The aim of this study was to investigate phase formation under steam oxidation conditions and steam oxidation behaviours of two solid-solution-strengthened alloys—HAYNES^® 230^® and 617 alloy—two gamma-prime (γ′)-strengthened alloys—263 and HAYNES^® 282^®—and finally three austenitic steels rich in Cr—309S, 310S and HR3C. The samples were tested under 1 bar pressure in 100 % water–steam–water system at 800 °C for 1000 h. It was found that Ni-based solid-solution-strengthened alloys, HAYNES^® 230^® and 617 alloy, developed mainly Cr₂O₃ and MnCr₂O₄ phases on their surfaces, whereas the γ′-strengthened alloys, 263 and HAYNES^® 282^®, formed Cr₂O₃, TiO₂ and MnTiO₃ phases, indicating slightly higher corrosion degradation rate. The austenitic steels exposed for 1000 h formed Cr₂O₃, Fe₃O₄ and MnCr₂O₄ with traces of Fe,Mn(SiO)₄. Some sites on the austenitic steel surfaces were enriched with Fe₃O₄ with little amount of Cr. During the test, no spallation of the external oxide scale was observed. The kinetic data showed that only the 263 alloy oxidized according to parabolic behaviour, whereas the other alloys deviated from the parabolic rate law, with time exponents of 0.4–0.6 or 0.3. Finally, cross-sectioned investigations of the exposed samples revealed that Ni-based alloys underwent extended internal oxidation, with the highest extent in HAYNES^® 282^® reaching 25 μm and the lowest in HAYNES^® 230^® alloy reaching 7 μm. The austenitic steels showed no internal oxidation phenomena.

For a successful implementation of newly proposed silicon-based latent heat thermal energy storage systems, proper ceramic materials that could withstand a contact heating with molten silicon at temperatures much higher than its melting point need to be developed. In this regard, a non-wetting behavior and low reactivity are the main criteria determining the applicability of ceramic as a potential crucible material for long-term ultrahigh temperature contact with molten silicon. In this work, the wetting of hexagonal boron nitride (h-BN) by molten silicon was examined for the first time at temperatures up to 1750 °C. For this purpose, the sessile drop technique combined with contact heating procedure under static argon was used. The reactivity in Si/h-BN system under proposed conditions was evaluated by SEM/EDS examinations of the solidified couple. It was demonstrated that increase in temperature improves wetting, and consequently, non-wetting-to-wetting transition takes place at around 1650 °C. The contact angle of 90° ± 5° is maintained at temperatures up to 1750 °C. The results of structural characterization supported by a thermodynamic modeling indicate that the wetting behavior of the Si/h-BN couple during heating to and cooling from ultrahigh temperature of 1750 °C is mainly controlled by the substrate dissolution/reprecipitation mechanism.

In this work, the surface tension and density of Si-Ge liquid alloys were determined by the pendant drop method. Over the range of measurements, both properties show a linear temperature dependence and a nonlinear concentration dependence. Indeed, the density decreases with increasing silicon content exhibiting positive deviation from ideality, while the surface tension increases and deviates negatively with respect to the ideal solution model. Taking into account the Si-Ge phase diagram, a simple lens type, the surface tension behavior of the Si-Ge liquid alloys was analyzed in the framework of the Quasi-Chemical Approximation for the Regular Solutions model. The new experimental results were compared with a few data available in the literature, obtained by the containerless method.