Transparent β-quartz glass-ceramics with low lithium content

Abstract

The present application provides transparent glass-ceramics of β-quartz of composition containing a small content of lithium, articles constituted at least in part of said glass-ceramics, glasses precursors of said glass-ceramics, and also a method of preparing said articles. Said glass-ceramics have a composition, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed as percentages by weight of oxides, containing: 62% to 68% of SiO.sub.2; 17% to 21% of AI.sub.2O.sub.3; 1% to <2% of Li.sub.2O; 1% to 4% of MgO; 1% to 6% of ZnO; 0 to 4% of BaO; 0 to 4% of SrO; 0 to 1% of CaO; 1% to 5% of TiO.sub.2; 0 to 2% of ZrO.sub.2; 0 to 1% of Na.sub.2O; 0 to 1% of K.sub.2O; with Na.sub.2O+K.sub.2O+BaO+SrO+CaO<6%; optionally up to 2% of at least one fining agent comprising SnO.sub.2; and optionally up to 2% of at least one coloring agent.

Claims

1. A transparent glass-ceramic containing a solid solution of β-quartz as its main crystalline phase, the composition of which, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed as percentages by weight of oxides, comprises: 62% to 68% of SiO.sub.2; 17% to 21% of Al.sub.2O.sub.3; 1% to <2% of Li.sub.2O; 1% to 4% of MgO; 1% to 6% of ZnO; 0 to 4% of BaO; 0 to 4% of SrO; 0 to 1% of CaO; 1% to 5% of TiO.sub.2; 0 to 2% of ZrO.sub.2; 0 to 1% of Na.sub.2O; 0 to 1% of K.sub.2O; with Na.sub.2O+K.sub.2O+BaO+SrO+CaO≤6%; optionally up to 2% of at least one fining agent comprising SnO.sub.2; and 0.01% to 2% of at least one coloring agent, wherein the coloring agent comprises 0.005% to 0.1% V.sub.2O.sub.5 mixed with at least one other coloring agent selected from CoO, Cr.sub.2O.sub.3, and Fe.sub.2O.sub.3; wherein the transparent glass ceramic comprises a coefficient of thermal expansion CTE.sub.25° C.-300° C. of less than 20.Math.10.sup.−7K.sup.−1; and the transparent glass ceramic has a thickness from 1 mm to 8 mm and an integrated transmission of less than 10% while maintaining transmission at 625 nm greater than 1% and at 950 nm from 50% to 75%.

2. The glass-ceramic according to claim 1, wherein the composition comprises 1% to 1.9% of Li.sub.2O.

3. The glass-ceramic according to claim 1, wherein the composition comprises 17.5% to 19% of Al.sub.2O.sub.3.

4. The glass-ceramic according to claim 1 wherein the composition comprises 1% to 3% of MgO.

5. The glass-ceramic according to claim 1, wherein the composition comprises 1% to 4% of ZnO.

6. The glass-ceramic according to claim 1, wherein the composition comprises ZrO.sub.2.

7. The glass-ceramic according to claim 1, wherein the composition comprises 0.05% to 0.6% of SnO.sub.2.

8. An article constituted, at least in part, of a glass-ceramic according to claim 1.

9. A method of preparing an article constituted, at least in part, of a glass-ceramic containing a solid solution of β-quartz as its main crystalline phase, comprising in succession: melting a charge of raw materials able to vitrify, followed by fining the resulting molten glass; cooling the resulting fined molten glass and simultaneously shaping it to the shape desired for the intended article; and applying ceramming heat treatment to said shaped glass; wherein said charge has a composition that makes it possible to obtain the transparent glass-ceramic, the composition of which, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed as percentages by weight of oxides, comprises: 62% to 68% of SiO.sub.2; 17% to 21% of Al.sub.2O.sub.3; 1% to <2% of Li.sub.2O; 1% to 4% of MgO; 1% to 6% of ZnO; 0 to 4% of BaO; 0 to 4% of SrO; 0 to 1% of CaO; 1% to 5% of TiO.sub.2; 0 to 2% of ZrO.sub.2; 0 to 1% of Na.sub.2O; 0 to 1% of K.sub.2O; with Na.sub.2O+K.sub.2O+BaO+SrO+CaO≤6%; 0 to 2% of at least one fining agent comprising SnO.sub.2; and 0.01% to 2% of at least one coloring agent, wherein the coloring agent comprises 0.005% to 0.1% V.sub.2O.sub.5 mixed with at least one other coloring agent selected from CoO, Cr.sub.2O.sub.3, and Fe.sub.2O.sub.3, wherein the transparent glass ceramic comprises a coefficient of thermal expansion CTE.sub.25° C.-300° C. of less than 20.Math.10.sup.−7K.sup.−1, the transparent glass ceramic having a thickness from 1 mm to 8 mm and an integrated transmission of less than 10% while maintaining transmission at 625 nm greater than 1% and at 950 nm from 50% to 75%.

