γ-Fe_(2)O_(3)纳米颗粒尺寸及碳化气氛对碳化过程的影响

Study on size effect ofγ-Fe_(2)O_(3) nanoparticles and gas atmosphere on carburization process

采用油酸铁热分解法制备出不同尺寸(4−19 nm)的γ-Fe_(2)O_(3)纳米颗粒,在350℃下,于5%CO/He、5%CO/10%H_(2)/He和5%CO/20%H_(2)/He的三种气氛中,使用原位XRD反应装置研究了γ-Fe_(2)O_(3)纳米颗粒的碳化过程与物相变化规律,同时结合Raman、CO-TPR和TEM等手段对样品进行了表征。结果表明,γ-Fe_(2)O_(3)纳米颗粒完全碳化后会形成稳定比例的χ-Fe5C_(2)和θ-Fe_(3)C的混合相;在相同碳化气氛下,随γ-Fe_(2)O_(3)颗粒尺寸增大完全碳化所需时间缩短,尺寸较小的γ-Fe_(2)O_(3)颗粒表面残留炭较多,会抑制碳化反应进程,碳化相中θ-Fe_(3)C相对含量随γ-Fe_(2)O_(3)纳米颗粒尺寸增大而增高;相同尺寸的γ-Fe_(2)O_(3)颗粒在不同气氛下碳化,完全碳化所需时间随H_(2)分压增大先缩短后略有延长,碳化相中θ-Fe_(3)C相对含量随H_(2)分压增大而增高。通过调节γ-Fe_(2)O_(3)颗粒尺寸和碳化气氛可定向制得合适比例的χ-Fe5C_(2)和θ-Fe_(3)C混合相,这一结果有益于费托合成铁基催化剂中的铁碳化物活性相结构的优化。

Different sizes ofγ-Fe_(2)O_(3) nanoparticles(4−19 nm)were prepared by thermal decomposition of iron oleate and carburized in three different gas atmosphere of 5%CO/He,5%CO/10%H_(2)/He and 5%CO/20%H_(2)/He at 350℃.The carburization process and phase transformation ofγ-Fe_(2)O_(3) nanoparticles were investigated by in situ XRD,Raman spectroscopy,CO-TPR and TEM.The results showed thatχ-Fe_(5)C_(2) andθ-Fe_(3)C phases with a stable ratio were formed after carburization.The time to complete carburization was shortened for increasing sizes ofγ-Fe_(2)O_(3) particles under the same carburization atmosphere.While the smallerγ-Fe_(2)O_(3) particles showed more residual carbon on the surface,which could inhibit the carburization process.The relative content ofθ-Fe_(3)C increased with the increase of the size ofγ-Fe_(2)O_(3) nanoparticles.Forγ-Fe_(2)O_(3) nanoparticles with the same sizes,the time to complete carburization in different atmospheres was firstly shortened and then slightly lengthened with the increase of H_(2) partial pressure,while the relative content ofθ-Fe_(3)C increased with the increase of H_(2) partial pressure.By adjusting the particle size ofγ-Fe_(2)O_(3) and the carburization atmosphere,the mixed phases ofχ-Fe_(5)C_(2) andθ-Fe_(3)C can be optimized.