In this study, the Si3N4 was pressureless sintered with various sintering additives and its thermal and physical properties were investigated. The sintering additive systems consisted of MgO as a basic fixed additive, Y2O3, Yb2O3, La2O3 as rare-earth oxide additives, and SiO2 as a non-rare-earth oxide additive, whose properties were evaluated. It was confirmed that the density of the sintered body was increased as the amount of Y2O3 added was increased, and the maximum relative density of that additive system was 98.3%. The 3-point bending strength of MgO-Y2O3 additive system was also measured, and it was confirmed that the bending strength was also increased in proportion to the density, showing a maximum value of 963 MPa. The thermal conductivity of each additive system was measured by laser flash method. As the amount of Y2O3 got higher, the thermal conductivity decreased. In the case of Yb2O3, even though the density was lower than that of Y2O3, it showed a maximum thermal conductivity of 76.9 W/mK which is similar or higher than that of MgO-Y2O3 additive system. In order to analyze the factors affecting the thermal conductivity, the existence and the distribution of the secondary phase in grain boundary were investigated through the microstructure analysis using X-ray diffraction and scanning electron microscope.
In the later part of this study, the investigation of thermal conductivity was approached by using Raman spectroscopy instead of the conventional laser flash method. This approach was based on a research of AlN ceramics that the oxygen-related defect in lattice and the FWHM (Full-Width of Half Maximum) of specific Raman peaks have a proportional relationship. For this, the relationship between the thermal conductivity of sintered specimens and the FWHM of the Raman peaks was shown, and the inverse relationship was found at 229 cm-1 and 451 cm-1.
본 연구에서는 다양한 소결조제를 첨가하여 질화규소를 상압소결 하고, 그의 열적, 물리적 물성을 분석하였다. 소결조제로는 산화 마그네슘을 기본으로 하고 그에 더해 희토류 산화물인 산화 이트륨, 산화 이터븀, 산화 란타늄과, 비 희토류 산화제인 산화규소를 첨가하였으며, 각각의 소결체 물성을 평가 분석하였다. 그 중에 산화 이트륨 첨가량을 높일수록 소결체의 밀도가 상승하는 것을 확인했고, 98.3 퍼센트의 최고 상대밀도를 보였다. 산화 마그네슘-산화 이트륨 첨가제 소결체들의 3점 굽힘 강도도 측정되었는데 최대 963 메가 파스칼의 값을 보였다. 각 소결조제 계에 대한 열전도도는 산화 이트륨의 양이 많아 질수록 낮아졌고 산화 이터븀계 같은 경우에는 산화 이트륨 계보다 소결 밀도가 낮음에도 불구하고 비슷하거나 상회하는 최대 77의 열전도도 값을 보였다. 본 연구의 뒷부분에서는, 기존의 레이저 플래시 법이 아닌 라만 분광법을 사용하여 열전도도 물성에 접근해보았다. 이를 위하여 앞선 실험에서 소결된 실험체들의 열전도도 값과 라만 픽들의 반치폭 값 간의 관계를 도시해 보았고, 그 중에 229와 451 픽에서 반비례 관계를 확인하였다.
