Glasses

Abstract

Glasses are disclosed having a composition comprising the following oxides (in weight %): SiO.sub.2 61 to 70%, Al.sub.2O.sub.3 0 to 9%, Na.sub.2O 10 to 13%, K.sub.2O 0 to 1%, MgO 2 to 6%, CaO 6 to 16%, SrO 0 to 1%, ZrO.sub.2 0 to 1%, TiO.sub.2 2 to 15%, the glasses having a strain point greater than 570 C. The glasses have good dimensional stability at high temperatures, making them suitable for fire protection glazings and substrates which are processed at elevated temperatures, e.g. substrates for display panels, information storage discs and semiconductor devices, including photovoltaic cells. Physical properties of the glasses, such as thermal expansion coefficient, density and refractive index, are disclosed, as are the melting and liquidus temperatures. The glasses are suitable for manufacture by the float process, yielding flat glass in the form of sheets.

Claims

1. A soda lime silica glass having a strain point greater than 570 C., comprising the following oxides (in weight %): TABLE-US-00004 SiO.sub.2 61 to 69% Al.sub.2O.sub.3 3 to 8% Na.sub.2O 10 to 13% K.sub.2O 0 to 1% MgO 2 to 6% CaO 7 to 13% SrO 0 to 1% ZrO.sub.2 0 to 1% TiO.sub.2 3 to 12% B.sub.2O.sub.3 0 to 1%.

2. The glass as claimed in claim 1, comprising from 3 to 11% TiO.sub.2.

3. The glass as claimed in claim 1, comprising from 4 to 10% TiO.sub.2.

4. The glass as claimed in claim 1, comprising from 4 to 6% TiO.sub.2.

5. The glass as claimed in claim 1 having a strain point greater than 580 C.

6. The glass as claimed in claim 1 having a melting temperature (at which viscosity=log 2 poise) less than 1500 C.

7. The glass as claimed in claim 1 having a liquidus temperature less than 1200 C.

8. The glass as claimed in claim 1 having a working range (defined as T log 4 poise minus the liquidus temperature) greater than 100 C.

9. The glass as claimed in claim 1 having a coefficient of thermal expansion from 70 to 9010.sup.7 C..sup.1 (50-350 C.).

10. The glass as claimed in claim 1 having a density from 2.50 to 2.70 g cm.sup.3 at 25 C.

11. The glass as claimed in claim 1 having a refractive index from 1.50 to 1.62.

12. A sheet of glass formed from glass as claimed in claim 1.

13. A glass substrate comprising glass as claimed in claim 1.

14. A photovoltaic cell comprising the glass substrate of claim 13.

15. A flat glass produced by an on-line float glass process, having a strain point greater than 570 C., comprising the following oxides (in weight %): TABLE-US-00005 SiO.sub.2 61 to 69% Al.sub.2O.sub.3 3 to 8% Na.sub.2O 10 to 13% K.sub.2O 0 to 1% MgO 2 to 6% CaO 7 to 13% SrO 0 to 1% ZrO.sub.2 0 to 1% TiO.sub.2 3 to 12%.

16. A glass substrate for a photovoltaic cell comprising the flat glass as claimed in claim 15.

17. A flat glass substrate having a strain point greater than 570 C., comprising the following oxides (in weight %): TABLE-US-00006 SiO.sub.2 61 to 69% Al.sub.2O.sub.3 0 to 8% Na.sub.2O 10 to 13% K.sub.2O 0 to 1% MgO 2 to 6% CaO 9.2 to 13% SrO 0 to 1% ZrO.sub.2 0 to 1% TiO.sub.2 3 to 13% B.sub.2O.sub.3 0 to 1%.

18. A photovoltaic cell comprising the flat glass substrate of claim 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) It has also been found that increasing the amount of Al.sub.2O.sub.3 in the glass composition, in addition to increasing the amount of TiO.sub.2, further increases the strain point of the glass.

