This Division of Earth Sciences Instrumentation and Facilities Program grant supports acquisition of push rod dilatometer capable of high precision measurements of the thermal expansivity of minerals, glasses and materials over a broad range of temperatures (180 ? 2000 deg C ) relevant to study of the thermal evolution of deep Earth and crustal phases. This would be the first such instrument of its kind in an Earth Sciences academic research department. The effect of temperature on the expansion and contraction of Earth materials is a fundamental property needed to constrain models of mantle convection. Few reliable data of thermal expansivity of deep Earth phases exist that were acquired at in situ temperature conditions and with sufficient confidence to provide realistic constraints on geodynamic models. The PI would use the instrument to develop an extensive database on the thermal expansivity of a wide range of geomaterials starting first with well characterized single-crystals phases and glasses relevant to the Earth's crust and mantle. The PI intends to engage students in experiential learning through hands on measurements.
***
Thermal expansivity is a temperature derivative of volume. This is a fundamental physical property of materials that is needed to address diverse and important problems in geoscience (detailed below). Most data are collected using X-ray techniques which record volume, which is not as accurate as measuring expansion. The purpose of this proposal is to acquire an instrument capable of providing highly accurate data on thermal expansivity over a wide range of temperature for the diverse materials relevant to geology and geophysics. This grant purchased a vacuum-tight, pushrod dilatometer (Netzsch DIL-402c) which accesses -180 to 2000oC and can measure a at each temperature within 1% for crystals, ceramics, glasses (including at the glass transition), powders, pastes, and molten metals.. This instrument has two interchangeble furnaces. Both furnaces were calibrated using standards of fused silica for low temperature and optical quality corundum for high temperature. The instrument was used to collect data for the PhD thesis of Everett Criss at UCSD, Department of Mechanical Engineering. The most difficult part of the measurements is sample preparation, which requires rods of about 6mm by 12 to 25 mm (for increased accuracy). No comparable instrument exists in Earth Science research facilities in the U.S. The initial focus will be on oriented crystals of volumetrically important minerals, and glasses to proxy melts. Long term goals are building an extensive database on all types of materials. This research is scientifically important to understand contraction and buoyancy effects in plate tectonics. Thermodynamic properties are interrelated, so data on thermal expansivity is useful for self-consistent databases as well as understanding microscopic behavior and anharmonicity. Thermal expansivity is part of the equation of state which is underlies mineralogical models of the mantle. Modernizing the outdated mineralogical database on the temperature dependence of a via state-of-the-art instrumentation will enhance the infrastructure of the geosciences because this material property is a key parameter in the equation of state and hence is used by many scientists in diverse applications in petrology, mineral physics, geophysics, planetary science, and tectonophysics.
