• 한국진공학회지
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• 제22권6호
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• pp.335-340
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• 2013

본 논문은 InP 식각정지층을 갖는 MHEMT 소자의 항복전압을 증가시키기 위한 시뮬레이션 설계 논문이다. MHEMT 소자의 게이트 리세스 구조 및 채널 구조를 변경하여 시뮬레이션을 수행하였고 비교 분석하였다. MHEMT 소자의 드레인 측만을 완전히 제거한 비대칭 게이트 리세스 구조인 경우 $I_{dss}$ 전류가 90 mA에서 60 mA로 줄어들지만 항복 전압은 2 V에서 4 V로 증가함을 확인하였다. 이는 $Si_3N_4$ 보호층과 InAlAs 장벽층 사이의 계면에서 형성되는 전자-포획 음의 고정전하로 인해 채널층에서의 전자 공핍이 심화되어 나타나는 현상으로 이는 채널층의 전류를 감소시켜 충돌이온화를 적게 형성시켜 항복전압을 증가시킨다. 또한, 동일한 구조의 비대칭 게이트 리세스 구조에서 채널층을 InGaAs/InP 복합 채널로 바꾸어 설계한 구조에서는 항복전압이 5 V로 증가하였다. 이는 높은 드레인 전압에서 InP 층의 적은 충돌이온화와 이동도로 인해 전류가 더 감소했기 때문이다.

• 공업화학
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• 제24권4호
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• pp.350-356
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• 2013

페로니켈 제조공정 슬래그를 대상으로 aging 조건에 따른 용출 특성을 연구하였다. 시료의 주성분은 54.05% $SiO_2$, 34.33% MgO, and 5.51% $Fe_2O_3$이었다. 주 결정구조는 Enstatite [(Mg, $Fe^{2+}$)$SiO_3$]이었다. 페로니켈 슬래그를 침수, 공기유입 침수, 습윤공기 조건에서 3개월간 aging 처리하였다. 습윤공기 aging 조건이 가장 효과적이었다. 습윤공기 aging 처리한 슬래그에서 마그네슘과 철의 침출율이 각각 80.0%, 75.1%로 가장 우수하였다. XRD, SEM 분석결과 습윤공기 aging 처리한 슬래그에서 결정성분의 파괴정도가 가장 크게 나타났다.

• 세라미스트
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• 제9권6호
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• pp.42-48
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• 2006

The structural ceramic, such as $A1_2O_3,\;ZrO_2\;and\;Si_3N_4$ have applied as several parts of precision machines, automotives and instruments for semiconductor. The mechanical properties depended on purity, morphology and microstructure of the ceramic and its fabrication process. High purity and fine starting powder for the structural ceramic was prepared mainly by wet process and powder processing such as milling, mixing, drying and granulating strongly influenced on the fabrication process. Powder processing included powder synthesis technology is essential for ceramic manufacture. Also, the advanced mechanical treat[neat in powder processing to create nano composite powder was developed to improve several properties of ceramic materials. Innovation of powder processing will lead to improve mechanical and functional properties of the ceramics.

• Steel and Composite Structures
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• 제43권5호
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• pp.523-532
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• 2022

Turbocharger technology is one of the ways to survive in a competitive market that is facing increasing demand for fuel and improving the efficiency of vehicle engines. Turbocharging allows the engine to operate at close to its maximum power, thereby reducing the relative friction losses. One way to optimally understand the behavior of a turbocharger is to better understand the heat flow. In this paper, a 1.7 liter, 4 cylinder and 16 air valve gasoline engine turbocharger with compressible, viscous and 3D flow was investigated. The purpose of this paper is numerical investigation of the number of heat transfer in gasoline engines turbochargers under 3D flow and to examine the effect of different types of coatings on its performance; To do this, modeling of snail chamber and turbine blades in CATIA and simulation in ANSYS-FLUENT software have been used to compare the results of turbine with experimental results in both adiabatic and non-adiabatic (heat transfer) conditions. It should be noted that the turbine blades are modeled using multiple rotational coordinate methods. In the experimental section, we simulated our model without coating in two states of adiabatic and non-adiabatic. Then we matched our results with the experimental results to prove the validation of the model. Comparison of numerical and experimental results showed a difference of 8-10%, which indicates the accuracy and precision of numerical results. Also, in our studies, we concluded that the highest effective power of the turbocharged engine is achieved in the adiabatic state. We also used three types of SiO₂, Sic and Si₃N₄ ceramic coatings to investigate the effect of insulating coatings on turbine shells to prevent heat transfer. The results showed that SiO₂ has better results than the other two coatings due to its lower heat transfer coefficient.

