineral composition provided in step a) may be sieved in order to remove undesired particles with bigger or smaller dimensions.
  • Such sieving can be carried out with any conventional sieving means known to the skilled person, and may be carried out using one or more mesh sizes. Suitable mesh sizes are, but not limited to mesh sizes of 710 pm, 500 pm, 180 pm, 90 pm, and 45 pm. For example, sieving is carried out with a vibrating sieve tower of Vibro Retsch, Switzerland. It lies within the understanding of the present invention that other mesh sizes and combination of other mesh sizes lie within the spirit of the present invention.
  • the sieved mixture may have a grain size of more than 710 pm, more than 500 pm, more than 180 pm, more than 90 pm, or more than 45 pm, and preferably more than 90 pm.
  • the mineral composition of step a) is compacted, preferably roller compacted, and subsequently, sieved before step b).
  • the composition of step a) is sieved before step b).
  • the composition of step a) is first sieved, then compacted, preferably roller compacted, and subsequently, sieved before step b).
  • the method for manufacturing a ceramic body may comprise the following steps: a) providing a mineral composition comprising surface-reacted calcium carbonate, wherein the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more HsO + ion donors, wherein the carbon dioxide is formed in situ by the HsO + ion donors treatment and/or is supplied from an external source, a’) compacting the mineral composition of step a) to form a compacted composition, a”) sieving the compacted composition of step a’) to form a sieved composition, b) forming the sieved composition of step a”) into a green body, and c) sintering the green body formed in step b) to form a ceramic body.
  • the compacting step a’) may be carried out by roller compaction and the forming step b) is carried out by powder compression.
  • a lubricant is added before and/or during step b).
  • Suitable lubricants are known to the skilled person and may be selected from metallic salts of fatty acids, fatty acids, hydrocarbons, fatty alcohols, fatty acid esters, alkyl sulfates, polymers, or inorganic materials.
  • the lubricant is selected from the group consisting of magnesium stearate, calcium stearate, zinc stearate, stearic acid, palmitic acid, glyceryl monostearate, talc, or mixtures thereof.
  • the lubricant may be added in an amount from 0.1 to 10 wt.-%, based on the total weight of the mineral composition of step a), preferably in an amount from 0.2 to 5 wt.-%, more preferably in an amount from 0.4 to 2 wt.-%, and most preferably in an amount from 0.5 to 1 wt.-%.
  • magnesium stearate is added before step b), preferably in an amount from 0.1 to 1 wt.-%, based on the total weight of the composition.
  • step c) the green body formed in step b) is sintered to form a ceramic body.
  • the green body is heated to a high temperature below its melting point in order to consolidate the particles of surface-reacted calcium carbonate, and if present, other mineral materials, within the green body.
  • the atoms in the materials may diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece.
  • volatile compounds may be removed from the green body at the beginning of this sintering step.
  • the equipment used in the sintering step is not particularly limited and will be suitably selected by the skilled person from the commercially available sintering furnaces according to the scale of manufacture and the conditions.
  • suitable equipment are directly or indirectly heated kilns, shuttle kilns, sliding batt kilns, muffle furnaces, or microwave furnaces.
  • the sintering may be carried out at an atmospheric pressure or under increased pressure.
  • the sintering step c) is carried out under atmospheric pressure.
  • the sintering step c) may be carried out under a pressure slightly above the atmospheric pressure, for example, at a pressure from 1 .05 to 1 .5 bar, preferably at 1 .1 to 1 .2 bar.
  • Performing step c) under slight overpressure may prevent contamination with gas molecules from outside the sintering furnace.
  • the sintering may be carried out at a temperature of at least 850°C, preferably from 900°C to 1400°C, more preferably from 950 to 1300°C, and most preferably from 1000 to 1200°C.
  • the period of time over which the sintering is carried out, i.e. the sintering temperature is being held, may be between 30 min and 8 hours.
  • the sintering is carried out for at least 30 min, preferably at least 1 h, more preferably at least 2 h, even more preferably at least 3 h, and most preferably at least 5 h.
  • the sintering is carried out from 30 min to 8 h, preferably from 1 h to 7 h, more preferably from 1 .5 h to 8 h, and most preferably from 2 to 5 h.
  • the sintering step c) is carried out at a fixed temperature for a certain time period.
  • the sintering step c) may be carried out at a first temperature for a first time period, and subsequently, at a second temperature for a second time period.
  • the sintering step c) is carried out at a first temperature for a first time period, then at a second temperature for a second time period, and subsequently, at a third temperature for a third time period.
  • further sintering temperature stages may be included in the inventive process and may adapt the sintering temperature profile accordingly.
  • the sintering step c) may be conducted under different atmospheres.
  • the sintering step c) may be carried out in an atmosphere comprising carbon dioxide.
  • the sintering is carried out in an atmosphere comprising at least 50 vol.-% carbon dioxide, preferably at least 80 vol.-% carbon dioxide, more preferably at least 90 vol.-%, even more preferably at least 95 vol.-%, and most preferably in an atmosphere consisting of carbon dioxide.