(2) Glasses according to the invention are suitable for processing at higher temperatures than normal float glass. The inventive glasses are less susceptible to deformation or distortion at elevated temperatures, and so have higher dimensional stability and improved heat resistance.

(3) Preferably, the glass comprises certain oxides in the following ranges (in weight %):

(4) TABLE-US-00002 SiO.sub.2 61 to 69% Al.sub.2O.sub.3 0 to 8% CaO 7 to 13% TiO.sub.2 .sup.2 to 13%.

(5) Advantageously, the glass comprises from 3 to 12% TiO.sub.2, preferably from 3 to 11% TiO.sub.2, more preferably from 4 to 10% TiO.sub.2, still more preferably from 4 to 9% TiO.sub.2, yet more preferably from 4 to 8% TiO.sub.2, most preferably from 4 to 7% TiO.sub.2. Particularly suitable glass compositions may contain from 4 to 6% TiO.sub.2. Optionally, such glass compositions may also contain from 3 to 8% Al.sub.2O.sub.3, preferably from 4 to 7% Al.sub.2O.sub.3, more preferably from 5 to 6% Al.sub.2O.sub.3. Since titania (TiO.sub.2) is more expensive than other raw materials employed in the manufacture of float glass, this allows glasses according to the invention to be tailored to achieve the desired balance between performance and cost.

(6) Optionally, the glass is free of any one, or any number, of the following oxides: As.sub.2O.sub.3, BaO, B.sub.2O.sub.3, BeO, CeO.sub.2, Er.sub.2O.sub.3, GeO.sub.2, Li.sub.2O, P.sub.2O.sub.5, PbO, Sb.sub.2O.sub.3, SnO.sub.2, SrO, V.sub.2O.sub.5, ZnO, ZrO.sub.2. These oxides may be objectionable for reasons of toxicity, cost or their adverse effect on the furnace structure. However, traces of these oxides may be present as a result of impurities in the raw materials. In particular, the glass composition may contain from 0 to 1% BaO or B.sub.2O.sub.3. In many of the applications contemplated, it is not necessary or not desirable to tint the glass, so in such cases the glass is free of colourants, e.g. CdO, CeO.sub.2, CoO, Co.sub.3O.sub.4, Cr.sub.2O.sub.3, CuO, Er.sub.2O.sub.3, MnO.sub.2, Nd.sub.2O.sub.3, NiO, Se, V.sub.2O.sub.5.

(7) Preferably, a glass according to the invention has a strain point greater than 580 C., preferably greater than 585 C., more preferably greater than 590 C. As mentioned above, it is desirable to provide glasses which are readily manufactured by the float process. Therefore, while increasing the strain point of a glass, it is also important to take account of other properties of the glass, such as melting temperature, liquidus temperature and working range, which determine how readily the glass may be melted and formed. Surprisingly, the inventors were able to tailor all these properties simultaneously, to provide glasses with high strain points and favourable manufacturing properties.

(8) Preferably, a glass according to the invention has a melting temperature (defined as the temperature at which the viscosity is 100 poise, i.e. log 2 poise, denoted T log 2 poise) less than 1500 C., preferably less than 1480 C., more preferably less than 1460 C. This allows the raw materials to be melted and turned into glass without excessive fuel usage and without causing undue wear to the structure of the furnace in which the glass is melted.

(9) Advantageously, a glass according to the invention has a liquidus temperature less than 1200 C., preferably less than 1180 C., more preferably less than 1160 C., yet more preferably less than 1140 C., still more preferably less than 1120 C., most preferably less than 1100 C. A lower liquidus temperature reduces the risk of devitrification in molten glass in the cooler regions of the furnace. The term devitrification refers to the formation of crystals such as wollastonite (abbreviated to Woll. in Table I below) or diopside in the glass, which is undesirable because such crystals may end up in the final product, causing it to be rejected.

