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Abstract
Surface-segregating calcium impurity is removed from a polycrystalline gold sample by heating, exposing to oxygen, and ion-bombarding over an extended period of time. The rate of oxygen chemisorption is found to decrease drastically from that at the beginning of the purification period where calcium segregation is substantial to that at the end where segregated calcium is nearly undetectable. The effect of calcium appears to involve dissociative chemisorption of molecular oxygen at the calcium sites followed by migration of oxygen atoms to gold sites, in a manner analogous to “hydrogen spillover” occurring on the surface of supported catalysts. It is also found that oxygen previously chemisorbed to a gold surface can promote the surface segregation of calcium even in the absence of gas-phase oxygen. Equations are presented to account for simultaneous catalysis of oxygen chemisorption to gold by calcium, and promotion of calcium surface-segregation by oxygen chemisorbed to gold.
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