WC-Al₂O₃composite was prepared by vacuum hot pressing sintering(HPS)method.The effect of metal elements(Cr,Mo,Ti)on the corrosion behavior of WC-Al₂O₃composite in NaCl solution was studied by electrochemical corrosion method,and open circuit potential,electric polarization curve and electrochemical impedance spectroscopy were mainly measured.The experimental results show that Cr and Mo additives can improve the corrosion resistance of WC-Al₂O₃composite,and the enhancement effect of Cr additive is significantly better than that of Mo additive while Ti additive reduces the corrosion resistance of WC-Al₂O₃composite.Based on analysis,oxide film formed on the surface of the Cr-containing composite in the corrosive medium is more complete and denser,thereby effectively reducing the corrosion rate of the composite.

The WC-reinforced Ni60 gradient coating was generated on the surface of H13 steel by laser cladding.The microstructure,phase composition,microhardness and friction&wear properties of the coating were analyzed by metallographic microscope,scanning electron microscope,X-ray diffractometer,microhardness tester and universal friction&wear tester.The results indicate that there are relatively few pores and cracks in WC-reinforced Ni60 gradient coating.The coating and the substrate form a good metallurgical bond.The phases of gradient coating surface are mainly iron-carbon compound(FexC),iron-nickel solid solution((Fe,Ni)₂₃C₆,Ni₄B₃)and ceramic-reinforced phases such as WC,W₂C and Cr₇C₃.The hardness and wear resistance of the die steel surface are significantly improved by the gradient coating.The maximum microhardness of the coating surface is about 4 times of the substrate,and its wear amount is only about 18%of the substrate.The wear mechanism of the coating mainly includes adhesive wear,brittle spalling and abrasive wear,which can prolong the service life of the die and reduce the waste of resources.

Bayan Obo rare earth tailings were pretreated with sulfuric acid and then loaded with 5%manganese acetate by impregnation and roasted by microwave to prepare denitration catalysts.And the effects of sulfuric acid concentration(0 mol/L,0.5 mol/L,1 mol/L,and 3 mol/L)on the denitration performance of the catalysts were investigated.The catalysts were characterized by XRD,NH₃-TPD,H2-TPR,and XPS.The results of denitration activity tests show that the denitration activity of the catalysts at 100~250℃increases at first and then decreases with the increase of sulfuric acid concentration,and reaches the best when the sulfuric acid concentration is 0.5 mol/L.The higher concentration(3 mol/L)of sulfuric acid deteriorates the originally good low-temperature activity of the catalyst.The catalyst treated with 0.5 mol/L sulfuric acid has a wide temperature window with good activity in the range of 150℃to 250℃and the conversion rate of nitrogen oxides reaches 92%at 200℃.The characterization results show that the loaded manganese exists in amorphous state or is highly dispersed on the surface of the rare earth tailings.The concentration of Mn4+on the catalyst surface decreases with the increase of sulfuric acid concentration,and both the ammonia adsorption capacity and redox capacity of the catalysts decrease,thereby reducing the denitration activity.

The continuous cooling in the casting process of rare earth glass-ceramics would change the microstructure of the melt.Through Raman,XRD,and SEM-EDS,samples with different quenching temperatures(1550~1100℃)were analyzed to study the effect of temperature on high-temperature melt structure of La₂O₃-SiO₂-CaO-Al₂O₃-MgO system.The results show that the quenched samples are amorphous at high temperatures and crystalline at relatively low temperatures.After the decomposition of Raman spectra of amorphous quenched samples,it is found that with the temperature decreasing,the Raman peak positions of the basic structural unit of each silicon oxygen/aluminum oxygen tetrahedron have a shift towards the high frequency.The shift of the peak positions of the low-frequency(200~800 cm^-1)structural unit is large while that of the high-frequency(800~1200 cm^-1)structural unit is small,and La₂O₃inhi-bits the peak positions of each structural unit from shifting towards the high frequency.The results of XRD and SEM-EDS show that the addition of La₂O₃reduces the temperature at which CaMg(SiO₃)2crystalline phase is produced in La₂O₃-SiO₂-CaO-Al₂O₃-MgO melt.

The recovery of the niobium layer and tantalum layer from waste niobium/steel and tantalum/titanium/steel by hydrogenation stripping was studied.The results show that the hydrogenation temperature and hydrogenation time have a great impact on the stripping of the composite layer.Among them, the best stripping conditions for the niobium/steel layered composite are the hydrogenation temperature of 800 ℃ and hydrogenation time of 1.0 h, and the content of the impurity element Fe in the niobium hydride block which is obtained by stripping is about 0.007 8%.The best stripping conditions for the tantalum/titanium/steel layered composite are the hydrogenation temperature of 600 ℃ and hydrogenation time of 1.5 h, and the content of the impurity element Ti in the obtained tantalum hydride block is about 0.127%.

