Chromium plating is traditionally made from a solution of chromic acid (CrO3 which forms H2CrO4 after dissolving in water) and sulfuric acid (H2SO4) using insoluble anodes. The chromium is reduced to metal from the hexavalent state due to the catalytic effect of sulfate ions. There are also other catalysts in addition to sulfate, for example, fluorides and fluorosilicates. Sometimes several catalysts, for example, sulfate and fluoride, are used together, and those baths are called mixed-catalyst baths. The process with mixed-catalyst baths is faster, has better coverage, current efficiency, and larger operating range, is less sensitive to impurities and current interruptions, and is harder and more corrosion and wear resistant in hard chromium applications, but it is more expensive to use and fluorides are more corrosive, which may be detrimental for uncovered areas of the parts to be plated. (REF. SCIENCEDIRCT.COM)
WATER & WASTEWATER
The presence of caustic soda in sodium hypochlorite means the pH of water increases when the chemical is added. When sodium hypochlorite dissolves in water, two substances are formed that play a role in oxidation and the disinfection processes. These are hypochlorous acid and the less active hypochlorite ion. The pH of the water determines how much hypochlorous acid is formed. When sodium hypochlorite is used, hydrochloric acid is used to lower the pH and increase the disinfection ability. Sodium hypochlorite can be produced in two ways. One is by dissolving salt in softened water, resulting in a concentrated brine. This brine is then electrolyzed to form a sodium hypochlorite solution containing 150 grams of active chlorine per liter. During this reaction hydrogen gas is also formed. The chemical also can be produced by adding chlorine gas to caustic soda, producing sodium hypochlorite, water and salt.
FOOD & PHARMA
Sodium metabisulfite has found use as a reducing agent in the manufacture of biscuits, especially the low-fat, low-sugar types embraced by the generic term ‘semi-sweet’. The level of gluten development occurring during the mixing of semi-sweet biscuit dough is considerably less than that achieved in bread dough mixing, but with stronger flours, it is still sufficient to contribute to biscuit shrinkage. This shrinkage may be seen during the sheeting processes but is commonly seen when the biscuit units have been cut from the sheet. In severe cases, the shrinkage is immediately after cutting, whereas in less severe cases, it may only be observed as shrinkage after the biscuit has been baked. In this case, the biscuit dimensions will differ from those used in cutting and round biscuit shapes commonly develop eccentricity. The use of sodium metabisulfite is not universally accepted (Manley, 2000), and common ‘additive-free’ approaches are to more closely specify the qualities of the flour to be used or to add more water during dough mixing to yield a less elastic gluten network.
(REF. BAKING PROBLEMS SOLVED, STANLEY P. CAUVAIN)