Preparation of micro-nano Mo(C, N) powders by low temperature carbothermal and micro-positive pressure of nitrogen
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摘要: 金属Mo的碳氮化物对改善金属基复合材料的结构性能起到重要作用，而Mo（C，N）固溶体综合了金属及碳氮化物的性能，其改善复合材料结构的效果优于单纯的Mo2C或者MoN粉末。本研究采用机械合金化技术和微正压碳热氮化法，低温下制备微纳米Mo（C，N）固溶体粉末。利用热重分析-示差扫描量热法（thermogravimetric analysis-differential scanning calorimetry，TG-DSC）、X射线衍射仪（X-ray diffraction，XRD）、扫描电子显微镜（scanning electron microscope，SEM）分析考察机械力及氮化条件对粉体结构及粒度的影响。结果表明：MoO2粉末和碳粉经9 h高能球磨后，机械力足够使粉末细化，同时能够增加界面能和缺陷，以提供MoC-N化学吸附向微纳米Mo（C，N）固溶体粉末转变所需的激活能，并借此改变Mo原子表面电子的不饱和性，结合微正压N2气气氛，促使混合粉末在碳化阶段Mo与N有效键合；最终，在N2气压力0.2 MPa、850 ℃下制备出了Mo（C，N）微纳米类球形粉未；碳氮化温度低，有效地降低了能耗，节约了成本，有重要的工业应用前景。Abstract: The carbonitride of Mo (Mo2C or MoN) is important to improve the structural properties of metal matrix composites. The solid solution of Mo(C, N) combined the characteristics of metal and carbonitride of Mo shows the better structural properties of metal matrix composites. The micro-nano Mo(C, N) spherical solid solution powders were prepared by mechanical alloying technique and carbothermal method at low temperature and low-pressure of nitriding in this study. The effects of mechanical force and nitriding conditions on the structures and particle sizes of powders were studied by thermogravimetric analysis-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscope (SEM).The results show that, after high-energy ball mill for 9 h, enough mechanical force can refine the mixture powders of MoO2 and carbon, improve the interface energy, and increase the defects, which can provide the activation energy of MoC-N chemical adsorption to transform to the micro-nano Mo (C, N) solid solution powders. Moreover, it can change the unsaturation of electrons on the surface of Mo atoms and promote the Mo-N bonding when the mixture powders are carbothermal at the condition of micro-positive pressure of nitrogen. Finally, the micro-nano Mo(C, N) spherical solid solution powders are prepared at the N2 pressure of 0.2 MPa and the temperature of 850 ℃; it can effectively reduce the energy consumption and save cost at this low carbothermal temperature, showing the important prospects of industrial applications.
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图 1 钼酸铵热分解工艺参数曲线：（a）加热；（b）冷却
Figure 1. Decomposition of ammonium molybdate: (a) heating period; (b) cooling period
图 2 碳热氮化工艺参数曲线：（a）加热；（b）冷却
Figure 2. Carbothermal nitrogenization: (a) heating period; (b) cooling period
图 4 不同球磨时间钼酸铵的扫描电子显微组织形貌：（a）0 h；（b）5 h；（c）10 h；（d）12 h
Figure 4. SEM images of ammonium molybdate under different milling time: (a) 0 h; (b) 5 h; (c) 10 h; (d) 12 h
图 5 球磨10 h不同温度下钼酸铵烧结产物的X射线衍射图谱（a）、钼酸铵在550 ℃烧结后扫描电子显微组织形貌（b）及对应的能谱图（c）
Figure 5. XRD patterns of ammonium molybdate (milling for 10 h) sintered at different temperatures (a), SEM image of ammonium molybdate (milling for 10 h) sintered at 550 ℃ (b), and the corresponding EDS analyse (c)
图 6 氧化钼与碳粉在不同球磨时间后的扫描电子显微组织形貌：（a）3 h；（b）6 h；（c）9 h
Figure 6. SEM images of MoO2 and C under different milling times: (a) 3 h; (b) 6 h; (c) 9 h
图 7 氧化钼与碳粉高能球磨9 h后不同氮气压力下900 ℃碳热反应的X射线衍射图谱
Figure 7. XRD patterns of carbothermal reaction of MoO2 and C (milling for 9 h) at 900 ℃under different nitrogen pressure
图 8 不同球磨时间氧化钼和C粉在不同碳热温度下反应的X射线衍射图谱（氮气压力0.2 MPa）
Figure 8. XRD patterns of carbothermal reaction of MoO2 and C in the nitrogen pressure of 0.2 MPa at different temperatures for different milling times
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