Sinter Plus HIP에 의한 $Al_2$$O_3$-SiC 나노복합재료의 치밀화 거동

채기웅 한국세라믹학회 2001 한국세라믹학회지 Vol.38 No.2

Al$_2$O$_3$-5 vol% SiC 나노복합재료의 sinter plus HIP에 의한 치밀화시 일어나는 기공의 변화에 초점을 두어 치밀화 거동을 관찰하였다. $Al_2$O$_3$-SiC 시편은 질소분위기 중의 상압소결과 이후의 열간정수압소결(HIP)에 의해 완전치밀화가 이루어졌다. 155$0^{\circ}C$의 상압소결에 의해서는 90%의 비교적 낮은 상대밀도가 얻어졌으나, 기공의 폐기공화로 이후의 열간정수압소결(HIP)에 의해 99.6%의 완전치밀화가 가능하였다. 상압소결한 시편을 X-선 회절기와 주사전자현미경(SEM)으로 관찰한 결과, 선택적으로 시편 표면부에서만 SiAl$_{6}$O$_2$N$_{6}$과 AlN 등으로 이루어진 치밀화된 반응층을 확인할 수 있었으며, 이러한 표면 반응층이 비교적 낮은 상대밀도의 시편내의 모든 기공을 폐기공화하는 효과를 주는 것을 알 수 있었다.

Al2O3-SiC 복합재료의 미세조직 및 기계적 물성에 미치는 SiC 원료분말의 크기 영향

채기웅 한국세라믹학회 2004 한국세라믹학회지 Vol.41 No.2

The effect of SiC particle size on the microstructures and mechanical properties of Al2O3-SiC composite was investigated. Two types of SiC powders having average particle sizes of 0.15 ㎛ and 3 ㎛ were used. The grain growth in the specimen containing 0.15 ㎛ SiC was effectively inhibited due to the fine SiC particles. However, after the formation of some abnormal grains, fast and exaggerated grain growth occurred which led to the microstructure of large grains with irregular shape. Fracture strength decreased due to the abnormal large grains. On the other hand, for specimen containing 3 ㎛ SiC showed normal grain growth behavior from initial sintering stage. Large SiC particles, however, effectively inhibited exaggerated grain growth after nucleation of a few abnormal grains. As a consequence, microstructure was consisted of homogeneous elongated grains. In the Al2O3-2.5SiC(0.15㎛)-2.5SiC(3㎛) composite fabricated by mixing the two types of SiC powder, abnormal grain growth occurred. However, the good fracture strength was maintained regardless of microstructural changes in this specimen. 서로 다른 크기의 SiC 원료분말을 첨가한 Al2O3-SiC 복합재료의 미세조직과 그에 따른 기계적 물성의 변화를 관찰하였다. 0.15㎛의 SiC가 첨가된 복합재료의 경우 기지상의 입성장이 효과적으로 억제되었다. 그러나, 소수의 비정상입자가 생성된 이후에는 이들 입자의 급격한 성장으로 불규칙한 형상의 커다란 입자로 구성된 미세조직을 보이며, 파괴강도값은 급격히 감소하였다. 3 ㎛의 SiC가 첨가된 경우에는 기지상의 입성장이 일어났으나, 소수의 비정상입자가 생성된 이후에는 과도한 입성장은 억제되고 일정한 크기의 비정상입자가 시편 전체에 균일하게 형성된 미세조직을 보였다. 한편, 0.15㎛와 3㎛의 SiC 입자를 동시에 첨가한 시편은 균일한 크기의 비정상입성장의 미세조직을 보였으나, 비정상입성장이 일어났음에도 불구하고 기계적 물성은 우수하게 유지되었다. 즉, 비정상입성장에 의해 미세조직에는 큰 변화가 일어났으나, 파괴강도값에는 변화가 없었다.

Rietveld 정밀화법과 SEM-EDS 분석에 의한 DPF용 코디어라이트 하니컴 세라믹스의 결정성장 과정 분석

채기웅,김강산,김정석,김신한,Chae, Ki-Woong,Kim, Kang San,Kim, Jeong Seog,Kim, Shin-Han 한국결정성장학회 2021 한국결정성장학회지 Vol.31 No.3

