Abstract The effect of ultrasonic irradiation on direct maghemite (γ-Fe2O3) preparation by a co-precipitation method with Fe3+ salt (Fe(NO3)3) and an excess amount of alkaline (KOH) solution without going through the conventional magnetite (Fe3O4) formation route was explored in comparison with impeller stirring. The preparation procedure for obtaining iron oxide nanoparticles was designed using the sequential processes of precipitation, decantation, drying and thermal dehydration, and ultrasonic irradiation or impeller stirring was done during the precipitation process. γ-ferric oxyhydroxide (γ-FeOOH) was partially formed in addition to α-ferric oxyhydroxide (α-FeOOH) and thermally dehydrated to γ-Fe2O3 and hematite (α-Fe2O3) by ultrasonic-assisted co-precipitation of Fe3+ salt and the excess KOH solution, whereas only α-FeOOH and α-Fe2O3 were synthesized by impeller stirring. The difference between the products of the two methods was explained by the Lamer model associated with the nucleation and growth of FeOOH. Magnetization increased as the crystallite diameter decreased, which is estimated to facilitate partial formation of magnetic γ-Fe2O3. Magnetization was enhanced by a lower ultrasonic frequency due to the stronger shock wave induced by the cavitation effect.

中文翻译：

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超声辐照对Fe3+盐和碱溶液共沉淀法生成γ-Fe2O3的影响

摘要 超声辐照对不经过常规磁铁矿 (Fe3O4) 与 Fe3+盐 (Fe(NO3)3) 和过量碱 (KOH) 溶液的共沉淀法直接制备磁赤铁矿 (γ-Fe2O3) 的影响与叶轮搅拌相比，探索了形成路线。采用沉淀、倾析、干燥和热脱水的顺序过程设计获得氧化铁纳米颗粒的制备工艺，在沉淀过程中进行超声辐照或叶轮搅拌。除了 α-羟基氧化铁 (α-FeO​​OH) 外，还部分形成了 γ-羟基氧化铁 (γ-FeOOH)，并通过 Fe3+ 盐和 Fe3+ 盐的超声辅助共沉淀热脱水成 γ-Fe2O3 和赤铁矿 (α-Fe2O3)。过量的 KOH 溶液，而通过叶轮搅拌仅合成 α-FeO​​OH 和 α-Fe2O3。两种方法的产物之间的差异由与 FeOOH 的成核和生长相关的 Lamer 模型解释。随着微晶直径的减小，磁化强度增加，据估计这有利于磁性 γ-Fe2O3 的部分形成。由于空化效应引起的更强冲击波，较低的超声频率增强了磁化。