高频热等离子体制备纳微球形钨粉的研究
文献类型：学位论文
| 作者 | 张海宝 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-06-04 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 袁方利 |
| 关键词 | 纳米钨粉 球形钨粉 高频等离子体 光谱诊断 |
| 其他题名 | RF Thermal Plasma Synthesis of Nano/micro Spherical Tungsten Powders |
| 学位专业 | 化学工程 |
| 中文摘要 | 金属钨粉的球形化和超细化是开发高附加值钨粉的两个重要方向。致密规则的球形钨粉，不仅流动性好，而且堆积密度大、烧结收缩小，能够获得理想微结构的钨材料；而纳米钨粉可以降低钨粉的烧结温度，是制备性能优异的超细晶粒硬质合金的主要原料。传统的固相合成法和液相合成法存在操作步骤多、反应时间长、产物纯度低等问题。因此，本论文主要围绕高频氢等离子体制备纳微球形钨粉进行研究，主要的研究工作及结果如下：（1）利用发射光谱法开展了高频热等离子体光谱诊断及强化还原机理的研究。分别研究了高频氩等离子体、高频氢等离子体、以及加入仲钨酸铵后高频氢等离子体弧的发射光谱。高频热等离子体中存在的活性基团有激发态的原子和离子，激发态原子的谱线强度随放电频率的增加而升高，随放电管内气压的升高而降低。采用多谱线斜率法由谱线强度计算得到，在8 kW到15 kW的频率范围内，高频氩等离子体的电子激发温度在8923.70K至10670.07K的范围内变化，据此结果估算得到8 kW高频等离子体的热效率为17.19%。在高频氢等离子体中加入仲钨酸铵，在毫秒级的时间内，等离子体中的活性H基团就可以与原料发生反应，引起激发态氢原子谱线Hα的减弱和Hβ的消失。与常规还原反应相比，高频氢等离子体还原在动力学上具有明显优势，可极大地强化常规还原反应。（2）高频氢等离子体一步还原仲钨酸铵制备纳米钨粉，得到粒度均匀、分散性良好的纳米球形钨粉，颗粒尺寸在50 nm以下，平均粒径为20 nm左右。通过风冷的方式调控冷却室温度梯度，可以实现对纳米球形钨粉粒径的调控。与蓝色氧化钨为原料制备纳米钨粉相比，采用仲钨酸铵为原料具有产量高、成本低、特别是工艺流程简单的优势。在相同的实验参数下，仲钨酸铵更容易得到还原。与传统的还原仲钨酸铵制备钨粉的多步工艺路线相比，高频氢等离子体新工艺可以不经过氧化钨阶段直接一步还原到金属钨粉状态，而且反应产物无残留也不会污染环境，有利于实现绿色生产。（3）仲钨酸铵在不同气氛高频热等离子体中的可控反应研究。通过调控等离子体的工作气体构建不同性质的等离子体反应气氛，从而使仲钨酸铵在不同性质的等离子体反应气氛中生成不同价态的反应产物。在氧化性的空气等离子体气氛中，仲钨酸铵生成黄色单斜晶系的八面体WO3，在中性的氩气等离子体气氛中生成棕绿色的单斜晶系的八面体WO3，在弱还原性的氨气等离子体气氛中主要生成蓝色棒状的WO2.72，以及在强还原性的氢气等离子体气氛中生成黑色的纳米球形钨粉。（4）高频氢等离子体球化微米级钨粉研究。采用FSSS粒径为1～3 μm的钨粉为原料球化，球化后粉体的松装密度增加19.56%，流动速度为球化前的2.33倍。高频等离子体球化钨粉实验在实验室连续运行1小时，产量可达927.33 g/h。另外将此工艺推广到球化常规钼粉，证明高频等离子体球化工艺具有很好的稳定性和普适性。 |
| 英文摘要 | Spheriodizing and superfining of tungsten powder are two main research directions on developing high value product in recent years. The dense and regular spherical tungsten powder which is of good mobility, big packing density and small sintering shrinkage is suitable for obtaining the desired micro-structure of tungsten materials. And at the same time, the sinterability of the nanosized tungsten powder is better than the microsized tungsten powders. The nanosized tungsten powder is the main raw material for the preparation of high quality cemented carbide. However, the main drawbacks of conventional methods are involved of several routes, long reative time and impurity. So, in this thesis, the prepatation of nano/micro spherical tungsten powders by RF thermal plasma method was studied systematically and continuous preparation was carried out in a laboratory level. The main work and results are summarized bellow: (1) Optical emission spectroscopy diagnosis of the RF theremal plasma was carried out to characterize the reactive radicals in the plasma and the reaction technique. The optical emission spectroscopys of RF Ar plasma, RF Ar-H2 plasma and RF Ar-H2 plasma after adding ammonium paratungstate were studied, respectively. The results show that the emission intensity of the reactive radicals increases as the applied power increases, and the emission intensity of the reactive radicals decreases as the system gas pressure increases. In addition, the electron temperature of RF Ar plasma was calculated to be 8923.70K～10670.07K from the slope of the Boltzmann’s plot. According to this result, the thermal efficency of the RF Ar plasma at 8 kW is about 17.19%. The reactive radicals Hα and Hβ in the Ar-H2 plasma reduce after adding ammonium paratungstate into the plasma jet in millisecond. Compared with conventional reduction, the RF Ar-H2 plasma assistant reduction is of significant kinetics advantage and can maximum accelerate reaction speed. (2) Preparation of tungsten nanosized powders via a single-step pathway by the RF thermal plasma process using ammonium paratungstate as the precursor. The crystallized product is well dispersed spherical tungsten nano-powder with a particle size of less than 50 nm and mean is about 20 nm. Moreover, the particle sizes of the tungsten nanosized powders were successfully controlled by adjusting the quenching rate in RF thermal plasma system. Compared with blue tungsten oxide, in other identical condition, the ammonium paratungstate was reduced easily and had the advantages of high yield, low cost and simple technique. Compared with the conventional reduction process of ammonium paratungstate, the plasma reduction from ammonium paratungstate to metallic tungsten powder was completed in one step. It also guaranteed the products of high purity and the processing of environmental satety. (3) The reaction mechanism study of ammonium paratungstate in RF thermal plsama. Different products were successfully synthesized by ammonium paratungstate in different RF thermal plasma ambiences. The yellow monoclinic octahedra WO3, breen monoclinic octahedra WO3, blue rodlike WO2.72 and black cubic W powder were synthesized in air-argon plasma, argon plasma, ammonia-argon plasma and hydrogen- argon plasma, respectively. (4) Spheriodizing of micro tungsten powder in RF thermal plasma. Tungsten powder with Fsss particle size of 1～3 μm were used as starting materials. The apparent density was improved 19.56% and fluidity is 2.33 times after spheroidization. A production yiled of 927.33 g/h was achieved in the laboratory. In addition, molybdenum powder was spheriodized by this plasma technique, it means that the RF plasma technology has good stability and universality. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1789]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 张海宝. 高频热等离子体制备纳微球形钨粉的研究[D]. 中国科学院研究生院. 2012. |
入库方式： OAI收割
来源：过程工程研究所
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