CRYSTALLIZED GLASS FOR MAGNETIC DISK SUBSTRATE, MAGNETIC DISK SUBSTRATE AND MAGNETIC DISK

摘要

PROBLEM TO BE SOLVED: To significantly decrease the center line average surface roughness of a Li2 O-Al2 O3 -SiO2 crystallized glass for a magnetic disk substrate after the surface of the crystallized glass is subjected to precision polishing and to control the coefft. of thermal expansion of the glass at 100 deg.C-300 deg.C to 80-100×10<-7> /K. SOLUTION: The main crystal phase of the crystallized glass consists of lithium disilicate. The peak intensity of the cristobalite phase by X-ray diffraction method ranges 20 to 50 when the peak intensity of lithium disilicate is assumed to be 100. This reinforced glass contains Cr2 O3 by >=1.0 pts.wt.-<=3.0 pts.wt. (preferably >=1.5 pts.wt.-<=2.5 pts.wt.) in 100 pts.wt. of the sum amt. of metal oxides except for Cr2 O3 and MnO.