THE ROLE OF FORMIC-ACID AND METHANOL ON SPECIATION RATE AND QUALITY IN THE ELECTRODEPOSITION OF CHROMIUM FROM TRIVALENT ELECTROLYTES

A successful enhancement of both the quality and the deposition rate h as been obtained by the addition of some quantities of formic acid and methanol. The results were obtained by using very conventional condit ions such as 25 degrees C, no pH adjustment low current density and ve ry gentle agitation. An excellent quality of deposit with a deposition rate of 50-100 mu m/hr was obtained. And sustained deposition up to a pproximate to 200 mu m was achieved with prolonged electrolysis. The c hange in the chemical speciation of the electrolyte was studied by usi ng ion-exchange chromatography. A separation and identification of the various species, formed as the bath was aged with time, was obtained The chromium concentration of each band was measured using the ICP spe ctrometer, monitoring the change in the concentration of the species w ith ageing. U.V. visible spectrometry was also used to confirm identif ication of the species. A clear correlation has been established betwe en loss of deposition rate and the formation of higher oligomeric chro mium (III) species. The role of methanol and formic acid in inhibiting this effect is discussed.