Reduction Mechanism of Transition Metal Oxide Particles in Thermally Induced Nanobubbles during Pulsed Laser Melting in Ethanol |
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| Authors: | Kentaro Suehara Ryosuke Takai Dr Yoshie Ishikawa Prof Naoto Koshizaki Kazunobu Omura Prof Harunori Nagata Prof Yuji Yamauchi |
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| Institution: | 1. Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo, Hokkaido, 060-8628 Japan;2. Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1–1-1 Higashi, Tsukuba, Ibaraki, 305-8565 Japan |
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| Abstract: | Pulsed laser melting in liquid (PLML) is a technique to fabricate spherical submicrometer particles (SMPs) wherein nanosecond pulsed laser (several tens to several hundreds of mJ pulse−1 cm−2) irradiates raw particles dispersed in liquid. Raw particles are transiently heated above the melting point to form spherical particles, which enables pulsed heating of surrounding liquid to form thermally induced bubbles by liquid vaporization. These transient bubbles play an important role as a thermal barrier to rapidly heat the particle. Reduced SMPs are generated from raw metal-oxide nanoparticles by PLML process in ethanol. This reduction cannot be explained by high-temperature thermal decomposition, but by mediation of molecules decomposed from ethanol. Computational simulations of ethanol decomposition by pulsed heating for 100 ns at the temperature 1000–4000 K revealed that ethylene is generated as the main product. Gibbs free energies of oxide reduction reactions mediated by ethylene greatly decreased compared to those without ethylene mediation. This explanation can be applied to reductive SMP formation from various transition metal oxides by PLML. |
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| Keywords: | laser melting in liquid nanobubble nanoparticles reduction thermal decomposition |
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