Electrodeposition of Nanocrystalline Fe—W Coatings from a Citrate Bath

Abstract

<p>The electrode processes occurring during electrodeposition of nanocrystalline Fe−W alloy coatings<br> from a citrate bath containing iron(II) sulfate and a tungstate (pH 6.9; 80°C, graphite anode) are studied<br> by cyclic voltammetry. The current efficiency of alloy electrodeposition is up to 30%, if the applied current<br> density is confined to the range of 2−5 A/dm2. The limitation on range of applied current densities is twofold:<br> the lower limit is dictated by the diffusion-limited current density due to the reduction of the oxidized form<br> of iron−citrate complex that forms at the bath preparation stage as a result of oxidation of Fe(II) species in a<br> citrate solution; while the upper limit is imposed by the occurrence of side reactions such as the hydrogen evolution<br> reaction and/or reduction of organic components of the bath. The use of an iron anode seems to be<br> promising in this deposition process (the current efficiency of anodic dissolution of Fe in this bath is 93 ±<br> 2%). The deposited coatings contain ~25 at % tungsten and their microhardness (which can be up to<br> 900 kgF/mm2) depends on the volume current density. The studied system holds promise for application in<br> mask-free localized electrodeposition.</p>