Porous Diaphragm Research Articles

Electrolytic oxidation of anthracite

An anthracite slurry can be oxidized only with difficulty by electrolytic methods in which aqueous electrolytes are used if the slurry is confined to the region of the anode by a porous pot or diaphragm. However, it can be easily oxidized if the anthracite itself is used as the anode. No porous pot or diaphragm is needed. Oxidative consumption of the coal to alkali-soluble compounds is found to proceed preferentially at the edges of the aromatic planes. An oxidation model is proposed in which the chief oxidants are molecular and radical species formed by the electrolytic decomposition of water at the coal surface-electrolyte interface. The oxidation reactions proposed account for the opening of the aromatic rings and the subsequent formation of carboxylic acids. The model also explains the observed anisotropic oxidation and the need for the porous pot or diaphragm used in previous studies of the oxidation of coal slurries.

Irreversible thermodynamics of transport processes through porous media composed of particles of different size

An experimental investigation on liquids transport through porous media is described. Porous diaphragms of Pyrex glass particles, whose sizes were in three ranges, between 150 and 500 μm, as well as water, methyl-, ethyl-, and isopropyl alcohols have been used to perform the hydrodynamic and electroosmotic experiments. The hydrodynamic flow is linearly dependent on the pressure difference and independent on the direction of the flow. The dependence of L 11 on the size of the particles forming the porous diaphragm agrees with that predicted by the classic theory of the electrokinetic phenomena. The electroosmotic coefficient L 12 has been found to decrease as the particle size increases, this being verified for all the permeants used. This fact is explained on the basis of the Anderson and Koh's model.

Properties and applications of electrodes covered with a porous diaphragm—2. Theoretical and practical aspects of electrosynthesis in single compartment electrolysis cells

The use of porous coverings on the counterelectrode for the reduction of the rate of loss reactions in single compartment electrolytic reactors has been studied. The theoretical current efficiencies for various overall reaction schemes have been calculated. The method has been tested for the electrosynthesis of potassium permanganate, ceric sulphate and sodium hypochlorite. Considerably improved reactor performance was realised. The experimental performance was in accord with that calculated theoretically.

New materials for loudspeaker diaphragms and cones—An overview

Desirable properties of materials for loudspeaker diaphragms are high specific Young's modulus (E/ρ), large flexural rigidity and large internal loss (tanδ). In order to obtain large flexural rigidity, honeycomb structured diaphragms or porous metal diaphragms have been used. For the purpose of realizing ideal loudspeaker diaphragms which can be easily produced, however, the material itself should have high values of E/ρ and tanδ This paper is a review on recent developments of materials for loudspeaker diaphragms in Japan, such as beryllium, boronized titanium, carbon fiber reinforced olefin, and polymer-graphite composite diaphragms.

Properties and applications of electrodes covered with a porous diaphragm— 1. Mass transfer investigation

The use of porous coverings on counter electrodes is proposed for controlling the mass transfer rates to the electrode and therefore the extent of possible loss reactions. An experimental study was undertaken to determine the mass transfer rates to electrodes with and without coverings of porous materials (porous PVC, porous-polyethylene, non-woven polypropylene). Additionally the effect of simultaneous gas evolution was investigated. The electrochemical method, based on the measurement of the limiting current for ferricyanide reduction, was employed for most experiments with the exception of those in which gassing at the covered electrode occurred. In the latter case the mass transfer rates were calculated from the concentration change observed during the batch electrolysis with recirculation of Ce(IV) (reduction to Ce(III)). The results have been correlated for the case of the non-woven material type E 1583 with no simultaneous gassing according to ▪ where Sh, Sc and Re are the Sherwood and Schmidt and Reynolds numbers, respectively and l, d p and ϵ are the covering thickness, pore diameter and porosity, respectively. Reductions by a factor of 100 in mass transfer rate at the mass transfer surface are easily attainable through the use of porous coverings. Interestingly, the results obtained at covered gassing electrodes, showed that the mass transfer rate decreases with increasing gassing rate. This is the inverse behaviour to that obtained at uncovered gassing electrodes. The implications on the current efficiency for operation of a differential diaphragm-less electrolysis cell in which loss reactions can occur at the counter electrode are discussed. The use of porous electrode coverings on the counter electrode in diaphragm-less cells is a technique which opens up new applications for these simpler cells.

