Bi_2Te_3纳米粉末的直流电弧等离子体合成

以单质Bi,Te粉末为原材料,采用直流电弧等离子体蒸发法制备了Bi2Te3纳米粉末。通过XRD,EDS,TEM和SAED分析方法对Bi2Te3粉末的物相结构、成分和形貌进行了表征。Bi2Te3纳米粉末的平均粒径约为35 nm,粉末呈不规则的多面体结构,还有一些薄片状和棒状的结构,这与Bi2Te3半导体化合物的高度各向异性是一致的。研究了电弧电流和氩气压力对合成Bi2Te3纳米粉末的粒径和产率的影响,随着电弧电流或氩气气压的增加,粉末的粒径和产率都逐渐增大,但产率的增加并不明显。     

直流等离子体法制备Cu纳米粉

本实验利用直流等离子体法制备了Cu纳米粉末,并系统研究了工艺参数对Cu纳米粉末粒子产率、粒径和粒径分布规律的影响。正交实验、扫描电子显微镜、产率及粒径分析结果表明:Cu纳米粉末粒子最佳制备工艺参数为电流(380±5) A、制粉室内N₂气体比例为(15±2)%、风机转速为2 400～2 500 r/min。在此工艺条件下获得的Cu纳米粉末粒子呈球形,Cu纳米粉末粒子粒径分布均匀,分布范围较窄,粒径约为100 nm。随着N₂气体比例增加,电流强度增大,Cu纳米粉末产率提高,但同时会导致Cu纳米粉末粒子平均直径增大、粒径分布变宽。然而,随着轴流风机转速的提高,Cu纳米粉末产率提高,并且Cu纳米粉末粒子平均直径减小、粒径分布变窄,这与较快的转速引起Cu棒表面原子蒸气浓度下降有关。     

不同粒径氧化铝粉末涂覆隔膜电化学性能研究

采用浸泡方法制备了表面涂覆不同粒径氧化铝粉末的电池隔膜,并在制备扣式电池基础上表征了电化学性能。结果显示,随着掺杂粉末粒径的增加,涂覆隔膜的电化学性能降低。选用平均粒径0.77μm、分布较窄的氧化铝粉末作为涂层掺杂物,能提高隔膜的性能,循环充放电30次后容量维持率为96.3%,高于未涂覆的基膜,同时伏安循环性、交流阻抗均优于未涂覆隔膜,说明通过在普通隔膜的表面涂覆亚微米级的氧化铝粉末能有效改善电池隔膜的电化学性能。     

纳米碲粉体的制备及表征

利用惰性气体保护蒸发-冷凝法制备了碲（Te）纳米粉体颗粒。通过热力学计算得到碲的蒸汽压随温度的变化关系。利用X射线衍射（XRD）、透射电子显微镜（TEM）、激光粒度仪观测了碲纳米颗粒的晶体结构、形貌,并研究了粉末粒径、分布及形貌与蒸发冷凝过程中气氛压力的关系。结果表明,随着气氛压力的增加,粉末粒径分布范围变窄,粉末粒度...     

一种金属纳米微粉制备装置的设计及实验

以自悬浮定向流技术为理论基础,研制了一种金属纳米微粉制备装置.该装置由高频电源、走丝部分、管路部分、颗粒分级收集部分等组成,可制备粒径范围为15～150 nm的金属或金属间化合物纳米微粉.粉末的基本结构为球形,粒径呈近似正态分布,具有良好的分散性,纯度高.通过实验研究了工艺参数对粒径大小分布的影响,结果表明气流流速、气流压强越大粒径越小,而走丝频率越快粒径越大.在原有装置的基础上,设计了开放式金属粉末制备装置,纳米粉末直接浸润在液体中,实现了粉末的原位封装,拓宽了其应用范围.     

