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Nickel leaching from low-grade nickel matte (LGNM) using aqueous ferric chloride solution was studied. The influence of factors such as leaching temperature and concentration of ferric chloride on the nickel leaching ratio was investigated. The results show that increasing leaching temperature and concentration of ferric chloride increases the nickel leaching ratio. The overall nickel leaching process follows the unreacted shrinking core model, and the surface chemical reaction is the rate-controlling step. The activation energy and the reaction order of the nickel leaching process, controlled by the surface chemical reaction, were calculated to be 52.96 kJ·mol−1 and 0.5, respectively. Therefore, the kinetics equation for the nickel leaching was found to be 1 − (1 − α)1/3 = 7.18 × 104C0.5exp[− 52,960/(RT)]t.

Molten salts can provide a high-temperature and oxygen-water-free environment, and the electrochemical polarization is able to reduce the oxide scale on the surface of Ti and Ni particles in molten salts and, thereby, enhance the sintering and accelerating atom diffusion between Ti and Ni. Thus, an electro-assisted powder metallurgical (EPM) approach was developed to prepare porous Ti and NiTi from metal powders in molten salts, where the porous pellet cathode made of the mixture of Ni and Ti powders is electrochemically polarized to facilitate the generation of the porous Ti and NiTi at a temperature lower than 1000 °C. The electrolytic product obtained under a cell voltage of 3 V for 12 hours is nearly pure NiTi with a tiny amount of undesired Ni3Ti and NiTi2 phases. Overall, the EPM route could be a straightforward and general way to prepare porous Ti and Ti-alloys for implants and other applications.

The interfacial reactions of chalcopyrite in ammonia–ammonium chloride solution were investigated. The chalcopyrite surface was examined by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) techniques. It was found that interfacial passivation layers of chalcopyrite were formed from an iron oxide layer on top of a copper sulfide layer overlaying the bulk chalcopyrite, whereas CuFe1–xS2 or copper sulfides were formed via the preferential dissolution of Fe. The copper sulfide layer formed a new passivation layer, whereas the iron oxide layer peeled off spontaneously and partially from the chalcopyrite surface. The state of the copper sulfide layer was discussed after being deduced from the appearance of S2–, S2−2, S2−n, S0 and SO2−4. A mechanism for the oxidation and passivation of chalcopyrite under different pH values and redox potentials was proposed. Accordingly, a model of the interfacial reaction on the chalcopyrite surface was constructed using a three-step reaction pathway, which demonstrated the formation and transformation of passivation layers under the present experimental conditions.

Self-doping of Ti3+ and Ti2+ in oxygen vacancies modified SrTiO3 crystal could significantly improve its photocatalytic properties. In this paper, a series of dark gray oxygen vacancies modified SrTiO3 with self-doping of Ti3+ and Ti2+ were synthesized by electrochemical reduction of SrTiO3 in molten SrCl2–NaCl. The samples were characterized by XRD, SEM, and UV–vis diffuse reflectance spectroscopy, respectively. The valence state of Ti ions on the surface of sample and its oxygen vacancies types were analyzed by XPS spectrum. XRD patterns showed that the diffraction angle (2θ) of samples shifted towards higher 2 theta as the increased cell voltage and the volume of the crystal decreased. XPS spectra indicated that the concentration of Ti3+ ions and oxygen vacancies in SrTiO3 increased as the increased cell voltage. The concentration of Ti3+ and oxygen vacancies in SrTiO3 obtained at cell voltage of 2.9 ​V were 66% and 24%, respectively. The absorption characteristic peak of the self-doping of Ti2+ in SrTiO3 was showed when the cell voltage exceeded 2.7 ​V. The optical absorption of the SrTiO3 extended to the visible light and its bandgap energy narrowed.

