$Si_3 N_4$ 결합 SiC의 소결과 기계적 특성에 미치는 첨가제의 영향

백용혁,신종윤,정종인,한창,Baik, Yong-Hyuck,Shin, Jong-Yoon,Jung, Jong-In,Han, Chang 한국세라믹학회 1992 한국세라믹학회지 Vol.29 No.7

In this study, SiC powder and Si powder were used as the raw materials. Mixture was prepared with addition of Al2O3 and Fe2O3 at 0.1~0.5wt% respectively. After this step, the mixture was pressed and nitrided for 30 hrs at 140$0^{\circ}C$ under NH3-N2 atmosphere. Mechanical properties of sintered specimens were investigated from measurement of porosity, bulk density and three point bending test. nitration reaction extent was observed at the change of mass before and after reaction, and the microstructure and the change of $\alpha$-Si3N4 and $\beta$-Si3N4 were observed by XRD and SEM. In the current work, the results are as follows 1. When Fe2O3 added, the nitridation increased with the content of Fe2O3, and the bending strength was increased from 0.1 wt% to 0.3 wt%, and decreased to 0.5 wt%. 2. When Al2O3 added, the nitridation and the bending strength increased little by little with the content of Al2O3 3. The bending strength of the specimen added with Fe2O3 were higher than that with Al2O3. Because the specimens contained Fe2O3 had much more the whisker type crystal of Si3N4 contributing to strength than contained Al2O3.

상압소결 탄화규소 소결체의 마찰마모특성

백용혁,최웅,서영현,박용갑,Baik, Yong-Hyuck,Choi, Woong,Seo, Young-Hean,Park, Yong-Kap 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.7

본 연구에서는 Boron과 Carbon black이 소결조재로 첨가된 탄화규소 분말을 $1950^{\circ}C$에서 상압소결 방법으로 시편을 제조하고 꺽임강도, 파괴인성, 비마모량을 측정하고 파단면 및 마찰마모면의 미세구조를 SEM으로 관찰하여 마찰마모특성과 미세구조와의 관계를 규명하였다. 또한 마모상대재료로서 SiC pin과 $Al_{2}O_{3}$ pin을 사용하였을때 마찰마모특성과 미세구조와의 관계도 비교 검토하였으며 다음과 같은 결론을 얻었다. 1. SiC pin을 사용한 경우 소결시편의 비마모량은 $Al_{2}O_{3}$ pin을 사용한 경우보다 많았으나, 가압하중이 증가하면 $Al_{2}O_{3}$ pin을 사용한 경우가 SiC pin을 사용한 경우보다 비마모량의 증가율이 6.5배로 되었다. 2. Pin의 비마모량은 SiC pin의 경우가 $Al_{2}O_{3}$의 경우보다 많았으나 가압하중이 증가하면 $Al_{2}O_{3}$ pin의 경우가 SiC pin의 경우보다 비마모향의 증가율이 약4배로 되었다. 3. 마모상대재료의 마찰계수가 작은 경우에는 마모면의 미세구조가 평활하면서 crack이 나타나지 않았으나, 마찰계수가 큰 경우에는 마모면이 평활치 못하고 crack의 전파현상이 크게 나타났다. 4. 사용된 Pin의 마찰계수가 큰 경우에는 고상소결한 SiC 시편도 액상소결한 시편과 마찰마모 특성이 유사하였다. In this study solid-phase sintered silicon caribide samples composed of SiC powder having boron and car-bon black as additives were prepared by pressureless sintering at $1950^{\circ}C$. The bending strength the frac-ture toughness and the specific werar rate of the samples were examined and the micro structures of the broken and the worn surface were observed by SEM to understand the relationship between the tri-bological charcteristics and the micro structure. Additionally the relationship between the micro struc-tures and the tribological characteristics of the samples for the frictional opponents SiC and $Al_{2}O_{3}$ pins were investigated Conclusions are as follows ; 1. The specific were rate of the samples for the SiC pin was larger than that for the $Al_{2}O_{3}$ pin. HOwever the specific wear rate for the $Al_{2}O_{3}$ pin was increased about 6,45 times as that for the SiC pin under the load increasing. 2. The specific wear rate of the SiC pin was larger than that of the $Al_{2}O_{3}$ pin. owever the specific wear rate of the $Al_{2}O_{3}$ pin was increased about 4 times as that of the SiC pin under the load increasing 3. The micro stucture of the worn surface showed a flat face without cracks in the case that the frictional opponents has the low friction coefficient but in the case of without cracks in the case that the frictional opponents has the low friction coefficient but in the case of the high friction coefficient the micro structure of the worn surface showed an uneven face having spread-ed cracks. 4. The tribological characteristics of thesolid-phase sintered SiC samples was similar to that of li-quid-phase sintered ones when the pin having the high friction coefficient was used.

