Beta-quartz glass-ceramics with high zinc content

Abstract

The present application provides LAS type transparent glass-ceramics of β-quartz of composition containing a high content of zinc, articles constituted at least in part of said glass-ceramics, glasses precursors of said glass-ceramics (with a low viscosity at high temperature), and also a method of preparing said articles. Said glass-ceramics present a composition, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed as percentages by weight of oxides, containing: 64.5% to 66.5% of SiO.sub.2; 19.0% to 20.6% of Al.sub.2O.sub.3; 3.0% to 3.6% of Li.sub.2O; 0 to 1% of MgO; 1.7% to 3.4% of ZnO; 2% to 3% of BaO; 0 to 3% of SrO; 0 to 1% of CaO; 2% to 4% of TiO.sub.2; 1% 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 of lithium aluminosilicate containing a solid solution of β-quartz as a main crystalline phase, a composition of which, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed in percentages by weight of oxides, comprises: 64.5% to 66.5% of SiO.sub.2; 19.0% to 20.6% of Al.sub.2O.sub.3; 3.0% to 3.6% of Li.sub.2O; 0 to 1% of MgO; 1.7% to 3.4% of ZnO; 2% to 3% of BaO; 0 to 3% of SrO; 0 to 1% of CaO; 2% to 4% of TiO.sub.2; 1% to 2% of ZrO.sub.2; 0 to 1% of Na.sub.2O; 0 to 1% of K.sub.2O; greater than 0.02% to 0.1% of Cr.sub.2O.sub.3; with Na.sub.2O+K.sub.2O+BaO+SrO+CaO≤6% and 0.07%≤V.sub.2O.sub.5+Fe.sub.2O.sub.3+Cr.sub.2O.sub.3≤0.39%; and optionally up to 2% of at least one fining agent comprising SnO.sub.2.

2. The glass-ceramic according to claim 1, wherein the composition comprises 3.1% to 3.5% of Li.sub.2O.

3. The glass-ceramic according to claim 1, wherein the composition comprises 1.7% to 2.8% of ZnO.

4. The glass-ceramic according claim 1, wherein the composition comprises 0.01 to 1% of MgO.

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

6. The glass-ceramic according to claim 1, wherein the composition further comprises V.sub.2O.sub.5 as coloring agent, alone or mixed with at least one other coloring agent selected from CoO and Fe.sub.2O.sub.3.

7. The glass-ceramic according to claim 1, having a coefficient of thermal expansion CTE.sub.25-700° C. in the range +/−3.Math.10.sup.−7K.sup.−1.

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

9. The glass-ceramic of claim 5, wherein the composition comprises 0.15 to 0.4% of SnO.sub.2.

10. The glass-ceramic according to claim 1, wherein the composition comprises: 0.005% to 0.2% of V.sub.2O.sub.5; 0.01% to 0.32% of Fe.sub.2O.sub.3; and 0% to 0.1% of CoO.

11. The glass-ceramic according to claim 1, wherein the composition comprises: 0.015% to 0.1% of V.sub.2O.sub.5; 0.07% to 0.25% of Fe.sub.2O.sub.3; and greater than 0.02% to 0.04% of Cr.sub.2O.sub.3.

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 tables 1 (1-A and 1-B) and 2 below (proportions expressed oxides (in % of oxides by weight)), were mixed together carefully.

(2) Tables 1-A′ and 1-B′ show said proportions of oxides expressed in molar percentages.

(3) The mixtures were placed for melting in crucibles made of platinum. The crucibles containing said mixtures were then placed in a furnace 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.

(4) The crucibles were then extracted from the furnace 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 tables 1 (1-A and 1-B) and 2 below.

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

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

(7) The resistivity (ρ) 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 tables give the resistivity (ρ.sub.30 Pa.Math.s) measured at the temperature at which the viscosity was 30 Pa.Math.s.

(8) T.sub.liq (° C.) is the liquidus temperature. The liquidus is actually given by a range of viscosities 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.

(9) The devitrification characteristics (low and high liquidus temperatures) were determined as follows. 0.5 cubic centimeter (cm.sup.3) samples of glass were subjected to the following heat treatment: placing in a furnace 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.

(10) 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 (specified) maximum (ceramming) temperature Tmax at a heating rate of 15° C./min; maintaining this temperature Tmax for 7 min; cooling down to 850° C. at 35° C./min; and cooling down to ambient temperature as a function of the inertia of the furnace.

(11) For certain examples (examples 1 to 4) 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). The properties of the glass-ceramics obtained are given in the last portions of Tables 1 (1-A and 1-B) and 2 below.

(12) The coefficients of thermal expansion from ambient temperature (25° C.) to 700° C. (CTE.sub.25-700° C.) were measured on bar-shaped samples of glass-ceramic with a high temperature dilatometer (DIL 402C, Netzsch) at a heating rate of 3° C./min.