Ni-TiC composite powder was synthesized from a NiO/TiO 2 /C mixture by a joint process of chemical reduction in argon atmosphere, electrochemical reduction of TiO 2 and subsequent carbonization of the reduced Ti in molten salt. The reduction was investigated by terminating the electrochemical experiments for various durations, as well as comparing with the results for direct electro-deoxidation of NiTi alloys from a NiO/TiO 2 mixture. The results showed that the product consisted of aggregated Ni-TiC composite particles about 1 μm and dissociative TiC particles about 100 nm. The composite particles owned a multicore-rim structure composed of approximately dispersed TiC particles in the Ni matrix. The formation of intermediates, such as CaTiO 3 , Ni 3 Ti and NiTi, was evaluated from the viewpoint of thermodynamics. Ni acted as a catalyst via generation and subsequent decomposition of Ni-Ti alloys. Carbon powder undertook a reducing agent for NiO in the sintering process as well as a reactant during carbonization of Ni-Ti alloys in molten salt. The introduction of Ni and C into the precursor accelerated the reduction by the chemical driving force derived from reactions between Ni, Ti and carbon.

The effect of several parameters on the recovery of silicon dioxide from calcined boron mud (CBM) such as stirring speed, temperature, sodium silicate concentration, and carbonation time was studied. The recovery of silicon dioxide is 88 % when the stirring speed is 450 r·min−1, temperature is 60 °C, sodium silicate concentration is 1 mol·L−1, and the carbonation time is 6 h. The effect of carbonation time on the recovery of silicon dioxide is divided into three kinetic regimes, and the carbonation process of sodium silicate solution follows a second-order reaction based on the double-film theory model. The apparent rate constant of the three kinetic regimes is 0.064, 3.178, and 1.130 L·h·mol−1, respectively. The amorphous SiO2 products obtained by carbonating the purified solution have 99.6 % purity and are spherical with diameters of about 100 nm.

The niobium carbide powder was prepared via electrochemical reduction of the mixture of Nb 2 O 5 and carbon in molten CaCl 2 –NaCl. The reaction pathway from the sintered precursor to the final product has been investigated. The effect of the working temperature on the reduction of the Nb 2 O 5 /C composite precursor was considered. The role of carbon during the electrochemical reduction of the composite pellet was discussed. The samples were analysed by XRD and SEM. The results indicated that the NbC powder was approximately 200 nm after the reduction. Nb 2 O 5 was gradually reduced to Nb, and NbC was subsequently obtained by the reaction of carbon with Nb metal. In addition, Nb 2 O 5 could spontaneously react with CaO in the melt to form a serious of calcium niobates. The participation of carbon was available for the efficiency of electro-reduction of Nb 2 O 5 .

A carbon film was electrochemically deposited on 304 stainless steel by reduction of carbonate ions in molten LiCl-KCl-K2CO3. A Cr-O-C interlayer was prepared by a joint process of thermal exposure of the steel in air and subsequent electrochemical reactions in molten salt for the enhancement of adhesion between the carbon film and the substrate. The bilayer film was delaminated gradually using electrochemical polarization in an aqueous NaCl solution, and was characterized by XRD, SEM, and XPS. Chromium element aggregates in the oxide scale from the 304 stainless steel substrate during the oxidation process, and transforms to chromium oxycarbide during electro-deoxidation of the oxide scale and diffusion of carbon nucleated from electro-reduction of carbonate ions. The interlayer mainly presents the CrO1.13C0.12 phase, which contains Cr-C and Cr-O bonds confirmed by XPS analysis. The presence of the CrO1.13C0.12 interlayer is an important factor for a continuous and adhesive carbon film on 304 stainless steel. © 2014 The Electrochemical Society. [DOI: 10.1149/2.1101501jes] All rights reserved.

By employing zinc acetate and sodium hydroxide as raw materials, ultrafine ZnO powders with different morphologies were successfully synthesized through hydrothermal method. The influences of the reaction temperature, the OH−/Zn2+ mol ratio and the reaction time on the morphologies of the ZnO powders were discussed. The reaction conditions were obtained, under which the ZnO of flower-like particles, micro-rods and flake particles was synthesized, respectively. The crystal structures and morphologies of those ZnO particles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ZnO with flower-like structures was composed of lots of micro-rods with hexagon morphology. The XRD patterns indicated that the ZnO powders were hexagonal wurtzite structures with high purity. Finally, the growth mechanism of the ZnO particles was discussed.