10. The method according to claim 9, wherein said charge of raw materials able to vitrify, free of As.sub.2O.sub.3 and Sb.sub.2O.sub.3, except for inevitable traces, contains SnO.sub.2 as fining agent.

11. The method of claim 10, wherein the charge of raw materials able to vitrify, free of As.sub.2O.sub.3 and Sb.sub.2O.sub.3, except for inevitable traces, comprises 0.05% to 0.6% of SnO.sub.2.

12. The glass-ceramic according to claim 2, wherein the composition comprises 1.5% to 1.9% of Li.sub.2O.

13. The glass-ceramic of claim 5, wherein the composition comprises 3% to 4% of ZnO.

14. The glass-ceramic according to claim 6, wherein the composition 0.5% to 2% of ZrO.sub.2.

15. The glass-ceramic according to claim 6, wherein the composition 1% to 2% of ZrO.sub.2.

16. The glass-ceramic according to claim 7, wherein the composition comprises 0.15% to 0.4% of SnO.sub.2.

Description

EXAMPLES

(1) To produce batches of 1 kilogram (kg) of precursor glass, the raw materials, in the proportions specified in the first portion of the table below (proportions expressed by (weight % of) oxides) (which table is spread over several pages), were mixed together carefully.

(2) The mixtures were placed for melting in crucibles made of platinum. The crucibles containing said mixtures were then placed in a oven preheated to 1550° C. They were subjected therein to a melting cycle of the following type: temperature rise from 1550° C. to 1670° C. in 1 h; temperature maintained at 1670° C. for 5 h 30.

(3) The crucibles were then extracted from the oven and the molten glass was poured onto a preheated steel plate. It was rolled on the plate to a thickness of 6 mm. Glass plates were thus obtained. They were annealed at 650° C. for 1 h and subsequently cooled down slowly. The properties of the resulting glasses are given in the second portion of the table below.

(4) Viscosities were measured using a rotational viscosimeter (Gero).

(5) T.sub.30 Pa.Math.s (° C.) corresponds to the temperature at which the viscosity of the glass was 30 Pa.Math.s.

(6) The resistivity of the glass was measured at high temperature, on a thickness of 1 centimeter (cm) of molten glass, using a 4-point contact RLC bridge. The table gives the resistivity measured at the temperature at which the viscosity was 30 Pa.Math.s.

(7) T.sub.liq (° C.) is the liquidus temperature. The liquidus is given by a range of associated temperatures and viscosities: the highest temperature corresponds to the minimum temperature at which no crystal was observed, the lowest temperature corresponds to the maximum temperature at which crystals were observed.

(8) The devitrification characteristics were determined as follows. 0.5 cubic centimeter (cm.sup.3) samples of glass were subjected to the following heat treatment: placing in a oven preheated to 1430° C.; maintaining this temperature for 30 min; lowering to the test temperature, T, at a rate of 10° C./min; maintaining this temperature for 17 h; and quenching the samples.

(9) The crystals present, if any, were observed by optical microscopy. The ceramming cycle performed was as follows: rapid temperature rise up to 500° C.; temperature rise from 500° C. to 650° C. at a heating rate of 23° C./min; temperature rise from 650° C. to 820° C. at a heating rate of 6.7° C./min; temperature rise from 820° C. to the maximum temperature Tmax (specified in the table) at a rate of 15° C./min; maintaining this temperature Tmax for 7 min (in all of the examples except example 18 (comparative example, see below) with the ceramming treatment Ceram 1); cooling down to 850° C. at 35° C./min; and cooling down to ambient temperature as a function of the inertia of the oven.

(10) For certain examples (examples 1, 2, 4, 18 and 20) the results are given as obtained at the end of two different ceramming treatments (Ceram 1 and Ceram 2, which differ in the value of their Tmax).