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

(14) These glass-ceramics contain a solid solution of β-quartz as the main crystalline phase (as verified by X-ray diffraction). Thus, example 6 contains 95% (by weight) of solid solution of β-quartz (relative to the total crystallized fraction) with the β-quartz crystals having a mean size of 35 nm. The percentages of solid solution of β-quartz and the mean crystal size were determined using the Rietveld method.

(15) Measurements of total transmission (TL) and of diffusion were performed at 4 mm with a Varian spectrophotometer (Cary 500 Scan model), fitted with an integrating sphere. On the basis of those measurements, the integrated transmission (TL (%)) in the visible range (between 380 and 780 nm) and the diffusion percentage (Diffusion (%)) were calculated using the standard ASTM D 1003-13 (under D65 illuminant with a 2° observer). Transmission values (at 625 nm (T.sub.625nm), at 950 nm (T.sub.950nm), at 1600 nm (T.sub.1600nm)) are also specified for some samples. Examples 1 to 7 (Table 1-A (1-A′) and 1-B (1-8′)) illustrate the present application. Examples 1 to 4 and example 6 (optimization of example 4 for viscosity at liquidus) and 7 (optimization of example 4 for CTE and devitrification properties) are preferred. Example 6 is most particularly preferred.

(16) Examples 1 to 5 relate to glasses and glass-ceramics of similar compositions with progressively varying contents of Li.sub.2O and ZnO. This can be seen more clearly by considering Tables 1-A′ and 1-B′ expressing the compositions as molar percentages. The concerned glasses have T.sub.30 Pa.Math.s, values progressively decreasing.

(17) Examples A to D (Table 2) are comparative examples.

(18) In examples A and B, the contents of Al.sub.2O.sub.3 and of ZnO lie outside the given ranges. The CTEs of the glass-ceramics are too high. The precursor glass of example B has devitrification into mullite, which is not favorable.

(19) In example C, the MgO content is too high. Consequently, the CTE of the glass-ceramic is too high. The contents of SiO.sub.2 and BaO likewise lie outside the given range.

(20) In example D, the MgO content is too high. Consequently, the CTE of the glass-ceramic is unacceptable.

(21) TABLE-US-00003 TABLE 1-A Examples (wt %) 1 2 3 4 SiO.sub.2 65.20 65.09 64.99 64.77 Al.sub.2O.sub.3 20.58 20.55 20.51 20.45 Li.sub.2O 3.60 3.50 3.40 3.20 MgO 0.37 0.37 0.37 0.37 ZnO 1.77 2.03 2.28 2.79 BaO 2.46 2.45 2.45 2.44 CaO 0.45 0.45 0.45 0.45 TiO.sub.2 2.96 2.95 2.95 2.94 ZrO.sub.2 1.30 1.30 1.29 1.29 Na.sub.2O 0.60 0.60 0.60 0.60 K.sub.2O 0.22 0.22 0.22 0.22 SnO.sub.2 0.30 0.30 0.30 0.30 Fe.sub.2O.sub.3 0.13 0.13 0.13 0.12 V.sub.2O.sub.5 0.04 0.04 0.04 0.04 Cr.sub.2O.sub.3 0.02 0.02 0.02 0.02 Na.sub.2O + K.sub.2O + BaO + 3.73 3.72 3.72 3.71 SrO + CaO Properties of the glass T.sub.30Pa .Math. s (° C.) 1617 1612 1608 1604 ρ.sub.300P (Ω .Math. cm) 3.3 3.8 4 4.3 T.sub.liq (° C.) 1283-1308 1323-1345 1322-1346 1320-1336 Viscosity at T.sub.liq (Pa .Math. s)  990-1460 570-780 530-750 600-760 Crystalline phase that spinel spinel spinel spinel devitrifies at the liquidus temperature Properties of the glass-ceramic Ceram 1: Tmax (° C.) 930 920 930 930 aspect trans- trans- trans- trans- parent parent parent parent colored colored colored colored CTE.sub.25-700° C. 1.0 2.1 1.5 2.0 (×10.sup.−7 K.sup.−1) Ceram 2: Tmax (° C.) 920 920 TL (%) 2.9 2.2 Diffusion (%) 0.4 0.6 T.sub.625 nm (%) 7.9 6.2

(22) TABLE-US-00004 TABLE 1-A Examples (mol %) 1 2 3 4 SiO.sub.2 71.14 71.14 71.14 71.14 Al.sub.2O.sub.3 13.23 13.23 13.23 13.23 Li.sub.2O 7.91 7.70 7.49 7.07 MgO 0.60 0.60 0.60 0.60 ZnO 1.43 1.64 1.84 2.26 BaO 1.05 1.05 1.05 1.05 CaO 0.53 0.53 0.53 0.53 TiO.sub.2 2.43 2.43 2.43 2.43 ZrO.sub.2 0.69 0.69 0.69 0.69 Na.sub.2O 0.63 0.63 0.64 0.64 K.sub.2O 0.15 0.15 0.15 0.15 SnO.sub.2 0.13 0.13 0.13 0.13 Fe.sub.2O.sub.3 0.05 0.05 0.05 0.05 V.sub.2O.sub.5 0.02 0.02 0.02 0.02 Cr.sub.2O.sub.3 0.01 0.01 0.01 0.01

