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Ablative materials are widely employed to protect space vehicles from the extreme thermal conditions experienced during their flight into a planetary atmosphere. Carbon-phenolic ablators are composed of a phenolic matrix and a fibrous carbon reinforcement. In the present study, the fibrous reinforcement has been modified through the deposition of thin protective layers of zirconium oxide and aluminum oxide, with the objective of reducing fiber recession and oxidation. The depositions were carried out via atomic layer deposition (ALD), a method that allows for the controlled deposition of uniform and conformal coatings on the carbon felt fibers. The depositions were subsequently evaluated through SEM-EDS analysis. Pristine and ALD-modified felts were impregnated with a phenolic resin matrix and the ablation performance of the composite materials was evaluated through oxyacetylene flame tests. The results demonstrated that, in comparison to uncoated ablators, the ALD-modified samples exhibited enhanced performance in terms of mass loss and surface recession: compared to uncoated ablators, the former was 14% lower and the latter was diminished by 50%. Moreover, the morphological characterization of the tested specimens revealed a significantly reduced degree of oxidation of the coated fibers which were directly exposed to the flame. [ABSTRACT FROM AUTHOR]

High phosphorus Ni-P coatings, both unreinforced and modified by the addition of alumina (Al2O3) and zirconia (ZrO2) nanoparticles, were manufactured by electroless deposition technique and heat-treated with different temperature and duration schedules. The effect of dehydrogenation (200 °C for 2 h) and its combination with crystallization heat treatment was studied in terms of microstructural changes and wear resistance. The amorphous structure of the coatings was not altered by the introduction of both Al2O3 and ZrO2 nanoparticles, and the addition of 1.5 g/L of ZrO2 yielded the highest microhardness due to better particles dispersion. Dehydrogenation improved hardness because of the early stages of grain growth; however, the greatest improvement in hardness (+120% compared to unreinforced Ni-P) was obtained after annealing at 400 °C for 1 h, because of the microprecipitation of the Ni3P crystalline phase induced by thermal treatment. No detectable differences in hardness and microstructure were detected when annealing at 400 °C for 1 h with or without prior dehydrogenation; however, the dehydrogenated coatings exhibited a lower Young's modulus. ZrO2-reinforced coatings demonstrated improved wear resistance, and wear tests revealed that dehydrogenation is fundamental for lowering the coefficient of friction (−14%) and wear rate (−97%) when performed before annealing at 400 °C for 1 h. The analysis of the wear tracks showed that the non-dehydrogenated samples failed by complete coating delamination from the substrate, with abrasion identified as the predominant wear mechanism. Conversely, the dehydrogenated samples demonstrated better resistance due to the formation of a protective oxide layer, leading to an overall increase in the coating wear resistance. [ABSTRACT FROM AUTHOR]