37 research outputs found
Small-Angle X-ray and neutron scattering from diamond single crystals
Results of Small-Angle Scattering study of diamonds with various types of
point and extended defects and different degrees of annealing are presented. It
is shown that thermal annealing and/or mechanical deformation cause formation
of nanosized planar and threedimensional defects giving rise to Small-Angle
Scattering. The defects are often facetted by crystallographic planes 111, 100,
110, 311, 211 common for diamond. The scattering defects likely consist of
clusters of intrinsic and impurity-related defects; boundaries of mechanical
twins also contribute to the SAS signal. There is no clear correlation between
concentration of nitrogen impurity and intensity of the scattering.Comment: 6 pages, 5 figures; presented at SANS-YuMO User Meeting 2011, Dubna,
Russi
Absorption spectra of hydrogen in C-13 diamond produced by high-pressure, high-temperature synthesis
Deep carbon cycle and geodynamics: the role of the core and carbonatite melts in the lower mantle
Intergranular diamonds derived from partial melting of crustal rocks at ultrahigh-pressure metamorphic conditions
An experimental demonstration of diamond formation in the dolomite-carbon and dolomite-fluid-carbon systems
Direct observation and analysis of a trapped COH fluid growth medium in metamorphic diamond
The role of mantle ultrapotassic fluids in diamond formation
Analysis of data on micro- and nano-inclusions in mantle-derived and metamorphic diamonds shows that, to a first approximation, diamond-forming medium can be considered as a specific ultrapotassic, carbonate/chloride/silicate/water fluid. In the present work, the processes and mechanisms of diamond crystallization were experimentally studied at 7.5 GPa, within the temperature range of 1,400–1,800°C, with different compositions of melts and fluids in the KCl/K2CO3/H2O/C system. It has been established that, at constant pressure, temperature, and run duration, the mechanisms of diamond nucleation, degree of graphite-to-diamond transformation, and formation of metastable graphite are governed chiefly by the composition of the fluids and melts. The experimental data suggest that the evolution of the composition of deep-seated ultrapotassic fluids/melts is a crucial factor of diamond formation in mantle and ultrahigh-pressure metamorphic processes