• Korean Journal of Materials Research
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• v.5 no.7
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• pp.869-879
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• 1995

TiAi intermetallic compound has been extensively studied for possible high temperature structural applications because of its high specific strength at high temperature, high creep resistance, and good oxidation resistance at elevated temperatures. In addition to its good properties, an economic manufacturing routes should be developed for this material to be used more extensively. One of the promising route in manufacturing TiAl intermetallics is the Self-propagating High-temperature Synthesis (SHS) method. Thus in this study, an attempt was made to study the mechanism of the SHS process in TiAl synthesis. The composition of the sample was Ti-(45, 50, 53)at% Al and the microstuctures of the products were analyzed using optical microscope and scanning electron microscope. When the phases formed at the main SHS reaction of whicyh combustion temperature is higher than the melting temperature of aluminum were identified as TiAl and Ti$_3$Al ; Ti$_3$Al cores surrounded by TiAl phase. In order to increase the combustion temperature, carbon was added 5 and 10at.%. When the carbon content was 10at.%, the heat of the reaction was large enough to melt the phase formed and that is consistent with the theoretical calculation results of the adiabatic temperature. The combution temperatue, which was measured by a computer data acquisition system, increased with the carbon content. The phases formed from the reaction involving the carbon added were indentified as TiAl and Ti$_2$AlC using XRD. The vickers hardness of the reaction product increased with the carbon content.

• Journal of the Korean Ceramic Society
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• v.44 no.6 s.301
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• pp.331-337
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• 2007

High temperature reaction behaviors of various oxide materials (such as bauxite, pyrophyllite, mullite and fused silica powders) used in the refractory materials for tap-hole plugging of blast furnace were investigated with varying temperature in the carbon surrounding. Kinetics of carbothermal reduction of $SiO_2$ for forming SiC with high corrosion resistance were strongly dependent on it's crystalline phase. SiC generation yield increased with increasing catalyst amount in oxide regardless of generated SiO gas amount at temperature of $<1500^{\circ}C$. However, in case of fused silica over $1500^{\circ}C$, SiC generation yield was dominantly influenced by SiO amount without catalyst effect. Bauxite showed the most effective carbothermal reduction reaction, since bauxite have a large amount of catalyst and well-dispersed $SiO_2$ phase in oxide matrix.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.164-170
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• 2001

The Self-propagating High-temperature Synthesis (SHS) for synthesizing ($Mo_{1-z}$ , $W_{z}$)$Si_2$was conducted experimentally with the mole fraction of Tungsten(W) from z=0.0 to z=0.5. The temperature profile was measured according to the reaction time through the thermocouple that was equipped into the center of these samples. When the reaction front is propagated around the thermocouple, the highest temperature appears and we regard this temperature as the adiabatic temperature. We found out by experimental results that the reaction velocity is in the range of 2.14~1.35mm/sec and the adiabatic temperature is in the range of 1883~1507K for the six samples. The reaction velocity and the adiabatic temperature were inclined to decrease with an increasing of the mole fraction of Tungsten (W). The SHS modeling is presented in order to predict the temperature profiles and these results are compared with the experimental results. It is predicted that in case of increasing the initial temperature of these six samples, the reaction temperature increased and that the sample of z=0.5 needs the preheating up to 800~900K in order to become reaction temperature 1900K.

• Journal of the Korean Ceramic Society
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• v.23 no.1
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• pp.33-43
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• 1986

The synthesis of high-purity AlN by a vapor-phase reaction was investigated using the $NH_3-AlCl_3-H_2$ reacting system. The theoretical yields of AlN were determined from th thermodynamic equilibrium composi-tions. It was shown that the yields above 90% could by obtained even in the range of relatively low temper-ature of 600-1200K. The reaction temperature and the initial amounts/ratios of the reacting gases showed significant effects on the yields but the total pressure did not. The experimental results showed that a high-purity AlN having a needle shape was the only product as a solid phase and its amount produced increased with the reaction temperature. While the degree of agglmera-tion of the synthesized AlN increased with the reaction temperature the size of each particle consisting of the agglomerates was independent of the temperature but grew from 0.09 to 0.115${\mu}{\textrm}{m}$ with the flow rate of NH3. These experimental results were compared with the theoretical aspects for the synthesis of a high-purity AlN.

