• Restorative Dentistry and Endodontics
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• v.39 no.1
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• pp.17-23
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• 2014

Objectives: This study evaluated the efficacy of Endosolv-R and Xylene in softening epoxy resin based sealer after 1 to 2 min exposure. Materials and Methods: Sixty Teflon molds ($6mm{\times}1.5mm$ in inner diameter and depth) were equally divided into 3 groups of 20 each. AH 26 (Dentsply/De Trey), AH Plus (Dentsply/De Trey), Adseal (Meta-Biomed) were manipulated and placed in the molds allotted to each group and allowed to set at $37^{\circ}C$ in 100% humidity for 2 wk. Each group was further divided into 2 subgroups according to the solvents used, i.e. Xylene (Lobachemie) and Endosolv-R (Septodont). Specimens in each subgroup were exposed to respective solvents for 1 and 2 min and the corresponding Vicker's microhardness (HV) was assessed. Data was analysed by Mauchly's test and two-way analysis of variance (ANOVA) with repeated measures, and one-way ANOVA. Results: Initial hardness was significantly different among the three sealers with AH Plus having the greatest and Adseal having the least. After 2 min, Xylene softened AH Plus and Adseal sealer to 11% and 25% of their initial microhardness, respectively (p < 0.001), whereas AH 26 was least affected, maintaining 89.4% of its initial microhardness. After 2 min, Endosolv-R softened AH 26, AH Plus and Adseal to 12.7, 5.6 and 8.1% of their initial microhardness, respectively (p < 0.001). Conclusions: Endosolv-R was a significantly more effective short term softener for all the tested sealers after 2 min whereas Xylene was an effective short term softener against AH plus and Adseal but less effective against AH 26.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2146-2148
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• 2005

The 2.5GeV linac of the Pohang Light Source(PLS) is planed to be converted to a XFEL. The PAL XFEL requires a new 1.2-GeV linac that will be combined to the existing linac to increase a beam energy upto 3.7GeV. This stability is mainly determined by a low level RF drive system and klystron-modulators. The stability level of the modulator has to be improved 10 times better to meet the pulse stability of 0.02 %. The regulation methods such as traditional de-Qing and precision inverter charging technology are reviewed to find out suitable upgrade scheme of the modulators. In order to obtain electron beam of the consequently stability for XFEL linac, the pulse-to-pulse beam voltage regulation is less than +/-0.5%. To get the reliable stability of the modulator which is less than +/-0.2%, a charging section is improved in a modulator which has been operated with inverter power supply and de-Q'ing.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1867-1869
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• 2003

In this paper, chamber(Circuit breaker compartment of C-GIS) made of stainless steel with 4 mm width is used. Artificial defect was made on enclosure or HV conductor of chamber and $SF_6$ gas was injected into it according to pressure. In this experiment, Acoustic emission sensors of different types was used to compare sensitivity to detect acoustic signal occurred by Partial discharge(PD) of according to types and resonance frequency in $SF_6$ gas atmosphere. Sensors used in tests was R6I, R15I and 2/4/6 Pre-Amplifier connected with R6IU without pre. amp. In case of R6IU, gain was adjusted with 40 dB like other sensors and operated by differential mode. Post amplifier(post. amp) and band pass filter(BPF) were developed Gain of post. amp. is 60 dB and BPF has band width of $50{\sim}300$ kHz. Also, envelope circuit developed reduces frequency of AE sensor. As a result, in $SF_6$ atmosphere, R6IU and R6I had resonance frequency of 60 Hz was better than R15I. Also, R6IU was better than R6I because of type property of pre.amp. had differential mode.

• Journal of Powder Materials
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• v.27 no.4
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• pp.333-338
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• 2020

In this study, we fabricate a thin- and dense-BCuP-5 coating layer, one of the switching device multilayers, through a plasma spray process. In addition, the microstructure and macroscopic properties of the coating layer, such as hardness and bond strength, are investigated. Both the initial powder feedstock and plasma-sprayed BCuP-5 coating layer show the main Cu phase, Cu-Ag-Cu₃P ternary phases, and Ag phase. This means that microstructural degradation does not occur during plasma spraying. The Vickers hardness of the coating layer was measured as 117.0 HV, indicating that the fine distribution of the three phases enables the excellent mechanical properties of the plasma-sprayed BCuP-5 coating layer. The pull-off strength of the plasma-sprayed BCuP-5 coating layer is measured as 16.5 kg/㎠. Based on the above findings, the applicability of plasma spray for the fabrication process of low-cost multi-layered electronic contact materials is discussed and suggested.

