Carborundum

“ It is a little more than one and a fifth times the weight of sand, is infusible at the highest attainable heat, but is decomposed in the electric arc, and is insoluble in any of the ordinary solvents, water, oils, and acids, even hydrofluoric acid having no effect upon it. Pure carborundum is white. In the commercial manufacture the crystals are produced in many colors and shades, partly as the result of impurities and partly by surface oxidation. The prevailing colors are green, black, and blue. The color has no effect upon the hardness. ”

“ In 1891 he carried on experiments with high currents and a mixture of ground coke and sand. He found a method of fusing these so that the oxygen of the sand passed off with carbon in the form of carbonic acid gas, and the reduced metallic silicon combined with an equal atomic weight of carbon and produced a new body which he named carborundum. The success met with in making carborundum led to the devising of a method of manufacturing artificial graphite in the electric furnace. A soft, non-coalescing graphite was made in 1906. ”

“ It has long been the practice on certain works to wash the face of firebrick work with a thin paste of some very refractory material—such as kaolin—in order to protect the firebricks from the direct action of the flue gases, &c., and quite recently a thin paste of carborundum and clay, or carborundum and silicate of soda has been more extensively used for the same purpose. So-called carborundum bricks have been put on the market, which have a coating of carborundum and clay fired on to the firebrick, and which are said to have a greatly extended life for certain purposes. ”

“ The color has no effect upon the hardness. Crude carborundum, as taken from the furnace, usually consists of large masses or aggregations of crystals, which are frequently very beautifully colored and of adamantine luster. ”

“ Nevertheless there can be no doubt that all kinds of carbon are fused under the molecular bombardment, but the liquid state must be one of great instability. Of all the bodies tried there were two which withstood best--diamond and carborundum. ”

“ When heated with nitrogenous substances, in the presence of carbonated or caustic alkali, it forms cyanides. It combines directly with silicon, at the temperature of the electric furnace, yielding carborundum, SiC; and H. Moissan has also shown that it will combine with many metals at the temperature of the electric furnace, to form carbides (q.v.) ”

“ The manufacture of calcium carbide is carried on on a very large scale at Niagara, with electric power obtained from the Falls, and at Odda in Norway, where the power is supplied by the river Tysse. Carborundum, a substance almost as hard as the diamond, is largely used for grinding and polishing purposes. It is manufactured by sending a strong current through a furnace containing a core of coke surrounded by a mixture of sand, sawdust, and carbon. The core becomes incandescent, and the heating is continued until the carbon combines with the sand, the process taking about a day. ”

“ A drill is merely a spiral chisel which revolves upon its own center. A saw is a gang of tiny chisels, and a file consists of still smaller chisels which are broader than those of the saw. In grinding we have rough surfaces in which particles of emery or carborundum act as tiny chisels. The shears, the punch, and the cutting torch are practically the only exceptions to the rule that metals are always cut by chisels, and even the shears may be conceived as consisting of a pair of broad coacting chisels, while it takes little imagination to see a form of chisel in the punch. ”

“ The top of the furnace now slowly settles, and cracks in long, irregular fissures, sending out a pungent gas which, when lighted, burns lambent blue. This gas is carbon monoxide, and during the process nearly six tons of it are thrown off and wasted. It seems, indeed, a somewhat extravagant process, for fifty-six pounds of gas are produced for every forty of carborundum.
"It is very distinctly a geological condition," said Mr. Fitzgerald; "crystals are not only formed exactly as they are in the earth, but we have our own little earthquakes and volcanoes." ”

“ The first American electric furnace, constructed by Robert Hare of Philadelphia. From "Chemistry in America," by Edgar Fahs Smith
The substance thus produced at Niagara Falls is known as "carborundum" south of the American-Canadian boundary and as "crystolon" north of this line, as "carbolon" by another firm, and as "silicon carbide" by chemists the world over. Since it is next to the diamond in hardness it takes off metal faster than emery (aluminum oxide) , using less power and wasting [Pg 250] less heat in futile fireworks. ”