(11) The ceramming cycle Ceram 1 of example 18 (Tmax=830° C.) does not actually correspond to the “general” ceramming cycle specified above. It was as follows: temperature rise up to 710° C. at a heating rate of 22.5° C./min; temperature maintained at 710° C. for 60 min; temperature rise from 710° C. to 830° C. at a heating rate of 24° C./min; temperature maintained at 830° C. for 30 min; and cooling to ambient temperature as a function of the inertia of the oven. The properties of the glass-ceramics obtained are given in the last portion of Table 1 below.

(12) These glass-ceramics contain a solid solution of β-quartz as the main crystalline phase (as verified by X-ray diffraction) (with the exception of that of comparative example 16). Thus, the glass-ceramics of examples 5 and 6 respectively contain 96% and 95% (wt. %) of solid solution of β-quartz phase (relative to the total crystallized fraction) and the mean sizes of their β-quartz crystals respectively were 46 nm and 43 nm. The percentage of β-quartz solid solution and the mean sizes of the crystals were determined by the Rietveld method.

(13) The CTE (coefficients of thermal expansion (from ambient temperature (25° C.) to 300° C. (CTE.sub.25-300° C.) were measured on bar-shaped glass-ceramic samples with a high-temperature dilatometer (DIL 402C, Netzsch) at a heating rate of 3° C./min.

(14) The aspect of the samples (transparency, color) is given in the table.

(15) For some samples, total and diffuse transmission measurements were carried out at 4 mm using a Varian spectrophotometer (model Cary 500 Scan), fitted with an integrating sphere. On the basis of these measurements, the integrated transmission (TL (%)) in the visible range (between 380 and 780 nm) and the diffusion percentage (Diffusion (%)) were calculated in application of the standard ASTM D 1003-13 (with D65 illuminant and 2° observer). Transmission values (at 625 nm (T.sub.625 nm), at 950 nm (T.sub.950 nm)) are also specified for some samples. Examples 1 to 14 in the table illustrate the present application. Examples 1 to 4 are preferred because of the values for the liquidus viscosity of the precursor glasses.

(16) Examples 15 to 21 (of the table) are comparative examples.

(17) In example 15, the Al.sub.2O.sub.3 content is too high (21.48%>21%) and the observed devitrification of the glass is unacceptable (said glass does not have the required properties).

(18) In example 16, the Li.sub.2O and Al.sub.2O.sub.3 contents are too small and the Na.sub.2O+K.sub.2O+BaO+CaO content is too large. Only a small quantity of crystals formed during the heat treatment and they were spinel crystals and not a solid solution of β-quartz. Consequently, the CTE after ceramming was too high.

(19) In example 17, the Li.sub.2O, Al.sub.2O.sub.3, and ZnO contents are too large, the SiO.sub.2 content is too small. Consequently, the glass possesses devitrification characteristics that are unacceptable.

(20) In example 18, the MgO content is too large, and consequently the CTE of the glass-ceramics is too high.

(21) In example 19, the MgO content is too small and the ZnO content is large. Consequently, the liquidus temperature is very high and the viscosity at the liquidus is too low (the glass does not have the required properties).

(22) In example 20, the ZnO content is too small and the MgO content is high. Consequently, the CTE of the glass-ceramic is too high or the glass-ceramic shows optical properties that are unacceptable.

(23) In example 21, the ZnO content is too high. Consequently, the high-temperature viscosity of the glass is very low and the liquidus temperature is high, so the viscosity at the liquidus is too small (the glass does not have the required properties).

