Progress on Developing a High Temperature Zr, Y-oxide pH Sensor

Gene C. Ulmer (gulmer@astro.ocis.temple.edu)¹, David E. Grandstaff (grand@vm.temple.edu)¹, Mark Manna (wat_wace@hotmail.com), Ed Vicenzi (evicinzi@volcano.si.edu)², Serguei Lvov (lvov@essc.psu.edu), Hubert L. Barnes (barnes@geosc.psu.edu), X. Zhou (xzhou@essc.psu.edu) & Sergei Ulyanov (smu3@email.psu.edu)

¹ Geology Dept., Temple University, Rm 303 Beury Hall, Philadelphia, PA 19122, USA

² Department of Mineral Science, Smithsonian Institution, Washington, D.C. 20560, USA

Cubic ZrO₂, stabilized by > 8 mole% Y₂O₃, has long been known to be electrolytically responsive to fO₂, but only since 1980 has its sensitivity to pH been reported (Niedrach, 1980a and b and 1981). Its advantages as a hydrothermal pH sensor, even for supercritical fluids, are due to chemical inertness, potentiometric response as a specific ion concentration cell, high-temperature Nernstian behavior, and capability to be formed into pure ceramic geometric shapes for durable sensors.

To test its behavior, an electrochemical module with four access/insertion ports has been developed and used up to 23 MPa and to 400°C to compare, in pumped-flow-through mode, zirconia cells with standard H₂(Pt) electrodes. Both types of sensor allow measurements of pH accurate to 0.05 pH units or better. For example, the association constant of HCl(aq) at a temperature of 320^oC derived from our measurements is in good agreement with a regression equation from compiled literature data (Lvov et al., in press). The flow-through design apparently minimizes interference from both contamination and the Soret effect.

Examination of commercially available stabilized ZrO₂ suitable for durable pH sensors reveals that these are far from ideal, both texturally and compositionally. Impurity phases, sometimes purposely added as fluxes to aid in the sintering/firing of the ZrO₂ ceramics, cause premature hydrothermal decay and loss of the integrity of the sensor. While this decay is slow enough to permit some successful measurements as described above, the desire for robust, long-term-'down-hole' utility of these sensors has stimulated more developmental research employing hot isostatic pressing for fabrication of compositionally and texturally improved yttria-stabilized ZrO₂.

Lvov SN, Zhou XY, Ulyanov SM, Bandura AV, Chem. Geol, (in press).

Niedrach LW, J. Electrochem. Soc, 127, 2122-2130, (1980a).

Niedrach LW, Science, 207, 1200-1202, (1980b).

Niedrach LW, U. S. Patent 4,264,424; Assignee:General Electric Corp, 8 pp & 5 drawings, (1981).

New Aspects for the Interpretation of High-pressure Experiments Containing Hydrous Fluid

Peter Ulmer (pulmer@erdw.ethz.ch) & Roland Stalder (stalder@erdw.ethz.ch)

Department of Earth Sciences, ETH-Zentrum, CH-8092 Zurich, Switzerland

Numerous high-pressure experimental studies have been performed to constrain the stability of hydrous phases in mantle-like bulk compositions. Despite the large number of studies conducted with sophisticated experimental equipment, large, yet unresolved discrepancies exist in the stability of the principal hydrous phases such as talc, serpentine, and the DHMS phases.

Most studies at high-pressure were either straight forward synthesis experiments or 'reversal' experiments to determine phase boundaries were reactants were mixed in equal proportions and the stable parageneses at a given P and T was determined by X-ray powder diffraction. In many studies more phases than the phase rule allow have been observed over large P-T ranges.

The recovered charges of a study on the stability of post serpentine phases in the MgO-SiO₂-H₂O have been sectioned longitudinally and analyzed by optical microscopy, micro-Raman spectroscopy and EMP analyses. We observed a strong zoning of the charges. The hydrous fluid is concentrated at the top of the capsule and along the capsule wall. The hydrous phases are mostly concentrated at the interface between fluid and the anhydrous solids. The phase separation is probably driven by density contrast and the different dihedral angles between fluid and the capsule and between fluid and the silicate phases. A single experiment often covered an entire cross-section through the MSH composition space ranging from the anhydrous MgO - SiO₂ join to the join were fluid coexists with the most hydrated MSH-phases. The anhydrous parageneses and the fluid quench generally occupy by far the largest volume of the capsule and the hydrate-bearing zones are very small. X-ray powder diffraction analyses of such charges would indicate stability of the anhydrous parageneses as they provide by far the largest contribution to the X-ray pattern. As a consequence the stability fields of hydrous phases in mantle-like bulk compositions have strongly been underestimated (e.g. OH-clinohumite).

New Geochemical Data on the Central Pontide Magmatism, the Devrekani Granitoid, N Turkey

Timur Ustaömer (timur@istanbul.edu.tr) & P. Ayda Ustaömer (petekayd@istanbul.edu.tr)

Istanbul Universitesi, Jeoloji Mühendisligi Bölümü, 34850 Avcilar-Istanbul, Turkey

The Central Pontides of Northern Turkey comprises of pre-Late Jurassic oceanic assemblages, assembled by plate tectonic processes. These units are intruded by a number of granitoidic plutons in the northern areas and some of these are unconformably overlain by Late Jurassic basal conglomerates. One of the most southerly located of these is the Devrekani granitoid. The Devrekani granitoid is a tonalitic/dioritic intrusion. Plagioclase + alkali feldspar + amphibole + biotite ± quartz ± zircon ± apatite ± sphene mineral assemblage characterise the pluton. Textural characteristics suggest shallow depths of emplacement. Geochemical data show that the intrusion is an I-type granitoid, contaminated to some extent by continental crust. Tectonic discrimination diagrams imply genesis in a supra-subduction zone environment. Patterns in ORG-normalised spidergrams indicate genesis in an arc environment. Biotite chemistry data is compatible with those of arc type granitoids. Calcic amphibole palaeobarometry suggest very shallow depths of emplacement. The Devrekani granitoid is thought to have emplaced in an arc environment. Subduction responsible for the genesis of the arc magmatism is interpreted as the southward closing Küre back-arc basin.

Key Words: Granitoid intrusions, Central Pontides, Küre Basin, Palaeotethys