Search results for "MINERALOGY"
showing 10 items of 1516 documents
Characterization of the Altered Zone Around a Fracture in Palmottu Natural Analogue
1996
AbstractA drill core sample penetrating at a natural fracture has been analysed by helium gas techniques and by α-autoradiography. Porosity and diffusivity profiles away from the fracture have been determined and compared with structural profiles. Model calculations are used to determine the effects of sample size on the measured porosities and diffusivities.
Quantification of pedogenic particles masked by geogenic magnetic fraction
2021
AbstractPedogenic magnetic fraction in soils is attributed to fine-grained particles, i.e. superparamagnetic grains. In the case of a strongly magnetic geogenic fraction, pedogenic magnetic contribution is hard to detect. To the best of our knowledge, detailed research into the masking of pedogenic superparamagnetic grains and quantification of this effect has not yet been carried out. The principal aim of our research is to quantify the influence of coarse-grained ferrimagnetic fraction on the detection of the superparamagnetic grains. In order to describe the masking phenomenon, volume and frequency-dependent magnetic susceptibility were determined on a set of laboratory prepared samples …
Fracture flow due to hydrothermally induced quartz growth
2017
Abstract Mineral precipitations are a common feature and limitation of initially open, permeable rock fractures by forming sealing structures or secondary roughness in open voids. Hence, the objective of this numerical study is the evaluation of hydraulic properties of fractures sealed by hydrothermally induced needle and compact quartz growth. Phase-field models of progressive syntaxial and idiomorphic quartz growth are implemented into a fluid flow simulation solving the Navier–Stokes equation. Flow simulations for both quartz types indicate an obvious correlation between changes in permeability, fracture properties (e.g. aperture, relative roughness and porosity) and crystal growth behav…
Metallic interconnects for solid oxide fuel cell: Effect of water vapour on oxidation resistance of differently coated alloys
2009
International audience; The need of interconnect to separate fuel and oxidant gasses and connect individual cells into electrical series in a SOFC stack appears as one of the most important point in fuel cell technology. Due to their high electrical and thermal conductivities, thermal expansion compatibility with the other cell components and lowcost, ferritic stainless steels (FSS) are nowconsidered to be among the most promising candidate materials as interconnects in SOFC stacks. Despite the formation at 800 ◦C of a protective chromia Cr2O3 scale, it can transform in volatile chromium species, leading to the lost of its protectiveness and then the degradation of the fuel cell. A previous…
Laser-Calorimetric Study of Fundamental Absorption Edge in Pb,La(ZrTi)O3 (PLZT) Perovskite Ceramics
2000
The values of the light absorption coefficient of PLZT 10/65/35 ceramics at selected wavelengths have been obtained by laser calorimetric measurements. The absorption coefficient of the PLZT ceramics is an exponential function of the photon energy. Two values of characteristic Urbach energy have been found ΔE1 = 106 meV and ΔE2 = 238 meV. The first one is a characteristic of the potential of electron-phonon interaction of the optically excited transitions from the valence band to the conduction band and does not depend on lattice defects or admixtures. The other characterises the electron-phonon interaction at optical transitions between two localized electron states in the energy gap separ…
CO2 laser-induced structure changes in lead zirconate titanate Pb(Zr0.58Ti0.42)O3 sol–gel films
2003
Based on absorption spectra of lanthanum modified lead zirconate titanate Pb0.9La0.1(Zr0.65Ti0.35)O3 (PLZT10/65/35) ferroelectric ceramics an idea of local and selective treatment of lead zirconite titanate Pb(ZrXTi1−X)O3 (PZT) sol–gel film in the multi-layer structure by CO2 laser radiation was formulated. The possibility to obtain PZT perovskite film on the SiO2/Si substrate by irradiation with CO2 laser was shown experimentally. X-ray studies revealed the PZT perovskite structure ratio growth at the expenses of pirochlore structure with an increased power density of laser radiation.
Grain size effect and local disorder in polycrystalline relaxors via scanning probe microscopy
2007
Local piezoresponse of individual grains in polycrystalline Pb0.9125La0.0975(Zr0.65Ti0.35)0.976O3 (PLZT 9.75/65/35) relaxor ceramics is studied using the scanning probe microscopy (SPM) technique. The observed piezoelectric contrast consisting of irregular (labyrinth-type) polarization patterns is attributed to the compositional disorder and consequent charge imbalance caused by high La concentration. A measure of this disorder, the polarization correlation length ξ, is directly determined using an autocorrelation analysis function implemented in the SPM software. The analysis of the obtained images shows that ξ taken at the scale ~200 nm varies as a function of the position inside the grai…
Phase evolution by thermal treatment of equimolar cobalt–magnesium cordierite glass powders
2004
Abstract The structural evolution with annealing time at temperatures between 900 and 1100 °C of loosely compacted equimolar cobalt–magnesium cordierite glass powder was reported. The glass, with composition MgCoAl4Si5O18, was prepared by melting a glass precursor, previously synthesized by a semiwet method, at 1650 °C. Field emission scanning electron microscopy (FESEM) of isothermally heated glasses at 900 and 950 °C revealed increased phase separation with thermal treatment. X-ray diffraction (XRD) results of these powders indicated that the first crystalline phase formed was μ cobalt-containing cordierite which transformed to α cordierite with longer annealing. At the beginning of the μ…
The Influence of Morphological Aspects in the Reaction Pathway and Superconductive Properties of Bi2223-Ca2CuO3 Ceramic Composites
1994
ABSTRACTA variation of the solid-state matrix technique has been developed as a procedure for the preparation of 2223 bismuth superconducting phases [(Bi,Pb)2Sr2Ca1-nCunO4+2n, n=3]. The adequate processing of samples of nominal compositions 2223+x 0021, obtained both by this procedure and by the polymer matrix method, has allowed the modification of the microstructure of the calcium copper excess, with no noticeable change in that of the 2223 grains. The study of the phase evolution in the processing of the samples has shown that the formation rate of the 2223 phase is faster when the particle size of the calcium cuprate is smaller. A dependence of the intergranular superconducting properti…
(La0.8Sr0.2)(Mn1−yFey)O3±δ oxides for ITSOFC cathode materials?
2005
The oxygen transport properties in (La 0.8 Sr 0.2 )(Mn 1-y Fe y )O 3±δ (LSMF) with various iron contents y = 0, 0.2, 0.5, 0.8 and 1 were determined by the IEDP technique. Both oxygen diffusion and surface exchange coefficients were found to be greater for y = 0.8 and 1 than those of LSM (y=0). Moreover, for y ≤0.5, grain boundary diffusion was the rate limiting step especially at lower temperatures. Thus, in the LSMF perovskite materials, the oxygen diffusion via oxygen vacancies is enhanced by Fe. The LSMF electrical performances were measured by impedance spectroscopy. Compared to LSM and LSF (y= 1), porous LSMF cathodes with y= 0.2-0.8 exhibit poor electronic conductivity: Fe, by reducin…