CHAPTER II

COPPER ALLOYS

§ 21. Copper forms with other metals a series of alloys far more numerous and important than that of any other metal, which may be accounted for by its red colour, high malleability, ductility, toughness, softness, and tenacity; which properties it imparts in a great measure to many of its alloys, even when united with metals opposite to it in character, such as zinc. Next to iron, it may be considered the most useful of all the metals both from its valuable properties when used alone, and its intrinsic value as a constituent of alloys. The very properties which make copper so useful are sometimes a disadvantage for certain purposes; for instance, the toughness and closeness of grain make it more difficult to turn in a lathe than brass; and its softness makes it unfit to be used alone for objects subjected to great wear and tear. In the vast majority of cases in which copper is used it has to be melted and cast into moulds of various kinds, in order to prepare it for further treatment, and the difficulties in producing sound castings are so great, that it can only be successfully manipulated in the hands of a very skilful and experienced workman; even then a common practice is to add some other substance, so that it is probably not too much to say that pure copper has never been cast in considerable quantity, so as to produce a good ductile casting free from blow-holes. Great attention has been directed to this subject of late years in consequence of the demand for

solid-drawn copper tubes, rollers, etc.; and different physics have been added to the copper in melting, with a view of overcoming the inherent defects.

It must be borne in mind that pure copper is not a commercial article, and although copper is now manufactured on the large scale in a purer state than previously, the metal retains ingredients which modify the valuable properties the metal possesses in its chemically pure state. The common impurities are iron, arsenic, antimony, and sometimes sulphur. These elements even in very small quantities seriously affect copper, but they may be neutralised to some extent by uniting them with oxygen. When such metal is melted in contact with air, some of the copper is oxidised, forming cuprous oxide Cu2O, which makes the whole mass brittle and unworkable; some air or carbonic oxide is also retained in the gaseous state, and on the metal solidifying at the surface some of this gas will be enclosed in the interior of the mass, and produce a honeycombed structure. To prevent access of air, the metals may be covered with charcoal, and this when used judiciously may be effective, but the great difficulty is to know when the carbon has done its work. Carbon in contact with air will produce carbonic oxide, and this gas probably penetrates the copper to some extent and removes the oxygen, but if any further excess of carbonic oxide is admitted, it may reduce the oxides present as impurities, as well as oxide of copper, and the elements being liberated, will alloy with the copper, making it brittle and analogous in properties to what is technically known as "overpoled" copper. Seeing then that commercial copper is impure, but that the impurities may be neutralised to a great extent by oxygen, the problem is to discover the point when this end has been attained, without introducing an excess of air. On the other hand, it may be as efficacious, and much more easy, to admit an excess of oxygen, and subsequently remove it, by adding some body which has a stronger affinity for oxygen than copper has. To this end Mr. Walton, of the Ansonia copper works

of the United States of America, has patented a process of preparing copper for casting, which, in the words of the patentee, is as follows:

"My present invention is for treating copper in crucibles, so as to exclude the action of the atmosphere, and subject the copper to the action of carbon sufficiently to remove the oxygen, and render such copper solid when cast, and increase its malleability and ductility. I take eight pounds of zinc, either in the form of an oxide or carbonate, and mix it with one bushel of ground charcoal, wet it, and make it into a stiff paste, portion it out into, say twenty-four parts, make it into rough balls, and dry at a moderate heat. The copper is placed in a crucible in a furnace, and when on the point of melting, one of the balls is dropped upon the copper, and gradually falls in pieces and covers the copper as it melts down, thereby entirely excluding the atmosphere from the surface of the copper; at the same time the zinc in the mass is evolved, and dispels any oxygen which may remain in the crucible. It may be supposed that the oxide of zinc will impregnate the copper, but such is not the case; the charcoal coming in contact with the copper, and oxide of zinc being volatile under the action of heat,1 no combination with the copper takes place, and the zinc is volatilised and carried off through the flue, while the charcoal remains on the surface of the copper, and combines with any excess of oxygen and burns. Copper treated in this way becomes perfectly malleable, and is thoroughly toughened, and is, in fact, improved by this treatment. My improvement is especially available when the copper is melted in a crucible, but it may be used when melted on a hearth or otherwise. The impurities of common copper are thrown to the surface in a slag, and the copper made so that it will work better either hot or cold, and stand a greater test for either tension or ductility.

