• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.7
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• pp.88-93
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• 1998

For the self-aligned AlGaAs/GaAs HBTs, the surface states at the interface between the extrinsic base surface and the passivation nitride is a major cause of degradation of dc characteristics. In this paper the degradation mechanisms of self-aligned AlGaAs/GaAs HBT were analyzed, and GaAs HBTs, which employed an InGaP ledge emitter structure formed by the nonself-aligned process to cover the surface of the extrinsic base and reduce the surface states, produced high reliability. Accoridng to the acceleration lifetime test, the nonself-aligned InGaP/GaAs HBTs produced very reliable dc characteristics comparing with the self-aligned AlGaAs/GaAs HBTs. The activation energy was 1.97eV and MTTF $4.8{\times}10^{8}$ hrs at $140^{\circ}C$ which satisfied the MIL standard.

• Elastomers and Composites
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• v.58 no.4
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• pp.191-200
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• 2023

In this study, MoS₂ nanoparticles were synthesized and analyzed through powder X-ray diffraction, Raman, ultraviolet-visible, and X-ray photoelectron spectroscopies. The surface morphologies of the as-synthesized MoS₂ nanoparticles were investigated through scanning and transmission electron microscopies. The sonocatalytic activity of the MoS₂ nanoparticles toward Orange II removal was evaluated by utilizing a Box-Behnken design for response surface methodology in the experimental design. The sonocatalyst dosage, Orange II dye concentration, and ultrasound treatment time were optimized to be 0.49 g/L, 5 mg/L, and 150 min, respectively. The maximum efficiency of Orange II degradation on MoS₂ nanoparticles was achieved, with a final average value of 82.93%. Further, the results of a kinetics study on sonocatalytic Orange II degradation demonstrated that the process fits well with a pseudo-first-order kinetic model.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04b
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• pp.49-52
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• 2002

Degradation characteristics of cathodoluminescence (CL) of ZnS:Ag,Cl phosphor were investigated with measurements of CL and photoluminescence (PL). Phosphoric acid treatment was performed to phosphor particles in order to improve CL degradation of phosphor screen that occurred during panel sealing process, and we will discuss mechanisms of degradation and improvement of luminescence mainly with help of AES (auger electron spectroscopy) analysis.

• Journal of the Korean Wood Science and Technology
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• v.39 no.2
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• pp.179-186
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• 2011

In an effort to understand the hydrolytic degradation process of cured urea-formaldehyde (UF) resins responsible for the formaldehyde emission of wood-based composite panels, this study analyzed the influence of acid hydrolysis on the morphology of cured UF resins with different formaldehyde/urea (F/U) mole ratios such as 1.6, 1.4, 1.2 and 1.0. Field emission-scanning electron microscopy (FE-SEM) was employed to observe both exterior and fracture surfaces on thin films of cured UF resins before and after the etching with hydrochloric acid as a simulation of the hydrolytic degradation process. FE-SEM images showed that the exterior surface of cured UF resin with the F/U mole ratio of 1.0 had spherical structures after the acid hydrolysis while the other cured UF resins were not the case. However, the fracture surface observation showed that all the samples possessed spherical structures in the cured state of UF resins although their occurrence and size decreased as the F/U mole ratio increased. For the first time, we found the spherical structures in cured UF resins of higher F/U mole ratio of 1.4. After the acid hydrolysis, the spherical structures became a much predominant at the fracture surface. These results indicated that the spherical structures in cured UF resinswere much more resistant to the hydrolytic degradation by the acid than amorphous region.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1254-1260
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• 1997

Influence of applied electric field on the low temperature degradation of 3 mol% YaO3 stabilized tetragonal zirconia polycrystals(3Y-TZP) was investigated using X-ray diffractometry of specimens aged under the dc field of 1.1 kV/mm in silicone oil both of 12$0^{\circ}C$-21$0^{\circ}C$. After the aging, the tetragonal to monoclinic phase transformation was observed only on the specimen surface of 3Y-TZP faced to the anode. This indicated that the surface was overcrowded with oxygen ions as a result of diffusion of oxygen vacancies toward the cathode-sided surface. To elucidate an influence of the applying time of the electric field on the extent of the degradation of 3Y-TZP in air, specimens were aged fore 0-2 hours under the electric field in the oil bath of 12$0^{\circ}C$ and then subsequently aged for 3h at 22$0^{\circ}C$ in air. The longer the specimens were aged under the field, the more extensive the transformation to the monoclinic phase was on the specimen surface faced to the cathode, probably originated from a high diffusion rate of oxygen ions due to a steep oxygen vacancy concentration gradient.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.523-527
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• 2013

