Naixiang Feng

Preparation of primary Al-Si alloy from bauxite tailings by carbothermal reduction process

Abstract Effects of various reaction parameters such as atmospheric pressure, treating temperature, sintering time and bituminite content on the preparation of primary Al-Si alloy by carbothermal reduction of bauxite tailings were investigated by XRD, XRF, infrared absorption carbon-sulfur analysis unit and SEM coupled with EDS. Meanwhile, the mechanism of carbothermal reduction of Al 2 O 3 and SiO 2 was discussed. It is found that pressure and temperature are major factors that influence the carbothermal reduction of bauxite tailings. The appropriate conditions for preparation of primary Al-Si alloy are as follows: atmospheric pressure of 0.1 MPa, heating temperature of 1 900 °C, bituminite content of 95% (mass fraction) of theoretic bituminite content and sintering time of 1 h. Among four mechanisms of carbothermal reduction of Al 2 O 3 and SiO 2 , the theory of the formation and decomposition of carbides might be the best one to interpret the reaction process.

Mechanism of extracting magenesium from mixture of calcined magnesite and calcined dolomite by vacuum aluminothermic reduction

Abstract The process of aluminothermic reduction of a mixture of calcined dolomite and calcined magnesite had been developed. The mechanism of the process was studied by SEM and EDS. The reduction process was divided into three stages: 0≤η t /η f ≤0.43±0.06, 0.43±0.06≤η t /η f ≤0.9±0.02 and 0.9±0.02≤η t /η f t and η f are the reduction ratio at time t and the final reduction ratio obtained in the experiment at temperature T , respectively. The first stage included the direct reaction between calcined dolomite or calcined magnesite and Al with 12CaO·7Al 2 O 3 and MgO·Al 2 O 3 as products. The reaction rate depended on the chemical reaction. The CA phase was mainly produced in the second stage and the overall reaction rate was determined by both the diffusion of Ca 2+ with molten Al and the chemical reaction. The CA 2 phase was mainly produced in the third stage and the reaction process was controlled by the diffusion of Ca 2+ .

Formation of Ti or TiC nanopowder from TiO2 and carbon powders by electrolysis in molten NaCl–KCl

A new route to produce pure Ti powder or TiC nanopowder with diameters of ∼50 nm by electrolysis in molten KCl–NaCl using TiO2 and carbon powder was reported in this paper. This electrochemical experiment was carried out with an innovative equipment unitizing the chlorination and electrolyzation. A fine titanium powder was obtained after electrolysis at 4.0 V for 5 h at 850 °C. TiC nanopowder could be prepared in the anode chamber with the cell voltage up to 4.5 V. Furthermore, the product was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that pure Ti or TiC nanopowder can be prepared after electrolysis. The TiC nanopowder exhibited a polymorphic structure, and it had good thermal stability and oxidation resistance below 345 °C in air investigated by TGA and DSC. Cyclic voltammograms were carried out and the electrode reaction mechanisms during the electrolysis process were discussed in the paper.

Preparation of casting alloy ZL101 with coarse aluminum-silicon alloy

The coarse Al-Si alloy produced by carbothermal reduction of aluminous ore contains 55% Al, 25% Si and some impurities. The main impurities are slag and iron. The process of manufacturing casting Al-Si alloy ZL101 with the coarse Al-Si alloy was studied. The phase constitution and microstructure of the coarse Al-Si alloy, slag and ZL101 were examined by X-ray diffractometry and scanning electron microscopy. The results show that the content of silicon and iron in the casting alloy reduces with the increase of the dosage of purificant and manganese, but increases with the rise of filtering temperature. It is found that casting Al-Si alloy conforming to industrial standard can be produced after refining by using purificant, and removing iron by using manganese and added magnesium.

Production of carbon anodes by high-temperature mould pressing

Abstract Laboratory-scale carbon anodes were produced by a new method of high temperature mould pressing, and their physico-chemical properties were studied. The influence of mould pressing conditions and coal pitch addition on the bulk density, crushing strength, and oxidation resistance was analyzed. The microstructure of carbon anodes was investigated by scanning electron microscopy (SEM), and the mechanism of producing carbon anodes by high-temperature mould pressing was analyzed. The results show that when the anodes are produced by high-temperature mould pressing, coal pitch can expand into the coke particles and fill the pores inside the particles, which is beneficial for improving the quality of prebaked anodes. The bulk density of carbon anodes is 1.64–1.66 g/cm 3 , which is 0.08–0.12 g/cm 3 higher than that of industrial anodes, and the oxidation resistance of carbon anodes is also significantly improved.