“ Firing.
Carborundum stones are often used in place of emery stones. They are rather more expensive than emery stones and wear out quicker, but they cut the work down much faster. No. 120 and No. 180 grits are the most satisfactory. These stones sometimes get filled up with metal, but in 33this case the metal can be eaten out with acid.
It is convenient when stoning to hold the piece to be stoned on a small block of wood, on which a mold of shellac has been made into which mold the piece of work will snugly fit. ”

“ In the tapping process a fixed crucible is used, lined with carbon, the electrode is nearly as big as the crucible and a much higher current density is used. The carbide is heated to complete liquefaction and tapped at short intervals. There is no unreduced material, and the process is considerably simplified, while less expensive plant is required. The run carbide, however, is never so rich as the ingot carbide, since an excess of lime is nearly always used in the mixture to act as a flux, and this remaining in the carbide lowers its gas-yielding power. ”

“ Carbon unites with iron and some of the metals to form carbides; [Pg 416] combined carbon of this kind is detected by the odour of the carburetted hydrogen evolved when the metal is treated with hydrochloric acid; for example, on dissolving steel in acid.
The natural carbon compounds, although, speaking generally, insoluble in hydrochloric or nitric acids, are more or less attacked by aqua regia. The assayer seldom requires these compounds to be in solution. The presence of "organic matter" [117] interferes with most of the reactions which are used for the determination of the metals. ”

“ The more or less reduced carbide is filled in the shell, either without any admixture or united into a compact mass by a binding agent, such as colophony, pitch, tar, sand, etc.
Deodorization Of Calcium Carbide.—Calcium carbide is known to possess a very unpleasant odor because it constantly develops small quantities of impure acetylene in contact with the moisture of the air. Le Roy, of Rouen, proposes for portable—especially bicycle—lamps, in which the evil is more noticeable than in large plants, simply to pour some petroleum over the carbide and to pour off the remainder not absorbed. ”

“ The metallic carbides are crystalline solids, the greater number being decomposed by water into a metallic hydrate and a hydrocarbon; sometimes hydrogen is also evolved. Calcium carbide owes its industrial importance to its decomposition into acetylene; lithium carbide behaves similarly. Methane is yielded by aluminium and beryllium carbides, and, mixed with hydrogen, by manganese carbide. The important carbides are mentioned in the separate articles on the various metals. The commercial aspect of calcium carbide is treated in the article Acetylene. ”

“ Carbides of other metals can be made in the electric furnace, but, owing to the cheapness of the new material, calcium carbide is the only one of these which has industrial value as a source of acetylene. One pound of pure carbide yields 5.89 cubic feet of acetylene.
Thus far carbide has been found industrially valuable for two other purposes. The one is for carbonizing steel; experiments in Germany show that iron or soft steel takes up carbon more readily when it is heated with carbide than when it is heated with coal dust or charcoal. Some steel works are now using carbide for this purpose. ”

“ By using pressure during consolidation this carbon may eventually be converted into diamonds.
Another valuable product of the electric furnace, acetylene gas, was discovered in Dublin by Edmund Davy in 1836. Subsequently numerous chemists discovered means for making carbides. T. Sterry Hunt, an American chemist, observed in 1886 that oxides of the alkaline metals and of calcium, magnesium, aluminum, silicon, and boron could be reduced in the electric furnace in the presence of carbon and could be alloyed with other metals. He also found that silicon and acetylene could be made that way. ”

“ To fix the nitrogen in the carbide it is necessary to cool the latter after it comes from the electric furnaces and grind it to a very fine powder. This powder is then placed in furnaces that look like steel barrels but are three or four times larger than an ordinary barrel. The oven filled with calcium carbide is then electrically heated with a carbon rod running through the center. When the temperature is about as hot as that of molten iron the pure nitrogen gas from the liquid air plant is pumped in and allowed to act on the calcium carbide for about a day and a half. ”