• 한국전기전자재료학회논문지
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• 제11권1호
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• pp.33-40
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• 1998

The composite SiO$_2$/Si$_3$N$_4$/SiO$_2$(ONO) film formed by oxidation on nitride film has been widely studied as DRAM stacked capacitor multi-dielectric films. Load lock(L/L) LPCVD system by HF cleaning is used to improve electrical capacitance and to scale down of effective thickness for memory device, but is brings a new problem. Nitride film deposited using HF cleaning shows selective deposition on poly silicon and oxide regions of capacitor. This problem is avoidable by carpeting chemical oxide using $H_2O$$_2$cleaning before nitride deposition. In this paper, we study the limit of nitride thickness for abnormal oxidation and the initial deposition time for nitride deposition dependent on underlayer materials. We proposed an advanced fabrication process for stacked capacitor in order to avoid selective deposition problem and show the usefulness of nitride deposition using L/L LPCVD system by $H_2O$$_2$cleaning. The natural oxide thickness on polysilicon monitor after HF and $H_2O$$_2$cleaning are measured 3~4$\AA$, respectively. Two substrate materials have the different initial nitride deposition times. The initial deposition time for polysilicon is nearly zero, but initial deposition time for oxide is about 60seconds. However the deposition rate is constant after initial deposition time. The limit of nitride thickness for abnormal oxidation under the HF and $H_2O$$_2$cleaning method are 60$\AA$, 48$\AA$, respectively. The results obtained in this study are useful for developing ultra thin nitride fabrication of ONO scaling and for avoiding abnormal oxidation in stacked capacitor application.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.223-226
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• 2002

Appropriate design/manufacturing conditions, to give outstanding material properties to the $Si_3$$N_4$-BN and AIN-BN based composite materials, will be investigated using the experimental design methods. Ultra-precision machinability of the developed ceramics will be systematically studied in the viewpoint of microstructure and material properties. Also, finite element methods will be applied to define basic principles to significantly improve machinability and various properties. Basic experiments will be performed to develop optimum ultra-precision machining technologies for the developed ceramics. For ultra-precision lapping machining, need to develop a ultra-precision lapping system, suitable metal bonded diamond wheel, and appropriate condition of ultra-precision lapping machining.

• The Plant Pathology Journal
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• 제37권3호
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• pp.215-231
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• 2021

Brown leaf spot disease caused by Nigrospora guilinensis on Phellodendron chinense occurs in a large area in Dayi County, Chengdu City, Sichuan Province, China each year. This outbreak has severely reduced the production of Chinese medicinal plants P. chinense and caused substantial economic losses. The bacterial isolate JKB05 was isolated from the healthy leaves of P. chinense, exhibited antagonistic effects against N. guilinensis and was identified as Bacillus megaterium. The following fermentation medium and conditions improved the inhibitory effect of B. megaterium JKB05 on N. guilinensis: 2% glucose, 0.1% soybean powder, 0.1% KCl, and 0.05% MgSO₄; initial concentration 6 × 10⁶ cfu/ml, and a 42-h optimal fermentation time. A composite of 0.1% nano-SiO₂ JKB05 improved the thermal stability, acid-base stability and ultraviolet resistance by 16%, 12%, and 38.9%, respectively, and nano-SiO₂ was added to the fermentation process. The best formula for the wettable powder was 35% kaolin, 4% polyethylene glycol, 8% Tween, and 2% humic acid. The following quality test results for the wettable powder were obtained: wetting time 87.0 s, suspension rate 80.33%, frequency of microbial contamination 0.08%, pH 7.2, fineness 95.8%, drying loss 1.47%, and storage stability ≥83.5%. A pot experiment revealed that the ability of JKB05 to prevent fungal infections on P. chinense increased considerably and achieved levels of control as high as 94%. The use of nanomaterials significantly improved the ability of biocontrol bacteria to control this disease.

• 한국공작기계학회논문집
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• 제17권4호
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• pp.104-111
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• 2008

The objective of this study is to evaluate micro end-milling characteristics and tool wear behavior of AlN-hBN composites. First, AlN based composites with hBN contents in the range of 10 to 20vol% were prepared by hot-pressing. Vickers hardness and flexural strength of the prepared composite specimens were measured and compared according to the vol% of hBN variations. Then, cutting force variations were measured and analyzed using a tool dynamometer during the micro end-milling experiments; and machined surface shapes and roughness were investigated using a 3D non-contact type surface profiler. After micro end-milling, worn tools were investigated using a tool microscope and SEM images. From the experimental results, it can be observed that the cutting forces decreased, and surface qualities were improved with increasing hBN contents. At low content of hBN, tool chipping was observed; and tool wear rate decreased with increasing hBN contents. The results of this study insist that proper machining conditions, including tool wear behavior investigation, should be determined for the micro end-milling of AlN-hBN composites for its further application.

