Part 28

1. Melt the least fusible, oxidizable, and volatile first, and then add the others heated to their point of fusion or near it. Thus, if it is desired to make an alloy of exactly 1 part of copper and 3 of zinc, it will be impossible to do so by putting proportions of the metals in a crucible and exposing the whole to heat. Much of the zinc would fly off in vapor before the copper was melted. First, melt the copper and add the zinc, which has been melted in another crucible. The zinc should be in excess, as some of it will be lost anyway.

2. Some alloys, as copper and zinc, copper and arsenic, may be formed by exposing heated plates of the least fusible metal to the vapor of the other. In making brass in the large way, thin plates of copper are dissolved, as it were, in melted zinc until the proper proportions have been obtained.

3. The surface of all oxidizable metals should be covered with some protecting agent, as tallow for very fusible ones, rosin for lead and tin, charcoal for zinc, copper, etc.

4. Stir the metal before casting and if possible, when casting, with a whitewood stick; this is much better for the purpose than an iron rod.

5. If possible, add a small portion of old alloy to the new. If the alloy is required to make sharp castings and strength is not a very great object, the proportion of old alloy to the new should be increased. In all cases a new or thoroughly well-cleansed crucible should be used.

To obtain metals and metallic alloys from their compounds, such as oxides, sulphides, chlorides, etc., a process lately patented makes use of the reducing qualities of aluminum or its alloys with magnesium. The finely powdered material (e. g., chromic oxide) is placed in a crucible mixed with aluminum oxide. The mixture is set afire by means of a soldering pipe or a burning magnesium wire, and the desired reaction takes place. For igniting, one may also employ with advantage a special priming cartridge consisting of pulverized aluminum to which a little magnesium may be mixed, and peroxide of magnesia, which is shaped into balls and lighted with a magnesium wire. By suitable additions to the pulverized mixture, alloys containing aluminum, magnetism, chromium, manganese, copper, iron, boron, silicic acid, etc., are obtained.

«ALUMINUM ALLOYS.»

M. H. Pecheux has contributed to the Comptes Rendus, from time to time, the results of his investigations into the alloys of aluminum with soft metals, and the following constitutes a brief summary of his observations:

«Lead.»—When aluminum is melted and lead is added in proportion greater than 10 per cent, the metals separate on cooling into three layers—lead, aluminum, and between them an alloy containing from 90 to 97 per cent of aluminum. {49} The alloys with 93, 95, and 98 per cent have densities of 2.745, 2.674, and 2.600 respectively, and melting points near that of aluminum. Their color is like that of aluminum, but they are less lustrous. All are malleable, easily cut, softer than aluminum, and have a granular fracture. On remelting they become somewhat richer in lead, through a tendency to liquation. They do not oxidize in moist air, nor at their melting points. They are attacked in the cold by hydrochloric and by strong sulphuric acid, with evolution of hydrogen, and by strong nitric acid when hot; strong solution of potassium hydroxide also attacks them. They are without action on distilled water, whether cold or hot.

«Zinc.»—Well-defined alloys were obtained, corresponding to the formulas Zn〈3〉Al, Zn〈2〉Al, ZnAl, ZnAl〈2〉, ZnAl〈3〉, ZnAl〈4〉, ZnAl〈6〉, ZnAl〈10〉, ZnAl〈12〉. Their melting points and densities all lie between those of zinc and aluminum, and those containing most zinc are the hardest. They are all dissolved by cold hydrochloric acid and by hot dilute nitric acid. Cold concentrated nitric acid attacks the first three, and cold dilute acid the first five. The Zn〈3〉Al, ZnAl〈6〉, ZnAl〈10〉, and ZnAl〈12〉 are only slightly affected by cold potassium-hydroxide solution; the others are strongly attacked, potassium zincate and aluminate probably being formed.

«Tin.»—A filed rod of tin-aluminum alloy plunged in cold water gives off for some minutes bubbles of gas, composed of hydrogen and oxygen in explosive proportions. An unfiled rod, or a filed rod of either aluminum or tin, is without action, though the unfiled rod of alloy will act on boiling water. The filed rod of alloy, in faintly acid solution of copper or zinc sulphate, becomes covered with a deposit of copper or zinc, while bubbles of oxygen are given off. M. Pecheux believes that the metals are truly alloyed only at the surface, and that filing lays bare an almost infinitely numerous series of junctions of the two metals, which, heated by the filing, act as thermocouples.

«Bismuth.»—By the method used for lead, bismuth alloys were obtained containing 75, 85, 88, and 94 per cent of aluminum, with densities 2.86, 2.79, 2.78, and 2.74 respectively. They were sonorous, brittle, finely grained, and homogeneous, silver-white, and with melting points between those of their constituents, but nearer that of aluminum. They are not oxidized in air at the temperature of casting, but are readily attacked by acids, concentrated or dilute, and by potassium-hydroxide solution. The filed alloys behave like those of tin, but still more markedly.

