HR: 0800h
AN: V31C-0603    [Abstracts]
TI: Bridging the piston-cylinder/multi-anvil gap
AU: * Leinenweber, K
EM: kurtl@asu.edu
AF: Department of Chemistry, Arizona State University, Tempe, AZ 85287-1604, United States
AU: Tyburczy, J A
EM: jim.tyburczy@asu.edu
AF: School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, United States
AU: Sharp, T G
EM: tom.sharp@asu.edu
AF: School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, United States
AU: Stoyanov, E
EM: estoyano@asu.edu
AF: Department of Chemistry, Arizona State University, Tempe, AZ 85287-1604, United States
AB: The piston-cylinder device is a favored tool for studying rocks under Earth's crust and uppermost mantle conditions. Experiments on fairly large sample volumes featuring careful control of pressure, temperature, oxygen fugacity, volatile content etc. are routine in this device, up to 3.0 GPa (non end-loaded) and 5.0 to 6.0 GPa (end-loaded). For higher-pressure studies, the multi-anvil takes the place of the piston-cylinder as the primary large-volume device. However, there is a notable gap in several capabilities when transitioning from the piston-cylinder to the multi-anvil. Because the furnace is necessarily shorter in a multi-anvil, thermal gradients are higher and the available volume is smaller. This makes it more difficult to control many environmental variables, such as oxygen fugacity, in a multi-anvil experiment. Much higher friction in the system means that pressure accuracy is lower. Also, it is more difficult to use quasi-hydrostatic media such as NaCl, which means that stresses and pressure gradients are likely to be higher. Current developments are aimed towards partially bridging this capability "gap" between piston-cylinders and multi-anvils. The development of new large-volume assemblies, through the COMPRES cell development project, will be described, in particular new larger octahedral assemblies with 18 and 25 mm edge lengths. A fundamental redesign of the furnace from the elongated furnaces characteristic of the piston-cylinder, which gain their low thermal gradients sinply from the length of the furnace (an infinite tubular furnace would have no thermal gradient inside) is necessary. While some laboratories have chosen step-heaters to reduce thermal gradients, we are experimenting with box heaters that are surrounded by a thermal insulating material (zirconia) and have very small electrical leads to avoid heat loss. The large sample volumes resulting from this design allow low- gradient experiments with sample volumes the same as those of a 3/4" piston-cylinder assembly up to 5 or 6 GPa (25/15 assembly) and a 1/2" piston-cylinder up to 8 or 10 GPa (18/12 assembly). This allows better control of external variables than is possible in smaller-volume or higher-gradient assemblies. Some problems, such as the higher friction and higher pressure uncertainty, are not solved, but we can combine the fact that the multi- anvil has been modified for in-situ x-ray experiments, allowing pressures to be measured directly, with more careful control of assembly components, to at least partially overcome this accuracy problem. These and other developments are being used to create a smoother transition from piston-cylinder to multi-anvil experimental conditions.
DE: 1094 Instruments and techniques
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3621 Mantle processes (1038)
DE: 3994 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting