Kabushiki Kaisya Ohara

Masashi Maekawa

Naoyuki Goto

Yasuyuki Kawashima

Futoshi Ishizaki

Nobuo Kawasaki

Yoshio Karasawa

A method for manufacturing a magnetic disk substrate includes a step of polishing a glass-ceramic having a crystal phase consisting of crystal grains having an average diameter of less than 3 .mu.m with a polishing material having a grain diameter smaller than the diameter of the crystal grain. In one aspect of the invention, the glass-ceramic includes lithium disilicate (Li.sub.2 O--2SiO.sub.2) and alpha-quartz (alpha-SiO.sub.2) as predominant crystal phases and grown crystal grains of the alpha-quartz each have a globular grain structure consisting of aggregated particles and have a diameter within a range of 0.3 .mu.m-3.0 .mu.m.

Method for manufacturing a magnetic disk substrate

Glass-ceramic for information recording disks have a crystalline structure suitably used for substrate materials and the like for magnetic disks and magneto-optic disks as well as have improved surface characteristics obtained by polishing the glass, and besides the base glass thereof is excellent in melting properties and moldability thereof. The base glass composition consists essentially of ingredients of SiO.sub.2 -Al.sub.2 O.sub.3 -ZnO-MgO-CaO-SrO-BaO-TiO.sub.2 system. The main crystalline phase of the glass-ceramic produced by heat-treating the base glass having a viscosity of log .eta.=3.0 poise or less at 1250.degree. C. is gahnite, a size of the crystal grain is within a range of from 50 to 1000 Angstrom, and a degree of surface roughness (Ra) of the polished glass-ceramic is within a range of from 0.5 to 9.0 Angstrom.

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Sagamihara, Japan

Masashi Maekawa