  • the sintering may be carried out in an atmosphere comprising carbon dioxide and water, preferably in an atmosphere having a CO2/H2O volume ratio from 99.9:0.1 to 1 :1 .
  • atmosphere comprising carbon dioxide and water
  • CO2/H2O volume ratio from 99.9:0.1 to 1 :1 .
  • the water molecules may react with residual calcium oxide to calcium hydroxide. Thereby the concentration of calcium oxide may be decreased.
  • the sintering step c) comprises the steps of c1) sintering the green body formed in step b) in an air atmosphere, and c2) sintering the sintered green body obtained in step c1) in an atmosphere comprising at least 50 vol.-% carbon dioxide, preferably at least 80 vol.-% carbon dioxide, more preferably at least 90 vol.-%, even more preferably at least 95 vol.-% , and most preferably in an atmosphere consisting of carbon dioxide.
  • the sintering step c) comprises the steps of c1) sintering the green body formed in step b) in an air atmosphere, and c2) sintering the sintered green body obtained in step c1) in an atmosphere comprising carbon dioxide and water, preferably in an atmosphere having a CO2/H2O volume ratio from 99.9:0.1 to 1 :1.
  • the sintering step c) is carried out in an inert atmosphere, preferably consisting of helium, nitrogen, argon, or mixtures thereof. After the sintering is completed, the ceramic body may be let to cool down to room temperature.
  • the inventors found that sintering in an atmosphere comprising carbon dioxide reduces the conversion of calcium carbonate into calcium oxide. Moreover, it was found that by varying sintering time and temperature, the composition and porosity of the ceramic body can be controlled.
  • additional mineral particles may be present in the mineral composition of step a) and/or may be added before and/or during method step b).
  • the mineral composition of step a) comprises additional mineral particles selected from the group consisting of ground calcium carbonate, precipitated calcium carbonate, dicalcium phosphate, calcium fluoride, or mixtures thereof.
  • the mineral composition may comprise the additional mineral particles in an amount of at least 10 wt.-%, preferably at least 20 wt.-%, more preferably at least 60 wt.-%, and most preferably at least 80 wt.-%, based on the total weight of the mineral composition.
  • the mineral composition comprises the additional mineral particles in an amount of from 10 to 90 wt.-%, preferably from 20 to 85 wt.-%, and most preferably from 40 to 80 wt.-%, based on the total weight of the mineral composition.
  • additional mineral particles are added before and/or during method step b).
  • the additional mineral particles may be added in an amount of at least 10 wt.-%, preferably at least 20 wt.-%, more preferably at least 60 wt.-%, and most preferably at least 80 wt.-%, based on the total weight of the green body.
  • the additional mineral particles are added in an amount of from 10 to 90 wt.-%, preferably from 20 to 85 wt.-%, and most preferably from 40 to 80 wt.-%, based on the total weight of the green body.
  • the addition of additional mineral particles does not only impact the composition of the ceramic body, but may provide a further measure to control the porosity of the ceramic material formed during the sintering step.
  • the porosity of a surface- reacted calcium carbonate may be reduced or increased by adding the additional mineral materials defined above, and further fine-tuned by adapting the sintering profile. In this way it is possible to tailor the porosity of a ceramic body.
  • Ground (or natural ground) calcium carbonate is understood to be manufactured from a naturally occurring form of calcium carbonate, mined from sedimentary rocks such as limestone or chalk, or from metamorphic marble rocks, eggshells or seashells.
  • Calcium carbonate is known to exist as three types of crystal polymorphs: calcite, aragonite and vaterite. Calcite, the most common crystal polymorph, is considered to be the most stable crystal form of calcium carbonate. Less common is aragonite, which has a discrete or clustered needle orthorhombic crystal structure. Vaterite is the rarest calcium carbonate polymorph and is generally unstable.
  • Ground calcium carbonate is almost exclusively of the calcitic polymorph, which is said to be trigonal-rhombohedral and represents the most stable of the calcium carbonate polymorphs.
  • the term “source” of the calcium carbonate in the meaning of the present application refers to the naturally occurring mineral material from which the calcium carbonate is obtained.
  • the ground calcium carbonate is selected from the group consisting of marble, chalk, limestone and mixtures thereof.
  • the source of the calcium carbonate may comprise further naturally occurring components such as magnesium carbonate, alumino silicate etc.
  • the GCC is obtained by dry grinding. According to another embodiment of the present invention the GCC is obtained by wet grinding and optionally subsequent drying.
  • the grinding step can be carried out with any conventional grinding device, for example, under conditions such that comminution predominantly results from impacts with a secondary body, i.e. in one or more of: a ball mill, a rod mill, a vibrating mill, a roll crusher, a centrifugal impact mill, a vertical bead mill, an attrition mill, a pin mill, a hammer mill, a pulveriser, a shredder, a de-clumper, a knife cutter, or other such equipment known to the skilled man.
