Preparation of ultramicro molybdenum carbide powders and study on wear properties of their coating

Using specially designed mechanochemical ball-mill equipment, ultramicro molybdenum carbide （MoC） powders were prepared by high-energy ball milling from pure molybdenum powders in civil coal gas atmosphere at room temperature. The structure and the particle size of the powders were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and Transmission Electron micros-copy （TEM）. The results showed that after milling for 30 h, the MoC powders of hexagonal structure were obtained, and their average parti-cle size was around 100 nm. It was found that chemisorption of CO in coal gas onto the fresh molybdenum surfaces created by milling was the predominant processes during the solid-gas reaction, and the energy input due to the introduction of highly dense grain boundaries and lattice defects provided the activation energy for the transition from Mo-C chemisorption to MoC. A coating was formed on the 40Cr steel base using plasma spray by mixing Ni60 alloy powders and ultramicro MoC powders of 5 wt.%, 10 wt.%, and 15 wt.%, respectively. Coat-ing abrasion tests under the condition of dry-grinding, 2 h wear time, and 300 N load showed that the wear resistance property of the coating added with ultramicro MoC powders could be improved greatly, and the wear resistance property of the coating increased with the increase of ultramicro MoC content. The wear mechanisms of ultramicro MoC coating is mainly plough wear and flaking wear assisted. In the abra-sion process, the evenly distributed ultramicro MoC particles play a dispersion strengthening and self-lubricating role in the coating.

Preparation and characterization of molybdenum powders with copper coating by the electroless plating technique

Molybdenum powders with a diameter of approximately 3 μn were coated with copper using the electroless plating technique in the pH 12.5-13 and temperature range of 55-75℃. The optimization of the electroless copper bath was evaluated through the combination of process parameters like pH and temperature. The optimized values ofpH and temperature were found to be 12.5 and 60℃, respectively, which attributes to the bright maroon color of the coating with an increase in weight of 46%. The uncoated and coated powders were subjected to microstructural studies using scanning electron microscope （SEM） and the phases were analyzed using X-my diffrction （XRD）. An attempt was made to understand the growth mechanism of the coating. The diffusion-shrinkage autocatalytic model was suggested for copper growth on the molybdenum surface.

Spheroidization of molybdenum powder by radio frequency thermal plasma

To control the morphology and particle size of dense spherical molybdenum powder prepared by radio frequency（RF） plasma from irregular molybdenum powder as a precursor, plasma process parameters were optimized in this paper. The effects of the carrier gas flow rate and molybdenum powder feeding rate on the shape and size of the final products were studied. The molybdenum powder morphology was examined using high-resolution scanning electron microscopy. The powder phases were analyzed by X-ray diffraction. The tap density and apparent density of the molybdenum powder were investigated using a Hall flow meter and a Scott volumeter. The optimal process parameters for the spherical molybdenum powder preparation are 50 g/min powder feeding rate and 0.6 m^3/h carrier gas rate. In addition, pure spherical molybdenum powder can be obtained from irregular powder, and the tap density is enhanced after plasma processing. The average size is reduced from 72 to 62 μm, and the tap density is increased from 2.7 to 6.2 g/cm^3. Therefore, RF plasma is a promising method for the preparation of high-density and high-purity spherical powders.

Developing polydopamine modified molybdenum disulfide/epoxy resin powder coatings with enhanced anticorrosion performance and wear resistance on magnesium lithium alloys

Epoxy resin powder coating has been successfully applied on the corrosion protection of magnesium lithium alloys.However,poor wear resistance and microcracks formed during the solidification have limited it extensive application.There are limited approaches to exploit such anti-corrosion and mechanical properties of magnesium lithium alloys.Herein,the epoxy resin powder coating with polydopamine modified molybdenum disulfide(MoS_(2)@PDA-EP powder coating with 0,0.1,0.2,0.5,1.0 wt.%loading)was well prepared by melt extrusion to investigate its anticorrosion performance and wear resistance.The results revealed that the addition of MoS_(2)@PDA enhanced the adhesion strength between coatings and alloys,wear resistance and corrosion protection of the powder coatings.Among them,the optimum was obtained by 0.2 wt.%MoS_(2)@PDA-EP powder coating which could be attributed to well dispersion and efficient adhesion with coating matrix.To conclude,MoS_(2)@PDA-EP powder coating is meaningfully beneficial for the anticorrosive and wear performance improvement of magnesium lithium alloys.

