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.

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.

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.

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.

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.

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.

소개글: 현수교 보강형의 가설중 내풍안정성

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

근대에 나타난 심미적 범주로서의 추

조경식(Cho Kyoung-Sik) 한국카프카학회 2009 카프카연구 Vol.0 No.21

소철지옥의 재현과 오키나와 협동조합 및 지역운동의 대응

조경식 ( Cho¸ Kyung-sik ) 한국일본근대학회 2021 일본근대학연구 Vol.- No.73

‘소철지옥’ 시기에 발표된 『떠도는 류큐인』 및 『멸망해 가는 류큐여인의 수기』는 당시 피폐해진 오키나와를 직접적으로 표현했던 작품이다. 이들 작품은 붕괴된 오키나와의 공동체를 가감 없이 그리고 있는데, 오키나와 반환을 앞둔 1970년에 다시 주목받으며 과거 본토-오키나와 사이의 문제를 돌아보고 다가올 반환 이후를 성찰하고자 촉구한다. 특히 작품을 통해 과거 ‘소철지옥’ 사태로 경험한바 있는 공동체의 붕괴를 다시금 상기시킴으로써, 다가올 반환 이후의 새로운 ‘소철지옥’을 대비한 협동조합의 형성과 지역운동의 활성화가 추동된다. 기지문제 및 환경문제를 외면한 국가적 이벤트로서 진행된 오키나와 반환을 새로운 형태의 ‘소철지옥’의 재현으로 볼 수 있었던 상황 속에서, 일찍이 과거 ‘소철지옥’ 시기를 통해 일본이라는 울타리의 한계를 경험한 시민들은 풀뿌리 지역운동을 기반으로 생활협동조합을 출범시킨다. 생활협동조합은 자발적이며 수평적 구조의 ‘반(班)조직’을 통해 생존을 위한 안전망을 구축하는 기반이 되었고, 이는 ‘소철지옥’ 시기에 구제의 존재로 대상화 된 오키나와 시민들이 스스로를 구한 높은 성취로 평가된다. 반환 이후 오키나와 지역을 둘러싼 다양한 문제들에 대응해 온 생활협동조합과 지역운동 조직들은 소외된 지역의 좋은 성장 본보기가 될 수 있을 것이다. The “Samayoeru ryuukyuujin” and “Memoirs of a Perishing Ryukyu Woman” published during the “Sotetsu Hell” period directly expressed the ravaged Okinawa at that time. These works depict the collapsed community of Okinawa without change. In 1970, before the return of Okinawa, it again drew attention, urging us to look back on the problems between the mainland and Okinawa in the past and reflect on the future after the return. In particular, the work reminds us of the collapse of the community that has been experienced in the past due to the ‘Sotetsu Hell’, thereby driving the formation of cooperatives and revitalization of local movements in preparation for a new ‘Sotetsu Hell’ after the coming return. In a situation where the return of Okinawa, which was conducted as a national event that ignored the base problem and environmental problems, could be seen as a reproduction of a new form of ‘Sotetsu Hell’, citizens who experienced the limits of Japan’s fence through the past ‘Sotetsu Hell’ Based on the grassroots local movement, a living cooperative is launched. Cooperatives have become the basis for establishing a safety net for survival through a voluntary and horizontal “HAN-organization”. And this is evaluated as a high achievement that the Okinawan citizens, who were objected to the existence of relief during the “Sotetsu Hell” period, saved themselves. Cooperatives and regional movement organizations that have responded to various problems surrounding the Okinawa region since the return will be a good example of growth in marginalized regions.