Black chromium electrodeposition on electrodes modified with formic acid and the corrosion resistance of the coating

The effect of modification of the electrode surface with formic acid on var ious stages of the electrodeposition process of black chromium and the susc eptibility of coatings to local corrosion have been studied. The current ef ficiency (CE) of black chromium increases on the modified electrode only at the beginning of electrodeposition until the thickness of the deposit reac hes 1 pm. The adsorption layer of formic acid (HCOOH) has an effect on the formation of the near-electrode film, this being typical for the chromium d eposition process and on the reaction Cr(VI)-->Cr(III) as well. It is suppo sed that a higher corrosion resistance of the black chromium coating produc ed on the modified surface is due to the formation of a thin, compact, amor phous layer (about 1 pm) under the influence of HCOOH. (C) 1999 Elsevier Sc ience S.A. All rights reserved.