Abstract

The morphology and composition of metal–oxide coronaparticles after the thermal oxidation of iron particles within the temperature range of 25–600°C under atmospheric conditions were investigated by in situ Raman-scattering spectroscopy. Thermal treatment at 100–300°C results in the predominant formation of a Fe₃O₄ and γ-Fe₂O₃ mixture, with a small amount of α-Fe₂O₃, on the surface of the iron particles, while annealing at higher temperatures results in further oxidation of iron, as well as phase transformation of Fe₃O₄ and γ-Fe₂O₃ phase transformation to the most thermodynamically stable form of iron oxide α-Fe₂O₃. At thermal treatment at 300°C and higher, localization of the reaction of hematite formation is observed: one-dimensional nanofilaments of the hematite-forming corona start to grow radially from spherical iron microparticles that are accompanied by depassivation and acceleration of growth of the oxide layer. With an increase of temperature and time of oxidation, the microparticles transform into multilayer metal–oxide coronaparticles consisting of a metal–oxide core and corona of the elongated crystalline α-Fe₂O₃ nanowhiskers growing transversely to the surface of the particles. Growth of the hematite nanowhiskers lasts until complete oxidation of the metal core has taken place. It has been hypothesized that the reason for the growth of hematite nanowhiskers at iron oxidation is associated with autolocalization of the topochemical reaction of maghemite formation in the magnetite–hematite interface phase boundary, as well as acceleration of transport of metal into the growing hematite whiskers by the effect of internal stresses in the growing oxide layer.

中文翻译：

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氧化铁核电晕纳米粒子的拉曼光谱：合成温度的影响

摘要

通过原位拉曼散射光谱研究了在大气条件下25–600°C的温度范围内的铁颗粒热氧化后，金属氧化物冠状颗粒的形貌和组成。在100-300℃下导致主要形成的Fe的热处理₃ ö ₄和γ-的Fe ₂ ö ₃混合物，用少量的α-Fe ₂ ö ₃，铁颗粒的表面上，而退火在铁的进一步氧化，以及铁的相变温度更高结果₃ ö ₄和γ-的Fe ₂ ö ₃相变到铁氧化物的α-Fe的热力学最稳定的形式₂ ö ₃。在300°C或更高温度下进行热处理时，观察到赤铁矿形成反应的局域性：形成赤铁矿的电晕的一维纳米丝从球形铁微粒开始径向生长，并伴随着氧化物的钝化和加速生长层。随着温度和氧化时间的，所述微粒转变成多层组成的细长结晶的α-Fe的金属氧化物核心和电晕的金属氧化物coronaparticles ₂ ö ₃纳米晶须横向于颗粒表面生长。赤铁矿纳米晶须的生长一直持续到金属核完全氧化为止。据推测，铁氧化时赤铁矿纳米晶须生长的原因与磁铁矿-赤铁矿界面相界中磁赤铁矿形成的拓扑化学反应的自动定位，以及通过铁加速金属向生长的赤铁矿晶须中的运输有关。内应力在生长的氧化层中的影响。