Phase-informed design strategy of volcanic ash analogues for jet engine degradation

Volcanic ash poses a severe threat to thermal barrier coatings (TBCs) in aero-engine hot sections, causing rapid degradation under high-temperature exposure. However, the compositional variability of natural ash hinders the reproducibility in corrosion testing and the development of standardized evaluation protocols. Here, we systematically evaluated trachyandesite volcanic ash and five synthetic glass analogues with increasing compositional complexity – from quaternary CMAS (CaO-MgO-Al₂O₃-SiO₂) to octonary CMAS-NKTF (additionally containing Na₂O, K₂O, Fe₂O₃, and TiO₂). Through comprehensive characterization of thermophysical properties up to 1600 ℃ and TBCs interactions study, we identified that the septenary CMAS-NKT (with Na₂O, K₂O, and TiO₂) analogue achieved 96 % overall similarity to vitrified natural ash across multiple metrics including viscosity, thermal expansion, and infiltration depth. This high fidelity stems from its compositional alignment with the Fe-depleted residual melt formed during high-temperature phase separation in natural ash, a mechanism validated across volcanic ashes with iron contents on the order of ∼ 6–13 wt% Fe₂O₃. Our findings establish a phase-informed design strategy for volcanic ash analogues, with CMAS-NKT serving as a standardized material for reproducible TBC degradation assessment under both isothermal and thermal cycling conditions.