Cooling Diaphragm forming

The nitrous acid liberated at the anode reacts with the amine to form a diazonium compound, and this immediately condenses with the phenolic substance which is present to produce the azo-dye. Cooling is desirable though not so important as in the ordinary chemical method, since the diazonium compound couples with the phenol immediately it is formed but a diaphragm must be used to separate anode from cathode. Orange II, Congo red, dianisidine blue, and many other colours have been formed in this way. 

Rarefaction waves have been used in shock tubes to produce rapid quenching of a reaction. Fig. 2 shows the usual experimental arrangement. The rupture of diaphragm 1 forms the initial shock and leads to the ordinary temperature rise in the reaction chamber. The temperature is increased to the required value by the return of the reflected shock wave from the end-wall. Diaphragm 2 is then ruptured mechanically at about the time that the rarefaction wave arrives this rupture produces a stronger expansion wave which rapidly cools the reacting gases. 

The characteristic feature is a large number of vertical anolyte channels (9 x 3 mm), on whose back foils of platinum as active material are attached on tantalum foils mounted on a supporting plate. This is cooled from behind to realize an anolyte temperature of 30-45 °C (to diminish acid-catalyzed hydrolysis of the peroxodisulfate anion formed). Graphite acts as a cathode block, separated from the anode channels by a microporous polymer diaphragm, preventing reduction processes at the cathode. 

In a mercury cell, the brine is removed before sodium hydroxide is formed, thus the resulting solution typically contains <50 mg kg of sodium chloride and even lower concentrations of other salts. The amount of water added to the decomposer is usually adjusted to make 50% sodium hydroxide, or rarely 73% sodium hydroxide. These solutions are simply cooled and filtered without the need for evaporation. This avoids contamination by nickel and other metals, which occurs during the concentration of sodium hydroxide from diaphragm cells. Because rayon production requires low concentrations of metals and salt, mercury cell sodium hydroxide is also called rayon grade. However, mercury cell sodium hydroxide typically contains 10-50 pg kg of mercury. Some of this mercury ends up in hypochlorite products, although the concentration is reduced by dilution and processing operations such as filtration. 

The limitation of the sodium hydroxide concentration to 12% means that an additional step must be introduced into the process if this product is to be traded in its normal form, i.e. 50% solution. The evaporation of water (note, to get from 10 to 50% solution, about S0% of the water must be removed) is an energy-intensive process which also requires additional plant. The evaporation stage does, however, reduce the problem from CP contamination since, on cooling, much of the sodium chloride crystallizes-out from the 50% sodium hydroxide solution. Even so, the chloride level remains about 1% and this is unacceptable in many applications, for example it increases corrosion problems in any situation where the sodium hydroxide contacts metals. Certainly, diaphragm plants are most attractive, if the sodium hydroxide can be used as a 10% solution containing the sodium chloride ... 

Because the laminate is not in contact with the mold, the temperature loss (in comparison to the stamp forming process) worsens, which means that the cooling or cycle times increase. The service life of the mold is increased in comparison to the stamp forming process because no fiber marks occur on the mold surface due to the protection of the diaphragms so mold wear is then significantly decreased. 

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