Glass composition and glass substrate
A glass substrate for use as the substrate of an information recording medium such as a magnetic disk, magneto-optical disk, DVD, or MD or of an optical communication device, and a glass composition for making such a glass substrate, contains the following glass ingredients: 45 to 75% by weight of SiO 2 ; 1 to 20% by weight of Al 2 O 3 ; 0 to 8% by weight, zero inclusive, of B 2 O 3 ; SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 60 to 90% by weight; a total of 0 to 20% by weight, zero inclusive, of R 2 O compounds, where R=Li, Na, and K; and a total of 0 to 15% by weight, zero inclusive, of TiO 2 +ZrO 2 +Ln x O y , where Ln x O y represents at least one compound selected from the group consisting of lanthanoid metal oxides, Y 2 O 3 , Nb 2 O 5 , and Ta 2 O 5 .
1. A glass composition comprising the following glass ingredients:
62.5 to 75% by weight of SiO 2 ;
1 to 16% by weight of Al 2 O 3 ;
an amount of B 2 O 3 sufficient to improve the fusibility of the glass composition but not more than 8% by weight;
SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 80.4 to 90% by weight;
a total of 0.3 to 15% by weight of R 2 O compounds, where R=Li, Na, and K, including 0.1 to 14.8% by weight of Li 2 O, 0.1 to 14.8% by weight of Na 2 O, and 0.1 to 10% by weight of K 2 O; and
a total of 0 to 15% by weight, zero inclusive, of TiO 2 +ZrO 2 +Ln x O y , where Ln x O y represents at least one compound selected from the group consisting of lanthanoid metal oxides, Y 2 O 3 , Nb 2 O 5 , and Ta 2 O 5 .
2. A glass composition as claimed in claim 1 , further comprising the following glass ingredients:
a total of 12% or less by weight of one or two or more R'O compounds, where R′ =Mg, Ca, Sr, Ba, and Zn.
3. A glass substrate formed of a glass composition comprising the following glass ingredients:
62.5 to 75% by weight of SiO 2 ;
1 to 16% by weight of Al 2 O 3 ;
at least 0.1% by weight of Li 2 O;
an amount of B 2 O 3 sufficient to improve the fusibility of the glass substrate but not more than 8% by weight;
SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 80.4 to 90% by weight;
R 2 O compounds in amounts sufficient to obtain a mixed akali effect, where R=Li, Na, and K, wherein each R 2 O compound present accounts for at least 0.1% by weight and total R 2 O is not more than 15% by weight; and
a total of 0 to 15% by weight, zero inclusive, of TiO 2 +ZrO 2 +Ln x O y , where Ln x O y represents at least one compound selected from the group consisting of lanthanoid metal oxides, Y 2 O 3 , Nb 2 O 5 , and Ta 2 O 5 .
4. A glass substrate as claimed in claim 3 , further comprising the following glass ingredients:
a total of 12% or less by weight of one or two or more R′O compounds, where R′=Mg, Ca, Sr, Ba, and Zn.
5. A glass substrate as claimed in claim 3 , wherein the glass substrate is not subjected to strengthening.
6. A glass substrate as claimed in claim 3 , wherein the glass substrate is a substrate for a magnetic disk.
7. A glass substrate as claimed in claim 3 , wherein the glass substrate has a fracture toughness Kc of 0.90 MPa/m 1/2 or greater.
8. A glass substrate as claimed in claim 3 , wherein the glass substrate has SiO 2 elution A in a range of from 10 to 450 ppb per 2.5-inch disk.
9. A glass substrate as claimed in claim 3 , wherein the glass substrate has a fracture toughness Kc of 0.90 MPa/m 1/2 or greater, and has SiO 2 elution A in a range of from 10 to 450 ppb per 2.5-inch disk, with a ratio of the SiO 2 elution A to the fracture toughness Kc in a range of from 3 to 500.
10. A glass substrate as claimed in claim 3 , wherein the glass substrate has alkali elution B of 350 ppb or lower per 2.5-inch disk.
11. A glass substrate as claimed in claim 3 , wherein the glass substrate is not subjected to strengthening, and has a specific elastic modulus E/ρof 30 or higher.
12. A glass substrate as claimed in claim 3 , wherein the glass substrate is not subjected to strengthening, and has a Vickers hardness Hv in a range of from 500 to 700.
13. A glass substrate as claimed in claim 3 , wherein the glass substrate is not subjected to strengthening, and has a linear thermal expansion coefficient α in a range of from 40 10 − 7 /° C. to 90×10 − 7 /° C.
14. A glass substrate as claimed in claim 3 , wherein the glass substrate exhibits a weight reduction factor lower than 8.0% when kept in a melted state at 1,500 ° for 24 hours.
15. A glass substrate as claimed in claim 3 , wherein the glass substrate has a glass transition temperature Tg of 600° C. or lower.
16. A glass substrate as claimed in claim 3 , wherein the glass substrate has a liquid phase temperature T L of 1,300° C. or lower.
17. A glass substrate as claimed in claim 3 , wherein a temperature T logη=2 at which the glass substrate has a melt viscosity of log η=2 is 1,550° C. or lower.
18. A magnetic disk substrate comprising a glass substrate as claimed in claim 3 and a magnetic film formed on at least one surface thereof.
19. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate further comprises the following glass ingredients:
a total of 12% or less by weight of one or two or more R′O compounds, where R′ =Mg, Ca, Sr, Ba, and Zn.
20. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate is not subjected to strengthening.
21. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate has a fracture toughness Kc of 0.90 MPa/m 1/2 or greater.
22. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate has SiO 2 elution A in a range of from 10 to 450 ppb per 2.5-inch disk.
23. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate has a fracture toughness Kc of 0.90 MPa/m 1/2 or greater, and has SiO 2 elution A in a range of from 10 to 450 ppb per 2.5-inch disk, with a ratio of the SiO 2 elution A to the fracture toughness Kc in a range of from 3 to 500.
24. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate has alkali elution B of 350 ppb or lower per 2.5-inch disk.
25. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate is not subjected to strengthening, and has a specific elastic modulus E/ρ of 30 or higher.
26. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate is not subjected to strengthening, and has a Vickers hardness Hv in a range of from 500 to 700.
27. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate is not subjected to strengthening, and has a linear thermal expansion coefficient α in a range of from 40×10 − 7 /° C. to 90 10 − 7 /° C.
28. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate exhibits a weight reduction factor lower than 8.0% when kept in a melted state at 1,500° C. for 24 hours.
29. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate has a glass transition temperature Tg of 600° C. or lower.
30. A magnetic disk substrate as claimed in claim 18 , wherein the glass substrate has a liquid phase temperature T L of 1,300° C. or lower.
31. A magnetic disk substrate as claimed in claim 18 , wherein a temperature T logη=2 at which the glass substrate has a melt viscosity of log η=2 is 1,550° C. or lower.