• Journal of Korea Foundry Society
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• v.17 no.4
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• pp.338-346
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• 1997

Mechanical properties of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composites fabricated by the reaction squeeze casting were compared with those of ($15%Al_2O_3{\cdot}SiO_2$)/Ai composites. Al-Ni intermetallic compounds ($10{\sim}20 {\mu}m$) formed by the reaction between nickel powder and molten aluminum were uniformly distributed in the Al matrix. These intermetallic compounds were identified as $Al_3Ni$ using X-ray diffraction analysis and they resulted in beneficial effects on room and high temperature strength and wear resistance. Microhardness values of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composite were greater by about 100Hv than those of ($15%Al_2O_3{\cdot}SiO_2$)/Al composite. Wear resistance of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composites was superior to that of ($15%Al_2O_3{\cdot}SiO_2$)/Al composites regardless of the applied load. While tensile and yield strength of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composites were greater at room temperature and $300^{\circ}C$, strength drop at high temperature was much smaller in hybrid composites.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2002.08a
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• pp.70-71
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• 2002

Exchange-coupled cluster of transition-metal ions are relevant to many different scientific areas, ranging from chemistry to solid-state physics, biology, material science and has been the subject of much research in recent years(1,2). Single crystal EPR spectroscopy works as a very effective tool for the measurement of J values for small exchange interactions. This makes EPR technique very suitable for detection of weak exchange coupling transmitted over long distances via extended atomic and melecular bridges. Large polyoxometallates (3) may provide ideal structural environments for the study of interactions between paramagnetic ions. The detailed nature of magnetic interaction (positive sign and magnitude of J~0.006 $cm^{-1}$ /) was clearly determined for di-copper(II) system by single crystal EPR spectroscopy (4). The single-triplet (S-T) transitions are forbidden by different symmetries of the wave functions. However, when the singlet ground state is mixed into triplet states, the S-T transitions can be allowed and observed as weak lines. These weak S-T lines are positioned symmetrically with respect to the main transitions in the distance equals to 2J from the center of the spectrum. This lines allow one to determine the J-value with very high accuracy when │J│ ＜ hv 0.32 $cm^{-1}$ /. Unfortunately, the S-T transitions in the single crystal were detected by EPR method only in a few complexes until now. We have measured single-triplet transition lines for several magnetically coupled cluster systems and determined their J values accurately. The temperature dependency of J was studied by monitoring the changes in S-T.

• Journal of the Korean Society of Safety
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• v.34 no.6
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• pp.7-12
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• 2019

Flux Cored Arc Welding (FCAW), which has been widely used in many industries, was developed in the 1950s to supplement shortcomings of the Shielded Metal Arc Welding (SMAW). FCAW has an advantage in that it can weld regardless of postures and give good quality results in the filed with many different working conditions. In this study, SM490A (rolled steel for welding structural purpose) with different thicknesses (L:25T+R:30T) were welded using FCAW. Then the mechanical properties (tension test, bending test, hardness test, impact test and macro test) were analyzed and the following conclusions were drawn. In the tensile test, it exceeds the KS standard tensile strength range (400~510) in all welding positions, which means there is a problem in the tensile force transmission performance. In the bending test, it was found that most of the specimens did not exhibit surface rupture or other defects during bending test and they exhibit sufficient toughness even after plastic deformation. In the hardness test, all the results were lower than the standard value of 350 Hv of KS B 0893, which means they have good hardness. In the impact test, all results were larger than the KS reference value of 27J. In the macro test, they showed uniform structure state by the shape of the weld, and there was risk of lamination because no internal defects, bubbles, or impurities were found on the surface of the weld.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.231-238
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• 2020

