The ferric/ferrous ratio in basalt melts at different oxygen pressures

Samples of two types of natural basalt were equilibrated over a range of oxygen pressures at four different temperatures, and then quenched to room temperature. Except at the lowest temperature, where magnetic crystals formed under the most oxidizing conditions, totally amorphous samples were obtained. The Mössbauer spectra of 45 samples of the quenched basaltic melts were measured at room temperature. The relationship obtained between the oxidation state and oxygen fugacity differs to some extent from those relations previously described in the literature, in not yielding a linear relationship between log(farric/ferrous) and log(fo₂). This might indicate a more involved redox process than that described by a simple reaction between oxides and/or the influence of the cation composition in the process of glass formation. An investigation was made of the kinetics of the redox process. For the experimental setup used, redox equilibrium would be reached within three hours. Finally, three naturally quenched basalt glasses were analyzed for comparison; two showed lower oxidation states than previously found in Icelandic rocks.     

Structural properties of the progressive hedging algorithm

This short note discusses some structural properties of the progressive hedging algorithm. It is based on the finite case, but allows for event trees that are unbalanced and where the nodes can have a varying number of children. Generic procedures and a generic record definition for the algorithms are presented.     

Maghemite in basalt studied by Mössbauer spectroscopy in external magnetic field

In the present study, we investigate the feasibility of detecting and determining the presence of maghemite in rock samples, by obtaining Mössbauer spectra in an external magnetic field of 1.6 T at room temperature. The interaction of the external magnetic field and the magnetic moments of the sublattices will induce differential shifts in the peak positions. By this method, we can assign some lower limit of the amount of maghemite in the sample. The results are compared with a model for a mixture of maghemite and stoichiometric magnetite.     

Influences of Electrolytes, Polymers and a Surfactant on Rheological Properties of Bentonite–Water Systems

Characteristic rheological properties, such as viscosity, shear stress, yield point, gel strength and thixotropy, of natural Ca- bentonite and Na-peptized bentonite were studied after adding LiCl, KCl, CaCl2, MgCl2·6H2O electrolytes; (NaPO3)n, polyvinyl pyrolidone (PVP) polymers and an anionic surfactant (linear alkyl benzene sulphonate, LABS). Changes in flow properties under the influence of various additives at different quantities were investigated in these slurries. The experimental results are discussed in terms of bentonite forms, types and concentrations of additives and influence of exchangeable cations. Bivalent and monovalent cations display entirely different rheological properties in two groups of muds. Furthermore, the difference in the degree of activity of PVP polymer on the viscosity of two mud systems depend on the clay mineral structure. The slurry prepared with Na-bentonite contains a minimum number of tactoids and a maximum number of sheet-bearing clay particles, which reduces the surface area of the clay minerals and increases viscosity by adding PVP polymer.     

Characterization of burned soil profiles by Mössbauer spectroscopy

The characteristics of both natural burned and experimentally burned soil profiles as seen by Mössbauer spectroscopy are described. The results help in the identification of profiles where biological and/or chemical processes may have been involved.     

57Fe Mössbauer Studies of the Bulky Ring-Substituted Ferrocenes; [C5Me4(p-C6H4Y)]2Fe

A series of bulky ring-substituted ferrocenes [⁵-C₅Me₄(p-C₆H₄Y)]₂Fe (Y = H, Me, OMe, F, Cl or CF₃) or (Cp^xpy )₂Fe has been synthesized and studied by ⁵⁷Fe Mössbauer spectroscopy at different temperatures. The hyperfine parameters for all the samples are almost identical, except for Y = H, (Cp^xph )₂Fe, where the quadrupole splitting (QS) is significantly larger. The X-ray crystal structure was determined for (Cp^xph )₂Fe, (Cp^xpcl )₂Fe and (Cp^xpom )₂Fe. Two different orientations of the C₆H₄Y rings are observed in the molecular structures; a perpendicular one for (Cp^xph )₂Fe and a parallel one for (Cp^xpcl )₂Fe and (Cp^xpom )₂Fe. However, this structural difference is not reflected in a study on the temperature dependency of the recoil free fraction of these three ferrocenes.     

Processes in Geophysics Studied by Mössbauer Spectroscopy

Time Differential gamma–gamma Perturbed Angular Correlation spectroscopy has traditionally been done using scintillation detectors along with constant–fraction discriminators, spectroscopy amplifiers, single channel analyzers, and time to amplitude detectors. We describe a new generation spectrometer where these electronics are replaced by high speed digital transient recorders that record the output from each scintillation detector. The energy and time-of-arrival of gamma rays in any detector can be determined accurately. Many experimental difficulties related to electronics are eliminated; the number of detectors can be increased with no increase in complexity of the apparatus; coincidences among any two detectors are measurable; and coincidences separated by as little as a ns are detectable in principle within one detector. All energies are collected, and energy windows are imposed by software filtering, permitting both high energy resolution and high data-gathering power.