CA1299590C - Glass-ceramic article, process for its production and thermally crystallizable glass - Google Patents
Glass-ceramic article, process for its production and thermally crystallizable glassInfo
- Publication number
- CA1299590C CA1299590C CA000568921A CA568921A CA1299590C CA 1299590 C CA1299590 C CA 1299590C CA 000568921 A CA000568921 A CA 000568921A CA 568921 A CA568921 A CA 568921A CA 1299590 C CA1299590 C CA 1299590C
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- CA
- Canada
- Prior art keywords
- glass
- na2o
- total
- cao
- sio2
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000011521 glass Substances 0.000 title claims abstract description 61
- 239000002241 glass-ceramic Substances 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 title claims description 10
- 238000004519 manufacturing process Methods 0.000 title description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 37
- 238000002425 crystallisation Methods 0.000 claims abstract description 37
- 230000008025 crystallization Effects 0.000 claims abstract description 37
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 claims abstract description 34
- 238000010438 heat treatment Methods 0.000 claims abstract description 21
- 229910052906 cristobalite Inorganic materials 0.000 claims abstract description 20
- 229910052681 coesite Inorganic materials 0.000 claims abstract description 17
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 17
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 17
- 229910052682 stishovite Inorganic materials 0.000 claims abstract description 17
- 229910052905 tridymite Inorganic materials 0.000 claims abstract description 17
- 239000013078 crystal Substances 0.000 claims abstract description 16
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052700 potassium Inorganic materials 0.000 claims abstract description 13
- 239000011591 potassium Substances 0.000 claims abstract description 13
- 238000011065 in-situ storage Methods 0.000 claims abstract description 9
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052593 corundum Inorganic materials 0.000 claims abstract description 7
- 229910001845 yogo sapphire Inorganic materials 0.000 claims abstract description 7
- FUJCRWPEOMXPAD-UHFFFAOYSA-N Li2O Inorganic materials [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 claims abstract description 5
- XUCJHNOBJLKZNU-UHFFFAOYSA-M dilithium;hydroxide Chemical compound [Li+].[Li+].[OH-] XUCJHNOBJLKZNU-UHFFFAOYSA-M 0.000 claims abstract 4
- 239000000203 mixture Substances 0.000 claims description 30
- GOLCXWYRSKYTSP-UHFFFAOYSA-N Arsenious Acid Chemical compound O1[As]2O[As]1O2 GOLCXWYRSKYTSP-UHFFFAOYSA-N 0.000 claims description 9
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 claims description 8
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 8
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 claims description 8
- QDOXWKRWXJOMAK-UHFFFAOYSA-N dichromium trioxide Chemical compound O=[Cr]O[Cr]=O QDOXWKRWXJOMAK-UHFFFAOYSA-N 0.000 claims description 8
- GNTDGMZSJNCJKK-UHFFFAOYSA-N divanadium pentaoxide Chemical compound O=[V](=O)O[V](=O)=O GNTDGMZSJNCJKK-UHFFFAOYSA-N 0.000 claims description 8
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 claims description 8
- 238000007665 sagging Methods 0.000 claims description 8
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 7
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 6
- 230000009466 transformation Effects 0.000 claims description 6
- 229910011255 B2O3 Inorganic materials 0.000 claims description 5
- ADCOVFLJGNWWNZ-UHFFFAOYSA-N antimony trioxide Inorganic materials O=[Sb]O[Sb]=O ADCOVFLJGNWWNZ-UHFFFAOYSA-N 0.000 claims description 5
- 238000002844 melting Methods 0.000 claims description 5
- 230000008018 melting Effects 0.000 claims description 5
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 claims description 4
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 claims description 4
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(II) oxide Inorganic materials [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 claims description 4
- YEAUATLBSVJFOY-UHFFFAOYSA-N tetraantimony hexaoxide Chemical compound O1[Sb](O2)O[Sb]3O[Sb]1O[Sb]2O3 YEAUATLBSVJFOY-UHFFFAOYSA-N 0.000 claims description 4
- 238000002834 transmittance Methods 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 3
- 230000000694 effects Effects 0.000 claims description 2
- YEXPOXQUZXUXJW-UHFFFAOYSA-N lead(II) oxide Inorganic materials [Pb]=O YEXPOXQUZXUXJW-UHFFFAOYSA-N 0.000 claims 3
- GNRSAWUEBMWBQH-UHFFFAOYSA-N nickel(II) oxide Inorganic materials [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 claims 3
- IATRAKWUXMZMIY-UHFFFAOYSA-N strontium oxide Inorganic materials [O-2].[Sr+2] IATRAKWUXMZMIY-UHFFFAOYSA-N 0.000 claims 3
- BYFGZMCJNACEKR-UHFFFAOYSA-N aluminium(i) oxide Chemical compound [Al]O[Al] BYFGZMCJNACEKR-UHFFFAOYSA-N 0.000 claims 2
- 239000006092 crystalline glass-ceramic Substances 0.000 claims 1
- 239000007800 oxidant agent Substances 0.000 claims 1
- 239000006064 precursor glass Substances 0.000 abstract description 9
- 238000002360 preparation method Methods 0.000 abstract description 3
- 239000012071 phase Substances 0.000 description 13
- 230000005540 biological transmission Effects 0.000 description 10
- 238000005191 phase separation Methods 0.000 description 8
- 230000007423 decrease Effects 0.000 description 7
- 239000011022 opal Substances 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 6
- 229910052731 fluorine Inorganic materials 0.000 description 6
- 239000011737 fluorine Substances 0.000 description 6
- 239000006132 parent glass Substances 0.000 description 6
- 210000000988 bone and bone Anatomy 0.000 description 5
- 230000001419 dependent effect Effects 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 229910000272 alkali metal oxide Inorganic materials 0.000 description 3
- 238000000280 densification Methods 0.000 description 3
- 230000001747 exhibiting effect Effects 0.000 description 3
- 239000012467 final product Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000000155 melt Substances 0.000 description 3
- 238000007669 thermal treatment Methods 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 239000003086 colorant Substances 0.000 description 2
- 239000006025 fining agent Substances 0.000 description 2
- 239000004615 ingredient Substances 0.000 description 2
- 229910044991 metal oxide Inorganic materials 0.000 description 2
- 150000004706 metal oxides Chemical class 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 229910052573 porcelain Inorganic materials 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 2
- 238000011282 treatment Methods 0.000 description 2
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- 235000003166 Opuntia robusta Nutrition 0.000 description 1
- 244000218514 Opuntia robusta Species 0.000 description 1
- 241000212342 Sium Species 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910000287 alkaline earth metal oxide Inorganic materials 0.000 description 1
- 239000005347 annealed glass Substances 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000006105 batch ingredient Substances 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000005337 ground glass Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000009533 lab test Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 239000012768 molten material Substances 0.000 description 1
- 238000009740 moulding (composite fabrication) Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 235000010344 sodium nitrate Nutrition 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- KUAZQDVKQLNFPE-UHFFFAOYSA-N thiram Chemical compound CN(C)C(=S)SSC(=S)N(C)C KUAZQDVKQLNFPE-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Glass Compositions (AREA)
Abstract
Abstract of the Disclosure This invention relates to the preparation of glass ceramic articles in which potassium fluorrichterite and/or a related fluormica constitutes the predominant crystal phase(s). The precursor glasses can be crystallized in situ very rapidly and exhibit very little thermal deforma-tion during the crystallization heat treatment. The base glasses are essentially free of Li2O and consist essen-tially, expressed in terms of weight percent on the oxide basis, of:
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25
Description
Andrleu-Comte-Ferry-Mazeau 8A-lA-1-17A
59~
GLASS-CERAMIC ARTICLE, PROCESS FOR ITS PRODUCTION
AND THERMALLY CRYSTALLI ZABLE GLASS
:
Background of the Invention Glass-ceramic articles are traditionally prepared through the closely controlled heat treatment of precursor glass articles. On that account, glass-ceramic articles are customarily produced by following three general steps:
first, a vitrifiable batch of a predetermined c~mposition is melted; second, this molten mass is cooled to a tempera-tux at least within the limits of, and normally below, the transformation range and simultaneously made into the form of a glass article having a desired configuration; and, third, this glass article is exposed to a predetermined heat treatment in order to cause the generation of crystals in situ. (The transformation range has been defined as the temperature at which a molten material is transformed into an amorphous mass; this temperature in general being estimated as being in the vicini y of the annealing point of a glass.) During the crystallization heat treatment the glass is heated to temperatures above the transformation range of ; 25 the glass and which approach and ordinarily go beyond its softening point. It is well known that, in these condi-tions, the v~scosity of the glass becomes sufficiently low ~; ' ~
~95~V
so that the article becomes susceptible to thermal deforma-tion~ The severi~y of this phenomenon obviously increases as the temperature approaches the softening point of the glass and goés beyond it.
