• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.585-588
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• 2005

The dissolution characteristic of metal shows the different tendency according to the applied electrical potential, the kind of electrolyte and pH value, etc. In the micro electrochemical machining (ECM), unfavorable oxide/passive layer formation and overall corrosion of electrodes must be prevented. The anodic polarization curve of nickel has distinct three dissolution regions, i.e. two active regions and the transpassive dissolution region. In this paper, the stable electrode potentials of workpiece and tool were determined in sulfuric acid and hydrochloric acid solution, respectively. In each solution, different machining property was shown and possible electrochemical reactions were discussed. On the basis of this experiment, the methodology to obtain the proper electrode potential was suggested.

• 대한치과보존학회:학술대회논문집
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• 대한치과보존학회 2003년도 제120회 추계학술대회 제 5차 한ㆍ일 치과보존학회 공동학술대회
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• pp.603-603
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• 2003

I. Objectives The purpose of this study is to evaluate the effect of immediate or delayed composite placement on dentinal micro-tensile bond strength. Caries-free human third molars were used in this study. At first, the occlusal enamel was removed so that the middle dentin was exposed. And then the exposed dentin was polished with 1200-grit silicon carbide paper for the formation of smear layer. The polished dentin was etched with 32% phosphoric acid, dried with gentle air and applicated by dentin adhesives. The specimens were divided into 12 groups.(omitted)

• 한국표면공학회지
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• 제32권1호
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• pp.43-48
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• 1999

Oxidation behavior of 304 and 316 stainless steels was studied. After solution heat treatment, specimens were polished up to 1$mu \textrm{m}$ using $Al_2O_3$ powder and then subjected to oxidation between $300^{\circ}C$ and 50$0^{\circ}C$ in dry air. TEM and EDS were used for analyzing the components and structure of oxide film. TEM analysis of oxide film revealed that thin amorphous Fe oxide ($Fe_2O_3$) was formed on the top of surface while polycrystalline (Cr, $Fe_2O_3$ was formed below the amorphous Fe oxide layer. The specimens oxidized at $500^{\circ}C$ showed that 316 stainless steel had higher oxidation resistance than 304 stainless steel. These results suggest that Mo component of 316 stainless steel suppresses the formation of Cr carbide which may result in a local Cr depleted area.

• 한국표면공학회지
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• 제29권5호
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• pp.494-497
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• 1996

The effect of implanted nitrogen and carbon ion into SUS 304 on the absorption of hydrogen by cathodic chaging were studied. Implantations of $N^+$, $C^+$ were performed with doses of $3\times10^{17}$ ions $\textrm{cm}^2$ and $5\times10^{17}N^+cm^2$, and $5\times10^{17}C^+cm^2$, at an energy of 90 keV. Nitrides and carbide were investigatedby X-ray diffraction, Auger electron spectroscopy (AES) and scanning electron microscope (SEM). Formation of hydrides during cathodic charging were depressed by a modified surface layer. It is concluded that the both nitrides and carbides act as the barrier of hydrogen migration and the catalyst of desorption of cathodically charged hydrogen.

• The Korean Journal of Ceramics
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• 제2권1호
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• pp.19-24
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• 1996

The phase distribution and interface chemistry by the solid-state reaction between SiC and nickel were studied at temperatures between $550 \;and\; 1250^{\circ}C$ for 0.5-100 h. The reaction with the formation of silicides and carbon was first observed above $650^{\circ}C$. At $750^{\circ}C$, as the reaction proceeded, the initially, formed $Ni_3Si_2$ layer was converted to $Ni_2$Si. The thin nickel film reacted completely with SiC after annealing at $950^{\circ}C$ for 2 h. The thermodynamically stable $Ni_2$Si is the only obsrved silicide in the reaction zone up to $1050^{\circ}C$. The formation of $Ni_2$Si layers with carbon precipitates alternated periodically with the carbon free layers. At temperatures between $950^{\circ}C$ and $1050^{\circ}C$, the typical layer sequences in the reaction zone is determined by quantitative microanalysis to be $SiC/Ni_2$$Si+C/Ni_2$$Si/Ni_2$$Si+C/…Ni_2$Si/Ni(Si)/Ni. The mechanism of the periodic band structure formation with the carbon precipitation behaviour was discussed in terms of reaction kinetics and thermodynamic considerations. The reaction kinetics is proposed to estimate the effective reaction constant from the parabolic growth of the reaction zone.

