Diaphragm deterioration

Of all the cell components, the diaphragm usually has the shortest life. The ability of a diaphragm to resist the back migration of hydroxide slowly becomes impaired with service life. The performance of the diaphragm deteriorates for the following reasons ... 

In the obsolescent asbestos diaphragm cell, the product on the cathode side is typically 11% in NaOH and 16% NaCl (i.e., about 2.7 mol of each per kilogram of solution). Evaporation to about 50% NaOH causes most of the NaCl to crystallize, leaving about 1% NaCl in solution this caustic soda is sufficiently pure for many industrial uses. The Si-0 links in the asbestos are attacked by the alkali (Section 3.5 and Chapter 7), and the diaphragm soon deteriorates. 

The working life of these porous diaphragms is satisfactory, the early ones having shown a life of over four years without noticeable deterioration while operating 9 hours a day excepting holidays.011 Cleaning is easily accomplished when necessary by washing with water. 

As with the mercury cell, the introduction of metal anode technology led to a considerable review of cell design and the opportunity to optimize the anode-cathode gap, which as with the mercury cell, increased with time as the anode deteriorated, but unlike the mercury cell, could not be adjusted with the cell in service. Diaphragm technology improved, with the replacement of wet... 

The voltage drop in each monopolar electrolyzer is equal to the voltage drop of a single cell. This depends primarily on the type of cell, the current density, and the choice of membrane or type of diaphragm. The number of electrolyzers contained in a cell line then fixes its total voltage. The design voltage must be sufficient to allow for losses in buswork and interceU connectors, the maximum current density to be used, and the deterioration with time of the components of the circuit. 

In the diaphragm process, the removal of sulfate is not always necessary because 504 can be removed from the cell liquor as pure Na2S04 during the concentration process. In the membrane process, the brine must be purified to a much higher degree to avoid the deterioration of the membrane. The Ca and Mg " concentration must be < 0.02 ppm (20 ppb), so a second, fine purification step is required (see Section 7.2.1). 

In healthy volunteers, acute increases of arterial carbon dioxide to 54 mmHg (corresponding to a pH of about 7.29) reduces the capacity of the unfatigued diaphragm to generate pressure by 10-30% (Fig. 12) (98). This direct inhibitory effect of respiratory acidosis on respiratory muscle function could provide a potential mechanism for the rapid clinical deterioration that can occur with severe asthma and during COPD exacerbations (98). Yet, the human data suggesting a direct deleterious effect of respiratory acidosis on respiratory muscle function... 

Fig. 13.20. A 67 year old man, 2 days after total gastrectomy. At the level of the oesophagojejunostomy black arrow), an extensive extravasation develops in the left lateral direction and delineates the left dome of the diaphragm (white arrow). This was a typical leak and he was reoperated upon immediately as his clinical course was deteriorating rapidly...

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