반응소결 SiC/Graphite 복합체에서 Graphite 입자의 크기에 따른 마찰마모특성

백용혁,서영현,최웅,이종호,Baik, Yong-Hyuck,Seo, Young-Hean,Choi, Woong,Lee, Jong-Ho 한국세라믹학회 1997 한국세라믹학회지 Vol.34 No.8

The tribological property of ceramics is very important for use in seal rings, pump parts, thread guides and mechanical seal, etc. In the present study, which RBSC/graphite composites were manufactured by adding graphite powders with different particle sizes to mixtures of SiC powder, metallic silicon, carbon black and alumina, effects on the tribological property of each RBSC/graphite composite was investigated in accordance with the particle size of the added graphite powder. The water absorption, the bending strength and the resistance for the friction and wear were measured, and the crystalline phase and the microstructure were respectively examined by using XRD and SEM. In case that the particle size of the graphite powder was fine(2${\mu}{\textrm}{m}$), the formation of $\beta$-SiC was accelerated, thereby making the increase of the bending strength and the decrease of the water absorption, but no improvement for the tribological properties. Furthermore, in case that the particle size of the graphite powder was some large(88~149${\mu}{\textrm}{m}$), the formation of $\beta$-SiC was not accelerated, to thereby make the decrease of the bending strength and the increase of the water absorption, but the improvement for the tribological property of only the composite having the graphite powder of 20 vol%. In addition, in case that the particle size distribution of the graphite powder was large (under 53 ${\mu}{\textrm}{m}$), there was no improvement for every properties. However, the composites, which the graphite powder with the particle size of 53~88 ${\mu}{\textrm}{m}$ was added in 10~15 vol%, had the most increased resistance for the friction and wear which show the worn out amount of 0.4~0.6$\times$10-3 $\textrm{cm}^2$, and the value of the bending strength is 380~520 kg/$\textrm{cm}^2$.

가압소결 $SiC/Si_3N_4$ 복합체의 마찰마모특성

백용혁,최웅,박용갑,Baik, Yong-Hyuck,Choi, Woong,Park, Yong-Kap 한국세라믹학회 1999 한국세라믹학회지 Vol.36 No.10

SiC-Si3N4 composites were prepared by mixing $\alpha$-Si3N4 powder to $\alpha$-SiC powder in the range of 10 to 30 vol% with 10vol% interval. 6wg% Al2O3 and 6wt% Y2O3 were respectively added as sintering aids. Hot pressing was performed at 1,80$0^{\circ}C$ for 1 hour with 25 MPa pressure. In the case of adding 20vol% of $\alpha$-Si3N4 powder the relative density to theoretical value and the flexural strength were 99.1% and 34,420 MPa respectively and the worn amount was 2.09$\times$10-3 mm2 which were the highest values in the all range of he composition. Although the composite containig 10 vol% of $\alpha$-Si3N4 powder showed the highest fracture toughness(KIC) of 4.65MN/m3/2 the reduction of the wear resistance in this composite is likely to be affected by the homogeneity and the uniformity of the grain coalescence and growth during the sintering process.

