Method of manufacturing a lithium aluminosilicate glass product for a glass-ceramic product

Abstract

A method of manufacturing a lithium aluminosilicate glass product suitable for making a glass-ceramic product, includes melting a vitrifiable mixture of raw materials, which are free from arsenic oxides and antimony oxides, apart from unavoidable traces, refining the molten material, cooling the molten material so as to form a glass, forming of the glass, wherein the vitrifiable mixture of raw materials includes petalite having a fraction by weight of total iron, expressed as Fe.sub.2O.sub.3, less than or equal to 200 ppm.

Claims

1. A method of manufacturing a lithium aluminosilicate glass product comprising: a. melting a vitrifiable mixture of raw materials to form a molten material, b. refining the molten material, c. cooling said molten material so as to form a glass, d. forming of said glass, wherein said vitrifiable mixture of raw materials comprises petalite having a fraction by weight of total iron, expressed as Fe.sub.2O.sub.3, less than or equal to 200 ppm, and wherein the fraction by weight of said petalite in said vitrifiable mixture of raw materials is at least 50%.

2. The method as claimed in claim 1, wherein the mixture of vitrifiable materials is free from arsenic oxides and antimony oxides, apart from unavoidable traces.

3. The method as claimed in claim 1, wherein a refining temperature in step b is at most 1700° C.

4. The method as claimed in claim 1, wherein said petalite comprises petalite mineral in a fraction by weight greater than or equal to 90%.

5. The method as claimed in claim 1, wherein said petalite has a fraction by weight of total iron, expressed as Fe.sub.2O.sub.3, less than or equal to 100 ppm.

6. The method as claimed in claim 1, wherein said vitrifiable mixture of raw materials comprises one or more fining agents selected from SnO.sub.2, CeO.sub.2, MnO.sub.2, fluorides and chlorides.

7. The method as claimed in claim 6, wherein said fining agent is SnO.sub.2, and the fraction by weight of said SnO.sub.2 in the final glass is less than 0.5%.

8. The method as claimed in claim 1, wherein the fraction by weight of total iron, expressed as Fe.sub.2O.sub.3, in the vitrifiable mixture of raw materials is between 4 ppm and 200 ppm.

9. The method as claimed in claim 1, wherein the glass obtained comprises the following constituents in the ranges defined below expressed in fractions by weight: TABLE-US-00015 SiO.sub.2 52-75% Al.sub.2O.sub.3 12-27% Li.sub.2O  2-5.5% Na.sub.2O  0-3%, K.sub.2O  0-3%, CaO  0-5%, MgO  0-5%, SrO  0-5%, BaO  0-5%, ZnO  0-5%, TiO.sub.2  1-6%, ZrO.sub.2  0-3%, P.sub.2O.sub.5  0-8%.

10. A glass product obtainable by the method as claimed in claim 1.

11. The method as claimed in claim 1, further comprising a ceramizing step e).

12. A glass-ceramic product obtainable by the method as claimed in claim 11.

13. Cooking equipment, fireplace insert, glazing for fire protection comprising a glass-ceramic product as claimed in claim 12.

14. The method as claimed in claim 3, wherein a refining temperature in step b is at most 1550° C.

15. The method as claimed in claim 1, wherein the fraction by weight of said petalite in said vitrifiable mixture of raw materials is at least 80%.

16. The method as claimed in claim 1, wherein said petalite has a fraction by weight of total iron, expressed as Fe.sub.2O.sub.3, less than or equal to 50 ppm.

17. The method as claimed in claim 7, wherein said fining agent is SnO.sub.2, and the fraction by weight of said SnO.sub.2 in the final glass is between 0.4% and 0.1%.

18. A method of manufacturing a lithium aluminosilicate glass product comprising: a. melting a vitrifiable mixture of raw materials to form a molten material, b. refining the molten material, c. cooling said molten material so as to form a glass, d. forming of said glass, wherein said vitrifiable mixture of raw materials comprises petalite having a fraction by weight of total iron, expressed as Fe.sub.2O3, less than or equal to 200 ppm, and wherein said petalite has a fraction by weight of fluorine greater than or equal to 0.10%.

