Abstract
Crack-free iron-molybdenum alloy coating having a micro-vickers hardness of a bout 450 and a light black hue has been electroplated onto mild steel substrates at cathodic current densities of 1-1.5A/dm2 and at 35°C. The optimum electrolyte composition was found to be 0.26mol/l Na3C6H5O7, 0.12mol/l Na2MoO4, and 0.14mol/l of FeSO4 at pH 4.0 adjusted with dilute H2SO4. The alloy composition exactly corresponds to Fe3Mo. Transmission and reflection electron diffraction patterns of the alloy showed an amorphous structure but the surface was found to be crystallized. Three kinds of the alloy plating baths in which sodium or potassium concentration is kept constant at two different levels have been prepared for the analysis of the current-potential characteristics. In addition, the catholyte pH was directly measured by using an antimony microelectrode. It was found that the electrodeposition involves a cycle of electrolytic reduction-reoxidation by the sodium, potassium and molybdenum ions. It was also revealed that sodium and potassium atoms form a layer on the electrode to protect the electrode surface from the reoxidation of electrolytically formed lower oxide of molybdenum. This provides a good explanations for the previously reported characteristics of the induced molybdenum codposition.