(24) TABLE-US-00002 TABLE Examples (wt %) 1 2 3 4 5 SiO.sub.2 66.71 66.61 66.51 65.97 64.10 Al.sub.2O.sub.3 18.10 18.10 18.10 18.89 19.72 Li.sub.2O 1.63 1.63 1.63 1.62 1.86 MgO 2.17 2.17 2.17 2.16 2.47 ZnO 3.08 3.08 3.08 3.07 3.56 BaO 2.47 2.47 2.47 2.46 2.46 CaO 0.44 0.44 0.44 0.44 0.44 TiO.sub.2 2.99 2.80 2.62 2.98 2.98 ZrO.sub.2 1.33 1.62 1.90 1.33 1.33 Na.sub.2O 0.61 0.61 0.61 0.61 0.61 K.sub.2O SnO.sub.2 0.30 0.30 0.30 0.30 0.30 Fe.sub.2O.sub.3 0.12 0.12 0.12 0.12 0.12 V.sub.2O.sub.5 0.03 0.03 0.03 0.03 0.03 Cr.sub.2O.sub.3 0.02 0.02 0.02 0.02 0.02 CoO Na.sub.2O + K.sub.2O + BaO + CaO + SrO 3.53 3.53 3.53 3.51 3.51 T.sub.30 Pa .Math. s (° C.) 1636 1621 1619 1628 1571 T.sub.liq (° C.) 1350-1366 1338-1350 1350-1366 1350-1360 1350-1372 Viscosity at T.sub.liq 600-800 700-850 500-650 600-700 300-450 (Pa .Math. s) Crystalline phase spinel zircon + spinel zircon spinel spinel that devitrifies at the liquidus temperature Resistivity at 8.4 9.4 9.9 8.8 7.9 30 Pa .Math. s (Ω .Math. cm) Ceram 1 Tmax (° C.) 890 900 890 880 880 Aspect transparent transparent transparent transparent transparent colored colored colored colored colored CTE.sub.25-300° C. 18.4 17.6 19.7 20 17.5 (×10.sup.−7 K.sup.−1) Ceram 2 Tmax (° C.) 920 920 920 Aspect transparent transparent transparent colored colored colored CTE.sub.25-300° C. 17.5 16.3 18.3 (×10.sup.−7 K.sup.−1) TL (%) 1 3 Diffusion (%) 1.5 1 T.sub.625 nm (%) 3.1 8.3 T.sub.950 nm (%) 58 64 Examples (wt %) 6 7 8 9 SiO.sub.2 63.70 65.34 65.65 65.45 Al.sub.2O.sub.3 19.60 19.67 19.79 17.99 Li.sub.2O 1.84 1.62 1.63 1.62 MgO 1.85 2.15 2.78 2.15 ZnO 4.77 3.06 1.84 3.06 BaO 2.45 2.46 2.47 3.48 CaO 0.44 0.44 0.44 0.63 TiO.sub.2 2.96 2.97 2.99 2.97 ZrO.sub.2 1.32 1.32 1.33 1.32 Na.sub.2O 0.61 0.61 0.61 0.86 K.sub.2O SnO.sub.2 0.29 0.30 0.30 0.30 Fe.sub.2O.sub.3 0.12 0.01 0.12 0.12 V.sub.2O.sub.5 0.03 0.03 0.03 0.03 Cr.sub.2O.sub.3 0.02 0.02 0.02 0.02 CoO Na.sub.2O + K.sub.2O + BaO + CaO + SrO 3.50 3.51 3.53 4.97 T.sub.30 Pa .Math. s (° C.) 1584 1621 1604 1632 T.sub.liq (° C.) 1370-1387 1350-1373 1350-1367 Viscosity at T.sub.liq 250-350 500-700 500-600 (Pa .Math. s) Crystalline phase spinel mullite + spinel mullite that devitrifies at the liquidus temperature Resistivity at 8.1 7.8 9.9 30 Pa .Math. s (Ω .Math. cm) Ceram 1 Tmax (° C.) 880 880 890 920 Aspect transparent transparent transparent transparent colored colored colored colored CTE.sub.25-300° C. 15.8 21.3 22.4 20.2 (×10.sup.−7 K.sup.−1) Ceram 2 Tmax (° C.) Aspect CTE.sub.25-300° C. (×10.sup.−7 K.sup.