氯化钙熔盐中电解-刻蚀制备碳化钛衍生碳研究

在氯化钙熔盐中首先通过电还原高钛渣/碳制备碳化钛,对碳化钛进行电化学刻蚀得到碳化钛衍生碳(TiC-CDC)。研究了熔盐温度对碳化钛产物组成和结构的影响规律,获得制备形貌结构良好的碳化钛前驱体的条件,以便下一步电化学刻蚀。研究结果表明:熔盐温度是重要的影响因素,在较低的温度下反应速率较慢,温度过高则会造成产物烧蚀现象和能源浪费,在950℃下得到的产物形貌结构较好。对950℃下制备的碳化钛电化学刻蚀18 h,得到无定型碳和有序石墨带结构共存的碳化钛衍生碳,其孔结构主要为微孔,比表面积为327.88 m^(2)/g,证明通过熔盐电还原-刻蚀能够制备出不同结构的碳化物衍生碳。与氯化法相比,该方法更环保,但是刻蚀时间较长,刻蚀效率还有待提高。

Electrodeposition of Ir on platinum in NaCl-KCl molten salt

The reduction mechanism of Ir in the NaCl-KCl-IrCl3 molten salt was investigated by cyclic voltammetry and chronopotentiometry, and Ir film was deposited effectively on platinum in potentiostatic mode. The morphology and constitution of Ir film were examined by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. It is found that the reduction mechanism of Ir（III） is a three-electron step and electro reaction is a reversible diffusion controlled process; the diffusion coefficients of Ir（III） at 1083, 1113, 1143 and 1183 K are 1.56×10-4, 2.23×10-4, 2.77×10-4 and 4.40×10-4 cm2/s, respectively, while the activation energy of the electrode reaction is 102.95 kJ/mol. The compacted Ir film reveals that the applied potential greatly affects the deposition of Ir, the thickness of Ir film deposited at the potential of reduction peak is the highest, the temperature of the molten salt also exerts an influence on deposition, the film formed at a lower temperature is thinner, but more micropores would occur on film when the temperature went too high.

Electrochemical mechanism of electrolysis codeposition of Mg-Sr alloy in molten salt

The electrochemical process of Mg-Sr codeposition was studied in MgCl2-SrCl2-KCl melts containing different MgCl2 concentrations at 700 ℃ by cyclic voltammetry, chronopotentiometry and chronoamperometry. The results show that the actual precipitation potential of Sr reduces by nearly 0.5 V because of the depolarization effects of Sr activity reduced by forming Mg-Sr alloy. The codeposition potential condition of Mg and Sr to form Mg-Sr alloy is as follows： When electrode potential is more negative than -1.5 V, the magnesium will precipitate; when electrode potential is more negative than -2.0 V, the magnesium and strontium will both deposit. The control step of codeposition process of Mg and Sr is not diffusion control step. The codeposition current condition of Mg and Sr to form Mg-Sr alloy by chronoptentiometry is as follows： cathode current densities are higher than 0.71, 1.57 and 2.83 A/cm^2 in MgCl2-SrCl2-KCl melts with MgCl2 concentrations of 2%, 5% and 10% （mass fraction）, respectively. Key words：

Coating titanium on carbon steel by in-situ electrochemical reduction of solid TiO_2 layer

Ti coating on A3 steel was successfully prepared by direct electrochemical reduction of high-velocity oxy-fuel （HVOF） thermally sprayed and room-temperature dip-coating titanium dioxide coating on A3 steel in molten CaCl2 at 850 ℃. The interfacial microstructure and mutual diffusion between coating and steel substrate were investigated using scanning electron microscopy （SEM） and energy dispersive X-ray （EDX） spectroscopy. The results show that the precursory TiO2 coating prepared by HVOF has closer contact and better adhesion with the A3 steel substrate. After electrolysis, all of the electro-generated Ti coatings show intact contact with the substrates, regardless of the original contact situation between TiO2 layer and the steel substrate in the precursors. The inter-diffusion between the iron substrate and the reduced titanium takes place at the interface. The results demonstrate the possibility of the surface electrochemical metallurgy （SECM） is a promising surface engineering and additive manufacturing method.

Electrolytic production of Cu-Ni alloys in CaCl_2-Cu_2S-NiS molten salt

An alternative metal/alloy production method,known as direct electrochemical reduction(DER),was introduced for the fabrication of CuNi alloys from mixed sulfides(Cu2S,NiS)under both galvanostatic and potentiostatic conditions.The influences of the process parameters(e.g.,cell voltage and current)on the compositions of the reduced compounds were investigated to yield industrially desirable alloys,namely,CuNi10,CuNi20,and CuNi30.The electrochemical behaviors of Cu2S and NiS in CaCl2 melt were examined at a temperature of 1200°C via cyclic voltammetry(CV).Based on the CV results,the cathodic reduction of Cu2S occurred in one step and cathodic reductions of NiS occurred in two steps,i.e.,Cu2S?Cu for copper reduction and NiS?Ni3S2?Ni for nickel reduction.Galvanostatic studies revealed that it was possible to fabricate high-purity CuNi10 alloys containing a maximum sulfur content of 320×10-6 via electrolysis at 10 A for 15 min.Scanning electron microscopy along with energy-dispersive X-ray spectrometry and optical emission spectroscopy(OES)examinations showed that it was possible to fabricate CuNi alloys of preferred compositions and with low levels of impurities,i.e.,less than 60×10-6 sulfur,via DER at 2.5 V for 15 min.

Effect of fluoride addition on electrochemical behaviors of V(Ⅲ) in molten LiCl-KCl

X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy were used to analyze the complexes in LiCl−KCl eutectic salt containing VCl_(3) and KF.The additional fluoride ions would replace chloride ions and combine with V(Ⅲ)to form VF_(6)^(3-).The electrochemical behavior of V(Ⅲ)was evaluated under condition of the molar concentration ratio of F−to Vn+(α)equal to 0:1,1:1,2:1,5:1,20:1 and 50:1,respectively.The results showed that a new reduction step appeared:VF_(6)^(3-)→V^(2+),and the reduction mechanism of vanadium ions became more complicated.The metallic vanadium was deposited on the tungsten electrode at−2.90 V in the LiCl−KCl melts for 6 h,and the products were characterized by SEM−EDS.It was indicated that the particle size of the product decreased with adding fluoride ions for the forming of the coordination compound VF_(6)^(3-).

Electrochemical synthesis of Nb C-Sn composite powder in molten chloride

NbC-Sn composite powder was successfully prepared from SnO2,Nb2O5and carbon by electrochemical reduction andcarbonization in CaCl2-NaCl molten salt at900°C.The reaction pathway was investigated by terminating electrochemicalexperiments for various durations.The influence of carbon on the final products was considered.NbC particles were obtained byleaching the composite with acid.The results showed that the aggregated NbC-Sn composite powdev contained NbC particles about50-100nm and Sn particles about200nm.SnO2was reduced to Sn in the sintering process.Nb2O5was electrochemically reduced toNb in molten salt,experiencing some intermediate products of calcium niobates and niobium suboxides.Nb metal obtained wasconverted to NbC with assistance of carbon.The reduction of Nb oxides may be incomplete and Nb3Sn would be formed if carbon isinsufficient in the cathodic pellet.NbC with good dispersity is produced by leaching NbC-Sn with HCl.