A self‐healing thermal barrier coating (TBC) system is manufactured by air plasma spraying (APS) and tested by thermal cycling. The ceramic topcoat in the self‐healing APS TBC system consists of an yttria stabilised zirconia (YSZ) matrix and contains self‐shielding aluminium containing MoSi2 healing particles dispersed close to the topcoat/bond coat interface. After spraying the healing particles the material was annealed to promote the formation of an oxygen impermeable Al2O3 shell at the MoSi2‐TBC interfaces by selective oxidation of the aluminium fraction. The samples were subsequently thermally cycled between room temperature and 1100°C. The study focussed on the spontaneous formation of the Al2O3 shell as well as the subsequent damage evolution in the APS produced TBC during thermal cycling. Experimental evidence showing characteristic signs of crack healing in the topcoat is identified and analysed. The study shows that while the concept of the self‐healing APS TBCs containing self‐shielding MoSi2 particles is promising, future study is needed to improve the protectiveness of the Al2O3 shells by further tailoring the aluminium content in the MoSi2 and the particle shape to avoid the premature oxidation of the healing particles and maximise crack healing efficiency.@en

Hydrogen is the most desirable green energy carrier and electrocatalytic hydrogen evolution reaction (HER) from water is a promising route for hydrogen production. The search for efficient, low-cost HER catalysts is a challenging and attracting topic. In this work, we report that inorganic fullerene-like WS₂ supported Pd nanoparticles (Pd/WS₂), with Pd loading of 0.76 wt%, are active for electrocatalytic HER conducted in 0.5 M H₂SO₄ solution, with overpotential at 10 mA cm⁻² current density of ~130 mV and Tafel slope of 82.4 mV dec⁻¹, which is comparable to that of Pt/WS₂ (0.88 wt% Pt loading) with higher costs. Characteristic results indicate that WO₃ impurities were in-situ produced on the WS₂ surface and the Pd NPs are primarily located inside the WS₂ nanocages. Contrasting experiments suggest that the WO₃ impurities play a crucial role in generating H_ads intermediate and the Pd NPs are active sites of H₂ production, and a reaction mechanism is proposed. The Pd/WS₂ catalyst also shows good long-term stability owing to the location of Pd NPs inside the WS₂ cages. The high HER activity, low costs and good stability make the Pd catalyst a potential alternative to Pt catalyst for HER.

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Yttria – partially stabilised zirconia (YPSZ) MoSi₂ composites have been designed to prolong the lifetime of the matrix by self – healing cracks during thermal cycling. The healing reaction at high temperatures is based on the decomposition of MoSi₂, leading to a volumetrically expanding reaction product, which seals the crack. In this work, coefficient of thermal expansion (CTE) and the fracture toughness of composites containing MoSi₂ particles, produced by spark plasma sintering (SPS) have been compared to conventional YPSZ. The CTE mismatch between YPSZ and MoSi₂ was found to be small, implying that thermally induced mismatch stresses will be small and the composites have a similar CTE to conventional YPSZ. Fracture toughness was found not to be affected by the particles and showed similar values to unreinforced YPSZ. Cracks introduced by indentation have been shown neither to prefer, or avoid, the particles suggesting that such a composite system is capable of autonomously activating the self – healing reaction.

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To prolong the lifetime of thermal barrier coatings (TBCs) recently a new method of microcrack healing has been developed, which relies on damage initiated thermal decomposition of embedded molybdenum disilicide (MoSi₂) particles within the TBC matrix. While these MoSi₂ particles have a beneficial effect on the structural stability of the TBC, the high thermal conductivity of MoSi₂ may have an unfavourable but as yet unquantified impact on the thermal conductivity of the TBCs. In this work the thermal conductivity of spark plasma sintering (SPS) produced yttria-stabilised zirconia (YSZ) model thermal barrier coatings containing 10 or 20 vol.% of MoSi₂ healing particles was investigated using the laser flash method. Measurements were performed on free-standing composite material over a temperature range from room temperature up to 1000 °C. Microstructural analysis was carried out by SEM combined with image analysis to determine the size, distribution and area fraction of healing particles. The measurements were compared with the results from microstructure-based multi-physics finite element (FE) models and analytical models (the asymmetric Bruggeman model and the Nielsen model) in order to study the effects of the addition of MoSi₂ particles as well as the presence of micro-pores on the apparent thermal conductivity. The results show a strongly non-linear increase in the thermal conductivity of the composite material with the MoSi₂ volume fraction and a dependence on the aspect ratio of MoSi₂ particles. Interparticle connectivity is shown to play a big role too.

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