The presence of small amounts of tellurium in certain kinds of copper, and its exceptionally deleterious influence in producing red-shortness of this metal, led the author to conduct a few experiments on the influence of tellurium on the properties of brass. While these experiments were not intended to be exhaustive, they demonstrate that, as far as the rolling of brass is concerned, tellurium, unless it occurs in far greater amounts than exist in refined copper, cannot be called an injurious impurity. In comparatively large amounts it appears to impart cold-shortness to high-brass.
Tellurium, the rare element that it is considered to be, has recently been extracted on a large scale from the slimes of an American electrolytic copper-works. They have, in attempts to discover some commercial use for it, sent it out promiscuously and gratuitously in quantities which would lead the young chemical student to fancy that a rare element exists only in name. Through the courtesy of Mr. R. L. Whitehead, of Baltimore, the author was able to obtain somewhat over 2 lbs., and use it in quantities which, at the market price, would be prohibitive.
In order to add specific quantities of tellurium to brass, a rich alloy of copper and tellurium was previously made. The method was as follows, viz.:
Nine and one-half lbs. of Lake copper were melted under charcoal in a new plumbago crucible, and then ½ pound of tellurium was added in small portions at a time. The mixture was stirred with a plumbago-stirrer and poured into ingots. Considerable heat was generated when the tellurium and copper combined, the metal surrounding the portion of tellurium which was introduced becoming white hot as soon as the combination took place. The cupro-tellurium alloy ran without any film of oxide, and quite freely. The ingots, both hot and cold, broke easily, with a homogeneous and crystalline fracture. This fracture possesses a characteristic brownish-red color.
The copper and tellurium, from which the alloy was made, were carefully weighed on Robervahl balances, and the weight of the ingots of the alloy obtained was exactly 10 lbs. The loss by volatilization or oxidation, then, was too insignificant to be taken into consideration. The composition of this alloy is:
As a standard brass alloy to be used for the experiments, a mixture consisting of 60 per cent, copper and 40 per cent, zinc was used. This alloy, as previously stated, was employed because it is practically the only high-brass alloy which will work both hot and cold.
The copper was melted in a plumbago crucible under charcoal. The cupro-tellurium alloy was next added, the mixture stirred, and lastly the zinc added. Care was used to obtain the purest copper and zinc. The temperature was kept as low as possible, to guard against excessive loss of zinc. The mixture was poured in an iron mold of internal dimensions of 5/8 x 2 3/8 x 24 in. The mold was warmed and coated with sperm oil.
Experiment No. 1.—Four lbs. of Lake copper and 2 lbs. of the 5-per-cent, cupro-tellurium alloy were melted together. Then 4 lbs. of Bertha zinc were added. The composition of this alloy is :
The metal ran into the mold like any high-brass mixture, and, as far as outside appearance was concerned, the plate could not be told from ordinary brass. The presence of the tellurium was not superficially disclosed. This plate was rolled cold from a thickness of 0.605 in. to 0.430 in., when it cracked to pieces. The fractures showed large patches of segregated matter. The parent metal, however, was free from crystallization, and possessed a peculiar light-rose color. An ingot having the dimensions of ¾ x 1 x 12 in. was forged at a cherry-red heat. When flattened it showed no cracks, but when bent over upon itself a few appeared at the bend. The alloy was quite soft while hot, which indicates that tellurium does not harden the brass appreciably. As the cold fracture of this ingot disclosed no crystalline structure, the cause of the cracking of the plate during the rolling was undoubtedly the segregation.
Experiment No. 2.—Five lbs. of Lake copper and 1 lb. of the 5-per-cent, cupro-tellurium alloy were melted and 4 lbs. of Bertha zinc added. The composition is :
The plate was rolled from a thickness of 0.606 in. to 0.427 in., and cracks appeared upon the edges. It was then annealed and rolled to a thickness of 0.317 in., and the plate cracked to pieces. An ingot of this mixture forged as well at a cherry-red heat as pure brass of the same composition. Even when bent over upon itself and flattened, no sign of cracking at the bend appeared. The cold fracture still has the rose-red tinge and is not crystallized.
Experiment No. 3.—Five and one-half lbs. of Lake copper and 4 lb. of the 5-per-cent, cupro-tellurium alloy were melted and 4 lbs. of Bertha zinc added. This gives the following composition :
The plate was rolled from a thickness of 0.605 in. to 0.425 in., and a slight cracking took place at the edges. It was then annealed and rolled to a thickness of 0.295 in., and the edge-cracks increased in size slightly. The plate was annealed a second time and rolled to 0.112 in., and the sheet split in many places, so that further rolling was useless. Perhaps this sheet, by careful working and frequent annealing, might have been rolled to a much thinner gauge; but as pure brass stands these reductions, it is evident that this percentage of tellurium appreciably affects the working-qualities of the brass.
In the hot-forging, this alloy revealed no sign of hot-shortness, and in its behavior was identical with the previous mixture.
Experiment No. 4.—Five lbs. of Lake copper and 1 lb. of an alloy of tellurium and copper containing 1 per cent, of tellurium (made by reducing the 5-percent, alloy with copper) were melted and 4 lbs. of Bertha zinc added. The composition is :
The plate was cold-rolled from a thickness of 0.600 in. to 0.403 in., and no cracks appeared. It was annealed and rolled to 0.273 in., and cracked badly on the edges. This plate was annealed a second time and rolled to 0.050 in., and while the edge-cracks increased in size, the sheet rolled as well as a plate of poor brass would under similar conditions. This amount of tellurium appears to be the dividing-line between the quantity which can be allowed in good brass and that which will cause cracks in rolling. In forging, this alloy behaved like pure brass of the same proportions.
Experiment No. 5.—Five and one-half lbs. of Lake copper and ½ lb. of the cupro-tellurium containing 1 per cent, of tellurium were melted and 4 lbs. of Bertha zinc added, which gave the following composition :
The plate was cold-rolled from a thickness of 0.611 in. to 0.405 in. No cracks appeared. It was annealed only once, and rolled to a thickness of 0.050 in. When 0.120 in. was reached, however, the sheet began to crack on the edges, but only in the same degree that pure brass would under like conditions. As far as could be seen, this alloy rolled equally as well as brass free from the tellurium. No cracks appeared in forging, even when bent and flattened at the bend, which indicates that this percentage of tellurium has no effect on the hot-working qualities of high-brass.
The results of these experiments show that the amount of tellurium usually contained in refined copper does not appreciably affect the rolling properties of high-brass. If, however, the copper contains over 0.10 per cent, (giving about 0.06 per cent, in the brass), the metal manifests a tendency to crack in the rolling.
The hot-working qualities of high-brass, paradoxical as it may seem, do not appear to be much affected by the presence of tellurium ; a marked contrast to that of copper in which the presence of a few thousandths of one per cent, renders the metal appreciably red-short.