The Miedema model was used to study the separation characteristics and rules of Ca,Mg,Mn and other impurities during the vacuum distillation purification of metal ytterbium.Based on the theoretical analysis results,vacuum distillation purification experiments of ytterbium at different temperatures were carried out.The calculation results show that the difference in saturated vapor pressure(p*)between the impurities Fe,Al,Cu,and Ni and Yb is extremely large,while the p*between the impurities Mg,Ca,and Mn and Yb is very small below 1000℃.As the temperature decreases,the separation coefficient β_Ca,Yb gradually increases,β_Mg,Yb and β_Mn,Yb remain stable,and the volatilization rate of the impurities Mg,Ca,and Mn decreases sharply.The experimental results show that vacuum distillation can effectively remove the impurities Mg,Ca,and Mn in metal ytterbium at 700℃.

In order to reduce the content of Al impurity in the crude ZrCl₄ prepared by traditional boiling chlorination process and meet the accuracy requirement of high-quality zirconium precursor,the zinc-ion Lewis acid molten salt system suitable for high efficiency removal of Al from crude ZrCl₄ was developed.As a result,the content of Al impurity is reduced from 0.16%to 0.001%.According to the reaction of Lewis acid molten salt system with Al³⁺in crude ZrCl₄,the binding amount and binding energy of Al³⁺in composite salts were analyzed by CASTEP module based on density functional theory,and then the Al re-moval mechanism from crude ZrCl₄ was established.The decrease of the binding amount of Al³⁺and the increase of the binding energy contribute to the separation of Al³⁺from the composite salts,thus reducing the Al content in the crude ZrCl₄.It is proved that the zinc-ion Lewis acid molten salt system can effective-ly remove Al from the crude ZrCl₄ by experiments and theoretical calculation.This study can provide a new idea and theoretical basis for the preparation of high-quality nuclear-grade zirconium.

Mo-47.5Re pre-alloyed powder was prepared by wet chemical sol-gel method with ammonium heptamolybdate tetrahydrate,ammonium perrhenate and anhydrous oxalic acid as raw materials.The ther-mal decomposition and material change rule of wet gel of molybdenum-rhenium precursor during drying-calcination process were studied.Molybdenum-rhenium pre-alloyed powder containing molybdenum matrix phase with solid solution rhenium and molybdenum-rhenium intermediate phase(σ-phase andχ-phase)was prepared.The particles of the pre-alloyed powder are fine,the laser particle size D50 is about 5.09μm,and the distribution of molybdenum and rhenium elements is uniform and highly dispersed.Therefore,it is an ideal powder metallurgy raw material for preparation of molybdenum-rhenium alloy with high rhenium content.

A two-step hydrothermal method was used to prepare two kinds of ceramic powders containing semi-hollow spheres with chemical composition ofZr_0.87Y_0.07Gd_0.02Sc_0.04O_1.94(Gd-Sc-YSZ)and Zr_0.87Y_0.08Gd_0.03Yb_0.02O_1.94(Gd-Yb-YSZ),respectively.The above ceramic powders were granulated and coated by atmospheric plasma spraying on the surface of the Al-permeated coating,to prepare two kinds of ceramic layers and form ceramic layer/Al-permeated layer/NiCrAlY/DZ40M thermal barrier coatings.The thermal insulation temperature at the heat source temperatures of 1050℃and 1400℃and CMAS hot corrosion resistance at 1250℃of the two kinds of thermal barrier coatings and the traditional YSZ coating were tested.The results demonstrates that both the Gd-Yb-YSZ and Gd-Sc-YSZ coatings remain intact and do not peel off after thermal insulation at 1400℃for 6 h.The two coatings are primarily composed of a metastable tetragonal phase(t'-ZrO₂),which indicates that both the Gd-Yb-YSZ and Gd-Sc-YSZ coatings are expected to serve at 1400℃for a long term.At the high temperature,the Al-permeated layer plays a crucial role in maintaining the bonding stability of the ceramic layer on the surface of NiCrAlY alloy.The thermal insulation temperature of Gd-Yb-YSZ and Gd-Sc-YSZ coatings is higher than that of YSZ coating at the heat source temperatures of 1050℃and 1400℃.Furthermore,their thermal conductivities are only 0.35~0.5 times that of YSZ coating.It can be concluded that doping with Gd,Yb and Sc significantly en-hances the thermal insulation effect of the YSZ coating.Following exposure to hot corrosion of CMAS at 1250℃for 1 h,the edges of the YSZ coating exhibits peeling,whereas the centre of the Gd-Yb-YSZ coa-ting only becomes rough and the Gd-Sc-YSZ coating remains intact after 6 h.The CMAS hot corrosion re-sistance of the Gd-Sc-YSZ and Gd-Yb-YSZ coatings is much better than that of the YSZ coating,particular-ly for the former.

Mg-Gd-Y-Sm-X-Zr(X=La,Ce,Sr,Sb)alloys were prepared using pure magnesium and magne-sium-based intermediate alloys as raw materials.The instruments of Vickers hardness tester,inductively coupled plasma atomic emission spectrometer,metallographic microscope,scanning electron microscope and tensile testing machine were used to test the sample.The Vickers hardness of solid solution-aged Mg-Gd-Y-Sm-X-Zr(X=La,Ce,Sr,Sb)alloys was studied firstly.The influence of rare earth element Gd and Y content on the Vickers hardness of aged Mg-Gd-Y-Sm-La-Zr alloy was also studied.And then the micro-structure,aging hardening characteristics,and mechanical properties of as-cast and solid solution-aged Mg-8Gd-3Y-2Sm-0.15La-0.5Zr alloy were further studied.The results indicate that La is the optimal streng thening element.The Vickers hardness of the alloy with Gd/Y mass ratio of 8/3 is better than that of the alloy with Gd/Y mass ratio of 6/4 and 9/2.The grain size of as-cast Mg-8Gd-3Y-2Sm-0.15La-0.5Zr alloy is mainly concentrated in the range of 20~45μm,and its peak hardness of 132.87 HV is reached after 16 h aging.The tensile strength and yield strength of the aged alloy are 259.02 MPa and 240.31 MPa respec-tively,increased by 42.32%and 51.87%compared with the as-cast alloy respectively.

