Glass for magnetic recording medium substrate or for glass spacer to be used in magnetic recording/reproducing device, magnetic recording medium substrate, magnetic recording medium, glass spacer to be used in magnetic recording/reproducing device, and magnetic recording/reproducing device
Provided is a glass for a magnetic recording medium substrate or for a glass spacer for a magnetic recording/reproducing apparatus, in which the total content of Li 2 O, Na 2 O, K 2 O, B 2 O 3 , and ZnO (Li 2 O+Na 2 O+K 2 O+B 2 O 3 +ZnO) is in a range of 0 mol % or more and 3 mol % or less, the mole ratio of the total content of Al 2 O 3 and MgO relative to the total content of SiO 2 and CaO [(Al 2 O 3 +MgO)/(SiO 2 +CaO)] is in a range of 0.30 or more and 0.6 or less, the total content of SiO 2 and Al 2 O 3 (SiO 2 +Al 2 O 3 ) is in a range of 64 mol % or more and 85 mol % or less, and the total content of SiO 2 , Al 2 O 3 , MgO, and CaO (SiO 2 +Al 2 O 3 +MgO+CaO) is in a range of 87 mol % or more and 98 mol % or less.
1. A glass for a magnetic recording medium substrate or for a glass spacer for a magnetic recording/reproducing apparatus,
wherein a mole ratio of the total content of Al 2 O 3 and MgO relative to the total content of SiO 2 and CaO [(A 2 O 3 +MgO)/(SiO 2 +CaO)] is in a range of 0.417 or more and 0.6 or less,
the total content of SiO 2 and Al 2 O 3 (SiO 2 +Al 2 O 3 ) is in a range of 64 mol % or more and 85 mol % or less,
the total content of SiO 2 , Al 2 O 3 , MgO, and CaO (SiO 2 +Al 2 O 3 +MgO+CaO) is in a range of 87 mol % or more and 98 mol % or less,
the total content of TiO 2 and ZrO 2 (TiO 2 +ZrO 2 ) is 0.5 mol % or more,
the glass has a glass transition temperature of 740° C. or more,
an average linear expansion coefficient of the glass at 100° C. to 300° C. is 68×10 −7 /° C. or less, and
the total content of Li 2 O, Na 2 O, K 2 O, B 2 O 3 , and ZnO (Li 2 O+Na 2 O+K 2 O+B 2 O 3 +ZnO) is in a range of 0 mol % or more and 3 mol % or less.
2. The glass according to claim 1 ,
wherein the glass has the glass transition temperature of 760° C. or more.
3. The glass according to claim 2 ,
wherein the SiO 2 content is in a range of 55 mol % or more and 66 mol % or less.
4. The glass according to claim 2 ,
wherein the Al 2 O 3 content is in a range of 10 mol % or more and 18 mol % or less.
5. The glass according to claim 2 ,
wherein the MgO content is in a range of 8 mol % or more and 20 mol % or less.
6. The glass according to claim 2 ,
wherein a mole ratio of the CaO content relative to the total content of MgO, CaO, SrO, and BaO [CaO/(MgO+CaO+SrO+BaO)] is 0.4 or less.
7. The glass according to claim 2 ,
wherein the glass has a Young's modulus of 86 GPa or more.
8. The glass according to claim 2 ,
wherein the glass has a specific gravity of 2.8 or less.
9. The glass according to claim 2 ,
wherein the glass has a specific elastic modulus of 30 MNm/kg or more.
10. A magnetic recording medium substrate comprised of the glass according to claim 2 .
11. A magnetic recording medium comprising:
the magnetic recording medium substrate according to claim 10 ; and
a magnetic recording layer.
12. The glass according to claim 1 ,
wherein the SiO 2 content is in a range of 55 mol % or more and 66 mol % or less.
13. The glass according to claim 1 ,
wherein the Al 2 O 3 content is in a range of 10 mol % or more and 18 mol % or less.
14. The glass according to claim 1 ,
wherein the MgO content is in a range of 8 mol % or more and 20 mol % or less.
15. The glass according to claim 1 ,
wherein a mole ratio of the CaO content relative to the total content of MgO, CaO, SrO, and BaO [CaO/(MgO+CaO+SrO+BaO)] is 0.4 or less.
16. The glass according to claim 1 ,
wherein the glass has a Young's modulus of 86 GPa or more.
17. The glass according to claim 1 ,
wherein the glass has a specific gravity of 2.8 or less.
18. The glass according to claim 1 ,
wherein the glass has a specific elastic modulus of 30 MNm/kg or more.
19. A magnetic recording medium substrate comprised of the glass according to claim 1 .
20. A magnetic recording medium comprising:
the magnetic recording medium substrate according to claim 19 ; and
a magnetic recording layer.