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%.

The lithium-rich manganese-based cathode material of Li1.2[Mn0.54Ni0.13Co0.13]O2 was prepared by electrospinning in order to overcome the shortcomings of low first-cycle efficiency and poor rate performance of lithium-rich manganese-based materials.The experimental results show that the nanofibers prepared by electrospinning have three-dimensional structure and larger specific surface area,which can improve the reactivity and reduce the conduction impedance of lithium ions,thus improving the rate performance and discharge capacity of the materials.At 5 C rate,the discharge specific capacity of the spinning fibers is 175 mA·h/g,while that of the precipitated particles is only 154 mA·h/g.In addition,the first-cycle efficiency is improved from 72.87% to 81.93%,and discharge capacity is also improved.Thus Li-rich manganese-based materials prepared by electrospinning have better performance.

In order to shorten the forming time of powder metallurgy,Be-Al alloy was subjected to hot extrusion after cold isostatic pressing,and the effect of hot extrusion on the microstructure and properties of Be-Al alloy was studied.The results show that after hot extrusion deformation,the beryllium phase of Be-Al alloy distributes in continuous aluminium phase in granular form,the microstructure is compact,and the density of material significantly increases.At the same time,the hardness of Be-Al alloy after hot extrusion increases to 80 HRB,accompanied by larger internal stress.The grain orientation of beryllium and aluminium phases after cold isostatic pressing is relatively random.After hot extrusion,beryllium phase has no obvious preferential orientation,and aluminum phase mainly forms the fiber texture with strong 〈100〉 orientation and weak 〈110〉 orientation.

Polyaluminum ferric chloride(PAFC) was prepared from acid leaching solution obtained by hydrochloric acid leaching of red mud,and its performance of kaolin wastewater treatment was studied.The effects of hydrochloric acid concentration,leaching temperature,leaching time and liquid-solid ratio on the leaching rate of Al and Fe in red mud were investigated.Also the effects of PAFC dosage,kaolin quality concentration,wastewater pH value and water temperature on the turbidity removal rate of kaolin during wastewater treatment with PAFC were studied.The experimental results show that the leaching rate of Al and Fe is 76.5% and 33.7%,respectively,under the conditions of 50% hydrochloric acid concentration,80 ℃ leaching temperature,1.5 h leaching time and 5 mL/g liquid-solid ratio.The highest turbidity removal rate of PAC for kaolin wastewater treatment is 90%,while that of self-made PAFC is 94%,under the conditions of PAC/PAFC dosage of 8 mL(10 g/L),wastewater pH value of 7.0,kaolin suspension(mass concentration 125 mg/L) volume of 500 mL and wastewater temperature of 20 ℃.

CoCrFeNiAlx(x=1,1.5,2) high-entropy alloys were prepared by non-consumable vacuum arc melting.The effects of Al content on the oxidation behavior of CoCrFeNiAlx alloys at 900 ℃ were studied by scanning electron microscopy,X-ray diffractometer and electron probe.The results indicate that all the three alloys with different Al contents are in the oxidation resistance level,and their oxidation kinetics curves basically conform to the parabolic law.With the increase of Al content,the oxidation weight gains of the alloys gradually decrease.When the Al content is x=1,the oxide film of the alloy is mainly composed of the outer layer of Cr2O3 spinel phase and the inner layer of Al2O3.When the Al content is x=1.5 or x=2,the oxide film of the alloy is mainly composed of the outer layer of Al2O3,the intermediate layer of spinel phase and the inner layer of Al2O3.

The effect of pulsed frequency on microstructure and microhardness of WC-13 Ni cemented carbide irradiated by intense pulsed electron beam(IPEB) was investigated by scanning electron microscope,surface profiler,X-ray diffractometer and Vickers microhardness tester.The results show that at a lower energy density of 3 J/cm^2,the increase of pulse frequency enhances the cumulative effect of thermal shock of IPEB irradiation,resulting in an increase in the number of thermal erosion pits and the content of Ni phase on the surface of the cemented carbide,the surface roughness slowly increasing,and the hardness decreasing at first and then slowly increasing.At a higher energy density of 13 J/cm^2, the increase of pulse frequency enhances the cumulative effect of surface remelting of IPEB irradiation,resulting in an increase in the number and size of ablated holes and the content of WC1-x and W2C phases on the surface of the cemented carbide. At the same time,the surface roughness and microhardness increase at first and then decrease.When the pulse frequency is 1 Hz,the surface microhardness reaches the maximum of 1 380 HV0.2.