The β-γ polymorphic transition of calcium orthosilicate (C₂S) is a key phenomenon in cement chemistry. During this transition, the compound expands due to structural changes and a significant reduction in its density is observed, leading to its disintegration into a powder with a very high specific surface area. Owing to this tendency of the C₂S material to “self-disintegrate”, its production is energy-efficient and thus environmentally friendly. A physicochemical study of the self-disintegration process was conducted with the aim of determining how the amount of dodecacalcium hepta-aluminate (C₁₂A₇) in calcium orthosilicate (C₂S) affects the temperature at which the polymorphic transi-tions from α’L-C₂S to β-C₂S and from β-C₂S to γ-C₂S undergo stabilization. The applied techniques included differential thermal analysis (DTA), calorimetry and X-ray diffraction (XRD), and they made it possible to determine what C₂S/C₁₂A₇ phase ratio in the samples and what cooling rate constitute the optimal conditions of the self-disintegration process. The optimal cooling rate for C₂S materials with a C₁₂A₇ content of up to 60 wt% was determined to be 5 K·min⁻¹. The optimal mass ratio of C₂S/C₁₂A₇ was found to be 70/30, which ensures both efficient self-disintegration and desirable grain size distribution.

The development of the oxide scale on model Fe20Cr5Al-type alloys unmodified and containing implanted yttrium was studied in oxygen-dominated atmosphere at 1,100 °C for up to 1 h. A two-stage-oxidation exposure was applied with the use of ¹⁸O₂ as a tracer. The choice of the exposure durations ensured the possibility to follow the consecutive stages of scale development. The oxidized samples were characterized using SEM (morphology); PLS (phase composition), and SIMS (elemental distributions). The obtained results are discussed in terms of the mechanism of the development of protective α-Al₂O₃ scale and the effect of the additions on this process taking into account the necessity of distinguishing the mechanism and kinetics of the scale evolution. Similar scale evolution stages were found on both studied materials and in both cases the protective α-Al₂O₃ scale developed rapidly, already after the exposure for 3 min. Implanted yttrium appeared to have a negligible effect on the evolution of the scale. It only slightly retarded the evolution which can be attributed rather to a kinetic effect than to mechanistic one. However, the mechanical failure of the scales via formation of cracks at the asperities of convolutions occurred on the yttrium-implanted alloy but not on the non-implanted one.

This work presents the results of oxidation studies on commercially available Nirosta 4016/1.4016 ferritic steel, which contains 16.3 wt.% chromium, as well as the electrical properties of steel/scale layer systems in order to determine the usefulness of this steel for constructing metallic interconnects in solid oxide fuel cell (SOFC) and solid oxide electrolyzer cell (SOEC) stacks. The E-Brite ferritic steel, consisting of up to 26 wt.% chromium, was chosen as a reference material. High-temperature isothermal oxidation kinetics studies were carried out on both steels at 1073 K for 255, 505, 760 and 1010 h in air atmosphere. These conditions are representative of those present in the cathode compartment of a SOFC and the anode compartment of a SOEC. Area specific resistance (ASR) measurements were performed on steel/scale layer systems, obtained after the previous oxidation of both steels in the above-mentioned conditions, in the air in the temperature range of 573–1073 K using the pseudo-DC four-probe method. On the basis of these studies, complemented by morphology observations, as well as chemical and phase composition analysis of the oxidation products, the usefulness of Nirosta 4016/1.4016 ferritic steel for manufacturing interconnects in energy conversion electrochemical devices operating at 1073 K was confirmed.

The oxidation behavior of four γ/γ′ Ni-based alloys: without additions, and containing: Hf (1.0 wt%), a combination of Hf and Y (0.3 wt% and 0.03 wt%, respectively), and a combination of Hf and Si (1.0 wt% and 1.0 wt%, respectively) was studied in air under isothermal (50 h) and thermal cycling (up to 2225 1-h cycles) conditions. Samples were characterized using SEM, EDX and XRD techniques. The results indicated that all the additions improved the oxidation resistance of the alloy but only in the case of materials containing the (Hf + Y) combination of additions was a long-term effect achieved. Substantial weight losses were observed on the other unmodified and (Hf + Si)-containing materials during thermal cycling after short exposure periods, while on material containing only additions of Hf, they occurred significantly later. Kinetic studies showed the highest oxidation rate in the case of the (Hf + Si)-containing alloys and the fastest initial oxidation, prior to the parabolic law-obeying stage, of alloy with Hf-additions, only. The results indicate the superior effect of simultaneous application of Hf and Y additions at levels not exceeding their solubility limits and that lowering its effectiveness Hf overdoping (1 wt%) cannot be effectively counteracted by the addition of 1% Si.