The present invention provides a high thermal conductive silicon nitride sintered body having a thermal conductivity of 50 W/m.Math.K or more and a three-point bending strength of 600 MPa or more, wherein when an arbitrary cross section of the silicon nitride sintered body is subjected to XRD analysis and highest peak intensities detected at diffraction angles of 29.3±0.2°, 29.7±0.2°, 27.0±0.2°, and 36.1±0.2° are expressed as I.sub.29.3°, I.sub.29.7°, I.sub.27.0°, and I.sub.36.1°, a peak ratio (I.sub.29.3°)/(I.sub.27.0°+I.sub.36.1°) satisfies a range of 0.01 to 0.08, and a peak ratio (I.sub.29.7°)/(I.sub.27.0°+I.sub.36.1°) satisfies a range of 0.02 to 0.16. Due to above configuration, there can be provided a silicon nitride sintered body having a high thermal conductivity of 50 W/m.Math.K or more, and excellence in insulating properties and strength.

A sintered body includes a crystal grain containing silicon nitride, and a grain boundary phase. If dielectric losses of the sintered body are measured while applying an alternating voltage to the sintered body and continuously changing a frequency of the alternating voltage from 50 Hz to 1 MHz, an average value ε.sub.A of dielectric losses of the sintered body in a frequency band from 800 kHz to 1 MHz and an average value ε.sub.B of dielectric losses of the sintered body in a frequency band from 100 Hz to 200 Hz satisfy an expression |ε.sub.A−ε.sub.B|≤0.1.

Provided is a member for optical glass manufacturing apparatus. The member is used for optical glass manufacturing apparatus and exposed to a gas containing a halogen element in a high temperature environment of 1100° C. or higher. The member includes dense ceramics containing silicon nitride as a main component, and a porosity of a surface layer of the member is smaller than a porosity of the inside of the member.

Phosphors include a CaAlSiN.sub.3 family crystal phase, wherein the CaAlSiN.sub.3 family crystal phase comprises at least one element selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb.

A phosphor plate including: a complex containing an α-sialon phosphor and a sintered body containing spinel represented by a general formula M.sub.2xAl.sub.4-4xO.sub.6-4x (where M represents at least one of Mg, Mn, and Zn, and 0.2<x<0.6). In addition, there is provided a light emitting device including: a group III nitride semiconductor light emitting element; and the phosphor plate provided on one surface of the group III nitride semiconductor light emitting element. Further, there is provided a method for manufacturing the phosphor plate.

A method for molding a ceramic material includes: mixing a ceramic powder, a resin, a curing agent and a solvent to obtain a raw material slurry for a ceramic material; injecting the raw material slurry into an elastic container; curing the resin in the raw material slurry injected into the elastic container to form a molded body having a desired shape; and demolding the molded body from the elastic container.

A silicon nitride sintered body includes a silicon nitride crystal grains and grain boundary phases. Further, when D stands for width of the silicon nitride sintered body before being subjected to surface processing, relations between an average grain diameter dA and an average aspect ratio rA of the silicon nitride crystal grain in a first region from an outermost surface to a depth of 0 to 0.01D and an average grain diameter dB and an average aspect ratio rB of the silicon nitride crystal grain in a second region inside the first region satisfy the inequalities:

0.8≤ dA/dB≤ 1.2; and

0.8≤ rA/rB≤ 1.2.

A sintered body includes a crystal grain containing silicon nitride, and a grain boundary phase. If dielectric losses of the sintered body are measured while applying an alternating voltage to the sintered body and continuously changing a frequency of the alternating voltage from 50 Hz to 1 MHz, an average value ε.sub.A of dielectric losses of the sintered body in a frequency band from 800 kHz to 1 MHz and an average value ε.sub.B of dielectric losses of the sintered body in a frequency band from 100 Hz to 200 Hz satisfy an expression |ε.sub.A−ε.sub.B|≤0.1.

A member for optical glass production apparatus is a member exposed to a gas containing a halogen element in a high temperature environment; the member includes a first member (4) directly or indirectly supporting an optical glass (10) and a second member (5) supporting the first member (4).

Phosphors include a CaAlSiN.sub.3 family crystal phase, wherein the CaAlSiN.sub.3 family crystal phase comprises at least one element selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb.