Richard Walshaw

Electrochemical studies of iron meteorites: phosphorus redox chemistry on the early Earth

The mineral schreibersite, (Fe,Ni)(3)P, a ubiquitous component of iron meteorites. is known to undergo anoxic hydrolytic modification to afford a range Of phosphorus oxyacids. H-phosphonic acid (H3PO3) is the principal hydrolytic product under hydrothermal conditions, as confirmed here by P-31-NMR spectroscopic studies oil shavings of the Seymchan pallasite (Magadan, Russia, 1967), but in the presence of photochemical irradiation I more reduced derivative, H-phosphinic (H3PO2) acid, dominates. The significance Of Such lower oxidation state oxyacids of phosphorus to prebiotic chemistry upon the early Earth lies with the facts that Such forms Of Phosphorus are considerably more Soluble and chemically reactive than orthophosphate, the commonly found form of phosphorus oil Earth, thus allowing nature a mechanism to circumvent the so-called Phosphate Problem. This paper describes the Galvanic corrosion of Fe3P, a hydrolytic modification pathway for schreibersite, leading again to H-phosphinic acid as the key P-containing product. We envisage this pathway to be highly significant within a meteoritic context as iron meteorites are polymetallic composites in which dissimilar metals, with different electrochemical potentials, are connected by all electrically conducting matrix. In the presence of a Suitable electrolyte medium, i.e., salt water, galvanic corrosion call take place. In addition to model electrochemical studies, we also report the first application of the Kelvin technique to map surface potentials of a meteorite sample that allows the electrochemical differentiation of schreibersite inclusions Within an Fe:Ni matrix. Such experiments, coupled with thermodynamic calculations, may allow LIS to better understand the chemical redox behaviour of meteoritic components with early Earth environments.

Dating of crustal fluid flow by the Rb-Sr isotopic analysis of sphalerite: a review

Abstract The sphalerite Rb-Sr isochron technique is a relatively new and powerful geochronological tool allowing the direct dating of zinc sulphide mineralization. Recently, insights have been gained into the Rb-Sr isotope systematics of sphalerite, in particular the crystallographic residence sites of Rb and Sr and the mechanisms by which the Rb/Sr ratio of sphalerite is fractionated over that of its parent hydrothermal fluid. This, along with independent testing against three other dating techniques, has resulted in the vindication of the sphalerite Rb-Sr isochron technique. The resultant isochron ages have allowed very precise chronological constraints to be placed on the genesis of American and Australian Mississippi Valley-type deposits, greatly reducing the controversy which has surrounded this class of base metal deposit.

Electric-field-induced phase switching in textured Ba-doped bismuth ferrite lead titanate

The template grain growth technique was used to synthesis textured 60BiFeO3-PbTiO3 (60:40BFPT) by using platelets of BaTiO3 as template. Synchrotron measurement clearly showed textured 60:40BFPT. Moreover, in situ high energy synchrotron radiation was employed to investigate the influence of an external electric filed on crystallographic structure of mixed phase 60:40BFPT. Application of an electric field ≥ 1 kV/mm resulted in phase transformation from mixed rhombohedral/tetragonal phases (≈ 73.5% tetragonal / 26.5% rhombohedral) to predominately tetragonal phase (≈ 95%) at applied field of 6 kV/mm.