本文選題：等離子體 + 球形粉末　； 參考：《合肥工業(yè)大學》2017年碩士論文

【摘要】：球形粉末具有良好的流動性、高松裝密度等優(yōu)異性能,是目前粉體材料領(lǐng)域的熱門研究方向。本論文采用等離子體球化技術(shù)對工業(yè)鎢粉和鉻粉進行球化處理,重點探索等離子體球化處理工藝參數(shù)(送粉速率和載氣流量)對粉末球化效果的影響規(guī)律,系統(tǒng)研究了球化處理后粉末的性能(如粒度分布、流動性和松裝密度等)和產(chǎn)率。并結(jié)合放電等離子燒結(jié)技術(shù)(SPS),以球形鎢粉和鉻粉為原料制備了多孔材料,研究了球形粉末性能對多孔體微觀組織、孔隙結(jié)構(gòu)以及孔隙率的影響。同時對多孔鎢基體進行浸鹽處理制備了鋇鎢陰極,研究了多孔鎢基體的組織結(jié)構(gòu)對鋇鎢陰極電子發(fā)射性能的影響。利用掃描電子顯微鏡(SEM)、X射線衍射儀(XRD)、激光粒度分析儀和霍爾流速計等測試方法表征等離子體球化處理前后粉末的形貌、物相、粒徑分布、流動性及松裝密度等。結(jié)果表明采用等離子體球化處理技術(shù)可得到表面光滑、球形度好的單相球形鎢粉和球形鉻粉。當送粉速率和載氣流量分別為2.4 g?min~(-1)和4.0 L?min~(-1)時,鎢粉的球化率大于98%;原料鎢粉團聚嚴重導致球形鎢粉的粒徑略有增大;球化處理后,鎢粉的松裝密度和流動性均得到顯著改善,松裝密度由3.6 g?cm-3提高至7.6 g?cm-3,粉末流動性由0提高至27.96 s?(50g)~(-1)。當送粉速率和載氣流量分別為2.1 g?min~(-1)和3.5 L?min~(-1)時,鉻粉的球化率大于98%;球形鉻粉粒度均勻,分散度高;球化處理后,鉻粉的松裝密度由2.8 g?cm-3提高至5.1g?cm-3,粉末流動性由32.53 s?(50g)~(-1)提高至17.41 s?(50g)~(-1)。通過設(shè)計特定的燒結(jié)模具,采用放電等離子燒結(jié)(SPS)制備了名義孔隙率為20%的多孔鎢和多孔鉻基體;與原料粉末相比,采用球形粉末制備得到的多孔鎢基體的孔隙更為規(guī)則,孔隙分布更加均勻,且閉孔率顯著降低。采用球形鎢粉制備得到的多孔鎢基體鋇鎢陰極的飽和脈沖發(fā)射電流密度為11.2 A?cm-2,遠大于相同測試條件下采用常規(guī)鎢粉制備得到的鋇鎢陰極的8.7 A?cm-2;改善鎢粉性能,優(yōu)化多孔鎢基體的微觀組織(改善多孔鎢基體的開孔率、連通孔結(jié)構(gòu)以及孔隙分布等),可大幅度提高鋇鎢陰極的發(fā)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.).
【學位授予單位】：合肥工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG664;TB383.4

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