Diaphragms asbestos sheet

The middle iron plates e1, e2 etc. act as bipolar electrodes, and have on both sides extended perforated sheets n. The terminal monopolar electrodes have only one sheet n each. The diaphragm frame holds the asbestos cloth. The top edges of the electrodes and diaphragm frames have angle irons a, b, which are riveted and form a flat surface beneath the electrolyte level. This surface iB... 

This electrolyzer has a U-shaped concrete frame on the open sides diaphragms A are fastened these are made of asbestos cloth covered with a paste of iron oxide, asbestos powder and colloidal ferric oxide. Cathodes B made of perforated MS sheet are placed tightly against the diaphragms. 

The diaphragm cell has a membrane of sorts, with a sheet of asbestos felt separating the two compartments. The diaphragm keeps the chlorine gas out of the cathode compartment, but it offers no selectivity for diffusion and migration of ions. Therefore, the NaOH produced is dilute (12% maximum) and loaded with NaCl. Evaporation of the catholyte to concentrate the NaOH to 50% causes most of the NaCl to precipitate, but the chloride level of the product remains about 1%. In some cases the asbestos diaphragms have been replaced with other porous membranes (principally PVC) to improve membrane life and avoid environmental criticism. In other cases diaphragm cells have been converted to membrane cells. 

Diaphragms. The earliest asbestos diaphragms were made of sheets of asbestos paper. Asbestos was chosen because of its good chemical stability and its ion-exchange properties. Asbestos has been relatively inexpensive, since it is a relatively abundant natural material that was already being mined and processed for other industrial purposes, such as insulation. 

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