Effect of magnetic field on the synthesis of carbon nanotubes using MPECVD

• Main Author: Lugod, Cyril Benedict V.
• Format: text
• Language: English
• Published: Animo Repository 2018
• Subjects: Carbon nanotubes—Synthesis; Magnetic fields; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/6328; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/13393/viewcontent/Lugod_Thesis_Final_REVISED2.pdf
• Institution: De La Salle University

Carbon nanotubes (CNTs) are carbon allotropes characterized by their tubular structures and high aspect ratios. Their unique properties are highly prized for a myriad of practical applications, which has gained significant interest among the research community. Despite the multitude of applications in many fields, commercial production of CNTs are limited by production issues regarding CNT growth and morphology. Hence, further studies on experimental factors regarding CNT production are needed to optimize CNT production in a commercial scale. This study focuses mainly on the determination of the effects of the presence of a magnetic field during CNT synthesis in a Microwave Enhanced Plasma Chemical Vapor Deposition (MPECVD) process using a Whirlpool AVM585 conventional microwave oven. The study also determined the effects of hydrogen catalyst plasma pretreatment on CNT growth. The experiment was based on a Taguchi orthogonal array design. The effects of the experimental factors such as magnetic field strength (0, 5, and 10 mT), catalyst pretreatment time (10, 15, and 20 min), hydrogen gas flow rate (25, 50, and 75 mL/min), and microwave power (451, 570, and 740 W) on the responses such as the catalyst nanoparticle Feret diameter, CNT diameter, tortuosity, weight, and purity were investigated. Among the design factors, application of magnetic field at 10 mT improved all the responses, most notably the CNT diameter and tortuosity being reduced by 60% and 48% compared to runs with no magnetic field, respectively. Under tortuosity, magnetic field was the design factor which had the greatest effect on decreasing the tortuosity of the CNTs at around 100 times the effect measured under other design factors. Catalyst plasma pretreatment was most optimal at the highest hydrogen flow rate and microwave power setting, under the influence of the highest magnetic field strength. The effects of the factors during catalyst plasma pretreatment also resulted to improved characteristics of the CNTs during the CNT synthesis. Overall, the findings suggest that the application of a magnetic field during catalyst plasma pretreatment and the subsequent CNT synthesis results to catalyst nanoparticles and CNTs with improved properties such as lower catalyst nanoparticle Feret diameter, CNT diameter, tortuosity and higher CNT yield and purity.