By using methane as the carbon source,a layer of silicon-containing amorphous carbon(C:Si)film was prepared on the surface of titanium alloy plate for cell electrode plate by plasma enhanced chemical vapor deposition(PECVD).The discrepancies in conductivity,hydrophobicity,corrosion resistance,and thickness of the C:Si film prepared by different flow rates of SiH₄were compared,and the mechanism of SiH₄flow rate causing the change in the properties of C:Si film was analyzed in depth.The results show that the C:Si film bonds well with the substrate.When the SiH₄flow rate gradually increases,the film thickness increases.After increasing SiH₄flow rate,the hybridization ratio of the C:Si film increases from 0.58 to 1.11,and the half-peak width of G peak decreases from 168 cm^-1to 103 cm^-1.Thus it could be concluded that increasing SiH₄flow rate can induce graphitization transition of the C:Si film.The C:Si film prepared by the SiH₄flow rate at 6 mL/min has excellent corrosion resistance,and crystalline salt particles are formed on the film surface after polarization with no observation of peeling or micropore defects.The interfacial resistance of the C:Si film is significantly lower than that of the titanium substrate,and the hydrophobicity of the C:Si film is stronger than that of the titanium substrate.The lowest interfacial resistance and optimal hydrophobicity of the C:Si film are obtained at the SiH₄flow rate of 6 mL/min.

Lithium in spent LiFePO4cathode materials was recovered by the mechanochemical activation and water leaching process,and the effects of the molar ratio of co-grinding reagents to the spent LiFePO4cathode materials,the speed and time of ball milling on leaching rate of lithium were studied.Under the conditions that the molar ratio of four heterocrystalline sulfate co-grinding reagents to the spent LiFePO4cathode materials is 3∶1,the ball milling speed is 400 r/min,and the ball milling time is 4 h,lithium leaching rates with the co-grinding reagents of Na₂S₂O₃,Na₂SO₃,Na₂SO₄and Na₂S₂O₈are 42.7%,30.8%,58.3%and 99.3%,respectively.Relatively high leaching rate of lithium is achieved when using Na₂S₂O₈as the co-grinding reagent to recover lithium by mechanochemical activation and water leaching.Lithium in the filtrate was then precipitated,separated and purified by saturated Na₂CO3solution to obtain the recovered product Li2CO3with a purity of up to 98.5%.The method realizes the efficient recovery of valuable lithium metal from spent LiFePO4cathode materials.

WC,Co and Ni were used as raw materials to prepare cemented carbide samples with different nickel-cobalt ratios by powder metallurgy.The microstructure of the samples was studied, their mechanical properties, including hardness, wear resistance coefficient, bending strength, and fracture toughness were analyzed, and their corrosion resistance was studied through electrochemical experiments.The results show that with the increase of Ni content, the hardness, wear resistance coefficient and bending strength of WC-Co-Ni cemented carbides continue to decrease, while the fracture toughness increases at first and then decreases.The micro-grain structure of the three groups of samples with WC-10%Co, WC-9%Co-1%Ni and WC-7%Co-3%Ni is relatively fine and uniform while that of the remaining samples is coarse.The results of the electrochemical experiments in 3.5% NaCl solution with pH value of 7 show that the corrosion resistance of WC-Co-Ni cemented carbides increases with the increase of Ni content, and the WC-7%Co-3%Ni sample has the best comprehensive mechanical properties.Considering the corrosion resistan-ce of the sample, the optimized cemented carbides can better improve the working life of the shield tools.

Due to the extremely fine grain size and large specific surface area of WC and Co powder, ultrafine grain cemented carbides prepared by ultrafine WC powder(d≤500 nm) is easy to be affected by the ambient oxygen while waiting for sintering after the press molding of the blank, resulting in the different oxygen content of the surface and core of the blank to form an oxygen gradient, which affects the properties of the cemented carbide material.A novel oxidation pretreatment technology, combined with the self-developed pretreatment device, was used to perform the oxidation pretreatment before the sintering of WC-9%Co ultrafine grain cemented carbide blank and then the subsequent low-pressure sintering was performed on the pretreated blank.The oxygen content of each part of the blank before and after oxidation pretreatment, and the magnetic saturation(σs),flexural strength(TRS),Rockwell hardness(HRA),fracture toughness(KIC) and coercivity(Hc) of each part of the sintered cemented carbide were compared and analyzed.The results show that the total oxygen content in the blank increases and the oxygen content is more uniformly distributed after oxidation pretreatment.After sintering, the magnetic saturation of the cemented carbide is significantly reduced and its distribution is more uniform.At the same time, properties including flexural strength and hardness are effectively improved, while the density and porosity remain unchanged.

The research results on the gradient cemented carbides with cubic-phase free surface layer are summarized.The effects of chemical composition, particle size of raw materials and sintering atmosphere on the microstructure, elemental distribution and properties of the gradient cemented carbides with cubic-phase free surface layer are systematically introduced.The application of the gradient cemented carbides as coating substrate and the cutting application of the coated gradient cemented carbide tools are summarized.It is pointed that the research on the surface treatment technology of the gradient cemented carbides with cubic-phase free surface layer is an important direction to tap their application potential.