  • a ball mill i.e. in one or more of: a ball mill, a rod mill, a vibrating mill, a roll crusher, a centrifugal impact mill, a vertical bead mill, an attrition mill, a pin mill, a hammer mill, a pulveriser, a shredder, a de-clumper, a knife cutter, or other such equipment known to the skilled man.
  • the grinding step may be performed under conditions such that autogenous grinding takes place and/or by horizontal ball milling, and/or other such processes known to the skilled man.
  • the wet processed ground calcium carbonate comprising mineral material thus obtained may be washed and dewatered by well-known processes, e.g. by flocculation, centrifugation, filtration or forced evaporation prior to drying.
  • the subsequent step of drying may be carried out in a single step such as spray drying, or in at least two steps. It is also common that such a mineral material undergoes a beneficiation step (such as a flotation, bleaching or magnetic separation step) to remove impurities.
  • a beneficiation step such as a flotation, bleaching or magnetic separation step
  • the calcium carbonate comprises one type of ground calcium carbonate. According to another embodiment of the present invention, the calcium carbonate comprises a mixture of two or more types of ground calcium carbonates selected from different sources.
  • the calcium carbonate is in form of particles having a weight determined median particle size cfeo from 0.1 to 50 pm, preferably from 0.2 to 20 pm, more preferably from 0.5 to 10 pm, and most preferably from 1 to 5 pm.
  • the weight determined median particle size c o was evaluated using a SedigraphTM 5100 instrument or SedigraphTM 5120 instrument of Micromeritics Instrument Corporation.
  • the calcium carbonate is in form of particles having a weight determined top cut particle size daa from 0.2 to 100 pm, preferably from 0.4 to 40 pm, more preferably from 1 to 20 pm, and most preferably from 2 to 10 pm.
  • the weight determined top cut particle size daa was evaluated using a SedigraphTM 5100 instrument or SedigraphTM 5120 instrument of Micromeritics Instrument Corporation.
  • Precipitated calcium carbonate in the meaning of the present invention is a synthesized material, generally obtained by precipitation following reaction of carbon dioxide and calcium hydroxide in an aqueous environment or by precipitation of calcium and carbonate ions, for example CaCh and Na2CC>3, out of solution. Further possible ways of producing PCC are the lime soda process, or the Solvay process in which PCC is a by-product of ammonia production. Precipitated calcium carbonate exists in three primary crystalline forms: calcite, aragonite and vaterite, and there are many different polymorphs (crystal habits) for each of these crystalline forms.
  • Calcite has a trigonal structure with typical crystal habits such as scalenohedral (S-PCC), rhombohedral (R- PCC), hexagonal prismatic, pinacoidal, colloidal (C-PCC), cubic, and prismatic (P-PCC).
  • Aragonite is an orthorhombic structure with typical crystal habits of twinned hexagonal prismatic crystals, as well as a diverse assortment of thin elongated prismatic, curved bladed, steep pyramidal, chisel shaped crystals, branching tree, and coral or worm-like form.
  • Vaterite belongs to the hexagonal crystal system.
  • the obtained PCC slurry can be mechanically dewatered and dried.
  • the precipitated calcium carbonate is precipitated calcium carbonate, preferably comprising aragonitic, vateritic or calcitic mineralogical crystal forms or mixtures thereof.
  • the calcium carbonate comprises one precipitated calcium carbonate.
  • the calcium carbonate comprises a mixture of two or more precipitated calcium carbonates selected from different crystalline forms and different polymorphs of precipitated calcium carbonate.
  • the at least one precipitated calcium carbonate may comprise one PCC selected from S-PCC and one PCC selected from R-PCC.
  • the precipitated calcium carbonate is in form of particles having a volume determined median particle size dso from 1 to 75 pm, preferably from 2 to 50 pm, more preferably from 3 to 40 pm, even more preferably from 4 to 30 pm, and most preferably from 5 to 15 pm.
  • the volume determined median particle size dso was evaluated using a Malvern Mastersizer 3000 Laser Diffraction System.
  • the precipitated calcium carbonate is in form of particles having a volume determined top cut particle size daa from 2 to 150 pm, preferably from 4 to 100 pm, more preferably from 6 to 80 pm, even more preferably from 8 to 60 pm, and most preferably from 10 to 30 pm.
  • the volume determined top cut particle size daa was evaluated using a Malvern Mastersizer 3000 Laser Diffraction System.
  • a “dicalcium phosphate” in the meaning of the present invention refers to the inorganic compound with the chemical formula CaHPC and hydrates thereof.
  • dicalcium phosphate examples include anhydrous dicalcium phosphate (CaHPC ) such as the mineral monetite, dicalcium phosphate hemihydrate (CaHPC - 0.5 H2O), or dicalcium phosphate dihydrate (CaHPC ⁇ 2 H2O), such as the mineral brushite.
