Search results for "MINERALOGY"
showing 10 items of 1516 documents
X-ray fluorescence investigation of gilded and enamelled silver: The case study of four medieval processional crosses from central Italy
2013
Abstract The presence of multilayered structures is common in such cultural artefacts as paintings, corroded metals, objects that underwent a whatever form of surface qualification. One of the most usual and complete ways to investigate such structures is observing a cross section, which requires sampling. There are however situations where at least part of the stratigraphic information can be derived non-destructively: the literature shows that X-ray fluorescence (XRF) has frequently been used, in recent years, for this purpose, with special regard to paintings and gilded metals. Aim of this paper is to further explore the suitability of XRF-based techniques to characterise multilayered st…
Upconversion luminescence of Er3 +/Yb3 + and their role in the stabilization of cubic NaLaF4 nanocrystals in transparent oxyfluoride glass ceramics
2018
CC BY-NC-ND
Evolution of the structural and optical properties from cobalt cordierite glass to glass-ceramic based on spinel crystalline phase materials
2007
Co 2+ -containing cordierite stoichiometric glasses have been prepared by melting colloidal gel precursors. After controlled thermal processing in the range of temperatures between 900 and 1300 C different polycrystalline, almost single phase materials displaying l-, a-, and b-cordierite crystalline forms were synthesized. In addition, spinel glass-ceramic materials were also prepared from the base glasses. All these materials were characterized by X-ray powder diffraction and infrared spectroscopy. Room temperature (RT) absorption and emission spectra of Co 2+ – cordierites and – spinel-glass material have allowed determining the local environment of the Co 2+ in the crystalline structure …
Mechanism of crystallization of pyroxene-based glass-ceramic glazes
2004
Abstract The mechanism of crystallization of a powdered glass with composition in the pyroxene crystallization primary field within the CaO–MgO–Al 2 O 3 –SiO 2 quaternary system and containing some additives was studied. The crystallization sequence was compared with that from the same base glass without additives. After a short thermal anneal both powdered glasses showed phase separation. Further thermal treatment gave rise to the crystallization of pyroxene. Anorthite as secondary crystalline phase was also detected in the quaternary glass (without additives). The starting crystallization in the glass with additives took place in the outer surface of glass particles probably in the immisc…
Li2OSiO2Al2O3MeIIO Glass-Ceramic Systems for Tile Glaze Applications
1991
In order to verify the possibility of using glass-ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li2O─Al2O3─SiO2 glass-ceramic system were investigated by differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, devel…
Microstructural Evolution in Fast-Heated Cordierite-Based Glass-Ceramic Glazes for Ceramic Tile
2004
The crystallization mechanism of α-cordierite from a B 2 O 3 -and TiO 2 -containing glass submitted to fast heating in the cordierite primary phase field of the CaO-MgO-Al 2 O 3 -SiO 2 quaternary system was investigated. Addition of B 2 O 3 to a SiO 2 -rich glass suppressed the formation of μ-cordierite. This suppression facilitated densification by viscous flow before crystallization. Powder X-ray diffractometry, field-emission electron scanning microscopy, and energy-dispersive X-ray analysis revealed that α-cordierite nucleated directly from glass on the boundaries of original particles and was probably favored by TiO 2 , which acted as a nucleant. The growth kinetics of α-cordierite cry…
Effect of MgO/CaO ratio on the microstructure of cordierite-based glass-ceramic glazes for floor tiles
2005
Abstract The effect of the MgO/CaO ratio on the microstructure and microhardness of cordierite-based glass-ceramic glazes was studied. For this purpose glasses, with compositions in the cordierite primary phase field of the CaO–MgO–Al 2 O 3 –SiO 2 quaternary system and, with different MgO/CaO ratios, were prepared by melting. Glass powder pellets pressed under low pressure were fast heated at several temperatures simulating industrial floor-tile processing, and characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray emission spectroscopy (EDX). The studied glasses crystallized α-cordierite as the only crystalline phase…
Evidence of hexagonal WO3 structure stabilization on mica substrate
2009
International audience; WO3 nanorods are grown by a simple vapor deposition method on a mica substrate and characterized by Selected Area Electron Diffraction and Energy Dispersive X-rays Spectroscopy. Experimental results show the clear evidence of an unexpected WO3 hexagonal structure as well as an epitaxial growth on the mica substrate. Besides, potassium is evidenced inside the nanorods. It is thus deduced that a metastable WO3 hexagonal phase is stabilized by epitaxy through a tungsten bronze interlayer having same hexagonal structure.
Metal-organic chemical vapor deposition of Cr2O3 and Nd2O3 coatings. Oxide growth kinetics and characterization
2000
Thin oxide films of Cr2O3 and Nd2O3 were prepared, using Metal-Organic Chemical Vapor Deposition (MOCVD) technique, to protect stainless steels against corrosion at high temperature. The conditions of precursor volatilization were studied by thermogravimetry. Deposited film growth kinetics depended on the deposition parameters, particularly substrate temperature, gas flow rate and location of substrate in the coating reactor. The influence of the deposition parameters on the deposition rate and the uniformity of the films is discussed. The oxide films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force mi…
Testing laboratory methods to determine the anisotropy of saturated hydraulic conductivity in a sandy–loam soil
2009
Abstract Anisotropy, a (the log of the ratio of horizontal to vertical conductivity, log 10 ( K h / K v )), of saturated soil hydraulic conductivity, K s , affects transport processes in soil but is not routinely measured, probably because practical and validated methods are lacking. The objective of this investigation was to determine the effects of different constant-head laboratory and sampling procedures on anisotropy of saturated hydraulic conductivity measurements. The sequence of K s measurements was varied (vertical conductivity, K v , first, then horizontal, K h , second and vice versa) for an experimental set-up considering five variables: 1) water ponding type (Mariotte or siphon…