Electroless plating of Pd-P alloys from palladium-ethylenediamine complex solutions containing sodium phosphite as a reducing agent was investigated. The deposition process proceeded autocatalytically, as in the case using hypophosphite, but the phosphorus content of the deposits was much lower. The phosphorus content of the deposits increased with an increase in phosphite concentration.
In as-plated deposits with only a trace of phosphorus, X-ray diffraction data showed a crystalline structure, but with an increase in phosphorus content, the structure became microcrystalline. As-plated deposits containing 3.74wt% phosphorus showed a very diffused diffraction pattern, changing into sharp crystalline features of Pd and Pd
6P after heat-treatment at 300°C.
About 60∼80 per cent of consumed phosphite was utilized for alloy deposition, and the mechanism of this can be well explained by Van den Meerakker's proposal.
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