  • CaHPC anhydrous dicalcium phosphate
  • CaHPC - 0.5 H2O dicalcium phosphate hemihydrate
  • CaHPC ⁇ 2 H2O dicalcium phosphate dihydrate
  • the dicalcium phosphate is selected from the group consisting of anhydrous dicalcium phosphate (CaHPC ), dicalcium phosphate hemihydrate (CaHPC - 0.5 H2O), dicalcium phosphate dihydrate (CaHPC ⁇ 2 H2O), or mixtures thereof, and more preferably the dicalcium phosphate is anhydrous dicalcium phosphate (CaHPC ).
  • the dicalcium phosphate is in form of particles having a volume determined median particle size cfeo from 1 to 150 pm, preferably from 5 to 100 pm, more preferably from 10 to 80 pm, even more preferably from 8 to 60 pm, and most preferably from 10 to 30 pm.
  • the volume determined median particle size cfeo was evaluated using a Malvern Mastersizer 3000 Laser Diffraction System.
  • the dicalcium phosphate is in form of particles having a volume determined top cut particle size daa from 2 to 300 pm, preferably from 10 to 200 pm, more preferably from 20 to 160 pm, even more preferably from 16 to 120 pm, and most preferably from 20 to 80 pm.
  • the volume determined top cut particle size daa was evaluated using a Malvern Mastersizer 3000 Laser Diffraction System.
  • a porogen may be present in the mineral composition of step a) and/or may be added before and/or during method step b).
  • the term “porogen” refers to a particulate material that can be used to create pores within ceramic body and which burns, evaporate or gasifies upon heating without leaving residues.
  • the mineral composition of step a) further comprises a porogen.
  • a porogen may be added before and/or during step b).
  • a porogen may be added before or after an optional compaction and/or sieving step.
  • the porogen is added before an optional granulation and/or sieving step.
  • the mineral composition comprises the porogen in an amount from 1 to 80 wt.-%, preferably in an amount from 5 to 70 wt.-%, more preferably in an amount from 10 to 65 wt.-%, and most preferably in an amount from 15 to 60 wt.-%, based on the total weight of the mineral composition.
  • the porogen is present in the green body in an amount from 1 to 80 wt.-%, preferably in an amount from 5 to 70 wt.-%, more preferably in an amount from 10 to 65 wt.-%, and most preferably in an amount from 15 to 60 wt.-%, based on the total weight of the green body.
  • the porogen may have any suitable shape. According to one embodiment the porogen is in form of spheres, granules, fibers, beads, or mixtures thereof.
  • the porogen is in form of spheres having a volume determined median particle size dso from 5 to 500 pm, preferably from 10 to 400 pm, and most preferably from 20 to 300 pm.
  • the porogen is selected from the group consisting of organic polymers, polysaccharides, inorganic salts, waxes, naphthalene, or mixtures thereof, preferably consisting of polyethylene, polypropylene, sodium hydroxide, cellulose, starch, paraffin wax, or mixtures thereof, and most preferably the porogen is polyethylene and/or cellulose.
  • the porogen is in form of spheres having a volume median particle size dso from 5 to 500 pm, preferably from 10 to 400 pm, and most preferably from 20 to 300 pm, and is selected from the group consisting of polyethylene, polypropylene, sodium hydroxide, cellulose, starch, paraffin wax, or mixtures thereof, and most preferably the porogen is polyethylene and/or cellulose.
  • the porogen may decompose at least partially during the sintering step c). If necessary, the remaining porogen may be removed by any other suitable method known to the skilled person, for example, by leaching the porogen in solution.
  • the porogen is at least partially removed by sintering step c), and preferably the porogen is completely removed after sintering step c). If necessary, the complete removal of porogen could be confirmed by any suitable technique known to the skilled person, e.g. mass spectroscopy or FTIR spectroscopy analysis.
  • porogen content is in the mineral composition or green body, generally the higher the level of porosity is in the ceramic body.
  • concentration and size of the porogen it may also be possible to form an interconnected network of pores.
  • morphology of the pores can be controlled and tailored by the shape of the added porogens.
  • a ceramic body obtainable by a method according to the present invention is provided.
  • the ceramic body comprises at least one water-insoluble calcium salt selected from tricalcium phosphate, tetracalcium phosphate and/or apatitic calcium phosphate, calcium oxide, and optionally calcium carbonate.
  • the apatitic calcium phosphate may be preferably selected from the group consisting of hydroxylapatite, substituted hydroxylapatite, octacalcium phosphate, and mixtures thereof. Hydroxylapatite may be present in unsubstituted or substituted form. Examples of substituted hydroxylapatite are fluroroapatite or carboxyapatite.
  • the water-insoluble calcium salt is selected from the group consisting of hydroxylapatite, fluroroapatite, carboxyapatite, and mixtures thereof, and most preferably hydroxylapatite.
  • the calcium carbonate is calcite.
