일축 가압 소결법을 이용한 고밀도 탄화 붕소 제조 및 기계적 특성

채재홍,박주석,안종필,김경훈,Chae, Jae-Hong,Park, Joo-Seok,Ahn, Jong-Pil,Kim, Kyoung-Hun 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.1

$B_4C$ ceramics were fabricated by a hot-press sintering method and their sintering behavior, microstructure and mechanical properties were evaluated. Relative density of $B_4C$ ceramics were obtained by a hot-press sintering method reached as high as 99% without any sintering additives. The mechanical properties of $B_4C$ ceramics was improved by a methanol washing process which can remove $B_2O_3$ phase from a $B_4C$ powder surface. This improvement results from the formation of homogeneous microstructure because the grain coarsening was suppressed by the elimination of $B_2O_3$ phase. Particularly, mechanical properties of the sintered specimen using a methanol washed powder improved compared with the specimen using an as-received commercial powder.

$Al_2O_3-SiC$ 나노복합체의 방전 플라즈마 소결 특성 및 기계적 물성

채재홍,김경훈,심광보 한국결정성장학회 2003 韓國結晶成長學會誌 Vol.13 No.6

A spark plasma sintering technique has been used for the fabrication of $Al_2O_3$-SiC nanocomposites at the low temperature of $1100^{\circ}C$∼$1500^{\circ}C$. The sintered $Al_2O_3$-SiC composites shows very homogeneous microstructure without any particular abnormal grain growth, indicating that the addition of nano-sized SiC particles is very effective to control grain growth and to induce the residual stress in the $Al_2O_3$ matrix, resulting in the intragranular fracture. These SiC particles are present in the grain boundaries and also intragrain, depending on the sintering condition, and improve remarkably the mechanical properties of $Al_2O_3$-SiC composite through the mechanisms of strengthening and toughening induced by crack diffraction and crack bridging. 방전 플라즈마 소결법을 적용하여 $Al_2O_3$-SiC 나노 복합체를 150$0^{\circ}C$ 이하의 온도에서 완전치밀화를 이루었다. 제조된 $Al_2O_3$-SiC 복합체는 이상 결정립 성장 없이 매우 균질한 미세구조를 형성하고 있는데, 첨가된 SiC 입자는 주로 결정립 내 및 결정립계에 존재하면서 $Al_2O_3$기지상에서 결정립 성장을 억제하는데 매우 유호하였음을 확인 할 수 있다. 한편, SiC 입자의 첨가는 크랙 회절 및 브릿징 등에 의해서 유도된 재료 강도 및 인성 강화 기구에 의해서 $Al_2O_3$-SiC 복합체의 기계적 물성을 크게 향상시켰다.

상압 소결법으로 제조된 이트리아 첨가 질화 알루미늄 세라믹스의 미세 구조 및 열전도도

채재홍,박주석,안종필,김경훈,Chae, Jae-Hong,Park, Joo-Seok,Ahn, Jong-Pil,Kim, Kyoung-Hun 한국결정성장학회 2009 한국결정성장학회지 Vol.19 No.1