19. A method of manufacturing a lithium aluminosilicate glass product comprising: a. melting a vitrifiable mixture of raw materials to form a molten material, b. refining the molten material, c. cooling said molten material so as to form a glass, d. forming of said glass, wherein said vitrifiable mixture of raw materials comprises petalite having a fraction by weight of total iron, expressed as Fe.sub.2O.sub.3, less than or equal to 200 ppm, and wherein the mixture of raw materials comprises nitrates of alkali metals or of alkaline earths, and wherein an amount of the nitrates of alkali metals or of alkaline earths is in a fraction by weight of greater than 0% and at most 4%.

Description

EXAMPLE 1

(1) The advantages of the method of the invention are illustrated perfectly by a first nonlimiting example described below, comparing three green glasses with the same nominal chemical composition, one of which is manufactured according to an embodiment of the method of the invention and the other two according to two methods of the prior art.

(2) The first method of the prior art is a reference method in which the oxides Li.sub.2O, SiO.sub.2 and Al.sub.2O.sub.3 are supplied in the mixture of raw materials in the form of lithium carbonate, silica and alumina, respectively. In said embodiment of the method of the invention, these three oxides are supplied in the form of alumina and petalite Q1. In the second method of the prior art, they are supplied in the form of alumina and petalite Q2. Table 1 below indicates the weights of raw materials making up the three vitrifiable mixtures, M1, M2 and M3 according to each of these methods, respectively. Each mixture contains tin oxide as fining agent in the same proportions. The nominal chemical composition of the green glass obtainable from these three vitrifiable mixtures is given in Table 2 below.

(3) TABLE-US-00002 TABLE 1 Weights of the raw materials (in grams) of the examples of vitrifiable mixtures of the method of the invention (M2) and of the methods of the prior art (M1 and M3). M1 M2 M3 Silica 631.10 — — Alumina 223.63 90.49 85.50 Lithium carbonate 95.04 7.2 5.00 Barium nitrate 33.17 33.17 33.20 Titanium dioxide 17.48 17.63 17.60 Zircon 32.28 32.28 32.30 Zinc oxide 15.47 15.47 15.50 Tin dioxide 3.37 3.37 3.40 Sodium nitrate 14.90 6.50 7.80 Magnesium oxide 5.13 4.70 4.80 Potassium carbonate 3.72 — 21.50 Calcium carbonate 23.47 23.47 — Petalite Q1 — 800.40 — Petalite Q2 — — 811.00 Total 1098.76 1034.68 1037.60

(4) TABLE-US-00003 TABLE 2 Nominal chemical composition, expressed as fraction by weight of oxides, of the green glass obtainable from the vitrifiable mixtures M1, M2 and M3 in Table 1. SiO.sub.2 Al.sub.2O.sub.3 MgO Na.sub.2O K.sub.2O BaO TiO.sub.2 ZnO Li.sub.2O ZrO.sub.2 SnO 67.80 20.11 1.24 0.15 0.19 0.80 2.61 1.61 3.47 1.71 0.30

(5) The chemical compositions of petalites Q1 and Q2, expressed in oxide fractions by weight, and the proportions of the mineral phases, expressed in fractions by weight, that these two petalites contain are given in Tables 3 and 4 below, respectively. The chemical compositions were obtained by chemical analysis by the wet method. The proportions of the mineral phases were calculated by quantifying, by the Rietvelt refinement method, the diffraction patterns obtained by X-ray diffraction.

(6) TABLE-US-00004 TABLE 3 Chemical compositions, in oxide fractions by weight, of the two examples of petalites, Petalite Q1 and Petalite Q2. Petalite Q1 is used in the method of the invention, and Petalite Q2 in the method of the prior art. Petalite Q1 Petalite Q2 Al.sub.2O.sub.3 16.604 16.911 Fe.sub.2O.sub.3 0.009 0.071 Li.sub.2O 4.238 4.435 SiO.sub.2 79.149 78.582

(7) TABLE-US-00005 TABLE 4 Proportions of the mineral phases, expressed in fractions by weight, contained in two examples of petalites, Petalite Q1 and Petalite Q2. Petalite Q1 is used in the method of the invention, and Petalite Q2 in the method of the prior art. (Error: ±1%) Petalite Q1 Petalite Q2 Petalite mineral 91.1 87.8 Quartz 3.8 5.4 Albite 2.6 3.6 Microcline 2.5 — Spodumene — 3.2

(8) Petalite Q1 and petalite Q2 are very similar in terms of composition. The contents of quartz and of albite are comparable in the error bars (±1%). These two petalites therefore different essentially by the total amount of iron, expressed as Fe.sub.2O.sub.3: 0.009% (90 ppm) for petalite Q1 and 0.071% (710 ppm) for petalite Q2.

