• Carbon letters
• /
• v.8 no.2
• /
• pp.91-94
• /
• 2007

The application of Carbon and graphite based materials in unprotected environment is limited to a temperature of $450^{\circ}C$ or so because of their susceptibility to oxidation at this temperature and higher. To over come these obstacles a low cost chemical vapour reaction process (CVR) was developed to give crystalline and high purity SiC coating on graphite and isotropic C/C composite. CVR is most effective carbothermal reduction method for conversation of a few micron of carbon layer to SiC. In the CVR method, a sic conversation layer is formed by reaction between carbon and gaseous reagent silicon monoxide at high temperature. Characterization of SiC coating was carried out using SEM. The other properties studied were hardness density and conversion efficiency.

• Journal of environmental and Sanitary engineering
• /
• v.14 no.1
• /
• pp.54-61
• /
• 1999

The industrial techniques of ultrasound have been used in the various fields, such as cleaning, medical surgery, emulsification, cell disruption etc. Especially the application of cell disruption was interested in the field of disinfection process in water by ultrasonic irradiation. It has been recognized that the ultrasounds are irradiated in aqueous solution, cavitation bubbles are generated and shock waves of high temperature and pressure are emitted as the bubbles are developed and finally broken, which function as a energy source to promote reaction efficiencies of various kinds of chemical reactions such as disinfection reaction in water. Therefore, this study was performed to apply the ultrasound for the disinfection method of infected drinking raw water and to discuss the limiting factors such as pH, sample volume and reaction temperature influenced on the removal efficiency of E. coli from experimental analysis of the results obtained in bench-scale plant. For the experiments to measure the influence of reaction parameters in the ultrasonic disinfection process, escalated reactivity of aqueous solutions was excellent when pH in aqueous solution was low, and sample volume was small. On the contrary, the reactivity of disinfection became elevated when reaction temperature was high. It was found that the rate constant of disinfection reaction was applied by Chick's law, reaction kinetics of Chick's law was irreversible and pseudo-first order at all the tested conditions.As a conclusion it appeared that the technology using ultrasonic irradiation can be applied to the treatment of disinfection in infected water which are difficult to be treated by conventional methods.

• Journal of Powder Materials
• /
• v.30 no.3
• /
• pp.233-241
• /
• 2023

In this study, we evaluated the effects of acid leaching on the properties of Cr powder synthesized using self-propagating high-temperature synthesis (SHS). Cr powder was synthesized from a mixture of Cr2O3 and magnesium (Mg) powders using the SHS Process, and the byproducts after the reaction were removed using acid leaching. The properties of the recovered Cr powder were analyzed via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), particle size analysis (PSA), and oxygen content analysis. The results show that perfect selective leaching of Cr is challenging because of various factors such as incomplete reaction, reaction kinetics, the presence of impurities, and incompatibility between the acid and metal mixture. Therefore, this study provides essential information on the properties under acidic conditions during the production of high-quality Cr powder using a self-propagating high-temperature synthesis method.

• Tribology and Lubricants
• /
• v.37 no.2
• /
• pp.62-70
• /
• 2021

The problem with intermetallics coating using the heat of molten casting is that the heat generated during combustion synthesis dissolves the coating and the substrate metal. This study investigates whether pre-annealing before synthesis can control the reaction heat, with the aim of Ni₃Al coating on the casting surface. Therefore, the effects of the annealing temperature and time on the combustion synthesis behavior of the powder compact of Ni-25at%Al after annealing were investigated. As results, the reaction heat when synthesized decreased as the annealing temperature was high and the annealing time was longer. This was attributed to the fact that Al was diffused to Ni particles during low temperature annealing and intermediate Ni-Al compounds were formed during high temperature annealing. After combustion synthesis, however, it was found that their microstructures were almost identical except for the amount of intermediate intermetallics. Furthermore, an annealing temperature above 450℃, at which intermediate compounds begin to form, is needed to prevent the dissolving problem during synthesizing. The intermetallics synthesized after annealing at higher temperature and prolonger annealing time showed a good wear resistance. This might be because much intermediate intermetallics of high hardness were remained in the microstructure.

