Preparation and characterization of chromium deposits obtained from moltensalts using pulsed currents

The electroplating of chromium from fused chloride electrolytes was investi gated. The experimental conditions were defined taking into account the mec hanisms of the electrochemical reduction of CrCl2 and of the chromium nucle ation and electrocrystallization phenomena. Chromium was plated on various substrates from concentrated LiCl-KCl-CrCl2 (600 to 800 mol m(-3) CrCl2) el ectrolyte. Direct or pulsed current electrolysis were carried out under a d ry argon atmosphere in the 400 to 440 degreesC temperature range. The shape of the current signals was chosen, taking into account the chromium electr ocrystallization phenomena onto a foreign substrate, so as to obtain well-d efined structures for the chromium layers. The chromium deposits were chara cterized by SEM and EDX analysis, and by microhardness determination. Unifo rm chromium electroplates of high purity, high adherence with no cracks, we re obtained by using pulsed current: signals with cathodic pulses and open- circuit periods preceded by cathodic pre-pulses. With this current shape, t he mean rate of the chromium electroplating process remained lower than 10 mum h(-1). However, using a repeated of periodic cathodic pre-pulse/cathodi c pulse/anodic pulse/open circuit sequences, the growth rate of compact chr omium layers increased to 100 mum h(-1) or more.