Mg(OH)2/Graphene Nanocomposites Prepared by Cathodic Electrodeposition for the Adsorption of Congo Red

A facile cathodic electrodeposition process was developed to prepare Mg(OH)2/Graphene nanocomposites (MGN), which was used to remove Congo Red (CR), an anionic dye from aqueous solution. The morphology and phase structure were analyzed by transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Raman and X-ray photoelectron spectroscopy (XPS). The effects of experimental parameters, such as graphene content, adsorption time, initial concentrations of CR and pH values, on the adsorption capacity of CR were studied. The obtained MGN shows the good performance in CR, with an adsorption capacity of 1986.43mgg−1. The equilibrium adsorption and kinetics data fit with Langmuir isotherm and the pseudo-second-order model, respectively. Thermodynamic data suggest that CR adsorption onto MGN is spontaneous (ΔG0: –9.62kJmol−1 at 313K, endothermic (ΔH0: 36.261kJmol−1) and the degree of disorder increased (ΔS0: 146.848JmoL−1K−1) at the solid-solution interface. Moreover, the adsorption activation energy (Ea: 38.929kJmol−1) of CR evaluated from the Arrhenius equation illustrates that it is a physical process. This adsorbent exhibits efficient adsorption properties and high recycling efficiency, making it a promising adsorbent for removing anionic dyes.

Preparation of Low-Carbon Ti2O3 by Carbonthermal Reduction of the Mixture of Titanium Dioxide and Activated Carbon Under Vacuum Condition

Low-carbon Ti2O3 was prepared by carbonthermal reduction of the mixture of titanium dioxide and activated carbon at vacuum condition. The kinetics and phase evolution of Ti2O3 formation process were investigated through X-ray diffraction and gravimetric analysis. The only intermediate phase detected is Ti3O5. The reduction time was reduced sharply to 4 h when temperature was raised to 1300 °C. The best molar ratio of activated carbon and TiO2 is 0.6–1. At this condition, the content of Ti2O3 in slag is up to 95.63% and the content of the carbon element is below 0.004%, which meets the requirements for the further preparation of metal Ti by FFC Cambridge process. At the same time, the microstructure of Ti2O3 generated presented porosity, which would promote the electro-deoxidation process extremely.

Metal flow performance in aluminium electrolytic cells with different side-wall types

ABSTRACT Three-dimensional aluminium electrolytic cells with inclined surface cathodes were simulated in ANSYS and CFX to predict the influence of different side-wall types on the horizontal current and metal flow. The simulated results showed that the ledge thickness decreased with the thermal conductivity of the side wall. The graphitised side wall with the highest thermal conductivity displayed the largest ledge toe extensions of 24.6 cm at the centre of the long side and 28.0 cm at its corner. The long ledge toe extension introduced large inverted horizontal current and increased the maximum metal velocity. Above the largest ledge toe extension, the metal deviation from the equilibrium was 1.6 cm at one quarter of the cell length and 1.8 cm at the cell corner, equal to the metal wave crest in the cell (1.8 cm). With decreasing ledge toe extension, the maximum metal velocity and metal deviation above the ledge toe extension from equilibrium decreased accordingly.

The influence of various LiF concentrations on the cathodic electrochemical behavior at the tungsten electrode in Na3AlF6–Al2O3 molten salt

The electrochemical deposition process of Al metal at the tungsten electrode in the melts of Na3AlF6–Al2O3 with various LiF concentrations was investigated at 1253 K by various electrochemical techniques. With the analysis of the potentiodynamic cathodic polarization curves, it can be demonstrated that LiF has an effect of increasing the conductivity of the molten salt. From the analysis of the potentiostatic electrolysis and chronopotentiometry curves, it can be deduced that the deposition potential of Na metal is more positive with the increase of LiF concentration. Spontaneous dissolution of the cathodic products occurs for the polarized electrode which is shown by the measurements of open-circuit chronopotentiometry. These show that the scanning time taken for the potential to reach zero is prolonged and the thickness of the reduced species to be dissolved increases with the increase of LiF concentration. Furthermore, it can be deduced that the Al activity also increases with the increase of LiF concentration. On the other hand, the deposited Al is more easily dissolved into the electrolyte and the physical dissolution is more intense with the increase of LiF concentration.

Electrochemical Study of Potassium Fluoride in a Cryolite-Aluminum Oxide Molten Salt

Selective and efficient electrochemical methods to characterize aluminum are necessary. Current methods are based on potentiodynamic polarization, recurrent potential double pulses, chronopotentiometry, open-circuit chronopotentiometry, and potentiostatic electrolysis, but have not been used to characterize the deposition of aluminum in Na3AlF6-Al2O3-KF molten salts. The control processes of the formation of aluminum-tungsten intermetallic compounds, and the deposition of aluminum have been investigated by using steady-state potentiodynamic cathodic polarization curves. The dissolution loss rate of aluminum was determined with an increase in KF concentration by the analysis of recurrent potential double pulses. Using chronopotentiometry, it was confirmed that the deposition potential of aluminum shifted more negative as the KF concentration increased, and a higher KF concentrations induced a higher cathodic overpotential. From open-circuit potential measurements and scanning electron micrographs, it was concluded that aluminum(III) ions react with tungsten substrates to form an aluminum-tungsten compound, and the reaction mechanism of aluminum was determined. These electrochemical methods applied with aluminum electrolysis were accurate, efficient, and reliable.