  • the ceramic body comprises at least one water-insoluble calcium salt selected from tricalcium phosphate, tetracalcium phosphate, and/or apatitic calcium phosphate, preferably selected from the group consisting of hydroxylapatite, substituted hydroxylapatite, octacalcium phosphate, and mixtures thereof, more preferably selected from the group consisting of hydroxylapatite, fluoroapatite, carboxyapatite, and mixtures thereof, and most preferably hydroxylapatite, calcium oxide, and calcium carbonate, preferably calcite.
  • apatitic calcium phosphate preferably selected from the group consisting of hydroxylapatite, substituted hydroxylapatite, octacalcium phosphate, and mixtures thereof, more preferably selected from the group consisting of hydroxylapatite, fluoroapatite, carboxyapatite, and mixtures thereof, and most preferably hydroxylapatite, calcium oxide, and calcium carbonate,
  • the ceramic body comprises tricalcium phosphate and/or tetracalcium phosphate and apatitic calcium phosphate, preferably hydroxylapatite.
  • apatitic calcium phosphate preferably hydroxylapatite.
  • tetracalcium phosphate may be beneficial for improving the bio-compatibility with tissues.
  • the inventors of the present invention surprisingly found that only after the calcium carbonate contained in the green body has almost completely to completely decomposed during the sintering step, hydroxylapatite may convert into tetracalcium phosphate so that a ceramic body with a defined tetracalcium phosphate content can be produced.
  • the surface-reacted calcium carbonate may comprise calcium carbonate and the waterinsoluble salt in a weight ratio in the range of 90:10 to 10:90, preferably in the range of 80:20 to 10:90, more preferably in the range of 60:40 to 10:90, even more preferably in the range of 40:60 to 10:90, and most preferably in the range of 25:75 to 10:90, e.g. 15:85 or 12:88.
  • the surface-reacted calcium carbonate comprises (i) calcium carbonate in an amount in the range of from 1 to 90 wt.-%, preferably in the range of from 5 to 80 wt.-%, especially preferably in the range of from 10 to 60 wt.-%, more preferably in the range of from 10 to 40 wt.-%, and most preferably in the range of from 10 to 25 wt.-%, and (ii) hydroxyapatite in an amount in the range of from 1 to 90 wt.-%, preferably in the range of from 20 to 90 wt.-%, especially preferably in the range of from 40 to 90 wt.-%, more preferably in the range of from 60 to 90 wt.-%, and most preferably in the range of from 75 to 90 wt.-%, based on the total weight of the surface-reacted calcium carbonate.
  • the ceramic body comprises the water-insoluble calcium salt in an amount of at least 40 wt.-%, preferably at least 50 wt.-%, more preferably at least 70 wt.-%, and most preferably at least 90 wt.-%, based on the total weight of the ceramic body.
  • the ceramic body also comprises calcium oxide.
  • Said calcium oxide may be formed during the sintering process in a minor amount.
  • the ceramic body comprises calcium oxide in an amount of less than 10 wt.-%, preferably less than 8 wt.-%, more preferably less than 5 wt.-%, and most preferably less than 2 wt.-%, based on the total weight of the ceramic body.
  • the ceramic body comprises calcium carbonate in an amount of less than 60 wt.-%, preferably less than 50 wt.-%, more preferably less than 30 wt.-%, and most preferably less than 10 wt.-%, based on the total weight of the ceramic body.
  • the ceramic body comprises calcium carbonate in an amount from 1 to 60 wt.-%, preferably from 1 to 50 wt.-%, more preferably from 1 to 10 wt.-%, and most preferably from 1 to 5 wt.-%, based on the total weight of the ceramic body, and the water-insoluble calcium salt in an amount from 30 to 95 wt.-%, preferably from 50 to 95 wt.-%, more preferably from 70 to 95 wt.-%, most preferably from 90 to 95 wt.-%, based on the total weight of the ceramic body, and calcium oxide in an amount from 0.1 to 10 wt.-%, preferably from 1 to 8 wt.-%, more preferably from 1 to 6 wt.-%, and most preferably from 1 to 4 wt.-%, based on the total weight of the ceramic body.
  • the ceramic body may comprise calcium pyrophosphate.
  • the ceramic body is a single phase material.
  • the ceramic body obtained by the inventive process comprises a high concentration of apatitic calcium phosphate.
  • apatitic calcium phosphate it was found that the conversion of hydroxyapatite into p-tricalcium phosphate during sintering, which typically occurs in ceramic materials produced from hydroxyapatite powders, can be significantly reduced, or even prevented.
  • porosity of the ceramic body can be tailored to the desired specification by varying sintering time and temperature as well as the composition of the employed mineral composition.
  • the ceramic body of the present invention may be a non-porous or porous material.
  • “Non- porous” in the meaning of the present invention refers to a material having a porosity of less than 20%, determined by mercury porosimetry measurement, while the term “porous” refers to a material having a porosity of 20% and more, determined by mercury porosimetry measurement.