코디어라이트(Mg₂Al₄Si₅O₁₈) 하니컴 세라믹스의 대표적 응용분야는 자동차 배기가스 정화용 필터(diesel particulate filter(DPF))이다. 천연광물, 조공제, 유기바인더를 혼합한 슬러리를 압출하여 DPF용 하니컴 코디어라이트를 성형한 후 980~1450℃ 범위에서 소결하였다. 소결온도에 따른 결정상(indialite, cordierite, cristobalite, alumina, spinel, mullite, pro-enstatite)의 형성과정을 XRD Rietveld 정밀화법을 이용하여 정량분석 하였다. 동시에, 세라믹 에칭(etching) 방법으로 소결 시료 표면의 비정질상을 제거한 후 SEM/EDS법을 사용하여 결정상들의 형상과 조성을 확인하였다. 이들 결과로부터 DPF 하니컴에서 결정상 형성 과정을 명확히 밝힐 수 있었다. 또한, DPF 하니컴의 소결온도에 따른 열팽창계수(linear coefficient of thermal expansion, CTE) 변화를 분석하였고, 결정상의 정량분석결과를 바탕으로 계산된 CTE와 비교하였다. 소결된 DPF 하니컴 내의 결정상들이 CTE 특성에 미치는 영향을 고찰하였다. Diesel particulate filter (DPF) is a typical application field of cordierite (Mg₂Al₄Si₅O₁₈) honeycomb. Green body for DPF honeycomb was extruded using slurry paste and sintered at the temperature range of 980~1450℃. Quantitative crystal phase analysis was carried out by using Rietveld refinement method for powder XRD data. In conjunction with the quantitative Rietveld analysis, SEM-EDS analysis was carried for the crystal phases (indialite, cordierite, cristobalite, alumina, spinel, mullite, pro-enstatite). After removing amorphous phase on the sintered surfaces by chemical etching method, the shape and composition of the crystal phases can be clearly identified by SEM-EDS method. By combining the Rietveld refinement method and SEM-EDS analysis, crystal phase evolution process in DPF cordierite ceramics could be clarified. In addition, the coefficient of thermal expansion (CTE) of the DPF honeycombs were measured and compared with the calculated CTEs based on the quantitative crystal phase analysis results.

Transparent and Highly Luminescent Eu-Oxide Thin Film Phosphors on Sapphire Substrates

채기웅,박타령,천채일,조남인,김정석 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.-

Transparent and highly luminescent thin film phosphors were prepared by the thermal evaporation of Euoxide and its subsequent deposition on (006) sapphire substrates in a vacuum in a strongly reducing atmosphere at 1200°C - 1300°C. The resulting phosphor films, which were 1 - 3 μm thick, strongly adhered to the substrate and exhibited photoluminescence spectra similar to those of Eu-doped β"-alumina, with an emission peak centered at about 525 nm. The films consisted of Eu2O3 and β"-alumina phases with preferential growth planes. The transparency of the thin film phosphors was measured over the UV-visible range (370 - 720 nm). The average transparency was 26% - 55% of the total incident light. The integrated photoluminescence intensities of the phosphor films were compared to that of a commercial powder phosphor with green-light emission.

VC의 첨가에 따른 Fe-TiC계의 미세조직변화

채기웅 한국세라믹학회 1999 한국세라믹학회지 Vol.36 No.4

The effect of VC addition on the microstructural evolution of Fe-TiC cermet has been investigated. The microstructures of the Fe-TiC varied with the amount of VC addition. The addition of 1wt% VC enhanced the instability of liquid-solid interface ; the dissolving interface showed round shape instead of facetted one which was ascribed to the increase of lattice mismatch between TiC and solid-solution carbide. in the speci-men with 10wt% VC the new set of solid-solution carbide grains of uniform and small size was formed in-side coarse TiC particles by diffusion induced recrystallizatin (DIR). With increasing the heat-treatment time fine recrystallized grains were dispersed homogeneously in the matrix and resulted in the increase in fracture strength.

수용액 합성법에 의한 ZnO 이중 나노구조물의 합성

채기웅,김정석,Chae, Ki-Woong,Kim, Jeong-Seog,Cao, Guozhong 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.6

Double-layered ZnO nanostructures have been synthesized by aqueous solution method on (001) plane of ZnO nanorod. A stepwise changing of aqueous solution concentration gave rise to a new nano-structured layer consisting of either multiple of nanorods or nanowires with much smaller radii than that of the ZnO nanorod on which the new layer was grown. As the first step the ZnO nanorods have been grown to have the (001) preferential orientation in the aqueous solution consisting of 0.1M zinc nitrate and 0.1 M HMT. This preferentially aligned ZnO nanorods have been regrown in either a less diluted solution of 0.01M zinc nitrate and 0.01 M HMT or a more diluted solution of 0.005M zinc nitrate and 0.01 M HMT. A new nano-layer consisting of numerous aligned nanorods or nanowires has been produced on the (001) planes of ZnO nanorods. The growth mechanism for this double layered ZnO nanostructure is ascribed to the (001) polar surface energy instability and inhibition of (001) plane growth due to the step-wise change of aqueous solution concentration; ZnO nuclei formed on the (001) plane grow preferentially in (010) plane instead of (001) plane to reduce the total surface energy. Surface area of ZnO nanostructure can be increased in orders of magnitudes by forming a new layer consisting of smaller nanorods/nanowires on (001) plane of ZnO nanorods.

