• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.249-254
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• 2003

AI, AIN and additives such as Li$_2$CO$_3$, Y$_2$O$_3$ and CaCO$_3$ which promoted nitridation were mixed, formed and heat-treated in nitrogen atmosphere. The effect of solvent, additive and temperature on nitridation of AI-AIN system was studied. When ethanol containing 1 wt% oleic acid was used as a mixing solvent, the formation of oxide was minimized due to surface modification of AI and AIN particles. The addition of Li$_2$CO$_3$ or CaCO$_3$ as an additive extremely diminished the formation of oxide which formed during heat treatment for nitridation compared with the addition of Y$_2$O$_3$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.2
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• pp.162-168
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• 2011

In this research, nitrogen plasma source ion implantation(PSII) of non-coated tungsten carbide endmill tools was conducted with low heat treatment for increasing wear resistance. After the low heat treatment of PSIIed tools to give a homogeneity of wear resistance, the surface modification of tools was analyzed by hardness test, surface roughness and cutting forces. As for the resultant cutting forces, low heat treatment in temperature of $400^{\circ}C$ and $500^{\circ}C$ is stable because of low cutting resistance. The 20-minutes heat treated tool at spindle speed 25000rpm has superiority of surface roughness, Ra of $0.420{\mu}m$ and was found to have good wear resistance. The higher hardness value was obtained by increasing temperature from $300^{\circ}C$ to $600^{\circ}C$ for PSIIed tools with low heat treatment. As the PSIIed tools under 10minutes at temperature of $600^{\circ}C$ have the highest hardness as Hv of 2349.8, It was analyzed that temperature processing give much influences on hardness.

• Journal of Korea Foundry Society
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• v.13 no.4
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• pp.323-332
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• 1993

An implicit finite difference formulation with three methods of latent heat treatment, such as equivalent specific heat method, temperature recovery method and enthalpy method, was applied to solidification analysis. The Neumann problem was solved to compare the numerical results with the exact solution. The implicit solutions with the equivalent specific heat method and the temperature recovery method were comparatively consistent with the Neumann exact solution for smaller time steps, but its error increased with increasing time step, especially in predicting the solidification beginning time. Although the computing time to solve energy equation using temperature recovery method was shorter than using enthalpy method, the method of releasing latent heat is not realistic and causes error. The implicit formulation of phase change problem requires enthalpy method to treat the release of latent heat reasonably. We have modified the enthalpy formulation in such a way that the enthalpy gradient term is not needed, and as a result of this modification, the computation stability and the computing time were improved.

• Advances in concrete construction
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• v.6 no.6
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• pp.659-677
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• 2018

The use of some superplasticizers in the production of mortar or concrete influences the hydration kinetic and the amount of total heat. This results in a modification of some properties, namely mortar workability, mechanical strength and durability. Three superplasticizers were used; a polynaphthalenesulfonate (PNS), a melamine resin (PMS) and a polycarboxylate (PC). They have been incorporated into various amount in a standardized mortar based on limestone cement. The aim of this study was to evaluate the rheological, mechanical and Calorimeters properties of this mortar. This will select the most compatible product and more able to be used depending on the climate of the country and the cement used. The PNS is incompatible with this type of cement registering a decrease of strength but the PMS and the PC modify the kinetics of hydration with significant heat generation and improved mechanical strength. The measured heat flow is significantly influenced by the type and dosage of superplasticizer especially for low dosage. Hydration heat and compressive strength of the different mixtures can be evaluated by determining their ultimate values and ages to reach these values where the correlation coefficients are very satisfactory.

• Elastomers and Composites
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• v.56 no.2
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• pp.72-78
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• 2021

A phase-change material (PCM) is a material that has the ability to delay heat transfer by absorbing heat from its environment or releasing heat to its environment while its phase changes from solid to liquid or liquid to solid at a specific temperature. As it is applied, it can contribute to environmental conservation such as energy savings and carbon dioxide emission reduction. In order for a PCM to store and release heat, the volume change during its phase transition should be large, and thus a phase transition space is required. When a PCM is used as a polymer additive, it is confined within the polymer, and there is no phase transition space; thus, its ability to absorb and release heat is significantly reduced. Therefore, in this study, porous silica was used to provide EVA/PCM compounds with sufficient space for their phase transition, and to improve the compatibility between the EVA and PCM, modified silica is used: surface-modified 5 wt% silica with 3-methacryloxypropyltrimethoxysilane. The compound was prepared and compared with the silica compound. The presence or absence of the modified silica surface modification was confirmed using Fourier-transform infrared spectroscopy and thermogravimetric analysis, the heat capacity of the compound was evaluated based on a differential scanning calorimetry analysis, and its mechanical strength and morphology were determined using scanning electron microscopy.

