Considering the cost, graded cemented carbide was prepared by one-step sintering in a vacuum furnace. The influence of sintering technological parameters on microstructure and density was studied. The results indicate that WC grains in alloy surface layer are larger than those in Co-rich layer and core region. As sintering temperature increases,WC grains in alloy surface layer become coarse,and density of the alloy increases at first and then decreases. Longer sintering time results in significantly increased thickness of two-phase area in alloy surface layer. The thickness of the graded layer of the prepared cemented carbide in the experiment can reach 1 168μm,and alloy density decreases with longer sintering time.

Abstract. WC-6 %Co cemented carbide samples were prepared with WC powder （FSSS= 2.5 μm） and Co powder （FSSS= 1.0 μm） as the raw material and ZrO2 （3Y） and CeO2 as the additive. The influence was investigated of different additives on microstructure and properties of WC-6%Co cemented carbide. The results show the ZrO2 （3Y） is dispersed in the binder phase in spherical form to improve bending strength of the alloy without significant effect on the grain size of WC. CeO2 can refine the WC grains,re- duce the porosity of cemented carbide and result in uniform microstructure distribution and improved ben- ding strength of the alloy.

The influence was investigated of vacuum sintering temperature on the microstructure and me- chanical properties of WC-8% Ni cemented carbide by using scanning electron microscope, metallographic microscope, X ray diffractometer, microhardness tester and other devices. The results show that WC-8% Ni cemented carbide sintered in vacuum at 1 450 ℃ has the most excellent mechanical properties with the rel- ative density of 99.81% ,HV30 hardness of 13.23 GPa and fracture toughness （Kic） of 24.22 MPa · m1/2. Based on Murakami etching and XRD detection,the alloy sintered at 1 475 ℃ or more has η phase. And the effect is also discussed of η phase on alloy mechanical properties.

Plasma nitride coating was prepared on the surface of cemented carbide blade under the conditions of nitrogen atmosphere and high pressure. The phase composition of the coating was characterized by XRD,its micro-hardness was tested by a micro-hardness tester, and its microstructure on surface and sec- tion was observed by SEM. Wear resistance of the coating was evaluated by contrasting friction coefficient between cemented carbide sample and coated sample. The wear mechanism of cemented carbide and coated sample was studied based on friction and wear surface morphology. The results show that the coating was mainly composed of TiN of about 5 pm layer thickness. The coating is tightly bonded to the substrate with- out obvious gap and crack. The friction coefficient of cemented carbide substrate is about 0.4 with relative- ly large fluctuation,while the coating has stable friction coefficient around 0.2. Plasma nitride coating on cemented carbide surface can effectively improve the wear resistance of the substrate.

Geometric and physical parameters were analyzed of sticking welding layer on the rake face of ce- mented carbide tool, and then theoretical heat transfer model and finite element model were established for tool rake face with or without sticking welding layer by using Laplace transform, inverse transform and the first law of thermodynamics, and combining the actual working conditions of cutting. The theoretical model solution and finite element model simulation were also carried out. The results show that the existence of sticking welding layer can affect temperature gradient of the tool substrate. The simulated temperature gradient change is verified by the theoretical model, resolving the problem that tool rake face temperature gradient change cannot be verified by experiments. Based on numerical simulation of the internal tempera- ture distribution of the tool with different sticking welding layer thickness and thermal coefficient, the in- fluence rules are obtained of sticking welding layer on temperature distribution in tool rake face. The error is less than 10% of cutting temperature of the tool with sticking welding layer from experiments and nu- merical simulation,verifying the accuracy of the finite element model.

MIBK has different extraction performance for Sb（Ⅲ）and Sb（Ⅴ）under certain acidity condition.Therefore,high purity niobium oxide（Sb content10×10^-6）can be obtained by controlling certain acidity and oxidizing Sb（Ⅲ）into Sb（Ⅴ）in the extraction system of HF-H2SO4-MIBK to meet the requirements of Sb extraction separation to the maximum extent.

Niobium metal production process by carbon reduction is briefly introduced,focusing on development of reduction equipment to large capacity,energy saving,intelligent control and so on.The development of reduction equipment results in more niobium strip installed furnace capacity,less power consumption and better automation level to improve the competitiveness of carbon reduction process in the field of metal niobium production.

Theφ-pH diagrams of acid decomposition process of oxides of cerium and terbium at 298.15 K were studied by thermodynamic calculation.The results show that CeO2 and TbO2are difficult to be directly decomposed by acid,but they can be transformed into Ce^3＋and Tb^3＋by acid decomposition in a reductive environment.Compared with CeO2 and TbO2,Ce2O3 and Tb2O3can be directly decomposed into Ce^3＋and Tb^3＋by acid with high pH value,which actualizes the extraction of cerium and terbium.

The new technologies of membrane separation methods and electrochemical-adsorptive methods for development of salt lake lithium resources are reviewed.The technical principles,advantages and disadvantages,and current research status of each method are also expounded,and the development prospects of the methods of extracting lithium from the salt lake brines in China are proposed.

Indium was recovered from zinc oxide flue dust by two stage leaching and solvent extraction,and technical conditions of two stage leaching were investigated.The test results show that the low acidity condition has a good selectivity for Zn and In leaching from zinc oxide flue dust,and zinc is selectively leached into the solution and indium is concentrated in the residue.The optimal conditions of low acid leaching to remove Zn are as follows：leaching temperature of 60 ℃,liquid to solid ratio of 10∶1,sulfuric acid concentration of 0.16mol/L and leaching duration of 30 min.Under the above conditions,Zn leaching rate reaches93.73% and In content reaches 1 254g/t in the leaching residue.The optimal conditions of high acid leaching to recover In are as follows：leaching temperature of 70℃,liquid to solid ratio of 6∶1,H2SO4 concentration of 0.8mol/L and leaching time of 2h.Under the above conditions,In leaching rate is 89.32%.