(10) Desirably, a glass according to the invention has a working range (defined as the forming temperature, i.e. T log 4 poise, minus the liquidus temperature) greater than 100 C., preferably greater than 80 C., more preferably greater than 60 C., yet more preferably greater than 40 C., still more preferably greater than 20 C., most preferably greater than 0 C., i.e. preferably the working range is positive. Some glass forming processes are more tolerant of a negative working range than others, and the float glass process is able to operate with a negative working range. A less negative, or more positive, working range facilitates forming of the molten glass into a product (e.g. a ribbon of flat glass) without devitrification occurring.

(11) It is advantageous for the physical properties of the final product (e.g. sheet of glass, glass substrate, display panel, disc, etc) to be suited to the particular application for which the glass is intended. For some of these applications, normal soda lime silica glass possesses suitable physical properties at room temperature, but, as mentioned previously, it cannot be processed at sufficiently high temperatures without negative effects. According to an additional aspect of the invention, glasses are provided which not only have increased strain points, and lend themselves to economic manufacture, but also retain suitable physical properties at room temperature.

(12) For instance, according to this aspect of the invention, a glass is provided having a coefficient of thermal expansion from 70 to 9010.sup.7 C..sup.1 (50-350 C.), preferably from 72 to 8810.sup.7 C..sup.1 (50-350 C.), more preferably from 74 to 8610.sup.7 C..sup.1 (50-350 C.), and most preferably from 76 to 8410.sup.7 C..sup.1 (50-350 C.).

(13) Moreover, properties such as density and refractive index are also important when the glass produced by a furnace is changed over from one composition to another. A changeover of particular significance is the changeover from normal float glass to a glass according to the invention. Such changeovers are carried out on the run, i.e. the mixture of raw materials fed to the furnace is changed to the mixture which is appropriate for the new composition without draining the furnace or stopping melting. The time taken for the changeover can be reduced if both glass compositions have similar density and refractive index, since mixing of the two compositions then occurs more readily.

(14) It is therefore also desirable to provide a glass having a density from 2.50 to 2.70 g cm.sup.3 at 25 C., preferably from 2.51 to 2.69 g cm.sup.3 at 25 C., more preferably from 2.52 to 2.68 g cm.sup.3 at 25 C., further preferably from 2.53 to 2.67 g cm.sup.3 at 25 C., yet more preferably from 2.54 to 2.66 g cm.sup.3 at 25 C., most preferably from 2.55 to 2.66 g cm.sup.3 at 25 C.

(15) Similarly, it is desirable if a glass according to the invention has a refractive index from 1.50 to 1.62, preferably from 1.51 to 1.60, more preferably from 1.52 to 1.59, more preferably from 1.53 to 1.58.

(16) The invention also encompasses glass articles having a glass composition according to the appended claims, and in particular a sheet of glass formed from glass having a glass composition as claimed herein. Additionally, the invention includes a fire resistant glazing made with one or more sheets of such glass. Furthermore, the invention also includes a glass substrate comprising glass as claimed herein, and any of the products manufactured using such a glass substrate, including but not limited to a display panel, a disc, a semiconductor device and a photovoltaic cell, especially a solar cell. Glass substrates according to the invention may be used for CdTe and CIGS (CuInGaSe) solar cells amongst others.

(17) The invention will now be further described with reference to the following non-limiting Examples set out in Table 1. In the table, Examples 3 to 7 are according to the invention, and Examples 1, 2 and 8 to 20 are comparative examples. In particular, Example 1 is representative of normal float glass, and has a strain point of 536 C. In contrast, Examples 2 to 20 have strain points ranging from 574 C. to 595 C., and the Examples according to the invention span the same range of strain points.

(18) It may be seen that Example 7 has the highest strain point, namely 595 C. This Example also has a very low melting temperature, namely 1290 C. In fact, this Example generally has relatively low viscosity at high temperature, including a forming temperature of only 972 C. Since the liquidus temperature of this glass is relatively high at 1171 C., this leads to a large negative working range of 199 C. Examples 5 and 6 concede only one or two degrees in terms of their strain points, and have working ranges of 91 C. and 108 C. respectively, which makes them better propositions from the manufacturing aspect.

