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필터 프레싱으로 제조한 대형 알루미나 세라믹스 성형체 및 소결체의 특성
이현권,조경식,장민혁,장철우,김상모,김미영,Lee, Hyun-Kwuon,Cho, Kyeong-Sik,Jang, Min-Hyeok,Jang, Chul-Woo,Kim, Sang-Mo,Kim, Mi-Young 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.3
The size of various alumina ceramics used in semiconductor and display industry is also required to increase with increase in wafer and panel size. In this research, large alumina ceramics was fabricated by filter pressing of alumina slurry using commercial powder and thereafter sintering at $1600^{\circ}C$ in gas furnace. The characteristics of large alumina ceramics thereby were compared to those of small alumina ceramics prepared by pressure forming such as uniaxial pressing and CIP. Careful control of properties of alumina slurry and filter pressing made the fabrication of large alumina ceramics possible, and its characteristics were equivalent to those of small alumina ceramics. The large alumina ceramics, prepared by sintering the green body of 63% relative density at $1600^{\circ}C$, exhibited both dense microstructure corresponding to 98.5% of relative density and 99.8% of high purity as in starting powder.
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.
기계적 합금화 및 스파크 플라즈마 소결에 의해 제조된 Al-Fe-X계 합금의 열적 안정성: II. Al-Fe-Cr and Al-Fe-Mo
이현권,이상우,조경식,Lee, Hyun-Kwuon,Lee, Sang-Woo,Cho, Kyeong-Sik 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.1
Mechanical alloying using high-energy ball mill and subsequent spark plasma sintering (SPS) process was applied to Al-Fe-Cr and Al-Fe-Mo powder mixture to investigate effects of Cr and Mo addition on thermal stability of Al-Fe, and thereby to enhance its thermal stability up to $500^{\circC}$. Various analytical techniques including micro-Vickers hardness test, SEM, TEM, X-ray diffractometry and corrosion test were carried out. It was found that addition of Cr and Mo to Al-Fe system played a role of grain growth inhibitor of matrix Al and some precipitates such as $Al_3Fe$ during SPS and subsequent heat treatment. The inhibition of grain growth resulted in increased Vickers hardness and thermal stability up to $500^{\circC}$ comparing to those of Al-Fe alloy system.
기계적 합금화 및 스파크 플라즈마 소결에 의해 제조된 Al-Fe-X계 합금의 열적 안정성: I. Al-Fe
이현권,이상우,조경식,Lee, Hyun-Kwuon,Lee, Sang-Woo,Cho, Kyeong-Sik 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.1
Mechanical alloying using high-energy ball mill and subsequent spark plasma sintering (SPS) process was applied to understand mechanical alloying processing of Al-Fe alloy system. The thermal stability of mechanically alloyed Al-Fe alloy was intended to be enhanced by SPS process. Various analytical techniques including particle size analysis, density measurement, micro-Vickers hardness test, SEM, TEM, and X-ray diffractometry were adopted to find optimum processing conditions for mechanical alloying and subsequent SPS and to estimate thermal stability of the prepared alloy. It was found from the treatment of mechanically alloyed Al-8wt.%Fe powder mixture that needle-shaped $Al_3Fe$ precipitates was formed in the Al-Fe matrix, and the alloy compact showed enhanced densification and reached its full density with little loss of its fine microstructure. After heat treatment at $500^{\circC}$, it was also shown that the thermal stability of Al-8wt.%Fe alloy fabricated in the present study was enhanced, which was due to its fine microstructure developed by fast densification of SPS.
용융코팅법에 의한 내플라즈마성 Y<sub>2</sub>O<sub>3</sub>-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>계 코팅 세라믹스 제조
박의근,이현권,Park, Eui Keun,Lee, Hyun-Kwuon 한국재료학회 2020 한국재료학회지 Vol.30 No.7
This study is aimed at improving the plasma resistance of Al<sub>2</sub>O<sub>3</sub> ceramics on which plasma resistant YAS(Y<sub>2</sub>O<sub>3</sub>-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>) frit is melt-coated using a simple heat-treatment process. For this purpose, the results of phase analysis and microstructural observations of the prepared YAS frits and the coating layers on the Al<sub>2</sub>O<sub>3</sub> ceramics according to the batch compositions are compared and discussed with regard to the results of plasma resistance test. The prepared YAS frits consist of crystalline or amorphous or co-existing crystalline and amorphous phases according to the batch compositions, depending on the role and content of each raw material. The prepared YAS frit is melt-coated on the densely sintered Al<sub>2</sub>O<sub>3</sub> ceramics, resulting in a dense coating layer with a thickness of at least ~ 80 ㎛. The YAS coating layer consists of crystalline YAG(Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>), Y<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>, and Al<sub>2</sub>O<sub>3</sub> phases, and YAS glass phase. Plasma resistance of YAS coated Al<sub>2</sub>O<sub>3</sub> ceramics is strongly dependent on the content of the YAG(Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>) and Y<sub>2</sub>Si<sub>2</sub>O<sub>7</sub> crystalline phases in the coating layer, especially on the content of the YAG phase. Comparing the weight loss of YAS coating ceramics with values obtained for commercial Y<sub>2</sub>O<sub>3</sub>, Al<sub>2</sub>O<sub>3</sub>, and quartz ceramics, the plasma resistance of the YAS coating ceramics is 6 times higher than that of quartz, 2 times higher than that of Al<sub>2</sub>O<sub>3</sub>, and 50 % of the resistance of Y<sub>2</sub>O<sub>3</sub>.
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.
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.
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.
최진석,이현권,안성진,Choi, Jin Seok,Lee, Hyun-Kwuon,An, Sung Jin 한국재료학회 2014 한국재료학회지 Vol.24 No.5
Silica nano-powder (SNP) is an inorganic material able to provide high-performance in various fields because of its multiple functions. Methods used to synthesize high purity SNP, include crushing silica minerals, vapor reaction of silica chloride, and a sol-gel process using TEOS and sodium silicate solution. The sol-gel process is the cheapest method for synthesis of SNP, and was used in this study. First, we investigated the shape and the size of the silica-powder particles in relation to the variation of HCl and sodium silicate concentrations. After drying, the shape of nano-silica powder differed in relation to variations in the HCl concentration. As the pH of the solution increased, so did the density of crosslinking. Initially, there was NaCl in the SNP. To increase its purity, we adopted a washing process that included centrifugation and filtration. After washing, the last of the NaCl was removed using DI water, leaving only amorphous silica powder. The purity of nano-silica powder synthesized using sodium silicate was over 99.6%.