Particle Size Distribution,Powder Agglomerates and Their Effects on Sinterability of Ultrafine Alumina Powders

An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.

Effect of Particle Size and Distribution of Rapidly Quenching NdFeB Magnetic Powder on Magnetic Properties of Polymer-Bonded NdFeB Permanent Magnet

The effect of particle size and distribution of rapidly quenching NdFeB magnetic powder on the magnetic properties of polymerbonded NdFeB permanent magnet was studied. The results show that the particle size and the distribution of rapidly quenching NdFeB magnetic powder have significant effects on the magnetic properties of polymerbonded NdFeB permanent magnet. As long as the size and the distribution of rapidly quenching NdFeB powder are within the right range, high magnetic properties of polymerbonded NdFeB permanent magnet can be obtained. This is mainly because the rapidly quenching NdFeB magnetic powder has high hardness and is scaleshaped. The larger the size of rapidly quenching NdFeB particles is, the more difficult it is to obtain high density of bonded NdFeB magnet. However the structure will be destroyed if the size is too small. It results in the deterioration of magnetic properties. The mechanism is also discussed.

Stability of the Dividing Distribution Function Method for ParticleSize Distribution Analysis in Small Angle X－Ray Scattering

The Dividing Distribution Function (DDF) method is one of the methods by which the particle size distribution of ultrafine powder can be evaluated from its small angle X-ray scattering data. In this paper, the stability of the solution obtained from DDF method has been investigated through optimizing the coefficient matrix, introducing a damping factor and a least square treatment. All calculations were accomplished with a microcomputer. It was shown that the average deviations of the size distribution obtained are not larger than the assigned random errors to the scattering intensities as long as the corresponding requirements are satisfied.

Effects of Particle Size and Content of Silicon Powder on Strength and Microstructure of Coked Al_2O_3-ZrO_2-C Refractories

Effects of particle size （A：d50 = 336. 9 μm, B：d50 =123.5μm, C： d50=19.5 μm, D： dso=2.21μm） and content （1 wt% , 3 wt% , 5 wt% , 7 wt% ） of silicon powder on cold crushing strength （CCS） , pore size distribution and microstructure of Al2O3 - ZrO2 - C refractories coked at high temperature had been investigated by means of mercury porosimeter, SEM, EDS, tic. The results indicated that particle size and content of silicon powder affected the cold crushing strength of coked specimens. It increased with the addition of silicon powder and its finer particle size. However, it decreased greatly when using too fine silicon powder. The particle size and content of silicon powder also impacted the phase evolution and microstructure of coked specimens, much more β-SiC whiskers constituted network structure and well distributed in specimens with reduction of their slenderness ratios when finer silicon powder was added, corresponding to that, the specimens＇ pore size distribution range became narrower with smaller pore diameter, but β-SiC whiskers were distributed sparsely and the specific pore volume of small pores increased when much finer powder was added. It was worthly mentioned that some nitride could form in specimens with addition of appropriate particle size and content of silicon powder.

Synthesis of nanocrystalline NiCrC alloy feedstock powders for thermal spraying by cryogenic ball milling

Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized using the cryogenic ball milling （cryomilling） method. The morphology, microstructure, size distribution, and phase transformation of the powders were characterized by scanning electron microscopy （SEM）, laser scattering for particle size analysis, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. After cryomilling for 20 h, the average grain size of the as-milled powders approached a constant value of 30 nm by XRD measurement. The average particle size slightly increased from 17.5 to 20.3 μm during the 20-h milling. About 90vol% of the powders satisfied the requirement for thermal spraying with the particle dimension of 10-50 μm, and most of the powders exhibited spherical morphology, which were expected to have good fluidity during thermal spraying. The Cr2O3 phase formed during the cryornilling process as revealed in the XRD spectra, which was expected to enhance the thermal stability of the as-milled powders during the followed thermal spraying or other heat treatment.

Effect of closed-couple gas atomization pressure on the performances of Al-20Sn-1Cu powders

Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron microscopy （SEM）, optical microscopy （OM）, and X-ray diffractometry （XRD）. The results show that the powders exhibit a bimodal size distribution and a higher gas pressure results in a broad size distribution. All particles in both cases are spherical or nearly spherical and satellites form on the surface of coarse particles. Dendritic and cellular structures coexist in the particle. With decreasing particle diameter, the secondary dendrite arm spacing （SDAS） decreases and the cooling rate increases. The particles processed under high gas atomization pressure （1.6 MPa） exhibit a lower SDAS value and a higher cooling rate than those of the same size under low gas atomization pressure （1.1 MPa）. The XRD results show that the Sn content increases with decreasing particle size.

