Eric Reusser

The influence of grain size on low‐temperature degradation of dental zirconia

UNLABELLED The purpose of this study was to evaluate the influence of grain size and air abrasion on low-temperature degradation (LTD) of yttria stabilized tetragonal zirconia polycrystalline (Y-TZP). Disc-shaped specimens were sintered at 1350, 1450, and 1600°C. Air abrasion was performed with different abrasive particles. The specimens were stored for 2 h at 134°C under 2.3 bar water vapor pressure. All specimens were characterized by X-ray powder diffraction analysis (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). Y-TZP sintered at a temperature of 1350°C did not undergo the t-m phase transformation during accelerated aging. The diffusion-controlled t-m phase transformation initiated with the specimens sintered at 1450°C. This transformation was remarkable for the specimens sintered at 1600°C. X-ray photoelectron spectroscopy (XPS) measurements did not confirm the generation of Zr-OH and Y-OH bonds. No increase of yttrium concentration on the grain boundaries of Y-TZP was detected, which could be responsible for the destabilization of dental zirconia ceramics. A slight increase of diffusion-controlled t-m phase transformations was observed for all abraded specimens sintered at 1350 and 1450°C. The size of abrasive particles did not play a crucial role on LTD of Y-TZP. The retardation of diffusion-controlled t-m phase transformation was evident for all abraded specimens sintered at 1600°C by comparison to non-abraded specimens. CONCLUSION The LTD of Y-TZP can be suppressed when the sintering temperature is set between 1350 and 1450°C.

Gas-driven filter pressing in magmas: Insights into in-situ melt segregation from crystal mushes

Gas-driven filter pressing is the process of melt expulsion from a volatile-saturated crystal mush, induced by the buildup and subsequent release of gas pressure. Filter pressing is inferred to play a major role in magma fractionation at shallow depths (<10 km) by moving melt and gas relative to the solid, crystalline framework. However, the magmatic conditions at which this process operates remain poorly constrained. We present novel experimental data that illustrate how the crystal content of the mush affects the ability of gas-driven filter pressing to segregate melt. Hydrous haplogranite (2.1 wt% water in the melt) and dacite (4.2 wt% water in the melt) crystal mushes, with a wide range of crystallinities (34–80 vol% crystals), were investigated using in-situ, high-temperature (500–800 °C) synchrotron X-ray tomographic microscopy with high spatial (3 μm/pixel) and temporal resolution (∼8 s per three-dimensional data set). Our experimental results show that gas-driven filter pressing operates only below the maximum packing of bubbles and crystals (∼74 vol%). Above this threshold, the mush tends to fracture and gas escapes via fractures. Therefore, the efficiency of gas-driven filter pressing is promoted close to the percolation threshold and in situations where a mush inflates slowly relative to build-up of pressure and expulsion of melt. Such observations offer a likely explanation for the production of eruptible, crystal-poor magmas within Earth’s crust.

Surface characterization of dental Y-TZP ceramic after air abrasion treatment.

OBJECTIVE The aim of this study was to characterize the surface of Y-TZP after abrasion with various airborne particles. METHODS The Y-TZP blanks were cut into 44 discs and sintered according to the manufacturers instructions. The specimens were treated as follows: (a) control specimens, (b) abraded with 50μm alumina, (c) abraded with 110μm alumina, (d) abraded with 30μm silica-coated alumina, (e) abraded with 110μm silica-coated alumina, (f) abraded with 110μm alumina followed by 110μm silica-coated alumina particles. Airborne abrasion was performed at a pressure of 2.5bar for 15s/cm(2). The Y-TZP was characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and X-ray diffraction analysis (XRD). RESULTS Surface morphology of Y-TZP ceramic was changed after the airborne abrasion process compared to the control specimens. The grain boundaries disappeared and part of the airborne particles are embedded and/or rested on the ceramic surfaces. The elemental composition of the Y-TZP surface after the airborne abrasion process depended on the type and size of these particles. The concentration of Si resulted higher after the airborne abrasion process with 110μm alumina followed by 110μm silica-coated alumina particles in comparison to the specimens abraded with 110μm silica-coated alumina particles. The ratio of elements normalized by yttrium for these specimens was: [Zr]/[Y]/[Al]/[Si]=15.2/1.0/26.0/73.6, respectively. CONCLUSION The change of grain topography occurred during each impact process. Silica nano-particles covered not only loosely the abraded ceramic surface after abrasion process, but the release of kinetic energy in form of thermal energy resulted in melting of the ceramic surface and in the formation of zirconium silicate.