The effect of ${Y_2}{O_3}$ as a sintering additive on thermal conductivity and microstructure of pressureless sintered AIN ceramics was investigated at sintering temperature range from 1,700 to $1,900^{\circ}C$. ${Y_2}{O_3}$ added AIN specimens showed higher densification rate than pure AIN because of the formation of the yttrium aluminates secondary phase by reaction of ${Y_2}{O_3}$ and ${Al_2}{O_3}$ of AIN surface. The thermal conductivity of AIN specimens was promoted by the addition of ${Y_2}{O_3}$ in spite of the formation of secondary phase in AIN gram boundaries and grain boundary triple junction, because ${Y_2}{O_3}$ addition could reduced the oxygen contents in AIN lattice which is primary factor of thermal conductivity. The them1al conductivity of AIN specimens was promoted by increasing sintering time because the increases of average grain size and the elimination of secondary phases from the grain boundary due to the evaporation. Particularly. the thermal conductivity of AIN specimen sintered at $1,900^{\circ}C$ for 5 hours improved over 20 %. $141\;Wm^{-1}K^{-1}$, compared with the specimen sintered at $1,900^{\circ}C$ for 1 hour. AIN 소결에 있어서 ${Y_2}{O_3}$를 소결 조제로하여 $1,700{\sim}1,900^{\circ}C$의 온도에서 상압소결하엿을 때 ${Y_2}{O_3}$ 첨가와 소결 유지 시간이 소결 특성, 미세 구조 및 열전도도에 미치는 영향에 관하여 평가하였다. ${Y_2}{O_3}$의 첨가에 따라 AIN 시편은 치밀화가 증진되고 열전도도가 증가됨을 확인할 수 있었다. 이러한 결과는 AIN 분말 표면의 ${Al_2}{O_3}$와 ${Y_2}{O_3}$의 반응으로 형성된 이차상에 기인한 것으로, 첨가된 ${Y_2}{O_3}$는 ${Al_2}{O_3}$와의 반응으로 치밀화에 기여를 하여 고온에서 액상의 형성으로 급속히 치밀화를 증진시키며, AIN 결정격자 내부로 유입될 수 있는 산소의 양을 감소시킴으로써 AIN 시편의 열전도도를 증가시키는 것을 알 수 있었다. 또한 소결시간의 증가에 따라 열전도도는 급격히 증가하였는데 이는 결정립계의 이차상이 고온에서 휘발되어 그 양이 감소함에 기인하는 것으로 파악되었다. $1,900^{\circ}C$ 5시간 소결한 시편의 열전도도는 약 $141\;Wm^{-1}K^{-1}$ 값을 나타내었고 이는 1시간 소결한 시편과 비교하여 20% 이상 증가된 값이었다.

Effects of Y2O3 Addition on Densification and Thermal Conductivity of AlN Ceramics During Spark Plasma Sintering

채재홍,박주석,안종필,김경훈,이병하 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.12

Spark plasma sintering (SPS) of AlN ceramics were carried out with Y2O3 as sintering additive at a sintering temperature 1,550~ 1,700 o C. The effect of Y2O3 addition on sintering behavior and thermal conductivity of AlN ceramics was studied. Y2O3 added AlN showed higher densification rate than pure AlN noticeably, but the formation of yttrium aluminates phases by the solid-state reaction of Y2O3 and Al2O3 existed on AlN surface could delay the densification during the sintering process. The thermal conductivity of AlN specimens was promoted by the addition of Y2O3 up to 3 wt% in spite of the formation of YAG secondary phase in AlN grain boundaries because Y2O3 addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. However, the thermal conductivity rather decreased over 3 wt% addition because an immoderate formation of YAG phases in grain boundary could decrease thermal conductivity by a phonon scattering surpassing the contribution of Y2O3 addition. Spark plasma sintering (SPS) of AlN ceramics were carried out with Y2O3 as sintering additive at a sintering temperature 1,550~ 1,700 o C. The effect of Y2O3 addition on sintering behavior and thermal conductivity of AlN ceramics was studied. Y2O3 added AlN showed higher densification rate than pure AlN noticeably, but the formation of yttrium aluminates phases by the solid-state reaction of Y2O3 and Al2O3 existed on AlN surface could delay the densification during the sintering process. The thermal conductivity of AlN specimens was promoted by the addition of Y2O3 up to 3 wt% in spite of the formation of YAG secondary phase in AlN grain boundaries because Y2O3 addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. However, the thermal conductivity rather decreased over 3 wt% addition because an immoderate formation of YAG phases in grain boundary could decrease thermal conductivity by a phonon scattering surpassing the contribution of Y2O3 addition.