Ultramicro molybdenum nitride powder prepared using high-energy mechanochemical method

Using the specially designed mechanochemical ball-mill equipment, ultramicro molybdenum nitride powders were prepared from pure molybdenum powders in ammonia atmosphere at room temperature by high-energy ball milling. The structure and the particle size of the powders were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results show that the mass ratio of grinding media to powder was 8：1, after milling for 30 h the Mo2N of fcc structure was obtained, and the average particle size of the powders was around 100 nm. It is found that the chemisorption of ammonia onto the fresh molybdenum surfaces created by milling was the predominant process during solid-gas reaction, and the energy input due to introduction of highly dense grain boundaries and lattice defects offered the activation energy for the transition from Mo-N chemisorption to molybdenum nitride. In addition, the change of Mo electronic undersaturation induced by the grain refining accelerated the bonding between Mo and N. The mechanism model of whole nitriding reaction was given, During the high-energy ball milling processing, the rotational speed of milling played a critical role in determining the overall reaction speed.

Selective laser sintering mechanism of polymer-coated molybdenum powder

A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.

Numerical simulation of temperature field during selective laser sintering of polymer-coated molybdenum powder

The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the temperature field during length-alterable line-scanning and laser sintering of polymer-coated molybdenum powder was presented. Finite element method (FEM) was used to simulate the temperature field during laser sintering process. In order to verify the simulated results, a measuring system was developed to study the laser sintering temperature field. Infrared meter was introduced to measure the surface temperature of sintering powder; the temperature of its inside part was measured by thermocouple. The measured results were compared with the numerical simulation results; the conformity between them is good and the relative error is less than 5%.

Effect of La_2O_3 nanoparticles on properties of molybdenum powder

The properties of La 2O 3 doped molybdenum powder were studied. The La 2O 3 nanoparticles on the surface of molybdenum powder which is produced by the reduction of La(NO 3) 3 doped MoO 2 in hydrogen decrease the intensity of feature energy loss peak of molybdenum substrate; but increase that of peak of Mo?3d. The surface of molybdenum powder exposed to the atmosphere can be reduced because the surface is mainly covered with La 2O 3 nanoparticles. As a result, the capability of anti oxidation of molybdenum is improved.

Properties, Application and Synthesis Methods of Nano-Molybdenum Powder

Nano molybdenum powder has been applied in many industrial fields in forms of lubricant additives, metallurgical additives, powder sintering additives, and one of raw materials of electrical components, cleaner and smoke suppressor. The processes, mechanisms and prospects of its synthesis methods are comprehensively analysized, including plasma physical vapor deposition technology (PPVD), reduction of MoCl4 vapor, activated reduction technology, electro-explosion of molybdenum wire (Elex process), pulsed wire discharge technology, electron beam irradiating method, hybrid plasma process, vapor phase reduction of MoO3, and microwave plasma chemical vapor deposition (MPCVD), etc.

Molybdenum Carbide Nano-Powder for Production of Mo-99 Radionuclides

At present, there are two ways to produce 99Mo in a reactor: 1) fission process—from U fission product by reaction 235U (n, f) 99Mo and 2) activation process—by radiation capture reaction 98Mo (n, γ) 99Mo. This paper presents the results of experiments performed with molybdenum carbide nano-powder to produce 99Mo. These results show the implementation of the above idea in practice.

