Fining of boroalumino silicate glasses
Glasses are disclosed which can be used to produce substrates for flat panel display devices, e.g., active matrix liquid crystal displays (AMLCDs). The glasses have MgO concentrations in the range from 1.0 mole percent to 3.0 mole percent and Σ[RO]/[Al 2 O 3 ] ratios greater than or equal to 1.00, where [Al 2 O 3 ] is the mole percent of Al 2 O 3 and Σ[RO] equals the sum of the mole percents of MgO, CaO, SrO, and BaO. These compositional characteristics have been found to improve the melting properties of batch materials used to produce the glass, which, in turn, allows the glasses to be fined (refined) with more environmentally friendly fining agents, e.g., tin as opposed to arsenic and/or antimony.
1. An alkali-free glass comprising in mole percent on an oxide basis:
SiO 2 :
64.0-71.0
Al 2 O 3 :
9.0-12.0
B 2 O 3 :
7.0-12.0
MgO:
1.0-3.0
CaO:
6.0-11.5
SrO:
0-2.0
BaO:
0-0.1
wherein:
(a) 1.00≦Σ[RO]/[Al 2 O 3 ]≦1.25,
where [Al 2 O 3 ] is the mole percent of Al 2 O 3 and Σ[RO] equals the sum of the mole percents of MgO, CaO, SrO, and BaO;
(b) the glass has the compositional characteristic that on an oxide basis, the glass comprises at least 0.01 mole percent SnO 2 ; and
(c) the glass has a density that is less than or equal to 2.41 grams/cm 3 .
2. The glass of claim 1 wherein the glass has the additional compositional characteristic that on an oxide basis, the glass comprises at most 0.05 mole percent Sb 2 O 3 .
3. The glass of claim 1 wherein the glass has the further compositional characteristic that on an oxide basis, the glass comprises at most 0.05 mole percent As 2 O 3 .
4. The glass of claim 2 wherein the glass has the further compositional characteristic that on an oxide basis, the glass comprises at most 0.05 mole percent As 2 O 3 .
5. An alkali-free glass comprising in mole percent on an oxide basis:
SiO 2 :
64.0-71.0
Al 2 O 3 :
19.0-12.0
B 2 O 3 :
7.0-12.0
MgO:
1.0-3.0
CaO:
6.0-11.5
BaO:
0-0.1
wherein the glass has the compositional characteristics:
(a) on an oxide basis, SrO is at most 1.0 mole percent;
(b) on an oxide basis, the glass comprises at least 0.01 mole percent SnO 2 ; and
(c) 1.00≦Σ[RO]/[Al 2 O 3 ]≦1.25, where [Al 2 O 3 ] is the mole percent of Al 2 O 3 and Σ[RO] equals the sum of the mole percents of MgO, CaO, SrO, and BaO.
6. The glass of claim 5 wherein the glass has a density that is less than or equal to 2.41 grams/cm 3 .
7. The glass of claim 1 wherein the glass has one or more of the following properties:
(a) a liquidus viscosity that is greater than or equal to 100,000 poise;
(b) a strain point that is greater than or equal to 650° C.;
(c) a linear coefficient of thermal expansion (CTE) over the temperature range 0-300° C. which satisfies the relationship:
28×10 −7 /° C.≦CTE≦34×10 −7 /° C.
8. An alkali-free glass comprising in mole percent on an oxide basis:
SiO 2 :
64.0-71.0
Al 2 O 3 :
9.0-12.0
B 2 O 3 :
7.0-12.0
MgO:
1.0-3.0
CaO:
6.0-11.5
SrO:
0-1.0
BaO:
0-0.1
wherein:
Σ[RO]/[Al 2 O 3 ]≧1.00,
where [Al 2 O 3 ] is the mole percent of Al 2 O 3 and Σ[RO] equals the sum of the mole percents of MgO, CaO, SrO, and BaO.
9. The glass of claim 8 wherein:
Σ[RO]/[Al 2 O 3 ]≦1.25.
10. The glass of claim 8 wherein the glass has a density that is less than or equal to 2.41 grams/cm 3 .
11. The glass of claim 8 wherein the glass has one or more of the following properties:
(a) a liquidus viscosity that is greater than or equal to 100,000 poise;
(b) a strain point that is greater than or equal to 650° C.;
(c) a linear coefficient of thermal expansion (CTE) over the temperature range 0-300° C. which satisfies the relationship:
28×10 −7 /° C.≦CTE≦34×10 −7 /° C.
12. The glass of claim 8 wherein the glass has at least one of the following compositional characteristics:
(a) on an oxide basis, the glass comprises at most 0.05 mole percent As 2 O 3 ;
(b) on an oxide basis, the glass comprises at most 0.05 mole percent Sb 2 O 3 ;
(c) on an oxide basis, the glass comprises at least 0.01 mole percent SnO 2 .
13. The glass of claim 12 wherein the glass has compositional characteristics (a) and (b).
14. The glass of claim 12 wherein the glass has compositional characteristics (a) and (c).
15. The glass of claim 12 wherein the glass has compositional characteristics (b) and (c).
16. The glass of claim 12 wherein the glass has compositional characteristics (a), (b), and (c).