Hydrodynamic effects on the efficiency of porous flow-through electrodes

Hydrodynamic conditions in porous flow-through electrodes are discussed with special emphasis on radial diffusion effects on the efficiency of reactant conversion. The effect of porosity and tortuosity on the conversion efficiency are also considered. It is shown experimentally that radial diffusion limits the electrode efficiency for(L)=vr ²/2DL>0.5 and normal porosity and tortuosity values; q1. For(L)<0.5, the electrode works with 100% efficiency.A porous flow-through electrode is divided, in the most general case, into three regions: (a) velocity entrance length h0.2vr²/v in which a steady velocity profile is developing; (b) diffusional entrance lengthHvr ²/2D for which(x)=vr ²/2Dx1; in this region a radial diffusional concentration profile is developing andh is usually much smaller thanH; (c) the region where the velocity and concentration profiles are fully developed. Only in region (c) does the electrode operate with 100% efficiency. In regions (a) and (b) radial diffusion limits the electrode efficiency.     

Studies in a modified cadoxen solvent

A cadmium ethylenediamine solvent (cadoxen) of modified composition containing 0.5 M sodium hydroxide, 5% cadmium, and 28–30 % ethylenediamine was found to dissolve high molecular cotton materials even under higher ambient temperature conditions as in India. The stability of cellulose solutions in this solvent was still high enough to enable viscosity measurements without exclusion of air. Intrinsic Viscosity values were determined for a large number of cellulosic materials. A study of the kinetics of degradation of cellulosic solutions in cadoxen gave comparatively higher rate constants in nitrogen atmosphere and a higher energy of activation as compared to other alkaline solvents indicating that degradation in cadoxen cannot be considered primarily oxidative in nature.     

A SIMPLE METHOD FOR STUDYING THE KINETICS OF GAS-SOLID REACTIONS IN A FLUIDIZED BED REACTOR

A methodology for studying the kinetics of gas-solid reactions in a fluidized bed reactor is presented. This procedure is based on the analysis of the response of the system (flue gases) when batches of solids of different weight are added to the reactor. The method has been applied to the study of limestone particle calcination. The calcination rate constants obtained are in good agreement with those found in the literature. The method offers the advantage of simplicity and avoids the use of model assumptions or empirical correlations.     

EMI shielding of intinsically conductive polymers

Results of this study, in which shielding efficiencies are measured for a number of blends containing various conductive fillers including intrinsically conductive polymers, are reported. It is shown that a very high level of shielding performance can be achieved by use of intrinsically conductive polymers in thermoplastic blends and that the most reliable measure of this performance is obtained from far-field shielding measurements. However, near-field measurements provide a useful method for comparing the relative shielding effectiveness of different samples. A PVC blend containing nearly uniformly dispersed intrinsically conductive polymer proved to be the best performing sample.     

Estimation of the contribution of heterogeneous reactions on the surface of aerosol particles to the chemistry of the atmosphere

Langmuir approach is used to estimate (i) the relative contribution of heterogeneous reactions on the surface of aerosol particles and (ii) the maximum values of the reaction coefficient for various reactions relevant to atmospheric chemistry.     

Reaction of sintered spinel and corundum refractories with some compounds

Conclusions We investigated the reaction of sintered spinel, spinel-corundum, and corundum refractories with certain oxides at 1500–1750°C. We established conditions in which refractories are stable in respect to the action of individual oxides. We also investigated the mineral compositions of the reaction zones.The least reaction with all the oxides investigated occurs in the spinel refractory, and the greatest in the corundum; that is, there is an increase with rise in alumina content. Magnesia spinel hardly reacts with iron oxides in the test conditions.Magnesia spinel is very resistant to sodium adipates which extensively damage sintered corundum.Carbonates of alkali and alkaline-earth elements, and also fused alkalis at temperatures exceeding their melting points by 200°C seriously damage spinel-corundum refractories, but do not react with sintered corundum or spinel.Metallic fluorides damage corundum but do not react with spinel and spinel-corundum sintered refractories.Thus, spinel sintered refractory should find extensive use in conditions of corrosive action, in particular, alkalis and oxides of iron.Translated from Ogneupory, No. 1, pp. 37–42, January, 1968.     

Morphology of conducting polymeric coatings: quantitative comparison between theory and experiment

The density profile of electrosynthesized polymeric layers on carbon fibers is obtained from gravimetric and scanning electron microscopy (SEM) data. The coating density ρ is found to decrease with increasing radial distance, r, subject to the power law . Based on a modified diffusion-limited aggregation (DLA) model, it is shown that lattice Monte Carlo simulation of the coating process predicts the experimentally observed power law exponent.     

Oxidation induction time correlations with radiation dose and antioxidant concentration in EPR and XLPE polymers

Oxidation induction time (OIT), as measured by differential scanning calorimetry, is useful in assessing the extent of degradation in polymeric materials. Values of OIT for typical EPR and XLPE polymer insulation materials used for electric cable insulation in nuclear power plants were measured as a function of both radiation dose and antioxidant concentration after accelerated aging. Irradiations were performed at the University of Virginia Cobalt Irradiation Facility. OIT was found to decrease exponentially with increasing radiation dose and with decreasing antioxidant concentration for both ethylene-propylene rubber (EPR) and cross-linked polyethylene (XLPE) insulations. It was determined experimentally that, when polymers are subjected to a constant radiation dose rate, antioxidant concentration decreases linearly with time, and it was shown that this variation is consistent with theoretical autoxidation kinetics. © 1993 John Wiley & Sons, Inc.     

Myristicin. The major volatile component in mature seed ofPortenschlagia ramosissima

Portenschlagia ramosissima (Port.) vis. (Umbelliferae) seed contains 15% essential oils, 70% of which is the aromatic ether myristicin. These structural assignments were made from nuclear magnetic resonance, combined gas chromatography-mass spectrometry (GC-MS), and infrared and ultraviolet data. GC-MS data also indicate the presence of pinene, cymene, terpinene, elemicin, methyl eugenol, and a variety of sesquiterpene hydrocarbons.