(9) In order to compare the fusibility and the refining of the three vitrifiable mixtures in Table 1, they were submitted to a test of fusibility and refining according to the following protocol.

(10) After being placed respectively in platinum crucibles, the mixtures were heated at 1550° C. or 1500° C. for 4 hours, and cooled in air with a holding stage at 750° C. for 2 h. Then the fused and then cooled materials corresponding to each vitrifiable mixture were extracted and cut out in the form of plates with a thickness of 4 mm. The two faces of each of the plates were polished mechanically. Six specimen polished plates, three for each temperature, were thus been obtained.

(11) Fusibility and refining were evaluated by measuring the area fraction of defects (bubbles and undissolved particles) present in each of said plates. For this, optical micrographs of each of the six plates were acquired using a suitable light microscope. On the micrographs, in gray scale, the defects appear darker than the fused material, and they can thus be discriminated using a method of image analysis by thresholding. Their area fraction is then calculated by measuring the area covered by the defects on the micrographs transformed by said imaging technique and by referring this area to the total area. The results are presented in Table 5 below.

(12) TABLE-US-00006 TABLE 5 Area fractions of defects (bubbles and undissolved particles) present in the plates of fused material obtained from the mixtures of raw materials M1, M2 and M3 in Table 1 after two tests of fusibility and refining carried out for 4 hours at 1550° C. and 1500° C., respectively. M1 M2 M3 1550° C.-4 h 10.5%  9.3% 45.5% 1500° C.-4 h 24.5% 30.2% —

(13) Comparing the data in Table 5 for the vitrifiable mixtures M1 and M2 corresponding respectively to the reference method of the prior art in which lithium carbonate, alumina and silica are used, and to the method of the invention in which petalite Q1 is used, it can be seen that the proportions of defects are roughly comparable for the green glasses obtained at 1550° C., and that at 1500° C. the proportion of defects in the green glass obtained by the method of the invention is slightly higher. Relative to mixture M3 corresponding to a second method of the prior art in which petalite Q2 is used, this proportion is 2 to 5 times lower at 1500° C. As a result, these results clearly demonstrate that the method of the invention improves the fusibility and the refining of the vitrifiable mixture of raw materials for manufacturing a glass product, starting from which a glass-ceramic product can be obtained.

EXAMPLE 2

(14) The advantages of the method of the invention are illustrated perfectly by a second nonlimiting example described below in which two green glasses with the same nominal chemical composition are compared, one of which is manufactured according to an embodiment of the method of the invention and the other according to a method of the prior art.

(15) The method of the prior art is a reference method in which the oxides Li.sub.2O, SiO.sub.2 and Al.sub.2O.sub.3 are supplied in the mixture of raw materials in the form of alumina, silica and petalite Q2. In the embodiment of the method of the invention, these three oxides are supplied in the form of alumina and petalite Q3. Table 6 below gives the weights of raw materials making up the two vitrifiable mixtures M4 and M5 according to each of these two methods, respectively. The fraction by weight of petalite in each of the vitrifiable mixtures M4 and M5 is above 80%. Each mixture contains tin oxide as fining agent in the same proportions. The nominal chemical composition of the green glass obtainable from these two vitrifiable mixtures is given in Table 7 below.

(16) TABLE-US-00007 TABLE 6 Weights of the raw materials (in grams) of the examples of vitrifiable mixtures of the method of the invention (M5) and of the method of the prior art (M4). M4 M5 Silica 17.85 — Alumina 80.63 78.01 Titanium dioxide 22.22 22.22 Zircon 11.75 11.75 Zinc oxide 13.4 13.4 Tin dioxide 4.1 4.1 Sodium nitrate 1.25 7.5 Potassium carbonate 11 12.1 Calcium carbonate 7 9 Petalite Q2 845 — Petalite Q3 — 860.4 Total 1014.2 1018.48

