Chapter 6 - Glasses and Glass-Ceramics for Vacuum and High-Temperature Applications

Abstract

This chapter presents a brief review of glass and glass-ceramics and their applications in the form of hermetic seals, especially for use in extreme condition of pressure and temperature. The beginning of this chapter is an overview of glass and glass-ceramics and their related properties. This section is followed by a general discussion on nucleation and growth phenomena and their importance in preparation of tailor-made glass-ceramics. Various aspects related to hermetic seal fabrications with various glass/glass-ceramics systems for high vacuum and high temperature are highlighted. A short discussion on various important parameters, i.e., thermal expansion behavior, different bonding mechanisms at the interfaces, calculation of stresses at the joints, and seal fabrication process parameter are also included in this chapter. Different techniques employed for glass-to-metal and glass-ceramics-to-metal seal fabrication are outlined, and a few glass-ceramics systems, i.e., lithium aluminum silicate, lithium zinc silicate, and barium calcium/strontium borosilicate, are discussed in detail with related thermomechanical, structural, and interface studies. Effects of nucleants and heat-treatment schedules in controlling the nature/concentration of crystalline phase formation on the sealing are reviewed for some selected systems. Some techniques used for characterization of glasses/glass ceramics/seals are described wherever necessary. In addition, glass systems used for high-temperature sealing applications are discussed with emphasis on their long-term stability. The chapter also covers an overview of graded seals, which make hermetic sealing possible when a gradual change in thermal expansion behavior is needed from glass to metal, thereby reducing the chances for cracking under thermal stress. The interesting and emerging area of machinable glass-ceramics is also reviewed in view of its growing relevance. Structure–property correlations are discussed to understand the role of various additive/constituents is various glass/glass-ceramics systems. The chapter concludes with a note on possible future directions of glasses and glass-ceramics in the field of application in extreme conditions of temperature and pressure along with an up-to-date bibliography.