Aspects of the Powder in Metal Additive Manufacturing: A Review

The most widely used metal additive manufacturing processes utilize powder that is spread or fed onto a building platform. Although there are reviews of the literature on some aspects of the powder, many aspects have been under-reviewed or unreviewed. The present work is a review of the literature on these aspects. Articles published in the open literature through the end of February 2022 were collected by consulting highly regarded relevant bibliographic databases, such as Google Scholar and Science Direct. The aspects reviewed were emerging methods of powder production, methods used to improve the quality of a powder after production by a well-established method, influence of variables of well-established powder production methods on powder properties, influence of powder production method on powder properties, and influence of powder reuse on properties of powders of a wide collection of alloys. One key finding was that with regard to powder reuse, the only consistent finding is that it leads to increase in the oxygen content of the powder. Another key finding was that the literature on the aspects of the literature reviewed herein contains many shortcomings and gaps, which suggest potential areas for future research, such as techniques for optimization of process variables for a given combination of metal powder and powder production method and development of methods for production of powders of new/emerging metallic materials.

Characterization of nanometer tungsten powders

Three types of tungsten powders were prepared by hydrogen reduction of three precursor powders at low temperature, which were used as samples, and were then characterized by Brunauer-Emmer-Teller （BET） method, scanning electron microscopy （SEM）, transmission electronic microscopy （TEM）, small angle X-ray scattering （SAXS）, and field-emission scanning election microscopy （FESEM） respectively. The results showed that although BET and SEM could not characterize the particle size of nanometer powders, they were important means of assistance to exclude non-nanometer powders. TEM and FESEM could directly measure the particle size of nanometer powders, but this needs a lot of time, to count the average particle size and particle size distribution. SAXS could not describe the state of agglomeration. By the combination of FESEM and SAXS, the particle size, particle size distribution, and particle shape of nanometer powders could be precisely characterized.

Preparation of CNT/AlS i10Mg composite powders by high-energy ball milling and their physical properties

This study investigated the effects of carbon nanotube （CNT） concentration on the micro-morphologies and laser absorption proper- ties of CNT/AlSi10Mg composite powders produced by high-energy ball milling. A scanning electron microscope, X-ray diffractometer, laser particle size analyzer, high-temperature synchronous thermal analyzer, and UV/VIS/NIR spectrophotometer were used for the analysis of micro- graphs, phases, granulometric parameters, thermal properties, and laser absorption properties of the composite powders, respectively. The results showed that the powders gradually changed from flake- to granule-like morphology and the average particle size sharply decreased with in- creases in milling rotational speed and milling time. Moreover, a uniform dispersion of CNTs in AlSi10Mg powders was achieved only for a CNT content of 1.5wt%. Laser absorption values of the composite powders were also observed to gradually increase with the increase of CNT concentration, and different spectra displayed characteristic absorption peaks at a wavelength of approximately 826 nm.

Research on the application of the wet scrubber on the BSSF slag processing system at Baosteel

Based on the analysis results of the dust size distribution of flue gas from Baosteel＇s short-flow （BSSF） slag processing system and the mechanism of the wet scrubber,a wet scrubber system was designed and installed in the No. 1 BSSF slag processing system at Baosteel. The results show that the dust removal efficiency of the previous system that had conventional water nozzles was only 69% with a liquid-gas ratio of 0.79 L/m^3 ,while the dust removal efficiency reached 94% when three sets of high-efficiency dual phase spray guns were installed inside both the flue and the chimney. For the latter system,the liquid-gas ratio was 0. 84 L/m^3 ,and the dust concentration in the cleaned emissions reduced to less than 40 mg/m^3.

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。

球磨法制备芡实超微粉及其理化功能性质分析

芡实淀粉属小颗粒淀粉,且以超聚合的复粒形式存在。为了解超微粉碎对淀粉复粒结构及其中功效组分溶出的影响,文中采用球磨法制备超微芡实粉,分析了不同球磨参数对芡实粉理化功能性质的影响。研究显示,芡实粉的适宜球磨参数为:转速200 r/min,m(用料量)∶m(研磨球)=1∶30,研磨球直径4 mm,研磨时间30 min。与对照相比,所得超微芡实粉中超细粉末(粒径0~1μm)占比达到85.04%,其中总黄酮溶出量增加不显著,但总酚溶出量有明显增加(P≤0.05)。所得超微芡实粉吸水性和吸油性显著提高,分别达到3.88、2.46 g/g,分别增加了3.26、1.34倍。X-衍射图谱和扫描电子显微镜照片显示,超微芡实粉中淀粉的复粒结构发生碎裂,淀粉颗粒完整性及其晶体结构也被严重破坏,印证了超微芡实粉理化功能性质改变的内在原因。研究结果表明,球磨处理不仅改善了芡实粉的理化功能性质,也有利于其中功效组分的溶出。