(17) TABLE-US-00008 TABLE 7 Nominal chemical composition, expressed as fraction by weight of oxides, of the green glass obtainable from the vitrifiable mixtures M4 and M5 in Table 6. SiO.sub.2 Al.sub.2O.sub.3 CaO Na.sub.2O K.sub.2O TiO.sub.2 ZnO Li.sub.2O ZrO.sub.2 SnO.sub.2 67.7 22.0 0.5 0.4 1.0 2.2 1.3 3.7 0.8 0.4

(18) The chemical compositions of petalites Q2 and Q3, expressed in oxide fractions by weight, are shown in Table 8 below. The chemical compositions were obtained by chemical analysis by the wet method.

(19) TABLE-US-00009 TABLE 8 Chemical compositions, in oxide fractions by weight, of the two example petalites, Petalite Q2 and Petalite Q3. Petalite Q3 is used in the method of the invention, and Petalite Q2 in the method of the prior art. Petalite Q2 Petalite Q3 Al.sub.2O.sub.3 16.911 16.817 Fe.sub.2O.sub.3 0.071 0.007 Li.sub.2O 4.435 4.330 SiO.sub.2 78.582 78.846

(20) Petalite Q2 and petalite Q3 are very similar in terms of composition, and different essentially by the total amount of iron, expressed as Fe.sub.2O.sub.3: 0.007% (70 ppm) for petalite Q3 and 0.071% (710 ppm) for petalite Q2.

(21) In order to compare the refining of the two vitrifiable mixtures in Table 6, they were submitted to a test of production and refining according to the following protocol.

(22) After being placed respectively in platinum crucibles, the mixtures were heated at temperatures between 1500° C. and 1600° C. for a time between 2 hours and 4 hours, and cooled in air with a holding stage at 710° C. for 1 hour. Then the fused and then cooled materials corresponding to each vitrifiable mixture were extracted and cut out in the form of a cylinder with a diameter of 2 cm and a height of about 2 cm. Six cylindrical specimens, one for each mixture and each production cycle, were thus obtained.

(23) Refining was evaluated by measuring the volume fraction of bubbles and the size distribution of the bubbles present in each cylinder. For this, each cylinder was analyzed by X-ray tomography using an EasyTom 150 tomograph. The power of the X-ray generator was fixed at 8 W. The acquisition rate was fixed at 3 images per second. The lateral resolution, also called voxel size, was fixed at 13 μm. The volume was reconstructed from the radiographic sections using the Avizo software from the company FEI/Thermo Scientific. The volume fraction of bubbles and the size distribution of the bubbles were calculated using the same Avizo software by a thresholding method.

(24) The values of the volume fractions of bubbles present in each cylinder are presented in Table 9 below. The size distributions of the bubbles present in each cylinder are presented in Table 10 below.

(25) TABLE-US-00010 TABLE 9 Volume fractions of bubbles present in the cylinders of fused material obtained from the mixtures of raw materials M4 and M5 in Table 6. M4 M5 1550° C.-2 h 0.81 0.43 1550° C.-4 h 0.26 0.15 1600° C.-2 h 0.28 0.18

(26) TABLE-US-00011 TABLE 10 Size distributions of the bubbles present in the cylinders of fused material obtained from the mixtures of raw materials M4 and M5 in Table 6. The distributions are expressed in relative proportions by volume in four ranges of bubble diameter. Diameter of the bubbles <100 μm 100-200 μm 200-300 μm >300 μm 1550° C.-2 h M4 50.7% 32.3% 12.4% 4.6% M5 47.8% 32.9% 12.4% 6.8% 1550° C.-4 h M4 71.6% 21.6%  5.8% 1.1% M5 49.3% 38.0% 10.8% 1.9% 1600° C.-2 h M4 93.9%  5.0%  0.9% 0.2% M5 81.0% 14.2%  4.0% 0.8%

(27) Comparing the data in Table 9 for the vitrifiable mixtures M4 and M5, it can clearly be seen that the volume fraction of bubbles is lower in the cylinders obtained with the method of the invention. Moreover, the data in Table 10 show that the proportions of bubbles of larger sizes are higher in the cylinders obtained using the method of the invention. A higher proportion of large bubbles corresponds to a more advanced state of refining. The method of the invention therefore gives quicker refining of a vitrifiable mixture of raw materials for manufacturing a glass product, starting from which a glass-ceramic product can be obtained.