真空气雾化法制备AlSi10Mg粉末参数优化及打印态组织性能研究

目的 探究利用真空气雾化法制备AlSi10Mg球形粉末过程中各参数对粉末质量的影响,以得到最佳的制粉工艺参数。以制备的粉末进行增材制造,研究块体组织及其力学性能。方法 针对制备的球形粉末,采用扫描电镜（SEM）观察粉末的球形度及其内部组织。通过分析球形粉末的平均粒径与粒度分布区间总结最优制粉参数。针对以球形粉末增材制造出的沉积态样品,采用X射线衍射仪（XRD）、扫描电镜（SEM）研究其微观组织形貌并通过拉伸试验研究其力学性能。结果 真空气雾化法制备出的粉末表面光洁且球形度良好,同时粉末平均粒径随雾化压力的增大呈现先减小后增大的趋势并在4.0 MPa时粒径最小,且与环孔喷嘴相比,环缝喷嘴制备出的粉末粒径更小。粉末内部组织由胞状晶与树枝晶构成。通过SLM制备的沉积态样品组织以沿沉积方向的枝晶为主,该样品的力学性能较优异,断裂方式主要为沿晶断裂。结论 在使用真空气雾化法制备增材制造用球形粉末时,应选择4.0 MPa的气雾化压力并选择环缝喷嘴,方能得到质量最佳的球形粉末。     

高频感应熔化金属丝气雾化制备球形钛粉

提出了新型低成本球形钛粉气雾化制备技术——高频感应熔化金属丝气体雾化技术(Wire induction heating-gas atomization,WIGA),研究了雾化气体压力、熔体温度、送料速度对粉末性能的影响。结果表明:所制钛粉末的形貌为球形,球形度较高,粉末表面存在少量"卫星球"颗粒,占比约为1%;提高雾化压力、熔体温度和降低送丝速度均使粉末平均粒径D50减小。实验所得最佳雾化参数为:雾化气体压力4.0 MPa,熔体温度2 000℃,送料速度0.8m/min,在此条件下得到的钛粉末平均粒径为41.8μm。     

B4C超细粉末的制备及烧结

采用气流粉碎对B4C粗粉（比表面积0.52m^2/g，中位粒径20.4μm)进行了一系列粉碎实验，研究了气流粉碎次数，成形压力和烧结温度对烧结密度的影响。结果表明，当粉碎次数达到3次后，可获得＜1μm的B4C超细粉末。经过4次气流粉碎的B4C超细粉末的比表面积为2.53m^2/g，中位粒径为0.56μm；该粉末分别于2200和2250℃无压烧结1h，其烧结密度分别达到理论密度的78．6％ 82．5％，平均晶粒尺寸分别为28和50μm，抗压强度分别为390和555MPa。     

水雾化法制备FeSiCr软磁合金粉末研究

采用水雾化法制备FeSiCr软磁合金粉末,系统研究了熔体温度、雾化压力及雾化水流量对合金粉末粉体性能的影响。利用激光粒度分析仪、扫描电子显微镜、氧氮分析仪和霍尔流量计等设备对粉末粒度、形貌、氧含量、松装密度及流动性进行测试、分析。研究结果表明:随着雾化压力和熔体温度的升高,粉末粒度逐渐变小;降低雾化水流量,制备的粉末形貌较为规则,粉末粒度减小、松装密度得到提高。最佳雾化工艺:雾化压力为50 MPa、熔体温度为1 750 ℃、水流量为15.24 L/min,制备的FeSiCr软磁合金粉末氧含量低,平均粒度小且形貌较规则。     

高压微波合成纳米TiO_2及其光催化性能

以TiCl4为钛源,利用微波加热在0.1~4.0MPa压力条件下制备了纳米TiO2粉末,研究了不同反应压力对TiO2物相成分,晶体结构及光催化活性的影响.结果表明:反应压力对纳米TiO2的晶相结构、微观形貌及光催化性能有较大的影响.在相对较低反应压力时,纳米TiO2产物以锐钛矿相为主,并有少量的板钛矿相存在,当压力达到4.0MPa时有大量的金红石相出现.TEM测试显示TiO2粉末的粒径在5~30nm范围内,且随着压力增大,晶粒尺寸增大,结晶性能增强.随制备压力的增大,TiO2粉末的光催化效率先升高而后单调性地降低,2.0MPa压力时光催化效率达到最高.     

