Thermal expansion of natural orthoenstatite to 1473 K

The volume thermal expansion of powdered natural orthoenstatite [(Mg_0.994Fe_0.002Al_0.004)₂(Si_0.996Al_0.004)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, α, that linearly increases with temperature as given by the expression α(T) = 29.7(16) × 10⁻⁶K⁻¹ + 5.7(11) × 10⁻⁹K⁻²T. An analysis in terms of the often-used constant expansion coefficient yields α₀ = 34.5(17) × 10⁻⁶ K⁻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.