Aqueous alteration oxidizing conditions

Tomeoka K. and Buseck P. R. (1990) Phyllosilicates in the Mokoia CV carbonaceous chondrite evidence for aqueous alteration in an oxidizing condition. Geochim. Cosmochim. Acta 54, 1745-1754. 

Of the secondary processes that have affected chondritic meteorites, aqueous alteration is among the most widespread. Evidence of varying degrees of aqueous alteration is present in all the major chondrite groups, with the exception of the enstatite chondrites. This alteration is typically indicated by the presence of hydrous phyllosilicates (principally serpentines and smectite clays), often associated with carbonates, sulfates, oxides (magnetite), and secondary sulfides. The variable alteration assemblages present in different chondrite groups are principally the result of alteration under different conditions (P, T, fo, water/rock ratio) (e.g., Zolensky et al., 1993). 

The quality of magnesium oxychloride cements is highly dependent on the reactivity of the magnesium oxide used in their preparation. Typically, such oxides are prepared by calcination of the basic carbonate (Eubank, 1951 Harper, 1967), but their reactivity varies according to the conditions under which such calcination is carried out. As the reactivity alters so does the amount of oxide that can be incorporated into a cement relative to the amount of aqueous MgClj (Harper, 1967). 

The electropolymerization of these monomers at constant current under the same micellar conditions led to the formation of thin, electroactive polymer films. The electropolymerization of 0.05 M EDOT in 0.1 M SDS containing O.IM LiC104 in water at a Pt electrode began at very low current (j = 0.1 mA/cm ), compared to that found in acetonitrile without SDS (j = 0.5 mA/cm ). This phenomenon nuy be attributed to a specific effect of the SDS surfactant, which alters the oxidation potentials of EDOT. Thin, electroactive and conductive poly(EDOT) films can be synthesized in the above aqueous micellar solution at constant currents ranging firom j = 0.1 mA/cm to j = 5 mA/cm. For j > 5 mA/cm the resulting poly(EDOT) films were non-electroactive and extremely degraded owing to the reaction between water molecules and the thienyl radical-cations formed (8). 

The direct electrooxidation of aqueous E>-g]uconic acid to l>arabinose on graphite has been performed in a very simple apparatus which may be suitable for practical application. The electrocatalytic oxidation of sucrose on smooth, lead-modified platinum electrodes has been examined with a view to finding experimental conditions for the selective electrosynthesis of value-added compounds. A paper in Bulgarian on the electrooxidation of diacetone-L-sorbose at low current densities in a nickel oxide electrolizer has been publi ed. The influence of the rize of palladium particles and their location on the support on their activity in the oxidation of glucose has been examined. An investigation of the effect of tonperature and pH on the platinum-catalysed oxidation of sucrose showed that changes in temperature affect mainly the reaction rate, where changes in pH alter the selectivity. ... 

Jarosite is a mineralogical marker for aqueous processes because it contains the equivalent of 10 wt. % H2O in its structure as the OH anion. The average S-rich outcrop rock at Meridiani Planum has the equivalent of 2 % H2O associated with jarosite alone. An important aspect of the jarosite detection is that acidic conditions (pH < 4 at room temperature) are required for its formation. The alteration of basaltic precursor material under oxidizing, acid-sulphate conditions to form jarosite and other phases in the S-rich outcrop rocks at Meridiani Planum could have occurred under conditions provided, for example, by interactions with acid-sulphate, possibly hydrothermal waters and/or condensation of S02-rich volcanic emanations [91]. 

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