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HfB 2 oxidized for 3 hours at 1250 o C in a 13%Ar-87%O 2 flow at 3.2 Torr

Discharge-Off. Ave. 13.6 m m. Ave. 25.1 m m. Discharge-On. (SEM images courtesy of Matt Gasch, NASA Ames). Collaborative Research: Oxidation of Ultra-High Temperature Ceramics in Dissociated Oxygen Environments Bridget Rogers, Vanderbilt University, DMR 0435843

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HfB 2 oxidized for 3 hours at 1250 o C in a 13%Ar-87%O 2 flow at 3.2 Torr

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  1. Discharge-Off Ave. 13.6 mm Ave. 25.1 mm Discharge-On (SEM images courtesy of Matt Gasch, NASA Ames) Collaborative Research: Oxidation of Ultra-High Temperature Ceramics in Dissociated Oxygen Environments Bridget Rogers, Vanderbilt University, DMR 0435843 Jochen Marschall, SRI International, DMR 0435856 Ultra-high temperature ceramic (UHTC) composites and coatings, containing silica formers and metal carbides, nitrides, and borides, are being developed to protect hypersonic vehicles from heat and chemical attack during flight. We are studying the oxidation behavior of UHTCs and their constituents in high-temperature, low-pressure dissociated-oxygen, using a microwave discharge to break apart molecular oxygen and a tube furnace to heat the specimens up to 1600 oC. We find dramatically enhanced oxidation rates on Si, SiC, and Si3N4 in dissociated versus molecular oxygen, under the same temperature and pressure conditions. Enhanced oxidation is also observed on metal borides. This research will produce new oxidation models for predicting UHTC performance in harsh flight environments, and may lead to new UHTC formulations with improved oxidation resistance. HfB2 oxidized for 3 hours at 1250 oC in a 13%Ar-87%O2 flow at 3.2 Torr

  2. Collaborative Research: Oxidation of Ultra-High Temperature Ceramics in Dissociated Oxygen Environments Bridget Rogers, Vanderbilt University, DMR 0435843 Jochen Marschall, SRI International, DMR 0435856 Three undergraduates, three graduate students and one post-doctoral fellow have contributed to this research project. This project has provided the graduate students the unique experience of building an Auger electron spectroscopy instrument from new and existing components. This exercise introduced the students to chamber design and manufacturing, pumping system design, ultra-high vacuum system assembly, and economic evaluations to determine the best use of grant funding, all resulting in an instrument critical to the success of this and future programs. Additional support for the summertime participation of undergraduate students at SRI came through an NSF-Research Experience for Undergraduates site grant and two SRI Academy scholarships.

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