The Design of Hafnium-Tantalum Carbide Systems and Their Corresponding Oxides for Ultra-High Temperature Oxidation Resistant Applications

Smith, Niquana

The Design of Hafnium-Tantalum Carbide Systems and Their Corresponding Oxides for Ultra-High Temperature Oxidation Resistant Applications 142 views

Author

Smith, Niquana, Materials Science - School of Engineering and Applied Science, University of Virginia

Advisors

Opila, Elizabeth , EN-Mat Sci & Engr Dept , University of Virginia

Abstract

The rate limiting oxidation mechanisms of (Hfx, Ta1-x) carbide system were investigated by tailoring the composition of Hf (x = 0, 0.6,0.7, 0.8,1) and oxidizing them in a resistive heating system (RHS) at temperatures between 1400 -1750°C for 2 minutes, 5 minutes, and 10 minutes in 1% O2/Ar. The observed results were linear oxidation kinetics for all compositions under these conditions. High resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), and microfocus X-ray diffraction (µ-XRD) were used to determine the oxide phases present on the post oxidized Hf/Ta carbides. Hf6Ta2O17 was successfully identified as the predominant phase to form throughout the mixed compositions.
It has been suggested that Hf6Ta2O17 shows prospects of being a protective oxide when thermally grown on Hf/Ta materials. This study investigated the intrinsic oxygen diffusivity in sintered Hf6Ta2O17 along with its binary constituents, HfO2 and Ta2O5 to address this possibility. Phase pure pellets of M-HfO2, O-Ta2O5, and O-Hf6Ta2O17 were fabricated by spark plasma sintering. Samples were equilibrated in 16O2 then encapsulated in 18O2 and exposed at temperatures between 500C and 1400C for exchange times up to 7 hours. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was used to determine the 18O concentration profiles. Concentration profiles were fit to a semi-infinite solution of the diffusion equation with a surface exchange limited boundary condition. It was observed that oxygen self-diffusion in Ta2O5 was the most rapid. The oxygen diffusivity in Hf6Ta2O17 was more rapid than HfO2 at temperatures less than 1340˚C and slower than HfO2 at higher temperatures due to the differences in activation enthalpy. These results suggest more protective oxide growth for (Hfx, Ta1-x)C at temperatures greater than 1340˚C.

Degree

PHD (Doctor of Philosophy)

Keywords

high temperature oxidation ; Ceramics; oxygen tracer diffusion

Rights

Issued Date

2025-12-11

Suggested Citation

Smith, Niquana. The Design of Hafnium-Tantalum Carbide Systems and Their Corresponding Oxides for Ultra-High Temperature Oxidation Resistant Applications. University of Virginia, Materials Science - School of Engineering and Applied Science, PHD (Doctor of Philosophy), 2025-12-11, https://doi.org/10.18130/k34b-8r80.