钼尾矿粉作为水泥基材料掺合料的适用性研究

为了解决钼尾矿资源化利用的问题,以黑龙江伊春鹿鸣矿业的钼尾矿为原材料制备了磨细钼尾矿粉。通过标准稠度用水量、凝结时间、流动性、强度、活性指数、微观结构及水化产物等性能指标,研究了钼尾矿粉作为掺合料对水泥基材料工作性能、力学强度和微观结构的影响。研究结果表明:钼尾矿粉的掺入使水泥的标准稠度用水量增大了3.2%,初凝时间和终凝时间分别延长了75%和93%;且钼尾矿粉的掺入降低了砂浆流动度,增大了砂浆需水量比,降低了砂浆60 min流动度经时变化;随着钼尾矿粉取代率增加,砂浆的抗折强度、抗压强度、活性指数均逐渐降低,但砂浆7 d、28 d活性指数均大于60%;当钼尾矿粉取代率为30%时,净浆微观结构存在较少孔隙,但内部结构较为致密,且净浆中除钙矾石、氢氧化钙等水化产物,还含有SiO_(2)、长石、云母等钼尾矿粉中矿物。实验结果可为钼尾矿作为水泥基材料掺合料提供基础性实验数据。

高纯钼粉的制备技术及研究进展

随着电子行业的精细化发展,高纯钼因其薄膜应力小、高温稳定性好,导电性能良好,比阻抗低广泛应用于电子行业。本文系统概述了高纯钼粉的制备技术,包括高纯钼原料(钼酸铵、MoO_(3)、MoCl_(5)、Mo(CO)_(6)、MoS_(3)等)清洁化还原分解技术和普通钼粉电子束熔炼及等离子球化提纯技术,重点讨论了沉淀法、溶剂萃取法、离子交换法、结晶法等提高钼酸铵纯度的方法,指出了不同提纯方法存在的优势与不足,并就高纯钼粉制备技术及应用前景进行了总结与讨论。

钼粉粒度与比表面积的关系

对钼粉的费氏粒度、粒度分布、颗粒尺寸、微观形貌和比表面积进行测量,并结合理论计算,研究了钼粉的粒度与比表面积之间的关系。结果表明:钼粉的比表面积与平均粒度成反比例函数关系,颗粒尺寸与实测比表面积规律大致符合理论计算的趋势;当钼粉颗粒形状为球形时,颗粒尺寸越均匀、团聚程度越低,实测的比表面积结果越接近理论计算的结果。

激光粉末床熔融纯钼组织及性能研究

钼作为一种难熔金属,由于其具有良好的高温力学性能和低膨胀系数而被广泛应用于核工业及航空航天。使用激光粉末床熔融(LPBF)制备的纯钼有着显著的设计优势和工业生产效率。为了提高LPBF生产效率,通过工艺优化,获得了30μm层厚选区激光熔化技术的最优工艺参数,制备出致密度为99.2%的无裂纹纯钼样品。经过XRD和EBSD表征发现,不同参数下纯钼样品均存在择优取向以及不同程度的晶格畸变,样品侧面织构强度大于底面。最优样品硬度为206HV,单向压缩强度和伸长率分别为566MPa和20.7%。该研究为LPBF制备30μm层厚的无裂纹且性能优异的纯钼构件奠定了基础。

Rapid synthesis of MoSi_2-Si_3N_4 nanocomposite via reaction milling of Si and Mo powder mixture

The nanocomposite of MoSi2-SiaN4 （molybdenum disilicide-silicon nitride） was synthesized by reaction milling of the Mo and Si powder mixture. Changing the processing parameters led to the formation of different products such as a- and B-MoSi2, SiaN4, Mo2N, and M05Si3 at various milling times. A thermodynamic appraisal showed that the milling of Moa2Siss powder mixture was associated with highly exothermic mechanically induced self-sustaining reaction （MSR） between Mo and Si. The MSR took place around 5 h of milling led to the formation of a-MoSi2 and the reaction between Si and N2 to produce Si3N4 under a nitrogen pressure of 1 MPa. By increasing the nitrogen pressure to 5 MPa, more heat is released, resulting in the dissociation of Si3N4 and the transformation of a-MoSi2 to β-MoSi2. Heat treatment was also performed on the milled samples and led to the formation of Mo2N and the transformation of a-MoSi2 to β-MoSi2 at the milling times of 10 and 40 h, respectively.

