难熔金属（钨、铬）粉末的等离子球化处理及多孔材料制备

发布时间：2018-07-10 03:43

本文选题：等离子体 + 球形粉末　；参考：《合肥工业大学》2017年硕士论文

【摘要】：球形粉末具有良好的流动性、高松装密度等优异性能,是目前粉体材料领域的热门研究方向。本论文采用等离子体球化技术对工业钨粉和铬粉进行球化处理,重点探索等离子体球化处理工艺参数(送粉速率和载气流量)对粉末球化效果的影响规律,系统研究了球化处理后粉末的性能(如粒度分布、流动性和松装密度等)和产率。并结合放电等离子烧结技术(SPS),以球形钨粉和铬粉为原料制备了多孔材料,研究了球形粉末性能对多孔体微观组织、孔隙结构以及孔隙率的影响。同时对多孔钨基体进行浸盐处理制备了钡钨阴极,研究了多孔钨基体的组织结构对钡钨阴极电子发射性能的影响。利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、激光粒度分析仪和霍尔流速计等测试方法表征等离子体球化处理前后粉末的形貌、物相、粒径分布、流动性及松装密度等。结果表明采用等离子体球化处理技术可得到表面光滑、球形度好的单相球形钨粉和球形铬粉。当送粉速率和载气流量分别为2.4 g?min~(-1)和4.0 L?min~(-1)时,钨粉的球化率大于98%;原料钨粉团聚严重导致球形钨粉的粒径略有增大;球化处理后,钨粉的松装密度和流动性均得到显著改善,松装密度由3.6 g?cm-3提高至7.6 g?cm-3,粉末流动性由0提高至27.96 s?(50g)~(-1)。当送粉速率和载气流量分别为2.1 g?min~(-1)和3.5 L?min~(-1)时,铬粉的球化率大于98%;球形铬粉粒度均匀,分散度高;球化处理后,铬粉的松装密度由2.8 g?cm-3提高至5.1g?cm-3,粉末流动性由32.53 s?(50g)~(-1)提高至17.41 s?(50g)~(-1)。通过设计特定的烧结模具,采用放电等离子烧结(SPS)制备了名义孔隙率为20%的多孔钨和多孔铬基体;与原料粉末相比,采用球形粉末制备得到的多孔钨基体的孔隙更为规则,孔隙分布更加均匀,且闭孔率显著降低。采用球形钨粉制备得到的多孔钨基体钡钨阴极的饱和脉冲发射电流密度为11.2 A?cm-2,远大于相同测试条件下采用常规钨粉制备得到的钡钨阴极的8.7 A?cm-2;改善钨粉性能,优化多孔钨基体的微观组织(改善多孔钨基体的开孔率、连通孔结构以及孔隙分布等),可大幅度提高钡钨阴极的发射性能。
[Abstract]:Spherical powder with good fluidity, high density and other excellent properties is a hot research direction in the field of powder materials. In this paper, plasma spheroidizing technology was used to treat industrial tungsten and chromium powder, and the effect of plasma spheroidizing process parameters (powder feeding rate and carrier gas flow rate) on the spheroidizing effect of the powder was studied. The properties of spheroidized powders (such as particle size distribution, fluidity and loose density) and yield were systematically studied. The porous materials were prepared by spark plasma sintering (SPS). The effects of the properties of spherical powders on the microstructure, pore structure and porosity of porous materials were studied. At the same time, barium tungsten cathode was prepared by impregnation of porous tungsten matrix. The effect of the structure of porous tungsten matrix on the electron emission properties of barium tungsten cathode was studied. Scanning electron microscope (SEM) X-ray diffraction (XRD), laser particle size analyzer and Hall flow meter were used to characterize the morphology, phase, particle size distribution, fluidity and loose density of the powder before and after plasma spheroidization. The results show that the spherical tungsten powder and chromium powder with smooth surface and good sphericity can be obtained by plasma spheroidizing. When the feed rate and carrier gas flow rate are 2.4 g / min ~ (-1) and 4.0 L / min ~ (-1), respectively, the spheroidizing rate of tungsten powder is greater than 98, the particle size of spherical tungsten powder is slightly increased due to the agglomeration of raw tungsten powder, and the loose density and fluidity of tungsten powder are improved significantly after spheroidizing treatment. The loose density was increased from 3. 6 g?cm-3 to 7. 6 g / cm ~ (-3), and the fluidity of the powder was increased from 0 to 27. 96 s? (50 g) ~ (-1). When the feed rate and carrier gas flow rate were 2.1 g / min ~ (-1) and 3.5 L / min ~ (-1), respectively, the spheroidizing rate of chromium powder was greater than 98, the particle size of spherical chromium powder was uniform and the dispersion was high. After spheroidizing treatment, the loose density of chromium powder increased from 2.8 g?cm-3 to 5.1 g / cm ~ (-3), and the fluidity of chromium powder increased from 32.53 s? (50 g) ~ (-1) to 17.41 s? (50 g) ~ (-1). Porous tungsten and chromium matrix with nominal porosity of 20% were prepared by spark plasma sintering (SPS), and the porous tungsten matrix prepared by spherical powder was more regular than that of raw material powder. The pore distribution is more uniform, and the closed porosity decreases significantly. The saturated pulse emission current density of the porous tungsten matrix barium tungsten cathode prepared by spherical tungsten powder is 11.2 Au cm-2, which is much higher than that of the barium tungsten cathode prepared by conventional tungsten powder under the same test conditions. The emission properties of barium tungsten cathode can be greatly improved by optimizing the microstructure of porous tungsten matrix (improving the porosity of porous tungsten matrix, connected pore structure and pore distribution, etc.).
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG664;TB383.4

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