Glass‐to‐metal seals for solid oxide cells at the Politecnico di Torino, an overview

Abstract

A summary and update of the research on the design, process, and testing of glass and glass-ceramic to metal seals for solid oxide cells (SOC) conducted during the last 13 years at the Politecnico di Torino, Italy, within our research group and with several international collaborations, is presented and discussed.Glass and glass-ceramic-based materials play a key role in SOC performance and durability as well as in the sealing and joining of metallic interconnects. The sinter-crystallization method is a powerful technique that is used to obtain dense and reliable glass-ceramics capable of providing hermetic joining and seals. The issues, learned from our experience, that have an impact on the lifetime behavior of glass and glass-ceramic to metal seals are briefly reviewed in terms of challenges and working conditions. The mechanical characterization of glassto-metal seal materials has a crucial impact on the overall performance, as the metal-glass interface plays a key role on the final joining strength and reliability.Several glass compositions are presented along with results on their characterization and behavior as joining materials for metallic interconnects, with a focus on their potential use as SOC seals.

Calibration for determination of compressive stress in glass‐to‐metal seals via photoluminescence spectroscopy

“…Next, the mixed powders were pressed into cylindrical green bodies whose diameter and height were both 5 mm, and the pressing pressure was set at 25 MPa. A binder burnout process consisting of gradually ramping up to 680 • C and preservation of 4 h was then conducted to obtain the glass preforms with a density of 2.52 g/cm 3 .…”

“…The as-prepared glass preforms were subjected to a heat treatment process at 960 • C with a heating rate of 10 • C/min and a dwell time of 30 min. After assembly with a graphite mould and an austinite 304 stainless steel (304SS) housing, the glass preforms were fabricated into unstressed (density: 2.40 g/cm 3 ) and pre-stressed samples. The manufacturing process and geometry of these two types of samples are schematically depicted in Figure 2.…”

“…Glass-to-metal compressive seals are an excellent option for the reliable fabrication of hermetic connectors, transducers, and electrical feed-through seals, which benefit from their high mechanical strength and exceptional hermeticity. [1][2][3][4] In terms of these compressive seals, the compressive stress at the sealing interface, which is generated from the coefficient of thermal expansion (CTE) mismatch among different materials, is the key to achieving and ensuring long-term hermeticity. 5,6 Hermeticity is related to stress distribution, cracks, and interfacial defects.…”