플라즈마 용사 Al₂O₃ 코팅의 특성에 미치는 CrO₃ 봉공처리의 영향

조경식,이현권,권정철,Cho, Kyeong-Sik,Lee, Hyun-Kwuon,Kwon, Jeong-Cheol 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.2

Plasma sprayed ceramic coatings inherently contain pores and usually also cracks. Post-treatment of the plasma sprayed coatings is a way to close the connected pores and cracks. In this study, post-sealing treatment in plasma sprayed $Al_2O_3$ coatings was employed to overcome the reduction of coating properties. $Al_2O_3$ plasma thermal spray coating was made on aluminum alloys plate, $CrO_3$ post coating and heat treatment at $550^{\circ}C$ was carried out in order for final $Cr_2O_3$ to be saturated through phase transformation. Chromia sealing began at the fine defect in coated microstructure, while larger pores were permeated later. The increase in concentration and treatment frequency of sealing solution resulted in the decrease of porosity of coating layer, while cracks occurred partially after the third treatment. After twice treatment of 10M $CrO_3$ solution, microhardness and breakdown voltage of $Al_2O_3$ coatings were found to increase by ${\fallingdotseq}$ 50% and ${\fallingdotseq}$ 390% respectively than without post-treatment.

Al-B-C 첨가 탄화규소의 스파크 플라즈마 소결에 의한 미세구조 발달

조경식,이광순,이현권,이상진,최헌진,Cho, Kyeong-Sik,Lee, Kwang-Soon,Lee, Hyun-Kwuon,Lee, Sang-Jin,Choi, Heon-Jin 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.8

Densification of SiC powder with additives of total amount of2, 4, 8 $wt\%$ Al-B-C was carried out by Spark Plasma Sintering (SPS). The unique features of the process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. The heating rate and applied pressure were kept at $100^{\circ}C/min$ and 40 MPa, while the sintering temperature and holding time varied from 1700 - $1800^{\circ}C$ for 10 - 40 min, respectively. The SPS-sintered specimens with different amount of Al-B-C at $1800^{\circ}C$ reached near-theoretical density. The $3C{\rightarrow}6H,\;15R{\rightarrow}4H$ phase transformation of SiC was enhanced by increasing the additive amount. The microstructure of SiC sintered up to $1750^{\circ}C$ consisted of fine equiaxed grains. In contrast, the growth of large elongated grains in small matrix grains was shown in sintered bodies at $1800^{\circ}C$, and the plate-like grains interlocking microstructure had been developed by increasing the holding time at $1800^{\circ}C$. The grain growth rate decreases with increasing amount of Al-B-C in SiC starting powder, however, the both of volume fraction and aspect ratio of large grains in sintered body increased.

제조 공정별 대형 알루미나 세라믹스의 전기적 특성

조경식,이현권,박용일,김미영,Cho, Kyeong-Sik,Lee, Hyun-Kwuon,Park, Young-Il,Kim, Mi-Young 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.2

The size of various alumina ceramics used in semiconductor and display industry is required to increase with increase in wafer and panel size. In this research, large alumina ceramics were fabricated by uniaxial pressing, cold isostatic pressing and filter pressing with commercial powder and thereafter sintering at $1600^{\circ}C$ in gas furnace. The large alumina ceramics exhibited dense microstructure corresponding to 98.5% of theoretical density and 99.8% of high purity. The impurities and microstructural defects of the alumina were found to influence the resistance and dielectric properties. The volume resistances in these four aluminas were almost the same while the pure alumina was higher value. The dielectric constant, dielectric loss and dielectric strength of aluminas were placed within the range of 10.3~11.5, 0.018~0.036, and 10.1~12.4 kV/mm, respectively.

CP-Ti 분말로부터 스파크 플라즈마 소결한 타이타늄의 미세구조와 기계적 성질에 미치는 소결 온도의 영향

조경식,송인범,장민혁,윤지혜,오명훈,홍재근,박노광,Cho, Kyeong-Sik,Song, In-Beom,Jang, Min-Hyeok,Yoon, Ji-Hye,Oh, Myung-Hoon,Hong, Jae-Keun,Park, Nho-Kwang 한국분말야금학회 2010 한국분말재료학회지 (KPMI) Vol.17 No.5

The evolution of sinterability, microstructure and mechanical properties for the spark plasma sintered(SPS) Ti from commercial pure titanium(CP-Ti) was studied. The densification of titanium with 200 mesh and 400 mesh pass powder was achieved by SPS at $750{\sim}1100^{\circ}C$ under 10 MPa pressure and the flowing $H_2$+Ar mixed gas atmosphere. The microstructure of Ti sintered up to $800^{\circ}C$ consisted of equiaxed grains. In contrast, the growth of large elongated grains was shown in sintered bodies at $900^{\circ}C$ with the 400 mesh pass powder and the lamella grains microstructure had been developed by increasing sintering temperature. The Vickers hardness of 240~270 HV and biaxial strength of 320~340 MPa were found for the specimen prepared at $950^{\circ}C$.

