Preparation and Studies of Structural and Thermo-mechanical Aspects of Some Special Glasses and Glass-ceramics

Glasses and glass-ceramics (GCs) used for sealing, coating and high voltage applications belong to a special class of materials in which among other requirements, matching of thermal expansion coefficient with that of metal as closely as possible up to set temperature is an important consideration. In this paper I shall concentrate on some indigenous efforts carried out in my laboratory on the preparation and studies related to structural and thermo-mechanical aspects of glasses such as lead silicate, borosilicate, sodium aluminium phosphate (NAP) and glass-ceramics such as magnesium aluminium silicate(MAS) and lithium zinc silicate(LZS). Glasses have been prepared by melt quench technique while bulk nucleation method has been followed for the preparation of glass ceramics. Structural aspects of lead silicate glasses having alkaliand alkaline earth metal oxides, and B2O3 have been studied using MAS-NMR, XRD and optical transmission and have been found to affect both micro-hardness and thermal expansion coefficients. As regards, MAS glassceramics a systematic study to find out the effect of MgF2 content and processing temperatures on the crystallisation process and thermo-mechanical properties was carried out. Some results related to structural and optical studies of NAP and LZS have been discussed. Finally high quality machinable MAS glass ceramic has been developed which has been found suitable for high voltage applications in ultra high vacuum at relatively high temperatures. Both lead silicate, borosilicate glasses and lithium zinc silicate glass-ceramics have been employed in special types of glass to metal and glass-ceramics to metal seals.