Equation of state, refractive index and polarizability of compressed water to 7 GPa and 673 K

The equation of state (EoS), refractive index n, and polarizability α of water have been determined up to 673 K and 7 GPa from acoustic velocity measurements conducted in a resistively heated diamond anvil cell using Brillouin scattering spectroscopy. Measured acoustic velocities compare favorably with previous experimental studies but they are lower than velocities calculated from the extrapolation of the IAPWS95 equation of state above 3 GPa at 673 K and deviations increase up to 6% at 7 GPa. Densities calculated from the velocity data were used to propose an empirical EoS suitable in the 0.6-7 GPa and 293-673 K range with a total estimated uncertainty of 0.5% or less. The density model and thermodynamic properties derived from the experimental EoS have been compared to several EoS proposed in the literature. The IAPWS95 EoS provides good agreement, although underestimates density by up to 1.2% at 7 GPa and 673 K and the thermodynamic properties deviate greatly (10%-20%) outside the estimated uncertainties above 4 GPa. The refractive index n of liquid water increases linearly with density and do not depend intrinsically on temperature. The polarizability decreases with pressure by less than 4% within the investigated P-T range, suggesting strong intermolecular interactions in H(2)O that are consistent with the prevalence of the hydrogen bond network in the fluid. The results will allow the refinement of interaction potentials that consider polarization effects for a better understanding of solvent-solvent and ion-solvent interactions in aqueous fluids at high pressure and temperature conditions.

Anisotropy of magnetic susceptibility in natural olivine single crystals

Mantle flow dynamics can cause preferential alignment of olivine crystals that results in anisotropy of physical properties. To interpret anisotropy in mantle rocks, it is necessary to understand the anisotropy of olivine single crystals. We determined anisotropy of magnetic susceptibility (AMS) for natural olivine crystals. High-field AMS allows for the isolation of the anisotropy due to olivine alone. The orientations of the principal susceptibility axes are related to the olivine’s crystallographic structure as soon as it contains >3 wt % FeO. The maximum susceptibility is parallel to the c axis both at room temperature (RT) and at 77 K. The orientation of the minimum axis at RT depends on iron content; it is generally parallel to the a axis in crystals with 3–5 wt % FeO, and along b in samples with 6–10 wt % FeO. The AMS ellipsoid is prolate and the standard deviatoric susceptibility, k0, is on the order of 8*10210 m3/kg for the samples with <1wt % FeO, and ranges from 3.1*1029 m3/kg to 5.7*1029 m3/kg for samples with 3–10 wt % FeO. At 77 K, the minimum susceptibility is along b, independent of iron content. The shape of the AMS ellipsoid is prolate for samples with <5 wt % FeO, but can be prolate or oblate for higher iron content. The degree of anisotropy increases at 77 K with p0 7757.160.5. The results from this study will allow AMS fabrics to be used as a proxy for olivine texture in ultramafic rocks with high olivine content.

Development and characterization of custom-engineered and compacted nanoparticles as calibration materials for quantification using LA-ICP-MS

The flame spray technique was used to produce a nano-material with a customized composition. Liquid organic precursors of Si, Ca, Ti, Mg, Fe, and Al in a concentration similar to the matrix of the well-known NIST SRM 610 glass standard were mixed with a selection of rare earth elements (Ce, Gd, Ho, and Tb), precious metals (Ag, Au, Pd, Pt, Rh, and Ru) and Pb at concentrations of approx. 400–500 mg kg−1. The liquid precursor mixture was sprayed and collected as nanopowder, compacted to pellets and analyzed by solution and laser-ablation inductively coupled plasma mass spectrometry. The bulk composition of the material was determined in several aliquots of the powder, either 25 mg or 50 mg. Electron microprobe analyses were carried out to further characterize the major element composition of the pressed nano-material. The pellet was ablated using different laser ablation systems with an aim of assessing the micro-scale homogeneity of the produced material. The manufactured material is homogeneous for major elements and REEs similar to the NIST glass (<5% RSD). However, the distribution of the PGEs showed some larger spatial variation in the order of <7.5%. In addition it is shown that contamination during production leads to heterogeneous distribution of Pb and Ag. Based on the results achieved for Ru, Rh, Pd, Au, Pt, Mg, Ti, and Fe, which are either absent or not available in sufficient concentration levels in NIST glass, it is demonstrated that flame spray synthesis allows production of suitable customized matrix-matched calibration materials for micro-analytical techniques.

Thermodynamic properties of aqueous sodium sulfate solutions to 773 K and 3 GPa derived from acoustic velocity measurements in the diamond anvil cell.

