Separation of Surface and Bulk Gases in Contact Materials of Vacuum Switches-Determination of Gases and Effect on Vacuum Breakdown

Meaningful analysis for very small quantities of gases in contacts can be obtained only by the method which permits differentiating between surface and bulk gases. The graphite capsule method and copper bath method in vacuum fusion analysis were compared, and the surface area variation method and two-stage gas extraction method were investigated for the separation of surface and bulk gases. As a result of these investigations, the surface and bulk gas content of the copper-tellurium alloy can be determined by the surface area variation method. The bulk oxygen content of the ingot, forged- and vacuum-refined copper-tellurium alloy is 3.8 parts per million (ppm), 1.7 ppm, and 0.1 ppm, respectively. The surface oxygen content, however, is conversely 1.5 µg/cm2, 2.4µg/cm 2 and 3.7µg/cm 2 , respectively. In high vacuum, gases are released from the electrodes as the voltage is applied between the electrodes. The released gases increase exponentially whether the spark breakdowns occur or not. It is suggested that the released gas at the spark breakdown corresponds to surface gas, which is considered as water vapor mostly absorbed on the electrode. After the spark breakdowns occur repeatedly, water vapor from the surface layers is depleted, namely, the surface conditioning takes place. Therefore, the released gas without spark breakdown corresponds to the bulk gas, which is mostly hydrogen.