Y₂O₃첨가와 소결 시간이 AlN 세라믹스의 일축 가압 소결 거동 및 열전도도에 미치는 영향

채재홍,박주석,안종필,김경훈,이병하 한국결정성장학회 2008 韓國結晶成長學會誌 Vol.18 No.6

Hot-press sintering of AlN ceramics were carried out with Y₂O₃as sintering additive at a sintering temperature 1,750~1,850℃. The effect of Y₂O₃addition and sintering time on sintering behavior and thermal conductivity of AlN ceramics was investigated. Y₂O₃added AlN showed noticeably higher densification rate than pure AlN. The thermal conductivity of AlN specimens was promoted by the addition of Y₂O₃in spite of the formation of YAG secondary phase in AlN grain boundaries and grain boundary triple junction because Y₂O₃addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. Typically, the thermal conductivity of 5 wt% Y₂O₃added specimen was dramatically improved by the increase of sintering time because the elimination of YAG secondary phases from the grain boundary due to the evaporation, as well as the grain-growth of AlN grains.

The Effect of Al2O3 addition on the Characteristics of Sintering Behavior, Phase Transformation and Mechanical Properties of Spark Plasma Sintered Si3N4 Ceramics

채재홍,김대근,김경훈,박주석,안종필,심광보 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.2

Silicon nitride(Si3N4) is one of the most widely used structural ceramic materials. However silicon nitride is difficult to sinter because of its strong covalent bonding characteristics. In this study, Si3N4 ceramics were fabricated by spark plasma sintering process with Y2O3 and Al2O3 addition to improve the sinterability and the mechanical properties and their phase transformation behavior, microstructure and mechanical properties were evaluated. Fully densified Si3N4 ceramics could be obtained by spark plasma sintering process at a lower temperature than conventional sintering method. The formation of network microstructure was affected by the addition of Al2O3 because it could accelerate α to β phase transformation of Si3N4. As a result, the mechanical properties depended on amounts of Al2O3 addition. The hardness value increased with increasing α-phase fraction, but fracture toughness value increase with increasing β-phase fraction. Silicon nitride(Si3N4) is one of the most widely used structural ceramic materials. However silicon nitride is difficult to sinter because of its strong covalent bonding characteristics. In this study, Si3N4 ceramics were fabricated by spark plasma sintering process with Y2O3 and Al2O3 addition to improve the sinterability and the mechanical properties and their phase transformation behavior, microstructure and mechanical properties were evaluated. Fully densified Si3N4 ceramics could be obtained by spark plasma sintering process at a lower temperature than conventional sintering method. The formation of network microstructure was affected by the addition of Al2O3 because it could accelerate α to β phase transformation of Si3N4. As a result, the mechanical properties depended on amounts of Al2O3 addition. The hardness value increased with increasing α-phase fraction, but fracture toughness value increase with increasing β-phase fraction.

알루미나 첨가에 의한 질화규소의 방전 플라즈마 소결 거동과 상전이 특성 및 기게적 특성에 미치는 영향

채재홍,김대근,김경훈,박주석,안종필,심광보,Chae, Jae-Hong,Kim, Dae-Gean,Kim, Kyoung-Hun,Park, Joo-Seok,Ahn, Jong-Pil,Sim, Kwang-Bo 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.2

Silicon nitride($Si_3N_4)$ is one of the most widely used structural ceramic materials. However silicon nitride is difficult to sinter because of its strong covalent bonding characteristics. In this study, $Si_3N_4$ ceramics were fabricated by spark plasma sintering process with $Y_2O_3$ and $Al_2O_3$ addition to improve the sinterability and the mechanical properties and their phase transformation behavior, microstructure and mechanical properties were evaluated. Fully densified $Si_3N_4$ ceramics could be obtained by spark plasma sintering process at a lower temperature than conventional sintering method. The formation of network microstructure was affected by the addition of $Al_2O_3$ because it could accelerate a to ${\alpha}$ to ${\beta}$ phase transformation of $Si_3N_4$. As a result, the mechanical properties depended on amounts of $Al_2O_3$ addition. The hardness value increased with increasing ${\alpha}$-phase fraction, but fracture toughness value increase with increasing ${\beta}$-phase fraction.

