In the present work the effects of single or combined minor additions of Zr, Hf, Ti and C on the oxidation behaviour of Y-containing, FeCrAl alloys have been studied. For this purpose high-purity, model alloys with single or multiple minor alloying additions were used. The results of long term discontinuous oxidation tests and detailed kinetics studies using thermogravimetry were complemented with extensive microstructural characterisation of the formed alumina scales using SEM and STEM. Hence, the oxidation kinetics and scale spallation rates and failure modes were correlated with the oxide composition and microstructure. The results demonstrate that the frequently reported positive effect of Zr, Hf and Ti on the lifetime oxidation behaviour of FeCrAl alloys can only be fully exploited if the concentrations of the above elements are carefully adjusted and the interaction with typical alloy impurities, such as carbon, is considered.

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The oxidation behaviour of 30 mm and 50 mm thick Aluchrom YHf and 50 mm thick Kanthal AF foils have been examined during discontinuous exposure (100 h cycles) to laboratory air at 800, 850, 900 and 950uC. Oxidation was continued out to 3000 h or until chemical failure ensued, whichever was the shorter. Resulting observations include two oxidation temperature domains, a two-stage oxidation process leading to a duplex (transitional-a) alumina scale and ultimately, a two-stage chemical failure process of the oxide scale leading to breakaway/non-protective attack. To unravel the underlying mechanisms involved, the scales were examined by a range of microscopy and analytical techniques, including optical and scanning electron microscopy (SEM), electron microprobe analysis (EPMA), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD).

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This study emphasizes tuning the synthesis conditions of MFI zeolites to achieve better catalytic properties by optimizing the mesoporosity, the balance between Brønsted and Lewis sites, and the zeolite particle sizes. The MFI zeolites were hydrothermally synthesized at various temperatures employing different silica sources. The synthesis temperature was varied between 110 to 180 °C at constant synthesis time (15 h). Different silicon sources led to variations in structure, morphology, and size of the MFI zeolite along with tuned Lewis and Brønsted acid sites in parallel correlation with shape selectivity of the reaction. The catalytic activities of synthesized zeolites were investigated in the catalytic cracking of n -dodecane to produce value-added chemicals. The zeolite synthesized at 180 °C using fumed silica presented the highest catalytic conversion (96.6%), while maximum light olefin gaseous products (73.1%) were obtained for the sample synthesized at 140 °C using tetraethyl orthosilicate as the silica source. The MFI zeolite synthesized at 180 °C employing tetraethyl orthosilicate as a silica source facilitated the formation of both naphthenes and aromatics (71.3%) as major liquid products.

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