Patent ID: 8119267
Filing Date: 2012-02-21
Classification: C03C,G11B

Abstract:
1. A glass substrate for a magnetic disk, the glass substrate being a disk-shaped glass substrate for a magnetic disk, having a main surface and an end face, and being subjected to chemical reinforcement treatment, wherein in the glass substrate, a penetration length in an uppermost-portion stress layer on the main surface is 49.1 μm or less, and assuming that an angle between the main surface and compressive stress in a stress profile by a Babinet compensator method is θ, the penetration length in the uppermost-portion stress layer is a value y of {12·t·1n(tan θ)+(49.1/t)} or less, the penetration length in the uppermost-portion stress layer is a length of a longer diagonal in an indentation when a diamond quadrangular pyramid indenter of rhombic transverse section with vertex angles of 172° P a compressive stress depth is from 100 μm to 150 μm, and glass materials forming the glass substrate include aluminosilicate glass, where SiO Al the total of ZrO Li Na K MgO is 0 to 4 percent by mass, CaO exceeds 0 percent and is up to 5 percent by mass or less, where the total amount of MgO and CaO is 5 percent by mass or less, and the content of CaO is higher than the content of MgO, and content of SrO+BaO is 0 to 3 percent by mass, and ZrO