In order to improve the thermal conductivity and mechanical properties of Al-Si based die casting aluminum alloys,the effects of La and Ce on microstructure,thermal conductivity and mechanical properties of Al-3Si-0.4Cu-1.0Fe die casting aluminum alloy were investigated using metallographic microscope,SEM,EDS,universal electronic tensile testing machine,and laser conductometer.The results indicate that the rare earth elements of La and Ce refine the alloy grains,transformingα-Al grains from dendrite to cellular morphology,and reducing the average secondary dentritic arm spacing.Meanwhile,the two elements also modify the eutectic Si phase to result in a uniform distribution of fine fibrous morphology.When the added contents of La and Ce are both 0.1%,the thermal conductivity,tensile strength and elongation after fracture are 167.62 W/(m·K),201.0 MPa,and 14.56%,respectively.Compared with the sample without rare earth elements,these values are increased by 11.19%,27.38%,and 246.67%.

Rare earth tailings contain a considerable amount of silicon and aluminum species for molecular sieve synthesis,and the difficulty of green synthesis of molecular sieves from natural minerals lies in the mineral activation.In this paper,rare earth tailings,being used as raw materials,were activated in ways of thermal activation,alkali fusion activation,and sub-molten salt activation,respectively,to depolymerize the silica and aluminum species in the highly polymeric state of rare earth tailings into reactive mono-polymeric silica and aluminum species,setting the basis for the synthesis of molecular sieves,thus to realize the se-condary utilization of rare earth tailings.The chemical composition,phase structure,and surface micromorphology of the activated rare earth tailings were analyzed by XRF,XRD,and SEM-EDS characterization to investigate the effects of different activation modes on the activation of rare earth tailings.The results show that the SiO_2 crystal form in the thermally activated rare earth tailings is stable and the activation effect is not obvious;the rare earth tailings could be more completely activated by alkali fusion and sub-molten salt,and alkali fusion activation could realize more efficient activation of rare earth tailings.And at the same time,the increase of alkali fusion activation temperature can promote the activation of rare earth tailings.When the mass ratio of NaOH to rare earth tailings is 3 and the alkali fusion activation temperature is 450℃,the dissolution rates of reactive silica and aluminum species in rare earth tailings are 84.2%and 63%.The results of the study provide a certain theoretical basis for the green synthesis of molecular sieves from natural minerals and the secondary utilization of rare earth tailings resources.

Aluminum ingots containing tantalum impurity underwent vacuum electron beam evaporation using a electron gun,resulting in the formation of a molten pool and aluminum vapor with increasing temperature.The tantalum content in different regions of the aluminum ingot was detected by inductively coupled plasma emission spectrometer(ICP-OES).The microstructure,chemical composition and phase composition of the aluminum ingot and evaporated aluminum film were investigated by scanning electron microscope(SEM),energy dispersive spectroscope(EDS)and X-ray diffractometer(XRD).The element speciation and composition of the aluminum ingot and aluminum film were analyzed using Auger electron spectrometer(AES)and X-ray photoelectron spectroscope(XPS),respectively.The results show that with the increase in tantalum content,the evaporation rate of the aluminum molten pool significantly increases.When the tantalum content is 41.39%,the evaporation rate is approximately 7.5 times that of the tantalum-free molten pool.During the evaporation process,tantalum is mainly concentrated in the middle and lower part of the molten pool,and the metal vapor does not contain tantalum.In the molten pool,tantalum primarily exists in the form of Al_3Ta with the existence of a small amount of pure tantalum.

Ti₂AlNb alloy was prepared using elemental powders of Ti,Al and Nb through spark plasma sintering(SPS).The microstructure and phase composition of the alloy were characterized using scanning electron microscope(SEM)and X-ray diffractometer(XRD),and the room temperature mechanical properties of the Ti₂AlNb alloy were also tested.The results show that the Ti₂AlNb alloy prepared by spark plasma sintering has uniform grain distribution and superior room temperature mechanical properties,with a tensile strength of 254 MPa.Compared with traditional sintering methods,spark plasma sintering offers advantages such as rapid heating and high densification of sintered samples.

