In order to provide a rare earth oxide-alumina type sintered body having no defect such as void and pore, and high strength, toughness and reliability, silica is added to a mixture of rare earth oxide and alumina to control a crystal grain size of the sintered body to not more than 30 .mu.m, whereby abnormal grain growth and occurrence of pore are restrained to produce a practically usable rare earth oxide-alumina-silica sintered body having excellent strength and toughness and uniform structure. According to this production method, rare earth oxide-alumina-silica sintered bodies having no defect such as void and pore, and high strength, toughness and reliability can easily be obtained.
In accordance with the present invention, a glass substrate of a disk for recording information, containing oxides of rare earth elements and fine particles dispersed therein, and a disk for recording information and a disk apparatus for recording information using the glass substrate of the disk are provided. The glass substrate of the disk for recording information having preferable mechanical characteristics, as well as superior chemical stability, thermal stability, flatness, and transparency is provided, and a disk for recording information and a disk apparatus for recording information using the glass substrate of the disk are provided.
In accordance with the present invention, a glass substrate of a disk for recording information, containing oxides of rare earth elements and fine particles dispersed therein, and a disk for recording information and a disk apparatus for recording information using the glass substrate of the disk are provided. The glass substrate of the disk for recording information having preferable mechanical characteristics, as well as superior chemical stability, thermal stability, flatness, and transparency is provided, and a disk for recording information and a disk apparatus for recording information using the glass substrate of the disk are provided.
A ceramic compound which undergoes martensitic transformation comprises a compound represented by compositional formula Ln.sub.1-x Si.sub.x AlO.sub.3+0.5x obtained by substituting a part of LnO.sub.1.5 in LnAlO.sub.3 -type compounds with SiO.sub.2, where Ln represents at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, and x=0.01 to 0.3.
Disclosed is a method for the preparation of a high-quality sintered body of a rare earth oxide or a composite oxide of a rare earth oxide and an adjuvant oxide such as aluminum oxide. The method comprises shaping a rare earth oxide powder characterized by specified particle diameter distribution values of D.sub.50 and D.sub.90 and a specified specific surface area or a powder blend of the rare earth oxide and adjuvant oxide into a powder compact and subjecting the powder compact to a sintering heat treatment at a specified sintering temperature by increasing and decreasing the temperature up to and from the sintering temperature each at a rate not exceeding a specified upper limit.
A glass substrate for a magnetic disk contains a transition metal. The substrate, which is subjected to formation of zone texturing by irradiating the substrate with a laser beam, has a high mechanical strength even if it is not chemically strengthened. The glass substrate contains a transition metal element and has a transmittance of 10% or less for light in a wavelength range of 300 to 2000 nm. The surface roughness of an information recording surface portion thereof is 2.0 nm or less. In addition to a transition metal element, the glass substrate may include a rare earth metal element.