"The above method of treatment can be applied to copper that is to be used in the manufacture of any article. Copper 1 Zinc oxide is practically non-volatile. See Percy's Metallurgy, p. 532.

so treated will remain in a very liquid state much longer than that treated in the ordinary manner, and the copper can be brought to a very great heat without losing its toughness. When casting such articles as tubes, or small or thin castings, a little phosphorus, added just before pouring, assists very materially in keeping the metal in a liquid state; and also prevents the absorption of oxygen from the atmosphere while cooling in the moulds."

§ 22. In addition to the statements already made concerning impurities in copper, the following summary of the effects of different elements will doubtless be of use to those interested in the manufacture of its alloys.

Phosphorus. A small quantity does not sensibly alter the colour of copper, but a large quantity renders it gray. One half per cent makes it very hot-short, and only capable of being rolled in the cold, without cracking. A little phosphorus added to molten copper in a crucible promotes soundness in the subsequent casting. Phosphorus increases the fusibility and hardness of copper, and when present in quantity, renders it brittle at the ordinary temperature. Copper containing 11 per cent of phosphorus is extremely hard, of a steel-gray colour, is susceptible of a fine polish, but readily tarnishes. In making phosphorised copper, by adding phosphorus direct, the metal should not be stirred. with an iron rod, as phosphorised iron will also be formed, and alloy with the copper.

Silicon.--Copper is contaminated with silicon when strongly heated in contact with sand and carbon. Copper containing 2 per cent of silicon resembles gun-metal in colour; is tough, harder than copper, red-short, but may be rolled in the cold. Mr. Anderson of Woolwich found copper containing 1.82 per cent of silicon tougher than gun-metal. If the temperature employed in heating the copper be too low, or not sufficiently prolonged, only a little silicon will be reduced, and the metal will resemble slightly under-poled

copper.

Arsenic.-Copper and arsenic readily combine when metallic arsenic is dropped into molten copper. When a

very small quantity is thus added, the metal may be cast into a sound ingot, which contracts during solidification like phosphorised copper, and may be rolled cold, and afterwards drawn into fine wire. Much arsenic is highly injurious, making the metal hard and brittle. Arsenic also readily combines with copper when one of its compounds is heated with charcoal in contact with copper.

Iron. The malleability of copper is seriously impaired by the presence of iron, which renders the copper harder, paler in colour, more infusible, and brittle. It may, however, be removed by the use of an oxidising flux.

Lead.-One half per cent of lead in copper makes it both hot- and cold-short, and can only be removed by causing some of the copper to pass into the slag. In quantities less than this, lead is sometimes added to copper intended for rolling.

Antimony renders copper hard and brittle, and imparts to the fractured surface a dull yellowish-gray colour. It is more injurious than arsenic.

Bismuth. This metal is stated to exert a specially injurious influence on copper, a very small quantity makes it hot-short, and makes it sensibly cold-short.

Zinc in very small quantity does not much alter the character of copper; it tends to impart a yellow colour and fibrous fracture. 1000 of zinc in copper makes the latter hot-short but not cold-short.

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Nickel and Cobalt occasionally occur in copper ores, and are reduced along with the copper. These metals make copper less malleable, especially in the presence of a little antimony. The metal is then harder and paler in colour.

Tin in very small quantity does not appear to affect the working properties of copper except to make it a little harder.

The foregoing remarks concerning the effect of small quantities of foreign metals on the properties of copper do not apply in the same degree when metals are added to copper in considerable quantities to form what is generally under