Abstract: A process for making barium titanate based materials and the like of positive temperature coefficient of resistivity having desirable and precisely predetermined thermal and electrical properties utilizes low cost starting materials and convenient and economical processing steps. Titanium dioxide powder is placed in suspension in an aqueous medium with dissolved compounds of barium and other selected materials while the pH of the medium is regulated within selected limits, whereby barium and other selected ions are adsorbed in predetermined ratio by suspended titanium dioxide particles and whereby water-soluble contaminants in the starting materials are placed in solution. An aqueous carbonate solution is then commingled with the titanium dioxide suspension in a controlled manner to form a precipitate which incorporates titanium dioxide and desired relative proportions of carbonates of barium and other selected materials in a homogenous mixture.

Abstract: Ceramic semiconductor elements having ohmic contact surfaces are made by dispersing bentonite clay in a bonding composition consisting of a metal powder in a phosphate-chromate-metal ion solution to form a thixotropic coating material, by screen printing the coating material onto limited surface areas of ceramic semiconductor bodies, and by heating the coated bodies for curing the coating material to form adherent ohmic contact layers on the limited surface areas of the ceramic bodies.

Abstract: A process for forming an electrical resistance heater on a metal substrate. At least one layer of a composition of a polyamic acid or polyamide-imide polymer and a solvent therefor is applied to a surface of the substrate. The substrate and layer are heated to remove the solvent and to effect only partial curing of the polymer thereby to form a partially cured insulating layer. A composition of a mixture of a polyamic acid or polyamide-imide polymer, a solvent therefor and flakes of an electrical conductivity-modifying material is applied to the insulating layer thereby to form an overlying layer having an electrical conductivity substantially greater then that of the insulating layer. The substrate, insulating layer and overlying layer are thereafter heated for a period of time and at a temperature sufficient to at least partially cure the overlying layer.