In a silicon nitride sintered body including silicon nitride crystal grains and a grain boundary phase, dislocation defect portions exists inside at least some of the silicon nitride crystal grains. A percentage of a number of the at least some of the silicon nitride crystal grains among any 50 of the silicon nitride crystal grains having completely visible contours in any cross section or surface of the silicon nitride sintered body is not less than 50% and not more than 100%. It is favorable that a plate thickness of the silicon nitride substrate, in which the silicon nitride sintered body is used, is within the range not less than 0.1 mm and not more than 0.4 mm. The TCT characteristics can be improved by using the silicon nitride substrate in the silicon nitride circuit board.

In a silicon nitride sintered body including silicon nitride crystal grains and a grain boundary phase, dislocation defect portions exists inside at least some of the silicon nitride crystal grains. A percentage of a number of the at least some of the silicon nitride crystal grains among any 50 of the silicon nitride crystal grains having completely visible contours in any cross section or surface of the silicon nitride sintered body is not less than 50% and not more than 100%. It is favorable that a plate thickness of the silicon nitride substrate, in which the silicon nitride sintered body is used, is within the range not less than 0.1 mm and not more than 0.4 mm. The TCT characteristics can be improved by using the silicon nitride substrate in the silicon nitride circuit board.

Disclosed herein are methods for functionalizing the surface of a biomedical implant. The biomedical implant may be a zirconia-toughened alumina implant surface functionalized with silicon nitride powder for promoting osteogenesis.

Ceramic particles for use in a solar power tower and methods for making and using the ceramic particles are disclosed. The ceramic particle can include a sintered ceramic material formed from a mixture of a ceramic raw material and a darkening component comprising MnO as Mn.sup.2+. The ceramic particle can have a size from about 8 mesh to about 170 mesh and a density of less than 4 g/cc.

A ceramic material for radome is illustrated comprising: -about 80-95% (wt %) of Si.sub.3N.sub.4; about 5-15% (wt %) of magnesium aluminosilicates including 2.5-12.5% (wt %) of Si0.sub.2, 0.5-3% (wt %) of MgO and 2-6% (wt %) of Al.sub.2O.sub.3; and having a density not lower than 2.5 g/cm.sup.3 and a dielectric constant not exceeding 6.5. A process for producing a radome is also illustrated.

A ceramic material for radome is illustrated comprising: -about 80-95% (wt %) of Si.sub.3N.sub.4; about 5-15% (wt %) of magnesium aluminosilicates including 2.5-12.5% (wt %) of Si0.sub.2, 0.5-3% (wt %) of MgO and 2-6% (wt %) of Al.sub.2O.sub.3; and having a density not lower than 2.5 g/cm.sup.3 and a dielectric constant not exceeding 6.5. A process for producing a radome is also illustrated.

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/rum 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.

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/rum 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.

A ceramic ball material according to an embodiment includes a spherical portion; and a band-shaped portion formed over a circumference of a surface of the spherical portion. In the ceramic ball material, the ceramic ball material has a ratio Rab/Rap of 0.70 or more and 1.03 or less, where Rab denotes an arithmetic average roughness on an outer peripheral surface of the band-shaped portion; and Rap denotes an arithmetic average roughness on an outer peripheral surface of the spherical portion.

A silicon nitride sintered body according to an embodiment includes not less than 0.1 mass % and not more than 10 mass % of zirconium when converted to oxide. In XRD analysis (2) of any cross section of the silicon nitride sintered body, 0.01I.sub.35.3/I.sub.27.00.5 and 0I.sub.33.9/I.sub.27.01.0 are satisfied; I.sub.35.3 is a maximum peak intensity detected at 35.30.2 based on -silicon nitride crystal grains; I.sub.27.0 is a most intense peak detected at 27.00.2 based on -silicon nitride crystal grains; and I.sub.33.9 is a most intense peak detected at 33.90.2 based on zirconium nitride.