Alkalis cast iron

Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25 percent of the rare-earth compounds produced. La203 improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron. 

Fig. 3.51 Effect of nickel additions to cast iron in reducing corrosion by caustic alkalis...

Animation by reduction is usually carried out in cast-iron vessels (1600 gallons capacity, or higher) and alkali reductions in carbon steel vessels of desired sizes. The vessel is usually equipped with a nozzle at the base so that the iron oxide sludge or entire charge may be run out upon completion of the reaction. 

The alkali layer is separated by decantation and distilled. The MNT recovered is added to the main product. The latter is conveyed from the distiller to a washing tank where it is washed with water, then again with alkali and finally with a sodium carbonate solution. The moist MNT is conveyed by means of compressed air to a cast iron tank for temporary storage. 

As an element, silicon is a hard brittle metallic-looking substance which crystallizes in the diamond lattice. It is produced commercially by the electrothermal reduction of silica, resulting in a product which contains about 97 per cent silicon. The element shows no visible oxidation or corrosion at ordinary temperatures and oxidizes very slowly below red heat. Halogens attack it more readily, and chlorination proceeds satisfactorily at 250° C. to form the silicon chlorides which are perhaps the best-known volatile compounds of silicon. Whenever the element is exposed to nascent hydrogen, or its metallic compounds are treated with acids, some hydrides usually are formed, as may be noticed by the odor which such hydrides impart to the gas evolved when cast iron is dissolved in dilute acids. A mixture of concentrated nitric and hydrofluoric acids will dissolve pure silicon, but mineral acids singly will not do so. Hot concentrated solutions of alkalies will dissolve it, however, with the evolution of hydrogen. 

Finally, iron can also exert a reducing action when used in the presence of caustic alkali and nitrobenzene is converted successively to azoxy-, azo-, and hydrazobenzene under these conditions. Especially finely ground cast iron powder must be used for this purpose, ind it must be etched before its use in some cases. 

By mixing different grades of metal in the cupola, different makers produce cast-iron vessels which resist the action of special chemicals particularly well. The manipulation of cast-iron in the cupola to produce castings which have specific resisting properties in relation to different chemicals is a matter which has not yet received the attention it deserves. That the properties of cast-iron are largely influenced by admixtures with other elements is well established and it is possible that when our knowledge has become more complete, we shall be able to use iron vessels in operations for which at present they are not suitable. It may be generally said that cast-iron will withstand the action of alkalies when they are in solution and... 

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