Eco-Materials Processing & Design VI

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Authors: Jae Won Kim, Seoung Soo Lee, Sung Kang Hur, Yeon Gil Jung, Chang Yong Jo
Abstract: A modified sol-gel method is proposed for the preparation of silicon carbide nano-particles and nano-whisker. Tetraethoxysilane (TEOS), SiO2 bead, and PMMA as precursor of carbon source were used for preparing a ternary carbonaceous silicon xerogel, and morpholine is employed in the sol-gel process as a catalyst reagent. SiC nano-particles and nano-whisker were obtained from carbothermal reduction and vapor-solid (VS) reaction of the ternary xerogel at 1300°C for 9h in a dynamic argon atmosphere (flow rate; 600 cm3/min), and then purified by removing excess silica, residual carbon, and other impurities. The purified SiC sample was characterized by TG/DTA, XRD, SEM, and HRTEM. The nano-particles and the nano-whisker were synthesized by different growth mechanisms, with an initial nucleation via a VS reaction between SiO vapor and carbon precursor (PMMA) and a partially subsequent growth via a vapor-vapor (VV) reaction between SiO and CO, respectively.
Authors: Jae Hyun Cho, Jung Suk Kim, Jun Boo Yu, Sung-Ok Sohn, Jeung Soo Huh
Abstract: The influence of oxidant on surface morphology and sensing property of polypyrrole (PPy) – poly (vinyl alcohol) (PVA) double layer sensors was investigated. PPy–PVA double layer sensors were prepared by vapor polymerization using FeCl3 as oxidizing agent and PVA as adhesive agent. The surface of PPy–PVA layer was observed on a scanning electron microscope (SEM). The surface morphology of sensor showed homogeneous layer and thickness of 1µm. And the sensing properties were investigated using a flow measuring system. The maximum sensitivity to methanol 1000ppm was proportional to increasing 12wt % FeCl3 concentration at 25°C. The response time was not affected by FeCl3 concentration, but the recovery time increased according to the amount of FeCl3. The best amount of FeCl3 was observed at 12wt%.
Authors: Yamato Hayashi, Hirotsugu Takizawa, Yoshitaka Saijo, Tohru Sekino, Katsuaki Suganuma, Koichi Niihara
Abstract: Applications of silver nano-sized metal particles were investigated for a new, ecologically friendly and economical liquid-solid (silver oxide-alcohol) system. Silver metal oxides as starting materials have merits in metal particles fabrication because these materials are decomposed only by heating in air. That is, noble metal oxide does not use thestrong reduction atmosphere. This reduction is ecologically clean because many noble metal oxides are not toxic, and because O2 is evolved during decomposition. We reduced silver metal oxides by ultrasound and fabricated silver nano metal nanoparticles at room temperature, and various applications were investigated. By choosing a suitable process and conditions, it is reasonable to expect that ultrasonic eco-fabrications can be extended to obtain various silver nano-particles containing materials.
Authors: Toshihiko Kujime, Soong Keun Hyun, Hideo Nakajima
Abstract: Lotus-type porous carbon steel with cylindrical pores was fabricated by a continuous zone melting method under pressurized mixture gases of hydrogen and helium. The microstructure of lotus-type porous steel was analyzed, and the tensile test was carried out. In the case of tensile test of the specimen with the cylindrical pores parallel to the solidification direction, the ultimate tensile strength was lower than the estimated value, but the yield strength was higher than the estimated value. It was assumed that the strength was decreased in proportion to decreasing cross section area of the specimen. The increasing of yield strength was attributed to precipitation strengthening. The influence of heat treatment (Quenching and tempering, normalizing) on the tensile properties was investigated.
Authors: Sang Yeup Park, Sung Whan Kim, Hee Gon Bang
Abstract: Mullite whiskers were synthesized by the reaction of fly-ash and alumina powder. During the reaction process, the effect of oxide additives on the formation of mullite whisker was investigated. Mullite whisker was synthesized above 1350oC with the addition of excess alumina, and the aspect ratio of mullite whisker increased with increasing sintering temperature and time. Also, the aspect ratio of mullite whisker is dependent on the liquid phase based on silicate composition. The effect of various oxide additives on the aspect ratio of mullite whisker was investigated.
