• 대한치과보철학회지
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• 제38권2호
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• pp.178-190
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• 2000

The purpose of this study was to evaluate the surface roughness of Ni-Cr-Be alloy($Verabond^{(R)}$, Aalba Dent Inc., USA) according to electrolyte concentration and etching time. Total of 150 metal specimens ($12{\times}10{\times}1.5mm$) composed of 5 polisded specimens, 5 sandblasted specimens, 140 etched specimens were prepared. Etched groups were divided into 28 groups by the $HClO_4$ concentrations(10, 30, 50, 70%) and etching times(15, 30, 60, 120, 180, 240, 300 seconds). The mean surface roughness(Ra) and the etching depth were measured with Optical 3-dimensional surface roughness measuring machine(Accura 1500M, Intek Engineering Co., Korea) and observed under SEM. The results obtaind were as follows: 1. Surface roughness(Ra) and etching depth were affected by the order of etching time, electrolyte concentration, and their interaction(P<0.05). 2. Surface roughness(Ra) and etching depth were increased with etching time in 10%, 30% electrolyte concentrations, but they had no significant difference with etching time in 70% (P<0.05). 3. Surface roughness(Ra) and etching depth decreased in the order of 30, 10, 50, 70% electrolyte concentrations from 120 seconds etching time(P<0.05). 4. The remarkable morphologic changes in etched surface were observed along the grain boundaries in 15, 30 seconds of 10%, 30% concentrations and the morphologic changes could be denoted in the grains themselves as well as along the boundaries with the lapse of time. Even though the noticeable morphologic changes also took place in etched surface with 50% concentration, the degree of changes were less than that of changes with 10%, 30%. However, there were little morphologic changes with 70% concentration regardless of etching time. 5. Surface roughness(Ra) of sandblasting group with $50{\mu}m\;Al_2O_3$ had no significant difference with 30%-30 seconds etched group(P<0.05).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.183-184
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• 2013

Two main MBE growth techniques have been used: plasma-assisted MBE (PA-MBE), which utilizes a rf plasma to supply active nitrogen, and ammonia MBE, in which nitrogen is supplied by pyrolysis of NH3 on the sample surface during growth. PA-MBE is typically performed under metal-rich growth conditions, which results in the formation of gallium droplets on the sample surface and a narrow range of conditions for optimal growth. In contrast, high-quality GaN films can be grown by ammonia MBE under an excess nitrogen flux, which in principle should result in improved device uniformity due to the elimination of droplets and wider range of stable growth conditions. A drawback of ammonia MBE, on the other hand, is a serious memory effect of NH3 condensed on the cryo-panels and the vicinity of heaters, which ruins the control of critical growth stages, i.e. the native oxide desorption and the surface reconstruction, and the accurate control of V/III ratio, especially in the initial stage of seed layer growth. In this paper, we demonstrate that the reliable and reproducible growth of GaN on Si (110) substrates is successfully achieved by combining two MBE growth technologies using rf plasma and ammonia and setting a proper growth protocol. Samples were grown in a MBE system equipped with both a nitrogen rf plasma source (SVT) and an ammonia source. The ammonia gas purity was ＞99.9999% and further purified by using a getter filter. The custom-made injector designed to focus the ammonia flux onto the substrate was used for the gas delivery, while aluminum and gallium were provided via conventional effusion cells. The growth sequence to minimize the residual ammonia and subsequent memory effects is the following: (1) Native oxides are desorbed at $750^{\circ}C$ (Fig. (a) for [$1^-10$] and [001] azimuth) (2) 40 nm thick AlN is first grown using nitrogen rf plasma source at $900^{\circ}C$ nder the optimized condition to maintain the layer by layer growth of AlN buffer layer and slightly Al-rich condition. (Fig. (b)) (3) After switching to ammonia source, GaN growth is initiated with different V/III ratio and temperature conditions. A streaky RHEED pattern with an appearance of a weak ($2{\times}2$) reconstruction characteristic of Ga-polarity is observed all along the growth of subsequent GaN layer under optimized conditions. (Fig. (c)) The structural properties as well as dislocation densities as a function of growth conditions have been investigated using symmetrical and asymmetrical x-ray rocking curves. The electrical characteristics as a function of buffer and GaN layer growth conditions as well as the growth sequence will be also discussed. Figure: (a) RHEED pattern after oxide desorption (b) after 40 nm thick AlN growth using nitrogen rf plasma source and (c) after 600 nm thick GaN growth using ammonia source for (upper) [110] and (lower) [001] azimuth.