Al-B-C 조제 β-SiC의 스파크 플라즈마 소결에 미치는 α-SiC seed 첨가 영향: 미세 구조 변화

조경식,이현권,이상우,Cho, Kyeong-Sik,Lee, Hyun-Kwuon,Lee, Sang-Woo 한국분말야금학회 2010 한국분말재료학회지 (KPMI) Vol.17 No.1

The unique features of spark plasma sintering process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. $\beta$-SiC powder with 0, 2, 6, 10 wt% of $\alpha$-SiC particles (seeds) and 4 wt% of Al-B-C (sintering aids) were spark plasma sintered at $1700-1850^{\circ}C$ for 10 min. The heating rate, applied pressure and sintering atmosphere were kept at $100^{\circ}C/min$, 40 MPa and a flowing Ar gas (500 CC/min). Microstructural development of SiC as function of seed content and temperature during spark plasma sintering was investigated quantitatively and statistically using image analysis. Quantitative image analyses on the sintered SiC ceramics were conducted on the grain size, aspect ratio and grain size distribution of SiC. The microstructure of SiC sintered up to $1700^{\circ}C$ consisted of equiaxed grains. In contrast, the growth of large elongated SiC grains in small matrix grains was shown in sintered bodies at $1750^{\circ}C$ and the plate-like grains interlocking microstructure had been developed by increasing sintering temperature. The introduction of $\alpha$-SiC seeds into $\beta$-SiC accelerated the grain growth of elongated grains during sintering, resulting in the plate-like grains interlocking microstructure. In the $\alpha$-SiC seeds added in $\beta$-SiC, the rate of grain growth decreased with $\alpha$-SiC seed content, however, bulk density and aspect ratio of grains in sintered body increased.

굴 패각 분말로부터 벌크 세라믹 구조체 제조

조경식,이현권,민재홍,Cho, Kyeong-Sik,Lee, Hyun-Kwuon,Min, Jae Hong 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.3

Waste oyster shells create several serious problems; however, only some parts of them are being utilized currently. The ideal solution would be to convert the waste shells into a product that is both environmentally beneficial and economically viable. An experimental study is carried out to investigate the recycling possibilities for oyster shell waste. Bulk ceramic bodies are produced from the oyster shell powder in three sequential processes. First, the shell powder is calcined to form calcium oxide CaO, which is then slaked by a slaking reaction with water to produce calcium hydroxide $Ca(OH)_2$. Then, calcium hydroxide powder is formed by uniaxial pressing. Finally, the calcium hydroxide compact is reconverted to calcium carbonate via a carbonation reaction with carbon dioxide released from the shell powder bed during firing at $550^{\circ}C$. The bulk body obtained from waste oyster shells could be utilized as a marine structural porous material.

고교시설 디자인 지표의 적용 분석 연구 - 경기도 고등학교를 중심으로 -

조경식,아이게림,Cho, Kyung-Sik,Belyalova, Aigerim 한국교육시설학회 2017 敎育施設 Vol.24 No.6

The purpose of this study is to provide the fundamental data to improve a school building through comparing and analyzing facilities of high schools located in Gyeonggi - do Province on the basis of the Design Indicator for the Korean Educational Buildings. Two types of high schools were examined for this study. Some of them are high schools selected by Korean Ministry of Education as a school equipped with superior facilities and the others are high schools equipped with general facilities. 8 items such as safety, comfort, the function of education, utilization, the public, eco-friendliness, technology performance, economical efficiency were examined by 5 point Likert scale. Findings showed that all facilities of both types of high schools received high ratings in terms of safety, utilization, and technology performance. However, the evaluation index on 'various used outdoor space' and 'public buildings harmonized with surroundings' of the education function of both types of high schools was low, which implies that the facility related to the education function needs to be improved. It infers that facilities are simplified and harmony with surroundings disappears when altering the design of the school building due to the convenience of building and the problem of the budget. Therefore, these need to be primarily controlled. Additionally, in high schools with general facilities, the evaluation index on 'aesthetic interior and exterior design of comfort', 'the responsive space to the demand for teaching and learning of the function of education', and eco-friendless were so low that these factors need to be considered when designing the school building.