The composition of martensite transformation in NiAl alloy is determined using pure nickel and aluminum powder by vacuum hot press powder metallurgy, which is a composition of martensitic transformation, and the characteristics of martensitic transformation and microstructure of sintered NiAl alloys are investigated. The produced sintered alloys are presintered and hot pressed in vacuum; after homogenizing heat treatment at 1,273 K for 86.4 ks, they are water-cooled to produce NiAl sintered alloys having relative density of 99 % or more. As a result of observations of the microstructure of the sintered NiAl alloy specimens quenched in ice water after homogenization treatment at 1,273 K, it is found that specimens of all compositions consisted of two phases and voids. In addition, it is found that martensite transformation did not occur because surface fluctuation shapes did not appear inside the crystal grains with quenching at 1,273 K. As a result of examining the relationship between the density and composition after martensitic transformation of the sintered alloys, the density after transformation is found to have increased by about 1 % compared to before the transformation. As a result of examining the relationship between the hardness (Hv) at room temperature and the composition of the matrix phase and the martensite phase, the hardness of the martensite phase is found to be smaller than that of the matrix phase. As a result of examining the relationship between the temperature at which the shape recovery is completed by heating and the composition, the shape recovery temperature is found to decrease almost linearly as the Al concentration increases, and the gradient is about -160 K/at% Al. After quenching the sintered NiAl alloys of the 37 at%Al into martensite, specimens fractured by three-point bending at room temperature are observed by SEM and, as a result, some grain boundary fractures are observed on the fracture surface, and mainly intergranular cleavage fractures.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.237.1-237.1
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• 2013

Ti 와 Al 은 금속간의 화합물이 내산화성에 우수한 성질을 가지고 있으며 낮은 밀도와 고온에도 큰 변화가 없는 성질을 가지고 있다. 그리하여 내식 및 부식 관련 연구나 고온재료를 필요로 하는 우주, 엔진 제품 등에 많은 연구가 진행되고 있다. 또한 Ti-Al-N 박막은 경도가 우수하여 고속 공구 부품에 널리 사용되고 있으며 최근 Ti-Al-N 에 Si 첨가로 인하여 40 GPa 이상의 고경도와 1,000도 이상의 산화온도를 지닌 나노 혼합물 코팅을 형성 시키는 것으로 알려져 있다. 본 연구에서는 Ti, Al, Si 원분말을 PBM (Planetary Ball Milling) 방법을 사용하여 Ti-Al-Si 혼합분말로 제조하고, 제조된 분말들은 SPS (Spark Plasma Sintering) 공정을 통하여 Ti-Al-Si 합금타겟을 제작하였다. 제작된 Ti-Al-Si 합급타겟을 사용한 Sputtering 공정을 수행하여 Ti-Al-Si 3원계 박막을 증착하였다. 그 결과 기존 Ti (82 ${\mu}m$), Al (32 ${\mu}m$), Si (16 ${\mu}m$) 크기의 원분말들이 PBM (Planetary Ball Milling) 공정 후 Ti-Al-Si (18 ${\mu}m$) 로 입도가 작아진 것을 확인 할 수 있었고, 소결 후 타겟이 99% 이상의 높은 밀도를 가졌으며 원분말의 조성과 동일한 조성을 가진 타겟이 제작되었음을 확인하였다. Ti-Al-Si 타겟의 경도는 약 1,000 Hv 이상의 값을 보였으며, Ti-Al-Si-N 박막의 경우 타겟의 조성과 동일하였고 경도는 약 35 GPa 로 높은 경도 값을 가지는 것을 확인하였다. 내산화 테스트 결과 Ti-Al-Si-N 박막은 1,000도 에서도 박막의 손상이 가지 않았다.

• Korean Journal of Materials Research
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• v.15 no.9
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• pp.585-588
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• 2005

Titanium and Titanium alloys are widely used as an orthopedic and dental implant material because of their excellent biocompatibility and mechanical strength. In this study, ECAP Cp-Ti and Cp-Ti were heat treated for different annealing time of 30 min, 90 min and 3 hours. The grain size for each condition was studied. The micro-Vicker hardness test was carried out f3r each different heat treated samples. The micro-Vicker hardness test for ECAP Cp-Ti, Cp-Ti and Cp-Ti (3hr) revealed hardness values of 239.5, 182 and 144 Hv, respectively. The grain size was increased from approximately $70{\mu}m\;to\;300{\mu}m$ with the increase in heat treatment time from 30 min to 3 hours. The heat treated samples were tested for their biocompatibility in simulated body fluid (SBF) and corrosion rates was determined using Polarization Curve test (PCT). The PCT results showed Cp-Ti with comparatively high corrosion potential of -0.18 V and corresponding corrosion current of $2\times10^{-6}$ A, while the corrosion rate in ECAP Cp-Ti and Cp-Ti (30 min annealed) showed very similar results of corrosion potential about -0.47 V with corresponding corrosion current of $7\times10^{-8}$ A.