Daniel Coillot

Characterization of self-healing glassy composites by high-temperature environmental scanning electron microscopy (HT-ESEM)

In situ high-temperature healing of cracks in composites made of glass and vanadium boride (VB) particles was observed using an environmental scanning electron microscope equipped with a high-temperature chamber (HT-ESEM). HT-ESEM is an adequate tool for studying the self-healing property of these materials. The change in crack length as a function of redox atmospheric conditions is reported. No self-healing behaviour was observed under reducing conditions, while a complete and rapid healing of the cracks was measured under oxidizing conditions. HT-ESEM image analyses enabled the monitoring of the healing effect. The self-healing mechanism was identified as a consequence of the VB active particles oxidation and subsequent pouring of fluid oxides into the cracks. These innovative composites offer an interesting potential in the domain of solid oxide fuel cell sealants.

Characterization and Performance of Glass-Ceramic Sealants for SOECs

Research into hydrogen production using high temperature electrolysis methods has increased significantly in the last few years. Consequently, development of sealing materials has become a major concern particularly for developers of Solid Oxide Electrolyser Cells (SOECs). Suitable sealants for SOECs must operate around 800°C for many hours under reducing and oxidizing conditions. Glass-ceramic compositions based on two glass systems CAS (CaO-Al2O3- SiO2) and SCAS (SrO-CaO-Al2O3-SiO2) with some minor additions (MnO2, B2O3 or TiO2) have been prepared and investigated. Thermal, chemical, and physical properties of the glass ceramics were examined along with the glass crystallization behaviour. Hot Stage Microscopy allowed observation of the sintering and wetting behaviour of glass-ceramics and showed it to be a complex process, significantly affected by glass composition, viscosity, glass transition temperature, crystallization rate and the nature of the crystalline phases formed. The bonding characteristics of parent glasses with ceramic and/or metallic interconnector were observed under air at the cell operating temperature. The results revealed the most suitable glass-ceramic compositions to meet the different criterions and the difficulties involved in formulating such materials.