• Progress in Superconductivity and Cryogenics
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• v.6 no.1
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• pp.1-5
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• 2004

Long length of Bi-2223/Ag superconducting wives were fabricated by stacking and drawing process with advanced heat-treatment schedules. Intermediate annealing was carried out to increase the homogeneity and uniformity of the superconducting filaments embedded in the silver matrix. Phase modification from tetragonal to orthorhombic Bi-2212 by pre heat treatment(PHT) was executed to improve the texture and phase transformation of Bi-2223. Drawing stress was measured to predict the sausaging and stress limit. Rolling Parameters such as thickness. width and winding tension were investigated to roll the tape with uniformity. 1 km length of Bi-2223/Ag superconducting wires were fabricated without any breakage. Critical current (Je) of 270 m length of superconducting tapes was measured over than $70 A/cm^2$ continuously after final sintering.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.199-204
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• 2000

This paper reports a thermal environmental analysis of a room in accommodated with multi-heat sources according to ventilation condition. Two case modification have been investigated to obtain the lower temperature distribution in the room. The temperature distribution of the original room were found about $25{\sim}35^{\circ}C$. As a result, the use of, three ventilating fans and two electric fans are useful for room ventilation respectively, and using two electric fan is more recommendable in side of economical efficiency.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.5
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• pp.380-385
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• 2016

Railway tracks are repeatedly overstressed and damaged owing to increase in passing tonnage and numerous contact cycles between wheels of train and rails. In order to ensure safe train operation, heat-treated rails are used in addition to regular inspection and maintenance of these rails. Normal rails were treated using ultrasonic nanocrystal surface modification (UNSM) to strengthen the surface of rails. A few changes in surface properties were detected with respect to hardness and compressive residual stress after UNSM treatment. Wear and rolling contact fatigue tests were performed using rails whose surfaces were hardened by UNSM and heat-treated rails. The amount of wear and fatigue life cycles were measured to estimate the effect of UNSM on the rail material. The material of the surfacehardened rail showed improved wear and rolling contact fatigue properties.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2009.04a
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• pp.278-283
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• 2009

This study aims to figure out the old people's needs for modification of their housing to maintain an independent lifestyle despite their health status and living arrangements. The total of 438 residents take part in the questionnaire survey research through the quota sampling method grouped by age (60-64 group, 65-69 group, 70-74 group, and over 75 group), sex (male and female), and house type (apartment houses and others). The results are as follows. (1) The old people's most inspired modification needs in interior spaces are remodeling the heating controls in the living room and the bedroom, ventilation facilities and storage spaces in the kitchen, non-slip tile flooring and ventilation facilities in bathroom, an easy door-lock, non-slip tile flooring, a draft cut-off, and storage spaces in the entrance. Besides they require emergency alarm, easy door and window locks, fire and gas alarm, and furniture with easy handling. It is necessary to supply the aged with the appropriate heating controls for their sensitivity to heat, with enough storage spaces for the increased possessions, and with diverse safety systems reflected blunting of mobility and sensibility. (2) As they grow older, the aged require more remote controls and safety facilities such as emergency alarm, easy locks and furniture with distinguishable colors. Male elderly is more concerned with safety, while female elderly do with convenience due to their different time spending in the house. The elderly residents in the apartment houses require the heating controls, a draft cut-off, and storage space less than other types of houses. Thus modification of the heating controls, a draft cut-off, and storage space are regards as basic needs for the elderly residents in non-apartment houses.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.10
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• pp.729-736
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• 2009

Pool boiling heat transfer and critical heat flux (CHF) of water-based nanofluids with alumina and titania nanoparticles of 0.01% by volume were investigated on a disk heater at saturated and atmospheric conditions. The experimental results showed that the boiling in nanofluids caused the considerable increase in CHF on the flat surface heater. It was revealed by visualization of the heater surface subsequent to the boiling experiments that a major amount of nanoparticles deposited on the surface during the boiling process. Pool boiling of pure water on the surface modified by such nanoparticle deposition resulted in the same CHF increases as what boiling nanofluids, thus suggesting the CHF enhancement in nanofluids was an effect of the surface modification through the nanoparticle deposition during nanofluid boiling. Possible reasons for CHF enhancement in pool boiling of nanofluids are discussed with surface property changes caused by the nanoparticle deposition.