Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture
Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture
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DOI：
10.1007/s11663-009-9307-2
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发表时间：
2010-02-01
影响因子：
3
通讯作者：
Seetharaman, Seshadri
中科院分区：
文献类型：
--
作者：
Ahmed, Hesham M.;Seetharaman, Seshadri
以NiO-WO 3氧化物为前驱体，在973 ~ 1273 K温度范围内，用H2-CH 4混合气体同时还原-碳化法合成了Ni-W-C三元碳化物。通过使用热重法（TGA）监测质量变化，密切关注气-固反应的动力学。当使用前体的薄层时，每个颗粒与气体混合物直接接触。结果表明，混合氧化物的氢还原在渗碳发生之前已经完成。通过还原形成的金属的初生颗粒可以与具有明确的碳势的气体混合物反应，形成均匀的Ni-W-C产物。因此，反应速率可以被认为是由化学反应控制的。从反应速率，还原和渗碳的阿氏活化能进行了评估。使用X射线衍射和扫描电子显微镜（SEM）结合电子色散谱（SEM-EDS）分析进行所产生的碳化物的表征。还测定了晶粒尺寸。工艺参数，如还原渗碳反应的温度和气体混合物的组成，对碳化物组成以及晶粒尺寸有很大的影响。根据氧化物的还原动力学和热力学约束的结果进行了讨论。
Ni-W-C ternary carbides were synthesized by simultaneous reduction-carburization of NiO-WO3 oxide precursors using H-2-CH4 gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas-solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.