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 15% by weight, zero inclusive, of B 2 O 3 ; SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 65 to 90% by weight; a total of 7 to 20% by weight of R 2 O compounds, where R=Li, Na, and K; and a total of 0 to 12% by weight, zero inclusive, of R′O compounds, where R′=Mg, Ca, Sr, Ba, and Zn. Moreover, the following conditions are fulfilled: B 2 O 3 =0% by weight, or Al 2 O 3 /B 2 O 3 ≧1.0; and (SiO 2 +Al 2 O 3 +B 2 O 3 )/(the total of R 2 O compounds+the total of R 2 O compounds)≧3.
1. A glass composition comprising the following glass ingredients:
45 to 75% by weight of SiO 2 ;
10.1 to 14.6% by weight of Al 2 O 3 ;
1.2 to 5.7% by weight of B 2 O 3 ;
SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 65 to 90% by weight;
a total of 7 to 12.8% by weight of R 2 O compounds, where R=Li, Na, and K; and
a total of 0% by weight of R′O compounds, where R′=Mg, Ca, Sr, Ba, and Zn; and
a total of 0 to 7.1% 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 ,
wherein the following conditions are fulfilled:
Al 2 O 3 /B 2 O 3 ≧1.0; and
7.78≧(SiO 2 +Al 2 O 3 +B 2 O 3 )/(the total of R 2 O compounds ≧3.
2. A glass composition as claimed in claim 1 , wherein the glass composition has a glass transition temperature Tg of 600° C. or lower.
3. A glass composition as claimed in claim 1 , wherein the glass composition has a liquid phase temperature T L of 1 300° C. or lower.
4. A glass composition as claimed in claim 1 , wherein a temperature T log η =2 at which the glass composition has a melt viscosity of log η=2 is 1 550° C. or lower.
5. A glass substrate formed of a glass composition comprising the following glass ingredients:
45 to 75% by weight of SiO 2 ;
10.1 to 14.6% by weight of Al 2 O 3 ;
1.2 to 5.7% by weight of B 2 O 3 ;
SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 72 to 90% by weight;
a total of 7 to 12.8% by weight of R 2 O compounds, where R=Li, Na, and K;
a total of 0% by weight of R′O compounds, where R′=Mg, Ca, Sr, Ba, and Zn; and
a total of 0% to 7.1% 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 ,
wherein the following conditions are fulfilled:
Al 2 O 3 /B 2 O 3 ≧1.0; and
7.78≧(SiO 2 +Al 2 O 3 +B 2 O 3 )/(the total of R 2 O compounds≧3.
6. A glass substrate as claimed in claim 5 , wherein the glass composition has a glass transition temperature Tg of 600° C. or lower.
7. A glass substrate as claimed in claim 5 , wherein the glass composition has a liquid phase temperature T L of 1 300° C. or lower.
8. A glass substrate as claimed in claim 5 , wherein a temperature T log η=2 at which the glass composition has a melt viscosity of log η=2 is 1 550° C. or lower.
9. A glass substrate as claimed in claim 5 , wherein the glass substrate is not subjected to chemical strengthening.
10. A glass substrate as claimed in claim 9 , wherein the glass substrate has a specific elastic modulus E/ρ of 31 or higher.
11. A glass substrate as claimed in claim 9 , wherein the glass substrate has a Vickers hardness Hv in a range of from 500 to 700 as measured at a load of 100g.
12. A glass substrate as claimed in claim 9 , wherein the glass substrate has alkali elution A of 350 ppb or lower per 2.5-inch disk.
13. A glass substrate as claimed in claim 9 , wherein the glass substrate has a linear thermal expansion coefficient in a range of from 60×10 — 7 /° C. to 90 10 — 7 /° C. within a temperature range of 25 to 100° C.
14. A glass substrate as claimed in claim 9 , wherein the glass substrate has a fracture toughness Kc of 0.80 or greater.