• 한국재료학회지
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• 제13권4호
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• pp.251-258
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• 2003

The effects of the salt and the precursor pH on the synthesizing behavior and the morphology of mullite have been studied. Two kinds of mullite precursor sols were prepared by the dissolution of two kinds of salt (aluminum nitrate enneahydrate, Al($NO_3$)$_3$ㆍ$9H_2$O; type I and aluminum sulfate 14∼18 water, (SO$Al_4$)$_3$$\cdot$$14∼18H_2$O; type II) into the mixture of colloidal silica sol, respectively. Precursor pH of the sols was controlled to the acidic (pH= 1.5∼2) and basic (pH= 8.5∼9) conditions. The co-products with nitrate and sulfate were completely eliminated at $500^{\circ}C$ and $850^{\circ}C$, respectively, which was confirmed by TG/DTA results. The synthesizing temperature of mullite phase was found to be above $1200^{\circ}C$ for pH= 1.5∼2 and above $1300^{\circ}C$ for pH= 8.5∼9 in type I. However, in type II, the synthesizing temperature of mullite was decreased to $850^{\circ}C$ for pH= 1.5∼2 and $1100^{\circ}C$ for pH= 8.5∼9. The grain size of the mullite synthesized at pH= 8.5∼9 was larger than that at pH= 1.5∼2 in overall heat-treated temperatures, showing smaller grain size in type II. Aspect ratio of the mullite grains was more increased at pH= 1.5∼2 than pH= 8.5∼9 in type I, showing similar aspect ratio at both pH conditions in type II. It was found that the synthesizing temperature and grain size were predominantly governed by the initial precursor pH and decomposition of the salt, with minor effect on the grain morphology.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.68-75
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• 2001

In this paper, a number of supported metal oxides and perovskite type catalysts were investigated for the NOx reduction from the diesel engine exhaust gas. All catalysts were made into pellets type with diameter of 3-4 mm alumina(Al$_2$O$_3$) as a supporter. These samples were tested by real diesel exhaust gas which contains CO, hydrocarbons and soot in the temperature range of 150~55$0^{\circ}C$ with the $3300h^{-1}$ space velocity (SV). Among the results, several promising catalysts showed NOx conversion above 50% in the temperature range of 150-35$0^{\circ}C$. From these results supported metal oxides catalysts and perovskite type could be recommended for the practical application to the automobile exhaust treatments.

• 유기물자원화
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• 제22권4호
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• pp.45-53
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• 2014

본 연구는 SCB 저농도 액비에 질소, 인산, 칼리 성분을 첨가한 개량 SCB 액비(DSCB)의 시비에 따른 한국 잔디의 생육에 미치는 영향을 평가하기 위해 수행되었다. 처리구는 비료의 종류와 시비량에 따라 무처리구(NF), 화학비료를 시비한 대조구(CF), 유안으로 질소 성분을 보정한 DSCB를 80% 시비한 처리구 1(DSCB-A1), 유안으로 질소 성분을 보정한 DSCB를 100% 시비한 처리구 2(DSCB-A2), 요소로 질소 성분을 보정한 DSCB 처리구(DSCB-U) 그리고 대조구에 SCB를 시비한 처리구(CF+SCB)로 설정하여 엽색 지수, 엽록소 지수, 건물 중 및 잔디의 양분 함유량을 가지고 생육을 평가하였다. 엽색 지수와 엽록소 지수를 조사한 결과, NF보다 각각 1~3%와 14~28% 증가하였고, CF와 비교할 때, DSCB-A1, DSCB-A2 및 CF+SCB의 엽록소 지수는 약 7~12% 높게 조사되었다. 잔디 생육량은 DSCB-A1와 DSCB-A2에서 CF보다 25%와 19%씩 증가하였고, 질소 흡수량은 19%와 6%씩 증가하였다. DSCB-A1은 잔디 품질과 잔디생육 및 시비 효율이 가장 효과적인 처리구로 평가되었다. 이러한 결과들을 통해 한국 잔디에서 DSCB-Al의 시비는 화학비료보다 양질의 잔디품질을 보여 골프코스 관리에서 DSCB-A1의 활용은 화학비료를 대체할 수 있을 것으로 기대되었다.

