Jie Dang

A Review of the Preparation Methods of WC Powders

Tungsten carbides, which can be widely used for cutting and drilling tools, chemical catalyst and aerospace coatings, have attracted widespread attentions. However, the cost of conventional processes to produce tungsten carbides can be very high, therefore, there is a permanent effort to synthesize WC powder at low temperature to minimize the production cost. Some novel processing techniques have been developed to partially solve this problem. This paper reviewed the current research trends in preparation of WC containing spark plasma sintering, combustion synthesis, sol-gel and in situ carburization method, chemical vapor reaction synthesis and the spray conversion process, etc. The present review also discussed the potential applications, the feasibility, the advantages and disadvantages of industrialization.

Effect of Cooling Rate on the Acidolysis of Titania Slag

Electro-titania slag is generally used as the raw material for titanium dioxide production by sulfate process. The phase composition of titanium as well as their disseminated grain size have significant effect on the acidolysis of titanium. Anosovite is considered as the most favorable Ti-bearing phase due to its high acidolysis efficiency, while silicates and rutile are not soluble in concentrated sulfuric acid. Different cooling rates will play a significant effect on the phase structure and particle size, which directly affects the acidolysis ratio of titania slag. In this paper, the influence on acidolysis ratio of titania slag at different cooling rates was studied. The results revealed that slower cooling rate resulted in the formation of larger particle size and a comparatively higher acidolysis ratio was obtained. On the contrast, rapid cooling was disadvantageous to the leaching of titanium as the smaller particle size anosovite was wrapped by glass phases.

Preparation of Ferronickel from Nickel Laterite Ore via Semi-molten Reduction Followed by Magnetic Separation

The rotary kiln-electric furnace (RKEF) process is the main method for producing ferronickel from nickel laterite ore. However, this process is energy intensive as it involves several high temperature steps. Therefore, a novel process is proposed to directly produce ferronickel from nickel laterite ore by semi-molten reduction, which is expected to be realized in a rotary hearth furnace (RHF). The RHF process is able to shorten the flow sheet, decrease the reaction temperature as well as reduce energy consumption. In this study, the influence of basicity on reduction of nickel laterite ore was investigated. The results showed that it is possible to produce the ferronickel nugget directly at 1400 °C when the quaternary basicity [(mCaO + mMgO)/(mSiO2 + mAl2O3)] was fixed at 0.60. Under this experimental condition, the grade and the recovery ratio of nickel reached 11.53% and 98.59%, and the grade and recovery ratio of Fe were 84.16% and 68.72%, respectively.

Preparation of Mo 2 C by reduction and carbonization of MoO 2 with CH 3 OH

Molybdenum hemicarbide (Mo2C) can be widely used in the fields of steel, metal ceramics, and catalyst of hydrogen-involved reactions. This work reported a new and simple method for preparing molybdenum hemicarbide by reducing and carbonizing MoO2 with methanol, and both thermodynamic and experimental studies were carried out. Based on the results, the reduction and carbonization routes are obtained: MoO2 was reduced and carburized directly to Mo2C in one step at lower temperatures, and first reduced to metallic Mo and then carburized to Mo2C at higher temperatures. The reduction mechanisms at low and high temperatures were proposed as well: The pseudomorphic transformation mechanism dominated the reaction at low temperatures, but at high temperatures, the reaction obeyed the chemical vapor transport mechanism.

Effect of basicity on the crystallization behavior of TiO2–CaO–SiO2 ternary system slag

Titanium-bearing blast furnace slag contains a considerable amount of unused titanium and thus causes both resource waste and environmental pollution. The enrichment and extraction of titanium from titanium-bearing blast furnace slag is an urgent problem to be solved. In the present work, the crystallization behavior of TiO2–CaO–SiO2 ternary system slag was investigated both theoretically and experimentally in the binary basicity (CaO/SiO2 mass ratio) range from 1.0 to 1.4. Thermodynamic calculation indicated that perovskite (CaTiO3) and sphene (CaTiSiO5) were the two main titanium-containing phases and perovskite was the first precipitated phase during the cooling process. With the increase of basicity, the mass percentage of both perovskite and wollastonite (CaSiO3) increased while that of sphene decreased. The experimental results showed good agreement with the thermodynamic calculation. Also, it was found that the crystals appeared to have hexagonal, leaf vein and dendritic shapes macroscopically, and their size reached the centimeter level. Observation of the three-dimensional topography suggested that the perovskite phase existed as dendrite with the orthorhombic crystal, and the sphene grew by taking the perovskite crystal as its nucleus and then wrapping the perovskite crystals.

Application of Sharp Analysis on Reduction Kinetics of Vanadium Titanium Magnetite Sintering Ore

The isothermal reduction kinetics of vanadium titanium magnetite sintering ore was investigated by thermo-gravimetric analysis at a temperature range of 1123–1223 K under 30% CO + 70% N2 gas mixtures. The apparent activation energy of reduction was calculated by iso-conversional method and its value is 36.7 kJ/mol. The model function describing the reduction mechanism was discussed by Sharp analysis and the results revealed that the reduction process is controlled first by random nucleation and nucleus growth mechanism (RNNGM) as reduction degree is lower than 0.5, followed by the mixed influence of RNNGM and phase boundary reaction when reduction degree is higher than 0.5.

Dry Granulation of Hot Metal and Heat Recovery from Off-Gas

Iron powders are mainly produced by Hoganas process and water atomization process, while both of which have the disadvantages of energy consumption. To obtain iron powders with higher particle sphericity, more uniform particle size distribution and higher proportion of total iron (TFe), a novel method considering of energy conservation was developed in this paper. The hot metal was transformed into granules with air cooling in a rotary disc atomizer, iron powder particles and hot off-gas were collected respectively. It was found that the property of the obtained iron powders was mainly controlled by the flow rate of the hot metal, the diameter of the rotary disc and the rotary speed and the heat of off-gas has a high level of value as well.