Characterization of Cobalt‐Hardened Gold Electrodeposits by Mo̸ssbauer Spectroscopy: I . State of Cobalt in the As‐Deposited Material

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Abstract
Hard gold electrodeposits containing Co57 have been studied using Mössbauer spectroscopy to establish the chemical state of the cobalt in the deposit. These deposits were prepared using standard cobalt‐hardened acid citrate baths which had been doped with Co57 ions. The radioactive decay of Co57 results in a 14.4 keV gamma ray which is used for the Mössbauer spectroscopy. This technique provides a unique, nondestructive method of observing the cobaltin situ in the gold. The measurements show that ≤70% of the Co is substitutionally dissolved in the gold host. The remainder appears to be in the form of complexes included in the deposit. No microprecipitates of metallic cobalt are seen in the as‐deposited layer or in samples which have been annealed at low temperatures. The relationship between this microstructure information and deposit hardness is discussed. Frozen plating solution and mercury and aqua regia extracts have also been studied to establish the identity of the cobalt species present.

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