• KSBB Journal
• /
• v.16 no.1
• /
• pp.76-81
• /
• 2001

Stigmastanol, a functional agent of cholesterol-lowering in humans, was synthesized from stigmasterol. To investigate the usability as a raw material, the contents of sterol in vegetable oils and extract of soybean chaff were analyzed. The total sterol contents showed high values of 213.7 and 209.8 mg/100g in corn and soybean oils respectively. The extract of soybean chaff has played a good role as a raw material with high sterol contents. The kinetics of hydrogenation of stigmasterol was studied using a 5% Pd/AC catalyst in the temperature range of 30~$60^{\circ}$C. Increasing temperature showed a prominent decrease in conversion. The optimum temperature was $40^{\circ}$C for high yield of stigmastanol. The effects of $H_2$ pressure, agitation speed, catalyst loading, and stigmasterol concentration on reaction rate profile were also examined. From the power law model analysis using the initial rates of reaction, the reaction order was calculated as 0.705 for stigmasterol concentration and 0.147 for hydrogen pressure.

• Transactions of the Korean hydrogen and new energy society
• /
• v.17 no.4
• /
• pp.425-433
• /
• 2006

Sepiolite was selected as a mineral carbonation candidate ore for carbon dioxide sequestration. Carbonation salt formation from alkaline earth metal ingredient needs to dehydroxylation of sepiolite at high temperature. An evident dehydroxylation was observed over $800^{\circ}C$ and the variations of sepiolite characteristics after high temperature treatment was synthetically evaluated. Remarkable weight loss were measured after high temperature thermochemical reaction then crystallographic and spectroscopic changes were analyzed. The resulted alkaline earth metal oxides could explained by dehydroxylation based on thermochemical reaction.

• Computers and Concrete
• /
• v.13 no.1
• /
• pp.97-115
• /
• 2014

Silica fume is a by-product of induction arc furnaces and has long been used as a mineral admixture to produce high-strength, high-performance concrete. Due to the pozzolanic reaction between calcium hydroxide and silica fume, compared with that of Portland cement, the hydration of concrete containing silica fume is much more complex. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of concrete containing silica fume. The heat evolution rate of silica fume concrete is determined from the contribution of cement hydration and the pozzolanic reaction. Furthermore, the temperature distribution and temperature history in hardening blended concrete are evaluated based on the degree of hydration of the cement and the mineral admixtures. The proposed model is verified through experimental data on concrete with different water-to-cement ratios and mineral admixture substitution ratios.

• Journal of the Korean Ceramic Society
• /
• v.37 no.4
• /
• pp.332-337
• /
• 2000

Forming mechanism of fibrous TiC during self-propagating high temperature synthetic reaction was analyzed and suggested. It was revealed that critical temperature for the stable fiber formation was not the melting point of TiC, but the eutectic reaction temperature of TiC and C. Minimum amount of TiC diluent addition required to form fibers was calculated to be 25.6%, which was consistent with the experimental result. Synthesized fibers were found hollow tube-like. The morphology was explained by the diffusion rates of C and Ti in TiC, and by the molar volume chnage of C during the reaction. Expanding shell model was suggested for the hollow fiber formation mechanism.

• Journal of the Korean Society of Combustion
• /
• v.21 no.4
• /
• pp.23-29
• /
• 2016

Reactivity of gasification defined by bouardard reaction is critical parameter in efficiency of the gasifier. In this study, char reactivity of the gasification was derived from the experiments using the intrinsic reaction kinetics model. Pressurized wire mesh heating reactor (PWMR) can produce high temperature and high pressure conditions up to 50 atm and 1750 K, respectively and PWMR was designed to evaluate the intrinsic reaction kinetics of $CO_2$ gasification. In this study, Kideco and KCH (sub-bituminous Indonesian coal) were pulverized and converted into char. Experiments used the PWMR were conducted and the conditions of the temperature and pressure were 1373~1673 K, 1~40 atm. To distinguish the pressure effect from high pressurized condition, internal and external effectiveness factors were considered. Finally, the intrinsic kinetics of the Kideco and KCH coal char were derived from $n^{th}$ order reaction rate equations.

• Transactions of the Korean hydrogen and new energy society
• /
• v.18 no.3
• /
• pp.317-324
• /
• 2007

The conversion reaction of ortho to para hydrogen was studied. The percentage of ortho and para hydrogen is mainly dependent on the equilibrium temperature. Because this reaction is known to be accelerated by the catalyst such as nickel-silicate and ruthenium on silica, we focused in the test and development of the catalysts. We studied metal-silicates because they provide high metal dispersion on support. Nickel-silicate, ruthenium-silicate and mixed-silicate were prepared by the coprecipitation method and used in the reaction at the temperature of liquid nitrogen. The conversion was measured by the difference of thermal conductivity between reference gas and sample gas. The activation condition was important and it affected the activities of the catalysts. Nickel-silicate showed high activities. Ruthenium-silicate also showed relative high activities but mixed-silicate showed poor activities.