“ Like aluminium carbide it is slowly decomposed by water with the production of methane. Several basic carbonates are known, being formed by the addition of beryllium salts to solutions of the alkaline carbonates; the normal carbonate is prepared by passing a current of carbon dioxide through water containing the basic carbonate in suspension, the solution being filtered and concentrated over sulphuric acid in an atmosphere of carbon dioxide. The crystals so obtained are very unstable and decompose rapidly with evolution of carbon dioxide. ”

“ For some purposes it is preferred to charcoal, in consequence of the bitumen it contains, which appears to contribute to the rapidity of the combustion. It is to be observed, that, as the base of coal is carbon, its action is the same as charcoal, and therefore, by producing the same effects, or nearly so, as charcoal itself, the phenomena it presents are analogous. As 12.709 parts of carbon, according to Kirwan, are required to decompose 100 parts of nitrate of potassa, we may readily ascertain the quantity of real carbon in any specimen of coal. ”

“ Calcium carbide is a hard, porous, grayish-black or bluish-gray incombustible material somewhat crystalline in form, odorless and unchangeable in a dry atmosphere, but when subjected to moisture gives off more or less acetylene gas. Carbide cannot be ignited and when well packed to prevent its coming in contact with water it is safe as regards all the conditions of transit and storage. ”

“ At temperatures between about 900° and 1100° the carbon exists in the form of carbide of iron dissolved in the iron, at a temperature of 890° the iron which can exist in different forms as an allotropic substance passes from the γ form to the β form, and in this form cannot dissolve more than .9 per cent, of carbon as carbide. Thus at this temperature a large proportion of the carbon passes out of the solution. ”

“ When a manufacturer strives to give his carbide the highest gas-making power possible he frequently increases the proportion of carbon in the charge submitted to electric smelting, until a small excess is reached, which remains in the free state amongst the finished carbide. After decomposition the fine particles of carbon stain the moist lime a bluish grey tint, the depth of shade manifestly depending upon the amount present. ”

“ The charcoal should, in particular, not be less than the nitre, as the smallest portion less than the whole atom would be the same as to leave out the whole atom, in which case there would be no carbonic oxide formed. If, for example, instead of the proportions of nitre 75·5, charcoal 16·2, sulphur 15, the carbon were 16, then there would be 4·2 of carbon left in the residuum, and no carbonic oxide would be formed, since bodies cannot unite but in definite proportions. ”

“ As charcoal enters into the composition of gunpowder, and the effective force of powder depends considerably on the quality, as well as the proportion of charcoal, it is obvious for this purpose, it should be as pure as possible.
Carbon is always obtained from some of its combinations, as from pitch, tar, rosin, wood, and oil. Various processes are employed for this purpose. Thus, by the combustion of rosin and oil, as well as pitch, tar, turpentine, &c. a soot is [90] formed that collects, called lampblack, which is nothing more than the carbon or charcoal. ”

“ The metallic chromium thus obtained has the appearance of a fine light-grey powder which is seen to be crystalline under the microscope; its sp. gr. at 16° is 6·7284. It fuses (with anhydrous borax) only at the highest temperatures, and after fusion presents a silver-white fracture. The strongest magnet has no action upon it.
Moissan (1893) obtained chromium by reducing the oxide Cr2O3 with carbon in the electrical furnace (Chapter VIII., Note 17) in 9–10 minutes with a current of 350 ampères and 50 volts. The mixture of oxide and carbon gives a bright ingot weighing 100–110 grams. ”

“ The purity of the carbide entirely depends on the purity of the material used in its manufacture, and before this fact had been fully grasped by manufacturers, and only the purest material obtainable employed, it contained notable quantities of compounds which during its decomposition by water yielded a somewhat high proportion of impurities in the acetylene generated from it. ”