  • the ceramic body is non-porous having a porosity of less than 20%, preferably less than 15%, more preferably less than 10%, and most preferably less than 5 %, determined by mercury porosimetry measurement.
  • the ceramic body may have a bulk density of at least 2.5 g/cm 3 , preferably at least 2.6 g/cm 3 , more preferably at least 2.7 g/cm 3 , and most preferably at least 2.8 g/cm 3 .
  • the ceramic body is non-porous having a porosity from 0.1 % to 19%, preferably from 1% to 15%, more preferably from 2% to 10%, and most preferably from 3% to 8%, determined by mercury porosimetry measurement.
  • the ceramic body may have a bulk density from 2.5 to 3.5 g/cm 3 , preferably from 2.6 to 3.2 g/cm 3 , and most preferably from 2.7 to 3.0 g/cm 3 .
  • the ceramic body is porous having a porosity of at least 20%, preferably at least 30%, more preferably at least 40%, still more preferably at least 50%, even more preferably at least 60%, and most preferably at least 70%, determined by mercury porosimetry measurement.
  • the ceramic body is porous having a porosity from 20% to 90%, preferably from 25% to 85%, more preferably from 28% to 80%, and most preferably from 30% to 75%, determined by mercury porosimetry measurement.
  • the ceramic body obtainable by the inventive method is suitable for a wide range of applications.
  • Table 1 Mineral materials used in the examples.
  • the minerals were produced as follows:
  • SRCC was obtained by preparing 2000 litres of an aqueous suspension of ground calcium carbonate in a mixing vessel by adjusting the solids content of a ground limestone calcium carbonate from Orgon, France having a mass based particle size distribution of 80% less than 1 pm, as determined by sedimentation, such that a solids content of 13 wt%, based on the total weight of the aqueous suspension, is obtained.
  • SRCC had a specific surface area of 81 m 2 /g, an intra-particle intruded specific pore volume of 1 .218 cm 3 /g (for the pore diameter range of 0.004 to 0.38 pm), and a weight ratio of hydroxyapatite to calcium carbonate of between 85:15 and 88:12, as determined by XRD.
  • 10 liters of an aqueous suspension of ground calcium carbonate was prepared in a mixing vessel by adjusting the solids content of a ground marble calcium carbonate from Karabiga, Turkey such that a solids content of 10 wt.-%, based on the total weight of the aqueous suspension, was obtained.
  • the ground calcium carbonate had a weight based particle size distribution of 70 wt.-% less than 2 pm and a mean particle size of 1 .4 pm, as determined by sedimentation.
  • Vitacel EPG-70 cellulose spheres, diameter: 200 pm (J. Rettenmaier & Sbhne GmbH + Co
  • the porosity, the pore volume and the pore size of the tablets were determined by means of mercury porosimetry (Autopore IV, Micromeritics).
  • the specific pore volume was measured using a mercury intrusion porosimetry measurement using a Micromeritics Autopore V 9620 mercury porosimeter having a maximum applied pressure of mercury 414 MPa (60 000 psi), equivalent to a Laplace throat diameter of 0.004 pm ( ⁇ nm).
  • the equilibration time used at each pressure step is 20 seconds.
  • the sample material is sealed in a 3 cm 3 chamber powder penetrometer for analysis.
  • the data are corrected for mercury compression, penetrometer expansion and sample material compression using the software Pore-Comp (Gane, P.A.C., Kettle, J.P., Matthews, G.P. and Ridgway, C.J., “Void Space Structure of Compressible Polymer Spheres and Consolidated Calcium Carbonate Paper-Coating Formulations”, Industrial and Engineering Chemistry Research, 35(5), 1996, p 1753-1764.).
  • the total pore volume seen in the cumulative intrusion data can be separated into two regions with the intrusion data from 214 pm down to about 1 - 4 pm showing the coarse packing of the sample between any agglomerate structures contributing strongly. Below these diameters lies the fine interparticle packing of the particles themselves. If they also have intraparticle pores, then this region appears bi-modal, and by taking the specific pore volume intruded by mercury into pores finer than the modal turning point, i.e. finer than the bi-modal point of inflection, the specific intraparticle pore volume is defined. The sum of these three regions gives the total overall pore volume of the powder, but depends strongly on the original sample compaction/settling of the powder at the coarse pore end of the distribution.
  • the specific surface area was measured via the BET method according to ISO 9277:2010 using nitrogen as adsorbing gas on a Micro me ritics ASAP 2460 instrument from Micro me ritics.
  • the samples were pre-treated in vacuum (10-5 bar) by heating at 120°C for a period of 60 min prior to measurement.
  • volume determined median particle size cfeo(vol) and the volume determined top cut particle size c/98(vol) was evaluated using a Malvern Mastersizer 3000 Laser Diffraction System (Malvern Instruments Pic., Great Britain) equipped with an Aero S accessory.
