A spark plug according to one embodiment of the present invention includes an insulator formed of an alumina-based sintered body, wherein the insulator contains 90 wt % or more of an aluminum component in terms of oxide, and wherein crystal grains of the insulator has an average grain size of 1.5 mm or smaller and a grain size standard deviation of 1.2 μm or smaller.

Disclosed is a method for fabricating a solid article from a boron carbide powder comprising boron carbide particles that are coated with a titanium compound. Further disclosed herein are the unique advantages of the combined use of titanium and graphite additives in the form of water soluble species to improve intimacy of mixing in the green state. The carbon facilitates sintering, whose concentration is then attenuated in the process of forming very hard, finely dispersed TiB2 phases. The further recognition of the merits of a narrow particle size distribution B4C powder and the use of sintering soak temperatures at the threshold of close porosity which achieve post-HIPed microstructures with average grain sizes approaching the original median particle size. The combination of interdependent factors has led to B.sub.4C-based articles of higher hardness than previously reported.

The invention relates to a copper-ceramic composite comprising: a ceramic substrate; and a copper or copper alloy coating on the ceramic substrate, the copper or copper alloy having grain sizes of 10 μm to 300 μm.

The composite sintered body includes Al.sub.2O.sub.3, and MgAl.sub.2O.sub.4. The content of Al.sub.2O.sub.3 in the composite sintered body is not less than 95.5% by weight. The average sintered grain size of Al.sub.2O.sub.3 in the composite sintered body is not less than 2 μm and not greater than 4 μm. The standard deviation of sintered grain size distribution of Al.sub.2O.sub.3 in the composite sintered body is not greater than 0.35. The bulk density of the composite sintered body is not less than 3.94 g/cm.sup.3 and not greater than 3.98 g/cm.sup.3. In the composite sintered body, the ratio of amount of crystal phase of MgAl.sub.2O.sub.4 to that of Al.sub.2O.sub.3 is not less than 0.003 and not greater than 0.01.

Disclosed is a method for fabricating a solid article from a boron carbide powder comprising boron carbide particles that are coated with a titanium compound. Further disclosed herein are the unique advantages of the combined use of titanium and graphite additives in the form of water soluble species to improve intimacy of mixing in the green state. The carbon facilitates sintering, whose concentration is then attenuated in the process of forming very hard, finely dispersed TiB.sub.2 phases. The further recognition of the merits of a narrow particle size distribution B.sub.4C powder and the use of sintering soak temperatures at the threshold of close porosity which achieve post-HIPed microstructures with average grain sizes approaching the original median particle size. The combination of interdependent factors has led to B.sub.4C-based articles of higher hardness than previously reported.

A support substrate 2 is a polycrystalline SiC substrate formed of polycrystalline SiC. Assuming that one of the two sides of the polycrystalline SiC substrate is a first side and that the other side is a second side, a substrate grain size change rate of the polycrystalline SiC substrate, which is a value obtained by dividing a difference between the average value of crystal grain sizes of the polycrystalline SiC on the first side and the average value of crystal grain sizes of the polycrystalline SiC on the second side by a thickness of the polycrystalline SiC substrate, is 0.43% or less. A radius of curvature of the polycrystalline SiC substrate is 142 m or more.

The present invention provides a ferrite sintered magnet comprising ferrite crystal grains having a hexagonal structure, wherein the ferrite sintered magnet comprises metallic elements at an atomic ratio represented by formula (1). In formula (1), R is at least one element selected from the group consisting of Bi and rare-earth elements, and R comprises at least La. In formula (1), w, x, z and m satisfy formulae (2) to (5). The above-mentioned ferrite sintered magnet further has a coefficient of variation of a size of the crystal grains in a section parallel to a c axis of less than 45%.

Ca.sub.1-w-xR.sub.wSr.sub.xFe.sub.zCo.sub.m(1)

0.360w=0.420(2)

0.110x0.173(3)

8.51z9.71(4)

0.208m0.269(5)

The invention relates to a copper-ceramic substrate comprising: a ceramic carrier, and at least one copper layer bonded to a surface of the ceramic carrier, which has a free surface for forming a conductor structure and/or for securing bonding wires, wherein the copper layer has a microstructure with an average grain size diameter of 200 to 500 m, preferably 300 to 400 m.

The composite sintered body includes Al.sub.2O.sub.3, and MgAl.sub.2O.sub.4. The content of Al.sub.2O.sub.3 in the composite sintered body is not less than 95.5% by weight. The average sintered grain size of Al.sub.2O.sub.3 in the composite sintered body is not less than 2 m and not greater than 4 m. The standard deviation of sintered grain size distribution of Al.sub.2O.sub.3 in the composite sintered body is not greater than 0.35. The bulk density of the composite sintered body is not less than 3.94 g/cm.sup.3 and not greater than 3.98 g/cm.sup.3. In the composite sintered body, the ratio of amount of crystal phase of MgAl.sub.2O.sub.4 to that of Al.sub.2O.sub.3 is not less than 0.003 and not greater than 0.01.

A dielectric composition includes: a base material powder including (Ca.sub.1-xSr.sub.x) (Zr.sub.1-yTi.sub.y)O.sub.3 (0<x0.7, 0<y0.03); a first subcomponent including at least one selected from the group of an oxide of manganese (Mn) and a carbonate of manganese (Mn); a second subcomponent including at least one selected from the group of an oxide of yttrium (Y) and a carbonate of yttrium (Y), where a content of the second subcomponent is within a range from 2 to 3 mol, based on 100 mol of the base material powder; and a third subcomponent including at least one selected from the group of an oxide of silicon (Si) and a carbonate of silicon (Si), and an electronic component uses the same.