가압소결 SiC/$Si_3$$N_4$/SiCw 복합체의 마찰마모특성

백용혁,최웅,강선명,박용갑,Baik, Yong-Hyuck,Choi, Woong,Kang, Seon-Myung,Park, Yong-Kap 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.11

$\alpha$-Si$_3$N$_4$가 20vol% 혼합된 SiC/Si$_3$N$_4$혼합물에서 $\alpha$-SiC의 일부를 SiC whisker로 치환하여 첨가한 후 180$0^{\circ}C$, 25MPa의 압력으로 hot pressing하여 SiC/Si$_3$N$_4$/SiCw 복합체를 제조하였다. SiC whisker의 첨가 함량이 증가할수록 상대밀도, 꺽임강도, 마모 저항성은 감소되었으나, 파괴인성은 크게 향상되었다. $\alpha$-SiC의 일부를 SiC whisker로의 치환은 치밀화를 억제하였으나 파괴인성의 증가는 마모 저항성을 향상시키지 않았다.

카올린으로부터 Si-Al 탄화물의 합성 및 Si$_3$N$_4$ 결합 소결 특성

백용혁,김영구,한창,권양호,Baik, Yong-Hyuck,Kim, Young-ku,Han, Chang,Kwon, Yang-Ho 한국세라믹학회 1991 한국세라믹학회지 Vol.28 No.9

In this study, Kaolin was carbonized at 1300~175$0^{\circ}C$ and its constituent mineral change was investigated. Carbonized kaolin at 1$650^{\circ}C$ was mixed with metallic silicon, formed and nitrified at 135$0^{\circ}C$ in N2-NH3 atmosphere. Properties of this product such as porosity, bulk density, MOR, nitrization rate and oxidation resistence were measured, and its mineralogical changes were investigated by XRD. The results were as follows; 1) $\beta$-SiC was initially synthesized at 150$0^{\circ}C$, and its amount was continuously increased with reaction temperature to 1$700^{\circ}C$. 2) At 1$600^{\circ}C$, mullite was rapidly decomposed and the amounts of $\beta$-SiC and $\alpha$-Al2O3 were increased simultaneously. 3) By adding alkali to kaolin, the decomposition temperature of mullite was dropped approximately 10$0^{\circ}C$, but the amount of $\alpha$-SiC was increased. 4) The highest values of their nitrization rate and MOR were obtained at the specimen of 35 wt% metallic silicon in nitrization reaction. 5) It seems that increment of $\alpha$-Si3N4 and $\alpha$-Al2O3 phase during nitrization was due to the decomposition of Al4SiC4 existed in carbonized kaolin. 6) Si3N4 bonded SiC-Al2O3 composite were fabricated from kaolin at relatively low temperature (135$0^{\circ}C$).

상압소결 $SiC/Si_3N_4$ 복합체의 마찰마모특성

백용혁,최웅,서영현,김인섭,김주영,Baik, Yong-Hyuck,Choi, Woong,Seo, Young-Hean,Kim, In-Sub,Kim, Joo-Young 한국결정성장학회 1999 韓國結晶成長學會誌 Vol.9 No.2

$\alpha$-SiC에 ${\alpha}-Si_3N_4$ 를 10~30 vol%까지 10 vol% 간격으로 혼합하고 소결 조제로$Al_2O_3$와$Y_2O_3$를 각각 6wt% 로 첨가하여 $1,780^{\circ}C$에서 2시간동안 질소 분위기에서 상압소결하여 $Si_3N_4$ 복합체를 제조하였다. 상대 이론 밀도 및 꺽임 강도는 ${\alpha}-Si_3N_4$를 20 vol% 첨가하였을 때 92% 및 3,560 MPa로 가장 우수하였으며, 비마모량도 $2.68{\times}10^{-3}\;mm^2$ 으로 가장 작았다. 그리고, 파괴 인성$(K_{1c})$)은 ${\alpha}-Si_3N_4$를 30vol% 첨가하였을 때 $4.9\;MN/m^{3/2}$로 가장 좋았으나 이 경우 기공의 영향으로 내마모성은 저하된 것을 확인할 수 있었다. $SiC/Si_3N_4$ composites were prepared by mixing ${\alpha}-Si_3N_4$ powder to $\alpha$-SiC powder in the range of 10 to 30 vol% with 10 vol% interval. 6 wt% of $Al_2O_3$ and $Y_2O_3$ were also added respectively as sintering aids. Then, pressureless sintering was performed at 1,78$0^{\circ}C$ for 2 hours in $N_2$ gas. In the case of adding 20 vol% of ${\alpha}-Si_3N_4$ powder, the relative desity to theoretical value and the flexutal strength were 92 % and 3,560 MPa, respectively. The smallest relative worn amount thereof was $2.68{\times}10^{-3}\;mm^2$ for 20 vol% ${\alpha}-Si_3N_4$. The composite containing 30 vol % of ${\alpha}-Si_3N_4$ powder showed the highest fracture toughness $(K_{1c})$ of $4.9\;MN/m^{3/2}$, although the reduction of the wear resistance due to the effect of the pores was observed.

