Siloxicon.—This substance is an oxygen carbon-silicon compound, intermediate between silica and carborundum. It is formed in the electric furnace by reducing silica with carbon, but not carrying the reduction so far as with carborundum. Siloxicon is an exceedingly re factory material, neutral toward both acid and basic slags, and infusible and insoluble in molten metals. It is used as a furnace lining, either made into bricks or as a protective wash with sodium silicate.
Silicon.— The production of metallic silicon (90 to 95 per cent pure) has been accomplished by the extension of the principles used in the production of silicon carbide and ferro-silicon.
It is made in an arc furnace consuming 1,200 to 1,500 horse power, having two electrodes dipping down into the charge, consisting of coke and sand. The principal impurities are iron and alumintim, with some carbon.
Titanium Carbide.—This compound can be made by a process exactly as for carborundurn, but subst:tuting the mineral nuile (titanium oxide) for the sand of the charge. Made into electrodes for arc lights, titanitun carbide gives twice the light given by carbon electrode.s.
Calcium Carbide.— The earliest of the large electric furnace industries to be established was the manufacture of calcium carbide. It is made in the electric furnace by the interaction of lime, CaO, and carbon, usually in the form af coke or anthrac:te coal. Charcoal can be used, and in fact, on account of its purity, is the most desirable of the three, but is always more e,x pensive. The raw materials should be as pure as possible, in order to prevent the collection of unnurities in the product. Phosphorus and arsenic are particularly to be avoided as im purit.es, and sulphur is also undesirable. The lime and fuel, coarsely crushed, are mixed and charged into the furnace, where they are heated to the reaction temperature mainly by the direct action of the arc.
The furnaces for the manufacture of carbide are all of the arc type and only a snaall portion of the heating is done by resistance. They may turn out the carbide either in solid bloc.ks or as a liquid, to be tapped out as collected. For merly the furnaces were of the block type, but now many are going over to the tapping furnaces.
The earliest form of furnace consisted of an electrode suspended in a car, which served as the other electrode and as a container for the carbide. This form of furnace was srnall
and of low efficiency, 100 to 200 Icilowatts at 40 to 70 volts, with a power consumption of 6 to 7 kilowatt hours per kilogram of 85 per cent carbide, an efficiency of only 40 per cent. The losses of raw materials were also high.
T13e modification of the block furnace for cont:nuous operation, the solidified material being drawn away front. underneath the work ing Ione of the furnace, inade possible a de crease in power consumption to 4.5 kilowatt hours per lcilogram of carbide. The size of the furnace was also increased up to 375 kilowatts.
Tapping furnaces are much larger, up to 1,200 to 1,400 kilowatts and have a power con sumption of 4.2 to 4.5 kilowatt hours per kilo gram of carbide. One ton of product requires 900 kilograms of lime and 600 kilograms of anthracite coal.
Three-phase carbide furnaces have been built up to 3,000 kilowatts per phase, or 9,000 kilowatts per furnace. This proved to be the limit in furnace extension for single units, as the handling of larger currents at the electrodes gave excessive heat and volatilized the charge. A unit of double this size was constructed by including two three-phase electrode systems in one furnace jacket. This gives an 18,000 kilo watt furnace with 6 electrodes, each electrode carrying up to 45,000 amperes. A furnace of this size will produce carbide with a power consumption of 4 to 4.2 kilowatt hours per kilogram. Using charcoal as a source of car bon, the 'power consumption can be cut as low as 3.8 kilowatt hours per kilogram, equivalent to about 69 per cent efficiency, but the extra cost of the charcoal over that of the coal will probably overbalance the extra saving in power.
Cyaisamide.—A large portion of the calcium carbide now made is for use as a raw material for the manufacture of cakium cyanamide. The carbide after being finely ground is heated to temperature of about 1,0M° C. (1,830° F.) in a special type of electric furnace, in the pres ence of pure nitrogen. The nitrogen combines with the carbide forming CaC142. This formula calls for 35 per cent of nitrogen in the product, but since the carbide is never entirely pure and since it is not entirely converted, the resulting product carries about 20 per cent of nitrogen.