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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.
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.
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 $950^{\circ}C$.
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.
플라즈마 용사 Al<sub>2</sub>O<sub>3</sub> 코팅의 특성에 미치는 CrO<sub>3</sub> 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.
조경식(Kyeong-Sik Cho),안기업(Ki-up An),이지엽(Ji-Yop Yi),곽종원(Jong-Won Kwark),곽임종(Im-Jong Kwahk) 한국철도학회 2015 한국철도학회 학술발표대회논문집 Vol.2015 No.10
철도교에서 가장 많이 사용되는 교량 형식으로는 PSC 박스 거더교를 꼽을 수 있다. 특히 현재까지 건설된 고속 철도교의 경우 PSC 박스 거더교가 90% 이상을 차지하고 있다. 그렇기 때문에 PSC박스 거더교를 최적 설계할 경우 국가 SOC 사업 비용을 절감하는 효과를 도출할 수 있다. 국내에서는 비교적 최근에 설계된 호남고속철도의 경우 과거에 비하여 많은 부분 최적설계가 이루어졌다. 하지만 2013년도 철도 설계 기준이 개정되었기 때문에 이를 적용한 최적 설계가 필요하다. 최근에 설계된 국내외의 PSC박스 거더교를 조사분석하고 이를 반영하여 PSC박스 거더교의 최적설계를 수행한 결과 주요 물량을 상당부분 절감하는 결과를 도출하였다. 이에 따른 경제성 향상도 기대 할 수 있을 것으로 사료된다. PSC box girder have been very widely used as type of rail road. PSC box girder have been very widely used as type of girder. Especially, high-speed railroad bridges in Korea have been constructed in PSC box girder type over 90% up to now. So, if PSC box girder is designed economically, the fund for SOC projects can be decreased. It’s designed more economical then predecessor that Honam high speed railway girder is designed recently as PSC box girder in Korea. But it need to be newly optimal design. Because train load changed from HL-25 into KRL-2012 and criteria of dynamic behavior design changed in accordance with change of Design Criteria for Railroad in 2013. Therefore I made an investigation into recent PSC box girder for railroad bridges and analyzed it. And then I designed the PSC box girder reflecting it. As a result I got the result reduced main resources of PSC box girder.
CP-Ti 분말로부터 스파크 플라즈마 소결한 타이타늄의 미세구조와 기계적 성질에 미치는 가압력의 영향
조경식 ( Kyeong Sik Cho ),송인범 ( In Beom Song ),김재 ( Jae Kim ),오명훈 ( Myung Hoon Oh ),홍재근 ( Jae Keun Hong ),박노광 ( Nho Kwang Park ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.9
The aim of this study was to determine the effect of applied pressure and sintering temperature on the microstructure and mechanical properties for spark plasma sintering (SPS) from commercial pure titanium (CP-Ti) powders. Spark plasma sintering is a relatively new sintering technique in powder metallurgy which is capable of sintering metal and ceramic powers quickly to full density at a fairly low temperature due to its unique features. SPS of ?200 mesh or ?400 mesh CP-Ti powders was carried out in an Ar+H2 mixed gas flowing atmosphere between 650℃ and 750℃ under 10 to 80 MPa pressure. When SPS was carried out at relatively low temperatures (650℃ to 750℃), the high (>60 MPa) pressure had a marked effect on densification and grain growth suppression. The full density of titanium was achieved at temperatures and pressures above 700℃ and 60 MPa by spark plasma sintering. The crystalline phase and microstructure of titanium sintered up to 700℃ consisted of α-Ti and equiaxed grains. Vickers hardness ranging from 293 to 362 Hv and strength ranging from 304 to 410MPa were achieved for spark plasma sintered titanium.
이현권,조경식,김미영,Lee, Hyun-Kwuon,Cho, Kyeong-Sik,Kim, Mi-Young 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.4
Need for plasma resistant ceramic materials has been continuously increased in semiconductor and display industry requiring plasma processing to realize ultra fine circuit process. Among promising candidates, alumina ceramics have still some advantages with respect to its economic aspect. In this study, fabrication of plasma resistant alumina ceramics was tried, and its processing optimization was also aimed. Careful processing control and thereby uniform microstructure of $Al_2O_3$ gave rise to enhanced plasma resistance, even comparable to market-governing commercial $Al_2O_3$. A further study is needed concerning ${\beta}-Al_2O_3$ materials system, presumably playing a decisive role in decreasing plasma resistance of $Al_2O_3$ ceramics.