HfO₂thin film and graphene are the main materials used in the fabrication of graphene field-effect transistors.Employing plasma enhanced chemical vapor deposition(PECVD)for the in-situ growth of graphene on HfO₂substrate represents a highly promising method for graphene synthesis,which mitigates the impact of the graphene transfer process on graphene quality to consequently improve the performance of graphene field-effect transistors.HfO₂thin film samples with a thickness of 100 nm were deposited on heavily doped single-side polished silicon substrates using vacuum electron beam evaporation at temperatures of 50℃,150℃and 250℃.Subsequently,the HfO₂thin film with the best quality was used as the substrate for the growth of graphene.Graphene thin films were synthesized in-situ by PECVD at a tempe-rature of 600℃and CH_4 flow rate of 4 sccm with varying H₂flow rates(0 sccm,5 sccm,10 sccm,15 sccm and 20 sccm).The results indicate that the HfO₂thin film evaporated at 150℃exhibits the lowest roughness,smoothest surface,and optimal dielectric properties.Graphene thin films with few layers can be obtained at the H₂flow rate of 10 sccm with minimal defects,smooth surface,and good continuity.Analysis of the growth mechanism of graphene on the HfO₂substrate reveals that the low surface energy of HfO₂substrate hinders the adsorption of carbon species onto the substrate,making it challenging for graphene to grow.However,the appropriate involvement of H₂effectively reduces the activation energy for CH₄decomposition,facilitating CH_4 cleavage and favoring the growth of large-area continuous graphene thin films.

Through single factor experiment,the effects of different cutting parameters on the damage layer and work hardening layer of beryllium cutting surface were studied,and the deformation mode of beryllium cutting process was analyzed in combination with the chip and surface microstructure changes.The results show that within a certain range,the thickness of the surface damage layer and hardening layer is less affected by cutting speed,and shows the trend of increasing with the increase of cutting feed and depth.Du-ring the cutting process of beryllium,there is no severe plastic deformation.The work hardening caused by a large amount of shear slip reaches the material fracture strength locally and then brittle fracture occurs to result in extrusion chip.A very small amount of twin crystal appears on beryllium cutting surface,and the dislocation movement generated by the extrusion of the flank face is the main mode of plastic deformation.

The fine tungsten powder was dispersed by a ball mill,and the effects of different rotating speeds and times on the particle size and agglomerated particles of it were studied.After ball-milling,the tungsten powder was prepared into tungsten carbide powder and cemented carbides.Through the comparative analysis of alloy metallographic microstructure,the correlation between the ball-milling process of the fine tungsten powder and the grain coarsening of the alloy was found,providing a new solution to the grain coarsening of the alloy.The results show that the tungsten powder dispersed with the ball-milling process of 21 r/min and 80 min has the fewest agglomerated particles,and the WC particles of the cemented carbide produced by the prepared tungsten carbide powder are uniform without coarsening.

The WC-xTi(C,N)-8Co cemented carbides were prepared by adding Ti(C,N)nanopowder with a particle size of 0.2μm to coarse-grained WC-8Co cemented carbides using low pressure sintering.The phase composition and microstructure of the nano Ti(C,N)-added cemented carbide samples were studied by XRD,SEM and EDS.Additionally,the cobalt magnetism,coercive force,Rockwell hardness and bending strength of the cemented carbides were analyzed and discussed.The results show that the cemented carbides sintered with the addition of nano Ti(C,N)show a typical Ti(C,N)core-ring structure,which improves the hardness of the cemented carbides.However,the trace addition of Ti(C,N)results in a decrease in the mechanical properties of the cemented carbides.The best comprehensive mechanical properties of the cemented carbides are obtained when the addition amount reaches 5%.However,an addition amount exceeding 15%causes the occurance of decarburization phase in the matrix,significantly reducing the bending strength of the cemented carbides.

作为社会的宝贵财富与承载希望的下一代,未成年人的身心健康至关重要。近期发生的恶性校园霸凌事件再一次将大众的目光聚焦于未成年人的身心安全问题,为未成年人营造安全健康的成长环境刻不容缓。

A separate CeO₂phase appears in the oxidized material of CeFeB waste and changes its valence state during the sulfation roasting process,which differs from NdFeB waste.Therefore,this paper conducted a comparative analysis of the sulfation roasting process of the oxidized materials of these two wastes.The research results show that the highest sulfation rates of the oxidized materials of NdFeB and CeFeB wastes are 91.7%and 96.1%,respectively.The sulfation process of the former mainly occurs in the medium-temperature roasting stage,while that of the latter mainly occurs in the low-temperature infiltration stage with the generation of an intermediate Ce(SO₄)₂in the medium-temperature roasting stage.The final products of sulfation roasting for both are Fe₂O₃and RE₂(SO₄)₃.Their high-temperature roasted materials have an loose structure with uneven pore size,and most of the rare earth-rich phases are encapsulated by the non-rare earth phases.Apart from CeO₂,the roasting mechanism of the CeFeB waste is consistent with that of the NdFeB waste:rare earth oxides and Fe₂O₃reacts with sulfuric acid to generate water-soluble rare earth sulfates and Fe₂(SO₄)₃;Fe₂SO₄₃is decomposed into Fe₂O₃and SO₃at high temperature,and SO₃further reacts with unreacted rare earth oxides to generate rare earth sulfates.CeO₂reacts with sulfuric acid to form Ce(SO₄₂at first,which is then decomposed into Ce₂(SO₄)₃.The SO₃generated during the decomposition process further reacts with CeO₂to generate water-soluble Ce₂(SO₄)₃.