Processing technologies for sealing glasses and glass‐ceramics

Abstract

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. K E Y W O R D Sadherence, crystallization, fresnoite, furnace sealing, glass-ceramics, laser welding, sinteringThis is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Foaming Species and Trapping Mechanisms in Barium Silicate Glass Sealants

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Glass powders are widely used in fabricating sintered glasses, sintered glassÀceramics, glass matrix composites, seals, and glass-bonded ceramics or pastes. [1][2][3] For many of these applications, glasses with low crystallization tendency are used, for example, for low-temperature cofired ceramics, [4,5] pastes, [6] or sealants [7,8] to ensure sufficient sinterability.Due to the low viscosity required for joining and gas tight sealing, gas bubble formation and subsequent swelling (foaming) often occur, even when organic aids are not used in powder processing. In contrast to the extensive and ongoing study of desired foaming phenomena utilized for foam glasses or glassÀceramic foams, [9][10][11][12][13][14][15] this nondesired foaming effect and its underlying mechanisms are rarely reported.

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“…Glass powders are widely used in fabricating sintered glasses, sintered glassÀceramics, glass matrix composites, seals, and glass-bonded ceramics or pastes. [1][2][3] For many of these applications, glasses with low crystallization tendency are used, for example, for low-temperature cofired ceramics, [4,5] pastes, [6] or sealants [7,8] to ensure sufficient sinterability.…”

Performance evaluation for Ag and Au nanoparticle containing K2O‐MgO‐B2O3‐Al2O3‐SiO2‐F glass sealants for SOFC application

“…From the corresponding DSC peaks, the crystalline volume fractions are measured to be within 50%–65% and the rest (35%–50%) is the residual glassy phase. Presence of the residual glassy phase is beneficial for the long‐term stability of the glass‐ceramics sealants due to the possibility of viscous flow and self‐healing during SOFC operation 29 …”

“…27,28 Overall, the interlocked microstructure in NPG-2 and NPG-3 glassceramics (Figure 3B′,C′) are seemingly quite suitable to resist the growth of micro-cracks that may generate due to thermal stresses during SOFC operation. [29][30][31] Important to note that the SEM micrographs do not explicitly reveal the residual glass matrix within the microstructures of the heat-treated glass-ceramics. It is to be noted that the crystal peak area measurement from DSC curves can be a better technique for quantification of residual glass within the heat-treated glass-ceramics.…”

Sintering/Crystallization and Viscosity of Sealing Glass-Ceramics

“…There is a vast body of research done on this topic that has been reflected in more than 500 papers (Scopus) in the last twenty years. Some papers are dealing directly with the optimization of the processing parameters of the sealant glass-ceramics, and some examples can be found in [7][8][9][10][11][12][13].…”