The effects of five factors of alkali types,pelletization water addition,alkali addition,roasting temperature and time on porosity and vanadium extraction rate of the roasted pellets from vanadium slag were studied.The results show that the surface of roasted pellets with NaOH addition has many large pores with a diameter of about 0.5 mm,while the surface of roasted pellets with Na2CO3 addition has no such macropores.Moreover,the porosity of the two pellets with NaOH and Na2CO3 addition is 32% and 6%,and the vanadium extraction rate is 92% and 52%,respectively.When water addition is 3%,the porosity of roasted pellets with NaOH addition reaches a maximum of 36.7%,while the vanadium extraction rate reaches a maximum of 97% with 4.5% water addition.When NaOH addition is 35.5%,the porosity of roasted pellets reaches a maximum of 38% and the vanadium extraction rate also reaches a maximum of 98%.When the roasting temperature is 740 ℃,the porosity of roasted pellets with NaOH addition reaches a maximum of 40%,while the vanadium extraction rate reaches a maximum of 97% at the roasting temperature of 680 ℃.When the roasting time is 60 min at 800 ℃,the porosity of roasted pellets with NaOH addition reaches a maximum of 40% and the vanadium extraction rate also reaches a maximum of 96%.There is a positive correlation between the porosity and the vanadium extraction rate of roasted pellets.

Tungsten carbide layers with a certain thickness were in-situ synthesized on the surface of sintered tungsten products by high temperature heat treatment in carbon atmosphere protected by hydrogen gas to prepare WC/W surface composites.The effects of heat treatment temperature and tungsten matrix density on microstructure and properties of in-situ synthesized WC/W surface composites were studied by density and hardness test and metallographic microscope.The element composition and phase composition of tungsten carbide layers were analyzed by SEM/EDS and XRD.The results show that high temperature heat treatment temperature has significant influence on the growth thickness and quality of tungsten carbide layer,while tungsten matrix density has no obvious influence on the growth of tungsten carbide layer.When the temperature is lower than 1 800 ℃,the thickness of the tungsten carbide layer is relatively thin and its strength is poor.However,too high temperature will lead to an increase in defects of the tungsten carbide layer.The tungsten carbide layer in-situ synthesized on the surface of tungsten matrix has columnar crystal microstructure and single phase composition,closely combining with tungsten matrix,and the interface is clean and free of impurities.The surface composites can fully exhibit the excellent properties of the two materials at high temperature.

To study the influence of cone angle on the morphology of WC/Co coating prepared by shaped charge explosive spraying,the numerical simulation about motion state of the powder particles under different cone angles was carried out with smoothed particle hydrodynamics(SPH) method based on ANSYS/LS-DYNA software,and the simulation results were experimentally verified.The simulation results reveal that when the cone angle of charge is 60°,the uniformity of particle flow is much higher than that of other angles,and the velocity is generally maintained at 2~2.75 km/s.The experimental results show that when the cone angle of charge is 60°,the coating area increases by 164.88% and 39.37%,respectively compared with the cone angle of 40° and 50°,and its uniformity is the best.

93W-Ni-Cu/ABS composite filaments with a diameter of about 1.70 mm were prepared by using industrial tungsten powder,nickel powder,copper powder and ABS powder as raw materials.Then,using the filaments as raw material,the green billets with complex structure were printed by FDM(fused deposition molding) technology.The properties of 93W-Ni-Cu/ABS composite filaments prepared under different conditions and the effects of solid volume fraction on the compactness and mechanical properties of green billets were studied.The results show that the addition of surfactants can enhance the cohesion between ABS and 93W-Ni-Cu particles and reduce the porosity of the composites.With the increase of solid volume fraction,the tensile fracture load and elongation at break of the filaments gradually decrease.The highest solid volume fraction of the composite filaments is 45%.When the solid volume fraction of the green billets is 40%,the elastic modulus of the composite filaments reaches the maximum value of 1 390 MPa,which is 55.3% higher than that of ABS.

TiC-based cermets with different contents of Mo substitute for Ni were prepared by powder metallurgy,the mass fraction of TiC matrix and cohesive phase Co is 75% and 5%,and the total massfraction Mo and Ni is 20%.The microstructure,flexural strength,density and electrical properties of the cermets were investigated.The results show that when the content of Mo substitute for Ni in TiC-based cermets changes,the properties of cermets also change.When the mass fraction of Mo is 4%,the composite properties of TiC-based cermets are the best,its bending strength is 149.18 MPa,resistivity is 1.45×10^-5Ω·m,and density is 94%.

