Iron oxide nanoparticles of reduced oxidation state, mainly in the form of magnetite, have been synthesized utilizing a new continuous, gas-phase, nonpremixed flame method using hydrocarbon fuels. This method takes advantage of the characteristics of the inverse flame, which is produced by injection of oxidizer into a surrounding flow of fuel. Unlike traditional flame methods, this configuration allows for the iron particle formation to be maintained in a more reducing environment. The effects of flame temperature, oxygen-enrichment and fuel dilution (i.e. the stoichiometric mixture fraction), and fuel composition on particle size, Fe oxidation state, and magnetic properties are evaluated and discussed. The crystallite size, Fe(II) fraction, and saturation magnetization were all found to increase with flame temperature. Flames of methane and ethylene were used, and the use of ethylene resulted in particles containing metallic Fe(0), in addition to magnetite, while no Fe(0) was present in samples synthesized using methane.

中文翻译：

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还原氧化态磁性氧化铁纳米粒子的气相火焰合成及性质

使用碳氢燃料的新型连续、气相、非预混火焰法合成了还原氧化态的氧化铁纳米颗粒，主要以磁铁矿的形式存在。这种方法利用了逆焰的特性，逆焰是通过将氧化剂喷射到周围的燃料流中而产生的。与传统的火焰方法不同，这种配置允许在更还原的环境中保持铁颗粒的形成。评估和讨论了火焰温度、富氧和燃料稀释（即化学计量混合分数）和燃料成分对颗粒尺寸、Fe 氧化态和磁性的影响。发现微晶尺寸、Fe(II) 分数和饱和磁化强度都随着火焰温度的增加而增加。