The thermodynamic properties of a 1 m Na(2)SO(4) solution have been determined to 773 K and 3 GPa from acoustic velocity measurements in externally heated diamond anvil cell using Brillouin spectroscopy. The measured acoustic velocities were inverted to obtain the density of the aqueous electrolyte solution with an accuracy of 0.3%-0.5%, and an equation of state (EoS) valid in the 293-773 K and 0.4-3 GPa range is proposed. The new EoS reproduces the experimental acoustic velocity data with a maximal deviation of 1.5% and allows deriving all thermodynamic properties of the aqueous solution, including isobaric heat capacity (C(P)), thermal expansion (α(P)), and compressibility (β) with an accuracy better than 3%-8%. The addition of dissolved sulfate species decreases the compressibility of water, consistent with the structure-maker character of SO(4)(2-) ions in solution that enhance the hydrogen-bond network of the solvent.

Assessment of the diamond-trap method for studying high-pressure fluids and melts and an improved freezing stage design for laser ablation ICP-MS analysis

Abstract Diamond-trap experiments in combination with laser ablation ICP-MS analyses of frozen samples have been used to directly determine the composition of fluids and melts in equilibrium with crust and mantle mineral assemblages. Here we: (1) describe an improved freezing cell that utilizes electronic cooling elements to facilitate routine laser ablation measurement on diamond traps and (2) demonstrate that the major element stoichiometry of subsolidus aqueous fluids in equilibrium with crystalline mineral assemblages can be measured using the diamond-trap method with comparable precision and accuracy to single-crystal weight-loss experiments

Growth and alteration of uranium-rich microlite

Uranium-rich microlite, a pyrochlore-group mineral, occurs in 440 Ma old lithium pegmatites of the Mozambique Belt in East Africa. Microlite exhibits a pronounced growth zoning, with a U-free core surrounded by a U-rich rim (UO{sub 2} up to 17 wt.%). The core exhibits conjugate sets of straight cracks (cleavage planes) which provided pathways for a late-stage U-enriched pegmatitic fluid which interacted with the U-free microlite to produce a distinct U enrichment along the cracks and led to the formation of the U-rich rim. Following the stage of U incorporation into microlite, a second generation of hydrothermal fluids deposited mica along the cleavage planes. Subsequent to these two hydrothermal stages, the host rock was uplifted and subjected to intense low-temperature alteration during which Na, Ca and F were leached from the microlite crystals. This alteration also led to a hydration of microlite, but there is no evidence of U loss. These low-temperature alteration effects were only observed in the U-rich rim which is characterized by a large number of irregular cracks which are most probably the result of metamictization, as indicated by electron diffraction images and powder X-ray patterns. The pyrochlore-group minerals provide excellent natural analogues for pyrochlore-based nuclear waste forms, because samples of variable age and with high actinide contents are available.

Geikielite exsolution in spinel

Abstract Euhedral crystals of purple spinel are associated with calcite and forsterite in the central zone of composite metasomatic veins of the Adamello contact aureole (Northern Italy). In thin section, spinel is generally colorless, but exhibits concentric zones of dark brown color. These zones are aligned parallel to prominent crystal faces and contain abundant anisotropic, lath-shaped inclusions with their long axis oriented in the six <110> directions of spinel. This orientation results from the alignment of {001}Geik and the {111}Sp crystallographic planes. The small (up to approximately 20 × 1 μm) inclusions were identified as geikielite by means of element distribution maps, micro-Raman spectroscopy, and transmission electron microscopy. Electron microprobe data revealed that spinel consists mainly of MgAl2O4, with only minor amounts of other components. The overall chemical variation within individual crystals is characterized by a continuous increase in FeOtot and ZnO from center to rim (0.6-2.1 wt% and <0.1-1.0 wt%, respectively). Whereas V2O3 is relatively constant (0.15 wt%), the bulk TiO2 concentration (analysis spot: 20 μm diameter) increases in general from center (0.12 wt%) to rim (1.2 wt%). This variation, however, is marked by several discontinuities that correspond to the zones containing geikielite inclusions. Where geikielite occurs, the spinel matrix is depleted in Ti relative to the inclusion-free zones. Geikielite was analyzed by analytical electron microscopy and has the formula Mg0.83Fe0.15Mn0.02(Ti0.99Fe0.01)O3. The textural relationships between geikielite inclusions and spinel matrix, combined with the analytical data, suggest that geikielite laths represent exsolution features, thus, a miscibility gap exists between Mg-Al-spinel and geikielite. The purple color results from scattering of light by the geikielite inclusions. Spinel with similar features was also observed in metasomatic veins of the Bergell contact aureole (Italy) and in granulite-facies marbles of Southern India.