Investigation on laser cladding of MoSi_2 powder on steel

The feasibility of the fabrication of coatings for elevated-temperature structural applications by laser cladding MoSi2 pow- der on steel was investigated. A dense and crack-free fine coating, well-bonded with the substrate has been obtained by this technique This coating consists of FeMoSi, Fe2Si and a small amount of MosSi3 due to dilution of the substrate in the coating. The microstructure of the coating is characterized of typical fine dendrites, The dendrites are composed of FeMoSi primary phase, and the interdendritic areas are two eutectic phases of FeMoSi and Fe2Si. The hardness of the coating reaches 845 Hv0.5, 3.7 times larger than that of the steel substrate （180 Hv05）.

PREPARATION AND PROPERTIES OF THE MICRO-POWDER PHASE AND A NEW PHASE OF AMMONIUM TETRAMOLYBDATES

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Research Progress in Production Process of Molybdenum Disilicide Based Heating Elements in China

The molybdenum disilicide （MoSi2 ） based heating element is more and more important in modern industries relating to thermal treatment, melting and sintering due to its high working temperature. In China, the consumption of the MoSi2 heating element continues to increase with development and upgrading of industries. However, the MoSi2 heating element .from local manufacturers still has poor quality and thus results in waste of precious molybdenum resource. In this review, the recent research results of production process of MoSi2 heating elements were briefly summarized. The purity and particle size distribution of starting MoSi2 powder as well as the mixing and sintering processes were identified as major impact fators on the performance of MoSi2 heating elements. This review points out the improving direction for local MoSi2 heating elements.

钼合金粉末冶金研究进展

钼及其合金具有优异的高温力学性能,被广泛应用于冶金、机械、化工、航空和核工业等领域。粉末冶金是钼合金的主要制备方法。通过固溶强化、第二相强化、细晶强化等多种强化手段可以提高钼合金的力学性能,从而拓宽钼合金的应用范围。本文介绍了粉末冶金制备钼合金的研究进展,包括粉体制备方法、压制工艺及坯体烧结工艺等,讨论了钼合金的强韧化方法及其机理,并展望了粉末冶金法制备钼合金的发展方向,以期对钼合金的设计和制备提供一些思路。

Synthesis of VIB Group Metals Silicides Dispersed Powders by Electrolysis of Halide-Oxide Melts

Study of electrochemical behavior of chromium （molybdenum, tungsten） and silicon containing melts allowed defining conditions for synthesis of silicides of chromium, molybdenum and tungsten in the form of fine powders by electrolysis of halide-oxide melts. Sequence of stages of electrosynthesis of silicides of molybdenum and tungsten was found as follows： deposition of more electroposifve metal （molybdenum or tungsten）, deposition of the second component （silicon） on the surface of metal deposited previously, and reaction diffusion of silicon into the deep of the metal-salt ＂pear＂ with the formation of silicide phases of different compositions up to the higher silicides. In contrast, during the electrodeposition of chromium silicides, one of the components （chromium） is deposited not in elemental form, but in oxide form, and the other （silicon） acts as a reducing agent for this oxide to form binary compounds. Duration of the synthesis first stage （deposition of refractory metal or of its oxide） depends on the refractory metal compound content in the system and on the cathode current density. Synthesis of silicides is possible due to retention of powders of molybdenum （tungsten） or chromium oxide at the cathode without scaling. Optimal values of concentrations ratio, current density, temperature, and duration of electrosynthesis were found. Phase composition of products were obtained, as well as their chemical and thermal stability, were studied.