Home About us Contact
|
Home About us Contact | ||
|
|
||
BET Method (bet + method)
Selected AbstractsPermselective and Preconcentration Properties of a Surfactant-Intercalated Clay Modified ElectrodeELECTROANALYSIS, Issue 22 2006E. Ngameni Abstract This work is focused on the voltammetric examination of the ion exchange properties of a smectite type clay, before and after its modification by the replacement of its native interlamellar cations (Na+, K+, Ca2+) by hexadecyltrimethylammonium cations (HDTMA+). The raw clay and its organically modified form were first characterized by X-ray diffraction (XRD) and N2 adsorption,desorption isotherms (BET method) that confirmed the modification via an intercalation process. These materials were subsequently coated onto glassy carbon surfaces, and the resulting modified electrodes were evaluated for the uptake of [Ru(NH3)6]3+ and [Fe(CN)6]3, ions used as redox probes. Some experimental parameters affecting the incorporation of the probes within the film, including the ionic strength, the surfactant loading and the solution pH are thoroughly examined, in order to highlight the mechanism of the process. The possibility of using the surfactant-intercalated clay modified electrode as an electrochemical sensor for [Fe(CN)6]3, is also evaluated. [source] Gas breakthrough experiments on fine-grained sedimentary rocksGEOFLUIDS (ELECTRONIC), Issue 1 2002A. Hildenbrand Abstract The capillary sealing efficiency of fine-grained sedimentary rocks has been investigated by gas breakthrough experiments on fully water saturated claystones and siltstones (Boom Clay from Belgium, Opalinus Clay from Switzerland and Tertiary mudstone from offshore Norway) of different lithological compositions. Sand contents of the samples were consistently below 12%, major clay minerals were illite and smectite. Porosities determined by mercury injection lay between 10 and 30% while specific surface areas determined by nitrogen adsorption (BET method) ranged from 20 to 48 m2 g , 1. Total organic carbon contents were below 2%. Prior to the gas breakthrough experiments the absolute (single phase) permeability (kabs) of the samples was determined by steady state flow tests with water or NaCl brine. The kabs values ranged between 3 and 550 nDarcy (3 × 10,21 and 5.5 × 10,19 m2). The maximum effective permeability to the gas-phase (keff) measured after gas breakthrough on initially water-saturated samples extended from 0.01 nDarcy (1 × 10,23 m2) up to 1100 nDarcy (1.1 × 10,18 m2). The residual differential pressures after re-imbibition of the water phase, referred to as the ,minimum capillary displacement pressures' (Pd), ranged from 0.06 to 6.7 MPa. During the re-imbibition process the effective permeability to the gas phase decreases with decreasing differential pressure. The recorded permeability/pressure data were used to derive the pore size distribution (mostly between 8 and 60 nm) and the transport porosity of the conducting pore system (10 -5,10 -2%). Correlations could be established between (i) absolute permeability coefficients and the maximum effective permeability coefficients and (ii) effective or absolute permeability coefficients and capillary sealing efficiency. No correlation was found between the capillary displacement pressures determined from gas breakthrough experiments and those derived theoretically by mercury injection. [source] Synthesis of Nanostructured Silicon Carbide through an Integrated Mechanical and Thermal Activation ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Ruiming Ren Changes of crystal structures and microstructures of SiO2 and graphite powder mixtures induced by high-energy milling, the effect of these changes on the reactivity of reactants, and the mechanism of enhanced SiC formation have been studied using a variety of analytical instruments, including X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, solid-state 29Si nuclear magnetic resonance, and nitrogen adsorption (i.e., the BET method). High-energy milling before carbothermic reduction leads to substantial changes in the structural and energy states of the reactants, which in turn increases the reactivity of the reactants and enhances the formation of nanostructured SiC particles. Furthermore, the structural and energy-state changes contribute to the enhanced SiC formation through the increased reaction kinetics as well as the increased reaction driving force. [source] Catalytic and Heating Behavior of Nanoscaled Perovskites under Microwave RadiationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2008T. Krech Abstract Perovskite powders of the types La0.5Ca0.5AlyM1,yO3,, (y = 0,0.8), M = Fe, Cr, Mn, Co and LaxSr1,xMnyCo1,y (x = 0.5,1, y = 0,1) were prepared via a sol-gel route according to the modified Pechini method. Incineration of the resins was performed before final sintering at 1000,°C for 6,h. The phase composition of the samples was established by X-ray powder diffraction analysis, and the lattice parameters were calculated using Rietveld analysis. The shape and size of the particles were determined via scanning electron microscopy and the specific surface area of the powder perovskites was established by the BET method. The principal particles were ca. 100,nm in size and formed agglomerates larger than 1.0,,m. The composition of the perovskites was established by EDX analysis. Following this, the catalytic behavior was tested by means of total oxidation of propane. The catalytic performance was measured at atmospheric pressure with 3,g of catalyst in a fixed-bed quartz reactor (i.d. = 18,mm) under thermal-assisted and microwave-assisted conditions. Initial results show a strong dependence of the catalytic and heating behavior on the nature of the M-atom and its number of unpaired d-electrons as well as on the particle size and its specific surface area. No significant difference in the results could be detected from comparison of the two heating methods. [source] | ||||||||||