HR: 1340h
AN: MR13A-0072    [Abstracts]
TI: High-Temperature Thermal Diffusivity Measurements of Silicate Glasses
AU: * Pertermann, M
EM: maik@levee.wustl.edu
AF: Washington University, Dept. of Earth and Planetary Sciences, Campus Box 1169, 1 Brookings Drive, St. Louis, MO 63130 United States
AU: Hofmeister, A M
EM: hofmeist@levee.wustl.edu
AF: Washington University, Dept. of Earth and Planetary Sciences, Campus Box 1169, 1 Brookings Drive, St. Louis, MO 63130 United States
AU: Whittington, A G
EM: whittingtona@missouri.edu
AF: University of Missouri - Columbia, Dept. of Geological Sciences, 101 Geology Building, Columbia, MO 65211 United States
AU: Spera, F J
EM: spera@geol.ucsb.edu
AF: University of California - Santa Barbara, Dept. of Geological Sciences and Institute for Crustal Studies, 552 University Road - Bldg 526, Santa Barbara, CA 93106 United States
AU: Zayac, J
EM: zayac@umail.ucsb.edu
AF: University of California - Santa Barbara, Dept. of Geological Sciences and Institute for Crustal Studies, 552 University Road - Bldg 526, Santa Barbara, CA 93106 United States
AB: Transport of heat in geologically relevant materials is of great interest because of its key role in heat transport, magmatism and volcanic activity on Earth. To better understand the thermal properties of magmatic materials at high temperatures, we measured the thermal diffusivity of four synthetic end-member silicate glasses with the following compositions: albite (NaAlSi₃O₈), orthoclase (KAlSi₃O₈), anorthite (CaAl₂Si₂O₈), and diopside (CaMgSi₂O₆). Thermal diffusivity measurements were conducted with the laser-flash technique and data were acquired from room temperature to a maximum temperature near 1100°C, depending on the glass transition temperature. The presence of sub-mm sized bubbles in one of the orthoclase samples had no discernable effect on measured diffusivities. At room temperature, the three feldspar-type glasses have thermal diffusivity (D) values of 0.58-0.61 mm²/s, whereas the diopside glass has 0.52 mm²/s. With increasing temperature, D decreases by 5-10% (relative) for all samples and becomes virtually constant at intermediate temperatures. At higher temperatures, the anorthite and diopside glasses exhibit significant drops in thermal diffusivity over a 50-100°C interval, correlating with previously published heat capacity changes near the glass transition for these compositions. For anorthite, D (in mm²/s) decreases from 0.48 at 750-860°C to 0.36 at 975-1075°C; for diopside, D changes from 0.42 at 630-750°C to 0.30 at 850-910°C, corresponding to relative drops of 24 and 29%, respectively. Albite and orthoclase glasses do not exhibit this change and also lack significant changes in heat capacity near the glass transition. Instead, D is constant at 400-800°C for albite, and for orthoclase values go through a minimum at 500-600°C before increasing slightly towards 1100°C but it never exceeds the room temperature D. Our data on thermal diffusivity correlate closely with other thermophysical properties. Thus, at least in case of simple compositions, measurement of thermal diffusivity of glasses above the glass transition may closely approximate the behavior of magmatic liquids. For the orthoclase composition, our new data show that the thermal diffusivity of glass in the range of 20-1100°C is clearly lower than that of orthoclase single crystals (Hoefer and Schilling, 2002, Phys Chem Minerals, 29, 571-584).
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3994 Instruments and techniques
DE: 5134 Thermal properties
DE: 5139 Transport properties
DE: 8130 Heat generation and transport
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005