An Electron Microscopic Study of Nucleation and Growth in Electrochemical Displacement Reactions: A Comparison of the Cu/Fe and Cu/AI Cementation Systems
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A novel technique was developed where vapor-deposited thin films of aluminum and iron approximately 0.2 /jm thick were utilized as substrates in the Cu/AI and Cu/Fe cementation systems. The nucleation of the incipient copper deposit upon the film surfaces was examined by transmission and scanning electron microscopy. Cement copper nuclei were observed to be crystal polyhedra which enlarged and coalesced in the Cu/Fe system to form a continuous, botryoidal deposit while in the Cu/AI system isolated nuclei and clusters developed dendritic structures which grew to massive form with extended solution contact times. There was more apparent initial replacement of individual iron grains with copper in the Cu/Fe system than aluminum replacement in the Cu/AI system but the overall cementation mechanism, while exhibiting differences on comparing these systems, was fundamentally consistent with earlier concepts involving galvanic corrosion.
KeywordsMetallurgical Transaction Cementation Copper Deposit Aluminum Film Bulk Deposit
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