Junli Xu

Polarization corrosion of the iron-nickel alloy in Na 3 AlF 6 -based system molten salts

Fe-Ni (with different wt.%) alloys were prepared by powder metallurgy process and used as anode for aluminum electrolysis. Electrolysis polarization of these anodes was conducted for 12 hours at 850 oC in a Na3AlF6-based molten salt. The anodic current density was 0.75 A/cm2. At the initial stage, the corrosion rate decreased with increasing ratio of Fe to Ni in the alloy, when the ratio of Fe to Ni was 1.42, the lowest value of the corrosion rate with 21mm/a was obtained. Then corrosion rate increased with increasing ratio of Fe to Ni. The analysis of Electron Probe Micro-analyzer and X-Ray Diffraction showed that the film formed on the anodic surface consisted of iron oxide as outer layer, and nickel oxide and nickel ferrite spinel as inner layer. The metal anode presented good performance in terms of anti-oxidation and corrosion resistance, and the purity of the produced aluminum was 98%.

Preparation of Solar Grade Silicon Precursor by Silicon Dioxide Electrolysis in Molten Salts

Al-Si alloy, a precursor of solar grade silicon, was prepared by direct electrolysis in cryolite molten salt at 950 °C using high purity silica as material, liquid aluminum as the cathode and high purity graphite as the anode. The electrochemical behavior of Si(IV) ion was investigated using cyclic voltammetry method. The electrolysis products were characterized by XRD, SEM/EDS and ICP. The results indicate that the reduction process of Si(IV) on tungsten electrode is a two-step process and there is about 0.6 V gap between the two steps. The contents of boron and phosphorus in the aluminum-silicon alloy are 3 ppmw and 8 ppmw, which will make the directional solidification purification effectively and reduce the cost of preparation solar grade silicon from metallurgical grade silicon.

Preparation of Al‐Ti Master Alloys by Aluminothermic Reduction of TiO2 in Cryolite Melts at 960°C

Al-Ti master alloys were prepared by aluminothermic reduction between the dissolved titanium dioxide and aluminum in cryolite melts at 960°C. The kinetic analysis by differential scanning calorimetry indicated that the apparent activation energy of the reaction of reducing titanium dioxide by aluminium is 22.3 kJ/mol, and the reaction order is 0.5. The products were analyzed by means of X-ray diffraction, X-ray fluorescence, scanning electron microscopy and energy dispersive spectrometer. Results from X-ray diffraction showed that the phase compositions of produced alloys are Al and Al3Ti. In addition, Al-Ti master alloys containing 2–6 mass% Ti were formed at different reduction time of 2–5h in aluminothermic reduction experiment.

Oxidation of Fe-Ni Alloys in Air at 700°C, 800°C and 950°C

Abstract The oxidation behavior of Fe-Ni alloys containing 10, 20, 43, 50, 57 and 80 (mass%) nickel was studied over the range 700°C–950°C in laboratory air atmosphere using thermogravimetric, XRD and SEM/EDAX techniques. The results showed that some oxidation kinetic curves of Fe-Ni alloys follow the parabolic law, some follow a cubic law, while the oxidation kinetic curves of 90Fe-10Ni is linear. XRD and SEM/EDAX results showed that the oxide scale consists of an outer layer of Fe2O3 and an inner layer of Ni-Fe-O and NiO compound. Ni content in the alloy has an important role for the formation of NiFe2O4 oxide. 20Fe-80Ni and 43Fe-57Ni can form NiFe2O4 at 700°C–950°C, while 50Fe-50Ni can form NiFe2O4 only oxidized at higher temperature of 950°C.