A composition includes granules in which zirconia particles are aggregated. The granules have an average circularity of 0.81 or greater based on a projected image.

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.

Solar reflective roofing granules include a binder and inert mineral particles, with solar reflective particles dispersed in the binder. An agglomeration process preferentially disposes the solar reflective particles at a desired depth within or beneath the surface of the granules.

Provided are a transparent fluorescent sialon ceramic having fluorescence and optical transparency; and a method of producing the same. Such a transparent fluorescent sialon ceramic includes a sialon phosphor which contains a matrix formed of a silicon nitride compound represented by the formula M.sub.x(Si,Al).sub.y(N,O).sub.z (here, M represents at least one selected from the group consisting of Li, alkaline earth metals, and rare earth metals, 0≤x/z<3, and 0<y/z<1) and a luminescent center element.

An electrostatic chuck device includes: a base having one principal surface which is a placing surface on which a plate-shaped sample is placed, wherein the base is made from a sintered compact of ceramic particles, which include silicon carbide particles and aluminum oxide particles, as a forming material; and an electrostatic attraction electrode which is provided on a surface of the base on the side opposite to the placing surface of the base, or in the interior of the base, in which the volume resistivity value of the sintered compact is 0.5×10.sup.15 Ωcm or more in the entire range from 24° C. to 300° C., a graph which shows the relationship of the volume resistivity value of the sintered compact to a temperature at which the volume resistivity value of the sintered compact is measured has a maximum value in the range from 24° C. to 300° C., and the amount of metal impurities in the sintered compact other than aluminum and silicon in the sintered compact is 100 ppm or less.

Shot-peening method. Projecting a powder onto a surface. The powder includes sintered particles, more than 95 wt % of the particles are beads. The powder has, in wt % based on the oxides: —ZrO.sub.2 partially stabilized with CeO.sub.2 and Y.sub.2O.sub.3: balance to 100%, CeO.sub.2 and Y.sub.2O.sub.3 present, in mol % according to the sum of ZrO.sub.2, CeO.sub.2 and Y.sub.2O.sub.3, CeO.sub.2: 2.5-11 mol % and Y.sub.2O.sub.3: 0.5-2 mol %, —Al.sub.2O.sub.3; 3-50%—additive chosen from CaO, manganese oxides, ZnO, praseodymium oxides, SrO, copper oxides, 0.2-6% Nd.sub.2O.sub.3, BaO, iron oxides, and mixtures thereof: CaO being less than 2%, —elements other than ZrO.sub.2, CeO.sub.2, Y.sub.2O.sub.3, Al.sub.2O.sub.3, CaO, manganese oxides, ZnO, praseodymium oxides, ≤5% SrO, copper oxides, Nd.sub.2O.sub.3, BaO, and iron oxides: manganese oxides, praseodymium oxides, copper oxides and iron oxides being expressed as MnO, Pr.sub.6O.sub.11, CuO and Fe.sub.2O.sub.3, respectively, and a relative density greater than 95%.

A process for preparing roofing granules includes forming kaolin clay into green granules and sintering the green granules at a temperature of at least 900 degrees Celsius to cure the green granules until the crystalline content of the sintered granules is at least ten percent as determined by x-ray diffraction.

Ferrite powder of the present invention is ferrite powder detectable with a metal detector, comprising: soft ferrite particles containing Mn of 3.5 mass % or more and 20.0 mass % or less and Fe of 50.0 mass % or more and 70.0 mass % or less. It is preferable that a volume average particle diameter of the particles constituting the ferrite powder is 0.1 μm or more and 100 μm or less. It is preferable that magnetization by a VSM measurement when magnetic field of 5 K.Math.1000/4πA/m is applied is 85 A.Math.m.sup.2/kg or more and 98 A.Math.m.sup.2/kg or less.

A method of producing high strength shaped alumina by feeding alumina power into an agglomerator having a shaft with mixers able to displace the alumina power along the shaft, spraying a liquid binder onto the alumina power as it is displaced along the shaft to form a shaped alumina, and calcining the shaped alumina. The shaped alumina produced having a loose bulk density of greater than or equal to 1.20 g/ml, a surface area less than 10 m.sup.2/g, impurities of less than 5 ppm of individual metals and less than 9 ppm of impurities in total, and/or crush strength of greater than 12,000 psi.

According to the present invention, a dielectric ceramic composition, which can be fired in a reducing atmosphere, has a high dielectric constant, has an electrostatic capacity exhibiting little change, when used as a dielectric layer of a ceramic electronic component such as a laminated ceramic capacitor even under a condition of 150 to 200° C., and has small dielectric losses at 25° C. and 200° C., can be provided.