Glass for magnetic recording medium substrate, magnetic recording medium substrate, magnetic recording medium and glass spacer for magnetic recording and reproducing apparatus
A glass for magnetic recording medium substrate is an amorphous oxide glass. In terms of mol %, SiO 2 content ranges from 45 to 68%, Al 2 O 3 from 5 to 20%, total content of SiO 2 and Al 2 O 3 60 to 80%, B 2 O 3 from 0 to 5%, MgO from 3 to 28%, CaO from 0 to 18%, total content of BaO and SrO 0 to 2%, total content of alkali earth metal oxides from 12 to 30%, total content of alkali metal oxides from 3.5 to 15%, and at least one kind selected from the group made of Sn oxide and Ce oxide being included, a total content of Sn oxide and Ce oxide ranges from 0.05 to 2.00%, a glass transition temperature ≥625° C., a Young's modulus ≥83 GPa, a specific gravity ≤2.85, and an average linear expansion coefficient at 100 to 300° C.≥48×10 −7 /° C.
1. A glass for magnetic recording medium substrate,
which is an amorphous oxide glass,
wherein, in terms of mol %:
an SiO 2 content ranges from 45 to 68%;
an Al 2 O 3 content ranges from 5 to 20%;
a total content of SiO 2 and Al 2 O 3 (SiO 2 +Al 2 O 3 ) ranges from 60 to 80%;
a B 2 O 3 content ranges from 0 to 5%;
an MgO content ranges from 3 to 28%;
a CaO content ranges from 0 to 18%;
a total content of BaO and SrO (BaO+SrO) ranges from 0 to 2%;
a total content of alkali earth metal oxides (MgO+CaO+SrO+BaO) ranges from 12 to 30%;
a total content of alkali metal oxides (Li 2 O+Na 2 O+K 2 O) ranges from 3.5 to 15%;
at least one kind selected from the group consisting of Sn oxide and Ce oxide being included, a total content of Sn oxide and Ce oxide ranges from 0.05 to 2.00%;
a content of Li 2 O is equal to or less than 8%;
a molar ratio of Li 2 O content relative to a total content of alkali metal oxides {Li 2 O/(Li 2 O+Na 2 O+K 2 O)} ranges from 0.4 to 1;
a content of TiO 2 ranges from 0 to 5%;
a total content of HfO 2 , Nb 2 O 5 , Ta 2 O 5 , La 2 O 3 and Y 2 O 3 (HfO 2 +Nb 2 O 5 +Ta 2 O 5 +La 2 O 3 +Y 2 O 3 ) ranges from 0 to 5%; and
a content of ZrO 2 ranges from 0 to 3%,
a glass transition temperature is equal to or higher than 625° C.;
a Young's modulus is equal to or more than 83 GPa;
a specific gravity is equal to or less than 2.85; and
an average linear expansion coefficient at 100 to 300° C. is equal to or more than 48×10 −7 /° C.
2. The glass for magnetic recording medium substrate according to claim 1 ,
wherein
a content of Na 2 O ranges from 0 to 10 mol %; and
a content of K 2 O ranges from 0 to 5 mol %.
3. The glass for magnetic recording medium substrate according to claim 1 ,
which comprises Sn oxide and Ce oxide.
4. The glass for magnetic recording medium substrate according to claim 1 ,
wherein a molar ratio of a total content of MgO and CaO relative to a total content of alkali earth metal oxides {(MgO+CaO)/(MgO+CaO+SrO+BaO)} ranges from 0.75 to 1.00.
5. A magnetic recording medium substrate, which is comprised of the glass for magnetic recording medium substrate according to claim 1 .
6. A magnetic recording medium, which comprises a magnetic recording layer on the magnetic recording medium substrate according to claim 5 .
7. A magnetic recording and reproducing apparatus, which comprises the magnetic recording medium according to claim 6 .
8. A magnetic recording and reproducing apparatus, which comprises
the magnetic recording medium according to claim 6 ; and
the glass spacer for magnetic recording and reproducing apparatus according to claim 7 .
9. A glass spacer for magnetic recording and reproducing apparatus,
which is an amorphous oxide glass,
wherein, in terms of mol %:
an SiO 2 content ranges from 45 to 68%;
an Al 2 O 3 content ranges from 5 to 20%;
a total content of SiO 2 and Al 2 O 3 (SiO 2 +Al 2 O 3 ) ranges from 60 to 80%;
a B 2 O 3 content ranges from 0 to 5%;
an MgO content ranges from 3 to 28%;
a CaO content ranges from 0 to 18%;
a total content of BaO and SrO (BaO+SrO) ranges from 0 to 2%;
a total content of alkali earth metal oxides (MgO+CaO+SrO+BaO) ranges from 12 to 30%;
a total content of alkali metal oxides (Li 2 O+Na 2 O+K 2 O) ranges from 3.5 to 15%;
at least one kind selected from the group consisting of Sn oxide and Ce oxide being included, a total content of Sn oxide and Ce oxide ranges from 0.05 to 2.00%;
a content of Li 2 O is equal to or less than 8%;
a molar ratio of Li 2 O content relative to a total content of alkali metal oxides {Li 2 O/(Li 2 O+Na 2 O+K 2 O)} ranges from 0.4 to 1;
a content of TiO 2 ranges from 0 to 5%;
a total content of HfO 2 , Nb 2 O 5 , Ta 2 O 5 , La 2 O 3 and Y 2 O 3 (HfO 2 +Nb 2 O 5 +Ta 2 O 5 +La 2 O 3 +Y 2 O 3 ) ranges from 0 to 5%; and
a content of ZrO 2 ranges from 0 to 3%,
a glass transition temperature is equal to or higher than 625° C.;
a Young's modulus is equal to or more than 83 GPa;
a specific gravity is equal to or less than 2.85; and
an average linear expansion coefficient at 100 to 300° C. is equal to or more than 48×10 −7 /° C.
10. A magnetic recording and reproducing apparatus, which comprises the glass spacer for magnetic recording and reproducing apparatus according to claim 9 .