The sodium combines with the silica and alumina of the re fractory brick to a liquid slag, which drops off. In conse quence of the development of chlorine the brick acquires a spongy appearance. An analysis of such brick showed a con tent of 7.17 per cent. of sodium. The brick of the walls of such coke ovens are completely dissolved by this action. Large quantities of free chlorine are contained in the gases of coke-ovens.
This destruction of coke-ovens has caused many losses. With coke-ovens, where the by-products are gained, the con tent of salt in the gases is not injurious. However, a portion of the salt remains in the coke, and according to recent experi ments, the different cokes used in the blast-furnaces of a large concern contained, on an average, o.181 per cent. of salts ble in water, namely: o.o62 per cent. of sodium sulphate (Na, and 0.119 per cent. of common salt (NaCI). According to this, 62 kilogrammes (136.4 lbs.) of sodium sulphate, and 119 kilogrammes (261.8 lbs.) of common salt are introduced into a furnace consuming only too tons of coke per day. As is well known, common salt is used for glazing vessels of clay and stoneware.
If now the refractory brick of the walls of blast-furnaces are constantly exposed to the action of such large quantities of salt, and hence become glazed, they will just as well wear out in a few months as those of the coke-ovens.
Ad. 1. In most beds of the best refractory clays occur pyrites which, at higher temperatures, are converted into ferrous sul phide ; the latter by the gases of the blast-furnace is converted into metallic iron.
With this metallic iron the gases of the furnace, in which large quantities of carbonic oxide occur, remain in further con tact. By the contact with the metallic iron the carbonic oxide is decomposed to carbon and carbonic acid, the carbon de positing upon the surface of the small iron balls and forming a shell around them. Notwithstanding this shell of carbon, new carbonic oxide gases constantly penetrate to the iron, fresh carbon being always deposited upon the latter.
The very minute balls of iron are thus gradually surrounded with an envelope of carbon the size of a pea and a hazel-nut. Nothing, and least of all the refractory brick of the furnace, can withstand this gradually augmenting separation of carbon ; the brick being thereby cracked and completely destroyed.
The brick-work of blast-furnaces, if constructed of carbon brick, would not be exposed to the three last-mentioned causes of destruction. Carbon brick are now made without the addition of clay, etc. They possess a considerable degree of hardness and solidity, so that they would oppose considerable resistance to abrasion by the downward passage of the charge. They may also be used not only for the boshes but also for the stack.
Carbon Deposits in Fire Brick. (Written for the Engineer ing and Mining Yournal by A. D. Elbers.) The following extract from a recent essay on " The causes of the destruction of fire-brick in blast-furnace linings," Stahl and Eisen, March 15th, 1892) is noteworthy: Cause No. from the formation of carbon de posits, within the brick, on particles of iron derived from pyrites.
This hypothesis—analogous to that of lumps of ore bursting in the blast furnace by reason of their impregnation with de posited carbon—is accounted for as follows : " The ferric disul phide (pyrites) changes at elevated temperatures to ferrous sulphide, the latter is changed by the blast-furnace gases to to metallic iron, and on this iron the carbonic oxide gas, in permeating the brick, deposits carbon according to the reaction : 2C0 = CO, + C. The particles of iron, which are quite dimin utive, thus become coated with carbon, and this deposition continues until the coated particles grow to lentil, pea, or even to hazel-nut size, and then—burst the brick !" The assumed but undefined reaction by which the gas-fur nace gases are supposed to " change" ferrous sulphide to me tallic iron, serves, in this instance, to support an apparently fallacious theory ; for at the temperature at which FeS or can lose the remainder of their sulphur, no deposition of car bon takes place. In other words, if the brick in any particular spot of the furnace is hot enough to render the complete oxida tion of the sulphur possible, then that brick is too hot for the carbonic oxide gas that enters its interstices to split up into carbonic acid gas and solid carbon.