J. Korean Ceram. Soc. > Volume 31(4); 1994 > Article
 Journal of the Korean Ceramic Society 1994;31(4): 389.
 $CaO-Al_2O_3$계 유리의 물성에 미치는 $SiO_2$의 영향 원종원, 박용완 한양대학교 무기재료공학과 Effect of $SiO_2$ on the Properties of $CaO-Al_2O_3$ Glasses ABSTRACT Calcium aluminate glasses transmit light at relatively long wavelengths up to 6 ㎛ and exhibit also low Rayleigh scattering values. However they have a tendency to get devitrified easily, which limits their use as routine optical materials. Here, the ternary system CaO-Al2O3-SiO2 glasses with low-silica (<30 mol%) were prepared to prevent the devitrification of CaO-Al2O3 glasses and the properties were investigated as functions of composition. The addition of SiO2 to calcium aluminate glasses promoted their stability, which was due to the decrease of non-bridging oxygens and the reconnection of network. As SiO2 was added, density, refractive index, molar volume of oxygens and thermal expansion coefficient decreased continuously. But the glass transition temperatures with increasing SiO2 contents were raised and then lowered. It was postulated that the anomaly was related to the changes of the middle range order as well as the short range order. As the amount of SiO2 in the glass was increased, the IR cut-off values moved to shorter wavelength owing to 'Si-O' antisymetric stretching vibration. The IR cut-off wavelength of the glasses with 5 and 30 mol% SiO2 was 4.90, 4.55 ㎛, respectively.
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