SINUSOIDAL POTENTIAL SCAN-BASED NICKEL EL ECTRODEPOSITION ON ANODIZEDALUMINUM V - INFLUENCES OF CONCENTRATION OF NICKEL SULFATE

Nickel electrodeposition was carried out in a series of electrolytic b aths containing various concentrations of NiSO4 in the range 0 similar to 8.7 w/v% under the conditions of constant pH(4.0) and constant H3B O4 concentration (4w/v%). The concentration of NiSO4 was found to give very conspicuous influences on the Hi deposition and H-2 evolution du ring one cycle of sinusoidal potential scan as well as on the lightnes s index L: with an increase in NiSO4 concentration, the Ni deposition and L went through a rather sharp maximum and a minimum, respectivel y, while the H-2 evolution showed lore complex behavior, The concentra tions for the extremes in gi deposition and L, 2.4 w/v% and about 2 w /v%, respectively, were far smaller than that (5 w/v%) Of Watts bath c onventionally used for Ni electrodeposition. It is speculated that the se anomalies are related with the corrosion of the barrier layer of an odized aluminum by the attack of the OH- ions produced during the Ha e volution (H2O + e(-) --> 1/2 H-2 + OH-): the aluminate ions thus forme d in the micropores of anodized aluminum increasingly tend to coagulat e together as the NiSO4 concentration (or the ionic strength of soluti on) increases, resulting in significant blockage of mass trnsport at t he concentrations exceeding 2.4 w/v%. The impedance of anodized alumin um decreased significantly with the electrodeposition in the concentra tion range lover than 1 w/v% Or higher than 5 w/v%, reflecting the par ticularly intensive corrosion of the barrier layer under these conditi ons. It Has also shown that the amounts of deposited Hi under the firs t current peak during the sinusoidal scan Here close to those of Ni2ions accommodated by the micropores of anodized alumina for the NiSO4 concentrations up to 2.4 w/v%, though discrepancy from this rule was o bvious for the higher concetrations.