Sang-Ho Oh, Dohun Kim, Ji-Yong Kim, Geosan Kang, Jooyoung Jeon, Miyoung Kim, Young-Chang Joo* and Dae-Hyun Nam*,
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引用次数: 0
Abstract
Fabricating nanoscale metal carbides is a great challenge due to them having higher Gibbs free energy of formation (ΔG°) values than other metal compounds; additionally, these carbides have harsh calcination conditions, in which metal oxidation is preferred in the atmosphere. Herein, we report oxocarbon-mediated calcination for the predictive synthesis of nanoscale metal carbides. The thermochemical oxocarbon equilibrium of CO–CO2 reactions was utilized to control the selective redox reactions in multiatomic systems of Mo–C–O, contributing to the phase-forming and structuring of Mo compounds. By harnessing the thermodynamically predicted processing window, we controlled a wide range of Mo phases (MoO2, α-MoC1–x, and β-Mo2C) and nanostructures (nanoparticle, spike, stain, and core/shell) in the Mo compounds/C nanofibers. By inducing simultaneous reactions of C–O (selective C combustion) and Mo–C (Mo carbide formation) in the nanofibers, Mo diffusion was controlled in C nanofibers, acting as a template for the nucleation and growth of Mo carbides and resulting in precise control of the phases and structures of Mo compounds. The formation mechanism of nanostructured Mo carbides was elucidated according to the CO fractions of CO–CO2 calcination. Moreover, tungsten (W) and niobium (Nb) carbides/C nanofibers have been successfully synthesized by CO–CO2 calcination. We constructed the thermodynamic map for the predictive synthesis of transition metal carbides to provide universal guideline via thermochemical oxocarbon equilibrium. We revealed that our thermochemical oxocarbon-mediated gas–solid reaction enabled the structure and phase control of nanoscale transition metal compounds to optimize the material–property relationship accordingly.
由于纳米级金属碳化物的吉布斯形成自由能 (ΔG°)值高于其他金属化合物,因此制造纳米级金属碳化物是一项巨大的挑战;此外,这些碳化物的煅烧条件苛刻,在大气中金属氧化是首选。在此,我们报告了以氧化碳为介质的煅烧方法,用于预测性合成纳米级金属碳化物。CO-CO2 反应的热化学氧化碳平衡被用来控制 Mo-C-O 多原子体系中的选择性氧化还原反应,从而促进钼化合物的相形成和结构化。通过利用热力学预测的加工窗口,我们控制了钼化合物/钼纳米纤维中的各种钼相(MoO2、α-MoC1-x 和 β-Mo2C)和纳米结构(纳米颗粒、尖晶石、染色和核/壳)。通过在纳米纤维中同时诱导 C-O(选择性 C 燃烧)和 Mo-C(Mo 碳化物形成)反应,控制了 Mo 在 C 纳米纤维中的扩散,为 Mo 碳化物的成核和生长提供了模板,从而精确控制了 Mo 化合物的物相和结构。根据 CO-CO2 煅烧的 CO 分数,阐明了纳米结构 Mo 碳化物的形成机制。此外,通过 CO-CO2 煅烧还成功合成了钨(W)和铌(Nb)碳化物/纳米纤维。我们构建了过渡金属碳化物预测合成的热力学图谱,通过热化学氧化碳平衡提供了通用指南。我们发现,热化学氧化碳介导的气固反应实现了纳米级过渡金属化合物的结构和相控制,从而相应地优化了材料-性能关系。
期刊介绍:
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