−1) TL (%) Diffusion (%) Examples (wt %) 10 11 12 13 14 SiO.sub.2 66.14 67.57 67.85 63.86 63.86 Al.sub.2O.sub.3 18.10 18.98 18.87 19.00 19.00 Li.sub.2O 1.63 1.28 1.84 1.84 1.84 MgO 2.17 2.49 1.75 1.75 1.75 ZnO 3.08 4.94 4.95 4.95 4.95 BaO 2.47 0.00 0.00 2.50 2.50 CaO 0.44 0.00 0.00 0.44 0.44 TiO.sub.2 2.99 2.62 2.63 3.02 2.62 ZrO.sub.2 1.90 1.75 1.75 1.35 1.75 Na.sub.2O 0.61 0.00 0.00 0.62 0.62 K.sub.2O 0.25 0.25 SnO.sub.2 0.30 0.30 0.30 0.28 0.28 Fe.sub.2O.sub.3 0.12 0.03 0.03 0.09 0.09 V.sub.2O.sub.5 0.03 0.04 0.03 0.03 0.03 Cr.sub.2O.sub.3 0.02 0.00 0.00 0.00 0.00 CoO 0.02 0.02 Na.sub.2O + K.sub.2O + BaO + SrO + CaO 3.53 0.00 0.00 3.81 3.81 T.sub.30 Pa .Math. s (° C.) 1635 1610 1617 1581 T.sub.liq (° C.) 1350-1366 1350-1375 1350-1375 1328-1353 1325-1355 Viscosity at T.sub.liq 600-750 450-650 450-650 450-700 (Pa .Math. s) Crystalline phase zircon + spinel mullite + spinel zircon + spinel that devitrifies at the liquidus temperature Resistivity at 8.3 12 7.8 30 Pa .Math. s (Ω .Math. cm) Ceram 1 Tmax (° C.) 890 975 975 880 855 Aspect transparent transparent transparent transparent transparent colored colored colored colored colored CTE.sub.25-300° C. 24.7 18.1 7.8 13 12.9 (×10.sup.−7 K.sup.−1) Ceram 2 Tmax (° C.) Aspect CTE.sub.25-300° C. (×10.sup.−7 K.sup.−1) TL (%) Diffusion (%) Comparative examples (wt %) 15 16 17 18 SiO.sub.2 63.55 65.81 54.21 63.03 Al.sub.2O.sub.3 21.48 14.57 25.50 20.00 Li.sub.2O 1.60 0.49 2.70 1.84 MgO 2.13 1.33 1.00 4.95 ZnO 3.04 4.70 7.70 1.75 BaO 2.44 6.24 1.00 2.50 CaO 0.44 0.99 1.30 0.45 TiO.sub.2 2.95 2.89 4.10 3.02 ZrO.sub.2 1.31 1.28 2.00 1.35 Na.sub.2O 0.60 1.01 0.62 K.sub.2O 0.21 SnO.sub.2 0.29 0.29 0.30 0.30 Fe.sub.2O.sub.3 0.12 0.13 0.13 0.13 V.sub.2O.sub.5 0.03 0.04 0.04 0.04 Cr.sub.2O.sub.3 0.02 0.02 0.02 0.02 CoO Na.sub.2O + K.sub.2O + BaO + SrO + CaO 3.48 8.45 2.30 3.57 T.sub.30 Pa .Math. s (° C.) 1587 1705 1421 T.sub.liq (° C.) >1400 >1370 Viscosity at T.sub.liq <200 <100 (Pa .Math. s) Crystalline phase mullite that devitrifies at the liquidus temperature Resistivity at 10.5 22.3 7.6 30 Pa .Math. s (Ω .Math. cm) Ceram 1 Tmax (° C.) 930 920 830 Aspect transparent transparent transparent colored colored colored CTE.sub.25-300° C. 38.1 14.9 25.8 (×10.sup.−7 K.sup.−1) Ceram 2 Tmax (° C.) 850 Aspect opalescent CTE.sub.25-300° C. (×10.sup.−7 K.sup.−1) TL (%) Diffusion (%) Comparative Examples (wt %) 19 20 21 SiO.sub.2 62.31 66.78 62.17 Al.sub.2O.sub.3 19.93 18.13 18.33 Li.sub.2O 1.80 1.63 1.51 MgO 0.47 2.91 1.83 ZnO 5.86 0.49 6.90 BaO 3.53 3.53 2.42 CaO 0.64 0.53 0.44 TiO.sub.2 2.90 3.00 3.28 ZrO.sub.2 1.29 1.34 1.84 Na.sub.2O 0.59 0.95 0.60 K.sub.2O 0.21 0.22 0.21 SnO.sub.2 0.29 0.30 0.29 Fe.sub.2O.sub.3 0.12 0.13 0.12 V.sub.2O.sub.5 0.04 0.04 0.04 Cr.sub.2O.sub.3 0.02 0.02 0.02 CoO Na.sub.2O + K.sub.2O + BaO + SrO + CaO 4.97 5.23 3.68 T.sub.30 Pa .Math. s (° C.) 1580 1658 1561 T.sub.liq (° C.) 1402-1415 1386-1402 Viscosity at T.sub.liq 170-210 160-200 (Pa .Math. s) Crystalline phase spinel spinel that devitrifies at the liquidus temperature Resistivity at 9.7 7.2 9.3 30 Pa .Math. s (Ω .Math. cm) Ceram 1 Tmax (° C.) 890 Aspect transparent colored CTE.sub.25-300° C. 30.2 (×10.sup.−7 K.sup.−1) Ceram 2 Tmax (° C.) 920 Aspect opalescent colored CTE.sub.25-300° C. 24.8 (×10.sup.−7 K.sup.−1) TL (%) 0.3 Diffusion (%) 8 T.sub.625 nm (%) 1.2