Abstract: A zirconia-based sinter containing a boron compound and stabilized with a rare earth metal oxide is provided which has excellent fracture toughness, mechanical strength and thermal stability. A zirconia-based sinter comprising ZrO.sub.2 as the main component, one or more rare earth metal oxides, R.sub.2 O.sub.3, selected from Yb.sub.2 O.sub.3, Er.sub.2 O.sub.3, Ho.sub.2 O.sub.3, Y.sub.2 O.sub.3, and Dy.sub.2 O.sub.3, and a boron compound or a boron compound and Al.sub.2 O.sub.3 and/or SiO.sub.2, wherein the molar proportion of R.sub.2 O.sub.3 /ZrO.sub.2 is from 1.3/98.7 to 2/98, excluding 2/98, and the content of boron components is from 0.05 to 8% by mole in terms of B.sub.2 O.sub.3 or in addition thereto the content of Al.sub.2 O.sub.3 is from 0.1 to 5% by mole and/or the content of SiO.sub.2 is from 0.05 to 1.5% by mole. A grinding part material and a bracket material for dental correction constituted of the zirconia-based sinter are provided.

Abstract: A highly corrosion resistant .alpha.-sialon-like sintered body consisting essentially of an .alpha.-sialon composition represented by the composition formulaMx(Si,Al).sub.12 (O,N).sub.16wherein M is at least one .alpha.-sialon-soluble element selected from the group consisting of Yb, Er and Dy, and 0<.times..ltoreq.0.8,and Sc.sub.2 O.sub.3 insoluble in the .alpha.-sialon composition and being in an amount of 0.01 to 15 wt % based on the weight of the sintered body, and containing as an intergranular phase a Sc.sub.2 O.sub.3 --SiO.sub.2 complex wherein the mole ratio of Sc.sub.2 O.sub.3 to SiO.sub.2 is within the range of 1:0.1 to 1:50. This sintered body has not only mechanical characteristics such as strength and toughness, but high corrosion resistance such that it can withstand use under an environment where corrosion resistance such as oxidation resistance or chemical resistance is required.