Electrochemical Preparation of Fe0.5CoNiCuSnx Medium Entropy Alloys and Their Corrosion Properties

The exploration of efficient preparation methods and corrosion-resistant medium entropy alloys (MEAs) has attracted significant attentions in recent years. In this paper, powdery Fe0.5CoNiCuSnx (x=0, 0.05, 0.08, and 0.1) MEAs were prepared by the one-step electrochemical reduction of metal oxides in molten Na2CO3-K2CO3 using a Ni11Fe10Cu oxygen-evolution inert anode. The effects of Sn on the structures, morphologies, and corrosion behaviors of the prepared MEAs were systematically investigated. The electrolytic MEAs exhibited a single face-centered cubic phase at x≤0.05, and the CuSn-rich phase would be segregated in the alloys at 0.08≤x≤0.1. Moreover, increasing Sn reduced the particles size of MEAs, and Sn improved the corrosion resistance of MEAs in 0.5 M H2SO4, 1 M KOH, and 3.5% NaCl solutions. The electrolytic MEA(Sn0.05) exhibited the best corrosion resistance, which had the corrosion current densities of 3.7×10-5 A/cm2 (0.5 M H2SO4), 1.2×10-5 A/cm2 (1 M KOH), and 1.6×10-5 A/cm2 (3.5 wt% NaCl) at room temperature. Overall, this paper not only provides a green approach to preparing Sn-containing MEAs, but also offers an efficient way to control structures and morphologies, thereby improving the corrosion resistance.

Proving the Availability of Ni-Fe Anode for Electro-Reduction of Solid V2O3 in Molten Fluoride Salts

The availability of casting Ni-Fe alloy as inert anode for direct electro-reduction of V2O3 in molten Na3AlF6-K3AlF6-AlF3 was investigated. The electrochemical oxidation behavior of anode as well as microstructural evolutions of formed oxide scale were systematically studied. The electrochemical characterization and reaction mechanism of cathode oxide were also investigated to evaluate the influence of alloy anode on cathodic reduction process. The in situ formed three-layered oxide scale is compact and coherent, which is composed of an outermost Fe2O3+FeAl2O4 skin layer, a Fe2O3 middle layer and a FeAl2O4 inner layer. The skin layer has a continuous, smooth structure and shows electrochemical activity. The Fe2O3 layer with compact structure prevents inward diffusion of electrolyte and outward migration of metal cations. The innermost FeAl2O4 layer shows a loose structure and functions as buffer layer to improve the peeling resistance of oxide scale. With the continuous extension of polarization time, the inner FeAl2O4 layer is slowly oxidized and becomes thinner, simultaneously, the dense Fe2O3 layer becomes thicker. Ultimately, metal vanadium product with fine rod-like particles can be obtained and the oxygen content in the metal vanadium is below 0.3 mass% within electrolyzing time of 2 h. The corresponding current efficiency is around 63%.

Formation of Solid Solution and Metallic Nickel Phases During Suspension Plasma Spraying of Co Oxide and Ni Oxide

The focus of this study is the formation of a solid solution and metallic nickel in the cobalt-nickel mixed oxide coatings during suspension plasma spray (SPS) deposition. The (Co,Ni)O solid solution is a potential material for inert anode applications in aluminum production. SPS coatings and in-flight collected particles are studied to gain further insight into the melting and mixing phenomena of the NiO and CoO powders as well as phase formation in the deposited coatings. Moreover, the role of suspension feedstock particle sizes on the microstructure of coatings is discussed. SEM, EDS and X-ray diffraction studies helped better understanding the formation of different crystalline phases within the as-sprayed coatings. It was found that the formation of metallic nickel is possible in the coatings. The results support the importance of substrate temperature on the formation of metallic Ni, so that keeping the substrate at low temperature results in an increase of the Ni content in the coatings. In this study, possible causes for the formation of metallic Ni during spraying are discussed.

Oxidation and electrical properties of chromium–iron alloys in a corrosive molten electrolyte environment

Chromium–iron (CrFe) binary alloys have recently been proposed to serve as the “inert” anode for molten oxide electrolysis (MOE). Herein, the effects of anodic polarization on physical and functional properties of CrFe anodes in the corrosive environment of MOE are studied via empirical observations and theoretical calculations. The findings indicate that the alloys form an inner chromia–alumina solid-solution covered by an MgCr2O4 spinel layer. A survey into the electrical properties of the detected oxides suggests that the layered oxide scale function as an efficient conductor of electricity at elevated temperature. The formation mechanism of the oxides is also investigated.