Oxide reduction during triggered-lightning fulgurite formation
Oxide reduction during triggered-lightning fulgurite formation
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DOI：
10.1016/j.jastp.2004.11.005
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发表时间：
2005-03-01
影响因子：
1.9
通讯作者：
Uman, MA
中科院分区：
文献类型：
--
作者：
Jones, BE;Jones, KS;Uman, MA
本研究以99.9%纯锰（MnO）和镍（NiO）二元氧化物为基体，制备雷电致电流石，研究其氧化还原机理。在佛罗里达州布兰丁营的国际闪电研究和测试中心，电火花的形成过程包括将氧化物包装在PVC容器中，并使用标准的火箭和电线技术通过氧化物触发闪电。这两种氧化物是用埃林厄姆图从氧化物稳定性的热力学外推中选择的。该图表明，NiO的稳定性明显低于MnO。用扫描电子显微镜（SEM）分析了纯氧化物的电火花；利用二次电子图像、背散射图像和能谱分析（EDS）对其微观结构和成分进行了表征。在电火花形成之前，对NiO和MnO进行了SEM/EDS分析，证实它们是纯二元氧化物，没有金属污染。电流石形成后，发现氧化镍电流石中含有金属镍颗粒；氧化锰fulgurite未形成金属相。透射电子显微镜（TEM）检查证实MnO为纯氧化物，没有金属相形成的迹象。然而，TEM结果表明，约50%的NiO被还原为金属面心立方Ni。观察到Ni和NiO与[100]Ni//[100]NiO和[110]Ni//[110]NiO相一致。这些结果与上述热力学稳定性计算一致，并表明碳质物质或氧化物混合物的存在对电流石形成过程中的氧化物还原不是必需的。这些研究并不排除电解在氧化物还原中起作用的可能性。然而，这些电流石是在同一雷击中同时产生的，因此受到相同的电流，因此提出氧化物的热力学稳定性必须在氧化物还原中发挥作用。(C) 2004 Elsevier Ltd.版权所有。
In this study triggered-lightning induced fulgurites were formed in 99.9% pure binary oxides of manganese (MnO) and nickel (NiO) in order to study oxide reduction mechanisms. The fulgurite formation process involved packing the oxide in PVC holders and using the standard rocket-and-wire technique to trigger a lightning strike through the oxide at the International Center for Lightning Research and Testing in Camp Blanding, Florida. These two oxides were chosen from the thermodynamic extrapolation of the oxide stability using the Ellingham Diagram. This diagram indicates that NiO is significantly less stable than MnO. Fulgurites from the pure oxides were analyzed in a scanning electron microscope (SEM); secondary electron images, backscattered images and energy dispersive spectroscopy (EDS) were used to determine the microstructure and composition of the fulgurites. SEM/EDS analysis of the NiO and MnO prior to fulgurite formation confirmed they were pure binary oxides with no metallic contamination. After fulgurite formation, it was found that the nickel oxide fulgurite contained metallic nickel particles; the manganese oxide fulgurite showed no metallic phase formation. Transmission electron microscopy (TEM) examination confirmed that the MnO was a pure oxide with no sign of metallic phase formation. However, TEM results of the NiO showed that approximately 50% of the NiO was reduced to metallic face-centered cubic Ni. The Ni and NiO were observed to be coherent with the [100]Ni//[100]NiO and [110]Ni//[110]NiO. These results are consistent with the aforementioned thermodynamic stability calculations and show that the presence of carbonaceous material or mixtures of oxides is not necessary for oxide reduction during fulgurite formation. These studies do not rule out the possibility that electrolysis plays a role in oxide reduction. However, these fulgurites were made simultaneously during the same lightning strike and therefore were subjected to the same electrical current, and thus it is proposed the thermodynamic stability of the oxide must play a role in oxide reduction. (C) 2004 Elsevier Ltd. All rights reserved.