Search results for "Mineral"
showing 10 items of 2711 documents
Multi-elemental EDXRF mapping of polluted soil from former horticultural land.
2004
The distribution of major and trace elements was systematically investigated by use of energy dispersive X-ray fluorescence spectrometry (EDXRF) on a former horticultural soil. The purpose of the study was to combine mapping of soil element concentration levels with multivariate statistics for characterisation of soil metal pollution in relation to previous and present land use. A 1-ha study site was chosen from a former horticulture where a previous preliminary survey indicated increased concentration levels of toxic elements. The soil was sampled from the top 20 cm of the soil surface in a 10×10-m grid-like pattern covering the 1-ha study area. In addition, three soil profiles were studie…
Catalytic activity of humic substances in condensation reactions
1998
Abstract Humic substances (HS) have considerable impact on the fate of organic xenobiotics in natural environments. This paper reports on the catalytic activity of HS in condensation reactions of carbonyl compounds with active methylene compounds, using Knoevenagel and Claisen-Schmidt reactions as examples. Of the HS, the aquatic fulvic acids are the most active, but the velocity of condensation reactions depends also on the temperature, concentration and form of HS (free or salt) used, and the solvent.
Effects of Briquetting and High Pyrolysis Temperature on Hydrolysis Lignin Char Properties and Reactivity in CO-CO2-N2 Conditions
2021
Carbonaceous reductants for pyrometallurgical applications are usually obtained from fossil-based sources. The most important properties of the reductants greatly depend on the application and the feeding of the reductant into the process. However, the mechanical strength, calorific value, fixed carbon content, and reactivity of the reductant are the properties that usually define the applicability of the reductant for different processes. The reactivity of the biochars is usually high in comparison to metallurgical coke, which may restrict the applicability of the biochar in reduction processes. One cause of the higher reactivity is the higher surface area of the biochars, which can be sup…
Fast and accurate methodology for direct mercury determination in hair and nails
2015
AbstractA solvent-free, easy, fast and waste-free methodology was developed for the determination of total mercury levels in hair and nails. Samples were taken from several volunteers and directly analysed, with levels of mercury in the range between 0.5 and 8 ng/mg. The influence of quantity of hair, as well as the addition of small amount of solvent and the necessity of previous treatment were studied. Also, a history of mercury exposure was provided by the distance of the hair from the scalp of each volunteer, the results of which were correlated with fish consumption. Furthermore, a short study of mercury in nails was carried out and correlated to the results from hair mercury levels. A…
Corundum Anorthosites-Kyshtymites from the South Urals, Russia: A Combined Mineralogical, Geochemical, and U-Pb Zircon Geochronological Study
2019
Kyshtymites are the unique corundum-blue sapphire-bearing variety of anorthosites of debatable geological origin found in the Ilmenogorsky-Vishnevogorsky complex (IVC) in the South Urals, Russia. Their mineral association includes corundum-sapphire, plagioclase (An61&ndash
An integrated analytical approach to define the compositional and textural features of mortars used in the underwater archaeological site of castrum …
2019
This paper aims to carry out an archaeometric characterization of mortar samples taken from an underwater environment. The fishpond of the archaeological site of Castrum Novum (Santa Marinella, Rome, Italy) was chosen as a pilot site for experimentation. The masonry structures reached the maximum thickness at the apex of the fishpond (4.70 m) and consisted of a concrete conglomerate composed of slightly rough stones of medium size bound with non-hydraulic mortar. After sampling, for a complete characterization of selected mortar fragments, different and complementary techniques (stereomicroscopy, polarizing optical microscopy, and X-ray powder diffraction analysis) were carried out in order…
Comparative ultrastructure and carbohydrate composition of gastroliths from Astacidae, Cambaridae and Parastacidae freshwater crayfish (Crustacea, De…
2012
21 pages; International audience; Crustaceans have to cyclically replace their rigid exoskeleton in order to grow. Most of them harden this skeleton by a calcification process. Some decapods (land crabs, lobsters and crayfish) elaborate calcium storage structures as a reservoir of calcium ions in their stomach wall, as so-called gastroliths. For a better understanding of the cyclic elaboration of these calcium deposits, we studied the ultrastructure of gastroliths from freshwater crayfish by using a combination of microscopic and physical techniques. Because sugars are also molecules putatively involved in the elaboration process of these biomineralizations, we also determined their carbohy…
Evidencias de un recubrimiento de magnetita artificial en el armamento íbero
2011
A metallographic study of two pre-roman Iberian arms, affected by a cremation process, revealed the presence of an outer magnetite layer, providing highly protective properties. This layer is extraordinarily tenacious and of very homogeneous thickness, indicating an intentional manufacturing process rather than an accidental formation during the severe heating/cooling cycles the artefact suffered. Up to date, the intentional production of these types of layers has been attributed to a welding process of three different metallic sheets, here an alternative model is proposed, allowing, as could be simulated in the laboratory, the virtually exclusive formation of a magnetite coating.<br>…
The Effect of Dopants on Sintering and Microstructure of Lead-free KNN Ceramics
2011
Lead-free potassium sodium niobate (K0.5Na0.5)NbO3 (KNN) has been prepared via conventional ceramic processing method. The influence of 0.5 wt% - 1.5 wt% MnO2 and WO3 addition on the sintering, crystallographic structure, microstructure and dielectric properties of KNN has been investigated. Optimal sintering temperatures of KNN ceramics were observed to be in the narrow interval: 1090 °C - 1110 °C for MnO2 doped KNN; 1150 °C - 1170 °C for pure KNN and doped with WO3. XRD patterns showed that all the samples have single perovskite structure with monoclinic structure. Microstructure of ceramics was changed greatly by using dopants.http://dx.doi.org/10.5755/j01.ms.17.1.251
Pietre figurate. Forme del fantastico e mondo minerale
2004
Le pietre figurate sono particolari sezioni di minerali che mostrano meravigliosi disegni, capaci di evocare nell’immaginazione dell’uomo organismi vegetali e animali, ma anche paesaggi o motivi geometrici. Dall’antichità al Novecento le pietre figurate hanno cambiato più volte statuto ontologico. Esse sono state considerate oggetti da collezione, emblemi di prodigiosità o curiosità; opere d’arte attribuite alla natura o ad un artefice supremo, in concorrenza con le opere degli artisti; sono state, infine, contemplate come scrigni e custodi di un segreto rivelato nella “scrittura lapidea”, insieme, sotterranea e palese. Il volume è rivolto allo studio delle forme dell’immaginario minerale, …