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首页> 外文会议>5th International Conference on Tungsten, Hard Metals, and Refractory Alloys, 5th, Sep 25-27, 2000, Annapolis, Maryland >REDUCTION OF APT PRECURSORS IN EXPERIMENTAL RF DISCHARGE PLASMA REACTOR
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REDUCTION OF APT PRECURSORS IN EXPERIMENTAL RF DISCHARGE PLASMA REACTOR

机译：实验性射频放电等离子体反应器中APT前体的减少

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For the reduction of pulverised ammonium paratungstate (APT) to tungsten metal powder by hydrogen plasma we used in this work a barrel shaped reactor, in which the reduction was carried out under reduced pressure (0.8-1.2 kPa). The central part of quartz discharge tube with an inner diameter of 4.2 cm and a length of 90 cm was inserted into the electrically heated cylindric oven. Vacuum tightness of the tube was accomplished by means of two stainless steel flanges. Output flange besides being connected to a pumping system, contained also a removable cover with feedthrough for a turnable glass rod. Using this rod, the inner quartz cylinder (outer diameter 3.9 cm, length 30 cm) was allowed to rotate. Both edges of the inner cylinder were bend inside by 2 mm to prevent possible escape of pulverised APT during rotation. The feeds of working gases as well as the pressure sensor were placed in the input flange. The working pressure and flow of gases were controlled by needle valves and by throttling of the pump. We used hydrogen as the main gas, in some cases admixture of argon was applied. The discharge was maintained by means of two cylindrical electrodes, placed in the exterior of quartz discharge tube near the ends of the oven. The high frequency power (max. 500 W) was fed from RF generator working at 13.56 MHz through an impedance matching network. Due to a capacitive character of the discharge, the plasma was strongly non-isothermic. The resulting powder treated in C/RF reactor under experimental conditions (p_(H2)= 1300 -1010 Pa ; T_n = 600-720 K, T_e ～11 000K and total power input 400 W) was mostly a mixture of metallic W and WO_(3-x) oxides. The series of experiments with APT of different granulometry demonstrated that reduction takes place even at 600℃ and that the kinetics of the reaction is mainly influenced by diffusion of hydrogen into solid phase pores. In spite of this, the decisive factors of plasmachemical reduction were clearly displayed, which were present in other setups to lower extent. Relatively low hydrogen flow in highest concentration permitted maximum ionisation and atomisation with longer time of retention in reaction volume. The controlling phenomenon of this reduction arrangement was the diffusion of hydrogen into the solid reactant. The fact that reduction proceeded even at 500 - 600 ℃ shows the important role of decrease in activation energy, which is caused by plasma activated reactants.
机译：为了通过氢等离子体将粉碎的仲钨酸铵（APT）还原为钨金属粉末，我们在这项工作中使用了桶形反应器，在其中进行了减压（0.8-1.2 kPa）还原。将内径为4.2cm，长为90cm的石英放电管的中央部分插入电加热的圆筒炉中。管的真空密封性是通过两个不锈钢法兰实现的。输出法兰除了连接至泵送系统外，还包含一个带有用于直通玻璃棒的穿通孔的可移动盖。使用该杆，使内部石英圆柱体（外径3.9 cm，长度30 cm）旋转。内圆柱体的两个边缘向内弯曲2毫米，以防止旋转过程中粉碎的APT可能逸出。工作气体的进料以及压力传感器都放置在输入法兰中。工作压力和气体流量由针形阀和节流阀控制。我们使用氢气作为主要气体，在某些情况下使用了氩气混合物。通过两个圆柱形电极保持放电，两个圆柱形电极放置在靠近烤箱末端的石英放电管的外部。高频功率（最大500 W）由工作在13.56 MHz的RF发生器通过阻抗匹配网络提供。由于放电的电容特性，等离子体强烈不等温。在实验条件下（P_（H2）= 1300 -1010 Pa； T_n = 600-720 K，T_e〜11 000K和总功率输入400 W）在C / RF反应器中处理的所得粉末主要是金属W和WO_的混合物（3-x）氧化物。使用不同粒度的APT进行的一系列实验表明，即使在600℃时，还原反应也会发生，并且反应动力学主要受氢扩散到固相孔中的影响。尽管如此，仍清楚地显示出等离子体化学还原的决定性因素，这些因素在其他装置中存在的程度较低。最高浓度的氢气流量相对较低，可实现最大程度的电离和雾化，并保留更长的反应时间。该还原装置的控制现象是氢扩散到固体反应物中。甚至在500-600℃进行还原的事实显示出活化能降低的重要作用，这是由等离子体活化的反应物引起的。

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