【作者】 柴永新；

【导师】 吴晓东；

【作者基本信息】 江苏大学 ， 钢铁冶金， 2006， 硕士

【摘要】 本研究选取煅烧仲钨酸铵自制的三氧化钨（WO₃）为原料，通过氧化—还原法来制备超细钨粉，并对其还原过程的动力学进行了初步研究。本实验所采用的氧化—还原法是一种全新的工艺，是先将三氧化钨还原成钨粉，然后在空气中氧化成三氧化钨后再次还原，如此反复进行多次，则可得超细钨粉。对于三氧化钨还原过程动力学的研究，采用热重分析方法，利用样品发生相变时常伴有重量变化的现象，得到不同还原条件下的动力学（热失重—时间或还原率—时间）曲线，由失重情况判断反应速度及其影响因素。分别对三氧化钨（WO₃）到蓝钨(WO_2.90)和蓝钨到钨粉两个阶段进行了研究。通过研究，得到如下结论：（1）本研究选取的三氧化钨原料，通过氧化—还原法（4次氧化5次还原）是可以制备出超细钨粉的；所得金属钨粉的平均粒度约为0.38μm。（2）也可用任意粒度的钨粉做初始原料，将其在一定条件下氧化和还原，便能得到可作为高性能硬质合金原料的超细钨粉。（3）金属钨粉在规定条件下进行氧化，得到的三氧化钨粒度与初始原料金属钨粉的粒度无关。对于金属钨粉的氧化，低温慢速氧化可得到松散多孔状态的三氧化钨颗粒，还原此种三氧化钨可得到超细钨粉。（4）在490～500℃的温度下，约35min即可完成WO₃到WO_2.90的还原过程。而且，还原温度越高、氢气流量越大，实现完全转化的时间越短，即反应速度越快。（5）实现WO_2.90还原到W粉的最低还原温度约为750℃，低于该温度反应时间则较长或者反应进行得不完全。此过程可能伴有WO₂的生成，从而WO₂的挥发和WO₂→W的快速反应成为反应速度发生变化的可能原因。另外，在更高的温度下（＞775℃），反应过程中往往会生成WO_2.72相，可能会越过WO_2.72→WO₂这一阶段直接发生WO_2.72→W的快速反应，而生成的大量W晶核的新表面对还原反应具有很强的催化作用，从而使还原反应始终处于较快的速度下进行。（6）氢气流量对物料反应速度的影响较温度更为强烈。更多还原

【Abstract】 Self-made tungsten trioxide （WO₃） by calcining ammonium paratungstate （APT） was selected as the raw material to produce ultrafme and homogenous tungsten powder by oxidation-reduction method. The mechanics of the oxidation-reduction method and the reduction kinetics characteristic of tungsten trioxide were studied.The oxidation-reduction method in this article is a quite new processs for preparing ultrfme tungsten powder. The process is that as follows: tungsten trioxide is reduced to tungsten powder at first, then the tungsten powder will be oxidated to tungsten trioxide, and then the tungsten trioxide will be reduced to tungsten powder again, ultrafine and homogenous tungsten powder will be produced by repeating this cyclic process several times.The studies on kinetics of hydrogen reduction of tungsten trioxide were carried out by thermogravimetry. According to the phenomenon of the sample’s weight will change if phase transformation occur during the reduction, the weight changing of tungsten trioxide during the reduction was investigated by balance. To draw the reduction kinetics curves of tungsten trioxide, two stages of tungsten trioxide being reducing to tungsten were studied respectively. From the data of weight loss, reaction speed and the factors affecting it could be determined.The main conclusions are as following:（1） Ultrafine tungsten powder can be produced from tungsten trioxide choosen in this research through the oxidation-reduction method （4 oxidations and 5 reductions） in right conditions; the average grain size of ultrafine tungsten powder is about 0.38μm（2） Through several circles of oxidation-reduction, tungsten powders in random grain sizes can be used as the starting material to produce ultrafine tungsten powders which can be used as raw material for high-performence cemented carbide.（3） The particle size of tungsten trioxide prepared from the oxidation of tungsten powder in right conditions has nothing to do with the starting material tungsten powder. By oxidation of tungsten powder at low temperature and slow speed, porous tungsten trioxide can be produced, and reduce this kind of tungsten trioxide will prepare ultrafine tungsten powder.（4） Tungsten trioxide can be completely reduced to TBO (WO_2.90) at 490～500℃after about 35 minutes. Furthermore, the complete conversion time will be shorten with the reduction temperature rising and the hydrogen flowrate increasing.（5） The lowest temperature of the TBO (WO_2.90) being reduced to tungsten is about 750℃. If the temperature below 750℃, the reaction time will delay or the reduction will be incomplete. In the process of TBO reduction to tungsten, tungsten dioxide （WO₂） formation may occurr simultaneously, so the tungsten dioxide volatilization and the quick-reaction of reducing WO₂ to W may be the possible reason why the reaction speed changing. Furthermore, at a higher reaction temperature （above 775℃）, WO_2.72 phase may be formed in this reduction process, then the quick-reaction of reducing WO_2.72 to W may directly be occurred without the path of reducing WO_2.72 to WO₂, and those large numbers of new surfaces of produced W-nuclei have catalytic activity for the reducing reaction, so the reducing reaction have a quicker reaction speed from the beginning to the end.（6） The influence of hydrogen flowrate on reaction speed is more enormous than reaction temperature.更多还原