有机硅单体合成用复合铜粉催化剂的研究

采用硅粉与氯甲烷,于直管式固定搅拌床反应器中合成甲基氯硅烷,通过计算二甲基二氯硅烷(M2)的选择性和硅转化率,评价3种复合铜催化剂的催化性能。结果表明,自产复合铜粉C的催化性能相对较佳,采用复合铜粉C的体系在整个反应期间的M2选择性均值为91.89%,硅转化率为59.24%。复合铜粉C具有更薄、更细、比表面积更高、松装密度更低、粒度更细的特点,有利于其在甲基氯硅烷合成反应中与硅粉形成更多的活性中心。

气体温度对VIGA制备GH4169合金粉末的影响

研究采用真空感应气雾化(Vacuum Induction Gas Atomization,VIGA)技术制备GH4169合金粉末,系统探究气体温度对粉末特性的影响规律。结果表明,随着气体温度从100℃升高到600℃,粉末的粒度分布明显向左移动,D50由75μm减小到42μm。扫描电子显微镜(Scanning Electron Microscope,SEM)分析表明,较高气体温度有助于提高粉末的球形度,减少卫星粉的生成。X射线衍射(X-Ray Diffraction,XRD)分析揭示,气体温度对粉末的物相组成影响不大,但是较高温度下粉末具有更高的结晶度和更大的晶粒尺寸。此外,粉末的流动性随气体温度的升高而显著改善。

矿渣型泥石流形成条件分析及主要物源特征研究:以栾川县康山金矿区为例

栾川县曾多次暴发山洪、泥石流灾害,矿渣型泥石流隐患发育十分典型,矿渣型泥石流与自然泥石流最大的差异在于物源不同。以栾川县康山金矿区为研究对象,通过对地形地貌、气象水文和泥石流物源进行调查研究,总结分析了区内矿渣型泥石流形成条件,泥石流主要物源来自废石弃渣(包括废石渣场和尾矿库),其次是残坡积物、以往泥石流堆积物和沟道内人造耕地。通过实地调查、室内试验和原位试验,对区内废石弃渣、尾矿砂、残坡积土等主要泥石流物源的宏观特征、颗粒级配、渗透特性进行研究,研究结果表明:废石渣场属于砾类土,其不均匀系数C_(u)=35.87,曲率系数C_(c)=1.5,具有明显的颗粒粒径分层规律,级配良好;研究区废石渣场d≥2 mm的颗粒平均含量为76.68%,属于狭义泥石流类型;废石渣场的渗透系数平均值为0.069600 cm/s,是自然泥石流渗透系数(0.021800 cm/s)的3.2倍,是残坡积土渗透系数(0.017320 cm/s)的4倍,是尾矿砂渗透系数(0.001869 cm/s)的37倍;不同泥石流物源的渗透系数与其粗颗粒含量呈正相关关系。

基于CT扫描技术矿渣微粉改良黄土孔隙特性的试验研究

【目的】随着黄土地区基础设施的大力开发及减碳理念的不断深化,迫切需要使用环保材料解决黄土承载能力低、孔隙率大等问题。【方法】使用不同掺量矿渣微粉对黄土进行改良,并利用工业CT仪对矿渣微粉黄土进行微观试验,从孔隙分布、形态、大小等角度进行分析,研究矿渣微粉对黄土孔结构的影响,从而为黄土力学性能变化提供参考。【结果】结果显示:掺量为15%时,黄土孔隙分形维数最小值为0.65,孔隙丰度主要集中在0~2之间,孔隙结构较为简单;掺量为5%、10%、15%、20%的矿渣微粉黄土孔隙率较素黄土分别下降14.69%、34.18%、73.42%、45.51%。【结论】结果表明:矿渣微粉掺入可有效改变黄土孔隙大小、分布、形态,使黄土孔隙结构趋于简单,利于黄土力学性能提升。适量矿渣微粉可有效降低孔隙直径,同时孔隙角度分布趋于均匀。

