V-Mo/Ti and V-Mo-Nb/Ti denitration catalysts were prepared,and the denitration activity and resistance to Na poisoning of the two catalysts were investigated and compared.XRD,BET,NH3-TPD,H2-TPR and XPS were used to characterize the catalysts.The results show that the addition of Nb can effectively inhibit the decrease in acidity and reducibility of the catalyst caused by Na poisoning,and the decrease of chemisorbed oxygen on surface of the Na-poisoned catalyst.Thus,V-Mo-Nb/Ti-Na catalyst exhibits better denitration activity than V-Mo/Ti-Na catalyst.

La0.5Sr0.5CoO3 samples were prepared by solid-state reaction.The structure of the samples was analyzed by X-ray diffractometer and Raman spectrometer.XRD results indicate that La0.5Sr0.5CoO3 samples are of single-phase cubic perovskite structure.In the Raman spectrum,the peak caused by the rotation of oxygen octahedron and the secondary Raman peak formed by the vibration of Co—O bond angle and length can be observed.The energy band,density of states and partial density of states of La0.5Sr0.5CoO3 are calculated by the first-principles method.The results show that the conductivity of non-conductive pe-rovskite oxide LaCoO3 can be changed by doping Sr2+,which has guiding significance for the study of conductivity of perovskite oxide LaCoO3.

Single-host white-emitting Gd3PO7∶Dy^3+ phosphor was synthesized by wet chemical method.The phase structure,morphologies and optical properties of the as-prepared samples were characterized by X-ray powder diffraction(XRD),scanning electron microscope(SEM),Fourier transform infrared spectroscopy(FT-IR),and fluorescence spectroscopy.The XRD results show that the samples are Dy^3+ doped Gd3PO7 crystals with monoclinic structure and slight impurity.The fluorescence spectra show that under the excitation with the characteristic excitation band of Gd^3+ ions at 276 nm,Gd3PO7∶Dy^3+ samples emit the characteristic emission bands of Dy^3+ ions in yellow light region(4F9/2→6H13/2) and blue light region(4F9/2→6H15/2),which indicates that the energy transfer from Gd^3+ to Dy^3+ occurs in the Gd3PO7∶Dy^3+matrix.The luminescence intensity of the samples depends on pH values and Dy^3+ dosage.When the pH value is 6.00 and the Dy^3+ dosage is 0.5%,the sample exhibits a relatively high luminescence intensity.The Dy^3+ dosage directly affects the luminescence color of Gd3PO7∶Dy^3+ samples,and the as-synthesized Gd3PO7∶Dy^3+ sample with 3% Dy^3+ can emit white light with the coordinate of(0.335,0.345),which indicates that Gd3PO7∶Dy^3+ is a potential single-host white-emitting phosphor.

Bastnaesite was synthesized with hydrothermal method using cerium nitrate,sodium bicarbonate and sodium fluoride as raw materials.The effects of reaction time on the surface properties and denitration activity of the synthetic bastnaesite were investigated,and the reasons for the different synthetic products caused by different sodium bicarbonate dosages were analyzed.The crystal structure,particle size and surface morphology of the bastnaesite were characterized by SEM and XRD.The denitration performance of the obtained bastnaesite was investigated by H2-TPR and simulated flue gas denitration experiment.The results show that the longer the reaction time,the larger the main particles of the synthesized bastnaesite,the higher the crystal growth degree and the easier the particle polymerization.The concentration of bicarbonate ions in the initial reactant determines the product composition.When bicarbonate ions are excessive,the synthesized product is relatively pure bastnaesite.When bicarbonate ions are insufficient,there is cerium fluoride in the product.The optimal conditions for preparing high-grade bastnaesite determined by experiments are reaction time of 2 h and molar ratio of sodium bicarbonate to cerium nitrate of 3∶1.

The creep mechanism of rare earth magnesium alloys is mainly introduced.Research progress is reviewed in creep resistance of Mg-Al-RE series,Mg-Zn-RE series,Mg-Gd-RE series,Mg-Y-RE series and Mg-Sc-RE series multi-element rare earth magnesium alloys.Suggestions for its future research directions are provided.This article provides theoretical guidance and reference information for further research on the creep resistance of rare earth magnesium alloys.