Non-Linear Coefficients for Electroosmotic Transport of Alcohols through Porous Diaphragms

Non-Linear Coefficients for Electroosmotic Transport of Alcohols through Porous Diaphragms

Wetting and impregnation of porous metal diaphragms

The wetting and impregnation of porous metal diaphragms such as those investigated in this work occur almost instantaneously when their surfaces are hydrophilic, but are unsatisfactory (are hindered by air) when their surfaces are partially hydrophobized. When a partially hydrophobized diaphragm and a liquid react with each other, full wetting is obtained, brough about by the processes of dissolution and diffusion of gases adsorbed inside pores on organic contaminants. A number of methods are proposed for improving the wetting and impregnation of partially hydrophobized diaphragms.

Heat transfer through and out of the diaphragm of an electrolytic cell working in non aqueous medium

Removal of the heat produced in a porous diaphragm during electrolysis may be a controlling factor of the cd and thus of productivity of a cell. A model has been developed of various practical situations where the heat produced within the membrane can be removed either through one compartment or through both. The model allows a prevision of the maximum process temperature allowing this heat removal. The diverse cases have been compared and discussed. The validity of the model was verified experimentally in one case, and the agreement between measured and computed values is satisfactory.

ChemInform Abstract: DIFFUSION POTENTIALS AND TRANSPORT NUMBERS IN MOLTEN ALKALI CHLORIDES AND THEIR BINARY MIXTURES

Abstract Diffusion potentials at porous asbestos diaphragms separating chloride melts of different cation compositions have been measured as functions of temperature making use of cells with chlorine electrodes. Between individual molten alkali chlorides the diffusion potentials were found to increase with the difference in their cation radii reaching a maximum of ∼ 35 mV for and a minimum of ∼ 2 mV for The melts with smaller alkali cations were more electropositive in all cases. From the experimental data for the systems where M 1  Cs or K and M II  Li or Na, transport numbers of those cations were computed as functions of N . They proved to be smaller for Li + and Na + and larger for Cs + and K + as compared with their additive values. The cation mobilities were calculated. For Cs + or K + they are a little higher in the salt mixtures than in their individual chlorides whereas for Li + or Na + they are considerably lower. Such changes in cation transport numbers and mobilities can be explained in terms of autocomplex structure model for molten alkali halides developed recently by M. V. Smirnov.

Diffusion potentials and transport numbers in molten alkali chlorides and their binary mixtures

Diffusion potentials at porous asbestos diaphragms separating chloride melts of different cation compositions have been measured as functions of temperature making use of cells with chlorine electrodes. Between individual molten alkali chlorides the diffusion potentials were found to increase with the difference in their cation radii reaching a maximum of ∼ 35 mV for ▪ and a minimum of ∼ 2 mV for ▪ The melts with smaller alkali cations were more electropositive in all cases. From the experimental data for the systems ▪ where M 1  Cs or K and M II  Li or Na, transport numbers of those cations were computed as functions of N. They proved to be smaller for Li + and Na + and larger for Cs + and K + as compared with their additive values. The cation mobilities were calculated. For Cs + or K + they are a little higher in the salt mixtures than in their individual chlorides whereas for Li + or Na + they are considerably lower. Such changes in cation transport numbers and mobilities can be explained in terms of autocomplex structure model for molten alkali halides developed recently by M. V. Smirnov.

An experimental study of a single layer packed bed cathode in an electrochemical flow reactor

Experimental measurements are reported for a packed bed electrode consisting of a single planar layer of uniform copper plated spheres located between platinum anodes and restrained by two plane porous PVC diaphragms. Two mass transfer controlled reactions, namely the reductions ofm-nitrobenzene sulphonic acid and copper sulphate, were investigated and the electrochemical mass transfer data in the range 23 <Re < 520 correlated by the equationShSc−1/3 = 0-83Re0.56, the Reynolds and Sherwood numbers being defined in terms of a particle diameter. Variations of electrode potential throughout the bed were found to be small enough to ensure reaction selectivity in the system.

