Surface resistivity or nonporous ceramic and organic insulating materials at high humidity with observations of associated silver migration

An investigation was made of the behavior of the surface resistivity of a number of ceramic and organic materials during exposure to high relative humidity. Particular emphasis was given to glazed high alumina ceramics from commercial sources. The effects of variables such as contamination, standing direct current potential, firing atmosphere, surface finish and electrodes of different metals were investigated. The uncontaminated specimens of the materials examined can be listed in the order of diminishing surface resistivity as follows: High molecular weight polymers, glazed high alumina ceramics, glasses and glazed ceramics, unglazed ceramics and glass bonded mica. All of the materials are very sensitive to contamination, which tends to reduce them to a nearly common level of surface resistivity. Severe and rapid migration of silver from silver electrodes under the test conditions were observed. Electrodes of solder, tin, copper and platinum showed no discernible migration. The necessity for the development of better means for avoiding contamination and its effects, maintaining high surface resistivity and eliminating silver migration is emphasized by the results of this work.