$Y_2O_3$ 첨가와 소결 시간이 AlN 세라믹스의 일축 가압 소결 거동 및 열전도도에 미치는 영향

채재홍,박주석,안종필,김경훈,이병하,Chae, Jae-Hong,Park, Joo-Seok,Ahn, Jong-Pil,Kim, Kyoung-Hun,Lee, Byung-Ha 한국결정성장학회 2008 韓國結晶成長學會誌 Vol.18 No.6

AlN 소결체를 제조함에 있어서 $Y_2O_3$를 소결 첨가제로 하여 일축 가압 소결법을 적용하여 소결 조제 첨가량의 변화와 소결 시간의 변화에 따른 소결 특성, 미세구조 및 열전도도 측성에 대하여 조사하였다. $Y_2O_3$의 첨가로 인하여 AlN의 치밀화가 첨가하지 않은 경우보다 증진됨을 확인할 수 있었으며, 결정립계 및 결정립계 삼중점에서 YAG 이차상을 형성함으로써 AlN 결정 격자 내의 산소 결함 농도를 낮춰 열전도도를 향상시킴을 알 수 있었다. 특히, 소결 시간을 증대함에 따라 결정립 성장 및 열전도도의 방해 요소인 YAG 이차상이 고온에서 휘발됨에 따라 열전도도가 크게 향상됨을 확인할 수 있었다. Hot-press sintering of AlN ceramics were carried out with $Y_2O_3$ as sintering additive at a sintering temperature $1,750{\sim}1,850^{\circ}C$. The effect of $Y_2O_3$ addition and sintering time on sintering behavior and thermal conductivity of AlN ceramics was investigated. $Y_2O_3$ added AlN showed noticeably higher denazification rate than pure AlN. The thermal conductivity of AlN specimens was promoted by the addition of $Y_2O_3$ in spite of the formation of YAG secondary phase in AlN grain boundaries and grain boundary triple junction because $Y_2O_3$ addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. Typically, the thermal conductivity of 5 wt% $Y_2O_3$ added specimen was dramatically improved by the increase of sintering time because the elimination of YAG secondary phases from the grain boundary due to the evaporation, as well as the grain-growth of AlN grains.

호기성 세균에 의한 콘크리트 열화에 관한 연구

이종렬,채재홍,이웅종 한국구조물진단유지관리공학회 2000 한국구조물진단유지관리공학회 논문집 Vol.4 No.1

방전플라즈마 소결법을 이용한 고밀도 탄화 붕소 제조 및 기계적 특성

김경훈,채재홍,박주석,김대근,심광보,Kim, Kyoung-Hun,Chae, Jae-Hong,Park, Joo-Seok,Kim, Dae-Keun,Shim, Kwang-Bo 한국결정성장학회 2007 한국결정성장학회지 Vol.17 No.3

방전플라즈마 소결법을 적용하여 탄화붕소 세라믹스를 제조하여 그 소결 특성, 미세 구조 및 기계적 특성을 평가하였다. 탄화붕소의 소결에 방전플라즈마 소결법을 적용하여 소결 조제의 첨가 없이 전통적인 소결법보다 낮은 온도에서 99% 이상의 완전 치밀화된 소결체를 제작할 수 있었으며, 탄화붕소 분말의 메탄을 세척을 통하여 분말 표면에 형성되어 있는 $B_2O_3$ 상을 사전에 제거함으로써 결정립의 조대화를 방지하여 균일한 미세구조의 형성을 유도할 수 있었으며 결과적으로 탄화붕소 소결체의 기계적 특성을 향상시킬 수 있었다. 특히 파괴인성의 경우 메탄을 세척을 통하여 30% 이상의 물성 향상을 달성하였다. [ $B_4C$ ] ceramics were fabricated by spark plasma sintering process and their sintering behavior, microstructure and mechanical properties were evaluated. Relative density of $B_4C$ ceramics were obtained by spark plasma sintering method reached as high as 99% at lower temperature than conventional sintering method, in addition, without any sintering additives. The mechanical properties of $B_4C$ ceramics was improved by a methanol washing process which can be removed $B_2O_3$ phase from a $B_4C$ powder surface. This improvement results ken the formation of homogeneous microstructure because the grain coarsening was suppressed by the elimination of $B_2O_3$ phase. Particularly, fracture toughness of the sintered specimen using a methanol washed powder improved over 30% compared with the specimen using an as-received commercial powder.