Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/06—Permanent moulds for shaped castings
  • B22C9/061—Materials which make up the mould
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/0087—Uses not provided for elsewhere in C04B2111/00 for metallurgical applications

Definitions

• the invention relates to a new process for the manufacture of an insulating, rigid refractory material with high open porosity; it also relates to isotropic rigid insulating refractory materials obtained in this way.
• Insulating refractory materials based on brick or concrete are known, the densities of which are between 0.5 and 1.5, but the purity or nature of which often limits the refractant at temperatures of 1200 ° C. and above.
• the porosity is closed, therefore not accessible, which greatly limits their applications.
• fibrous insulating materials have been proposed, in particular in the form of sheets, which have the drawback of not being rigid.
• these products are generally quite chemically pure, their temperature stability is often very insufficient and these products are not isotropic.
• the invention also relates to a method for manufacturing such materials which are dimensionally stable and isotropic.
• This process for the manufacture of a rigid insulating refractory material with high open porosity which consists of:
• the ceramic powders have dimensions of less than one hundred and fifty (150) micrometers and, once stacked, have an expanded density of less than 1.5;
• the binding composition contains from 20 to 150 grams per liter of ceramizable dry extracts
• the weight ratio between the binding material and the ceramic powder is between zero five (0.5) and one and a half (1.5).
• the ceramic powders have dimensions close to one hundred (100) micrometers and have an alumina content of at least 40%, preferably greater than 90% and even 95%; - The ceramic powders have a form factor or an internal porosity such that their expanded density is between 0.5 and 1.2; in practice, the powders are, for example, prepared by grinding ceramic fibers carefully selected for their chemical composition; -
• the binding composition is a liquid or a pseudo-liquid and comprises from 50 to 80 grams per liter of ceramizable dry extracts;
• the dry ceramizable extract is of the silica-alumina type and contains less than 0.5% of impurities
• the product obtained is dried at 110-130 ° C for at least twenty-four hours, then pyrolysis at a temperature of at least 980 ° C, preferably 1200 ° C, for example for six hours and more.
• a second binder composition of refractory oxide precursor chosen from the chemical groups containing zirconium and yttrium can be carried out either in the mixture before stirring, or before pyrolysis, or even after ceramization, which requires a new cycle of drying, pyrolysis and ceramization.
• the purpose of adding this second composition is essentially to modify certain properties such as, for example, the surface tension forces which induce non-wettability or the catalytic effects by formation of discrete deposits.
• the invention also relates to the rigid insulating refractory material obtained.
• This material based on bonded ceramic powders is characterized in that it is isotropic and contains powders or fibers whose dimensions are less than one hundred and fifty (150) micrometers, preferably close to one hundred (100) micrometers, and contains at least 80% alumina; this material has an open porosity of at least 70% and a mechanical strength allowing it to withstand a pressure of at least thirty centimeters of molten metal at 1550 ° C, and finally, a flexural modulus between 2 and 10 MPa and a thermal conductivity at 1000 ° C of the order of 0.3 W / mK.
• the powders or fibers have a dimension of less than one hundred and fifty (150) micrometers and preferably between ten (10) and one hundred and fifty (150) micrometers. It was observed that if this dimension was less than ten (10) micrometers, products were obtained which were much too dense and not very insulating. On the other hand, if the dimensions are greater than one hundred and fifty (150) micrometers, the material becomes too porous and consequently has insufficient mechanical strength. In addition, it becomes anisotropic.
• the ceramic powders contain at least 40% of alumina, the percentage being able to be much higher (95% and more) depending on the envisaged applications.
• the ceramic powders are ground fibers with lengths of less than 150 micrometers. This provides the finished product with regular open porosity, excellent dimensional stability at high temperatures and an isotropic structure significantly superior to that of conventional isometric crystalline powders.
• Binders in liquid form must be pure and compatible with ceramic powders.
• materials of common use are used for this type of application. Mention may be made of mineral binders such as for example those based on aluminum silicate, magnesium, calcium or zirconium, aluminum phosphate. It is also possible to use gelling solutions (sol / gel) comprising an appreciable proportion of silica and alumina.
• gelling solutions sol / gel
• organic binders which have the advantage of power. destroy itself completely during the pyrolysis treatment.
• silica-aluminous sol-gel binders or even of zirconia and / or yttrium oxide.
