• 한국세라믹학회지
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• 제55권5호
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• pp.498-503
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• 2018

Using the thermal ablation method, the oxidation behavior of $SiC_f/SiC$ composites was investigated in air and in the temperature range of $1,300^{\circ}C$ to $2,000^{\circ}C$. At the relatively low temperature of $1,300^{\circ}C$, passive oxidation, which formed amorphous phase, predominantly occurred in the thermal ablation test. When the oxidation temperature increased, SiO (g) and CO (g) were formed by active oxidation and the dense oxide layer changed to a porous one by vaporization of gas phases. In the higher temperature oxidation test, both active oxidation due to $SiO_2$ decomposition on the surface of the oxide layer and active/passive oxidation transition due to interfacial reaction between oxide and base materials such as SiC fiber and matrix phase simultaneously occurred. This was another cause of high temperature degradation of $SiC_f/SiC$ composites.

• Macromolecular Research
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• 제17권8호
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• pp.580-584
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• 2009

The effects of crystallinity and radiation crosslinking on the physical properties of a microporous high density polyethylene (HDPE) film with Millad3988 as a nucleating agent were investigated. The pores of the HDPE film were affected by the crystallinity. The crystallinity of the HDPE films increased with increasing Millad3988 amount up to 0.1 wt% but decreased with further addition. The mechanical characteristics of the HDPE containing Millad3988 films improved with increasing irradiation dose up to 50 kGy, but decreased at 75 kGy due to severe degradation. The thermal shrinkage behavior of the HDPE films decreased with increasing radiation dose up to 50 kGy. The porosity of the stretched HDPEIMillad3988 films after ${\gamma}$-ray radiation increased with increasing y-ray radiation dose up to 50 kGy. The pores of the irradiated films were formed more easily by a stretching due to the formation of a crosslinked structure.

• 한국세라믹학회지
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• 제38권7호
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• pp.602-607
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• 2001

Zirconia powder containing 3 mol% yttria (3Y-PSZ) was casted on the cast iron substrate by plasma spraying method. Coated specimens were then heat treated at 500$\^{C}$ in nitrogen plasma. Wear tests were performed on nitrogen heat treated and non heat treated samples at temperatures from 25$\^{C}$ to 600$\^{C}$. Wear results showed that the friction coefficient and the wear loss of both the treated and the non-treated samples showed maximum value at 400$\^{C}$. These results were explained by low temperature thermal degradation due to the monoclinic transformation. Nitrogen plasma treatment significantly improved the tribological performance. The effect of nitrogen heat treatment on tribological behavior was explained by the increased micro-hardness and decreased monoclinic faction.

• Elastomers and Composites
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• 제34권4호
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• pp.292-298
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• 1999

Lactide oligomer with number averagae molecular weight of 460 was synthesized and reacted with poly(oxyteramethylene)glycol(PTMG, Mn = 650) to obtain oligolactide oligomer-terminated PTMG. Polyurethanes were synthesized from the oligolactide-terminated PTMG, 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol. The mechanical and thermal properties of the polyurethanes and PTMG based polyurethane as control were measured by means of DSC and tensile tester. Degradation behavior of these polyurethanes put into a compost was evaluated by variation of mechanical properties, surface state, and weight loss. Modulus and weight significantly decreased with increasing time. The surface of the oligolactide polyurethane put into the compost during 6 weeks had a number of voids. On the other hand, These properties of the PTMG based polyurethane as control did not change. These results suggest that the novel polyurethanes incorporated oligolactide easily degrade under biodegradable condition.

• 한국결정성장학회지
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• 제22권5호
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• pp.218-222
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• 2012

FeNi alloy nanofibers have been prepared by an electrospinning process followed by air-calcination and H2 reduction to develop electromagnetic (EM) wave absorbers in the giga-hertz (GHz) frequency range. The thermal behavior and phase and morphology evolution in the synthetic processes were systematically investigated. Through the heat treatments of calcination and H2 reduction, as-spun PVP/FeNi precursor nanofiber has been stepwise transformed into nickel iron oxide and FeNi phases but the fibrous shape was maintained perfectly. The FeNi alloy nanofiber had the high aspect ratio and the average diameter of approximately 190 nm and primarily composed of FeNi nanocrystals with an average diameter of ~60 nm. The FeNi alloy nanofibers could be used for excellent EM wave absorbing materials in the GHz frequency range because the power loss of the FeNi nanofibers increased up to 20 GHz without a degradation and exhibited the superior EM wave absorption properties compared to commercial FeNi nanoparticles.

