Dalkeun Park

Photocatalytic TiO2 deposition by chemical vapor deposition

Dip-coating, spray-coating or spin-coating methods for crystalline thin film deposition require post-annealing process at high temperature. Since chemical vapor deposition (CVD) process is capable of depositing high-quality thin films without post-annealing process for crystallization, CVD method was employed for the deposition of TiO2 films on window glass substrates. Post-annealing at high temperature required for other deposition methods causes sodium ion diffusion into TiO2 film from window glass, resulting in the degradation of photocatalytic efficiency. Anatase-structured TiO2 thin films were deposited on window glass by CVD, and the photocatalytic dissociation rates of benzene with CVD-grown TiO2 under UV exposure were characterized. As the TiO2 film deposition temperature was increased, the (112)-preferred orientations were observed in the film. The (112)-preferred orientation of TiO2 thin film resulted in a columnar structure with a larger surface area for benzene dissociation. Obviously, benzene dissociation rate was maximum when the degree of the (112) preferential orientation was maximum. It is clear that the thin film TiO2 should be controlled to exhibit the preferred orientation for the optimum photocatalytic reaction rate. CVD method is an alternative for the deposition of photocatalytic TiO2.

Electrochemical properties of PAN-based carbon fibers as anodes for rechargeable lithium ion batteries

Abstract Polyacrylonitrile(PAN)-based carbon fibers were tested as anodes for lithium ion rechargeable batteries. PAN-based fibers were first stabilized under tension in air at about 200°C (stabilization tension) and then carbonized in different gas environments (carbonization atmospheres) at heat treatment temperatures (HTT) between 700 and 1500°C. The carbon fiber electrodes were prepared at various conditions using the stabilized PAN fibers and then their electrochemical characteristics were investigated. The PAN-based carbon fiber prepared at an oxidative stabilization tension of ca. 10 MPa showed the highest discharge capacity in our experimental range. We found that the effective diffusion coefficient of lithium in the carbon fiber electrode was influenced by the carbonization environment employed. The electrochemical intercalation process depended on mass transfer of lithium into carbon layer which is rate-determining during the electrode charge–discharge process. The effect of HTT on discharge capacity varied depending on the combined effect of both the amount of intercalation sites available and the electric conductivity of the carbon fiber used.

Synthesis of carbon nanotubes on metallic substrates by a sequential combination of PECVD and thermal CVD

Abstract Carbon nanotubes were synthesized from acetylene and hydrogen gas mixture directly on stainless steel plates by sequential combination of rf PECVD and thermal CVD. PECVD was used for nucleation and initial growth of carbon nanotubes while thermal CVD was utilized for further growth of them. In this way decoupling of nucleation and growth of carbon nanotubes was realized, and growth of carbon nanotubes was enhanced compared to growth by PECVD. Synthesized carbon nanotubes were curly in shape, and proper pretreatment of the substrate surface was required for the satisfactory growth of carbon nanotubes. Carbon nanotubes could be fabricated into electrodes for electric double layer capacitors without any further treatment. With an electrolyte composed of lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate, charge/discharge test showed specific capacitance in the range of 33–82 F/g.

Remediation of petroleum-contaminated soils by fluidized thermal desorption

A novel type of fluidized bed desorber was developed for the remediation of petroleum-contaminated soils at low temperature with high efficiency. Cahn balance® was utilized to investigate the thermal desorption behavior of soils contaminated by various hydrocarbons. The performance of the fluidized-bed desorber was investigated at different operating modes. Batch operation of the fluidized-bed desorber exhibited 99.9% desorption efficiency at temperatures of ca. 300°C within a half hour. Continuous operation of the fluidized-bed indicated that Q/F (the ratio of the mass flow rate of fluidizing gas to feeding rate of contaminated soils) is less important at higher temperature (>300°C), if proper fluidization is ensured. The periodic operation of the fluidized bed desorber shows the possibility to reduce off-gas volume significantly.

Electrochemical characteristics of graphite coated with tin-oxide and copper by fluidised-bed chemical vapour deposition

Abstract Anodes for a lithium secondary battery are prepared with synthetic graphite (meso-phase carbonaceous microbead: MCMB) which is coated with tin-oxide and copper by fluidised-bed chemical vapour deposition (FCVD). In the present study, three different samples was prepared, and their electrochemical characteristics are examined by using X-ray diffraction, electrochemical voltage spectroscopy (EVS), scanning electron micrography, ac impedance measurements, and galvanostatic charge–discharge experiments. The electrode coated with tin-oxide gives higher capacity than uncoated MCMB, but the capacity decreases with cycling. This is probably due to severe volume changes. The cycleability is improved, however, by coating copper on the surface of the carbonaceous material coated with tin-oxide. The copper plays an important role as an inactive matrix which provides a buffer against volume changes.

Kinetics of steam reforming over a Ni/alumina catalyst

AbstractSteam reforming of methane over a commercially available, nickel/alumina catalyst was experimentally studied. The reactor employed for the study was made of 7 mm i.d. quartz tube and catalyst particles were 0.84-1 mm in size. The amount of catalyst charge in the reactor was around 0.3 gram. Experiments were carried out varying the steam to methane ratio in the feed gas from 1 to 10 and reaction temperature from 823 to 1073 K. Nitrogen gas was used to control partial pressure of methane and steam. Using Marquardt method reaction rate derived from the experiments was fitted to

Hydrogen production from fluidized bed steam reforming of hydrocarbons

reaction rate = 1,527 exp( - 14,820/RT) P^{1.014} _{CH_4 } P^{ - 0.9577} _{H_2 0}

Structural Analysis on Photocatalytic Efficiency of TiO2 by Chemical Vapor Deposition

Thus reaction order was close to one for methane and close to minus one for steam, respectively.