不同雾化压力下GH3536合金粉末制备和气雾化过程模拟

使用真空感应熔炼气体雾化方法,在不同雾化压力(7、8、9MPa)下制备了球形GH3536合金粉末。通过使用多相流模型和离散相模型对喷嘴下方区域进行了数值模拟,再现了不同雾化气压下的一次雾化和二次雾化过程。实验和模拟的结果表明:回流区的气体速度和滞止压力随雾化气压的提高而增加,雾化气压的增加使粉末粒度不断减小,模拟结果与实验结果吻合,验证了雾化模型的可靠性。提高雾化气压可提高细粉收得率,但颗粒尺寸的减小和颗粒形貌的改变会对粉末的流动性能造成直接影响,在雾化压力8MPa下制备的粉末具有最佳的流动性和松装密度,分别为14.34(s·50g^(-1))和4.728g·cm^(-3)。

合成聚晶金刚石过程的颗粒冷压破碎

为提升聚晶金刚石的致密度,研究在初装、冷等静压后以及六面顶压机内等不同压力条件下,不同金刚石粉体粒径和配比在加压前后的粉体密度、粒径分布及重排微观结构变化,发现金刚石粉体的变化规律。合成过程包括初装料的无序排列到220 MPa等静压后的细颗粒填充孔隙与重排,再到超高压力下大颗粒被挤压破碎,孔隙被逐步填充。由于细颗粒的缓冲效应,大颗粒G_(20~30)在双粒径配方G_(2~4)和G_(20~30)中比在单一粒径G_(20~30)配方中破碎更少,更有利于提升金刚石粉体堆积密度。

婴幼儿配方奶粉粉体流动性研究

流动性是婴幼儿配方奶粉粉体特性的重要指标。为探究婴幼儿配方奶粉的粉体粒度分布、水分与流动性的相互关系,本研究以国内外14种不同品牌婴幼儿配方奶粉为研究对象,以压缩度、Carr指数为流动性评价指标,建立粉体粒度分布与压缩度的相互关系及Carr指数的多元线性回归模型。结果表明,国产婴幼儿配方奶粉的压缩度显著高于进口奶粉,而Carr指数低于进口奶粉,细粉颗粒(≤100μm)的颗粒体积占比显著高于进口奶粉,而粗粉颗粒(≥200μm)的颗粒体积占比显著低于进口奶粉。细粉颗粒(0~30、0~50、0~100μm)的颗粒体积占比与压缩度呈极显著正相关(P<0.01),与Carr指数呈极显著负相关(P<0.01);粗粉颗粒(200~300、300~500、>500μm)的颗粒体积占比与压缩度呈极显著负相关(P<0.01),与Carr指数呈极显著正相关(P<0.01)。通过回归分析得到粒度分布0~30、0~50、0~100、200~300、300~500、>500μm的颗粒体积占比分别为0.78%~1.64%、2.24%~4.81%、8.64%~16.45%、24.21%~27.64%、11.10%~16.26%、5.36%~6.65%,粒度分布宽度(径距)和均匀性(一致性)分别为1.45~1.71和0.45~0.52时,婴幼儿配方奶粉拥有较好的压缩度(范围为15%~20%)。基于最小二乘估计法建立粒度分布、水分活度及水分含量与Carr指数的多元线性回归模型,可用于改善和预测婴幼儿配方奶粉的流动性。本研究为婴幼儿配方奶粉生产工艺的改进提供了参考。

碳化条件下电石渣-氧化镁固化淤泥土的试验研究

软土是一种分布广泛的工程性质差的土类,使用水泥对其进行固化处理已不再符合当今社会发展要求。采用电石渣-活性MgO复合固化剂及CO_(2)气体对淤泥质土进行碳化固化处理,设置固化剂掺量(单掺电石渣)及固化剂掺和比(电石渣:MgO)两组变量,从物理力学和化学等方面分析碳化固化土的工程性质。结果表明:(1)当单掺电石渣含量为20%时,碳化土体强度最高;掺入混合固化剂时,碳化后试样强度随电石渣掺入比的升高呈先上升后下降趋势;(2)碳化后试样密度较碳化前有显著增长,单掺电石渣时,碳化后试样密度随电石渣掺量的增加而增加;掺入混合固化剂时,碳化试样密度的变化规律与强度变化一致;(3)碳化土的pH较碳化前有显著下降,单掺电石渣时,碳化土的pH随电石渣掺量的增加而增加,掺入电石渣∶MgO=4∶3的混合固化剂时,碳化土pH明显减小;(4)碳化土样的粗颗粒(>75μm)含量显著提高,碳化土样的粗颗粒比例随固化剂掺量增加而降低,但掺入混合固化剂时,碳化土样的粗颗粒比例与电石渣和MgO比例无显著相关性。研究结果有利于提高电石渣固废的资源化利用,拓展电石渣-MgO碳化固化技术在软土处理中的工程应用。