Slip의 점도가 slip casting 및 casting 및 cordierite 소결체의 특성에 미치는 영향

백용혁,장복기,곽효섭,Baik Yong-Hyuck,Chang Pok-Kie,Kwak Hyo-Sup 한국결정성장학회 2005 한국결정성장학회지 Vol.15 No.5

Kaolin과 규석 및 $Mg(OH)_2$등의 원료로 만들어진 slip을 casting 할 때 slip의 점도가 slip casting 속도와 소결체의 미세조직에 미치는 영향을 보면 slip-casting속도는 slip의 점도가 낮을 경우 감소하였으며 slip의 점도범위는 $3.0\~17.0\;cP$가 적당하였다. Slip의 점도를 조절하면 표면층, 표면 내부층, 중간층, 내면층의 미세조직을 비교적 균일하게 casting 할 수 있다 소성온도 $1350^{\circ}C$에서 시편의 구성광물은 cordierite 결정만으로 되어있었다. We have investigated the relationship between a viscosity of the slip prepared from kaolin, quartz, $Mg(OH)_2$, etc and its influence on the speed of slip casting and the microsturcture of a sintered body. The speed of slip casting decreases as a viscosity of a slip decreases. The optimized viscosity range of a slip was found to be around $3.0\~17.0\;cP$. By careful controlling a viscosity of slip, homogeneous microstructure of outer surface layers, inner surface layers, intermediate layers, and inside layers were obtained by casting process. The specimen sintered at $1350^{\circ}C$ consists of a cordierite crystalline phase only as a constituent mineral.

화학제품용 및 금속제련용 수산화알루미늄 제품 특성

김대웅,백용혁,Kim, Dae-Woong,Baik, Yong-Hyuck 한국세라믹학회 2001 한국세라믹학회지 Vol.38 No.9

Bayer process는 보오크사이트로부터 수산화알루미늄을 추출시키는 가장 일반적인 방법으로 공정 조건에 따라 수산화알루미늄의 1차 입자경, 입도분포도 및 생산효율 등이 달라지게 된다. 본 실험에서는 앞선 석출실험 결과를 기준으로 화학제품용 및 금속제련용 수산화알루미늄 제조조건을 설정하여 석출제품의 특성을 검토하였다. 그 결과 석출율은 화학제품용 원료 제조조건이 높게 나타났으며 입자크기는 화학제품용은 42∼44${\mu}$m, 금속제련용은 74∼77${\mu}$m로 금속제련용 원료 제조조건이 입자크기가 크게 나타났다. 산용해 실험결과는 화학제품용 원료가 금속제련용 원료보다 용해성이 좋게 나타났으며, 금속제련용 제품의 마모도는 상업용 금속제련용 제품에 비해 다소 떨어지는데 이러한 이유는 타사 제품에 비해 1차입자가 작가 때문인 것으로 판단된다. Bayer process is based on the extraction of aluminium trihydroxide from bauxite. The process is operated with the several criteria such as primary crystal size, particle size distribution and yield etc.. In this study basing on the previous results, an investigation on the effect of chemical grade and smelting grade aluminium trihydroxide precipitation condition were undertaken. As a result, particle size was 42∼44${\mu}$m form chemical grade product and 74∼77${\mu}$m for smelting grade product. The yield and solubility by acid of chemical grade product was higher than smelting grade product. The attrition index of smelting grade product was lower than that of other commercial product because primary crystal size of the smelting grade product was small.