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Title: Oxidation Resistance, Electrical and Thermal Conductivity, and Spectral Emittance of Fully Dense HfB2 and ZrB2 with SiC, TaSi2, and TaB2 Additives
Abstract:
The proposed research will investigate material properties of ZrB2 and HfB2-based com-
pounds pertaining to their ability to resist oxidation and dissipate heat at elevated tempera-
tures. Additives will be investigated for their beneficial oxidation-resistant effects. Materials
which are able to function at extreme temperatures in oxidizing environments are candidates
for components of advanced air- and spacecraft. Current research in these materials, termed
Ultra High Temperature Ceramics (UHTCs), lacks a profundity of data pertaining to tem-
peratures above 1500 deg.C. In particular, experiments concerning oxidation behavior and heat
dissipation are needed.
Specifically, the proposed research will utilize in situ thermogravimetric analysis of a
spectrum of compositions of ZrB2 and HfB2-based compounds with additives of SiC, TaSi2,
and TaB2. The former is known to produce a protective silicate glass layer (up to ~ 1500 deg.C), and the latter have been shown by some to confer oxidation resistance at higher temperatures.
A labratory balance mounted on a lifting table beneath a furnace with Zircothal heating
elements able to reach 2000 deg.C is used to perform the oxidation studies.
In addition to the oxidation studies, characterization of the materials' ability to dissipate
excess heat will be performed. The thermal expansion of the samples will be determined with
a graphite differential dilatometer, the thermal diffusivity is determined by the laser flash
method, and these values will be used to calculate the thermal conductivity. As the materials
will be expected to not only conduct heat but radiate it away also, the spectral emittance of each sample will be determined using a spectral radiometer.
This research will contribute to the understanding and modeling suitability of a class
of materials expected to find use in the next generation of supersonic aircraft and reusable
spacecraft. In addition, it will contribute to the science of UHTC materials and offer new
understanding as to the mechanics of oxidation resistance at high temperatures.
