Stringent dimensional stability requirements are called for in present and future aerospace systems, components and structures. The availability of a zero coefficient of thermal expansion (CTE) material would help to solve numerous design and performance problems. At present the best materials are ULE, Zerodur, fused SiO2, Super Invar and some pseudo-isotropic graphite epoxy composites. All of these exhibit thermal strains (Δ L/L) in excess of 20–50 microinches per inch when cooled, for example, from room temperature to −250°C. Since immediate applications for a zero CTE material include mirror substrates, metering rods and optics supports, an optimum material should also be isotropic, dimensionally stable with time (under constant temperature and low stress levels) and exhibit as high a thermal conductivity as possible.
KeywordsThermal Expansion Measurement Niobium Pentoxide Microcracking Effect Thorium Fluoride Niobium Oxidation Film
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