EXAMPLE 3

(28) The advantages of the method of the invention are illustrated perfectly by a third nonlimiting example described below in which two green glasses with the same nominal chemical composition are compared, one of which is manufactured according to an embodiment of the method of the invention and the other according to a method of the prior art.

(29) The method of the prior art is a reference method in which the oxides Li.sub.2O, SiO.sub.2 and Al.sub.2O.sub.3 are supplied in the mixture of raw materials in the form of alumina, silica and petalite Q2. In the embodiment of the method of the invention, these three oxides are supplied in the form of alumina, silica and petalite Q1. Table 11 below indicates the weights of raw materials making up the two vitrifiable mixtures M6 and M7, according to each of these two methods, respectively. The fraction by weight of petalite in each of the vitrifiable mixtures M6 and M7 is 50%. Each mixture contains tin oxide as fining agent in the same proportions. The nominal chemical composition of the green glass obtainable from these two vitrifiable mixtures is given in Table 12 below.

(30) TABLE-US-00012 TABLE 11 Weights of the raw materials (in grams) of the examples of vitrifiable mixtures of the method of the invention (M7) and of the method of the prior art (M6). M6 M7 Silica 235.6 233.7 Alumina 142.55 144.3 Lithium carbonate 47.7 50.7 Barium nitrate 20.23 20.23 Titanium dioxide 27.9 27.9 Zircon 26.85 26.85 Zinc oxide 1.95 1.95 Tin dioxide 3.06 3.1 Magnesium oxide 3 3 Potassium carbonate 8.75 4.69 Calcium carbonate 6.5 7.5 Petalite Q1 — 524 Petalite Q2 525 — Total 1049.1 1047.9

(31) TABLE-US-00013 TABLE 12 Nominal chemical composition, expressed as fraction by weight of oxides, of the green glass obtainable from the vitrifiable mixtures M6 and M7 in Table 11. SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Li.sub.2O Na.sub.2O K.sub.2O TiO.sub.2 ZrO.sub.2 BaO ZnO SnO.sub.2 65.03 22.72 0.43 0.31 4.18 0.26 0.75 2.77 1.83 1.22 0.19 0.3

(32) The chemical compositions of petalites Q1 and Q2, expressed in oxide fractions by weight, are identical to those of example 1 given in Table 3.

(33) In order to compare the refining of the two vitrifiable mixtures in Table 11, they were submitted to a production and fining test according to the following protocol.

(34) After being placed respectively in platinum crucibles, the mixtures were heated at temperatures between 1500° C. and 1650° C. for a time between 2 hours and 4 hours, and cooled in air with a holding stage at 710° C. for 1 hour. Then the fused and then cooled materials corresponding to each vitrifiable mixture were extracted and cut out in the form of a cylinder with a diameter of 2 cm and a height of about 2 cm. Six cylindrical specimens, one for each mixture and each production cycle, were thus been obtained.

(35) Refining was evaluated by measuring the volume fraction of bubbles present in each cylinder. For this, each cylinder was analyzed by X-ray tomography using an EasyTom 150 tomograph. The power of the X-ray generator was fixed at 8 W. The acquisition rate was fixed at 3 images per second. The lateral resolution, also called voxel size, was fixed at 13 μm. The volume was reconstructed from the radiographic sections using the Avizo software from the company FEI/Thermo Scientific. The volume fraction of bubbles was calculated using the same Avizo software by a thresholding method.

(36) The values of the volume fractions of bubbles present in each cylinder are presented in Table 13 below.

(37) TABLE-US-00014 TABLE 13 Volume fractions of bubbles present in the cylinders of fused material obtained from the mixtures of raw materials M4 and M5 in Table 11. M6 M7 1550° C.-4 h 0.17 0.12 1600° C.-2 h 0.43 0.11 1650° C.-2 h 0.03 0.02

(38) Comparing the data in Table 13 for the vitrifiable mixtures M6 and M7, it can be seen that the volume fraction of bubbles is lower in the cylinders obtained with the method of the invention. These results demonstrate that the method of the invention improves the refining of the vitrifiable mixture of raw materials for manufacturing a glass product, starting from which a glass-ceramic product is obtainable.