• the liquid binder composition must have sufficient rheological properties to properly coat the ceramic powders.
• the binder composition may also contain plasticizers.
• the binding composition contains from 20 to 150 grams per liter of dry extracts, preferably between 50 and 80 grams per liter.
• the ratio between the binder composition and the powder must be between 0.7 and 10 to be pourable. It has been observed that if this ratio is less than 0.7, the mixture obtained is not pourable because it is too pasty. On the other hand, if this ratio exceeds 10, the mixture becomes too liquid to be homogeneously pourable.
• the binder and the powder are mixed by any known method.
• the mixture is then poured in a known manner either in the form of a blank which will subsequently be machined, or in the form of a block.
• This mixture is then drained by gravity, by overflow after sedimentation, or by the process which simultaneously consists of vibrating, pressing and draining as described in document EP-A-0 145 621 of the Applicant.
• the material is poured, it is dried in particular in a dry oven at 110-130 ° C for twenty-four to thirty-six hours until a constant weight is obtained, then in known manner, it is pyrolysed at more than 950 ° C, preferably at 1200 ° C.
• the ceramic powders are obtained by grinding ceramic fibers by any known means, until the desired particle size is obtained so that when these powders are put in heaps, their bulk density is less than 1.5.
• the powders are agglomerated into porous granules, so that the bulk density is less than 1.5.
• the dried and cooked material is then impregnated with a precursor solution of an oxide, such as yttrium acetate, a rare earth acetate, zirconium acetate, or a precursor solution of a meta-catalyst such as platinum or nickel chloride, etc.
• a precursor solution of an oxide such as yttrium acetate, a rare earth acetate, zirconium acetate, or a precursor solution of a meta-catalyst such as platinum or nickel chloride, etc.
• this precursor lines the pores of the material without plugging them and thus gives the material either properties of non-wettability by molten metals, such as steel or copper, or gives the material the desired catalytic properties.
• Ceramic fibers containing 97% of alumina are ground, so as to obtain powders of dimensions close to 100 microns and of bulk density when put in a heap of 0.7.
• the mixture is then poured into a mold, the bottom of which is lined with a perforated fabric to allow the excess binder to be drained.
• the mixture is vibrated to remove air bubbles.
• This mixture cast in the form of a block, is dried in an oven for twenty-four hours at 130 ° C. and pyrolysis for six hours at 1200 ° C.
• An insulating refractory material is obtained, the density of which is 0.8, which has an alumina content greater than 85%, a flexural modulus of 3 MPa, a thermal conductivity at 1000 ° C. of 0.34 W / mK and a fully open porosity close to 80%.
• This material has sufficient mechanical strength to contain a height of 20 cm of stainless steel melted at 1550 ° C without penetration of the metal into the pores.
• Example 1 is repeated.
• the mixture When the mixture has been dried, it is impregnated with a concentrated zirconium acetate composition and the whole is dried so as to obtain a continuous deposit of zirconium salt on all the walls of the pores.
• an insulating material of density 0.9 is obtained having the same physical characteristics as the material of Example 1, and having no surface attack by molten steels, even slight after several casting passes.
• Example 3 Example 1 is repeated, but using powders close to fifty (50) micrometers. We get an expanded density of 1.15. The material obtained has mechanical characteristics up to 10 MPa. On the other hand, it is slightly less porous (70%) and therefore less insulating. It lends itself without problem to the treatment of Example 2.
• Example 2 The mixture is poured, vibrated and dried as in Example 1 and pyrolysis at 1500 ° C. A rigid machinable material with a density close to 0.7 is obtained, very refractory and very stable in size usable for thermal insulation between 1700 and 2000 ° C., as well as for the casting of copper alloys.
• the rigid insulating refractory materials obtained in this way are isotropic, moderately dense, rigid and therefore machinable and stable without sintering up to temperatures up to 1550 ° C. and above. These materials also have a totally open porosity, that is to say the pores of which are interconnected with one another and open onto the faces of the material.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Ceramic Engineering (AREA)
• Mechanical Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Porous Artificial Stone Or Porous Ceramic Products (AREA)

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• 1992
  • 1992-01-14 FR FR9200518A patent/FR2686081B1/fr not_active Expired - Fee Related
  • 1992-12-17 WO PCT/FR1992/001198 patent/WO1993014045A1/fr not_active Ceased
  • 1992-12-17 CA CA 2104379 patent/CA2104379A1/fr not_active Abandoned
  • 1992-12-17 JP JP5512179A patent/JPH06506437A/ja active Pending
  • 1992-12-17 AU AU33571/93A patent/AU3357193A/en not_active Abandoned
• 1993
  • 1993-07-27 EP EP19930902343 patent/EP0580832A1/de not_active Withdrawn

Non-Patent Citations (1)

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