Metal Nanoparticles Encapsulated in Amorphous Carbon and Carbon/Nanofibers Formed in a Canola Methyl Ester Air-Flame

摘要

Many investigations of soot formation have been conducted on traditional hydrocarbon fuels in order to increase the radiant heat transfer in sooting oxygen flames, reduce NO_x and prevent the tremendously hazardous impact on human health of traditional fuels. However, the study of soot morphology produced from biofuels is a nearly unexplored area of research and little is known about soot formation in these types of flames. Biofuels, such as alcohols and esters, are chemically more aggressive to metal surfaces than traditional gasoline and diesel fuels. The interaction of a solid support with a wick-generated open air-flame formed using canola methyl ester (CME) fuel was studied experimentally. The metallic support consists of a nichrome (73% Ni/17%Cr/10%Fe) alloy wire with a 0.6 mm diameter. The probes were inserted at two different heights into the flame Z=12 and Z=18 mm. Z represents the distance from the edge of the fuel nozzle to the center of the probe. Transmission electron microscopy (TEM) and atomic resolution TEM analysis show that the deposits on the surface of the probe are composed of soot-like structures containing encapsulated metal nanoparticles, elongated carbon nanofibers and soot clusters accompanied by elongated metallic nanostructures. Interestingly, the encapsulated nanoparticles within the amorphous soot have diameters of only a few nanometers. It is observed that the time and flame height parameters of the probe/flame interaction are an important factor for the formation of the structures. Residence times ranging from 40 seconds to 5 minutes established a strong correlation to particle morphology. The density of the metallic nanoparticles encapsulated within the soot-like particles increased significantly with the probe/flame interaction time. X-ray diffraction analysis (XRD) of the soot/metal composites reveals the presence of carbon, iron, nickel, chromium and oxygen.