Solidification and fcc to metastable hcp phase transition in krypton under variable compression rates

We present time-resolved synchrotron x-ray diffraction measurements to study kinetics associated with theliquid-solid and solid-solid high-pressure phase transitions in Kr under dynamic loading in a dynamic-diamondanvil cell. The results show a strong compression-rate dependence of the solidification/melting process in liquidKr. The analysis of the compression-rate dependent melting/solidification, using an Avrami equation with theparameter n = 1, indicates a spontaneous nucleation and one-dimensional growth mechanism. In contrast, theface-centered-cubic to metastable hexagonal close-packed transition in solid Kr occurs rapidly at 0.8 GPa nearthemelting line, which has negligible compression-rate dependence within the range of compression rates studied(0.004–13 GPa/s)

Fullerene formation in sputtering and electron beam evaporation processes

The authors report the formation of fullerenes from graphite by sputtering and electron beam evaporation. Under conditions that differ dramatically from those in the previously known fullerene production processes, the new methods preferentially yield the soluble higher fullerenes C70, C76, C78, and C84 in addition to minor amounts of C60 only. Upon passage of carbon particles formed by electron beam evaporation through an electrostatic field, fullerenes are mainly isolated from the cathode, not from the anode, which supports the formation of cationic intermediates in fullerene growth mechanisms. The variables thought to be important for fullerene production can be controlled efficiently in the new processes

A role for subducted super-hydrated kaolinite in Earth’s deep water cycle

Water is the most abundant volatile component in the Earth. It continuously enters the mantle through subduction zones,where it reduces the melting temperature of rocks to generate magmas. The dehydration process in subduction zones, whichdetermines whether water is released from the slab or transported into the deeper mantle, is an essential component of thedeep water cycle. Here we use in situ and time-resolved high-pressure/high-temperature synchrotron X-ray diffraction andinfrared spectra to characterize the structural and chemical changes of the clay mineral kaolinite. At conditions correspondingto a depth of about 75 km in a cold subducting slab (2.7 GPa and 200 °C), and in the presence of water, we observe thepressure-induced insertion of water into kaolinite. This super-hydrated phase has a unit cell volume that is about 31% larger,a density that is about 8.4% lower than the original kaolinite and, with 29 wt% H$_2$O, the highest water content of any known aluminosilicatemineral in the Earth. As pressure and temperature approach 19 GPa and about 800 °C, we observe the sequentialbreakdown of super-hydrated kaolinite. The formation and subsequent breakdown of super-hydrated kaolinite in cold slabssubducted below 200 km leads to the release of water that may affect seismicity and help fuel arc volcanism at the surface

Dynamic diamond anvil cell (dDAC): a novel device for studying the dynamic-pressure properties of materials

We have developed a unique device, a dynamic diamond anvil cell (dDAC), which repetitively applies a time-dependent load/pressure profile to a sample. This capability allows studies of the kinetics of phase transitions and metastable phases at compression (strain) rates of up to 500 GPa/s (approximately 0.16 s(-1) for a metal). Our approach adapts electromechanical piezoelectric actuators to a conventional diamond anvil cell design, which enables precise specification and control of a time-dependent applied load/pressure. Existing DAC instrumentation and experimental techniques are easily adapted to the dDAC to measure the properties of a sample under the varying load/pressure conditions. This capability addresses the sparsely studied regime of dynamic phenomena between static research (diamond anvil cells and large volume presses) and dynamic shock-driven experiments (gas guns, explosive, and laser shock). We present an overview of a variety of experimental measurements that can be made with this device

The stability of subducted glaucophane with the Earth’s secular cooling

The blueschist to eclogite transition is one of the major geochemical–metamorphic processes typifying the subduction zone, which releases fluids triggering earthquakes and arc volcanism. Although glaucophane is an index hydrous mineral for the blueschist facies, its stability at mantle depths in diverse subduction regimes of contemporary and early Earth has not been experimentally determined. Here, we show that the maximum depth of glaucophane stability increases with decreasing thermal gradients of the subduction system. Along cold subduction geotherm, glaucophane remains stable down ca. 240 km depth, whereas it dehydrates and breaks down at as shallow as ca. 40 km depth under warm subduction geotherm or the Proterozoic tectonic setting. Our results imply that secular cooling of the Earth has extended the stability of glaucophane and consequently enabled the transportation of water into deeper interior of the Earth, suppressing arc magmatism, volcanism, and seismic activities along subduction zones