Search results for "MINERALOGY"

Formation of nanostructures in Eu3+ doped glass-ceramics: an XAS study.

2012

We describe the results of x-ray absorption experiments carried out to deduce structural and chemical information in Eu(3+) doped, transparent, oxyfluoride glass and nanostructured glass-ceramic samples. The spectra were measured at the Pb and Eu-L(III) edges. The Eu environment in the glass samples is observed to be similar to that of EuF(3). Complementary x-ray diffraction experiments show that thermal annealing creates β-PbF(2) type nanocrystals. X-ray absorption indicates that Eu ions act as seeds in the nanocrystal formation. There is evidence of interstitial fluorine atoms around Eu ions as well as Eu dimers. X-ray absorption at the Pb-L(III) edge shows that after the thermal treatmen…

2016

AbstractDetermining the manganese concentration in shells of freshwater bivalves provides a unique way to obtain information about climate and environmental changes during time-intervals that pre-date instrumental data records. This approach, however, relies on a thorough understanding of how manganese is incorporated into the shell material –a point that remained controversial so far. Here we clarify this issue, using state-of-the-art X-ray absorption and X-ray emission spectroscopy in combination with band structure calculations. We verify that in the shells of all studied species manganese is incorporated as high-spin Mn2+, i.e. manganese always has the same valence as calcium. More impo…

Typologie du zircon des bentonites du Frasnien (carrière du Lion, Belgique) : utilité avant la datation U-Pb.

2006

5 pages; National audience

Spatiotemporal dynamics in the oxidation of groups IV?V metals: study of zirconium

1997

Abstract This paper focus on the mechanism of zirconium oxidation at 850 °C by X-ray diffraction (XRD) and the interactions between chemical (oxide growth, phase proportion) and physical processes (oxide scale texture, mechanical stresses). The structural gradients in the oxide scale composed of monoclinic ZrO 2 (higher proportion) and tetragonal ZrO 2 were revealed by XRD at variable incidence. The spatial evolution of the monoclinic zirconia texture through the oxide scale was shown and quantified. Relaxation of the oxide compressive stresses was observed for different oxidation times and correlated to kinetic breakaway evidenced by other methods. A structural mechanism of the oxide forma…

Micromechanical approach of the high temperature oxidation of zirconium: study of the Zr/ZrO2 interfacial epitaxy with Bollmann's method

1997

The method of Bollmann has been used to determine the role of epitaxy in the formation of the mechanical stress field near the metal/oxide interface during the high temperature oxidation of zirconium. The strains due to epitaxy combine with those due to both oxygen diffusion in metal and thermal expansion of the metal/oxide composite in a model based on a micromechanical formalism. The calculated values are compared to experimental results and the applicability of Bollmann's method to this problem is discussed.

Study on the initial stages of water corrosion of fluorozirconate glasses

2004

Abstract The surface corrosion process associated with the hydrolysis of fluorozirconate glass, ZBLAN (53ZrF 4 , 20BaF 2 , 20NaF, 4LaF 2 , 3AlF 3 ) was investigated using X-ray photoelectron spectroscopy (XPS), grazing-incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR) and scanning electron microscopy (SEM). After a short exposure period (25 min) of the glass surface to deionized water the XPS data indicate an increase of the oxygen content accompanied by a decrease of fluorine concentration. The analysis of the chemical bonding structure identified the predominant surface reaction products as zirconium hydroxyfluoride and oxyfluoride species. The second most abundant…

V-containing ZrO2 inorganic yellow nano-pigments

2015

In this work we report new results on the preparation, characterization and color properties of the inorganic yellow nano-pigmenting system based on monoclinic V–ZrO2 solid solution nanoparticles. The series of solid solution nanopowders were obtained by a polyol technique where the precipitates, obtained after heating at 180 °C ethylene glycol solutions of vanadyl acetonate and zirconium n-propoxide, were annealed at different temperatures up to 1300 °C for a short duration, in order to improve their crystallinity and control the crystalline form of the final nanoparticles. On annealing at around 450 °C highly crystalline tetragonal V-containing zirconia particles were developed, which tra…

Microstructure of Fe–ZrSiO4 solid solutions prepared from gels

2012

Abstract Microstructural changes associated with chemical and structural evolution from gels to Fe x –ZrSiO 4 solid solutions are reported. Mineralizer-free Fe x –ZrSiO 4 gels in the compositional range 0 ≤  x  ≤ 0.15 were prepared by sol–gel liquid-phase route from mixtures of alkoxides of silicon and zirconium, and iron (III) acetylacetonate, and annealed at different temperatures and/or times. The first step on the whole process to the final Fe x –ZrSiO 4 solid solutions was the formation of aggregated of tetragonal Fe-doped ZrO 2 nanocrystals with diameters smaller than 50 nm. At this stage the tetragonal Fe–ZrO 2 were embedded in amorphous silica resulting nanocomposite materials. The …

Synthesis and characterization of V2O5SiO2ZrO2 pigments by sol-gel method

1992

Abstract Polymeric gels in the V2O5 SiO2 ZrO2 system were prepared from tetraethylorthosilicate (TEOS), zirconium(IV)-n-propoxide and vanadium(IV) oxyacetylacetonate, precursors. The effects of prehydrolysis time of TEOS and drying gel method on the stabilization of tetragonal zirconia in the silica amorphous matrix, nucleation and growth of the zircon (ZrSiO4) phase, and stabilization of the blue and green stains of vanadium zircon were studied. Results provide evidence that long time of prehydrolysis and fast drying do not favour zircon crystallization but stabilize the tetragonal zirconia in the amorphous matrix.

Microstructural Evolution from Praseodymium-Containing Zircon Gels to Prx-ZrSiO4 Solid Solutions

2012

Structural evolution and coupled microstructural transformations occurred on annealing mineralizer-free Pr-containing ZrSiO4 gels up to final praseodymium-doped zircon yellow pigments are reported. Gels with nominal compositions Prx-ZrSiO4, 0 ≤ x ≤ 0.125, were prepared from mixtures of zirconium and silicon alkoxides and praseodymium acetylacetonate. Crystallization pathway and microstructural changes of thermally treated dried gels were followed by infrared spectroscopy, X-ray diffraction, field emission scanning and transmission electron microscopies, respectively. Results indicated that the crystallization pathway through the whole process of final Prx-ZrSiO4 solid solutions formation di…