Oxidation Mechanisms of Refractory Materials in Ultra-High Temperature Molecular and Dissociated Oxygen
Abstract
The oxidation mechanisms of early transition metal carbides and corresponding metals, including Ti, Ta, Zr, and Hf are explored in three environments- cool atomic oxygen, ultra-high temperature molecular oxygen, and ultra-high temperature atomic oxygen. The aim of this study is probe oxidation mechanisms of transition metal carbides in high-temperature oxidative plasma-present environments representative of high Mach number hypersonic flight, separating thermal effects (high temperature) from chemical effects (atomic oxygen). Oxidation exposures of these materials will be conducted using a custom resistive heating system designed for micro-plasma atomic oxygen exposures at ultra-high temperatures (1500 to 1800C). Three research questions are explored. First, carbides are hypothesized to have faster oxidation rates than corresponding metals due to formation of non-protective porous oxide scales resulting from CO(g) outgassing during oxidation, however, densification of the oxide scale may mitigate this effect. In this work, a systematic study of transition metal carbides is employed to evaluate the effect of oxide densification on oxidation kinetics. Second, the effects of catalycity (tendency to promote atomic oxygen surface recombination) of carbides versus metals are unknown. We propose to evaluate increased temperatures that arise due to surface atomic oxygen recombination relative to temperatures observed in molecular oxygen for both carbides and metals. Finally, we seek to understand the effect of atomic oxygen on oxidation rates relative to molecular oxygen. This work will establish a fundamental mechanistic understanding of refractory metal carbide oxidation in ultra-high temperature environments relevant for hypersonic applications. This research enables development of ultra-high temperature ceramic composite materials based on refractory carbides.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 07, 2023
- Source ID
- FA95502110102
Entities
People
- Elizabeth Opila
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Virginia