Processable
preceramic materials are critically important to a
range of applications, especially with regard to biomedical coatings
and filling interstitial spaces in preform materials to produce ceramic
matrix composites useful for aerospace propulsion. Preceramic polymers
(PCPs) with added nanoparticle (NP) components are an attractive way
to influence the final ceramic composition and reduce the changes
in density and volume during PCP conversion to inorganic material.
Cross-linking a polymer to an NP surface is one potential route to
mitigating phase separation and potentially improving char yields
for the combined materials. In this report, two pyridine-functionalized
PCPs were studied by linking the polymers to pyridine-terminated SiO2 nanoparticle (NP) surfaces via a zirconium metal center.
The polymer–metal–nanoparticle (PMN) system was studied
in an assembled, polymeric form during pyrolysis (i.e., via thermogravimetric
analysis) and post-conversion (at 1600 °C) by X-ray diffraction,
Raman spectroscopy, scanning transmission electron microscopy with
energy-dispersive X-ray spectroscopy (EDS), and scanning electron
microscopy (SEM) with EDS. A dramatic 57% increase in char yield of
the PMN relative to the summed char yields of the individual components
is observed, showing a significant synergistic effect and yielding
a SiO2–ZrO2 nanocomposite.
Tantalum carbide (TaC) and hafnium carbide (HfC) have some of the highest melting temperatures among the transition metal carbides, borides, and nitrides, making them promising materials for high‐speed flight and high‐temperature structural applications. Solid solutions of TaC and HfC are of particular interest due to their enhanced oxidation resistance compared to pure TaC or HfC. This study looks at the effect of Hf content on the oxidation resistance of TaC–HfC sintered specimens. Five compositions are fabricated into bulk samples using spark plasma sintering (2173 K, 50 MPa, 10 min hold). Oxidation behavior of a subset of the compositions (100 vol% TaC, 80 vol% TaC + 20 vol% HfC, and 50 vol% TaC + 50 vol% HfC) is analyzed using an oxyacetylene torch for 60 s. The TaC–HfC samples exhibit a reduction in the oxide scale thickness and the mass ablation rate with increasing HfC content. The improved oxidation resistance can be attributed to the formation of a Hf6Ta2O17 phase. This phase enhances oxidation resistance by reducing oxygen diffusion and serving as a protective layer for the unoxidized material. The superior oxidation resistance of TaC–HfC samples makes these materials strong contenders for the development of high‐speed flight coatings.
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