In this study, the effect of the content of MgO-CaO-Al2O3-SiO2 (MCAS) glass additives on the properties of AlN ceramics is investigated. Dilatometric analysis and isothermal sintering for AlN compacts with MCAS contents varying between 5 and 20 wt% are carried out at temperatures ranging up to 1600℃. The results showed that the shrinkage of the AlN specimens increases with increasing MCAS content, and that full densification can be obtained irrespective of the MCAS content. Moreover, properties of the AlN-MCAS specimens such as microhardness, thermal conductivity, dielectric constant, and dielectric loss are analyzed. Microhardness and thermal conductivity decrease with increasing MCAS content. An acceptable candidate for AlN application is obtained: an AlN-MCAS composite with a thermal conductivity over 70 W/m·K and a dielectric loss tangent (tan δ) below 0.6 × 10−3, with up to 10 wt% MCAS content.

In this study, MgO–CaO–Al2O3–SiO2 (MCAS) nanocomposite glass powder having a mean particle size of 50 nm and a specific surface area of 40 m2/g is used as a sintering additive for AlN ceramics. Densification behaviors and thermal properties of AlN with 5 wt% MCAS nano-glass additive are investigated. Dilatometric analysis and isothermal sintering of AlN-5wt% MCAS compact demonstrates that the shrinkage of the AlN specimen increases significantly above 1,300oC via liquid phase sintering of MCAS additive, and complete densification could be achieved after sintering at 1,600oC, which is a reduction in sintering temperature by 200oC compared to conventional AlN-Y2O3 systems. The MCAS glass phase is satisfactorily distributed between AlN particles after sintering at 1,600oC, existing as an amorphous secondary phase. The AlN specimen attained a thermal conductivity of 82.6 W/m·K at 1,600oC.

The nitrogen solubility and nitride capacity of CaO-SiO2-Al2O3-MgO-CaF2 slag systems were measured by using gas-liquid equilibration at 1773K. The nitrogen solubility of this slag system decreased with increasing CO partial pressure, with the linear relationship between nitrogen contents and oxygen partial pressure being -3/4. This system was expected to show two types of nitride solution behavior. First, the nitrogen solubility decreased to a minimum value and then increased with the increase of CaO contents. These mechanisms were explained by considering that nitrogen can dissolve into slags as "free nitride" at high basicities and as "incorporated nitride" within the network at low basicities. Also, the basicity of slag and nitride capacity were explained by using optical basicity. The nitrogen contents exhibited temperature dependence, showing an increase in nitrogen contents with increasing temperature.

Unreported dielectrics based on the binary system of MgO-SiO2 were investigated as potential candidates for microwave dielectric applications, particularly those demanding a high fired density and high quality factors. Extensive dielectric compositions having different molar ratios of MgO to SiO2, such as 2:1, 3:1, 4:1, and 5:1, were prepared by conventional solid state reactions between MgO and SiO2. 1 mol% of V2O5 was added to aid sintering for improved densification. The dielectric compositions were found to consist of two distinguishable phases of Mg2SiO4 and MgO beyond the 2:1 compositional ratio, which determined the final physical and dielectric properties of the corresponding composite samples. The increase of the ratio of MgO to SiO2 tended to improve fired density and quality factor (Q) without increasing grain size. As a promising composition, the 5MgO.SiO2 sample sintered at 1400 ˚C exhibited a low dielectric constant of 7.9 and a high Q × f (frequency) value of ~99,600 at 13.7 GHz.

Sputter Cu(1-4.5at.%Mg) alloy를 100mTorr이하의 산소압력에서 온도를 증가시키며 열처리하였을 때 표연과 계면에서 형성된 MgO의 확산방지막 특성을 살펴보았다 먼저, Cu(Mg)/SiO2/Si 구조의 샘플을 열처리했을 때 계면에서는 2Mg+SiO2→2MgO+Si의 화학반응에 의해 MgO가 형성되는데 이 MgO충에 의해 Cu가 SiO2로 확산되는 것이 현저하게 감소하였다. TiN/Si 기판 위에서도 Cu(Mg)과 TiN 계면에 MgO가 형성되어 Cu(4.5at.%Mg)의 경우 800˚C까지 Cu와 Si의 확산을 방지할 수 있었다. 표면에 형성된 MgO위에 Si을 증착하여 Si/MgO(150 Å)/Cu(Mg)/SiO2/Si구조로 만든 후 열처리했을 때 150 Å의 MgO는 700˚C까지 Si과 Cu의 확산을 방지할 수 있었다. 표면에 형성된 MgO(150 Å)의 누설전류특성은 break down 5V, 누설전류 10-7A/cm2의 값을 나타냈다. 또한 Si3N4/MgO 이중구조에서는 매우 낮은 누설전류밀도를 나타냈으며 MgO에 의해 Si3N4 증착시 안정적인 계면이 형성됨을 확인하였다.