Patent ID: 8883330

Claim:
A glass for use in chemical reinforcement for use in the substrate of an information recording medium employed in a perpendicular magnetic recording system, in which the glass is in an amorphous state, exhibits the glass transition temperature of greater than or equal to 650° C., and has a Young's modulus of greater than or equal to 75 GPa and less than 100 GPa, wherein the glass has a composition comprising, denoted as mol %: SiO 2 - 47% to 70%, Al 2 O 3 - 1% to 10% (where the total of SiO 2 and Al 2 O 3 is 57% to 80%), Na 2 O - 1% to 10%, K 2 O - 0 to 15%, (where the total of Na 2 O and K 2 O is 3% to 16%), Li 2 O - less than 1%, and at least one of MgO, CaO, SrO, BaO, and ZnO, where the total of MgO, CaO, SrO, BaO, and ZnO is 3% to 30%.