Ti-based coatings following laser ablation were studied to compare degradation behaviors by thermomechanical stress. TiN, TiCN, and TiAlN coatings were degraded by a Nd:YAG pulsed laser with an increase in the laser pulses. A decrease in the hardness was identified as the pulses increased, and the hardness levels were in the order of TiAlN > TiCN > TiN. The TiN showed cracks on the surface, and cracks with pores formed along the cracks were observed in the TiCN. The dominant degradation behavior of the TiAlN was surface pore formation. EDS results revealed that diffusion of substrate atoms to the coating surface occurred in the TiN. Delamination occurred in the TiN and TiCN, while the TiAlN which has higher thermal stability than the TiN and TiCN maintained adhesion to the substrate. It was considered that the decrease in the hardness of the Ti-based hard coatings is attributed to surface cracking and the diffusion of substrate atoms.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.921-927
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• 1989

One of the most important problems in recent life prediction is to introduce the degradation effects into life prediction procedure. In the present paper, the effect of the material degradation on the fatigue surface crack growth and fatigue life prediction in a 2 1/4 Cr-1Mo steel were investigated. The 2 1/4 Cr-1Mo steel has been used in a plant having operated for over 60000hours and subjected to material degradation due to temper-embitterment. A Monte-Carlo simulation was made on the basis of the data obtained in the experiment in order to determine the P-S-N diagrams of surface crack growth for the degraded and recovered steels.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.10
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• pp.1068-1078
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• 2004

In this paper we investigated the characteristics of surface degradation in silicone rubber due to corona exposure and recovery mechanism. It was shown that surface free energy was 22.42 mJ/$m^2$ on initial sample but surface free energy was approximately increased to 71.14 mJ/$m^2$ after 45 minutes. However, surface free energy on silicone rubber after corona discharge treatment was completely recovered within a short time due to diffusion of low molecular weight(LMW) silicone fluid. It was shown that corona discharge insured the increase of diffusible LMW chains, which could lead to recover the surface hydrophobicity. 200～370 g/mol distribution of LMW silicone fluid which was extracted by solvent-extraction with gel permeation chromatography (GPC) was contributed to recovery. The surface degradation characteristics on silicone rubbers and the recovery mechanism based on our results were discussed.

• Journal of the Korean Solar Energy Society
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• v.22 no.3
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• pp.57-65
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• 2002

The photocatalytic degradation of TCE using solar energy in POFR was studied. The use of solar energy was investigated in plastic optica fiber photocatalytic reactor (POFR). In POFR, the main parameters of photocatalytic degradation of TCE were lihgt intensity, thickness of $TiO_2$-coated film on plastic fiber core, the same of total $TiO_2$-coated surface area with changed length. We studied the apparent photonic efficiency and photocatalytic degradation rate of TCE in POFR. The apparent photonic efficiency of various light intensities was decreased by an incresed intensities. The photocatalytic activities of $TiO_2$-coated optical fiber reactor system depended on the coating thickness, and total clad-stripped surface area of POF. Photocatalytic degradation of trichloroethylene ($C_2HCl_3$, TCE) in the gas-phase was elucidated by using $TiO_2$-coated plastic optical fiber reactor. In TCE degradation, in-situ FTIR measurement resulted in mineralization into $CO_2$.

• Textile Coloration and Finishing
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• v.29 no.4
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• pp.181-194
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• 2017

The biodegradability of polylactic acid(PLA) fabrics was evaluated by two methods: enzyme and soil degradation. Three different enzymes were selected to evaluate. Degradation times were measured at optimal enzyme treatment conditions. Biodegradation by enzymatic hydrolysis was compared with soil degradation. As a result, biodegradation created cracks on the fiber surface, which led to fiber thickening and shortening. In addition, new peak was observed at $18.5^{\circ}$ by degradation. Moreover, cracks indicating biofragmentation were confirmed by enzyme and soil degradation. By enzyme and soil degradation, the weight loss of PLA fabrics was occurred, there through, the tensile strength decreased about 25% by enzyme hydrolysis when 21 days after, and 21.67% by soil degradation when 60 days after. Furthermore, the biodegradability of PLA fabrics by enzymatic and soil degradation was investigated and enzymatic degradation was found to be superior to soil degradation of PLA fabrics. Among the three enzymes evaluated for enzymatic degradation, alcalase was the most efficient enzymes. This study established the mechanism of biodegradation of PLA nonwovens, which might prove useful in the textile industry.