Apparatus for the determination and study of the permeability of porous diaphragms and filters

Apparatus for the determination and study of the permeability of porous diaphragms and filters

Three-compartment cell for diffusion measurements at boiling points

A diaphragm cell for experimental determinations of diffusion coefficients at elevated temperatures, up to the normal boiling point, was developed and is described. The cell consists of three compartments and is designed to operate at pressures up to 25 lb in-2 gauge. Two compartments separated by a porous diaphragm constitute the diffusion cell proper. The third compartment is used for storing one of the test liquids during the preheating period. At higher temperatures the cell is operated at pressures sufficient to suppress the boiling, which would interfere with the diffusion process. The operating procedure is described in detail.

Ontogeny of Foliar Diaphragms in Typha Latifolia

Morphogenetic pulsations in the intercalary meristem of the leaf of Typha latifolia (Typhaceae) produce regular alternating sequences of vascular and stellate-celled diaphragms separated at first by rib-meristem derivatives. The collapse of these derivatives in the region of elongation in and above the intercalary meristem, and the separation of the diaphragms from each other, produce a mature compartmentalized leaf, the compartments bridged by porous diaphragms but separated from each other by rigid vascularized partitions.

ONTOGENY OF FOLIAR DIAPHRAGMS IN TYPHA LATIFOLIA

Morphogenetic pulsations in the intercalary meristem of the leaf of Typha latifolia (Typhaceae) produce regular alternating sequences of vascular and stellate‐celled diaphragms separated at first by rib‐meristem derivatives. The collapse of these derivatives in the region of elongation in and above the intercalary meristem, and the separation of the diaphragms from each other, produce a mature compartmentalized leaf, the compartments bridged by porous diaphragms but separated from each other by rigid vascularized partitions.

A Theoretical Study of Bipolar Porous Electrodes

When electrical current passes through a porous metal diaphragm, the potential gradient in the electrolyte can serve to drive an electrochemical reaction provided that reactive species are present. One portion of the metal will act as an anode while the remainder will act as a cathode. A one‐dimensional model is presented for determining how the reaction rate distribution is affected by system parameters including charge‐transfer, resistance of the diaphragm, diffusion of solute species, and forced convection through the diaphragm. The results are presented in a series of dimensionless figures.

Proton Mobility in Water in Glass Pores of 15 µm Diameter

OUR work on hydrogen ion mobility1–4 led us to compare values of diffusion coefficients measured by polarography and by porous diaphragm cells. When D/D° (D = diffusion coefficient of an ion in a supporting electrolyte solution, D° = diffusion coefficient at infinite dilution, calculated from the Nernst equation) was plotted against concentration of supporting electrolyte, the curves for metallic cations4 approached a D/D° value of 1 at infinite dilution. Our curves for the hydrogen ion in alkali halides also approached 1 but those obtained by Woolf5 using porous diaphragm cells approached a lower value.

Hydrogen ion mobility in aqueous electrolyte solutions. Comparison of polarographic and diaphragm cell methods

Results for the diffusion coefficient of the hydrogen ion in aqueous solutions of the chlorides, bromides and iodides of sodium and potassium, and tetrabutylammonium bromide obtained from polarography using the modified form of the Ilkovic equation with A= 17 are compared with those determined by the porous diaphragm cell.The different results obtained by Woolf (using the diaphragm cell method) appear to be due to partially immobilized layers of water in the pores of the sintered glass diaphragm.

Theory and practice of an experimental technique for evaluating the permeability of thin porous diaphragms and filters

Theory and practice of an experimental technique for evaluating the permeability of thin porous diaphragms and filters

Convective diffusion across a porous diaphragm

Convective diffusion across a porous diaphragm