The results of a study on the anode dissolution of two heat-resistant chrome-nickel alloys containing tungsten (12 wt %) as well as tungsten and rhenium (8 wt % of W and 6 wt % of Re) are described. The experiments took place in 2 M NaCl at a current density of up to 40 µ /cm 2 using a rotating disk electrode. It is shown that the alloy with the greater tungsten content dissolves at a lower rate (due to the formation and accumulation of insoluble oxides layers on the surface) and at a current density lower than the maximum anode current density for the basic component (nickel, and, probably, cobalt) of the anodic dissolution. Transpassive dissolution takes place under conditions of thermokinetic instability of the electrode process. In this case, a decreasing dependence of the current efficiency on the current density is observed, and the dissolution rate is independent of the tungsten concentration in the alloy. In the region of the maximum anode currents and the transition from one area of dissolution to another, abnormal anode dissolution takes place due to chemical oxidation of intermediate products by oxidizers-anode-dissolution products or solution components. The results of varying the chemical composition on surfaces depending on the treatment mode are presented.
The electrode processes occurring during electrodeposition of nanocrystalline Fe−W alloy coatings from a citrate bath containing iron(II) sulfate and a tungstate (pH 6.9; 80°C, graphite anode) are studied by cyclic voltammetry. The current efficiency of alloy electrodeposition is up to 30%, if the applied current density is confined to the range of 2−5 A/dm 2 . The limitation on range of applied current densities is twofold: the lower limit is dictated by the diffusion-limited current density due to the reduction of the oxidized form of iron−citrate complex that forms at the bath preparation stage as a result of oxidation of Fe(II) species in a citrate solution; while the upper limit is imposed by the occurrence of side reactions such as the hydrogen evolution reaction and/or reduction of organic components of the bath. The use of an iron anode seems to be promising in this deposition process (the current efficiency of anodic dissolution of Fe in this bath is 93 ± 2%). The deposited coatings contain ~25 at % tungsten and their microhardness (which can be up to 900 kgF/mm 2 ) depends on the volume current density. The studied system holds promise for application in mask-free localized electrodeposition.
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