Search results for "MINERALOGY"
showing 10 items of 1516 documents
Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under red…
2009
Abstract A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce 0.6 Zr 0.4 O 2 homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs. By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic …
PLZT—Synthesis, sintering and ceramics microstructure
2006
Abstract Producing of PLZT powders by original two-stage co-precipitation method from mixed solution of inorganic salts ZrOCl 2 ·8H 2 O, TiCl 4 , La(NO 3 ) 3 ·6H 2 O, Pb(NO 3 ) 2 , was carried out. The sequence of phases formed during PLZT synthesis has been studied by X-ray and DTA analysis. Ceramic samples were prepared by two-stage hot-pressing technology. Dielectric, ferroelectric and optical properties have been measured. Ceramic microstructures were studied by SEM with energy dispersive analytical capability (EDX). The fine-grained microstructure was quite uniform with the average grain size of 5–7 μm, without internal or grain boundary porosity. The optical transmittance of ceramic p…
Colloidal zeolites and zeolite membranes
2002
The synthesis of zeolite membranes and thin films using the secondary growth process is briefly described. In this process colloidal zeolite particles (sols) are prepared hydrothermally and then subsequently deposited on substrates to produce uniform layers of controlled thickness. In order to optimise this process, an understanding of the nature of the sols and an insight into the structure of the consolidated layer so formed, is required. Such studies are illustrated here with silicalite and zeolite A. The formation and growth of silicalite sols has been investigated in situ by small angle neutron scattering (SANS). SANS measurements on sols at progressively higher concentrations have pro…
Structural model of gelation processes of a sodium silicate sol destabilized by calcium ions: combination of SAXS and rheological measurements
2005
This study deals with the physico-chemical processes involved in the formation of basic fractal silica gels derived from a sodium silicate sol destabilized by calcium ions. Using small-angle X-ray scattering and dynamic rheological measurements, structural and viscoelastic properties have been investigated in situ during aggregation and gelation processes. The experimental results lead to a consistent model that describes the structural features and aggregation mechanisms involved in the formation of these gels.
Testing the concentric-disk tension infiltrometer for field measurement of soil hydraulic conductivity
2010
Abstract The concentric-disk tension infiltrometer (CDTI) may be used to simultaneously measure the confined ( K c ) and the unconfined ( K u ) soil hydraulic conductivity, but it has received little testing. Comparison between K c and K u can be affected by the calculation approach applied to analyze unconfined steady-state infiltration rates. The objectives of this investigation were to: i) establish the effect of the calculation approach on the estimates of K u ; and ii) compare the K c and K u values measured by the CDTI. A clay soil, a structureless sandy loam soil, and a sandy loam soil with a relatively high gravel content were sampled using a disk of radius equal to 107.5 mm, compri…
Hierarchical porous carbon with designed pore architecture and study of its adsorptive properties
2010
Abstract Ordered mesoporous carbon nanoparticles have been synthesized by a nanocasting procedure from furfuryl alcohol impregnation into alumino–silica UVM-7 material. By a proper adjustment of the synthesis parameters, furfuryl alcohol volume vs . template pore volume, it was possible to obtain a carbonaceous templated material which keeps the hierarchical bimodal porosity of the silica together with its high surface area (>1000 m 2 /g), as it was confirmed by means of electron transmission microscopy and N 2 adsorption isotherms. This carbon material was evaluated by testing it as a sorbent for several pesticides in aqueous solutions. Its absorption efficiency was compared with typical c…
Crystallization and microstructural development of nickel-containing aluminosilicate glasses with cordierite stoichiometry
2001
Abstract The crystallization behaviour of two glasses with chemical compositions MAl2O4/SiO2=1/2.5, being MNi and equimolar mixtures of Mg and Ni, was investigated. Glasses were prepared by cooling samples melted at 1650 °C. During thermal treatment over the range of temperature up to 1200 °C both glasses were first crystallized to form a β-quartz solid solution, then transformed to α-cordierite or spinel depending on the amount of nickel. The temperatures of both the crystallization of β-quartz solid solution and its further transformation were also dependent on the nominal amount of nickel. Lower temperatures were found for glasses with a large amount of nickel. UV–Vis diffuse reflectanc…
Influence of iron non-stoichiometry on spinel zinc ferrite gas sensing properties
2012
Abstract It is demonstrated for the first time that the gas sensing properties of a spinel ferrite complex metal oxide semiconductor can be improved by controlling iron stoichiometry. Conductivity and sensitivity was analyzed for ZnFe2+zO4± spinel type ferrite with z from −0.01 to 0.15. By increasing iron content from z = −0.01 to z = 0.1, sensitivity increases up to 3 times but for samples with z > 0.1 sensitivity drops. It was observed from impedance spectroscopy measurements that resistance decreases with an increase of the iron content. Complex impedance spectra reveal two phases with different resistance attributed to depletion layer (Rd) and bulk (Rb). With increasing iron content inc…
Effect of thermal treatment on the structural evolution of 3:2 and 2:1 mullite monophasic gels
2005
Abstract Single phase mullite gels with composition 3Al2O3 · 2SiO2 (3:2) and 2Al2O3 · SiO2 (2:1) were prepared by the semialkoxide method using aluminum nitrate nonahydrate and tetraethylorthosilicate as reagents. The influence of the thermal processing conditions on the reaction sequence was investigated. Both 3:2 and 2:1 mullite gels formed orthorhombic mullite under fast heating (40 °C/min) at 900 °C. Slow heatings delayed the formation of mullite in both gel compositions but no formation of spinel was detected between 1000 °C and 1100 °C. The slow transformation of pentacoordinated aluminum to octahedral and tetrahedral arrangements probably depends on the larger size and extent of the …
Wide Temperature Operation of 40-Gb/s 1550-nm Electroabsorption Modulated Lasers
2006
Electroabsorption modulated lasers (EMLs) exploiting the quantum confined Stark effect need thermoelectric coolers to achieve stable output power levels and dynamic extinction ratios. Temperature-independent operation is reported between 20/spl deg/C and 70/spl deg/C for InGaAlAs-InP-based monolithically integrated 1550-nm EMLs exploiting a shared active area at 40 Gb/s by actively controlling the electroabsorption modulator bias voltage. Dynamic extinction ratios of at least 8 dB and fiber-coupled mean modulated optical power of at least 0.85 mW are obtained over the mentioned temperature range.