Al2O3:xCr2O3 고용상의 발광특성과 적색형광체의 연색성 향상을 위한 첨가제로의 응용

채기웅,천채일,김정석 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.2

In this article photoluminescence of the Al2O3:xCr2O3 solid solutions prepared by solid state reaction method are represented. The effect of Cr2O3-activator concentration and heat treatment time on the PL characteristics have been discussed in conjunction with microstructure of phosphor samples. The Al2O3:xCr2O3 phosphors show the highest PL intensity at x=0.003 mole when the samples are reacted at 1600oC for 5 h. The PL emission and absorption spectra show the maximum peaks at 698 nm and at 398 nm respectively. The CIE color coordinate is (x=0.646, y=0.316) at 0.003 mole Cr2O3, which value is very close to the NTSC coordinate of red color. This characteristic feature of Al2O3:xCr2O3 has been applied for an additive to improve the color haracteristic of other red phosphor LiEuW2O8 which has a relatively poor color purity with an emission peak centered at 615 nm and with a CIE coordinate (x=0.530, y=0.280). The Al2O3:0.003Cr2O3 phosphor has been mixed with the LiEuW2O8 phosphor powder and the PL characteristics and CIE color coordinates are characterized. The Al2O3:xCr2O3 phosphor was found effective for improving the CRI (color rendering index) of LiEuW2O8 phosphor.

Al₂O₃:xCr₂O₃ 고용상의 발광특성과 적색형광체의 연색성 향상을 위한 첨가제로의 응용

채기웅,천채일,김정석,Chae, Ki-Woong,Cheon, Chae-Il,Kim, Jeong-Seog 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.2

In this article photoluminescence of the $Al_2O_3:xCr_2O_3$ solid solutions prepared by solid state reaction method are represented. The effect of $Cr_2O_3$-activator concentration and heat treatment time on the PL characteristics have been discussed in conjunction with microstructure of phosphor samples. The $Al_2O_3:xCr_2O_3$ phosphors show the highest PL intensity at x=0.003 mole when the samples are reacted at $1600^{\circ}C$ for 5 h. The PL emission and absorption spectra show the maximum peaks at 698 nm and at 398 nm respectively. The CIE color coordinate is (x=0.646, y=0.316) at 0.003 mole $Cr_2O_3$, which value is very close to the NTSC coordinate of red color. This characteristic feature of $Al_2O_3:xCr_2O_3$ has been applied for an additive to improve the color characteristic of other red phosphor $LiEuW_2O_8$ which has a relatively poor color purity with an emission peak centered at 615 nm and with a CIE coordinate (x=0.530, y=0.280). The $Al_2O_3:0.003Cr_2O_3$ phosphor has been mixed with the $LiEuW_2O_8$ phosphor powder and the PL characteristics and CIE color coordinates are characterized. The $Al_2O_3:xCr_2O_3$ phosphor was found effective for improving the CRI (color rendering index) of $LiEuW_2O_8$ phosphor.

TiC-$Cr_3C_2$ 계 확산구동 재결정에 미치는 ZrC와 VC 첨가영향

채기웅 한국세라믹학회 1996 한국세라믹학회지 Vol.33 No.2

The effect of ZrC and VC addition on the diffusion induced recrystallization (DIR) of TiC-Cr3C2 has been investigated. With in creasing the amount of added ZrC to Cr3C2 the DIR of TiC was suppressed at the begining and then occurred. On the contrary the DIR was accelerated with the addition of VC to Cr3C2 Because the lattice parameters of (Ti, Cr)C and (Ti,V)C are smaller and that of (Ti, Zr)C is larger than that of TiC the lattice parameter of (Ti,Cr,Zr)C is expected to be similar to that of TiC,. The results indicate that the strain energy due to lattice mismatch between TiC and solid-solution carbide is the driving force of the observed energy due to lattice mismatch between TiC and solid-solution carbide is the driving force of the observed DIR.

$Al_2O_3-SiC$ 복합재료의 상압소결시 치밀화에 미치는 SiC 원료분말의 크기영향

채기웅 한국세라믹학회 1999 한국세라믹학회지 Vol.36 No.11

Effect of SiC particle size of the densification of Al2O3-SiC composite during pressureless sintering was investigated. Two types of SiC powders having average particle size of 0.15${\mu}{\textrm}{m}$ and 3${\mu}{\textrm}{m}$ were used. Densification rate of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was slower than that of the specimen containg 3${\mu}{\textrm}{m}$ SiC particles. Although the relative density of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was below 90% of theoretical density after sintering at 155$0^{\circ}C$ the complete closure of open pores occurred. Therefore full densification could be obtained by subsequent HIP. On the other hand in the specimen containing 3${\mu}{\textrm}{m}$ SiC particles the complete closed pore was observed at 95% of theoretical density. Such a fast pore closure in the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles is likely to occur as a result of dense reaction layer formation on the specimen surface which is attributed to the high reactivity of small size particles with sintering atmosphere.