Influence of melt superheat on breakup process of close-coupled gas atomization

In close-coupled gas atomization（CCGA）, the influences of melt superheat on breakup process are fundamental to obtain desired or finer powder. Based on a series of Cu atomization experiment under different superheating conditions, the influences of melt superheat on breakup process were studied. Experimental results indicate that as the melt superheat is increased to 150, 200, 250 and 300 K, the mean particle size （D50） decreases consequently to 34.9, 32.3, 30.9 and 19.7 μm. Theoretical analysis reveals that the primary breakup and secondary breakup processes are close coupled, and the melt superheat radically influences the melt properties, and plays a crucial role on governing the filming process of primary breakup and the atomization modes of secondary breakup. There exists a strong nonlinear decrease of contact angle of melt to nozzle orifice wall when the superheat is increased fi＇om 250 K to 300 K, leading to a marked fall of the film thickness formed in primary breakup, and D50 of copper powders is therefore sharply reduced. However, the log-normal distribution feature of particle size has not been substantially improved.     

莫来石材料的研究现状及其应用

较详细地介绍了莫来石的性能、生产、研究现状和用途。尤其对多元复合莫来石韧性陶瓷及莫来石超细粉末的制备进行了评述,同时展望了莫来石作为高级陶瓷材料的发展前景。     

Rolling contact fatigue behavior of sintered and hardened steels

Powder-metal-processed bearings and gears are finding increasing application because of their economical and technical advantages. The residual pores from the sintering operatives act as lubricant pockets and dampen sound and vibration. However, porosity also decreases the mechanical strength and reduces the life of components fabricated by powder processing relative to similar wrought components. The rolling contact fatigue behavior of sintered and heat treated steel rollers was investigated using a fatigue test machine designed and fabricated for that purpose. The powder-metal-processed and the wrought steel rollers that were tested had similar composition and hardness and were mated against wrought steel rollers of high hardness. The contact stress versus number of cycles to failure data showed that the wrought steel had a very high endurance limit under rolling contact fatigue compared to the sintered steels investigated. Rolling contact fatigue behavior was found to depend on the porosity present in the material. Large surface peeling failures and pitting type fatigue failures were observed in the sintered and hardened steels, while only pitting type failures were observed in the wrought steels     

钼还原过程相变化研究

采用钼酸铵直接氢还原及钼酸铵先焙解然后再分段氢还原两种不同的还原方法进行了钼粉还原。通过Ｘ射线衍射方法分析了两种工艺还原过程中的反应序列及相变化规律，并讨论了不稳定相Ｍｏ４Ｏ１１对于钼粉还原过程的影响。     

碳热还原法制备氮化硅粉体的反应过程分析

对以碳热还原法制备氮化硅粉体的ＳｉＯ２－Ｃ－Ｎ２系统进行化学反应热力学和动力学的分析，从而发现在氮气氛不足的条件下，这一系统的反应产物将由氮化硅变为碳化硅；在氮气充足的情况下，随着温度的升高，生成物中碳化硅的量也会逐步增加，这一分析结果通过实验得到了验证。     

粉末冶金自润滑止推板的研究和应用

采用粉末冶金技术制备出车辆发动机涡轮增压器用自润滑止推板,研究了材料的基体强化、组织结构和摩擦磨损特性,分析了装机台架综合考核数据,并且与国际上同类产品进行比较,结果表明:该材料综合性能优于国际上同类产品,现已投入工业化生产和批量使用。     

粉末布法制备SiC/Ti基复合材料

用粉末布法制备了低成本SiC/Ti基复合材料.结果表明,采用合适的轧制参数即可容易地获得厚度合适、均匀的粉末布;热失重分析和热解残余物分析指出用来制备粉末布的有机粘结剂的去除过程分成两个阶段,合理除气后,基本没有残余物.使用真空热压工艺制备的SiC/Ti基复合材料,纤维分布基本均匀,纤维与基体的界面结合良好.     

苦味酸钾点火药在电点火头中的应用

通过理论分析和试验,从机械感度、燃烧精度、热安定性、性能、长贮等方面,对比分析了苦味酸钾点火药与DDNP点火药.结果表明:在电点火头制造中,采用苦味酸钾作为点火药的主要组分,具有热稳定性好、药头机械强度高、生产过程废品少、无环境污染等优点,尤其有利于提高电雷管的发火可靠性和一致性.     

Direct Methods Optimised for Solving Crystal Structure by Powder Diffraction Data: Limits,Strategies, and Prospects

The ab-initio crystal structure solution by powder diffraction data requires great efforts because of the collapse of the experimental information onto the one dimensional 2θ axis of the pattern. Different strategies will be described aiming at improving the process of extraction of the integrated intensities from the experimental pattern in order to make more straightforward the structure solution process by direct methods. Particular attention will be devoted to the EXPO program. Some of its performance will be analysed and results will be shown.     

THE STICKY ISSUES OF DRYING

Unconrolled agglomeration of particles and adhesion of the particulate mass to wall surfaces are common severe problems in many drying operations. This paper reviews the mechanisms of interparticle and particle-surface attraction as well as the theory and the existing tests for characterising powders in terms of internal strength, wall friction and adhesion. The usefulness of the information obtained from these tests in dryer design and operation is critically reviewed. The importance of powder stickiness in various types of dryers is discussed and established methods of combating the problem are presented Recommendations an made for further research in the area of powder cohesion and adhesion.