Thermal expansion of natural orthoenstatite to 1473 K

The volume thermal expansion of powdered natural orthoenstatite [(Mg_(0.994)Fe_(0.002)Al_(0.004))2(Si_(0.996)Al_(0.004))_2O_6] has been measured to 1473 K using energy dispersive synchrotron X-ray diffraction. Over the temperature range examined, the data are consistent with a volume thermal expansion, α, that linearly increases with temperature as given by the expression α(T) = 29.7(16) × 10^(−6)K^(−1) + 5.7(11) × 10^(−9)K^(−2)T. An analysis in terms of the often-used constant expansion coefficient yields α_0 = 34.5(17) × 10^(−6) K^(−1), which is in good agreement with several previous experimental results on orthoenstatite (Mg_2Si_2O_6) over a similar temperature range. Our results do not support the extreme upper and lower bounds reported in earlier studies for the thermal expansivity of Fe-rich orthoenstatite, but rather suggest that the thermal expansion of this phase is approximately midway between those extreme values.