✍ Scribed by Dr. Denis Jérome
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about 450-500 "C as in the glass case, leading to improved performance of the device. In the coating examples cited, the glass-ceramic coatings can withstand temperatures up to about 900 "C and so are capable of withstanding the firingon of thick film circuitry at temperatures in the region of 850 "C.
Further developments are taking place which will allow these structures to be used and/or processed at temperatures in excess of 1000 "C.
Glass-ceramics have also been developed for the joining together of ceramic and glass parts. For example, glassceramic joining media are available for alumina ceramics which will enable high quality, complex shapes to be built up from relatively simple shapes and so eliminate the need for complicated machining procedures. Interestingly, glassceramic bonding media are also used to bond glass face plates onto the glass conical sections of TV tubes and other CRTs-in these cases bonding temperatures in the region of 500 "C are employed thus avoiding distortion of the glass.
In further developments, improved understanding of interfacial regions is being generated together with the development of means of testing the strength of glass-ceramic bonds to metals, both as methods of optimizing given combinations and as aids in the development of new systems. The possibility of developing glass-ceramic bonding media which exhibit a gradation of thermal expansion across the system to enable materials of widely different thermal expansion characteristics to be joined by glass-ceramics is being investigated.
ADVANCED MATERIALS
Glass-ceramic joins to other materials such as glasses, ceramics and metals are now well established and new materials and combinations are being developed. This technology in many instances, offers an attractive and more readily realizable alternative to other bonding techniques such as brazing or diffusion bonding.
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