Authors: Kyung Nam Kim, Dae Yong Shin, Se Gu Son, Yong Do Kim
Abstract: Calcium carbonate(CaCO3) was synthesized from aqueous CaCl2 solution, using the homogeneous precipitation technique, which uses the hydrolysis of urea. The effects of reaction conditions on the morphology of CaCO3 were examined at 50-90°C. Particle size of CaCO3 decreases, as the concentrations of urea and [Ca2+] are increased. Calcite is produced more, as the concentration of [Ca2+] is increased. Method to stir the reaction solution affects significantly the particle size and morphology of CaCO3. Uniform needle-like aragonite particles were obtained, when left at 90°C for 4hours without stirring.
Authors: Kyung Nam Kim, Yong Do Kim
Abstract: CaCO3 powders were prepared by the homogeneous precipitation method using CaCl2, urea as the starting materials. Uniform CaCO3(calcite, aragonite, vaterite) powders were obtained by various conditions. The surfaces of CaCO3 powders were modified by coating them with a lithium precursor using two different precipitation techniques: homogeneous decomposition of precipitating agents(urea, NaHCO3, NH4HCO3) and forced hydrolysis in pure water. Selecting the Ni(NO3)26H2O and urea(or NaHCO3, NH4HCO3) as Ni-source and precipitating agent respectively, the NiO could be uniformly coated on the CaCO3 powder in the aqueous system. The coating NiO layer dominated the surface properties of the coated lime powders. Calcination of these nickel hydroxide crystals in air at 500°C transformed them into NiO.
Authors: Dock Young Lee, Ki Bae Kim, Do Hyang Kim
Abstract: Forming of alloy and composite within a solid-liquid region, i.e. thixo-forming and rheo-forming, has been recognized as a technology offering several potential advantages over casting and forging such as a low forming pressure, reduction of macrosegregation, and reduction of porosity. In this paper, a globularization for primary solid phase by a forced fluid flow in melt due to electromagnetic stirring during solidification and isothermal stirring at solid-liquid region, was examined to produce Al alloy having a globular solid phase to get a thixotropic behavior. The electromagnetic stirrer was specially designed and manufactured to create all kind of fluid flow pattern such as a circumferential, vertical, helicoidally and contra-rotating flow pattern during the solidification of a melt. The size and roundness of primary solid phase of the quenched sample after isothermal stirring at solid-liquid region were measured with respect to a stirring time and frequency. The globularization of solid phase was enhanced with incresing the stirring time and electromagnetic flux density, i.e. stirring strength.
Authors: J.B. Park, S.-W. You, K.W. Cho, J.I. Lee, Soon Chul Ur, Il Ho Kim
Abstract: Induction melting was attempted to prepare the undoped and Nb-doped CoSb3 compounds, and their thermoelectric properties were investigated. Single phase d-CoSb3 was successfully obtained by induction melting and subsequent annealing at 400°C for 2 hours in vacuum. The positive signs of Seebeck coefficients for all the specimens revealed that Nb atoms acted as p-type dopants by substituting Co atoms. Electrical conductivity decreased and then increased with increasing temperature, indicating mixed behaviors of metallic and semiconducting conductions. Electrical conductivity increased by Nb doping, and it was saturated at high temperature. Maximum value of the thermoelectric power factor was shifted to higher temperature with the increasing amount of Nb doping, mainly originated from the Seebeck coefficient variation.
Authors: Ju-Young Jung, Myung Hoon Kim, Hee Soo Moon, Jong Wan Park
Abstract: We have prepared the Si/Mo multilayer consisting of active/inactive material using rf/dc magnetron sputtering. The pre-treatment using an ECR plasma were introduced at current collector for the adhesion and removal of surface contamination. The structural and electrochemical characteristics of multilayers have been investigated. The multilayer nearly maintained more than 90 % of the initial capacity (2653 mAh/g) after 100 cycles whereas the Si thin film was gradually degraded after 40 cycles.

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