On the Mechanisms of Chromium Electrodeposition

Abstract

Steady‐state polarization measurements were made on Pt bead cathodes in N2‐normalstirred solutions of Na2CrO4 , Na2Cr2O7 , and chromic acid. Three main regions can be distinguished: oxide reduction, H2 evolution, and Cr(VI) reduction to Cr(III) or to black Cr or both. To obtain the black Cr deposit, a polychromate must be present and a low pH must be maintained. Steady‐state polarization measurements were made on Pt bead cathodes in N2‐normalstirred solutions of Na2CrO4 and Na2Cr2O7 to which Na2SO4 had been added and of chromic acid to which Na2SO4 or H2SO4 had been added. These data indicate that the active catalyst is HSO4− ion which catalyzes only the reduction of the chromous products of the reduced cathode film. Bisulfate ion also acts as a blocking agent which inhibits electron transfer to chromium ions. A detailed mechanism for the reduction of Cr(VI) solutions to Cr metal is proposed. To prevent the formation of stable normalCrfalse(H2O)6+3 complexes, a cathodic film of chromic dichromate is formed with one end blocked by complexing with HSO4− ions. Decomposition of the film by reaction with H3O+ ions produces chromous hydroxide, the reduction of which to metallic Cr is catalyzed by HSO4− ions. By the concept of a distribution function of trichromatebisulfate complexes, the narrow range of HSO4− ion concentrations which must be controlled to maintain successful Cr deposition is made understandable.

Soft magnetic properties of Ni–Cr and Co–Cr alloy thin films electrodeposited from aqueous solutions containing trivalent chromium ions and glycine

“…However, it is quite difficult to obtain Cr alloys at room temperature due to the high T m and the mechanical hardness. On the contrary, in a conventional electroplating process, metallic Cr films can be synthesized by electrodeposition from an aqueous solution containing hexavalent chromium ions (Cr 6+ ) under the condition of room temperature and atmospheric pressure [1][2][3]. However Cr 6+ ions are known to toxic and carcinogenic substances, hence, in recent years, the solution containing trivalent chromium ions (Cr…”

Study of the Effect of Temperature on the Hardness, Grain Size, and Yield in Electrodeposition of Chromium on 1045 Steel

“…This behavior is explained by the progressive decrease in grain size of the chromium with increase in temperature, which produces greater homogeneity and compactness of the deposited grains. , where the chromate ions form a polymer by sharing corner oxygen atoms 4 . Zone (B) is where the release of hydrogen begins and stop when the formation of the cathodic film is complete.…”

“…Zone (B) is where the release of hydrogen begins and stop when the formation of the cathodic film is complete. The third zone (C) is attributable to the reduction of the Cr 6+ to Cr 0 , as well to the release of hydrogen; where Cr 6+ and other species of chromium with less oxidation states are part of trichromate ion 4,[8][9][10][11] . The trichromate ion is necessary by protection the Cr +3 ions, preventing the formation of a stable aquo complex.…”

Characterization of cathodic film formed during reduction of chromic acid: role of sulphuric acid concentration

“…7 Indeed, from the literature 5 -7 it is known that, when Cr 3C ions are not protected, very stable non-reducible Cr(III) aquo complexes will be formed. In addition, the amount of sulphate plays a role in the width of region II.…”

“…V, IV, III, II, I), which considerably increases the number of reduction pathways. 7 Most uncertainties, however, Ł Correspondence to: Annick Hubin, VUB-TW-META, Pleinlaan 2, 1050 Brussels, Belgium. E-mail: anhubin@vub.ac.be Contract/grant sponsor: EC; Contract/grant number: BE97-4761.…”