Study of factors affecting the synthesis of carbon nanotubes by spray pyrolysis.

摘要

Carbon nanotubes have interesting electronic, mechanical and molecular properties, which own great application potential in many fields. For this reason, a significant amount of research on the synthesis of carbon nanotubes has arisen. Using the method of catalytic spray pyrolysis of hydrocarbon method to produce carbon nanotubes, the effect of several parameters on yield and alignment of carbon nanotubes was studied in this project because of its relatively simple experimental set up. The simplest method is to spray catalyst nanoparticles directly into the chemical vapor deposition chamber. Organometallic compounds are often used as catalyst precursors. These precursors on heating usually get sublimed, and catalyst nanoparticles are formed when the compound is decomposed by heat. It is commonly used for the mass production of carbon nanotubes by chemical vapor deposition.;Suitable experimental equipment and related parameters were chosen and a set of experiments was designed, with three factors: temperature, carbon source and catalyst concentration. Carbon nanotubes were grown inside quartz tubes using spray pyrolysis of catalyst/carbon source solution under argon flow. Ferrocene was used as the catalyst. Methanol, isopropyl alcohol, cyclohexane were each separately used as carbon sources. The different experimental results in three carbon sources, in three different temperatures, 800°C, 950°C, 1100°C; and in two different ferrocene concentrations 0.75g/ml, 1g/ml (ferrocene/carbon source) were studied and compared.;A set of semi-quantitative scale was devised to evaluate the yield, alignment and purity of the syntheses carbon nanotubes. Results from this experiment indicate that temperature is a critical variable in the production of carbon nanotubes for the experimental conditions used in the work. According to our results, the best temperature for the formation of carbon nanotubes was 1100°C. Higher ferrocene concentration was helpful to produce more dense and aligned carbon nanotube bundles. Cyclohexane is the carbon source which produced the best results in the study. The straight, aligned, dense and pure carbon nanotube bundles were synthesized at 1100°C, using cyclohexane as carbon source. The effect of carbon sources appears to be closely related to its molecular structure. The deposit composition was determined for each run in the experiment. The three factors have no direct influence to it. The atom percent of carbon of the carbon nanotube bundles was very high, which means the bundles have high purity. The deposit formed different zones along the quartz tube. At 1100°C, using cyclohexane carbon source, the carbon nanotube bundles only grown in a zone 36cm far from the orifice.