Shuchen Sun

Effect of CaO on Fluorine in the Decomposition of REFCO3

Abstract Influence of CaO on thermal decomposition of REFCO 3 was studied. The results showed that CaO did not affect significantly the decomposition ratio of REFCO 3 . The XRD experiment showed that there was a great deal of CaF 2 in the roasting production, the gas chromatographic analysis on the gas of REFCO 3 decomposed, and the 70% content of fluorine in the gas of REFCO 3 added 15% CaO was reduced. CaO could absorb the fluorine from the decomposition of REFCO 3 , and the environmental pollution of the fluorine was greatly alleviated.

Effect of gas bubble on cell voltage oscillations based on equivalent circuit simulation in aluminum electrolysis cell

Abstract A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalent circuit was modeled with Matlab/Simulink simulation software. The time-series signals of cell voltage and anode current were obtained under different bubble conditions, and analyzed by spectral and statistical analysis methods. The simulation results show that higher bubble release frequency has a significant effect on the cell voltage oscillations. When the bubble coverage of one anode block exceeds 80%, the cell voltage may exceed its normal fluctuation amplitude. The simulation also proves that the anode effect detected by computer in actual production is mainly the whole cell anode effect.

Deposition behavior of TiB2 by microwave heating chemical vapor deposition (CVD)

Abstract Microwave heating chemical vapor deposition (CVD) is used to deposit titanium diboride (TiB2) films on graphite substrate using a gas mixture of TiCl4, BCl3, H2 and Ar. The influences of microwave power and the growth rate of TiB2 are studied by using X-ray diffraction, field emission scanning electron microscopy (FESEM) and energy dispersive spectrometer (EDS). In the range of experimental conditions, the TiB2 film’s micro-hardness evaluated by using a computer controlled micro-hardness tester increases with increasing deposition temperature and microwave power. The grain size and the growth rate of TiB2 film are also improved with increasing microwave power at a fixed gas flow ratio of TiCl4 and BCl3, and the bulk TiB2 is obtained at a higher hardness.

The Microstructure of Nanocrystalline TiB2 Films Prepared by Chemical Vapor Deposition

Nanocrystalline titanium diboride (TiB2) ceramics films were prepared on a high purity graphite substrate via chemical vapor deposition (CVD). The substrate was synthesized by a gas mixture of TiCl4, BCl3, and H2 under 1000 °C and 10 Pa. Properties and microstructures of TiB2 films were also examined. The as-deposited TiB2 films had a nano-sized grain structure and the grain size was around 60 nm, which was determined by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Further research found that a gas flow ratio of TiCl4/BCl3 had an influence on the film properties and microstructures. The analyzed results illustrated that the grain size of the TiB2 film obtained with a TiCl4/BCl3 gas flow ratio of 1, was larger than the grain size of the as-prepared TiB2 film prepared with a stoichiometric TiCl4/BCl3 gas flow ratio of 0.5. In addition, the films deposited faster at excessive TiCl4. However, under the condition of different TiCl4/BCl3 gas flow ratios, all of the as-prepared TiB2 films have a preferential orientation growth in the (100) direction.

Glass-forming ability and mechanical properties of a Zr52.8Cu29.1Ni7.3Al9.8Y1 bulk metallic glass prepared by hereditary process

Abstract Zr-based bulk metallic glass possesses the highest potential as a structural material among metallic glasses. However, the production conditions have a great effect on its glass-forming ability (GFA) and mechanical characteristics. In this paper, an attempt was made to find the effect of a hereditary structure on the GFA and mechanical properties of a solid Zr52.8Cu29.1Ni7.3Al9.8Y1 bulk metallic glass in order to evaluate a novel process of using binary alloys as precursors, which have a hereditary relation to the aim metallic glass (MGs). When the quenching temperature is below the threshold overheating temperature, the hereditary process can improve the GFA and compressive strength obviously. At a quenching temperature of 1523 K, the hereditary process can improve the supercooled liquid region ΔTx from 33 K to 55 K and the compressive strength from 1555 MPa to 1652 MPa.