• 한국결정성장학회지
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• 제31권6호
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• pp.276-281
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• 2021

반도체 회로를 제조하기 위해서 에칭, 세척, 증착 등의 공정들이 반복적으로 진행된다. 따라서 이러한 공정이 진행되면 진공장비 내부는 부식성이 높은 가혹한 플라즈마 환경에 노출되게 된다. 따라서 반도체 공정 장비의 내부를 플라즈마 노출에 강한 재료를 사용하여 코팅층의 에칭과 오염 입자의 생성을 최소화하여야 한다. 본 연구에서는 고상합성법에 의해 Y₂O₃와 YF₃ 분말을 원료물질로 옥시불화이트륨(YOF)를 성공적으로 합성하였다. Y₂O₃와 YF₃ 분말의 혼합비율은 1.0:1.0에서 1.0:1.6까지 조절하였으며, 혼합비율이 합성된 YOF 분말의 결정구조와 미세구조에 미치는 영향을 XRD와 FE-SEM으로 조사하였다. 합성된 YOF 분말을 이용하여 알루미늄 기판에 플라즈마 스프레이법으로 성공적으로 코팅하였다.

• 대한소아치과학회지
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• 제24권1호
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• pp.112-124
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• 1997

According to extensive use of composite resin which have superior esthetic property, every effort on improving bonding strength between a tooth and composite resin has been continued. Acid etching technique is a method that micro-etches the tooth surface which provides bonding with composite resin possible. Recently, there were several reports that mechanical treatment obtained from air-abrasion can provide similar bonding strength with acid etching technique. So, this experimental study was designed to compare the shear bonding strength between using air-abrasion technique and using acid etching technique. Initially, bovine teeth were divided into enamel and dentin experimental groups. Respectively each group was categorized into three subgroups. One subgroup was acid etched with 35% phosphoric acid, then bonded with composite resin. The other subgroup was air-abraded with $50{\mu}m$ $Al_2O_3$ particles sprayed with 160psi air pressure using air abrasion unit(KCP-1000, A.D.T., U.SA), and composite resin was bonded. In another subgroup, composite resin was bonded after acid etching following air-abrasion. So, enamel experimental groups were made of E1 (acid etched only), E2(air-abraded only), E3(acid etched following air-abraded), and dentin experimental groups were made of D1(acid etched only), D2(air-abraded only), D3(acid etched following air-abraded). Each subgroup had 10 specimens. Dentin bonding system(Scotchbond Multi-purpose, 3M Co., U.S.A.) and composite resin(Z-100, 3M Co., U.S.A.) were applied on treated surface using 5mm diameter gelatin capsule as manufacturer's direction. After 1200 times thermocycling between $5^{\circ}C$ and $55^{\circ}C$, shear bond strength was measured in 5mm/min crosshead speed with Instron(Instron Co., U.S.A.), and also treated enamel and dentin were observed with SEM(JEOL Co., Japan). The following results were obtained: 1. In the enamel experimental groups, acid etched following air-abraded group had highest shear bond strength, but there was no significant difference compared to acid etched group. Air-abraded only group had lowest shear bond strength, and there was significant difference compared to the rest of groups. 2. In the dentin experimental groups, acid etched following air-abraded group had highest shear bond strength, but there was no significant difference compared to acid etched group. Air-abraded only group had lowest shear bond strength, and there was significant difference compared to the rest of groups. 3. In the SEM study, air-abraded enamel and dentin had irregular and rough surfaces.

