A silicon nitride substrate including silicon nitride crystal grains and a grain boundary phase and having a thermal conductivity of 50 W/m.Math.K or more, wherein, in a sectional structure of the silicon nitride substrate, a ratio (T2/T1) of a total length T2 of the grain boundary phase in a thickness direction with respect to a thickness T1 of the silicon nitride substrate is 0.01 to 0.30, and a variation from a dielectric strength mean value when measured by a four-terminal method in which electrodes are brought into contact with a front and a rear surfaces of the substrate is 20% or less. The dielectric strength mean value of the silicon nitride substrate can be 15 kV/mm or more. According to above structure, there can be obtained a silicon nitride substrate and a silicon nitride circuit board using the substrate in which variation in the dielectric strength is decreased.

The friction stir welding tool member according to the present invention is made of a silicon nitride sintered body, wherein the silicon nitride sintered body contains 15% by mass or less of additive components except silicon nitride in such a manner that the additive components include at least one element selected from lanthanoid elements and at least one element selected from Mg, Ti, Hf, and Mo. In addition, it is preferable that the additive components further include at least one element selected from Al, Si, and C. According to the above-described configuration, a friction stir welding tool member having an excellent durability can be provided.

The friction stir welding tool member according to the present invention is made of a silicon nitride sintered body, wherein the silicon nitride sintered body contains 15% by mass or less of additive components except silicon nitride in such a manner that the additive components include at least one element selected from lanthanoid elements and at least one element selected from Mg, Ti, Hf, and Mo. In addition, it is preferable that the additive components further include at least one element selected from Al, Si, and C. According to the above-described configuration, a friction stir welding tool member having an excellent durability can be provided.

A ceramic ball material according to an embodiment including: a spherical portion; and a band-shaped portion formed in a band shape. When C denotes circularity of the band-shaped portion as observed from a height direction thereof, the circularity C is in a range of more than 0% and 2.5% or more.

A ceramic ball material according to an embodiment including: a spherical portion; and a band-shaped portion formed over a circumference of a surface of the spherical portion. The ceramic ball material has a ratio Rtb/Rts of 1.0 or more, where Rtb denotes a maximum cross-sectional height of a roughness profile on an outer peripheral surface of the band-shaped portion; and Rts denotes a maximum cross-sectional height of roughness on an outer peripheral surface of the spherical portion.

According to an example, a green body may include from about 1 wt. % to about 20 wt. % of a metal nanoparticle binder and a build material powder, wherein the metal nanoparticle binder is selectively located within an area of the green body to impart a strength greater than about 3 MPa.

According to an embodiment, a highly thermally conductive silicon nitride sintered body includes silicon nitride crystal grains and a grain boundary phase. A thermal conductivity of the silicon nitride sintered body is not less than 80 W/(m.Math.K). An average value of solid solution oxygen amounts of the silicon nitride crystal grains existing in a 20 ?m?20 ?m unit area in any cross section is not more than 0.2 wt %. An average value of major diameters of the silicon nitride crystal grains existing in a 50 ?m?50 ?m unit area in any cross section is not less than 1 ?m and not more than 10 ?m. An average of aspect ratios of the silicon nitride crystal grains existing in the 50 ?m?50 ?m unit area is not less than 2 and not more than 10.

According to an embodiment, a highly thermally conductive silicon nitride sintered body includes silicon nitride crystal grains and a grain boundary phase. A thermal conductivity of the silicon nitride sintered body is not less than 80 W/(m.Math.K). An average value of solid solution oxygen amounts of the silicon nitride crystal grains existing in a 20 ?m?20 ?m unit area in any cross section is not more than 0.2 wt %. An average value of major diameters of the silicon nitride crystal grains existing in a 50 ?m?50 ?m unit area in any cross section is not less than 1 ?m and not more than 10 ?m. An average of aspect ratios of the silicon nitride crystal grains existing in the 50 ?m?50 ?m unit area is not less than 2 and not more than 10.

Provided is a ceramic-resin composite body that has good mass productivity and product properties (heat dissipation properties, insulation properties and adhesive properties), and particularly a ceramic-resin composite that can dramatically improve the heat dissipation properties for electronic devices. The ceramic-resin composite body includes: 35 to 70% by volume of a sintered body having a monolithic structure in which non-oxide ceramic primary particles having an average major diameter of from 3 to 60 m and an aspect ratio of from 5 to 30 are three-dimensionally continuous; and 65 to 30% by volume of a thermosetting resin composition having an exothermic onset temperature of 180 C. or more and a curing rate of from 5 to 60% as determined with a differential scanning calorimeter, and having a number average molecular weight of from 450 to 4800, wherein the sintered body is impregnated with the thermosetting resin composition.

A thermally conductive insulator consisting essentially of a silicon nitride member, comprise: a first region provided 10 m or more away from a first surface of the member along a depth direction in a section vertical to the first surface and containing at least one substance selected from the group consisting of silicon carbide and a carbon material; and a second region provided between the first surface and the first region. A concentration of silicon nitride of the second region is higher than a concentration of silicon nitride of the first region.