The crystals developed in a glass-ceramic exhibit a melting point higher than the softening point of the precursor glass. Consequently, by causing crystallization in situ during the heat treatment of a parent glass article in order to convert it into a glass-ceramic, care must be taken in raising the temperature above the transformation range of the glass to develop sufficient crystallization in order to provide an adequate internal structure to support the article, thereby minimizing thermal deformation. One must also realize that the composition of the glass remain-ing in the article continually changes as its componentsbecome an integral part of the crystals during the heat treatment process. In most cases the viscosity of the residual glass is greater than that of the parent glass.
Nevertheless, thermal deformation is an ever present problem; particularly with articles having two dimensions which are large but have narrow cross sections, such as dinner plates. Such products have required the use of formers or supports during the heat treatment of the precursor glass article in order to assure the desired geometry in the final product.
Furthermore, the in situ crystallization of a glass article is effected more rapidly and to a greater extent as the temperature is raised above the transformation range and into the region of the softening point of the glass.
Consequently, for reasons of industrial economy, it is necessary to raise the temperature of crystallization as rapidly as possible up to a temperature as high as possible.
Such practice obviously increases the risk of thermal deformation of the precursor glass article. Therefore, continued research has been carried out to discover glass compositions capable of rapid in situ crystallization and exhibiting only minimum, and preferably practically no, g~
thermal deformation. These researches have been particu-larly active in the area of tableware articles where a primary objective has been to remove the need for formers to support the articles during the heat treatment of the parent glass bodies.
Summary of the Invention The Applicants were able to achieve that objective through the discovery of a very narrow range of glass compositions in the system K2O-Na2O-MgO-CaO-SiO2-Al2O3-F, which compositions can be rapidly crystallized in situ to glass-ceramics wherein potassium fluorrichterite will preferably constitute at least the predominant, if not essentially the sole, crystal phase. In the preferred products, stringently limited concentrations of BaO and P2O5 will also be present. The degree of thermal deforma-tion during the crystallization heat treatment of the precursor glass is so little that it is not necessary to use supports to maintain the dimensions of tableware articles, even for table plates having a diameter of about 28 cm. Furthermore, the final glass-ceramic products have a particularly pleasing aesthetic appearance for tableware, exhibiting the slight translucency associated with fine English porcelain. The tableware articles prepared from precursor glass bodies made from the inventive compositions can be heat treated up to complete crystallization by following a program having a duration as short as two hours. It is necessary to apply a glaze on these articles because the glass-ceramic articles do not display a surface gloss and are not durable enough for tableware use. As the ;; ~ low thermal deformation removes the need for formers, the glaze can be applied on the initial glass articles and be fired during the crystalliæation heat treatment.
The compositions permitting the above-mentioned objective to be achieved are composed essentially, as analyzed in ~eight percent on the oxide basis, of:
.
59~
.~
SiO2 61-70 Na20 0.5-3 A123 2.75-7 K20 2.5-5.5 MgO 11-16 Na20+K20 <6.8 CaO 4.75-9 F 2-3.25 Up to about 2.5% P20~ may be included to reduce the tendency of the ylass to devitrify and up to 3.5% BaO to redu~e its tendencies to devitrify and to opalize.
Some As203 and/or Sb203 may be present in an amount up to 1% in order to perform their usual role as fining agents, while stabilizing the redox state of the glass. Up to about 2~ total of such compatible metal oxides as B203, TiO2, PbO, SrO, ZnO, and ZrO2 can be included with no substantial adverse effect; the B203 level will preferably not exceed 1%.
Thus in one embodi~ent the invention prov~des a glass-ceramia article containi.ng pota~sium ~luorrich-terite and/or a related fluormica as the predominant crystal phase(s) which, in ~he form of bars measuring 9 cm X 1 cm X 5mm, will exhibit sagging during the crystalliza-tion heat treatment not greater than 0.75 mm over a span of : 6.8 cm, and whiCh displays such opacity that the diffuse transmittance of a sample of 2.75 mm thickness is in the j 40-180 r~ngej said glass-ceramic article having a composi-tion essentially free of Li20 and consisting essentially, 25 as expressed in terms of.weight percent on the oxide basis, of:
Si~261-70 Na20 0.5-3 ~aO 0-3.5 A1232075-7 K20 2.5-5.5 P205 0-2.5 MgOll-1~ Na20~K20 <6.8 CaO 4.75-9 F . 2-3~25 ' : 35 -4a;~ 5~.9 In another embodiment the lnvention provides a thermally c~y~tallized glaes characterized in that it ls capable of being crystallized ~n situ in a period o~
two hours to form a highly crystalline glas~-ceramic article containing potassium fluorrichterite and/or a related fluormica ~s the predominant crystal phasels) and which, in the form of bars measuring 9 cm X 1 cm X 5 mm, will exhibit sagging during the crystallization heat treatme~t not greater than 0.75 mm over a span of 6.8 cm, said glass-ceramic article having a composition essentially free of Li2o and consisting essentially, as expressed in terms of weight percent on the oxide basis, of:
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al23 2.75-7 K2O 2.5-5.5 P2O5 0-~.5 MgO11-16 Na2O~K2O ~6.8 CaO4.75-9 F 2-3.25 In a further embodiment the invention provides a method for making such a glass-ceramic article, comp~.sing th~ steps of (a) melting a vitrifiable batch essentially f~ee of Li2o consisting ~ssentially, as expressed in t~rms of weight percent on the oxide basis, : SiO261-70 Na2O 0.5-3 BaO 0-3.5 Al23 2.75-7 K2O 2.5-5.5 P2O5 Q 2.5 MgO11-16 Na2O+K2O <6.8 CaO4.75-9 F 2-3.25 (b~ cooling the resultant melt to a temperature below the transfoxmation range and simultaneously ~orming a glass article having a desired configuration, and ~ c) exposing said glass article to a temperature between about 950~-1050C ~or a period o~ time sufficient to ef~ect the growth of crystals in situ.
B
-4b-It is possible to utilize conventional colorants for glass, such as Fe2O3, CeO2, CoO, Cr2O3, CuO, MnO2, Nio~ and V2O5, in small amounts (t~pically less than 1% total).
An amount of Fe2O3 up to 0.5% produces a yellow tint in the glass-ceramic. An amount of 0.15-0.2% yields a color very near to that of English Wedgwood porcelain.
Given that the yellow tint is due to the presence of the Fe+3 ion, it is preferable to include As2O3 and/or Sb2O3 in the batch and an oxidizing ingredient, such as NaNO3, in order to oxidize the glass and stabilize its redox state.
Laboratory experiments have indicated that when the parent glass bodies are heated, metastable phases are formed above 700C which are transformed at higher tempera-tures (~950-1050C) into potassium fluorrichterite (KNaCaMg5Si8022F'2) as the predominant crystal phase with, perhaps, one or more other crystallographically-related phases, for example, a fluormica.
With compositions o~ the invention in which elements are borderline with respect to the disclosed composition ranges (for example, containing 0.5% Na2O or 7% A12O3), the glass-ceramic probably contains, in addition to, or instead of, potassium fluorrichterite, other related phases. These phases have not been studied in detail and are not readily distinguishable from potassium fluorrichterite. Such necessary detailed study has not been deemed mandatory since the phases impart properties to the final product which are closely related to those exhibited when potassium fluorrichterite constitutes the predominant crystal phaseO
A significant feature o the disclosed glasses is that they undergo a liquid-liquid phase separation when their molten masses are cooled to a glass body (they form dense opal glasses when cooled slowly). It seems that the occurrence of this phase separation, which leads to a large increase in the viscosity of the glass, is a critical factor in obtaining opaque glass-ceramics exhibiting very little thermal deformation, while applying a short crystal-lization heat treatment thereto. Hence, it has been visually observed that the thermal deformation of the parent glass article during the heat treatment decreases in the proportion that it demonstrates a much greater tendency to phase separate. Moreover, the viscosity measurements carried out during the crystallization heat treatment program have indicated that the phase separated glass bodies begin to crystallize at a higher viscosity than those which are practically free of phase separation, and that they retain a higher viscosity during the r~mainder of the heat treatment. It is believed that this behavior is due to differences in the viscosities of the residual glass matrices.
P2O5, F, and, to a lesser extent, A12O3 and SiO2, favor phase separation. In contrast, alkali metal oxides and, to a lesser extent, alkaline earth metal oxides inhibit it. Therefore, according to the amount of each of these elements, it is possible to adjust the value of the opalization liquidus (phase separation liquidus). Values ranging from about 1050C to 1400C can be obtained (a viscosity of about 3000 Pa.S and 20 Pa.S, respectively).
An opalization liquidus lower than 1050C leads generally to a high thermal deformatlon, while a high opalization 9~g :. liquidus makes the glass difficult to form since the opalization leads to a viscosity increas~.
Not only has it ~een observed that the low thermal deformation is related to the phase separation, but also it has been observed that it is a function of the amounts of several critical elements which have to be carefully controlled:
(1) Because MgO is a major constituent of the crystal-line phases which form during the thermal treatment (especially of fluormicas and potassium fluorrichterite), too small an amount leads to insufficient crystallization which, in turn, results in excessive thermal deformation.
59~
GLASS-CERAMIC ARTICLE, PROCESS FOR ITS PRODUCTION
AND THERMALLY CRYSTALLI ZABLE GLASS
:
Background of the Invention Glass-ceramic articles are traditionally prepared through the closely controlled heat treatment of precursor glass articles. On that account, glass-ceramic articles are customarily produced by following three general steps:
first, a vitrifiable batch of a predetermined c~mposition is melted; second, this molten mass is cooled to a tempera-tux at least within the limits of, and normally below, the transformation range and simultaneously made into the form of a glass article having a desired configuration; and, third, this glass article is exposed to a predetermined heat treatment in order to cause the generation of crystals in situ. (The transformation range has been defined as the temperature at which a molten material is transformed into an amorphous mass; this temperature in general being estimated as being in the vicini y of the annealing point of a glass.) During the crystallization heat treatment the glass is heated to temperatures above the transformation range of ; 25 the glass and which approach and ordinarily go beyond its softening point. It is well known that, in these condi-tions, the v~scosity of the glass becomes sufficiently low ~; ' ~
~95~V
so that the article becomes susceptible to thermal deforma-tion~ The severi~y of this phenomenon obviously increases as the temperature approaches the softening point of the glass and goés beyond it.
The crystals developed in a glass-ceramic exhibit a melting point higher than the softening point of the precursor glass. Consequently, by causing crystallization in situ during the heat treatment of a parent glass article in order to convert it into a glass-ceramic, care must be taken in raising the temperature above the transformation range of the glass to develop sufficient crystallization in order to provide an adequate internal structure to support the article, thereby minimizing thermal deformation. One must also realize that the composition of the glass remain-ing in the article continually changes as its componentsbecome an integral part of the crystals during the heat treatment process. In most cases the viscosity of the residual glass is greater than that of the parent glass.
Nevertheless, thermal deformation is an ever present problem; particularly with articles having two dimensions which are large but have narrow cross sections, such as dinner plates. Such products have required the use of formers or supports during the heat treatment of the precursor glass article in order to assure the desired geometry in the final product.
Furthermore, the in situ crystallization of a glass article is effected more rapidly and to a greater extent as the temperature is raised above the transformation range and into the region of the softening point of the glass.
Consequently, for reasons of industrial economy, it is necessary to raise the temperature of crystallization as rapidly as possible up to a temperature as high as possible.
Such practice obviously increases the risk of thermal deformation of the precursor glass article. Therefore, continued research has been carried out to discover glass compositions capable of rapid in situ crystallization and exhibiting only minimum, and preferably practically no, g~
thermal deformation. These researches have been particu-larly active in the area of tableware articles where a primary objective has been to remove the need for formers to support the articles during the heat treatment of the parent glass bodies.
Summary of the Invention The Applicants were able to achieve that objective through the discovery of a very narrow range of glass compositions in the system K2O-Na2O-MgO-CaO-SiO2-Al2O3-F, which compositions can be rapidly crystallized in situ to glass-ceramics wherein potassium fluorrichterite will preferably constitute at least the predominant, if not essentially the sole, crystal phase. In the preferred products, stringently limited concentrations of BaO and P2O5 will also be present. The degree of thermal deforma-tion during the crystallization heat treatment of the precursor glass is so little that it is not necessary to use supports to maintain the dimensions of tableware articles, even for table plates having a diameter of about 28 cm. Furthermore, the final glass-ceramic products have a particularly pleasing aesthetic appearance for tableware, exhibiting the slight translucency associated with fine English porcelain. The tableware articles prepared from precursor glass bodies made from the inventive compositions can be heat treated up to complete crystallization by following a program having a duration as short as two hours. It is necessary to apply a glaze on these articles because the glass-ceramic articles do not display a surface gloss and are not durable enough for tableware use. As the ;; ~ low thermal deformation removes the need for formers, the glaze can be applied on the initial glass articles and be fired during the crystalliæation heat treatment.
The compositions permitting the above-mentioned objective to be achieved are composed essentially, as analyzed in ~eight percent on the oxide basis, of:
.
59~
.~
SiO2 61-70 Na20 0.5-3 A123 2.75-7 K20 2.5-5.5 MgO 11-16 Na20+K20 <6.8 CaO 4.75-9 F 2-3.25 Up to about 2.5% P20~ may be included to reduce the tendency of the ylass to devitrify and up to 3.5% BaO to redu~e its tendencies to devitrify and to opalize.
Some As203 and/or Sb203 may be present in an amount up to 1% in order to perform their usual role as fining agents, while stabilizing the redox state of the glass. Up to about 2~ total of such compatible metal oxides as B203, TiO2, PbO, SrO, ZnO, and ZrO2 can be included with no substantial adverse effect; the B203 level will preferably not exceed 1%.
Thus in one embodi~ent the invention prov~des a glass-ceramia article containi.ng pota~sium ~luorrich-terite and/or a related fluormica as the predominant crystal phase(s) which, in ~he form of bars measuring 9 cm X 1 cm X 5mm, will exhibit sagging during the crystalliza-tion heat treatment not greater than 0.75 mm over a span of : 6.8 cm, and whiCh displays such opacity that the diffuse transmittance of a sample of 2.75 mm thickness is in the j 40-180 r~ngej said glass-ceramic article having a composi-tion essentially free of Li20 and consisting essentially, 25 as expressed in terms of.weight percent on the oxide basis, of:
Si~261-70 Na20 0.5-3 ~aO 0-3.5 A1232075-7 K20 2.5-5.5 P205 0-2.5 MgOll-1~ Na20~K20 <6.8 CaO 4.75-9 F . 2-3~25 ' : 35 -4a;~ 5~.9 In another embodiment the lnvention provides a thermally c~y~tallized glaes characterized in that it ls capable of being crystallized ~n situ in a period o~
two hours to form a highly crystalline glas~-ceramic article containing potassium fluorrichterite and/or a related fluormica ~s the predominant crystal phasels) and which, in the form of bars measuring 9 cm X 1 cm X 5 mm, will exhibit sagging during the crystallization heat treatme~t not greater than 0.75 mm over a span of 6.8 cm, said glass-ceramic article having a composition essentially free of Li2o and consisting essentially, as expressed in terms of weight percent on the oxide basis, of:
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al23 2.75-7 K2O 2.5-5.5 P2O5 0-~.5 MgO11-16 Na2O~K2O ~6.8 CaO4.75-9 F 2-3.25 In a further embodiment the invention provides a method for making such a glass-ceramic article, comp~.sing th~ steps of (a) melting a vitrifiable batch essentially f~ee of Li2o consisting ~ssentially, as expressed in t~rms of weight percent on the oxide basis, : SiO261-70 Na2O 0.5-3 BaO 0-3.5 Al23 2.75-7 K2O 2.5-5.5 P2O5 Q 2.5 MgO11-16 Na2O+K2O <6.8 CaO4.75-9 F 2-3.25 (b~ cooling the resultant melt to a temperature below the transfoxmation range and simultaneously ~orming a glass article having a desired configuration, and ~ c) exposing said glass article to a temperature between about 950~-1050C ~or a period o~ time sufficient to ef~ect the growth of crystals in situ.
