Processing technologies for sealing glasses and glass-ceramics

This paper embraces two different approaches for the joining of materials through glass sealants. First, the conventional method of furnace sealing in which paste technology is normally employed. The glass sealant is applied in powder form mixed with agglomerant and with the help of dispenser robots, tape casting, or screen printing. Glass-ceramics for sealing of solid oxide fuel cells (SOFC) are described as an example of this type of processing. Glass composition, thermal properties, particle size of the glass powder, sintering and crystallization competition, and final crystalline phases together with a suitable chemical compatibility with the metallic and ceramic elements to be sealed need to be carefully adjusted for this specific application. Second, laser welding is presented as an alternative sealing technology. A general overview about laser welding through glass sealants is presented. Particularly, the welding of sapphire and fused silica glass through a BTS.2SiO(2) thin film glass sealant by employment of a nanosecond-pulsed laser is detailed. Laser parameters (frequency, power, scan speed, and number of passes) were optimized to get the best molten conditions of the BTS thin film, while allowing its crystallization. BTS crystallization upon laser welding leads to a strong blue emission upon UV excitation. Finally, both processing technologies were compared.