Disc substrates for information recording discs and magnetic discs

Disc substrates for information recording discs, wherein said substrates consist of glass comprising, as oxides constituting the glass, SiO2:

• 25-52%, Al2O3:
• 5-35%, MgO:
• 15-45%, Y2O3:
• 0-17%, TiO2:
• 0-25%, ZrO2:
• 0-8%, CaO:
• 1-30%, B2O3+P2O5. 0-5%, provided that Y2O3+TiO2+ZrO2+CaO:
• 5-30%, in molar %, and having a specific elastic modulus of 36×106 Nm/kg or more.

Disc substrates for information recording discs, wherein said substrates consist of glass comprising, as oxides constituting the glass, SiO2:

• at least 25%, Al2O3:
• 0% to 40%, CaO:
• 0% to 30%, Y2O3:
• 0% to 15%, in molar %, and having a specific elastic modulus of 36×106 NM/kg or more.

Disc substrates for information recording discs, wherein said substrates consist of glass comprising, as oxides constituting the glass, SiO2:

• at least 30%, Al2O3;
• 0% to 35%, MgO:
• 0.40%, Li2O:
• 0-20%, Y2O3, 0-27%, La2O3:
• 0-27%, CeO2:
• 0-27%, Pr2O3:
• 0-27%, Nd2O3:
• 0-27%, SM2O3:
• 0-27%, Eu2O3:
• 0-27%, Gd2O3:
• 0-27%, Tb2O3:
• 0-27, Dy2O3:
• 0-27%, HO2O3:
• 0-27%, Er2O3, 0-27%, TM2O3:
• 0-27%, Yb2O3:
• 0-27%, provided that Y2O3+La2O3+CeO2+Pr2O3+Nd2O3+SM2O3+Eu2O3+Gd2O3+Tb2O3+Dy2O3+Ho2O3+Er2O3+Tm2O3+Yb2O3, 1-27% and Li2O+MgO+Y2O3+La2O3+CeO2+Pr2O3++Nd2O3+Sm2O3+Eu2O3+Gd2O3+Tb2O3+Dy2O3+Ho2O3+Er2O3+Tm2O3+Yb2O3>15%, in molar %, and having a Young's modulus of 90 GPa or more.

Disc substrates for information recording discs, wherein the substrates consist of glass comprising, as oxides constituting the glass, SiO2:

• at least 30%, Al2O3— 0% to 35%, MgO:
• more than 0, equal to or than 40%, CaO:
• 0-15%, TiO2:
• 2-20%, Y2O3:
• 1-27%, ZrO2 0-8% in molar %, and further containing an alkali metal oxide.

Disc substrates for information recording discs, wherein the substrates consist of glass comprising, as oxides constituting the glass, SiO2:

• 30-60%, Al2O3:
• 2-35%, MgO:
• 0-40%, CaO:
• 0-15%, Y2O3:
• 1-27%, ZrO2:
• 0-8%, in molar %, and containing an alkali metal oxide, and wherein the glass substantially does not contain TiO2.

Disc substrates for information recording discs, wherein the substrates consist of glass comprising, as oxides constituting the glass, SiO2—:

• 30-60%, Al2O3:
• 15-35%, MgO:
• 0-40%, CaO:
• 0-15%, TiO2:
• 2-20%, Y2O3:
• 1-27%, ZrO2:
• 0-8% in molar % and containing an alkali metal oxide.

Disc substrates for information recording discs, wherein the substrates consist of glass comprising, as oxides constituting the glass, SiO2:

• 30-60%, Al2O3:
• 2-35%, MgO:
• 0-40%, CaO:
• 0-15%, TiO2;
• 2-20%, Y2O3;
• 1-27%, ZrO2:
• 0-8% in molar %, and wherein the glass substantially does not contain alkali metal oxides.