Chapter 8 - Development of a rotational Drickamer apparatus for large-strain deformation experiments at deep Earth conditions

Abstract

This chapter describes a new type of torsion apparatus—that is, the rotational Drickamer apparatus (RDA). Large-strain deformation experiments have been performed in the RDA at pressures and temperatures up to ∼15 GPa and ∼1700 K, respectively. The apparatus consists of opposing tungsten carbide anvils that are supported by a pyrophyllite gasket. The sample is sandwiched between the two anvils, and alumina or YAG insulating disks. The sample space is heated by two disk heaters made of a mixture of TiC and diamond. In the RDA, the deformation piston is supported by a gasket and a cylinder as in static high-pressure experiments with a conventional Drickamer apparatus. Consequently, deformation experiments can be performed at conditions similar to those of static high-pressure experiments (—20 GPa with tungsten carbide anvils). A conical window is made in the confining cylinder for in situ X-ray stress and strain measurements. In the apparatus discussed in the chapter, both uniaxial compression and shear deformation occur. The actual shear strain rates are lower presumably due to deformation of portions of the sample assembly other than the sample itself. To determine the uniaxial stress and the shear stress separately, X-ray diffraction measurements are done at five different angles with respect to the rotation (compression) axis (i.e. 0, 45°, 90°). The sample thickness change and shear deformation are monitored by an imaging system during the synchrotron experiments. This apparatus allows quantitative studies of plastic deformation and microstructural development at a prescribed strain rate at pressure and temperature conditions equivalent to the deep mantle (500 km).