Abstract: A mold for molding an optical disc includes a first mold member having a recess, and a second mold having a body and a plate-like sintered ceramic member secured to the body and having a flat seat surface. The recess and the flat seat surface jointly provides a mold cavity when the first and second mold members are mated together. A disc-shaped thin stamper is adapted to be seated on and detachably secured to the flat seat surface. The ceramic member is made of a ceramic material having Rockwell hardness (A-Scale) of not less than 90, so that the flat seat surface is not subjected to undue damage for a prolonged period of time.

Abstract: In the manufacture of a wiring board, or a heat discharge plates and the like in the field of the electronics, composite materials consisting of substrates and organic polymeric materials and epoxy resin, as well as ceramic materials such as alumina plates, have heretofore been used as substrates of printed wiring boards and heat sinks. These substrate materials, however, are defective in that, because of a low thermal conductivity and an insufficient heat radiation.A highly thermal conductive and electrical insulating substrate of the invention comprises a highly thermal conductive metal plate, such as aluminum, and a film formed thereon, said film being composed of a dispersion of metal oxide particles having a shape factor, of 1 to 1.4, and also, having a polyhedral shape including smooth surfaces in an adhesive organic polymer. The space factor is an average value of the long diameter/short diameter ratio of the metal oxide particles.

Abstract: A method for preparing corundum particles by a hydrothermal process which comprises adding fine particles of corundum to a starting alumina hydrate, and subjecting the resulting mixture to a hydrothermal reaction or treatment, the alumina in the alumina hydrate being deposited on the surfaces of the fine corundum particles while suppressing formation of new corundum crystal nuclei.