The total voltage required for the cells is 2.3 to 3.6 volts. The energy requirement for one cubic meter of mixed gases is 3.7 to 5.9 kilowatt hours, the alkaline cells giving the lower figure, and the acid cells the higher. In the acid cells, lead anodes are used, which peroxidize, and the presence of PbO, causes the oxygen to contain some ozone. The chlorides in the alkaline solu tion allow the anodes, usually of iron or nickel, to be slowly attacked, requiring occasional re placement. The purity of the gases is usually 97 to 99 cent.
Electric One of the earliest commercial processes in electrochemistry was that devised by E. H. and A. H. Cowles in 1884. A mixture of about two parts of alumina, one or two parts of granulated copper and one or two parts of carbon was introduced in a brick work chamber. Bundles of carbon rods inserted at the ends formed the electrodes between which a current of 3,000 amperes at 50 volts was main tained. At a very high temperature the alumina was reduced (Al20. + 3C=.2A1 3C0) and the resulting aluminum combined with the cop per to form aluminum bronze. This was the forerunner of the various types of electro thermal operation described in the following paragraphs.
Iron and Steel can be produced by reducing iron ore with carbon in an electric furnace. For example, a mixture of magnetite and carbon can be heated by passing a current through it, as in the Cowles aluminum bronze process, by passing the current through a carbon core in contact with the material as in the carborundum proc ess; or by the action of an arc as in the carbide process. The reaction is simply Fes0.-f 3Fe 4CO. Pure iron, cast iron or steel may be produced, depending upon the proportion of carbon. The chief advantages are the directness of the process and the fact that no impurities (sulphur, silicon, etc.) are introduced in the fuel, besides a considerable saving of fuel over the ordinary steel furnace. On the other hand it is a question of location, whether the electric furnace can compete in economy with the blast furnace, the Bessemer converter, and the open hearth furnace. Pig iron has been made in the electric furnace in places like California and Norway, where water power is cheap and fuels expensive. The grade of iron thus produced is equal to the best Swedish charcoal iron, and commands a higher price than ordinary pig iron.
The chief utilization of the electric furnace in the iron and steel industry, however, is not in the direct production of pig iron or steel, but in the conversion of low-grade metal from the Bessemer or open-hearth into a high-grade metal, or in the remelting and refining of scrap steel for high-grade castings. Ordinary metal from the Bessemer converter or the open-hearth furnace can, in the electric steel furnace, be con verted into metal of crucible quality or better, at a lower cost than crucible steel, and in large quantities, up to 25 tons to the charge.
One of the most important developments in the steel industry in recent years has been the production of the various al loy steels,— steels in which some special prop erty is secured by the addition of some other metal to the simple alloy of iron and carbon.
The simplest way to produce these steels is by the addition to ordinary steel of the proper amount of an iron alloy carrying a high per centage of the metal desired. This ferroalloy is usually, though not always, made electrother mally by the reduction by carbon in an electric furnace of an oxide of the metal, in contact with metallic iron to take up the reduced metal. Sometimes a reduction is made of a mixture of iron oxide and the oxide of the metal in question, but this necessitates the supplying of electric energy for the reduction of the Iron, as well as of the alloying metal; and the iron can usually be reduced more cheaply by other methods. Under these conditions the reduction of the oxide is much more readily accom plished than if there were no iron present, since the iron considerably reduces the melting point of the resulting mixture. The type of furnace used varies somewhat with the metal being pro duced, but in general are quite similar to those used for the production of calcium carbide.
The alloys that are made in this way are: ferromanganese, ferrosilicon, ferrochromium, f erronicicel, ferrotungsten, ferromolybdenum, ferrovanadium, and ferro-uranium.
Silicon Known under the trade names ecarborundum,a and lexo lon" silicon carbide is produced in large quanti ties by the process invented by E. G. Acheson. It is formed by intensely heating in an electric furnace a mixture of 35 per cent of ground coke, 52 per cent of sand, and about 11 per cent of sawdust and 2 per cent of salt, the yield being seven or eight tons of crystalline carborundum and a considerable amount of the amorphous material. The furnaces used at Niagara Falls consist of simple brick hearths 28 feet long and 11 feet wide, with brick walls at each end, these being about three feet thick and six or eight feet high. The side walls are built without cement or mortar to allow the escape of gases and because they have to be pulled down at the end of each run to dis charge the furnace. In the middle of each of the end walls there are iron frames holding together a large carbon electrode built up from a number of small electrodes, through which the current is led to a core about two feet in diameter composed of broken coke and ex tending the entire length of the furnace. This core is raised to a very high temperature by passing through it an alternating current, using about 1,600 kilowatts. The heat from the core permeates the mass and converts it at a tem perature of about 2,200° C. (4,100°F.) for some distance around the core into silicon car bide. The unchanged material on the outside is worked over in the next charge. The coke of the core is converted into graphite. The shell of carbide is broken up after the furnace has cooled and is used in the manufacture of grinding wheels and other forms of abrasives. It is also used to a limited extent as a refac tory material, since it is stable at high temper atures and is a good conductor of heat.