(19) Glasses having a glass composition according to the invention therefore offer a considerably increased strain point while retaining suitable manufacturing and room temperature properties, rendering it suitable for high temperature processing and other applications requiring increased dimensional stability at elevated temperatures.

(20) TABLE-US-00003 TABLE 1 Example Number 1 2 3 4 5 6 7 Composition (wt %) SiO2 72.8 69.7 64.2 61.5 66.6 65.4 62 Na2O 13.4 10 11.8 11.7 10.1 10.1 10.1 CaO 8.71 15.3 12.06 12.0 9.2 10.2 12.1 MgO 4.26 4.24 4.29 4.15 4.13 4.22 4.35 Al2O3 0.4 0.4 0.11 7.06 5.03 4.12 0.08 ZrO2 TiO2 7.2 3.1 4.6 5.5 10.8 SrO BaO SO3 0.31 0.34 0.31 0.34 0.24 0.28 0.34 Fe2O3 (Trace components) 0.015 0.015 0.013 0.107 0.102 0.105 0.103 K2O 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Forming Characteristics Liquidus Temperature ( C.) 1066 1201 1116 1157 1158 1154 1171 Working Range (liquidus minus T log 4) 39 179 143 135 91 108 199 Primary Devitrification Phase Woll. Woll. Woll. Woll. Woll. Woll. Woll. Physical Properties Coeff. of Thermal Expansion 87.1 84.9 89.0 86.4 76.2 77.9 83.1 (50-350 C.) Young's modulus E (GNm-2) 74.8 79.9 84.1 80.8 79.2 80.8 84.5 Shear Modulus G (GNm-2) 30.5 32.5 33.8 32.9 32.5 33.3 34.3 Poisson's Ratio 0.23 0.23 0.25 0.23 0.22 0.21 0.23 Density (g/cm3 @ 25 C.) 2.495 2.563 2.619 2.594 2.551 2.572 2.661 Refractive Index (Nad) 1.5182 1.5388 1.5688 1.5492 1.5441 1.5517 1.589 Viscosity Profile ( C.) T log 2 poise (Melting Temperature) 1448 1389 1309 1389 1476 1431 1290 T log 2.5 poise 1304 1265 1195 1264 1336 1300 1182 T log 3 poise 1191 1167 1105 1165 1227 1197 1097 T log 4 poise (Forming Temperature) 1027 1021 973 1021 1067 1046 972 T log 5 poise 912 919 881 921 957 941 885 T log 7.6 poise (Softening Point) 732 755 734 762 782 775 747 T log 13 poise (Annealing Point) 563 600 596 613 619 619 616 T log 13.4 poise 555 592 589 606 611 612 610 T log 14.5 poise (Strain Point) 536 575 574 589 593 594 595 Example Number 8 9 10 11 12 13 14 Composition (wt %) SiO2 68.0 68.7 69.1 66.2 64.8 67.7 67.0 Na2O 11.7 12 12.3 10.9 11.8 11.9 11.5 CaO 9.86 8.52 7.24 6.23 11.9 6.51 11.5 MgO 4.43 4.52 4.62 4.21 4.24 4.42 4.40 Al2O3 3.47 1.88 0.28 0.08 0.03 0.08 5.20 ZrO2 2.14 4.06 6.1 6.8 6.8 8.8 TiO2 SrO 5.0 BaO SO3 0.22 0.21 0.185 0.29 0.31 0.24 0.26 Fe2O3 (Trace components) 0.075 0.075 0.077 0.058 0.015 0.104 0.075 K2O 0.01 0.01 0.01 0.02 0.01 0.02 0.02 Forming Characteristics Liquidus Temperature ( C.) 1148 1129 1079 1030 1149 1075 1164 Working