(23) TABLE-US-00005 TABLE 1-B Examples (wt %) 5 6 7 SiO.sub.2 64.56 65.67 66.44 Al.sub.2O.sub.3 20.38 19.67 19.08 Li.sub.2O 3.00 3.20 3.21 MgO 0.37 0.38 0.30 ZnO 3.30 2.57 2.35 BaO 2.43 2.44 2.44 CaO 0.45 0.45 0.45 TiO.sub.2 2.93 2.75 2.58 ZrO.sub.2 1.29 1.57 1.85 Na.sub.2O 0.59 0.60 0.60 K.sub.2O 0.22 0.22 0.22 SnO.sub.2 0.30 0.30 0.30 Fe.sub.2O.sub.3 0.12 0.12 0.12 V.sub.2O.sub.5 0.04 0.04 0.04 Cr.sub.2O.sub.3 0.02 0.02 0.02 Na.sub.2O + K.sub.2O + BaO + 3.69 3.71 3.71 SrO + CaO Properties of the glass T.sub.30Pa .Math. s (° C.) 1601 1617 1633 ρ.sub.300P (Ω .Math. cm) 5.2 4.5 4.6 T.sub.liq (° C.) 1350-1360 1314-1331 1350-1360 Viscosity at T.sub.liq (Pa .Math. s) 410-480 730-950 580-670 Crystalline phase that spinel spinel zircon devitrifies at the liquidus temperature Properties of the glass-ceramic Tmax (° C.) 930 930 930 aspect trans- trans- trans- parent parent parent colored colored colored CTE.sub.25-700° C. 2.5 1.5 0.0 (×10.sup.−7 K.sup.−1) TL (%) 2.6 7.7 Diffusion (%) 0.4 1.0 T.sub.625 nm (%) 7.7 18.6 T.sub.950 nm (%) 64 T.sub.1600 nm (%) 68

(24) TABLE-US-00006 TABLE 1-B Examples (mol %) 5 6 7 SiO.sub.2 71.14 71.90 72.61 Al.sub.2O.sub.3 13.23 12.69 12.29 Li.sub.2O 6.65 7.05 7.05 MgO 0.60 0.62 0.49 ZnO 2.68 2.07 1.89 BaO 1.05 1.05 1.05 CaO 0.53 0.52 0.52 TiO.sub.2 2.43 2.27 2.12 ZrO.sub.2 0.69 0.84 0.99 Na.sub.2O 0.64 0.63 0.63 K.sub.2O 0.15 0.15 0.15 SnO.sub.2 0.13 0.13 0.13 Fe.sub.2O.sub.3 0.05 0.05 0.05 V.sub.2O.sub.5 0.02 0.02 0.02 Cr.sub.2O.sub.3 0.01 0.01 0.01

(25) TABLE-US-00007 TABLE 2 Comparative examples (wt %) A B C D SiO.sub.2 65.58 65.78 66.99 65.06 Al.sub.2O.sub.3 20.70 20.77 20.01 20.54 Li.sub.2O 3.30 3.00 3.00 3.00 MgO 0.37 0.37 1.30 1.18 ZnO 1.53 1.53 1.70 1.76 BaO 2.47 2.48 1.80 2.45 CaO 0.45 0.45 — 0.45 TiO.sub.2 2.98 2.99 3.01 2.95 ZrO.sub.2 1.31 1.31 1.40 1.30 Na.sub.2O 0.60 0.61 0.20 0.60 K.sub.2O 0.22 0.22 0.10 0.22 SnO.sub.2 0.30 0.30 0.30 0.30 Fe.sub.2O.sub.3 0.13 0.13 0.13 0.13 V.sub.2O.sub.5 0.04 0.04 0.04 0.04 Cr.sub.2O.sub.3 0.02 0.02 0.02 0.02 Na.sub.2O + K.sub.2O + BaO + 3.74 3.76 2.1 3.72 SrO + CaO Properties of the glass T.sub.30Pa .Math. s (° C.) 1627 1635 1618 — ρ.sub.300P (Ω .Math. cm) 3.9 4.8 5.1 — T.sub.liq (° C.) 1310-1326 1334-1354 — — Viscosity at T.sub.liq (Pa .Math. s)  910-1170 670-900 — — Crystalline phase that spinel mullite — — devitrifies at the liquidus temperature Properties of the glass-ceramic Tmax (° C.) 930 930 920 930 aspect trans- trans- trans- trans- parent parent parent parent colored colored colored colored CTE.sub.25-700° C. 3.6 5.1 7.2 9.1 (×10.sup.−7 K.sup.−1)