Abstract: An abrasive includes an alumina-based fiber bound by a matrix resin which contains diamond abrasive grains therein, and a diamond abrasive grain layer provided on the surface of the bound fiber. The abrasive is formed into, for example, a flat plate having a thickness in a range of 0.45 to 1.2 mm, and the diamond abrasive grain layer is provided on at least any one of opposite surfaces of the bound fiber. Flat filaments having a ratio of a long axis to a short axis of the cross-sectional shape thereof in a range of 1.3 to 1.8 are used for the alumina-based fiber.

Abstract: An object of the present invention is to provide an alumina-magnesia oxide which can be fine pulverulent bodies by pulverizing. In the alumina-magnesia oxide of the present invention includes: 70-73 WT % of alumina component, which is converted into alumina (Al.sub.2 O.sub.3); and 27-30 WT % of magnesia component, which is converted into magnesia (MgO). The alumina-magnesia oxide is formed into a pulverulent body, which is a hollow grain having loosed bulk density of 0.15 g/cm.sup.3 or less and average grain diameter of 10 .mu.m or more.

Abstract: The present invention relates to a ceramic fiber yarn, which has higher weaving and knitting performance. The ceramic fiber yarn comprises a group of filaments, the filaments being made by the steps of spinning mother liquid, which comprises colloidal silica and basic aluminum chloride, and firing, the filaments comprising 67-75 wt % of alumina and 25-33 wt % of silica and mainly having polycrystalline transition alumina, and is characterized in that: the loop strength of each the filament, which is measured by a wire having diameter of 0.5 mm, is at or greater than 2.5.times.10.sup.-2 N (N: Newton); and the crystal structure of the filament substantially changes to polycrystalline mullite after heating for 30 minutes at the temperature of 1,400.degree. C.