The pH condition of Fe, Ca and Mg removal from low-concentration coibalt solution and the process of impurity removal by P204 extraction were studied. The results form the preliminary iron removal experiment show that the process of iron removal with sodium jarosite and a pH value of 3.0-4.0 has a good effect of more than 99% iron removal rate. Using the process together with sodium jarosite and goethite,the iron removal rate is 95.65% and the cobalt loss rate is decreased from 21.3% to 4. 74%. The optimal pH value of the low-concentration cobalt solution to remove Ca and Mg for the above process is 3.5 4.0,and the optimal technical parameters of impurity removal by P204 extraction from orthogonal experiments are as follows, the volume fractions of P204 and petrol are 25% and 75%, respectively,the phase ra rio of oil to aqua is 1/2,and the saponification rate is 75%.

CoO was prepared by the thermal decomposition of CoC2O4 · 2 H2O in the air, and then reduced in the hydrogen gas with a 99. 999% purity and --40℃ dew point to obtain cobalt powder. The cobalt powder was oxidized in the air to obtain CoO again. The above processes of oxidation and reduction were circularly carried out. The product was characterized by scanning electron microscopy and laser particle size analyzer. The results show that coarse cobalt powder is obtained through three cycles of oxidation and reduction,of which the particles of 12-26 μm size distribution accounts for 93.53%.

Niobium metal was prepared by electro-deoxidization reaction in eutectic CaCl2-NaCl electrolyte with sintered Nb2O5 sheet as the cathode and graphite rod as the anode. The influence of compacting pressure and sintering temperature was investigated on the electro-deoxidization reaction of Nb2O5s sheet. The results show that lower compacting pressure （12 MPa） and suitable sintering temperature （1 200 ℃） are helpful to obtain fine-grained Nb2O5 sheet with higher open porosity , from which purer niobium can be prepared and higher electro-deoxidation efficiency of Nb2O5 sheet can be achieved.

Tantalum metal powder was prepared by electro-deoxidation of molten salt （FFC）. The morphology of the prepared tantalum powder was observed by SEM and TEM, and its size distribution, chemical composition and electrical properties were also analyzed. The results show that the prepared tantalum pow- der has an original particle size of 200~400 nm,and particle bonds with each other and looks like coral. Its oxygen content is decreased to 3.69）K 10^-3 and specific capacitance is above 80 000 μF·V/g to meet with the requirement for capacitor production. Based on calculation,the current efficiency of the above tantalum powder preparation process is only 30%. To achieve industrial application the low current efficiency of the electrolysis process must be improved

La0.75Mg0.25Ni3.47Co0.2Al0.03 alloy was prepared by intermediate-frequency induction vacuum melting. The reasons for the efficacy loss of the alloy electrode were investigated by electrochemical and gaseous cycle experiments,SEM and XPS. The results show that capacity attenuation in both discharge and hydrogen absorption cycles takes place in rapid and slow stages. With cycling number increasing,the corrosive oxide on the surface of alloy particle increases during electrochemical cycling, and the contact resistance and charge transfer resistance first decrease and then increase. During gaseous hydrogen absorption and desorp- tion cycling,the crack of the alloy particle increases and the split extent enlarges. The main reason of the alloy electrode capacity decay is the oxidation and corrosion of La and Mg. Alloy particle pulverization ac- celerates the corrosion of La and Mg, and further deteriorates the cycling performance of the alloy electrode.

Micron silver powder was prepared by step-by-step reduction in aqueous solution with ascorbic acid as the reducer and PVP as the dispersant. The growth pattern of silver particles at different reactant dropping rate and silver nitrate dosage was investigated by SEM and XRD, and their growth mechanism was studied by AFM. The results show that when the reactant dropping rate is 1 mL/min,uniform mono- disperse silver particles with an average diameter of 1. 8 /~m can be obtained, and particle size increases nearly linearly with the dosage of silver nitrate. The silver crystal grows through layered growth mode and step-cluster approach,which belongs to Kossel-Stranski two-dimensional nucleation model.

Al2O3 was doped into molybdenum powder by solid-solid, liquid-solid and liquid-liquid doping methods respectively, then doped molybdenum powder was prepared by powder metallurgy, and finally Al2O3 particle reinforced molybdenum composite material was prepared by pressing and sintering. The microstructure of doped molybdenum powder and molybdenum bar was observed by SEM. The results show that the Al2O3/Mo composite material prepared by liquid-liquid doping has small particle size and high density and hardness, and its doped Al2O3 particles are small and uniformly distributed.

Cr-Si co-impregnation on surface of γ-TiAl-based alloy was carried out by double glow plasma surface alloying technique. Morphology, composition and phase structure were investigated by OM, SEM and XRD. The hardness of the impregnation layer was determined by micro Vickers hardness tester. The influences of Cr-Si co-impregnation on wear resistance of γ-TiAl-based alloy surface were studied through ball-disc friction and wear experiments without lubrication. The results show that there are three sublayers on the alloy impregnation surface. The element content changes continuously in the impregnation layer. The impregnation layer is combined with the substrate by metallurgical bonding. Hardness of the alloy surface increases to HV0.11 200~ l 250. The transition layer connected to the substrate is of better strength and toughness ,which can effectively improve the wear resistance of the alloy.

The mechanism,influence factor and crystallization process of Ni-Ti alloy preparation by mechanical alloying are reviewed to provide a reference for parameter selection and optimization of mechanical alloying process,especially for Ni-Ti alloying.

The latest development of copper-based wear-resistant composite materials is reviewed, focusing on the type of copper-based wear-resistant materials and their preparation methods and enhancement mechanism. Ceramic particle-reinforced copper-based composite material has higher wear resistance, better hightemperature mechanical properties and lower thermal expansion coefficient, and its preparation process is simple with low cost. Powder metallurgy is still an important method for preparation and research of carbon fibre or ceramic particle-reinforced copper-based composite materials. And in-situ synthesis technology also has good development prospect due to its significant technical and economic advantages.