Synthesis of carbon nanotubes by microwave plasma chemical vapor deposition using nickel catalyst on iron substrates

• Main Authors: Baylas, Dominic F., Choi, Van Welly K., Santiago, Cherrylane E.
• Format: text
• Language: English
• Published: Animo Repository 2007
• Subjects: Carbon; Nanostructured materials; Tubes
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/5726
• Institution: De La Salle University

Carbon nanotubes, a product of nanotechnology, gained a lot of attention since its discovery in 1991. Carbon nanotubes (CNT) can be visualized as a sheet of graphite rolled into a tube with bonds at the end of the sheet forming the bonds that close the tube and cannot be found in a natural state. It is now considered as one of the allotropes of carbon and can be classified into two categories: single walled CNT (SWCNT) and multiwalled CNT (MWCNT). SWNTs are single, long graphene sheets while MWCNTs are collection of concentric SWCNT with different diameters. The physical and chemical characteristics of CNTs are very remarkable. CNTs can be use as energy storage, molecular electronics, nanoprobes and sensors, composite materials and templates. There are basically three (3) ways on producing CNT: electric arc discharge, laser ablation and chemical vapor deposition (CVD). Out of these three (3), CVD became the most viable candidate for producing CNT because of its low cost set-up and simple process. The group synthesized carbon nanotubes using Microwave Plasma Chemical Vapor Deposition (MPCVD) is a low temperature process. It uses microwave technology to produced plasma and to decompose hydocarbon gas into reactive cacrbon. In synthesizing CNT, acetylene and nitrogen were used as carbon source and carrier gas, respectively. These gases were introduced into the reactor at different C2H2 and N2 flow ratio (5:100, 10:95, 15:90). CNT's were grown on 1/8" flat washer substrates dipped in 0% w/v, 0.01% w/v or 0.1% w/v nickel solution. A domestic microwave oven was used as energy source. The setting (microwave setting = 6, 8 and 10) and operating time (time = 10, 15 and 20 minutes) were varied in the experimental runs. Plasma was induced inside a quartz glass reactor using a pencil lead of 0.5 mm diameter, and microwave excitation at low pressure of 20-21 in Hg vacuum. Experimental runs were based on the the Taguchi Design of Experimental (DOE). The orthogonal array used was L934 (9 runs, 3 levels and 4 factors). These four factors include C2H2 to N2 flow ratio, %w/v Ni, microwave setting and operating time. Through combinations of these variables, optimum conditions of the production were achieved. Scanning Electron Microscope (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) were used in charactering the products. Nickel metals were found on the flat washers when scanned using EDX proving that dipping the substrate in nickel solution can be an alternative way in impregnating the substrate with catalyst. CNTs, having diameters of about 50 nm to 900 nm based on SEM images, were produced. Upon the analysis of sample using XRD, peak at 20=25° was found in the diffractogram, suggesting that there were CNTs formed. In optimizing the production, minimum diameters were determined from SEM images for each run. The group found that the microwave setting of 87%, 5:100 C2H2 and N2 flow ratio, microwave operating time of 15 minutes and 0.01% Ni dip coat solution concentration, created CNT's with the least minimum diameters.