Thermal expansion and decomposition of jarosite: a high-temperature neutron diffraction study |
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| Authors: | Hongwu Xu Yusheng Zhao Sven C Vogel Donald D Hickmott Luke L Daemen Monika A Hartl |
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| Institution: | (1) Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA;(2) Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, NM 87545, USA |
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| Abstract: | The structure of deuterated jarosite, KFe3(SO4)2(OD)6, was investigated using time-of-flight neutron diffraction up to its dehydroxylation temperature. Rietveld analysis reveals
that with increasing temperature, its c dimension expands at a rate ~10 times greater than that for a. This anisotropy of thermal expansion is due to rapid increase in the thickness of the (001) sheet of Fe(O,OH)6] octahedra and SO4] tetrahedra with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion,
α = α0 + α1
T, where α0 = 1.01 × 10−4 K−1 and α1 = −1.15 × 10−7 K−2. On heating, the hydrogen bonds, O1···D–O3, through which the (001) octahedral–tetrahedral sheets are held together, become
weakened, as reflected by an increase in the D···O1 distance and a concomitant decrease in the O3–D distance with increasing
temperature. On further heating to 575 K, jarosite starts to decompose into nanocrystalline yavapaiite and hematite (as well
as water vapor), a direct result of the breaking of the hydrogen bonds that hold the jarosite structure together. |
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