• Tribology and Lubricants
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• 제5권1호
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• pp.12-20
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• 1989

The friction and wear behavior of molybdenum disulfide filled polymer composites sliding against metal has been investigated using pin-on-disc machine and microscope. The observed wear rates were reduced by the addition of MoS$_2$ to nylon and this can be attributed to the homogenous transfer of MoS$_2$ to the counteddace thereby modifying sliding conditions. The friction of filled and unfilled nylon was increased with increasing sliding speed, and the catastropic wear rate was occurred at high normal load. This have been explained by thermal degradation. In the case of HDPE, however, the wear rate was not always reduced by the addition of MoS$_2$ and the influence of MoS$_2$ was mainly even the opposite. Filled and unfilled HDPE had lower values of friction and wear rate than those of nylon. Micrographs appeared that the delamination of the worn surface in nylon/MoS$_2$ composite occurred and revealed that the worn surface of HDPE presented a number of characteristic features as wear grooves, pulls, and smears and crescents.

• 대한가정학회지
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• 제25권1호
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• pp.43-50
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• 1987

Non-durable flame retardant finish, borax/boric acid mixed solution, was applied to cotton fabric with pad-dry method. The LOI(limited oxygen index) was measured as the measare of the flame retardant effect. The TGA was investigated to know the thermal behavior of the samples. In addition, the solubility of the solutions was investigated. The results were as follows: 1) There was a synergism of flame retardant effect in the borax/boric acid mixed solution treatment and the maximum synergism was shown around the ratio of 7 : 3 2) After the borax/boric acid solution treatment, the degradation temperature was lowered and degraded at the larger temp range with slower rate. The residual char length also increased. 3) The solubility of borax/boric acid become higher when the ratio of borax/boric acid became similar. Compositions from 80/20 to 40/60 borax/boric acid mixtures were solubilized well in room temperatuare or warmwater therefor there was no problem for home use.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.2047-2049
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• 2000

In this study, we describe comparison of insulation characteristics of polyamid papers with heating conditions. The partial discharge behavior until breakdown and breakdown strength for thermal degradation films are observed in $SF_6$ gas chamber. The four layered NOMEX films of thickness of 50${\mu}m$ were used as solid insulation films and the sphere of which diameter is 40mm to sphere electrode system was used and each insulation films were inserted between sphere electrodes. The used gas pressure was 1.0bar and used temperature was each of 250$^{\circ}C$, 270$^{\circ}C$, 300$^{\circ}C$, 320$^{\circ}C$, 350$^{\circ}C$ and the voltage were applied until breakdown films.

• 한국초전도ㆍ저온공학회논문지
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• 제10권4호
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• pp.9-12
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• 2008

The residual stress induced in the superconducting layer was estimated using analytical approach coupled with electro-mechanical test results and XRD measurements. The residual stress measured based on the $I_{c}/I_{c0}$-strain degradation behavior showed similar value with the measured residual stress using XRD. The calculated residual stress based on the thermal analysis showed the lowest value. This could be explained by the additional intrinsic residual stresses induced in the superconducting film during deposition.

• 대한건축학회논문집:구조계
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• 제35권5호
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• pp.181-190
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• 2019

In high school classrooms, it is reported that ventilation is often insufficient, increasing health risks among students. Therefore, indoor air quality in school classrooms is very important in terms of students' health and learning abilities. In this study, the effect of window opening, which is a control mechanism for air control in summer high school classrooms, on the change in air and indoor environment of the classroom was analyzed and physical conditions of indoor and air environment were observed during the classroom course, and satisfaction of the students and teachers was assessed with questionnaires. It was found that change rate of $CO_2$ concentration in classroom was effectively reduced by carrying out activity of opening the window by active environment control activity of occupants at break time, intermission time and cleaning time. And optimal window opening by students was presented to prevent unpleasantness and degradation of indoor air quality and the effects were analyzed.