Range (liquidus minus T log 4) 84 46 14 57 105 44 110 Primary Devitrification Phase Diopside Diopside Woll. Woll. Woll. Physical Properties Coeff. of Thermal Expansion (50-350 C.) 81.8 80.9 79.9 78.7 84.2 76.8 84.7 Young's modulus E (GNm-2) 78.3 79.3 78.1 80.4 82.8 80 78 Shear Modulus G (GNm-2) 32.1 32.4 32.2 33.3 33.6 33.7 32.1 Poisson's Ratio 0.22 0.22 0.21 0.21 0.23 0.19 0.22 Density (g/cm3 @ 25 C.) 2.554 2.568 2.581 2.668 2.664 2.620 2.541 Refractive Index (Nad) 1.5322 1.5347 1.5361 1.5452 1.5544 1.5436 1.5298 Viscosity Profile ( C.) T log 2 poise (Melting Temperature) 1456 1472 1478 1453 1380 1482 1452 T log 2.5 poise 1324 1343 1352 1334 1269 1365 1317 T log 3 poise 1219 1239 1249 1237 1180 1268 1211 T log 4 poise (Forming Temperature) 1064 1082 1093 1087 1043 1118 1054 T log 5 poise 953 970 980 977 944 1007 944 T log 7.6 poise (Softening Point) 775 786 793 794 781 818 769 T log 13 poise (Annealing Point) 605 607 608 609 619 626 602 T log 13.4 poise 597 598 599 600 611 617 594 T log 14.5 poise (Strain Point) 577 577 577 579 592 594 575 Example Number 15 16 17 18 19 20 Composition (wt %) SiO2 65.8 67.7 63.9 64.0 64.8 63.3 Na2O 11.6 11.6 11.3 11.3 10.8 11.5 CaO 11.61 11.88 12.1 10.9 12.6 7.5 MgO 4.21 2.05 4.14 5.27 4.3 4.86 Al2O3 6.35 6.41 8.03 8.00 7.06 8.0 ZrO2 TiO2 SrO 4.3 BaO SO3 0.27 0.22 0.33 0.33 0.28 0.27 Fe2O3 (Trace components) 0.014 0.012 0.105 0.105 0.107 0.107 K2O 0.06 0.06 0.01 0.01 0.01 0.02 Forming Characteristics Liquidus Temperature ( C.) 1168 1174 1178 1209 1173 1140 Working Range (liquidus minus T log 4) 118 107 116 140 109 69 Primary Devitrification Phase Woll. Woll. Diopside Diopside Diopside Physical Properties Coeff. of Thermal Expansion (50-350 C.) 85.2 84.8 84.1 83.4 82.9 83.9 Young's modulus E (GNm-2) 79.8 77.2 78.9 79.1 79.7 78.7 Shear Modulus G (GNm-2) 32.8 31.5 32.8 32.4 32.6 32 Poisson's Ratio 0.22 0.22 0.20 0.22 0.23 0.23 Density (g/cm3 @ 25 C.) 2.5478 2.5225 2.556 2.550 2.556 2.582 Refractive Index (Nad) 1.5311 1.5268 1.5321 1.5317 1.5325 1.5294 Viscosity Profile ( C.) T log 2 poise (Melting Temperature) 1444 1495 1451 1462 1452 1472 T log 2.5 poise 1310 1347 1320 1329 1321 1337 T log 3 poise 1204 1233 1216 1224 1217 1230 T log 4 poise (Forming Temperature) 1049 1066 1062 1068 1064 1071 T log 5 poise 940 952 953 959 955 958 T log 7.6 poise (Softening Point) 768 772 780 783 782 776 T log 13 poise (Annealing Point) 604 605 615 616 617 602 T log 13.4 poise 597 598 607 608 609 594 T log 14.5 poise (Strain Point) 578 579 588 589 590 574