• Journal of the Korean Solar Energy Society
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• v.34 no.6
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• pp.11-18
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• 2014

Two-step water splitting thermochemical cycle with $CeO_2$ foam device was investigated by using a solar simulator composed of 2.5 kW Xe-Arc lamp and mirror reflector. The hydrogen production of $CeO_2$ foam device depending on reaction temperature of Thermal-Reduction step and Water-Decomposition step was analyzed, and the hydrogen production of $CeO_2$ and $NiFe_2O_4/ZrO_2$ foam devices was compared. As a result, the amount of reduced $CeO_2$ considerably varies according to the reaction temperature of Thermal-Reduction step. and hydrogen production was not much when the amount of reduced $CeO_2$ decreased even if the reaction temperature of Water-Decomposition step was high. Therefore, it is very important to keep the reaction temperature of Thermal-Reduction step high in two-step thermochemical cycle with $CeO_2$.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.738-751
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• 2018

The effect of the reaction temperature and reaction time on the thermal oxidative purification quality of detonation nanodiamond (NDsoot) was investigated in a gas-solid fluidized bed reactor of a $0.10m-ID{\times}1.0m$-high stainless steel column with zirconia beads ($d_{SV}=99.2{\mu}m$). The carbon conversion increased with increasing the reaction temperature; however, when the reaction temperature was greater than 773 K, the carbon conversion did not increase. The content of $sp^3$-hybridized carbon at the reaction temperature of 703 K barely changed when the reaction time was more than 30 minutes, but at 773 K, the content decreased as preferred. At 703 K, the purification quality increased with the increasing reaction time; however, at 773 K, the purification quality increased up to 30 minutes and then decreased rapidly.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.573-580
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• 1998

Self-propagating high temperature synthesis (SHS) technique was used to synthesize the spinel phase of $MgAl_2O_4$ from MgO and Al powder. Thermit reaction products of MgO and Al, The reaction products were heat treated at the temperature $800^{\circ}C$ preheating. Processing factors such as DTA/TG, combustium product and maxium temperature, synthesis of MgO and Al from "$MgO+2Al+3/2O_2$\rightarrow$MgAl_2O_4$". An activation energy (${\Delta}H^{\circ}$)-264.8 kcal/mol and reaction of maxium temperature 5634 K was calculated to form a $MgAl_2O_4$ spinel from unreacted materials. Pellet were increased volume 6% after thermit reaction. reaction.

• New & Renewable Energy
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• v.5 no.4
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• pp.52-58
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• 2009

Upgrading of pyrolysis wax oil using HZSM-5 catalyst has been conducted in a continuous fixed bed reactor at $450^{\circ}C$, 1hour, LHSV 3.5/h. The catalytic degradation was studied with a function of catalyst amount and reaction temperature. The raw pyrolysis wax oil shows relatively high boiling point distribution ranging from around $300^{\circ}C$ to $550^{\circ}C$, which has considerably higher boiling point distribution than that of commercial diesel. The catalytic degradation using HZSM-5 catalyst shows the high conversion of pyrolysis wax oil to light hydrocarbons. The liquid product obtained shows high gasoline range fraction as around 90% fraction and considerably high aromatic fraction in liquid product. Here, the experimental variable such as catalyst amount and reaction temperature was influenced on the product distribution.

• Journal of the Korea Institute of Building Construction
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• v.14 no.3
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• pp.273-284
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• 2014

Ultra-high-performance concrete (UHPC) consists of cement, silica fume (SF), sand, fibers, water and superplasticizer. Typical water/binder ratios are 0.15 to 0.20 with 20 to 30% silica fume. In the production of ultra-high performance concrete, a significant temperature rise at an early age can be observed because of the higher cement content per unit mass of concrete. 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 ultra-high performance concrete. The heat evolution rate of UHPC is determined from the contributions of cement hydration and the pozzolanic reaction. Furthermore, by combining a blended-cement hydration model with the finite-element method, the temperature history in the hardening of UHPC is evaluated using the degree of hydration of the cement and the silica fume. The predicted temperature-history curves were compared with experimental data, and a good correlation was found.

• Journal of Ceramic Processing Research
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• v.19 no.6
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• pp.514-518
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• 2018

The direct carbon fuel cell (DCFC) has attracted researcher's attention recently, due to its high conversion efficiency and its abundant fuel, carbon. A DCFC mathematical model has developed in two-dimensional, lab-scale, and considers Boudouard reaction and carbon monoxide (CO) oxidation. The model simulates the CO production by Boudouard reaction and additional electron production by CO oxidation. The Boudouard equilibrium strongly depends on operating temperature and affects the amount of produced CO and consequentially affects the overall fuel cell performance. Two different operating temperatures (973 K, 1023 K) has been calculated to discover the CO production by Boudouard reaction and overall fuel cell performance. Moreover, anode thickness of the cell has been considered to find out the influence of the Boudouard reaction zone in fuel cell performance. It was found that in high temperature operating DCFC modeling, the Boudouard reaction cannot be neglected and has a vital role in the overall fuel cell performance.