Thermal expansion of natural orthoenstatite to 1473 K

The volume thermal expansion of powdered natural orthoenstatite [(Mg0.994Fe0.002Al0.004)2(Si0.996Al0.004)2O6] 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, , that linearly increases with temperature as given by the expression (T) = 29.7(16) x 10-6K-1 + 5.7(11) x 10-9K-2T. An analysis in terms of the often-used constant expansion coefficient yields 0 = 34.5(17) x 10-6K-1, which is in good agreement with several previous experimental results on orthoenstatite (Mg2Si2O6) 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. Key-words: orthoenstatite, thermal expansion, high-temperature, X-ray diffraction.