The effects of reusing waste liquid of carbonate precipitation for multiple times on the quality of lanthanum carbonate products with low chlorine and the concentration of ammonium chloride in the supernatant were studied.The results show that the obtained lanthanum carbonate completely meets the product quality requirements with Cl-≤0.05% and REO>45% after reusing the waste liquor for many times.Meanwhile,the lanthanum carbonate crystals are uniform and orderly encapsulated under the conditions of reaction temperature 45 ℃,alkalinity of NH4HCO3 solution 2.4 mol/L,reaction time 5 h and rare earth concentration 180 g/L.After reusing the waste liquid,the concentration of ammonium chloride in the supernatant can be enriched to more than 80 g/L.Subsequently,the above supernatant is treated in the three-effect ammonium evaporation system,to obtain the optimized economic benefits and good environmental benefit.

The nano-granular Pr6O11 was prepared by thermal decomposition using Pr2(C2O4)3·6 H2O as the praseodymium source.The thermal decomposition process of Pr2(C2O4)3·6 H2O in air was studied by TG-DTA curves.The phases,morphologies and optical absorption properties of the thermal decomposition products of Pr2(C2O4)3·6 H2O in air were characterized by XRD,SEM and UV-Vis spectrophotometer,respectively.The results show that there are two main stages in the thermal decomposition process of Pr2(C2O4)3·6 H2O in air.The first stage is room temperature^300 ℃,and large flake-like Pr2(C2O4)3·6 H2O loses its adsorption water and crystal water to turn into small flake-like Pr2(C2O4)3.The second stage is 300~800 ℃,and small flake-like Pr2(C2O4)3 is thermally decomposed into small flaky Pr6O11.Nano-granular Pr6O11 is obtained by heat preservation at 900 ℃ for 10 min,and its absorption ability for visible light is significantly better than that of small flaky Pr6O11.

The rapid solidification samples of Sm-Fe alloy were prepared by copper mold spray casting.The cooling rate of Sm-Fe alloy in copper mold was calculated by the unsteady heat conduction equation of thin material.The changes of microstructure and phase of Sm-Fe alloy during rapid solidification after nitrogen spray casting were studied by means of optical microscope,scanning electron microscope,energy spectrometer,X-ray diffractometer and X-ray photoelectron spectrometer.The results show that the cooling rate of molten Sm-Fe alloy is about 16.8 K/s after it is sprayed into the copper mold by nitrogen gas.The relatively large cooling rate makes the dendrite spacing obviously decreased,promotes grain refinement of the alloy,and restrains interdiffusion of the phases,resulting in more homogeneous composition of the alloy.The nitridation reaction is basically carried out only on the surface of the casting sample,and the products are mainly Sm2Fe17Nx and nitrogen hydroxides with relative contents of 34.36% and 65.64%,respectively.

Gd-Yb-YSZ ceramic powder was synthesized with hydrothermal method and carbon spheres were used as the template.The synthetic ceramic powder was coated on the surface of GH4169 superalloy block with commercial ceramic binder,and then subjected to drying and heat treatment to obtain thermal barrier coating.The prepared Gd-Yb-YSZ coating can resist thermal shock for 25 cycles,and its adhesive strength is 32 MPa,higher than that of the YSZ coating prepared by plasma spraying.The average thickness of YSZ coating obtained by plasma spraying is 270 μm.The average thickness of the homemade Gd-Yb-YSZ coating is only 68 μm,but its insulation temperature is 15 ℃ higher than that of the above YSZ coating.The main phase of the Gd-Yb-YSZ coating is Yb0.5Zr0.5O1.75,meaning that the Yb element is likely to be incorporated into the ZrO2 crystal structure,while the Gd element exists as a separate GdO2 phase.Therefore,the improvement in the thermal insulation capacity of the Gd-Yb-YSZ coating may be caused by the incorporation of Yb.

Concentration gradient core-shell precursor Ni0.8Co0.08Mn0.12(OH)2 was prepared by co-precipitation,and then concentration gradient cathode material LiNi0.8Co0.08Mn0.12O2 was synthesized by calcining with lithium hydroxide.The doping of aluminum was carried out by dry mixing and precipitation,respectively.The results of XRD and electrolyte immersion test indicate that aluminum doping can stabilize the layered structure of concentration gradient cathode materials,reduce the degree of cationic mixing,and also inhibit the dissolution of cathode materials in electrolyte.Therefore,the electrochemical properties of materials can be improved.After the concentration gradient cathode material is doped by precipitation,its capacity maintaining rate of 100 cycles at 25 ℃ under 1 C increases from 92.5% to 94.5%,and its capacity maintaining rate of 50 cycles at 55 ℃ under 1 C increases from 91.3% to 95.8%.