Heat transport properties of feldspathoids and ANA zeolites as a function of temperature

Abstract

The phonon component of thermal diffusivity (D) was measured up to temperatures (T) of ~1350 K using laser-flash analysis from leucite, analcime, pollucite, nepheline, sodalite, and petalite, many of which were single crystals. From electron microprobe analysis, nepheline is a solid solution, Na2(Na1.2K0.71)Al3.88Si4.10O16, whereas the other minerals have nearly endmember chemical compositions. From near-IR spectra, hydroxyl contents range from ~200 ppm to 1 wt%. At 298 K, D is low (0.51–0.75 mm2 s−1) for the zeolites and the solid-solution nepheline but moderate (1.9–2.2 mm2 s−1) for the endmember feldspathoids. For leucite, D decreases with increasing T until reaching the tetragonal to cubic phase transition whereupon D increases. A complex polynomial is required to describe D(T) for leucite, due to the displacive transition. For the other samples, as observed for most minerals, D decreases up to dehydration which terminated the runs and is described by FT−G + HT where G varies from 0.14 to 1.44 and H is negligible to 0.0006 K−1. Available heat capacity and volumetric data were used to calculate thermal conductivity as a function of T. For sodalite and petalite, k decreases with T, whereas for the remaining phases, k is roughly constant and low, ~1.5 Wm−1 K−1.