  • the cfeo(vol) or cfo8(vol) value indicates a diameter value such that 50 % or 98 % by volume, respectively, of the particles have a diameter of less than this value.
  • the powders were dispersed in air with a standard disperser and a pressure of 2.0 bar. Measurements were conducted with red light for 10 s.
  • the model for non-spherical particle size using Mie theory was utilized, and a particle refractive index of 1.57, a density of 2.70 g/cm 3 , and an absorption index of 0.005 was assumed.
  • the methods and instruments are known to the skilled person and are commonly used to determine particle size distributions of fillers and pigments.
  • the weight determined median particle size cfeo(wt) and the weight determined top cut particle size c/9s(wt) was measured by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field.
  • the measurement was made with a SedigraphTM 5120 of Micromeritics Instrument Corporation, USA. The method and the instrument are known to the skilled person and are commonly used to determine particle size distributions of fillers and pigments.
  • the measurement was carried out in an aqueous solution of 0.1 wt.-% Na4P2O?. The samples were dispersed using a high speed stirrer and supersonicated.
  • Quantitative analysis of diffraction data refers to the determination of amounts of different phases in a multi-phase sample and has been performed using the DIFFRACsuite software package TOPAS.
  • quantitative analysis allows to determine structural characteristics and phase proportions with quantifiable numerical precision from the experimental data itself. This involves modelling the full diffraction pattern (Rietveld approach) such that the calculated pattern(s) duplicates the experimental one.
  • the Rietveld method requires knowledge of the approximate crystal structure of all phases of interest in the pattern.
  • the use of the whole pattern rather than a few select lines produces accuracy and precision much better than any single-peak-intensity based method.
  • Chemical resistance of the ceramic bodies obtained after sintering was evaluated by immersion of a corresponding sample in selected chemicals. The weight, diameter and height of a sample was measured prior to immersion. The sample was then immersed in a 50 ml polyethylene jar containing 30 ml of the selected chemical. The jar was closed and left at 25°C for 7 days. The sample was then removed from the jar and dried at 50 °C for 24 hours in a ventilated oven. The weight, diameter and height of the sample was measured to calculate the weight and volume losses after exposure to the selected chemical.
  • the mineral powder was compacted with a roller compactor (CCS series, Fitzpatrick) at a roller compaction force of 5 kN/cm.
  • CCS series, Fitzpatrick The compacted mineral was sieved with a sieving tower (AS 400, Retsch), with lowest mesh size of 90 pm. The product fines below 90 pm were discarded.
  • the angle of repose of the compacted, sieved material was then measured with a granulate flow tester (GT, ERWEKA) to ensure an angle of repose well below 50° (with 10 mm funnel).
  • the compacted, sieved material was mixed with 0.5 wt.-% magnesium stearate in a powder blender (Turbula T 10 F, Willi A.Bachofen) and eventually compressed into a tablet using a press (Fette 1200i, Fette Compacting) with a punch diameter of 13 mm and a filling curve of 16 mm. Tabletting speed was about 10 000 tablet /hour. Hardness and size of the final tablets were then measured (MultiTest 50, Pharmatron).
  • the mineral powder and porogen material were first mixed with a powder blender (Turbula T 10 F, Willi A.Bachofen) and then compacted with a roller compactor (CCS series, Fitzpatrick).
  • the compacted mixture was sieved with a sieving tower (AS 400, Retsch), with lowest mesh size of 90 pm. The product fines below 90 pm were discarded.
  • the angle of repose of the compacted, sieved mixture was then measured with a granulate flow tester (GT, ERWEKA) to ensure an angle of repose well below 50° (with 10 mm funnel).
  • GT granulate flow tester
  • the compacted, sieved mixture was mixed with 1 .0 wt.-% magnesium stearate in a powder blender (Turbula T 10 F, Willi A.Bachofen) and eventually compressed into a tablet using a press (Fette 1200i, Fette Compacting) with a punch diameter of 13 mm and a filling curve of 16 mm. Tabletting speed was about 10 000 tablet /hour. Hardness and size of the final tablets were then measured (MultiTest 50, Pharmatron).
  • the green bodies prepared according to Example 3.1 or 3.2., respectively were placed on a bed of zirconia beads on a ceramic charge tray which are then placed in a bench-top electric muffle furnace.
  • the inside of the furnace was flushed with the sintering gas to remove the air and the pressure was adjusted to be above the atmospheric pressure (1.1 - 1.2 bar) while keeping a flow of sintering gas through the furnace.
  • the muffle furnace was heated up and cooled down following the sintering parameters given below. If a change of sintering gas was required during sintering, the flow of the first sintering gas was stopped and replaced by the second sintering gas.
  • the pressure in the furnace was adjusted to be above the atmospheric pressure while keeping a flow of the second sintering gas through the furnace.
  • the pressure inside the furnace was decreased down to the atmospheric pressure. The furnace was opened and sintered ceramic parts were collected.
