Anke Wohlers

Paul Scherrer Institut PSI

Diamond's intrinsic hardness, excellent thermal conductivity and low atomic number make it a highly promising candidate as a plasma facing material. However, as with the previously used graphite, concerns over tritium retention and resultant chemical etching have so far limited research interest in the use of synthetic diamond. In order to study tr...

Molybdenum is used as plasma-facing material in tokamaks and as material for plasma optical diagnostics mirrors. Harsh conditions of neutron irradiation, exposure to hydrogen isotopes and helium ions, and high operating temperatures result in degradation of the molybdenum surface and ultimately limit their lifetime in a fusion power plant. In the c...

The ITER Tokamak Exhaust Processing (TEP) system relies on palladium membrane reactors (PMRs) for tritium recovery. The PMR consists of a palladium/silver membrane permeator filled with a catalyst, that can be used to recover hydrogen species (most importantly tritium) from methane and water impurities present in fusion reactor exhaust emissions. T...

We have performed experiments at 1.5 GPa over the temperature range 1400-2100°C to determine the partitioning of lithophile elements (U, Th, Eu, Sm, Nd, Zr, La, Ce, Yb) between sulfide liquid, low-S metals and silicate melt. The data demonstrate pronounced increases in partitioning of all the lithophile elements into sulfide at very low FeO content...

Recent (142)Nd isotope data indicate that the silicate Earth (its crust plus the mantle) has a samarium to neodymium elemental ratio (Sm/Nd) that is greater than that of the supposed chondritic building blocks of the planet. This elevated Sm/Nd has been ascribed either to a 'hidden' reservoir in the Earth or to loss of an early-formed terrestrial c...

Melt infiltration into quartzite took place due to generation and migration of partial melts within the high‐grade metamorphic rocks of the Big Cottonwood (BC) formation in the Little Cottonwood contact aureole (UT, USA). Melt was produced by muscovite and biotite dehydration melting reactions in the BC formation, which contains pelite and quartzit...

Aluminum is commonly regarded as one of the least soluble elements during metamorphic and metasomatic processes. However, abundant field evidence suggests that aluminum transport can occur in natural hydrothermal processes. For example, late formed aluminumsilicate-bearing and muscovite-bearing veins are widely observed in high-grade metamorphic ro...

Cylinders of synthetic periclase single crystals were annealed at 0.15–0.5 GPa and 900–1200 °C under water-saturated conditions for 45 min to 72 h. Infrared spectra measured on the quenched products show bands at 3,297 and 3,312 cm−1 indicating V OH− centers (OH-defect stretching vibrations in a half-compensated cation vacancy) in the MgO structur...

The solubilities of the assemblages albite + paragonite + quartz and jadeite + paragonite + quartz in H 2 O were deter-mined at 500 and 600 °C, 1.0–2.25 GPa, using hydrothermal piston-cylinder methods. The three minerals are isobarically and isothermally invariant in the presence of H 2 O, so fluid composition is uniquely determined at each pressur...

Aqueous fluids released due to dehydration reactions at the surface of a subducted slab at the blueschist-eclogite transition are predicted to be highly concentrated and capable of major mass tranfer. To estimate the initial composition of an aqueous fluid associated with high-pressure metamorpism we determined the solubility of albite (Ab) or jade...

The solubility of corundum in aqueous KOH solutions was measured at 700 °C and 1 GPa, using a piston-cylinder apparatus and a weight-loss method. Total potassium molality (mK) ranged from 0.0011 to 3.9. At the lowest mK, corundum solubility (mAl) was 0.0016 ± 0.0004 molal, which is slightly higher than that in pure H2O at the same conditions (0.001...

High pressure, low temperature conditions prevail at the surface of a subducted slab, where aqueous fluids released during dehydration reactions play an important role in mass transfer. To model the composition of aqueous fluids produced near the blueschist-to-eclogite transition, we investigated the solubility of albite+quartz, jadeite+quartz in H...

High P and T fluids associated with metamorphism and magmatism play an important role in crustal evolution and mass transfer. To understand aqueous fluids associated with model granitic crust at high P and T, we investigated the solubilities of K-feldspar (Ksp), muscovite (ms) and corundum (co) in H2O at 700°C and 10 kbar. Starting materials of nat...

Fluids associated with high-pressure metamorphism and magmatism play an important role in crustal evolution. However, the compositions of such fluids are poorly known. As an initial step toward characterizing fluids associated with average granitic, continental crust, we determined the solubility behavior of K-feldspar (K-fsp), muscovite (ms) and c...

We present 3D X-ray computer tomography of shape and distribution of oxide minerals in pelite cores which were partially molten at P = 2kbar, T = 700° C, 750° C and 800° C for different run durations (76-508hrs). X-ray absorption images were obtained of the sample in steps of 0.68 and 0.90° for a total rotation of 360° . X-ray tube conditions of 40...

Micro X-ray tomography is rapidly advancing to an important tool for non-destructive 3-D imaging of geological and engineering materials. We have been using a Skyscan 1072 system (Skyscan, Belgium) to successfully image as diverse geological materials as sandstones, foraminifers, run products of hydrothermal partial melting experiments, and metamor...

Experimental studies of melt segregation models for volatile phase-absent melting concluded that deformation and volume change due to hydrate breakdown are the driving force for melt migration. Volume increases can lead to micro crack formation, and additional deformation facilitates melt extraction. We performed cold-seal experiments on fine-grain...