• 한국재료학회지
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• 제33권2호
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• pp.77-86
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• 2023

High-temperature oxidation of a Ni-based superalloy was analyzed with samples taken from gas turbine blades, where the samples were heat-treated and thermally exposed. The effect of Cr/Ti/Al elements in the alloy on high temperature oxidation was investigated using an optical microscope, SEM/EDS, and TEM. A high-Cr/high-Ti oxide layer was formed on the blade surface under the heat-treated state considered to be the initial stage of high-temperature oxidation. In addition, a PFZ (γ' precipitate free zone) accompanied by Cr carbide of Cr₂₃C₆ and high Cr-Co phase as a kind of TCP precipitation was formed under the surface layer. Pits of several ㎛ depth containing high-Al content oxide was observed at the boundary between the oxide layer and PFZ. However, high temperature oxidation formed on the thermally exposed blade surface consisted of the following steps: ① Ti-oxide formation in the center of the oxide layer, ② Cr-oxide formation surrounding the inner oxide layer, and ③ Al-oxide formation in the pits directly under the Cr oxide layer. It is estimated that the Cr content of Ni-based superalloys improves the oxidation resistance of the alloy by forming dense oxide layer, but produced the σ or µ phase of TCP precipitation with the high-Cr component resulting in material brittleness.

• 대한치과교정학회지
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• 제26권5호
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• pp.613-622
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• 1996

도재브라켓의 제거방법에 따라 법랑질표면에 미치는 영향을 비교 평가하기 위하여 80개의 발거된 소구치를 대상으로 통법에 의해 도재브라켓을 부착시키고 일 주일후 각각 40개의 기계적 방법에 의한 제거군과 전기열전도 방법에 의한 제거군으로 구분하여 도재브라켓의 제거를 유도한 후, 그 탈락양상 및 도재브라켓과 법랑질 표면의 주사선사현미경 관찰을 시행하였으며, 전기열전도 방법에 의한 제거군을 다시 각가 10개씩 고속 tungsten carbide but에 의한 연마군, 저속 sof-lex disc에 의한 연마군, 고속 resin polishing bur에 의한 연마군, 그리고 초음파 치속제거기에 의한 연마군으로 분류하여 잔여레진의 연마를 시행한 후, 잔여레진의 평가에 의해 다음과 같은 결론을 얻었다. 1) 결찰와이어 절단용 겸자를 이용한 도재브라켓의 기계적 제거시, 0.69의 평균 잔여레진 부착지수를 보임으로써 법랑질과 레진 경계부에서 파절이 가장 빈발한 양상을 보였다. 2) 전기열전도 방법을 이용한 도재브라켓의 제거시 2.19의 평균 잔여레진 부착지수를 보임으로써 브라켓과 레진 경계부에서의 파절이 가장 빈발한 양상을 보였다. 3) 기계식 방법으로 도재브라켓의 제거시, 법랑질표면의 주사현미경 관찰소견은 실험군의 $7.5\%$에서 법랑질표면의 탈락과 패임 등의 손상을 보였다. 4) 잔여레진의 제거의 고속 resin polishing bur사용군에서 가장 적은 잔여레진막을 보였다.

