Xiaoxiao Huang

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.

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.

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.