Tritiated methane is a typical tritiated impurity in tritium-containing gases,which is characterized with low chemical activity and difficult to decompose.The methane decomposition ability of ZrTiNiMn alloy was tested at different reaction temperatures(500~700 ℃) with hydrogen containing 1.01% and 0.2% methane,and gas flow rate was controlled at 0.1~1 SLM.The surface morphologies,composition and phase structure of ZrTiNiMn alloy before and after reaction were analyzed by SEM,EDS and XRD.The results show that for the hydrogen containing 1.01% and 0.2% methane,ZrTiNiMn alloy hardly reacts with methane below 500 ℃,but efficiently decomposes methane by over 94% at 650 ℃ when the gas flow rate is 0.2 SLM.Generally,the decomposition rate of methane can be improved by decreasing the concentration of methane in feedstock,increasing the reaction temperature and decreasing the gas flow rate.The reaction products of ZrTiNiMn alloy with methane include hydrogen and solid products such as elemental carbon and metal carbide.

The effect of secondary hot pressing process on the microstructure and mechanical properties of Be-Al alloy prepared by powder metallurgy was studied,and the fracture morphology of the alloy was analyzed.The results show that in primary hot-pressed Be-Al alloy,nearly spherical beryllium particles is distributed in continuous aluminium matrix,and the alloy has tensile strength of 230 MPa,yield strength of 157 MPa and elongation of 3.5%.In secondary hot-pressed Be-Al alloy,the boundary of beryllium phase is rough,aluminum phase has grain boundaries with nearly round grains,and the alloy has increased tensile strength of 304 MPa,yield strength of 253 MPa and elongation rate of 1.5%.The fracture of primary hot-pressed Be-Al alloy has no obvious crack source,and shows uniform plastic deformation mainly with transcrystalline cleavage fracture of beryllium phase and ductile fracture of aluminum phase.The fracture of secondary hot-pressed Be-Al alloy has obvious crack source.In addition to plastic deformation fracture of the aluminum phase and a small amount of cleavage fracture of the beryllium phase,the fracture of beryllium aluminum phase boundary occurs in secondary hot-pressed Be-Al alloy.

Cemented carbides with different WC grain size distribution and different additives were prepared by powder metallurgy using coarse/fine WC and Co powders as the raw materials.Mo,Cu,VC,Cr3C2 and Y2O3 were selected as the additives.The phase composition,microstructure,density and mechanical properties of the prepared alloys were measured by XRD,SEM,drainage method and Vickers hardness tester.The results show that the phase composition of all the prepared alloys is almost the same,all having obvious WC peak.The number of abnormally grown WC grains in the alloy decreases with the decrease of the mass ratio of coarse-grained WC to fine-grained WC powder.Meanwhile,alloy hardness continuously increases but the fracture toughness decreases.The additives can effectively inhibit the growth of WC grains and improve alloy hardness,but the relative density of the alloys decreases with the increase of additive content.The dual crystal cemented carbide with 1% Cr3C2 has the best comprehensive properties.

Taking YG6 cemented carbide as the experimental object,the influence were studied of cutting fluid pH values(7.5, 8.5, 9.5,10.5 and 11.5) on the leaching rate of Co on the alloy surface,the leaching mechanism of Co was discussed,and the suitable pH value of cutting fluid was optimized.The results show that in the immersion experiments of cutting fluid,the leaching rate of Co on the surface of YG6 alloy sample is related to the pH value of cutting fluid and the placement state of samples,and the corrosion forms on the surface of the samples in different placement state are different.When the alloy samples are in overlapping contact,crevice corrosion occurs in the overlapping area and selective corrosion occurs on the upper surface of the non-overlapping sample.The corrosion degree is related to the pH value of cutting fluid,but it is not a simple linear relationship between the leaching rate of Co on the alloy surface and the pH value of cutting fluid.When the pH value of cutting fluid is 9.5,YG6 alloy sample has the lowest Co leaching rate of 4.30% on the surface.Therefore,during preparation or use in grinding of cutting fluid,controlling the pH value of cutting fluid at 9.5 can reduce the leaching rate of Co on the alloy surface,which greatly reduces the loss of Co on the alloy surface and ensures the product quality.

A large number of WC phase on the surface of cemented carbides was removed by chemical corrosion,and then an X-ray diffractometer was used to quickly determine the cobalt phase structure on alloy surface within the selected 2θ angle range.Jade software was used to analyze the characteristic peak areas of different cobalt phase structures,and mass fraction of different cobalt phase structures was calculated with K value method for phase quantification.The method is simple and fast,suitable for production analysis.