Influence of oxygen concentration and humidity on palladium oxide formation by a mechanochemical reaction

Palladium oxide formed on the electrode surfaces of palladium electrical contacts by a mechanochemical reaction during mechanical switching generally causes significant contact resistance rise. In the present paper, the influence of oxygen concentration and humidity on this phenomenon is examined. It has been found that palladium oxide is formed even when the oxygen concentration is less than 0.01% under the condition that influence of aqueous vapor or organic gases is negligible. As the oxygen concentration decreases, both the contact resistance and the palladium oxide formation rate decrease. Experimental results indicate that the presence of water delays or prevents palladium oxide formation. The proposed model for this effect is that water molecules absorbed onto the contact surfaces act to lubricate to smooth the contact spots, thereby minimizing the palladium oxide formation rate.