Diaphragms materials

The toxicological problems associated with asbestos have been widely pubHshed and asbestos has been banned from most uses by the EPA. However, modem diaphragm cell chlorine plants have not had difficulty meeting the required exposure limits for asbestos fibers, and, as of 1990, the chlorine industry had an exemption allowing the continued use of asbestos as a diaphragm material. 

Non-ferrous Metals and Alloys Diaphragm material, metal composite, refractory metal. 

Reactor type Electrochemical micro flow cell Diaphragm material PTFE... 

On forcing a liquid through a diaphragm, diaphragm currents are set up, a phenomenon noted by Wiedemann and Quincke and one hilly accounted for on the hypothesis of the existence of an electrical double lay er between the diaphragm material and the liquid. 

If the solid diaphragm material adsorbs both hydrogen and hydroxyl ions it is evident that electric endosmose will cease when equal ionic adsorption has taken place, the double layer potential or electrokinetic potential being at this point zero and the diaphragm is at the isoelectric point. 

Diaphragm material Solution Diaphragm charge Relative rate of electric endosmose... 

Most newer diaphragm materials are membranes made of highly alkali-resistant fluorocarbon polymers that incorporate cation-exchanging functional groups such as sulfonate.8 One such material, Nafion (Du Pont trade-name), is... 

Diaphragm material Silicon Mixing chamber length, width, thickness 6 mm, 6 mm, 0.2 mm... 

Table 2 Diaphragm material and range of applications, ++ resistant against almost all fluids, - resistant in a...

Common diaphragm materials used in commercial electrolytic cells are porous ceramics, asbestos, and microporous plastics, but they all suffer from poor mechanical strength and availability in limited sizes and shapes. It was only after the availability of the highly stable perfluori-nated ion-exchange membranes that the problems of cell separators for industrial production were solved. These ion-exchange membranes allow only cation or anion (with water) transport between electrode chambers. 

Diaphragm valves are difficult to specify because of the variety of solvents to which the diaphragm itself must be resistant. The only multi-purpose diaphragm material, poly(tetrafluoroethylene) or PTFE, is liable to be damaged by the solids that dirty solvents may contain. 

I. Physical and Chemical Properties. Asbestos is a generic term for a variety of hydrated silicate minerals (see Table 4.7.1), which are characterized by their fibrous structure [6-8]. Although there are six different asbestos minerals and several have found use in cell separators, chrysotile predominates as a chlorine cell diaphragm material. Chrysotile fibers consist of bundles of parallel fibrils. These fibrils are hollow needles with an outer diameter of about 30nm and an inner diameter of 4nm, and consist of... 

Abstract Ion-conducting materials are used as cell separators in electrolysis cells for the double purpose of carrying electric charges between electrodes and separating the products formed at each electrode. The purpose of this chapter is to provide an overview of chlor-alkali technology and associated cell separators. After a brief historical review of the chlor-alkali process, the main reaction characteristics (thermodynamics, cell reactions and kinetics) are detailed in Section 9.1. Main chlor-alkali technologies are described in Section 9.2. Main cell separators are described in Section 9.3 (diaphragm materials) and in Section 9.4 (membrane materials). Some improved electrolysis concepts are described in Section 9.5. 

The most popular types for bioprocessing plants are the diaphragm and ball valves types. The latter are more robust but contain crevices making sterilisation more difficult. Barnsleystated a preference for diaphragm valves since they are reasonably crevice free the material EPDM (ethylene propylene diene modified) was the preferred diaphragm material. 

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