  • Sintering profile 1 Tablets were sintered in CO2 atmosphere (grade 4.8) at fixed temperature (heat-up ramp of 5°C/min) for 2 or 5 hours and let to cool down.
  • Sintering profile 2 Tablets were sintered in air atmosphere at 1100 °C (heat-up ramp of 5 °C/min) for 1 hour and then at 800 °C for 1 hour in CO2 atmosphere (grade 4.8) and let to cool down.
  • Sintering profile 3 Tablets were sintered in He atmosphere (grade 6.0) at fixed temperature (heat-up ramp of 5 °C/min) for 2 hours and let to cool down.
  • Green bodies were prepared from a composition consisting of SRCC as described in Example 3.1 .
  • the sintering was carried out as described in Example 3.3., wherein sintering profile 1 was applied.
  • the effect of the sintering temperature and sintering duration is shown in Table 3 below.
  • Fig. 1 The effect of sintering temperature and sintering duration on the porosity of the obtained ceramic bodies is shown in Fig. 1 .
  • the graph proves that increasing the sintering temperature from 1000 °C to 1200 °C or the sintering duration from 2 hours to 5 hours results in a reduction of the porosity (see samples 2 to 5).
  • sintering temperatures of 1400 °C a slight increase of porosity was observed for sample 7, which seems to be related to the formation of a tetracalcium phosphate phase, as revealed by XRD.
  • Fig. 2 reveals the effect of sintering temperature and sintering duration on the mineralogical composition of the sintered parts.
  • Increasing the sintering temperature from 1000°C to 1200°C or the sintering duration from 2 hours to 5 hours resulted in a reduction of calcite and increase of lime content (see samples 2 to 5).
  • a sintering temperature of 1400 °C the hydroxyapatite phase was partially converted into tetracalcium phosphate.
  • Table 3 Effect of sintering temperature and sintering duration (comp.: comparative example ,* bulk density obtained from mercury porosimetry analysis).
  • Green bodies were prepared from different mineral compositions, as listed in Table 4 below, using the procedure described in Example 3.1 .
  • the sintering step was carried out as described in Example 3.3., wherein sintering profile 1 or 2 and different temperatures were applied, as indicated in Table 4 below.
  • Fig. 4 shows the mineralogical composition of selected samples before sintering (samples 1 , 8, and 10) and after sintering (samples 4, 9, and 11).
  • a green body produced in accordance with the invention resulted in a ceramic body having a hydroxyapatite content of 94 wt.-%, based on the total weight of the composition, which was higher than the original content contained in the unsintered green body (see Fig. 4, samples 1 and 4).
  • a green body produced in accordance with the invention resulted in a ceramic body having a porosity of 5.4% (sample 4), which was lower than the porosity of 17.4% of a ceramic body (sample 11) produced from the comparative green body with similar mineralogical composition as the invention (sample 10) (see Fig. 3, samples 1 and 4 and samples 10 and 11).
  • a ceramic body produced from hydroxyapatite powder (sample 8)
  • more than half of the hydroxyapatite was converted into p- tricalcium phosphate.
  • Table 4 Effect of mineral composition and sintering profile on the mineralogical composition of the ceramic body (comp.: comparative example, wt.-% based on total weight of the provided composition, * bulk density obtained from mercury porosimetry analysis).
  • Green bodies were prepared from different compositions of SRCC and porogens, as listed in Table 5 below, using the procedure described in Example 3.2.
  • the sintering step was carried out as described in Example 3.3., wherein sintering profile 2 was applied.
  • Fig. 6 shows a correlation between porogen amount and porosity of the samples listed Table 5 below. It can be seen that the porosity increased with the porogen concentration, while a higher compression force led to a decrease in porosity.
  • Green bodies were prepared from different compositions of SRCC and CaF2, as listed in Table 6 below, using the procedure described in Example 3.1.
  • the sintering step was carried out as described in Example 3.3., wherein sintering profile 3 was applied.
  • Samples 4, 21 , and 22 were subjected to the chemical resistance test described in section 2.7. above, wherein the sample mass loss is shown in Fig. 9. It can be seen that resistance to mild acidic conditions (citric acid) of the inventive sample 4 was improved by mixing SRCC with CaF2 and sintering according to sintering profile 1 (sample 21). Moreover, resistance to both mild acidic conditions (citric acid) and harsh acidic conditions (hydrochloric acid) was improved by mixing SRCC with CaF2 and sintering according to sintering profile 3 (sample 22).
  • Table 6 Effect of mineral composition on resistance to acidic conditions.

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Abstract

La présente invention concerne un procédé de fabrication d'un corps en céramique à partir d'une composition comprenant du carbonate de calcium ayant réagi en surface, un corps en céramique pouvant être obtenu à partir dudit procédé, et l'utilisation dudit corps en céramique.
PCT/EP2024/065488 2023-06-06 2024-06-05 Procédé de production d'un matériau biocéramique Pending WO2024251828A1 (fr)

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