프리드리히 쉴러 「미학편지」의 논리구조에 관하여

조경식 ( Kyoung Sik Cho ) 연세대학교 유럽사회문화연구소 2013 유럽사회문화 Vol.11 No.-

Astheische Briefe sind ein Kunstprogramm, mit dem Schiller als "Sachwalter" der Kunst in der Zeit der Aufdifferenzierung der Gesellschaft in Funktionssysteme die Funktion und die Selbstreferenz des Kunstsystems zu begrunden versucht. Im Prozeß der Ausdifferenzierung muss die Kunst allein mit dem Code Schonheit operieren. Insofern als soziale Systeme aufgrund ihrer spezifischen gesellschaftlichen Funktionen existieren, fragt sich der "Sachverwalter" der Kunst danach, welche spezifische Funktion der Schonheit bzw. der schonen Kunst zugeteilt wird. Das Konzept einer solchen Funktion, die in der Gesellschaft nur die Schonheit bzw. die schone Kunst erfullen kann, begrundet sich auf die Bildung der menschlichen Totalitat, deren Bedarf aus Kritiken an der Franzosischen Revolution und an der modernen Gesellschaft uberzeugend erortert wird. Und die Frage, wie die Schoneit die Totalitat des Menschen bildet, wird direkt danach durch die transzendentale Deduktion der Schonheit aus der Bedingungen der Totalitat des Menschen beantwortet. Und daraus ergibt sich außerdem auch eine neue Identitat der schonen Kunst, das "asthetische Spiel" mit dem "aufrichtigen" und "selbstandigen Schein". Diese Selbtlegitimation der Kunst druckt sich in dem homo ludens aus. Der asthetische Mensch, ein anderer Ausdruck des "asthetischen Zustandes", den die Kunst einlosen soll, ist der wahre Mensch bzw. die "Consummation" der Menschheit. Dagegen bedeuten homo politicus, homo oeconomicus und homo sapiens usw. "Bruchstucke" der Menschheit, Entfremdung des Menschen von sich selbst. Allein die Kunst nimmt das volle Dasein des Menschen in Anspruch.

패널회귀분석을 이용한 위험이 운전자본에 미치는 영향에 관한 연구

조경식(Cho Kyung Shick),김희석(Kim Hee Seog) 한국산업경영학회 2014 경영연구 Vol.29 No.4

본 연구는 2003년부터 2013년까지 우리나라 상장기업들을 대상으로 위험이 운전자본에 미치는 영향을 분석하였다. 종속변수로서 운전자본을 도입하였고, 위험의 대용변수로서 운영위험, 주가수익률의 변동성 및 시장위험을 도입하였다. 운전자본의 구성요소로서 현금, 매출채권, 재고자산 및 매입채무를 통제변수로서 사용하였다. 매출액증가율, 기업규모, 부채비율 및 자기자본이익률과 같은 기본요인들을 통제한 후, 운전자본의 변화를 또한 분석하였다. 분석의 결과는 다음과 같다. 첫째, 기본분석에서 운영위험은 운전자본과 양(+)의 관계, 개별기업 주가수익률의 변동성은 운전자본과 음(-)의 관계를 보이는 것으로 나타났다. 이같은 결과는 운전자본관리 측면에서 운영위험에 대비하기 위해서는 유동자산 수준을 높이는 보수적인 재무정책을 펴야할 필요성이 있고, 변동성에 대비하기 위해서는 유동부채 수준을 높이는 공격적인 재무정책을 펴야할 필요성이 있음을 의미한다. 둘째, 현금순환주기를 사용한 경우와 글로벌 금융위기 기간별로 구분한 추가분석에서는 운전자본을 결정하는 요인들은 혼재된 것으로 나타났다. 셋째, 매출액증가율, 기업규모, 부채비율, 수익성과 같은 기본적인 요인들을 통제한 후, 운전자본을 설명하는 요인에는 몇 가지의 변화가 관찰되었다. 매출액이 증가하거나 혹은 감소한 기업, 기업규모가 큰 기업과 작은 기업, 부채비율이 높은 기업과 낮은 기업, 그리고 당기순이익 기업과 당기순손실 기업에서 운영위험이 운전자본의 결정요인이 되는 것으로 나타났다. 매출액이 증가하거나 혹은 감소한 기업, 기업규모가 큰 기업, 부채비율이 높은 기업, 그리고 당기순이익 기업과 당기순손실 기업에서 개별기업 주가수익률의 변동성이 운전자본의 결정요인이 되는 것으로 나타났다. 본 연구의 추가분석 결과에서, 위험요인과 운전자본요소가 우리나라 기업들의 운전자본에 미치는 영향은 여러가지 상황에 따라 다양하게 나타난 것을 확인하였다. This study examine that the effects the risk on the working capital for Korean firms over the period 2003-2013. This study employ working capital as a dependent variable, also employ three risk proxies, which are operational risk, volatility and market risk. This paper use cash, accounts receivable, inventory and accounts payable as a proxies of composition of working capital. After controlling for fundamental factors such as sales growth, size, leverage and profitability, this paper observe significant changes in working capital. The results are as follows. First, the basic analysis using Panel least square reveals that there is a strong positive relationship between working capital and operational risk, and there is a strong negative relationship between working capital and firm's volatility. This means in short-term financial policy that it is necessary to maintain a conservative policy to handle a operational risk, and to maintain a aggressive policy to cope with a volatility. Second, the additional analysis shows that the variables influencing corporate profitability vary across both cash conversion cycle and global financial crisis. Third, after controling for fundamental factors(such as sales growth, size, leverage and profitability), this study observe significant changes in working capital. Operational risk is a statistically significant determinants of working capital for high or low sales growth firms, large or small firms, high or low leveraged firms and profitable or non-profitable firms. Firm's volatility is a statistically significant determinants of working capital for high or low sales growth firms, big firms, high leveraged firms and profitable or non-profitable firms. In additional analysis, we confirm that the effects of risk and composition of working capital on working capital varies across the various conditions face the firms.

소개글: 현수교 보강형의 가설중 내풍안정성

조경식(Kyung Sik Cho) 한국강구조학회 2007 韓國鋼構造學會誌 Vol.19 No.3