Surface Conductivity of Lead Silicate Glass after Hydrogen Treatment

Conductivity was developed in the surface layer of a lead silicate glass containing 61% lead oxide by certain prescribed hydrogen treatments. The conducting layer was found to be from 50 to 100 a.u. thick. The specific resistance was 800 ohm‐cm., or more, depending on the hydrogen treatment. The ratio of hot‐to‐cold resistance was constant for various values of cold resistance. This showed that the conducting substance was a semiconductor, probably with reduced lead atoms serving as the centers which supplied the electrons. Their density was found to be one‐millionth of the total density of lead atoms in the glass. The remainder of the lead gathered into aggregates which gave the glass a black color but made no contribution to the conductivity. A coating of this glass was applied to porcelain by powdering, spraying, and firing the glass. After hydrogen treatment the coating had a resistance of about 1000 megohms per square, which could be increased to higher values by treatment in boiling water. The coating was stable at voltage gradients up to 100 kv. per in. when the resistance was high enough to keep the wattage input below about 0.2 watt per sq. in. The resistance increased with increasing temperature, corresponding to bk = 0.065 e.v. at 25° to 100°C. and bk = 0.11 e.v. at 335° to 440°C.