对供给态和研磨态超细钨粉的颗粒粒度进行了表征. 将供给态粉和研磨态粉由激光衍射法、 FSSS法和BET法测量出颗粒粒度. 结果表明: 利用激光衍射法和 FSS S法所测量出来的供给态粉和研磨态粉的粒度结果是错误的, 这是因为测量系统的缺陷和测量原理的不合适导致的. 可以使用吸附等温线来获得表面粗糙度的分数维维数 D 和微孔的表面积 S t, 且用 D 和 S t来修正 d BET的计算公式. 使用修正公式得到的4种粉末的平均粒度值与扫描电镜的观测值相一致.
The processes of directly recycling high density tungsten alloy by oxidation reduction technique were investigated. The particle size of recycled powder is fine, and the shape of powder particle is regular when the final reduction temperature is 850?℃, in which the average size of the tungsten alloy particles reduced is about 1.5?μm. The average size of the alloy particles increase to 6?μm and 9?μm when increasing the reduction temperature to 900?℃ and 950?℃, respectively. However, if the reduction temperature is higher than 900?℃, the surface feature of powder is complicated. Increasing reduction temperature from 900?℃ to 950?℃, the content of oxygen of recycled powder decreases from 0.231?4% to 0.170?0%, and powder particles grow slightly. It has been also found that the chemical composition of the recycled alloy powder is the same as the initial powder.
Liu Fengxiao;Li Yong;Huang Baiyun;Zhou Kechao;He Yuehui
Transactions of Nonferrous Metals Society of China,2005年15(1):97-102 ISSN：1003-6326
[Liu, Y; He Yuehui; Zhou Kechao; Huang Baiyun; Liu Fengxiao] Cent S Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China.
[Liu, FX] Cent S Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China.
FeAl/TiC composites;TiC content;binder composition;Ni alloying;densification process
FeAl/TiC composites were fabricated by reactive hot pressing blended elemental powders. The effects of TiC content, composition of the binder phase and Ni alloying on the densification process and mechanical properties of the composites were studied. The results show that the densities of the composites decrease with the increase of TiC content. Closely related with their porosities and flaw densities, the hardness and bend strength of the composites show peak values with the increase of TiC content. Higher content of Al in the binder phase was beneficial to densification, however it deteriorates the mechanical properties of the composites. The addition of Ni significantly improves the densities of the composites by enhancing matter transfer in the binder phase. By alloying with Ni, the mechanical properties of the composites are greatly improved due to the increase of the density, together with solid solution-strengthening the binder phase and promoting ductile fracture of FeAl.
By a polarized light optical microscopy with a hot stage, liquid-phase nuclear magnetic resonance (13)C-NMR and (1)H-NMR, X-ray diffractometry and scanning electron microscopy (SEM), the factors that affect the formation of mesophase in C/C composites, such as pressure, quinoline insolubles (QI) and heterocylic compounds, were analyzed. Further, the graphitizability of the resultant carbon was discussed. The results indicate that to some degree, QI contents accelerate the formation of mesophase at atmospheric pressure; while at high pressure, the coalescence and growth of mesophase spherules are impeded and the resultant coke produced from higher QI content pitch is harder to be graphitized. This is in agreement with the transfer of microstructure from domain anisotropy to fine-grained mosaics.
injection molding;hot runner;drag material change process;mold design
Quick material change is often encountered for the different colors or kinds of polymer in hot runner injecting molding process. Time-costing and incompleteness of material change process often affects the quality and productivity of products. In the practical production, multi-injection or white material as the transition material is often adopted for quick material change. Based on the rheological behavior of the new and the previous plastic melt, the researches on the related problems were carried out. The concept of drag material change was originally presented. The physical and mathematical model on the simultaneous flow process of the new and the previous plastic melt in hot runner were built up, which can well explain the influence of the injection speed, pressure, viscosity difference, temperature and mold structure on the drag material change efficiency. When temperature in different position in the mold was increased and adjusted, the viscosity difference between the two kinds of melt can be controlled. Therefore the material change ability can be greatly improved during the whole material change process, getting rid of more and more difficult changing in the late stage.