Hot pressing of polycrystals of high-pressure phases of mantle minerals in multi-anvil apparatus     

Gabriel D. Gwanmesia  Baosheng Li  Robert C. Liebermann 《Pure and Applied Geophysics》1993,141(2-4):467-484

In the 1960s, E. Schreiber and his colleagues pioneered the use of hot-pressed polycrystalline aggregates for studies of the pressure and temperature dependence of the elastic wave velocities in minerals. We have extended this work to the high-pressure polymorphs of mantle minerals by developing techniques to fabricate large polycrystalline specimens in a 2000-ton uniaxial split-sphere apparatus. A new cell assembly has been developed to extend this capability to pressures of 20 GPa and temperatures of 1700°C. Key elements in the new experimental design include: a telescopic LaCrO₃ forT>1200°C; Toshiba Tungaloy grade F tungsten carbide anvils; and the use of homogeneous glasses or seeded powder mixtures as starting material to enhance reactivity and maximize densities. Cell temperatures are linearly related to electrical power to 1700°C and uniform throughout the 3 mm specimens. Pressure calibrations at 25°C and 1700°C are identical to 15 GPa. Cylindrical specimens of the beta and spinel phases of Mg₂SiO₄, stishovite (SiO₂-rutile), and majorite-pyrope garnets have been synthesized within their stability fields in runs of 1–4 hr duration and recovered at ambient conditions by simultaneously decompressing and cooling along a computer-controlledP-T path designed to preserve the high-pressure phase and to relax intergranualar stress in the polycrystalline aggregate. These specimens are single-phased, fine-grained (<5 micron), free of microcracks and preferred orientation, and have bulk densities greater than 99% of X-ray density. The successful fabrication of these high-quality polycrystalline specimens has made possible experiments to determine the pressure dependence of acoustic velocities in the ultrasonics laboratory of S. M. Rigden and I. Jackson at the Australian National University.CHiPR: NSF Science and Technology Center for High Pressure Research.  相似文献   

Elasticity of the pyrope (Mg3Al2Si3O12)-majorite (MgSiO3) garnets solid solution     

G. D. Gwanmesia  J. Liu  G. Chen  S. Kesson  S. M. Rigden  R. C. Liebermann 《Physics and Chemistry of Minerals》2000,27(7):445-452

Dense isotropic polycrystalline specimens of majorite-rich garnets (Py₁₀₀, Py₆₂Mj₃₈, Py₅₀Mj₅₀, Py₂₁Mj₇₉ and Mj₁₀₀) along the pyrope (Mg₃Al₂Si₃O₁₂ = Py₁₀₀)-majorite (MgSiO₃ = Mj₁₀₀) join were fabricated in a 2000-ton uniaxial split-sphere anvil apparatus (USSA-2000) at pressures from 10 to 18.5 GPa and temperatures from 1200 to 1850 °C, within their stability fields in runs of 2–4-h duration, using hot-pressing techniques developed by Gwanmesia et al. (1993). These specimens are single-phased, fine-grained (≤5 mm), free of microcracks, and have bulk densities greater than 99% of the corresponding single-crystal X-ray density. Elastic compressional (P) and shear (S) wave velocities were determined at room pressure and temperature for these polycrystalline garnet specimens by phase comparison ultrasonic interferometry. For Mj₁₀₀, the P and S wave velocities are within 1% of the Hashin-Shtrikman averages calculated from the single crystal elastic moduli measured by Brillouin spectroscopy. Both the elastic bulk modulus (K) and the shear modulus (G) decrease continuously with increasing majorite content from pyrope garnet (Py₁₀₀) to pure majorite garnet (Mj₁₀₀). The compositional dependence of K and G are given by K = 172.3 (40) − 0.085X, and G = 91.6 (10) − 0.038X, where X = mol% majorite), respectively, indicating that substitution of Si for Mg and Al decreases both K and G by about 5% along the solid solution series. Received: 25 March 1999 / Accepted: 12 July 1999  相似文献