Baotou mixed rare earth concentrate is a paragenetic mineral of bastnaesite(CeCO₃F)and mona-zite(CePO₄),with a complex structure that is difficult to decompose.Ca and Si impurities are embedded on the surface of the mineral,which affects the denitration activity of rare earth minerals.Consequently,it is essential to carry out impurity removal pretreatment before using natural minerals as catalysts.The spe-cific process for preparing denitrification catalysts from bastnaesite involves acid leaching,fluorine reten-tion and roasting,detailed as follows.In the first step,HCl is used to remove Ca,the concentrate of HCl is 6 mol/L and the mass ratio of bastnaesite to NaCl(fluorine retainer)is 1∶5.The mixture is stirred for 12 h before roasting at 500℃for 2 h.In the second step,HF is employed to remove Si,with a concentra-tion of 13 mol/L.The mass ratio of Ca-removed powder to NaCl is 1∶5.The mixture is stirred for 12 h and subsequently roasted at 500℃for 2 h.The Ca content in the catalysts prepared with Ca and Si-re-moved bastnaesite is reduced to 1.85%,while Si content decreases to 0.17%.Additionally,the concentra-tion of rare earth elements is increased by 22%compared with the raw ore.The removal of Ca and Si from bastnaesite results in the formation of a well-developed pore structure,which increases the specific surface area and active elements.Furthermore,the valence of some Ce ions transitions from+3 to+4,and lattice oxygen is formed.These structural changes provide more redox centers for the denitration process of the catalyst,significantly improving its denitration performance.Therefore,using bastnaesite after the removal of impurities as denitration catalysts has more advantages than directly using natural minerals.

Formed catalyst was prepared by adding binders(sesbania powder,sodium carboxymethyl cellu-lose and guar gum)into sulphuric acid activated rare earth tailings catalyst powder.The effects of types and amounts of binders on the denitration performance of formed catalysts were investigated.The formed catalysts were characterized by means of catalytic activity evaluation,compressive strength test,BET,XRD and H₂-TPR.The results show that after extrusion forming of catalyst powder,the specific surface area de-creases from 3.70 m²/g to 1.22 m²/g,and the denitration efficiency is only 56%.The addition of 2.5%guar gum enhances the adhesion among the rare earth tailings powder particles,enabling the catalyst to be smoothly extruded,and has the effect of pore formation,greatly improving the specific surface area and redox capacity of the catalyst.Under the combined action of 5%polyethylene glycol and 2.5%guar gum,the formed acid activated rare earth tailings catalyst has a denitration efficiency of 91.6%and excellent N₂ selectivity,truly realizing the resource utilization of rare earth tailings.

Ni/CaO-La₂O₂CO₃(NCaL)catalyst was prepared by supporting Ni with CaO carrier modified by rare earth compound La₂O₂CO₃.Its catalytic effect for hydrogen production by ethanol steam reforming was studied,compared with the unmodified Ni/CaO(NCa)catalyst.The phase of the catalyst was analyzed by X-ray diffractometer(XRD),the redox capacity was tested by temperature programmed chemisorption instrument(TPR),and the hydrogen production performance was analyzed by chromatography worksta-tion.The results show that the ethanol conversion rate at 300℃of NCa is less than 70%,while that of NCaL is more than 80%.The ethanol conversion rate at 400℃of NCaL reaches 100%,while that of NCa is less than 95%.The La₂O₂CO₃ modification can significantly improve the ethanol conversion rate and ca-talytic activity at low temperature of the catalyst.At 600℃,the H₂ selectivity of NCaL reaches the maxi-mum value of nearly 90%,which is 14.31%higher than the maximum H₂ selectivity of NCa.The selectivi-ty of H₂ and CO₂ of NCaL is higher than that of NCa,while its selectivity of CO and CH4 is decreased.The La₂O₂CO₃ modification can significantly improve the H₂ selectivity of the catalyst,and CaO carrier modified by rare earth can improve the hydrogen production effect of ethanol steam reforming catalyzed by Ni.

In order to solve the problems of poor product quality,long reaction time and high energy con-sumption in the one-step carbonization production process of niobium carbide,Nb(OH)₅ with relatively well controlled particle size was selected as the experimented raw material,carbon black was used as the re-ducing agent,and after ball minning and mixing,nano niobium carbide with high purity was directly pre-pared by one-step carbonization method.The effects of carbon fitting ratio(mass ratio of Nb(OH)₅ to car-bon black),ball milling time,reduction temperature and reduction time on the phase composition and mi-crostructure of NbC product were analyzed by XRD and SEM.The experimental results show that when the carbon fitting ratio is too high,the carbon black hinders the thermal decomposition of Nb(OH)₅,which leads to insufficient reduction.With the extension of ball milling time of the raw material,the increase of carbonization temperature and the extension of the reduction time,the purity of NbC product increases firstly and then tends to be stable.In view of energy saving and nanomaterial preparation,the optimized process parameters are as follows:carbon fitting ratio of 1∶0.3,ball milling time of 1 h,reduction tempe-rature of 1300℃,and reduction time of 3 h.Under the optimized experimental conditions,the purity of the obtained NbC product reaches 98.9%,and the particle size is less than 200 nm.