Simulation Method Based on Equivalent Circuit to Investigate the Circuit Characteristics in Aluminum Reduction Cell

In this paper, on the basis of simulation on the electric field of aluminum reduction cell, the simulation signals of cell voltage (CV) and anode currents were obtained through simulating the cell equivalent circuit which was established using Matlab/Simulink software. Several cell conditions, including potline current fluctuation, anode changing, low anode–cathode distance, metal pad contacting with anode surface and local anode effect, were simulated using this model. These obtained simulation data were analyzed comprehensively by time domain, frequency domain, and other statistical methods, such as skewness, and kurtosis. This study further demonstrates that the individual anode current can provide more information on local cell conditions. Different cell conditions produce different characteristics of CV and anode current in time domain or frequency domain, skewness and kurtosis are more sensitive to the change of signals.

Optimization of recovering cerium from the waste polishing powder using response surface methodology

Abstract Recovery of rare earth from the waste rare earth polishing powder is of great importance to improve the process economics. The current recovery methods result in the generation of large quantities of polluted discharge necessitating waste treatment systems. The present work attempts to extract cerium from rare earth slurry waste by thiourea reducing and hydrochloric acid leaching, towards which central composite technique of the response surface methodology is adopted to design the experiments and to optimize the process conditions to maximize the recovery rate. The effects of four major parameters such as temperature, duration of leaching, dosage of thiourea, and the concentration of HCl were assessed, and the optimal process conditions were identified. Analysis of variance (ANOVA) was utilized to identify the suitable model and to eliminate the insignificant model parameters. The optimized process conditions for maximizing the recovery rate are identified to be a leaching temperature of 90°C, duration of 150 min, thiourea dosage of 0.2 g/g, and HCl concentration of 3.5 mol/l. A recovery of 91.23% could be achieved and validated through repeat experimental runs at the optimized process conditions. The optimized process samples are characterized utilizing XRD to validate the recovery.

Chemical titration method for Determination of Concentration of REO in Rare Earth Fluoride Melts

In the present study, chemical titration method for determination of concentration of REO in REF3-LiF-RE2O3 melts was investigated. The melts with the composition of 40mol%REF360mol%LiF (RE=La and Nd) was taken as object for illustrating the measurement of concentration and solubility of REO by the chemical titration method. Then the changing of REO concentration in 40mol%REF3-60mol%LiF melts with electrolytic time in practical electrolysis production was studied. The concentration of REO decreases with the electrolytic time, and rate of the decreasing also declines with the electrolytic time. And the reasonable time interval for REO addition was recommended defining as 1.75 h which is very close to the empirical value 2 h, This would also illustrate the reliability of chemical titration method on determination of concentration of REO in the melts.

Optimization of Main Factors for Decarbonizing Ratio of TiB 2 Powders by Reverse Flotation Using Response Surface Methodology

The optimization of process conditions for decarbonizing ratio of titanium dibordie (TiB2) powders by reverse flotation was investigated using response surface methodology (RSM). The TiB2 powders was produced by using a powder mixture of C, TiO2 and H3BO3 in a DC electric arc furnace. The carbon is in the form of graphite in the product. The way of carbon removal from the powder of TiB2 produce is reverse flotation. Three key parameters TiB2 size, slurry concentration and collector dosage were chosen as variables. The optimum process conditions for decarbonizing ratio were determined by analyzing the response surface three-dimension surface plot and contour plot and by solving the regression model equation with Design Expert software. The central composite design (CCD) of RSM was used to optimize the process conditions, which showed that TiB2 size of 20µm, slurry concentration of 29.65% and collector dosage of 400 g/t were the best conditions. Under the optimal conditions, the decarbonizing ratio is 87.65%, and the relative error differed by only 1.2% from the predicted values of model (88.72%).

One-Step Preparation of TiB 2 -C Composite by DC Arc Furnace

Previous approaches to prepare bulk TiB2-C composite is sintering the TiB2 powder mixed with the C component, so that lead to a series of problems, due to the bad sintering properties. This paper discribes a one-step method of preparing the TiB2-C composite, especially for using as inert cathode in electrolytic aluminum, from the raw materials of TiO2, B2O3 and petroleum coke, by a dc arc furnance. The rapid and high-temperature heating process provided by the arc furnance leads to the carbothermal reaction to prepare TiB2, and the overdosed carbon is included in TiB2 matrix. The XRD(X-Ray Diffraction), SEM(Scanning Electron Microscope), and chemical component analysis are used in the testing part, and the one-step process of preparing bulk TiB2-C composite is studied.