Patent ID: 7857680

Claim:
A method for producing a glass substrate for a magnetic disk by polishing a circular glass plate, which comprises polishing the circular glass plate using a slurry containing a CeO 2 crystal powder, wherein the CeO 2 crystal powder is prepared by: (1) obtaining a melt containing from 5 to 50 mol % of CeO 2 , from 10 to 50 mol % of at least one alkaline earth metal oxide selected from the group consisting of MgO, CaO, SrO and BaO in total, and from 30 to 75 mol % of B 2 O 3 , by heating said composition containing CeO 2 to a temperature from 1200 to 1500° C.; (2) quenching the melt to obtain an amorphous material; (3) subjecting the amorphous material to heat treatment at from 650 to 850° C. to obtain a CeO 2 crystals-precipitated amorphous material; and (4) subjecting the CeO 2 crystals-precipitated amorphous material to acid treatment to separate and extract the CeO 2 crystal powder from the CeO 2 crystals-precipitated amorphous material; wherein the median diameter of the particles in the slurry is from 10 to 300 nm as measured by dynamic light scattering method.