B
-4b-It is possible to utilize conventional colorants for glass, such as Fe2O3, CeO2, CoO, Cr2O3, CuO, MnO2, Nio~ and V2O5, in small amounts (t~pically less than 1% total).
An amount of Fe2O3 up to 0.5% produces a yellow tint in the glass-ceramic. An amount of 0.15-0.2% yields a color very near to that of English Wedgwood porcelain.
Given that the yellow tint is due to the presence of the Fe+3 ion, it is preferable to include As2O3 and/or Sb2O3 in the batch and an oxidizing ingredient, such as NaNO3, in order to oxidize the glass and stabilize its redox state.
Laboratory experiments have indicated that when the parent glass bodies are heated, metastable phases are formed above 700C which are transformed at higher tempera-tures (~950-1050C) into potassium fluorrichterite (KNaCaMg5Si8022F'2) as the predominant crystal phase with, perhaps, one or more other crystallographically-related phases, for example, a fluormica.
With compositions o~ the invention in which elements are borderline with respect to the disclosed composition ranges (for example, containing 0.5% Na2O or 7% A12O3), the glass-ceramic probably contains, in addition to, or instead of, potassium fluorrichterite, other related phases. These phases have not been studied in detail and are not readily distinguishable from potassium fluorrichterite. Such necessary detailed study has not been deemed mandatory since the phases impart properties to the final product which are closely related to those exhibited when potassium fluorrichterite constitutes the predominant crystal phaseO
A significant feature o the disclosed glasses is that they undergo a liquid-liquid phase separation when their molten masses are cooled to a glass body (they form dense opal glasses when cooled slowly). It seems that the occurrence of this phase separation, which leads to a large increase in the viscosity of the glass, is a critical factor in obtaining opaque glass-ceramics exhibiting very little thermal deformation, while applying a short crystal-lization heat treatment thereto. Hence, it has been visually observed that the thermal deformation of the parent glass article during the heat treatment decreases in the proportion that it demonstrates a much greater tendency to phase separate. Moreover, the viscosity measurements carried out during the crystallization heat treatment program have indicated that the phase separated glass bodies begin to crystallize at a higher viscosity than those which are practically free of phase separation, and that they retain a higher viscosity during the r~mainder of the heat treatment. It is believed that this behavior is due to differences in the viscosities of the residual glass matrices.
P2O5, F, and, to a lesser extent, A12O3 and SiO2, favor phase separation. In contrast, alkali metal oxides and, to a lesser extent, alkaline earth metal oxides inhibit it. Therefore, according to the amount of each of these elements, it is possible to adjust the value of the opalization liquidus (phase separation liquidus). Values ranging from about 1050C to 1400C can be obtained (a viscosity of about 3000 Pa.S and 20 Pa.S, respectively).
An opalization liquidus lower than 1050C leads generally to a high thermal deformatlon, while a high opalization 9~g :. liquidus makes the glass difficult to form since the opalization leads to a viscosity increas~.
Not only has it ~een observed that the low thermal deformation is related to the phase separation, but also it has been observed that it is a function of the amounts of several critical elements which have to be carefully controlled:
(1) Because MgO is a major constituent of the crystal-line phases which form during the thermal treatment (especially of fluormicas and potassium fluorrichterite), too small an amount leads to insufficient crystallization which, in turn, results in excessive thermal deformation.
(2) Fluorine favors the desired crystallization: it decreases the temperature (or also increases the viscosity) at which crystallization begins. Therefore, too low an amount, i.e., less than 2%, leads to a very low viscosity before crystallization begins and, consequently, to a high thermal deformation. However, the presence of fluorlne in the residual glass decreases its viscosity. This is the reason a high sag is observed when the level exceeds 3.25%
(3) BaO seems to stay mainly in the residual glass.
Consequently, a too high level, viz., higher than 3.5%, leads also to a high thermal deformation.
As mentioned previously, the precursor glass bodies can be subjected to very rapid raises in temperature without undergoing substantial thermal deformation.
Nevertheless, as is the case with other glass-ceramics, crystallization is associated with densification, so that too rapid raises in temperature can lead to great distortion or even breakage, if there is a thermal gradient in the articles. Such gradients exist, for example, when the thermal treatment is perormed in a kiln where the front of the article is heated more rapidly than its rear. The maximum possible speed is, therefore, dependent on the furnace used and on the size and geometry of the articles.
To give an idea, the temperature of the parent glass bodies should generally be raised from about 700C to the maximum a5~q?
temperature ~950-1050C) over a period of time of not less than 30 mlnutes. An exposure period of no greater than 30 minutes at this maximum temperature, typically 10-15 minutes, is sufficient to attain essentially complete crystallization.
The sensitivity of a glass to breakage due to densifi-cation thereof is also strongly dependent on its composi-tion: the composition has an influence on the densification speed and the viscosity at which it occurs. The sensitivity of a glass to breakage inc~eases with this speed and this viscosity. For example, it has been observed that the introduction of Li2o~ in amounts of about 0.5%, frequently leads to fracture of the body during the cryst~llization heat treatment. This risk is particularly high in composi-tions which exhibit great phase separation. It is believedthat L12O favors the crystallization and that breakages are related to a sudden crystallization at temperatures where the glasses have a high viscosity.
On the contrary, it has been observed that K2O widens the temperature range in which densifica~ion takes place and that it decreases the breakage tendency.
The optimum maximum temperature of heating treatment is the temperature which gives the maximum opacity for a low thermal sagging. For a given composition, the opacity and the thermal sagging increase toyether with temperatures in the 950-1050C range. In this range, the optimum maximum temperature is dependent on the composition. In particular, we have observed that it increases when the fluorine level decreases.
Furthermore, the opacity of the final glass-ceramic is strongly dependent upon the amounts of Al2O3 and the alkali metal oxides, and to a lesser extent, the amount of CaO:
~a) A level o~ Al2O3 less than about 2.75~ leads to a product of low opacity.
(b) Similarly, an increase in the concentration of alkali metal oxides causes a decrease in opacity such that a total content of 7% yields a body of very low opacity.
59/C~
~8-(c) A too low CaO level, viz., lower than 4.75%, also gives a low opacity.
The inventive glasses exhibit crystallization liquidi in the temperature range of 1180-1260C which correspond, respectively, ~o viscosities of 300 Pa.S and 80 Pa.S. The viscosity at the crystallization li~uidus decreases with the MgO level. This is the xeason the level of MgO is limited to 16%. On the other hand, P2O5, which probably stays in the residual glass, increases the viscosity at the crystallization liguidus. Consequently, the preferred glasses contain at least 0.5% P2O5.
Below is specified the prefexred area of compositions which represent ~he best compromise between the physical properties of the final product and the melting, forming, and crystallization capabilities of the precursor glass.
Like all the glasses disclosed here, they can be txans-formed through a thermal treatment of less than 2 hours into glass-cerami~s displayiny an opacity close to Wedgwood bone china, and they undergo only a very little thermal deformation during the heat treatment. In addition, they are particularly advantageous from the standpoint of manufacturing because their opalization and crystallization liquidi are higher than 100 Pa.S.
SiO2 63-70 K2O 3.5-5 Al2O33-4.5 Na2O+K2O~5.25-<6.75 MgO 12-14.5 BaO0.75-2.25 CaO 5.5-7.5 P2O50.5-1.5 Na2O 1-2.75 F 2-<3 They may also contain the fining agents, compatible metal oxides, and colorants mentioned above in the amounts specified.
