Rupert Hochleitner

Mechanical properties of modern calcite- (Mergerlia truncata) and phosphate-shelled brachiopods (Discradisca stella and Lingula anatina)determined by nanoindentation

We measured distribution patterns of hardness and elastic modulus by nanoindentation on shells of the rhynchonelliform brachiopod Mergerlia truncata and the linguliform brachiopods Discradisca stella and Lingula anatina. The rhynchonelliformea produce calcitic shells while the linguliformea produce chitinophosphatic shells. Dorsal and ventral valves, commissure and hinge of the calcitic shell of M. truncata show different nanohardness values (from 2.3 to 4.6 GPa) and E-modulus (from 52 to 76 GPa). The hardness of the biocalcite is always increased compared to inorganic calcite. We attribute the effects to different amounts of inter- and intracrystalline organic matrix. Profiles parallel to the radius of curvature of the valves cutting through the different layers of shell material surprisingly show quite uniform values of nanohardness and modulus of elasticity. Nanoindentation tests on the chitinophosphatic brachiopods D. stella and L. anatina reflect the hierarchical structure composed of laminae with varying degree of mineralization. As a result of the two-phase composite of biopolymer nanofibrils reinforced with Ca-phosphate nanoparticles, nanohardness, and E-modulus correlate almost linearly from (H=0.25 GPa, E=2.5 GPa) to (H=2.5 GPa, E=50 GPa). The mineral provides stiffness and hardness, the biopolymer provides flexibility; and the composite provides fracture toughness. Gradients in the degree of mineralization reduce potential stress concentrations at the interface between stiff mineralized and soft non-mineralized laminae. For the epibenthic chitinophosphatic D. stella the lamination is also present but less pronounced than for the infaunal L. anatina, and the overall distribution of material strength in the cross-sectional profile shows a maximum in the center and a decrease towards the inner and outer shell margins (modulus of elasticity from 30 to 12 GPa, hardness from 1.7 to 0.5 GPa). Accordingly, the two epibenthic forms, calcitic M. truncata and chitinophosphatic D. stella display fairly bulky (homogeneous) nanomechanical properties of their shell materials, while the burrowing infaunal L. anatina is distinctively laminated. The strongly mineralized laminae, which provide the strength to the shell, are also brittle, but keeping them as thin as possible, allows some bending flexibility. This flexibility is not required for the epibenthic life style.

Über den transport von Wolfram und den Absatz von Wolfram-Doppel-Oxiden in fluiden wässrigen Lösungen

Zusammenfassung Mit bisher bekannten therodynamischen Daten wird der Transport von W in wassrigen Gasphasen bei und oberhalb von 500°C untersucht, der als Fluorid, und Oxifluorid moglich ist. Der Absatz von Wolfiramit erfolgt mit sinkender Temperatur und sinkendem Druck. Die Stabilitaten von Wolframaten in hydrothermalen Losungen werden fur den Temperaturbereich bis 300°C untersucht durch Eh-pH-Diagramme, Austauschreaktionen von Wolframaten mit Oxiden, Sulfiden und gelosten lonen. Fe2WO6 wird gegen Fe2O3 + WO3 oberhalb von 126°C stabil. Bei 300°C ist sein Stabilitatsbereich bei sehr hohen, in wassrigen endogenen Losungen nicht verwirklichten pO2-Bereichen. Infolge der auβerordentlich kleinen Freien Enthalpien von MgWO4, CaWO4 und BaWO4 sollten MgWO4 und BaWO4 als Mineralien wesentlich wichtiger sein als Wolframit, wenn Mg und Ba zugleich mit W in den Losungen sind. Ebenso sollten Spurengehalte von Co und Ni in Wolframit nachweisbar Scin, wenn zugleich mit W, Co und Ni in genugend groβen Konzentrationen gelost sind.

New Raman Spectroscopic Data of the Almahata Sitta Meteorite

ABSTRACT Raman spectroscopy is a convenient method to classify polytypes plus polymorphs and to investigate different compositions, structures, and modifications of minerals. This information is required to classify meteorites of different mineral compositions. Our intention was to examine different graphite modifications and to determine the opaque phases within the Almahatta Sitta (AS) meteorite. Our investigation focused on specimens AS39 and AS4. Both are multicomponent breccias, composed of different meteoritic lithologies, that is, anomalous polymict ureilite material, different types of chondrites, and an iron meteorite.[ 1-5 ] The mix of material implicates a crash of variable asteroids within time and space. This means that a primary ureilitic asteroid body has been the target of multiple meteorite or asteroid impacts, which did not completely destroy the asteroid but added new material (from chondritic to iron) to the main mass. For instance, Gabriel and Pack[ 6 ] suggested that the vein metal of monomict ureilites is introduced by the impact of a Ni-poor iron meteorite in a similar scenario as described above. Raman spectroscopy helped to investigate different carbon materials, that is, graphite and diamond. We used single-spectrum acquisition and spatial mappings to identify the different modifications. Furthermore, we classified minor opaque phases such as schreibersite, suessite, daubreelite, cohenite, and kamacite. The investigation of these opaque phases is dealt with in further papers.[1,2]

Electrical properties of rutile-type relaxor ferroelectric-like Fe0.9W0.05TiMO6 (M = Ta,Nb) ceramics

Electrical properties of rutile-type

Electrical conductivity, thermopower and 57Fe Mössbauer spectroscopy of an Fe-rich amphibole, arfvedsonite

\mathrm {Fe}_{0.9}{\kern 1pt} \mathrm {W}_{0.05}\\\mathrm {TiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})

Electrical properties of rutile-type In(Al) 0.025Nb 0.025Ti 0.95O2 ceramics

ceramics were measured at and above room temperature and the results are compared with those gained previously on rutile-type relaxor ferroelectrics

Electrical properties and Mössbauer spectra of rutile-type Fe1−xMnxTiTaO6 (0 ≤ x ≤ 0.3) ceramics

\mathrm {FeTiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})

Crystal chemistry of Xonotlite Ca6Si6O 17(OH)2 Part I: Determination of polytypes using X-Ray Powder Diffraction (XRPD)

. The aliovalent

Isokite, CaMg [FIPO4], from Senhora de Assunção, Portugal: New find and new data

{\rm W}^{6+}

Heterogeneous equilibria in the Wolframite group [Heterogene Gleichgewichte in der Wolframitgruppe]

cationsin the current compounds might change the suggested polar nanodomains, giving rise to very high dielectric constant