• 자원리싸이클링
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• 제31권6호
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• pp.60-65
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• 2022

본 논문에서는 반도체용 실리콘 기판 가공 과정에서 발생한 슬러지 재활용을 위해 탄화 반응에 의한 탄화규소(SiC) 분말 합성 공정을 적용한 결과를 제시하고자 한다. 입수한 슬러지는 실리콘 기판을 탄화규소 연마재를 사용하여 가공하는 과정에서 발생하므로 실리콘과 탄화규소가 혼합된 형태였으며 가공 설비로부터 발생한 철 불순물이 포함되어 있었다. 슬러지는 절삭유가 포함되어 있어 점성이 있는 유체 형태였으며 대기 건조를 통해 분말 형태로 변화된 후 산 세정을 통한 철 성분 제거 및 탄화에 의한 탄화규소 분말 합성 과정을 거치게 된다. 슬러지에 포함된 실리콘과 탄화규소의 비율에 따라 탄화 반응에 필요한 탄소량이 달랐으며 탄화규소의 함량이 커질수록 탄소 부족 현상으로 인해 비화학량론적 탄화물(SiC_x, x<1) 형성이 촉진되어 순수한 탄화규소 합성이 이루어지지 않는 것을 확인하였다. 이러한 비화학량론적 탄화물은 잉여 탄소 추가와 고에너지 밀링에 의한 탄화 반응성 증가를 통해 제거할 수 있었으며 결과적으로 산 세정과 밀링 과정에 의해 슬러지로부터 순수한 탄화규소 분말 합성이 가능함을 확인할 수 있었다.

• Journal of Periodontal and Implant Science
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• 제36권2호
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• pp.273-288
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• 2006

The purpose of this study was to evaluate exophytically vertical bone formation in rabbit calvaria by the concept of guided bone regeneration with a custom-made porous titanium membrane combined with bone graft materials. For this purpose, a total of 12 rabbits were used, and decorticated calvaria were created with round carbide bur to promote bleeding and blood clot formation in the wound area. Porous titanium membranes (0.5 mm in pore diameter, 10 mm in one side, 2 mm in inner height) were placed on the decorticated calvaria, fixed with metal pins and covered with full-thickness flap. Experimental group I was treated as titanium membrane only. Experimental group II, III, IV was treated as titanium membrane with BBM, titanium membrane with DFDB and titanium membrane with FDB. The animals were sacrificed at 8 and 12 weeks after surgery, and new bone formation was assessed by histomorphometric as well as statistical analysis. 1. Porous titanium membrane was biocompatable and capable of maintaining the regeneration space. 2. At 8 and 12 weeks, all groups demonstrated exophytic bone formation and there was a statistical significant difference among different groups only at 12 weeks. 3. The DFDB group revealed the most new bone formation compared to other groups (p<0.05). 4. At 12 weeks, DFDB and FDB groups showed the most significant resorption of graft materials (p<0.05). 5. The BBM was not resorbed at all until 12 weeks. 6. The fixation metal pin revealed excellent effect in peripheral sealing. On the basis of these findings, we conclude that a porous titanium membrane may be used as an augmentation membrane for guided bone regeneration, and DFDB as an effective bone forming graft material. The fixation of the membrane with pin will be helpful in GBR technique. However, further study is required to examine their efficacy in the intraoral experiments.

• 한국세라믹학회지
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• 제35권9호
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• pp.939-944
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• 1998

실리콘함유 고분자(Polysiloxane)의 세라믹변환과정에서의 부피수축효과를 조절하기 위하여 활성화금속으로 중석을 첨가하여 열분해 및 합성반응을 통해 신 세라믹 복합체를 개발하고 이의 세라믹화 과정이나 물성을 조사하였다. 제조된 시편의 미세조직은 고분자로부터 야기된 $S_{1}$-O-C게열의 Glass기지상과, 분해잔여물(고상,기상)등과 활성화금속과의 반응르로 생성된 고경도의 탄호물로 이루어져 있어 향후 내마모재료로서의 응용을 기대할 수 있을 것이다. 제조된 복합체의 물성은 반응조건에 많이 의존함을 알 수 있었다. 1400~$1500^{\circ}C$에서 열분해 시켜 제조한 복합체의 밀도는 95% 이상의 상대밀도와, 경도 값은 7~8GPa 정도이고 탄성률은 220~230 GPa, 파괴인성응ㄴ 6~6.8$MPam^{1/2}$, 파괴강도는 380~470 MPs정도의 값을 나타내었다.