Showing papers by "David L. Kohlstedt published in 1992"
TL;DR: In this article, the authors report the results of hydrothermal experiments on olivine single crystals, which show that at 1,573 K and 50-300 MPa, olivines can accommodate as much as 0.0034 wt % water.
Abstract: WATER plays an important role in geodynamic processes in the Earth's upper mantle: for example, hydrogen (as water) affects the amount and composition of magma generated by partial melting1 and a trace amount of hydrogen ( ∼0.001 wt% water) can markedly weaken the dominant upper-mantle mineral, olivine2,3. Migration of hydrogen ions may be responsible for the anomalously high electrical conductivity of the asthenosphere4. The quantitative importance of hydrogen in mantle processes must depend on how much water or hydrogen can be stored in nominally anhydrous olivine, and on where hydrogen resides in the olivine lattice. Here we report the results of hydrothermal experiments on olivine single crystals, which show that at 1,573 K and 50–300 MPa, olivine can accommodate as much as 0.0034 wt % water. Hydrogen solubility depends on hydrogen fugacity and oxygen fugacity to the first and the one-half powers, respectively, indicating that hydrogen ions are associated with either oxygen interstitials or magnesium vacancies. Extrapolation of our data to a depth of ∼ 100 km under oceanic areas yields a substantial hydrogen solubility (0.03 wt % water), demonstrating that olivine may indeed be a primary sink for hydrogen in the upper mantle.
196 citations
TL;DR: In this article, the authors examined the dislocation structures and densities in experimentally deformed single crystals of San Carlos olivine using the oxidation-decoration technique, and found that the dislocations structures are associated with different rate-controlling creep mechanisms.
120 citations
TL;DR: In this paper, a conical indenter was driven into a 1.2 μm thin Pt film at a rate of 15 nm/s and across the sample surface at a speed of 0.5 μm/s, until a load drop was observed indicating that the film had delaminated.
Abstract: The adhesion of as-sputtered Pt thin films to NiO single crystals has been characterized by a continuous microscratch technique. In these experiments, a conical indenter was driven into a 1.2 μm thick Pt film at a rate of 15 nm/s, and across the sample surface at a rate of 0.5 μm/s, until a load drop was observed indicating that the film had delaminated. Using the width of the scratch track at the point at which the film delaminated from the substrate, the critical load required for delamination, and the area of the delaminated region, a model has been developed to determine the work of adhesion of the Pt/NiO system. This model uses an elastic contact mechanics approach to relate the stresses acting in a scratch experiment to the strain energy released during film delamination. Using this model, the work of adhesion and hence the interfacial fracture toughness have been determined to be 0.023–0.06 J/m2 and 0.07–0.11 MPa$\sqrt m$, respectively. These values are in reasonable agreement with those determined by other methods for metal-ceramic systems.
89 citations
TL;DR: In this paper, the authors measured the dependence of steady-state creep rate on oxygen fugacity fo 2, temperature T, applied stress a, and loading orientation for unbuffered single crystals of San Carlos olivine.
Abstract: The dependence of steady-state creep rate on oxygen fugacity fo 2, temperature T, applied stress a, and loading orientation has been measured experimentally for unbuffered single crystals of San Carlos olivine. The stress exponent, approximately 3·5, is the same for all three 45° loading orientations and is also identical with the stress exponent for buffered samples. When compressed along the [101]c or [011]c axis, the mechanical results for unbuffered samples are similar to those for orthopyroxene (opx) buffered samples. However, when compressed along the [110]c orientation, the creep behaviour of unbuffered samples is substantially different from that of opx-buffered samples. For unbuffered samples compressed along the [110]c axis three power-law relations are required to describe the dependence of strain rate on Tand fo 2 over the full range of experimental conditions. It is proposed that each power-law relation describes the creep behaviour of a different rate-controlling creep mechanism. Fo...
28 citations
TL;DR: In this article, the influence of H2O and CO2 on the kinetics of melt migration via porous flow was investigated on a synthetic melt plus olivine and a natural melt-plus-livine system, and the results indicated that the amount of volatiles dissolved in the liquids investigated here has only a modest influence on the rate of melt infiltration and volume of melt that a rock can absorb.
Abstract: Experiments were conducted on a synthetic melt plus olivine and a natural melt plus olivine system to determine the influence of H2O and CO2 on the kinetics of melt migration via porous flow. For each experiment, a melt migration couple was formed between a disk of polycrystalline San Carlos olivine and a disk of fully dense glass, which was saturated with either H2O or CO2 and was in chemical equilibrium with San Carlos olivine. For comparison, 'volatile-free' glasses were also used. The melt migration experiments were conducted at a temperature of 1300°C and a confining pressure of 300 MPa for times of 6 and 7 hours for couples involving the synthetic and the natural glasses, respectively. Melt migrated into the dunite during the course of the experiment, in order to decrease the interfacial free energy of the system. Melt migration profiles indicate that the amount of volatiles dissolved in the liquids investigated here has only a modest influence on (i) the rate of melt infiltration and (ii) the volume of melt that a rock can absorb.
2 citations