Observation of particle behavior in copper powder compact during pulsed electric discharge

The behavior of spherical copper powder particles of uniform size (average diameter: 550 μm) in a powder compact was observed under an optical microscope during a single-pulse electric discharge of 500 ms duration. The morphologies of necks formed between powder particles were observed under a scanning electron microscope, and their diameters were measured. The results obtained are summarized as follows: pressure and pulsed current density determine whether or not a spark occurs. Spark is more likely to occur at interparticle contacts under low pressure and high current density. Where a spark occurs, particles are joined together by melting. Regardless of whether or not a spark is observed, necks are formed at points of contact between particles and neck diameter increases with pulsed current density. These results suggest that microscopic sparking, melting, and vaporization occur by means of extremely high temperature attained by local heat generation at the interparticle contacts in the initial stage of compaction.     

Low-pressure gas atomization of aluminum through a Venturi nozzle

A new concept of powder atomization based on the venturi phenomenon is presented in the current work. In the proposed method, the working gas speeds-up while flowing into the venturi nozzle. Under the low static pressure developing at the narrow part of the venturi, liquid metal is sucked and mixed perfectly with the gas. By controlling the operating parameters, metal powder of different sizes and shapes can be produced. Carbon dioxide and pure aluminum were mixed in the nozzle and the effect of different operating gas pressures on the produced particle size and shape were thoroughly investigated. Most of the particles were found to average to almost 150 μm, however, even sub-micron aluminum particles were produced at low mass fractions. With the increase of the gas pressure from 0.5 bar to 4 bar, finer aluminum particles are produced. One of the most attractive features of the proposed method is the low gas pressure required to cause melt atomization, which in certain cases may be up to 30 times lower compared to current industrial atomization methods.     

低压冷喷涂铝涂层微观结构与沉积特性研究

低压冷喷涂技术是一种不同于高压冷喷涂技术的新型喷涂工艺。本文以体积比为3:7的氧化铝粉末和铝粉的混合粉末为原料,以压缩空气为工作气体,利用低压冷喷涂设备在Q235钢基体上制备Al涂层,研究了温度、喷距、送粉速率和喷嘴横向移动速度等工艺参数对涂层沉积效率的影响。采用光学显微镜、扫描电镜,研究了涂层的微观结构和沉积特性。实验结果表明:在工作气体压力保持0.6 MPa不变的情况下,温度400℃、喷距25 mm、送粉速率为30—40 g/min、喷嘴横向移动速度4.0 m/min时,铝涂层沉积效率最佳;同时Al2O3陶瓷相的加入有利于涂层的沉积。     

Generating stationary electron beams by a forevacuum plasma source at pressures up to 100 Pa

It is shown that, as the gas pressure in a forevacuum plasma electron source increases, electric breakdown in the accelerating gap is caused by the reverse flow of ions from plasma that is generated by both the electron beam and high-voltage glow discharge (HGD). By modifying the electrode system geometry in the accelerating gap of the electron source, it is possible to provide for a two-to threefold decrease in the HGD current. This allows the upper pressure in the electron source to be increased up to about 100 Pa when air is used as the working gas and up to 160 Pa in the source filled with helium.     

The Shunting of Current and the Resultant Variation of Voltage in Channels of Plasmatrons with Self-Adjusting Length of Electric Arc

The characteristics of pulsation processes in dc plasmatrons with the cathode located in the channel center and the anode in the form of a cylindrical or a conical channel wall are investigated in plasmas of argon and nitrogen at atmospheric pressure. The fast Fourier transform of signals and their subsequent computer processing are used to obtain the dependences of the frequency of fluctuations of the arcing voltage on the working parameters of the plasmatron, namely, the electric arc current, the flow rate of plasma-forming gas, and the channel diameter. For plasmatrons with the self-adjusting length of the electric arc, analysis is performed of the mechanism of reclosing of the anode region of the arc, i.e., of the electric arc shunting associated with the stretching of the current filament by a flow of gas and with the electrodynamic interaction of different filament regions. A formula is derived which defines the dependence of the characteristic frequency of fluctuations of the arcing voltage on the external parameters of the problem, namely, the arc current, the flow rate of the working gas, and the characteristic channel diameter. It is demonstrated that the pattern of the dependence of the frequency of voltage fluctuations on the gas flow rate may vary with the values of the parameter of magnetohydrodynamic interaction. The formula generalizes the experimental results of numerous researchers obtained in a wide range of variation of the external parameters.     

