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Clay Coatings (clay + coating)

Distribution by Scientific Domains
Earth and Environmental Science75%

Selected Abstracts

A New Polyphenol Oxidase Biosensor Mediated by Azure B in Laponite Clay Matrix

ELECTROANALYSIS, Issue 19 2003
Dan Shan
Abstract Amperometric biosensor based on the entrapment of polyphenol oxidase within a laponite clay coating and cross-linked by glutaraldehyde is described for catechol detection. Laponite provides a hydrophilic enzyme surrounding increasing the long term stability of the biosensor compared to the corresponding biosensors obtained by chemical cross-linking of PPO with glutaraldehyde. Azure B, a cationic dye exchanged within the clay matrix, is used as an electron shuttle allowing the mediated detection of phenol derivatives at ,0.05 V. The detection limits obtained with the optimized biosensor configuration for catechol, p -cresol and phenol are 1, 1 and 17,nM, respectively. [source]

Micromorphology of soils derived from volcanic ash in Europe: a review and synthesis

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2007
G. Stoops
Summary An analysis of the available literature on European volcanic ash soils has been made. Most has been published in Congress proceedings and Journals of national societies, less than half in English. More than half of the papers deal with soils on the Canary Islands. Many papers focus only on one aspect, and complete descriptions are found only in recent publications. Often the use of vague micromorphological terminology and the absence of analytical data make interpretation and comparisons difficult or impossible. Nonetheless, some general features do emerge. In the least-weathered soils, the micromass forms first coatings around the coarse constituents, later granules, finally giving rise to a loose granular microstructure in the topsoil, and a compacted granular one in the Bw horizons of typic andic materials. The b-fabric of the micromass is undifferentiated. With increasing weathering, clay coatings appear, the microstructure becomes more blocky and the b-fabric becomes speckled or even striated. In Vertisols and Aridisols, micromorphological characteristics are not much different from those in the comparable non-volcanic soils, except generally for the tendency to granular (intrapedal) microstructures. In Icelandic soils, microstratification, lenticular microstructure and preservation of plant residues as a result of cryic conditions and permanent volcanic and aeolian activity are observed. Weathering of volcanic glass in well-drained conditions yields allophane alteromorphs similar to palagonite, which are easily subject to fragmentation by pedoturbation. The possible influence of surface transport and burial on the formation of Bw-horizons in andic materials is discussed. [source]

Weathering and allophane neoformation in soils developed on volcanic ash in the Azores

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2007
M. Gérard
Summary On Faial and Pico islands (Azores), we studied two profiles on basaltic pyroclasts that contain buried horizons, and we focussed on petrography, micropedology and mineralogy. Emphasis was given to weathering of the lapilli and ashes, and the neoformation of allophane. A combination of optical studies, in situ chemical analyses, X-ray diffraction and infrared spectroscopy of clay fractions revealed that allophane is present both in the micromass of the groundmass, in alteromorphs after lapilli or pumice, and in clay coatings. Whereas most studies describe allophane as a colloidal fraction formed by the congruent and total dissolution of the ashes, this study shows evidence for the formation of allophane alteromorphs, due to leaching of Si and cations, with preservation of the original shapes of the tephra. The allophane alteromorphs often display optical characteristics that resemble those of palagonite. Increasing alteration is observed through three steps: (i) hydration of the glass associated with strong cation and Si leaching, (ii) allophane hypocoatings, and (iii) allophane alteromorphs with development of intragrain bridges. The chemical signature of the alteromorphs varies from a pure alumino-silicate at one extreme to an Fe(Ti) enriched alumino-silicate at the other. Between those two extremes, the colour grades from yellow to dark orange, with microzonations. An Al-rich allophane composition is associated with gibbsite in the EUR6-Pico profile, whereas at the base of the EUR5-Faial profile, Si-rich allophane is associated with halloysite. Some variations of the palaeo-environment are also suggested by strong iron segregation observed with various secondary phases (ferrihydrite, haematite, iddingsite). [source]

Distribution and genesis of Fahlerden (Albeluvisols) in Germany

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2006
Peter Kühn
Abstract Fahlerden dominate large areas of the young and old moraine landscapes of N and E Germany. Fahlerden (part of Fahlerden corresponds to Albeluvisols) and their transitional subtypes are supposed to have a higher intensity of clay illuviation than Parabraunerden (Luvisols). Besides this macroscopic feature reflecting periglacial influence, micromorphological features such as lenticular platy microstructure, vesicles, and fragments of clay coatings in Bt streaks document the initiation of Fahlerde genesis, which began in the Late Glacial. A model of Fahlerde genesis chronologically connects sedimentological and periglacial processes, vegetation development, and soil-forming processes like decalcification, clay illuviation, and humification. The classification criterion of larger differences in clay contents between E and Bt horizons to distinguish Fahlerden from Parabraunerden needs to be reconsidered, because most Fahlerden have developed in stratified parent material in periglacially influenced landscapes. The interpretation of a soil data base listing data of both soil types distributed in Brandenburg demonstrates that the difference in clay contents between E and Bt horizons may even be smaller in Fahlerden than in Parabraunerden. [source]