• 대한치과보철학회지
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• 제45권5호
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• pp.611-620
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• 2007

Statement of problem: Second-generation indirect composite resins have been improved flexural strength, compressive strength, hydrolytic degradation resistance, wear resistance compared to first-generation indirect composite resins, but there are still some problems as hydrolysis and low wear resistance. Some manufacturers claim that wear resistance of their materials has been improved, but little independent study has been published on wear properties of these materials and the properties specified in the advertising materials are largely derived from in-house or contracted testing. Purpose: This study was to evaluate the wear of indirect composite resins (SR Adore, Sinfony, Tescera ATL) and gold alloy against the human enamel. Material and method: Extracted human incisors and premolars were sectioned to $2{\times}2{\times}2mm$ cube and embedded in the clear resin and formed conical shaped antagonist to fit the jig of pin-on-disk tribometer. Total 20 antagonists were stored in distilled water. Five disk samples, 24mm in diameter and 1.5mm thick, were made for each of three groups of indirect composite resins and gold alloy group, and polished to #2,000 SiC paper on auto-polishing machine. Disk specimens were tested for wear against enamel antagonists. Wear test were conducted in distilled water using a pin-on-disk tribometer under condition (sliding speed 200rpm contact load 24N, sliding distance 160m). The wear of the enamel was determined by weighing the enamel antagonist before and after test, and the weight was converted to volumes by average density. The wear tracks were analyzed by scanning electron microscopy and surface profilometer to elucidate the wear mechanisms. Statistical analysis of the enamel wear volume, wear track depth and wear tract width of disk specimens were accomplished with one-way ANOVA and the means were compared for significant differences with Scheffe's test. Results: 1. The enamel wear was most in gold alloy, but there were no statistically significant differences among all the groups (P>.05). 2. In indirect composite resin groups, the group to make the most shallow depth of wear tract was Sinfony, followed by Tescera ATL, SR Adoro (P<.05). Gold alloy was shallower than Sinfony, but there was no statistically significant difference between Sinfony and gold alloy (P>.05). 3. The width of wear tract of SR Adore was larger than the other groups (P<.05), and there were no statistically significant differences among the other groups (P>.05). 4. SEM analysis revealed that Sinfony and gold alloy showed less wear scars after test, Tescera ATL showed more wear scars and SR Adore showed the most. Conclusion: Within the limits of this study, Sinfony and gold alloy showed the least wear rates and showed similar wear patterns.

• 대한소아치과학회지
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• 제32권3호
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• pp.557-568
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• 2005

전남대학교 치과대학 소아치과학교실 및 치의학 연구소 수복재료로 사용되는 복합레진은 치아의 저작기능과 심미성을 회복할 수 있는 물리적, 화학적 성질뿐만 아니라 생물학적 적합성과 구강내 환경변화에 대한 내구성을 가지고 있어야 한다. 유치에 사용하려고 할 때에도 마모저항성과 구강내 환경에서의 분해저항성은 고려해야할 중요한 물성이다. 실험에 사용된 복합레진은 최근에 시판되고 있는 Metafil CX(Sun Medical, Japan) Solitaire 2(Heraeus Kulzer, USA), Composan LCM(Promedica, Germany), DenFil(Vericom, Korea)이었다. 각 제품의 분해저항성과 마모도를 평가하고자 마모시험 후 마모된 면의 깊이를 측정하였고 화학적분해를 얻기 위해 0.1N NaOH에 보관 시 각 제품의 분해저항성을 무게손실, 표면하 분해층 깊이, 용출된 Si 농도를 기준으로 평가하였고 주사전자현미경과 공촛점 레이저 현미경으로 분해층을 관찰하여 다음과 같은 결과를 얻었다. 1. 무게 손실량은 0.74~7.94%까지 다양하였으며 Metafil에서 가장 높았다. 2. 분해층 깊이는 Metafil이 가장 깊었고 Solitare 2, Denfil, Composan LCM순이었고 Metafil은 다른제품과 유의한 차이를 보였다(p<0.05). 3. Si 용출량은 Metafil이 가장 많았으며 Metafil CX와 Composan LCM, DenFil, Solitaire 2사이에 유의한 차이를 보였다(p<0.05). 4. 주사전자현미경 관찰시 표면 양상 및 분해층 깊이를 관찰할 수 있었고 공촛점 레이저 현미경 관찰시 NaOH 용액에 보관한 후 수복재의 기질과 충전제 사이의 결합의 파괴 양상을 관찰할 수 있었다. 5. 최대마모깊이는 DenFil에서 가장 낮았고, Metafil CX에서 가장 깊었으며 각 제품 간에는 유의한 차이를 보였다(p<0.05). 6. 각 제품의 Si 용출량과 분해층 깊이 사이(r=0.491, p<0.05), 최대마모깊이와 비커스경도 간(r=-0.942, p<0.01)에 유의한 상관관계를 보였다. 이상의 결과 복합레진의 평가요소로서 마모도와 함께 가수분해도 고려되어야 할 것으로 사료된다.