Numerical investigation for nano-particle synthesis in an RF inductively coupled plasma

Since plasma is regarded as one of the multifunctional fluids which has high energy density, chemical reactivity, controllability by an external electromagnetic field and variable transport properties such as electrical conductivity, it is considerably effective for the synthesis of nano-particles. Since a radio frequency inductively coupled plasma (RF-ICP) has several advantages, the synthesis of ultrafine powders of metals and ceramics with high purity can be easily achieved by the steep temperature gradients at the tail. In the present study, it is clarified how the number density, diameter and specific surface of the produced nano metal-particles of Al, Ti, Au and Pt are influenced by the operating conditions such as the quenching gas flow rate and the powder feed rate of the RF-ICP reactor by numerical investigation. For all the metals, the increase in the quenching gas flow rate results in the increase in the particle number density, the decrease in the mean diameter and the increase in the specific surface. The increase in the powder feed rate causes the increase in the mean diameter but the decrease in the specific surface. The results of four metals are markedly different from each other due to their own material properties of saturation pressure and surface tension.     

Investigations on surface quality of WEDM-manufactured meso bevel and helical gears

This article presents investigations on and analysis of surface finish of meso bevel and helical gears made of stainless steel (SS 304) manufactured by wire electric discharge machining (WEDM) process using thin soft plain brass wire of 0.25?mm diameter. Effects of eight WEDM process parameters, namely, peak current, pulse-on time, pulse-off time, wire feed rate, wire tension, servo-gap voltage, dielectric pressure, and cutting speed on average and maximum surface roughness of the meso bevel and helical gears have been studied by conducting 31 experiments using one-factor-at-a-time approach to identify their optimum ranges/values for further experiments. Tooth profile, microstructure, microhardness, and topography of tooth flank surface have been studied for the best quality meso gears. Average and maximum surface roughness of tooth flank surfaces of meso bevel and helical gears increase with increase in peak current, servo-gap voltage, pulse-on time, wire feed rate, wire tension and cutting speed, and decrease with increase in pulse-off time while dielectric pressure does not significantly influence surface roughness. This work establishes that WEDM process can be an economic and sustainable manufacturing alternative for net-shaped meso-sized bevel and helical gears having better surface finish which will eliminate need of any subsequent finishing processes.     

正交试验设计优化等离子喷涂纳米Al2O3-13%TiO2涂层工艺参数

为了深入研究等离子喷涂纳米Al2O3-13%TiO2(质量分数)工艺参数与涂层性能之间的关系,采用正交试验设计法,针对等离子喷涂过程中喷涂距离、喷涂电流、主气压力及辅气压力等4个主要参数,选用L9(34)正交表,以涂层结合强度为指标开展制备工艺参数的优化。结果表明,影响涂层结合强度的因素主次顺序是喷涂电流、喷涂距离、主气压力、辅气压力;等离子喷涂纳米Al2O3-13%TiO2最佳工艺参数为:喷涂距离110mm,喷涂电流870A,主气压力0.31MPa,辅气压力0.97MPa,优化工艺喷涂的涂层结合强度达到31.5MPa。     

Shortwave krypton-bromine excimer low-pressure lamp

The emission characteristics are reported for a small short-wavelength (UV) lamp filled with a krypton-bromine mixture and pumped by longitudinal glow discharge at a 100-mm distance between electrodes in a quartz tube with an internal diameter of 14 mm. The emission spectrum is formed by the resonance atomic lines of bromine (163.3 and 157.6 nm) and the molecular lines of bromine (Br₂) and krypton bromide (KrBr). An increase in the partial pressure of bromine in the working mixture from 50 to 270 Pa is accompanied by a decrease in the intensity of emission lines due to atomic bromine and leads to the formation of VUV-UV continuum based on the molecular bands due to Br₂ and KrBr. The operation regime was optimized with respect to the glow discharge current and the gas mixture pressure and composition. The optimum partial pressure of krypton is within 500–800 Pa, and that of bromine vapor is within 100–250 Pa. The average total VUV-UV output radiation power reached 5 W at an efficiency of 8–10%.