Electrical Insulating Properties of Porcelain Enamels on Copper

The electrical properties of copper oxide‐bearing porcelain enamels fired on sheet platinum and of the clear base porcelain enamel fired on sheet copper were measured. The dielectric constant, dissipation factor, and resistivity of the coatings were determined from room temperature to 700°F., and at frequencies varying from 0.1 to 100 kc. per second. The effect of firing time, firing temperature, and coating thickness on the copper ion content resulting in the coatings fired on copper was investigated. The copper ion concentration of the porcelain enamels fired on cop per was determined by X‐ray fluorescence analysis. Electrical measurements of coatings fired on platinum and on copper were correlated with the copper ion concentration of the coating. At concentrations in the coating below 5% CuO, some marked changes occurred in the electrical characteristics of the coatings as a function of CuO content. These changes were even more accentuated at elevated temperatures. At concentrations varying from 5% CuO to the saturation point of CuO in the coating (about 20% CuO for coatings fired at 1600°F.), the electrical properties of these coatings at room temperature were nearly unchanged throughout this range, whereas at elevated temperatures the general effect was that of a decrease in dielectric constant and dissipation factor as the CuO content was increased.