Prior Art U. S. Patent No. 4,467,039 describes the production of glass-ceramic articles containing potassium fluorrichterite as the predominant crystal phase. It has been stated that these articles exhi~it great toughness, great mechanical 3 ~35a5j5~q~
g strength, and low thermal deformation, and that they are essentially composed, in weight percent, of:
SiO2 50-70 K2O 2-12 MgO 8-25 Li2o 0-3 CaO 4-15 A12O3 0-7 Na2O 2-9 F 3-8 Although the broad ranges of components disclosed overlap those of the present invention, there was no recognition of a narrow range of compositions which can be crystallized ln situ very rapidly with nearly no thermal deformation. In fact, rates of temperature increases of 200C/hour to the crystallization temperature and minimum exposure periods of 30 minutes at the crystallization temperature are mentioned. In contrast, the temperature of the glass bodies of the present invention can be raised at rates up to 600C/hour and these bodies do not require more than 15 minutes at the crystallization temperature to arrive at essentially complete crystallization. No composi-tion of the working examples furnished in this patent iswithin the limits of the products of the present invention.
U. S. Patent NoO 4,608,348 describes the preparation of glass-ceramic articles which demonstrate great toughness and very low thermal deformation, which contain potassium fluorrichterite as the predominant crystal phase, but which also contain substantial ~uantities of cristobalite.
Compositions providing such products are compoSed essen-tially, in weight percent, of:
SiO265-69 Na2O1.5-3-3 A1230 75 3-5 K2O4~2-6.0 MgO13.5-17.5 BaO 0-2.5 .
CaO 3-4.8 P2O50-2.5 Li2O0.5-2.0 F 3.3-5.5 The CaO content is lower than that required in the compositions of the present invention; the F content is higher; and ~i2O is a required component. Furthermore, substantial quantities of cristobalite are desired in the glass-ceramic, whereas the presence of cristobalite is neither required nor desired in the products of the present invention.
Descr~ption of_Preferred Embodiments Table I records numerous glass compositions illus-trating the compositional parameters o~ the present inven-tion. The fluorine and oxide contents, except SiO2, havebeen analyzed in terms of weight percent in the glass. The SiO2 content was calculated from the batch materials.
Since it is not known with which of the cations the fluorine is combined, this last is simply indicated in the table in terms of fluorine, conforming to current practice in the material analysis of glass. The actual ingredients entering into the batch for tha preparation of the glass may consist of any materials, either oxides or other compounds, which, when melted together, will be transformed into the desired oxides in the correct proportions.
About 2500 grams of the batch ingredients were mixed, placed in platinum crucibles, and melted for four hours at 1500C. The melts were formed into bars of 1 cm thickness and then transferred to an annealer operating at 600C.
Whereas the compositions given as examples in Table I
only reflect studies conducted in a laboratory, it will be realized that the compositions of the examples conforming with the compositional parameters of the invention could be melted and fashioned by means of conventional industrial equipment for melting and forming glass on a large scale.
In order to determine the resistance of each composi-tion to ~hermal deformation, bars measuring 9 cm long, 1 cm wide, and S mm thick were cut from the annealed glass bars.
These bars were then placed on a ceramic support having a span gap of 6.8 cm and introduced into an electrically-heated furnace operating at 720C. The temperature was then raised to 800C at a rate of about 5C/minute; the ;9~
temperature was then raised to 1000C at a rate of about 16C/minute; this temperature was maintained for 15 minutes;
then the electric current to the furnace was cut off and the furnace left to cool to 800C at a proper rate (about 10C/minute); and thereafter the samples were withdrawn from the furnace.
Table II furnishes the results of various measurements conducted on the crystallized samples. For example:
The degree of sag (Sag) suffered by the 5 mm thick bars was determined. Experience of thermal deformation suffered by table plates of 28 cm diameter has shown that a thermal sag of 0.75 mm in the above test is the maximum that can be tolerated in order to permit the crystallization ln situ of these plates without the use of formers.
The opacity was evaluated by measuring the diffuse transmission of crystallized samples. Opacity is inversely proportional to the diffuse transmittance. The measurements have been made on samples having a thickness of 2.75 mm, a diameter of 32 mm and having their two faces polished. A
small part of one face of the sample (6 mm diameter) is illuminated with a filament lamp. The transmitted light is recorded on a larger surface detector (20 mm diameter) through a ground glass diffuser which is applied against the opposite face of the sample. The diffuse transmission (Diff.) values indicated in Table II reflect an arbitrary scale. On this scale English Wedgwood bone china exhibits diffuse transmissions included in the interval of 90-110, the Limoges porcelains have diffuse transmissions lower than 10, the opal glass of trademark "Arcopal Table" has a diffuse transmission of 250 and the laminated opal glass of trademark 'ICorelle'' a diffuse transmission of 200. It has been estimated that in order for tableware articles to look like English bone china, their diffuse transmission must be in the 40-180 range and preferably in the 50-160 range.
Moduli of rupture (MOR) were measured on ahrade~
samples using techniques conventionaI in the art. The values are indicated in terms of MPa.
s~
The opalization liquidus temperature (Opal) in C, i.e., the phase separation liquidus, was estimated by following the amount of light reflected by the glass during cooling of the melt. The viscosity (Vis.) of the glass, at that temperature, reported in terms of Pa.S, was determined from a viscosity curve measured on the melt in the conven-tion manner.
The crystallization liquidus temperature (Cryst.) in C was determined by conventional methods; i.e., the samples were subjected to isothermal treatments, then observed with an optical microscope. Again, the viscosity of the glass in Pa.S at that temperature was determined from a conventional viscosity curve measured on the glass.
Examples 1-10 are encompassed within the preferred composition region. In addition to a sag less than or e~ual to 0.75 mm, they display a diffuse transmission in the 50-160 range and viscosities at the opalization and crystallization liquidi higher than 100 Pa.S. Moreover, these glasses are the easiest to crystallize.
Example 7 is the most preferred: it displays the best compromise between all the properties. Examples l, 7, 8, 9, and 10 closely approximate the color of English Wedgwood bone china. For example, a glass having the composition of Example 1 and having undergone the heat treatment described above displayed the color coordinates x=0.3135, y=0.3233, and Y=86%, (Illuminant C). As a measure of comparison, Wedgwood bone china exhibited the color coordinates x=0.3139, y=0.3232, and Y=86%. Measurements have been conducted through diffuse reflection with a white back-ground.
Examples 19-22 are loca~ed outside the specified limits. To be precise:
The A12O3 content in Example 19 is too low. The fluorine level of Example 20 is too high. Each of those compositions exhibits excessive thermal sagging and a strong diffuse transmission.
.
35~
The total Na2O+K2O content is too high in Example 21, since the sum of Na20+K20 mus~ be less tha~ 7%. The amount of Na2O in Example 22 is excessive. Those two compositions demonstrate strong diffuse transmission.
Table I
1 2 3 _ 4 S 6 7 SiO2 66.0 66.965.9 66.7 65.2 65.5 67.0 A123 3.6 3.5 3.7 4.3 3.8 3.7 3.7 MgO 13.7 13.413.9 13.5 14.3 13.6 13.0 CaO 6.2 6.4 6.4 6.4 6.3 6.9 6.3 Na2O 2.3 2~2 2.5 2.2 2.4 2.3 1.5 K2O 4.2 4.1 3.8 3.6 4.3 4.3 4.3 ~aO 1.0 1.0 1.0 0.9 1.0 1.0 1.6 P2O5 1.1 1.0 1.2 0.7 1.2 1.2 0.g AS23 0.25 - - - - - 0.25 Fe2O3 0.18 - - - - - 0.17 F 2.6 2.5 2.7 2.9 2.6 2.6 2.4 Na2O+K2O 6.5 6.3 6.3 5.8 6.7 6.6 5.8 8 9 10 11_ 12 13 14 SiO2 65.6 67.366.6 66.7 66.7 66.6 68.0 A123 3-7 3.8 3.6 3.8 3.5 3.9 5O0 MgO 13.7 13.013.2 13.8 13.8 13.6 13.3 CaO 6.4 5.7 6.5 5.4 6.8 6.8 6.4 Na2O 1.0 1.5` 2.0 2.3 1.9 2.3 2.2 K2O 4.9 4.3 4.1 4.2 3.1 4.1 3.4 BaO 1.8 1.6 l.S 1.1 1.0 P2O5 1.0 0.9 0.6 1.2 l.S ~.2 AS23 0.2g Q.260.27 - - - _ 23 0.15 0.170.16 F 2.5 2.5 2.5 2.6 3.0 2.6 3.0 Na2O+K2O 5.9 5.8 6~1 6.5 5.0 6.4 5.6 5~
Table I (con't.) 16 17 18 19 20 21 ~2 SiO2 67~1 66.1 65.064.6 67.8 67.065.465.9 Al23 5 0 3.6 5.03.4 2.6 3.4 3.73.7 MgO 13.3 14.6 13.614.6 13.6 13.313.813.5 CaO 6.4 5.0 6.57.1 602 6.2 6.36.4 Na2O 2.2 2.3 2.22.3 202 2.1 2.73.2 K2O 3.4 3.5 4.13.9 4,1 4.1 4.33.5 BaO 0.9 0.9 1.00.9 0 9 0.9 1.00.9 P2O5 2.1 1.01.5 1.0 1.0 1.21.4 23 ~ ~ - _ _ F 3.0 3.25 2.73.0 2.7 3.5 2.72.6 2 5.6 5.8 6.36.2 6.3 6.2 7.06.7 Table II
1 2 3 4 5 6 _7_ Sag 0.25 0.25 0.250.25 0.25 0.5 0.25 Diff. 130 153 150109 145 141 104 MOR - 83 _ 83 - _ _ opal Temp. - 1160 -1220 - - 1210 Vis. - 600 - 220 - - 220 Cryst.
