Chang-Seop Lee

By Chang-Seop Lee and Yura Hyun

Among the various synthesizing technologies of carbon nanofibers (CNFs), chemical vapor deposition (CVD) technology, which uses hydrocarbon gas or carbon monoxide as a carbon source gas and pyrolyzes it to grow CNFs on transition metal catalysts, such as Ni, Fe, and Co, has been regarded as the most inexpensive and convenient method to produce CNFs for industrial use. Experimental variables for CVD are source gas, catalyst layers, temperature, and reaction time. Since the particle size of metal catalysts has an influence on the diameter of CNFs, it is possible to control the diameter of CNFs by varying particle sizes of the metal. As such, it is possible to synthesize CNFs selectively through the selective deposition of catalyst metals. In this study, CNFs were grown by CVD on C-fiber textiles, which had catalysts deposited via electrophoretic deposition. The CNFs were coated with a silica layer via hydrolysis of TEOS (tetraethyl orthosilicate), and the CNFs were oxidized by nitric acid. Due to oxidation, a hydroxyl group was created on the CNFs, which was then able to be used as an activation site for the SiO2. CNFs and the CNFs/SiO2 composite can be used in various applications, such as a composite material, electromagnetic wave shielding material, ultrathin display devices, carbon semiconductors, and anode materials of Li secondary batteries. In particular, there is an increasing demand for lightweight, small-scale, and high-capacity batteries for portable electronic devices, such as laptop computers or smart phones, along with the escalating concern of fossil energy depletion. Accordingly, CNFs and CNFs/SiO2 composites are receiving attention for their use as anode materials of Li secondary batteries, which are eco-friendly, lightweight, and high capacity. Therefore, the physicochemical properties and electrochemical performance data of synthesized CNFs and CNFs/SiO2 composite are described in this chapter.

Part of the book: Nanofiber Research

By Chang-Seop Lee and Yura Hyun

Hydrocarbon gas or carbon monoxide was pyrolyzed by chemical vapor deposition (CVD), and carbon nanofiber (CNF) synthesis was performed using transition metals such as Ni, Fe, and Co as catalysts. When synthesizing carbon nanofibers using the CVD method, experimental variables are temperature, catalysts, source gas, etc. Especially, the particle size of the catalyst is the most important factor in determining the diameter of carbon nanofibers. Hydrocarbon gases, such as CH4, C2H4, benzene, and toluene are used as the carbon source, and in addition to these reaction gases, nonreactive gases such as H2, Ar, and N2 gases are used for transportation. Synthesis occurs at a synthesis temperature of 600–900°C, and catalyst metals such as Ni, Co, and Fe are definitely required when synthesizing CNFs. Therefore, it is possible to synthesize CNFs in selective areas through selective deposition of such catalyst metals. In this study, CNFs were synthesized by CVD. Ethylene gas was employed as the carbon source for synthesis of CNFs with H2 as the promoting gas and N2 as the balancing gas. Synthesized CNFs can be used in various applications, such as composite materials, electromagnetic wave shielding materials, ultrathin display devices, carbon semiconductors, and anode materials of Li secondary batteries. In particular, there is an increasing demand for light-weight, small-scale, and high-capacity batteries for portable electronic devices, such as notebook computers or smartphones along with the recent issue of fossil energy depletion. Accordingly, CNFs and their silicon-series composites are receiving attention for use as anode materials for lithium secondary batteries that are eco-friendly, light weight, and high capacity.

Part of the book: Chemical Vapor Deposition

By Chang-Seop Lee and Yong Jae Kim

This study concerns gas sensors that may protect individuals by detecting hazardous gases that may be generated in hot spaces (≥50°C) with residues of organic waste. We investigated the responses and selectivities of the sensors to different kinds of hazardous gases such as acetaldehyde, toluene and hydrogen sulfide. We also investigated operating temperatures and catalysts for the sensors. The thick film semiconductor sensors that detected some hazardous gases were prepared using nano-sized sensing material powders (SnO2, WO3, ZnO) that were prepared through sol-gel and precipitation methods. The nano-sized sensing materials were blended with various amounts of metal oxides (SnO2, ZnO, WO3) and coated with transition metals (Pt, Pd, Ru, Au, Ag, Cu and In). The metal oxide thick films were fabricated on an Al2O3 plate with a Ni-Cr heater and a Pt electrode through a screen-printing method. Morphologies, compositions, phases, surface areas and particle sizes of sensor compounds were examined by SEM, EDS, XRD and BET analysis. The investigated response to the various hazardous vapors was expressed as the value of Ra/Rg, where Ra and Rg are the resistance of the sensor material in the air and in hazardous gas, respectively.

Part of the book: Electrochemical Sensors Technology