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首页> 外文期刊>Journal of Physics, D. Applied Physics: A Europhysics Journal >Study of morphology of aerosol aggregates formed during co-pyrolysis of C3H8+Fe(CO)(5)
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Study of morphology of aerosol aggregates formed during co-pyrolysis of C3H8+Fe(CO)(5)

机译：C3H8 + Fe（CO）（5）共热解过程中形成的气溶胶聚集体的形态研究

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Formation of aerosol nanoparticles as well as carbon nanotubes and nanofilaments is studied during co-pyrolysis of iron pentacarbonyl and propane with argon as a carrier gas in a flow reactor. Gaseous intermediates from propane thermal decomposition (CH4, C2H6 and C3H4) and Fe(CO)(5) conversion are monitored by gas chromatography and IR-spectroscopy, respectively. The aerosol morphology is studied by transmission electron microscopy (TEM) and high resolution TEM. The aerosol particle concentration and size distribution are measured by an automated diffusion battery. The crystal phase composition of particles is studied by x- ray diffractometry. The decomposition of the Fe(CO)(5) + Ar mixture resulted in an iron aggregate formation composed of fine primary particles. In the case of lower pyrolysis temperatures, about 450 K, the primary particle mean diameter is about 10 nm, and consequently, the majority of the primary particles are superparamagnetic, thus forming compact aggregates. At intermediate pyrolysis temperatures in the range 800-1040K the primary particle diameter is about 20-30 nm, and most of the particles are ferromagnetic in nature. The coagulation of these particles results in a chain- like aggregate formation. Finally, at temperatures higher than the Curie point (1043 K) the ferromagnetic properties vanish and the formation of compact aggregates is observed again. The co-pyrolysis of Fe(CO)(5) and C3H8 mixed with Ar carrier gas resulted in aerosol aggregate structures dramatically different from those formed by iron pentacarbonyl pyrolysis. In particular, in the temperature range 1070-1280 K, we observed Fe3C particles connected by long carbon nanotubes (CNTs). The aggregate morphology is described in terms of a fractal-like dimension D-f, which is determined from TEM images on the basis of a scaling power law linking the aggregate mass (M) and radius (R), M similar to R-Df. The Fe3C-CNT aggregate morphology is a function of the inlet ratio between propane and iron pentacarbonyl concentrations [C3H8](0)/[Fe(CO)5](0). At the low ratio of [C3H8](0)/[Fe(CO)(5)](0) < 80 the fractal dimension of aggregates decreases (from 1.7 down to about 1) with the increasing ratio of inlet concentrations. This effect, as observed by TEM, is due to the increase in the mean nanotube length. Vice versa, in the range [C3H8](0)/[Fe(CO)(5)](0) > 80 the fractal aggregate dimension is higher for a larger ratio of [C3H8](0)/[Fe(CO)(5)](0), which is explained by the larger thickness of growing nanotubes obtained for a relatively large propane concentration. The aggregate formation mechanism includes consecutive stages of iron aggregate formation due to Fe(CO)(5) decomposition, carbon deposition on iron particles from C3H8 pyrolysis intermediates, carbon dissolution in iron particles, nanotube nucleation at the carbon concentration of about 60 at.% in Fe-C solution and disruption of the Fe-C aggregates into small pieces by the growing nanotubes.
机译：在流动反应器中，对五羰基铁和丙烷与氩气作为载气共热解过程中，研究了气溶胶纳米颗粒以及碳纳米管和纳米丝的形成。丙烷热分解产生的气态中间体（CH4，C2H6和C3H4）和Fe（CO）（5）的转化分别通过气相色谱法和红外光谱法进行监测。通过透射电子显微镜（TEM）和高分辨率TEM研究气溶胶的形态。气溶胶颗粒浓度和尺寸分布由自动扩散电池测量。通过X射线衍射法研究了颗粒的晶相组成。 Fe（CO）（5）+ Ar混合物的分解导致形成由细小的初级颗粒组成的铁聚集体。在较低的热解温度（约450 K）的情况下，初级粒子的平均直径约为10 nm，因此，大多数初级粒子是超顺磁性的，因此形成紧密的聚集体。在800-1040K的中间热解温度下，一次粒径约为20-30 nm，并且大多数颗粒本质上是铁磁性的。这些颗粒的凝结导致链状聚集体的形成。最后，在高于居里点（1043 K）的温度下，铁磁特性消失，再次观察到致密聚集体的形成。 Fe（CO）（5）和C3H8与Ar载气混合共热解产生的气溶胶聚集体结构与五羰基铁热解形成的聚集体结构显着不同。特别是，在1070-1280 K的温度范围内，我们观察到由长碳纳米管（CNT）连接的Fe3C颗粒。聚集体的形态用分形维数D-f来描述，它是由TEM图像根据连接聚集体质量（M）和半径（R）的缩放幂律（类似于R-Df）确定的。 Fe3C-CNT聚集体形态是丙烷与五羰基铁浓度[C3H8]（0）/ [Fe（CO）5]（0）之间的入口比的函数。在[C3H8]（0）/ [Fe（CO）（5）]（0）<80的低比率下，聚集体的分形维数随入口浓度比率的增加而降低（从1.7降至约1）。如通过TEM观察到的，该效果是由于平均纳米管长度的增加。反之亦然，在[C3H8]（0）/ [Fe（CO）（5）]（0）> 80的范围内，对于较大比例的[C3H8]（0）/ [Fe（CO） （5）]（0），这是由于丙烷浓度较高而获得的正在生长的纳米管的厚度较大所致。聚集体形成机理包括由于Fe（CO）（5）分解而形成铁聚集体的连续阶段，C3H8热解中间体在铁颗粒上的碳沉积，铁颗粒中的碳溶解，碳浓度约60 at。％的纳米管成核作用。在Fe-C溶液中，Fe-C聚集体被不断增长的纳米管破坏成小块。

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