Thermal expansion of high-purity niobium and tantalum pentoxides is studied. It is shown that specimens of Nb2O5 and Ta2O5 obtained by melting in an optical furnace and subsequent rapid cooling in air to room temperature possess a domain of negative thermal expansion and hysteresis of the dependence of the elongation on the temperatures of heating and cooling. Since the volume of a test cell computed from data of x-ray measurement increases with growth in the temperature, the negative values of the elongation of specimens of melted Nb2O5 and Ta2O5 can be explained by merging of microcracks formed due to anisotropy of the thermal expansion when the ingots are cooled. When designing and fabricating ceramic articles with protective coatings from niobium and titanium pentoxides to be used at 1000°C, preference should be given to ceramics with low and even negative values of CLTE.
Refractories and Industrial Ceramics – Springer Journals
Published: Dec 13, 2007
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