Temp. - 1220 -1240 - - 1240 Vis. - 200 - 160 - - 160 .
Table II (con' t. ) 8 _9 10 11 12 13 14 Sag 0.25 0.50.5 0.5 0.25 0.25 0.25 Diff. 95 106127 180 60 138 150 Opal Temp. 12301200 - - 1380 1200 Vis. - - - - 30 240 Cryst .
Temp. ~ 1220 1220 Vis . - - - - - 180 16 _ 18 1920 21 22_ _ Sag 0.5 0.250.25 0.25 1.0 3.0 0.75 0.5 Diff. 100 - 100 165 316 242 295 254 Opal Temp. 1200 - 1240 - 1140 1280 Vis. 280 - 140 - - 90 Cryst .
20Temp. 1240 - 1240 1220 Vis. 160 - 140 120
Consequently, a too high level, viz., higher than 3.5%, leads also to a high thermal deformation.
As mentioned previously, the precursor glass bodies can be subjected to very rapid raises in temperature without undergoing substantial thermal deformation.
Nevertheless, as is the case with other glass-ceramics, crystallization is associated with densification, so that too rapid raises in temperature can lead to great distortion or even breakage, if there is a thermal gradient in the articles. Such gradients exist, for example, when the thermal treatment is perormed in a kiln where the front of the article is heated more rapidly than its rear. The maximum possible speed is, therefore, dependent on the furnace used and on the size and geometry of the articles.
To give an idea, the temperature of the parent glass bodies should generally be raised from about 700C to the maximum a5~q?
temperature ~950-1050C) over a period of time of not less than 30 mlnutes. An exposure period of no greater than 30 minutes at this maximum temperature, typically 10-15 minutes, is sufficient to attain essentially complete crystallization.
The sensitivity of a glass to breakage due to densifi-cation thereof is also strongly dependent on its composi-tion: the composition has an influence on the densification speed and the viscosity at which it occurs. The sensitivity of a glass to breakage inc~eases with this speed and this viscosity. For example, it has been observed that the introduction of Li2o~ in amounts of about 0.5%, frequently leads to fracture of the body during the cryst~llization heat treatment. This risk is particularly high in composi-tions which exhibit great phase separation. It is believedthat L12O favors the crystallization and that breakages are related to a sudden crystallization at temperatures where the glasses have a high viscosity.
On the contrary, it has been observed that K2O widens the temperature range in which densifica~ion takes place and that it decreases the breakage tendency.
The optimum maximum temperature of heating treatment is the temperature which gives the maximum opacity for a low thermal sagging. For a given composition, the opacity and the thermal sagging increase toyether with temperatures in the 950-1050C range. In this range, the optimum maximum temperature is dependent on the composition. In particular, we have observed that it increases when the fluorine level decreases.
Furthermore, the opacity of the final glass-ceramic is strongly dependent upon the amounts of Al2O3 and the alkali metal oxides, and to a lesser extent, the amount of CaO:
~a) A level o~ Al2O3 less than about 2.75~ leads to a product of low opacity.
(b) Similarly, an increase in the concentration of alkali metal oxides causes a decrease in opacity such that a total content of 7% yields a body of very low opacity.
59/C~
~8-(c) A too low CaO level, viz., lower than 4.75%, also gives a low opacity.
The inventive glasses exhibit crystallization liquidi in the temperature range of 1180-1260C which correspond, respectively, ~o viscosities of 300 Pa.S and 80 Pa.S. The viscosity at the crystallization li~uidus decreases with the MgO level. This is the xeason the level of MgO is limited to 16%. On the other hand, P2O5, which probably stays in the residual glass, increases the viscosity at the crystallization liguidus. Consequently, the preferred glasses contain at least 0.5% P2O5.
Below is specified the prefexred area of compositions which represent ~he best compromise between the physical properties of the final product and the melting, forming, and crystallization capabilities of the precursor glass.
Like all the glasses disclosed here, they can be txans-formed through a thermal treatment of less than 2 hours into glass-cerami~s displayiny an opacity close to Wedgwood bone china, and they undergo only a very little thermal deformation during the heat treatment. In addition, they are particularly advantageous from the standpoint of manufacturing because their opalization and crystallization liquidi are higher than 100 Pa.S.
SiO2 63-70 K2O 3.5-5 Al2O33-4.5 Na2O+K2O~5.25-<6.75 MgO 12-14.5 BaO0.75-2.25 CaO 5.5-7.5 P2O50.5-1.5 Na2O 1-2.75 F 2-<3 They may also contain the fining agents, compatible metal oxides, and colorants mentioned above in the amounts specified.
Prior Art U. S. Patent No. 4,467,039 describes the production of glass-ceramic articles containing potassium fluorrichterite as the predominant crystal phase. It has been stated that these articles exhi~it great toughness, great mechanical 3 ~35a5j5~q~
g strength, and low thermal deformation, and that they are essentially composed, in weight percent, of:
SiO2 50-70 K2O 2-12 MgO 8-25 Li2o 0-3 CaO 4-15 A12O3 0-7 Na2O 2-9 F 3-8 Although the broad ranges of components disclosed overlap those of the present invention, there was no recognition of a narrow range of compositions which can be crystallized ln situ very rapidly with nearly no thermal deformation. In fact, rates of temperature increases of 200C/hour to the crystallization temperature and minimum exposure periods of 30 minutes at the crystallization temperature are mentioned. In contrast, the temperature of the glass bodies of the present invention can be raised at rates up to 600C/hour and these bodies do not require more than 15 minutes at the crystallization temperature to arrive at essentially complete crystallization. No composi-tion of the working examples furnished in this patent iswithin the limits of the products of the present invention.
U. S. Patent NoO 4,608,348 describes the preparation of glass-ceramic articles which demonstrate great toughness and very low thermal deformation, which contain potassium fluorrichterite as the predominant crystal phase, but which also contain substantial ~uantities of cristobalite.
Compositions providing such products are compoSed essen-tially, in weight percent, of:
SiO265-69 Na2O1.5-3-3 A1230 75 3-5 K2O4~2-6.0 MgO13.5-17.5 BaO 0-2.5 .
CaO 3-4.8 P2O50-2.5 Li2O0.5-2.0 F 3.3-5.5 The CaO content is lower than that required in the compositions of the present invention; the F content is higher; and ~i2O is a required component. Furthermore, substantial quantities of cristobalite are desired in the glass-ceramic, whereas the presence of cristobalite is neither required nor desired in the products of the present invention.
Descr~ption of_Preferred Embodiments Table I records numerous glass compositions illus-trating the compositional parameters o~ the present inven-tion. The fluorine and oxide contents, except SiO2, havebeen analyzed in terms of weight percent in the glass. The SiO2 content was calculated from the batch materials.
Since it is not known with which of the cations the fluorine is combined, this last is simply indicated in the table in terms of fluorine, conforming to current practice in the material analysis of glass. The actual ingredients entering into the batch for tha preparation of the glass may consist of any materials, either oxides or other compounds, which, when melted together, will be transformed into the desired oxides in the correct proportions.
About 2500 grams of the batch ingredients were mixed, placed in platinum crucibles, and melted for four hours at 1500C. The melts were formed into bars of 1 cm thickness and then transferred to an annealer operating at 600C.