• 전기화학회지
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• 제25권3호
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• pp.105-112
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• 2022

전고체전지의 상용화를 위해서는 상온에서 작동이 가능한 고체전해질 개발이 필수적이며 이온전도도가 높은 물질을 채택하여 전고체전지를 제조해야 한다. 따라서, 기존의 옥사이드 계열의 고체의 이온전도도를 높이기 위하여 이종원소가 도핑된 Li₇La₃Zr₂O₁₂ (LLZO)를 필러소재(Al, Nb-LLZO)로 사용하였으며, 상온에서 작동이 가능하도록 Poly(ethylene oxide)/Poly(propylene carbonate) (PEO/PPC) 기반의 가넷형 무기계 고체고분자 전해질을 제조하였다. 이원금속 원소를 도핑한 가넷형 무기계 필러와 PEO/PPC (1:1 비율로 섞인) 고분자를 1:2.4의 비율로 균일하게 교반하여 전해질을 합성해 상온과 60 ℃에서 전고체 전지의 전기학적 성능을 분석하였다. 제조한 복합 전해질은 이원금속의 도핑으로 인하여 이온전도도가 향상되었으며, PEO 단독으로 사용하는 전해질보다 PPC를 1:1로 첨가하였을 때 이온전도도 향상을 도와 60 ℃ 뿐만 아니라 상온에서 전고체 전지의 용량과 용량 유지율이 개선되었음을 확인하였다.

• 한국대기환경학회지
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• 제24권5호
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• pp.594-603
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• 2008

A single particle analytical technique, named low-Z particle electron probe X-ray microanalysis, was applied to characterize four samples collected at an underground shopping area connected to Dongdeamun subway station, in January and May 2006. Based on the analysis of their chemical compositions of the samples, many distinctive particle types are identified and the major chemical species are observed to be soil-derived particles, iron-containing particles. sulfates. nitrates, and carbonaceous particles. which are encountered both in coarse and fine fractions. Carbonaceous particles exist in carbon-rich and organic. Soil derived particles such as aluminosilicates, AlSi/C, $CaCO_3\;and\;SiO_2$ are more frequently encountered in spring samples than winter samples. Nitrate- and sulfate-con taming particles are more frequently encountered in winter samples, and those nitrate- and sulfate-containing particles mostly exist in the chemical forms of $Ca(CO_3,\;NO_3),\;Ca(NO_3,\;SO_4),\;(Na,\;Mg)NO_3\;and\;(Mg,\;Na)(NO_3,\;SO_4)$. Fe-containing particles which came from nearby subway platform are in the range of about 10% relative abundances for all the samples. It is observed that nitrate- and sulfate-containing particles and carbonaceous particles are much more frequently encountered in indoor aerosol samples than in outdoor aerosols, implying that $NO_x,\;SO_x$, and VOCs at the underground shopping area were more partitioned into aerosol phase.

• 청정기술
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• 제16권2호
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• pp.95-102
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• 2010

MCM 41, HMS, SBA 15와 같은 메조다공 실리카에 post-synthesis와 co-condensation 방법으로 황산이 결합된 촉매를 제조하였다. 이 메조다공 실리카들을 자일로즈 탈수화반응의 촉매로 사용하여 푸르푸랄을 합성하였으며 관련된 반응특성을 연구하였다. 그 결과, 친환경적 용매인 물을 사용한 경우에도 양호한 전환율과 선택도를 얻을 수 있었다. 아울러 실리카 표면에 황산의 양이 증가할수록 자일로즈의 전환율이 증가하는 것을 알 수 있었고, 동일한 반응 조건에서 다른 고체산 촉매인 제올라이트와 감마알루미나를 사용했을 때 보다 양호한 선택도 결과를 얻었다.