Qiushi Song

In situ nano-sized ZrC/ZrSi composite powder fabricated by a one-pot electrochemical process in molten salts

ZrC/ZrSi nanocomposite powders are in situ synthesized from ZrSiO4 and carbon through a one-pot electrochemical process. The pathway from the precursor of ZrSiO4/carbon to ZrC/ZrSi composites is investigated by time-dependent electrochemical reduction experiments. The results show that the composite powder involving nano-sized ZrC particles dispersed inside the ZrSi matrix is fabricated through an electrochemical route. The ratio of ceramic phases to metallic phases in the final products can be controlled by adjusting the amount of carbon in the original materials. The electrochemical route in molten salt provides a feasible method for in situ preparation of nano-sized ZrC/ZrSi composite powders at relatively lower temperature.

Electrochemical Synthesis of Core–Shell-Structured NbC–Fe Composite Powder for Enforcement in Low-Carbon Steel

An NbC–Fe composite powder was synthesized from an Nb2O5/Fe/C mixture by electrochemical reduction and subsequent carbonization in molten CaCl2–NaCl. The composite has a core–shell structure, in which NbC acts as the cores distributing in the Fe matrix. A strong bonding between NbC and Fe is benefit from the core–shell structure. The sintering and electrochemical reduction processes were investigated to probe the mechanism for the reactions. The results show that NbC particles about several nanometers were embraced by the Fe shell to form a composite about 100 nm in size. This featured structure can feasibly improve the wettability and sinterability of NbC as well as the uniform distribution of the carbide in the cast steel. By adding the composite into steel in the casting process, the grain size of the casted steel was markedly deceased from 1 mm to 500 μm on average, favoring the hardening of the casted steel.

The Effect of Anodic Potential on Surface Layers of Chalcopyrite during Ammonia–Ammonium Chloride Leaching

The effect of the anodic polarization on the composition and morphology of the surface layer formed on chalcopyrite during ammonia–ammonium chloride leaching was investigated. The anodic polarization on the chalcopyrite electrode was used for oxidation and dissolution of chalcopyrite, and the resulting oxidized layers were characterized by XPS, SEM and optical microscopy. The results show that oxide layers exist on the chalcopyrite surface with or without any anodic polarization in the leaching solution at ambient atmosphere. However, the composition and morphology of the layers are strongly depended on the extent of polarization. The distribution of FeOOH and Fe2O3 within the oxidized layer was inhomogeneous for the sample at the open circuit potential (OCP). The composition and morphology of the oxidized layers which were formed at anodic potentials lower than 0.3 V versus SCE were similar to those of the chalcopyrite at the OCP. At anodic potentials above 0.4 V, the oxidized layers contained many cracks, and they were fragile and exfoliated. Furthermore, the sulfide had been oxidized to sulfur species with higher oxidation states. The oxidation of the chalcopyrite seemed to undergo a cyclically oxidative process that suggested growth and spallation of oxidation layers on chalcopyrite in a layer-by-layer sequence.

Electrochemical synthesis of NbC–Sn composite powder in molten chloride

Abstract NbC–Sn composite powder was successfully prepared from SnO2, Nb2O5 and carbon by electrochemical reduction and carbonization in CaCl2–NaCl molten salt at 900 °C. The reaction pathway was investigated by terminating electrochemical experiments for various durations. The influence of carbon on the final products was considered. NbC particles were obtained by leaching the composite with acid. The results showed that the aggregated NbC–Sn composite powdev contained NbC particles about 50–100 nm and Sn particles about 200 nm. SnO2 was reduced to Sn in the sintering process. Nb2O5 was electrochemically reduced to Nb in molten salt, experiencing some intermediate products of calcium niobates and niobium suboxides. Nb metal obtained was converted to NbC with assistance of carbon. The reduction of Nb oxides may be incomplete and Nb3Sn would be formed if carbon is insufficient in the cathodic pellet. NbC with good dispersity is produced by leaching NbC–Sn with HCl.