Whereas the compositions given as examples in Table I
only reflect studies conducted in a laboratory, it will be realized that the compositions of the examples conforming with the compositional parameters of the invention could be melted and fashioned by means of conventional industrial equipment for melting and forming glass on a large scale.
In order to determine the resistance of each composi-tion to ~hermal deformation, bars measuring 9 cm long, 1 cm wide, and S mm thick were cut from the annealed glass bars.
These bars were then placed on a ceramic support having a span gap of 6.8 cm and introduced into an electrically-heated furnace operating at 720C. The temperature was then raised to 800C at a rate of about 5C/minute; the ;9~
temperature was then raised to 1000C at a rate of about 16C/minute; this temperature was maintained for 15 minutes;
then the electric current to the furnace was cut off and the furnace left to cool to 800C at a proper rate (about 10C/minute); and thereafter the samples were withdrawn from the furnace.
Table II furnishes the results of various measurements conducted on the crystallized samples. For example:
The degree of sag (Sag) suffered by the 5 mm thick bars was determined. Experience of thermal deformation suffered by table plates of 28 cm diameter has shown that a thermal sag of 0.75 mm in the above test is the maximum that can be tolerated in order to permit the crystallization ln situ of these plates without the use of formers.
The opacity was evaluated by measuring the diffuse transmission of crystallized samples. Opacity is inversely proportional to the diffuse transmittance. The measurements have been made on samples having a thickness of 2.75 mm, a diameter of 32 mm and having their two faces polished. A
small part of one face of the sample (6 mm diameter) is illuminated with a filament lamp. The transmitted light is recorded on a larger surface detector (20 mm diameter) through a ground glass diffuser which is applied against the opposite face of the sample. The diffuse transmission (Diff.) values indicated in Table II reflect an arbitrary scale. On this scale English Wedgwood bone china exhibits diffuse transmissions included in the interval of 90-110, the Limoges porcelains have diffuse transmissions lower than 10, the opal glass of trademark "Arcopal Table" has a diffuse transmission of 250 and the laminated opal glass of trademark 'ICorelle'' a diffuse transmission of 200. It has been estimated that in order for tableware articles to look like English bone china, their diffuse transmission must be in the 40-180 range and preferably in the 50-160 range.
Moduli of rupture (MOR) were measured on ahrade~
samples using techniques conventionaI in the art. The values are indicated in terms of MPa.
s~
The opalization liquidus temperature (Opal) in C, i.e., the phase separation liquidus, was estimated by following the amount of light reflected by the glass during cooling of the melt. The viscosity (Vis.) of the glass, at that temperature, reported in terms of Pa.S, was determined from a viscosity curve measured on the melt in the conven-tion manner.
The crystallization liquidus temperature (Cryst.) in C was determined by conventional methods; i.e., the samples were subjected to isothermal treatments, then observed with an optical microscope. Again, the viscosity of the glass in Pa.S at that temperature was determined from a conventional viscosity curve measured on the glass.
Examples 1-10 are encompassed within the preferred composition region. In addition to a sag less than or e~ual to 0.75 mm, they display a diffuse transmission in the 50-160 range and viscosities at the opalization and crystallization liquidi higher than 100 Pa.S. Moreover, these glasses are the easiest to crystallize.
Example 7 is the most preferred: it displays the best compromise between all the properties. Examples l, 7, 8, 9, and 10 closely approximate the color of English Wedgwood bone china. For example, a glass having the composition of Example 1 and having undergone the heat treatment described above displayed the color coordinates x=0.3135, y=0.3233, and Y=86%, (Illuminant C). As a measure of comparison, Wedgwood bone china exhibited the color coordinates x=0.3139, y=0.3232, and Y=86%. Measurements have been conducted through diffuse reflection with a white back-ground.
Examples 19-22 are loca~ed outside the specified limits. To be precise:
The A12O3 content in Example 19 is too low. The fluorine level of Example 20 is too high. Each of those compositions exhibits excessive thermal sagging and a strong diffuse transmission.
.
35~
The total Na2O+K2O content is too high in Example 21, since the sum of Na20+K20 mus~ be less tha~ 7%. The amount of Na2O in Example 22 is excessive. Those two compositions demonstrate strong diffuse transmission.
Table I
1 2 3 _ 4 S 6 7 SiO2 66.0 66.965.9 66.7 65.2 65.5 67.0 A123 3.6 3.5 3.7 4.3 3.8 3.7 3.7 MgO 13.7 13.413.9 13.5 14.3 13.6 13.0 CaO 6.2 6.4 6.4 6.4 6.3 6.9 6.3 Na2O 2.3 2~2 2.5 2.2 2.4 2.3 1.5 K2O 4.2 4.1 3.8 3.6 4.3 4.3 4.3 ~aO 1.0 1.0 1.0 0.9 1.0 1.0 1.6 P2O5 1.1 1.0 1.2 0.7 1.2 1.2 0.g AS23 0.25 - - - - - 0.25 Fe2O3 0.18 - - - - - 0.17 F 2.6 2.5 2.7 2.9 2.6 2.6 2.4 Na2O+K2O 6.5 6.3 6.3 5.8 6.7 6.6 5.8 8 9 10 11_ 12 13 14 SiO2 65.6 67.366.6 66.7 66.7 66.6 68.0 A123 3-7 3.8 3.6 3.8 3.5 3.9 5O0 MgO 13.7 13.013.2 13.8 13.8 13.6 13.3 CaO 6.4 5.7 6.5 5.4 6.8 6.8 6.4 Na2O 1.0 1.5` 2.0 2.3 1.9 2.3 2.2 K2O 4.9 4.3 4.1 4.2 3.1 4.1 3.4 BaO 1.8 1.6 l.S 1.1 1.0 P2O5 1.0 0.9 0.6 1.2 l.S ~.2 AS23 0.2g Q.260.27 - - - _ 23 0.15 0.170.16 F 2.5 2.5 2.5 2.6 3.0 2.6 3.0 Na2O+K2O 5.9 5.8 6~1 6.5 5.0 6.4 5.6 5~
Table I (con't.) 16 17 18 19 20 21 ~2 SiO2 67~1 66.1 65.064.6 67.8 67.065.465.9 Al23 5 0 3.6 5.03.4 2.6 3.4 3.73.7 MgO 13.3 14.6 13.614.6 13.6 13.313.813.5 CaO 6.4 5.0 6.57.1 602 6.2 6.36.4 Na2O 2.2 2.3 2.22.3 202 2.1 2.73.2 K2O 3.4 3.5 4.13.9 4,1 4.1 4.33.5 BaO 0.9 0.9 1.00.9 0 9 0.9 1.00.9 P2O5 2.1 1.01.5 1.0 1.0 1.21.4 23 ~ ~ - _ _ F 3.0 3.25 2.73.0 2.7 3.5 2.72.6 2 5.6 5.8 6.36.2 6.3 6.2 7.06.7 Table II
1 2 3 4 5 6 _7_ Sag 0.25 0.25 0.250.25 0.25 0.5 0.25 Diff. 130 153 150109 145 141 104 MOR - 83 _ 83 - _ _ opal Temp. - 1160 -1220 - - 1210 Vis. - 600 - 220 - - 220 Cryst.
Temp. - 1220 -1240 - - 1240 Vis. - 200 - 160 - - 160 .
Table II (con' t. ) 8 _9 10 11 12 13 14 Sag 0.25 0.50.5 0.5 0.25 0.25 0.25 Diff. 95 106127 180 60 138 150 Opal Temp. 12301200 - - 1380 1200 Vis. - - - - 30 240 Cryst .
Temp. ~ 1220 1220 Vis . - - - - - 180 16 _ 18 1920 21 22_ _ Sag 0.5 0.250.25 0.25 1.0 3.0 0.75 0.5 Diff. 100 - 100 165 316 242 295 254 Opal Temp. 1200 - 1240 - 1140 1280 Vis. 280 - 140 - - 90 Cryst .
20Temp. 1240 - 1240 1220 Vis. 160 - 140 120
Claims (13)
1. A glass-ceramic article containing potassium fluorrich-terite and/or a related fluormica as the predominant crystal phase(s) which, in the form of bars measuring 9 cm X 1 cm X 5mm, will exhibit sagging during the crystalliza-tion heat treatment not greater than 0.75 mm over a span of 6.8 cm, and which displays such opacity that the diffuse transmittance of a sample of 2.75 mm thickness is in the 40-180 range, said glass-ceramic article having a composi-tion essentially free of Li2O and consisting essentially, as expressed in terms of weight percent on the oxide basis, of:
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25
2. A glass-ceramic article according to claim 1 charac-terized in that it consists essentially of:
SiO2 63-70 K2O 3.5-5 Al2O 3-4.5 Na2O+K2O >5.25-<6.75 MgO 12-14.5 BaO 0.75-2.25 CaO 5.5-7-5 P2O5 0.5-1.5 Na2O 1-2.75 F 2-<3
SiO2 63-70 K2O 3.5-5 Al2O 3-4.5 Na2O+K2O >5.25-<6.75 MgO 12-14.5 BaO 0.75-2.25 CaO 5.5-7-5 P2O5 0.5-1.5 Na2O 1-2.75 F 2-<3
3. A glass-ceramic article according to claim 1 charac-terized in that it also contains up to 4% total of at least one member in the indicated proportion of the following groups consisting of up to 1% total of Fe2O3, CeO2, CoO, Cr2O3, CuO, MnO2, NiO, and V2O5, up to 2% total of B2O3, PbO, SrO, ZnO, TiO2, and ZrO2, and up to 1% total of As2O3 and Sb2O3.
4. A glass-ceramic article according to claim 1 character-ized in that it is a tableware article.
5. A thermally crystallized glass characterized in that it is capable of being crystallized in situ in a period of two hours to form a highly crystalline glass-ceramic article containing potassium fluorrichterite and/or a related fluormica as the predominant crystal phase(s) and which, in the form of bars measuring 9 cm X 1 cm X 5 mm, will exhibit sagging during the crystallization heat treatment not greater than 0.75 mm over a span of 6.8 cm, said glass-ceramic article having a composition essentially free of Li2O and consisting essentially, as expressed in terms of weight percent on the oxide basis, of:
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25
6. A thermally crystallizable glass according to claim 5 characterized in that said glass consists essentially of:
SiO2 63-70 K2O 3.5-5 A12O3 3-4.5 Na2O+K2O >5.25-<6.75 MgO 12-14.5 BaO 0.75-2.25 CaO 5.5-7.5 P2O5 0.5-1.5 Na2O 1-2.75 F 2-<3
SiO2 63-70 K2O 3.5-5 A12O3 3-4.5 Na2O+K2O >5.25-<6.75 MgO 12-14.5 BaO 0.75-2.25 CaO 5.5-7.5 P2O5 0.5-1.5 Na2O 1-2.75 F 2-<3
7. A thermally crystallizable glass according to claim 6 characterized in that said glass displays a viscosity at the opalization liquidus higher than 100 Pa.S and a viscos-ity at the crystallization liquidus higher than 100 Pa.S.
8. A thermally crystallizable glass according to claim 5 characterized in that it also contains up to 4% total of at least one member in the indicated proportion of the follow-ing groups consisting of up to 1% total of Fe2O3, CeO2, CoO, Cr2O3, CuO, MnO2, NiO, and V2O5, up to 2% total of B2O3, PbO, SrO, ZnO, TiO2, and ZrO2, and up to 1% total of As2O3 and Sb2O3.
9. A method for making a glass-ceramic article containing potassium fluorrichterite and/or a related fluormica as the predominant crystal phase(s) and which, in the form of bars measuring 9 cm X 1 cm X 5 mm, exhibits sagging during the crystallization heat treatment of not greater than 0.75 mm over a span of 6.8 cm, and which displays such an opacity that the diffuse transmittance of a sample of 2.75 mm thickness is in the 40-180 range, comprising the steps of:
(a) melting a vitrifiable batch essentially free of Li2O consisting essentially, as expressed in terms of weight percent on the oxide basis, of:
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25 (b) cooling the resultant melt to a temperature helow the transformation range and simultaneously forming a glass article having a desired configuration; and (c) exposing said glass article to a temperature between about 950°-1050°C for a period of time sufficient to effect the growth of crystals in situ.
(a) melting a vitrifiable batch essentially free of Li2O consisting essentially, as expressed in terms of weight percent on the oxide basis, of:
SiO2 61-70 Na2O 0.5-3 BaO 0-3.5 Al2O3 2.75-7 K2O 2.5-5.5 P2O5 0-2.5 MgO 11-16 Na2O+K2O <6.8 CaO 4.75-9 F 2-3.25 (b) cooling the resultant melt to a temperature helow the transformation range and simultaneously forming a glass article having a desired configuration; and (c) exposing said glass article to a temperature between about 950°-1050°C for a period of time sufficient to effect the growth of crystals in situ.
10. A method according to claim 9 characterized in that said glass-ceramic consists essentially of:
SiO2 63-70 K2O 3.5-5 Al2O3 3-4.5 Na2O+K2O >5.25-<6.75 MgO 12-14.5 BaO 0.75-2.25 CaO 5.5-7.5 P2O5 0.5-1.5 Na2O 1-2.75 F 2-<3
SiO2 63-70 K2O 3.5-5 Al2O3 3-4.5 Na2O+K2O >5.25-<6.75 MgO 12-14.5 BaO 0.75-2.25 CaO 5.5-7.5 P2O5 0.5-1.5 Na2O 1-2.75 F 2-<3
11. A method according to claim 9 characterized in that the vitrifiable batch also contains a small quantity of an oxidizing agent.
12. A method according to claim 9 characterized in that said period of exposure to a temperature between about 950°-1050°C is at most about 30 minutes.
13. A method according to claim 9 characterized in that the vitrifiable batch also contains up to 4% total of at least one member in the indicated proportion selected from the following groups consisting of up to 1% total of Fe2O3, CeO2, CoO, Cr2O3, CuO, MnO2, NiO, and V2O5, up to 2% total of B2O3, PbO, SrO, ZnO, TiO2, and ZrO2, and up to 1% total of As2O3 and Sb2O3.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR88.01,288 | 1988-02-04 | ||
| FR8801288A FR2626871A1 (en) | 1988-02-04 | 1988-02-04 | VITROCERAMIC ARTICLE, PROCESS FOR MANUFACTURING THE SAME AND THERMALLY CRYSTALLIZABLE GLASS |
| US07/163,528 US4786617A (en) | 1986-10-13 | 1988-03-03 | Glass-ceramic article, process for its production and thermally crystallizable glass |
| US163,528 | 1988-03-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1299590C true CA1299590C (en) | 1992-04-28 |
Family
ID=26226477
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000568921A Expired - Lifetime CA1299590C (en) | 1988-02-04 | 1988-06-08 | Glass-ceramic article, process for its production and thermally crystallizable glass |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU603903B2 (en) |
| BR (1) | BR8900432A (en) |
| CA (1) | CA1299590C (en) |
| DE (1) | DE3861768D1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115784616A (en) * | 2022-11-15 | 2023-03-14 | 常熟佳合显示科技有限公司 | MAS microcrystalline glass and preparation method thereof |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4467039A (en) * | 1983-05-09 | 1984-08-21 | Corning Glass Works | Potassium fluorrichterite glass ceramics and method |
| US4608348A (en) * | 1985-11-04 | 1986-08-26 | Corning Glass Works | Glass-ceramics containing cristobalite and potassium fluorrichterite |
| EP0267682A1 (en) * | 1986-10-13 | 1988-05-18 | Corning Glass Works | Glass-ceramic article process for its production and thermally crystallizable glass |
-
1988
- 1988-06-08 CA CA000568921A patent/CA1299590C/en not_active Expired - Lifetime
- 1988-06-15 DE DE8888305454T patent/DE3861768D1/en not_active Expired - Lifetime
- 1988-06-20 AU AU18140/88A patent/AU603903B2/en not_active Expired
-
1989
- 1989-02-01 BR BR8900432A patent/BR8900432A/en not_active Application Discontinuation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115784616A (en) * | 2022-11-15 | 2023-03-14 | 常熟佳合显示科技有限公司 | MAS microcrystalline glass and preparation method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| BR8900432A (en) | 1989-10-31 |
| AU1814088A (en) | 1989-08-10 |
| DE3861768D1 (en) | 1991-03-14 |
| AU603903B2 (en) | 1990-11-29 |
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