«Magnesium.»—These were obtained with 66, 68, 73, 77, and 85 per cent of aluminum, and densities 2.24, 2.47, 2.32, 2.37, 2.47. They are brittle, with large granular fracture, silver-white, file well, take a good polish, and have melting points near that of aluminum. Being viscous when melted, they are difficult to cast, and when slowly cooled form a gray, spongy mass which cannot be remelted. They do not oxidize in air at the ordinary temperatures, but burn readily at a bright-red heat. They are attacked violently by acids and by potassium-hydroxide solution, decompose hydrogen peroxide, and slowly decompose water even in the cold.

«Tin, Bismuth, and Magnesium.»—The action of water on these alloys just referred to has been recently demonstrated on a larger scale, 5 to 6 cubic centimeters of hydrogen having been obtained in 20 minutes from 2 cubic centimeters of the filed tin alloy. The bismuth alloy yielded more hydrogen than the tin alloy, and the magnesium alloy more than the bismuth alloy. The oxygen of the decomposed water unites with the aluminum. Larger quantities of hydrogen are obtained from copper-sulphate solution, apart from the decomposition of this solution by precipitation of copper at the expense of the metal alloyed with the aluminum. The alloys of aluminum with zinc and lead do not decompose pure water, but do decompose the water of copper-sulphate solution, and, more slowly, that of zinc-sulphate solution.

Aluminum is a metal whose properties are very materially influenced by a proportionately small addition of copper. Alloys of 99 per cent aluminum and 1 per cent of copper are hard, brittle, and bluish in color; 95 per cent of aluminum and 5 per cent of copper give an alloy which can be hammered, but with 10 percent of copper the metal can no longer be worked. With 80 per cent and upward of copper are obtained alloys of a beautiful yellow color, and these mixtures, containing from 5 to 10 percent of aluminum and from 90 to 95 per cent of copper, are the genuine aluminum bronzes. The 10-per-cent alloys are of a pure golden-yellow color; with 5 per cent of aluminum they are reddish yellow, like gold heavily alloyed with copper, and a 2-per-cent admixture is of an almost pure copper red. {50} As the proportion of copper increases, the brittleness is diminished, and alloys containing 10 per cent and less of aluminum can be used for industrial purposes, the best consisting of 90 per cent of copper and 10 of aluminum. The hardness of this alloy approaches that of the general bronzes, whence its name. It can be stretched out into thin sheets between rollers, worked under the hammer, and shaped as desired by beating or pressure, in powerful stamping presses. On account of its hardness it takes a fine polish, and its peculiar greenish-gold color resembles that of gold alloyed with copper and silver together.

Alloys with a still greater proportion of copper approach this metal more and more nearly in their character; the color of an alloy, for instance, composed of 95 per cent of copper and 5 per cent of aluminum, can be distinguished from pure gold only by direct comparison, and the metal is very hard, and also very malleable.

«Electrical Conductivity of Aluminum Alloys.»—During three years’ exposure to the atmosphere, copper-aluminum alloys in one test gradually diminished in conductivity in proportion to the amount of copper they contained. The nickel-copper aluminum alloys, which show such remarkably increased tensile strength as compared with good commercial aluminum, considerably diminished in total conductivity. On the other hand, the manganese-copper aluminum alloys suffered comparatively little diminution in total conductivity, and one of them retained comparatively high tensile strength. It was thought that an examination of the structure of these alloys by aid of microphotography might throw some light on the great difference which exists between some of their physical properties. For instance, a nickel-copper aluminum alloy has 1.6 times the tensile strength of ordinary commercial aluminum. Under a magnification of 800 diameters practically no structure could be discovered. Considering the remarkable crystalline structure exhibited by ordinary commercial aluminum near the surface of an ingot, when allowed to solidify at an ordinary rate, the want of structure in these alloys must be attributed to the process of drawing down. The inference is that the great difference which exists between their tensile strengths and other qualities is not due to variation in structure.

«Colored Alloys of Aluminum.»—A purple scintillating composition is produced by an alloyage of 78 parts of gold and 22 parts aluminum. With platinum a gold-colored alloy is obtained; with palladium a copper-colored one; and with cobalt and nickel one of a yellow color. Easily fusible metals of the color of aluminum give white alloys. Metal difficult of fusion, such as iridium, osmium, titanium, etc., appear in abnormal tones of color through such alloyages.

«Aluminum-Brass.»—Aluminum, 1 per cent; specific gravity, 8.35; tensile strength, 40. Aluminum, 3 per cent; specific gravity, 8.33; tensile strength, 65. The last named is harder than the first.

«Aluminum-Copper.»—Minikin is principally aluminum with a small percentage of copper and nickel. It is alloyed by mixing the aluminum and copper, then adding the nickel. It resembles palladium and is very strong.

«Aluminum-Silver.»—I.—Silver, 3 per cent; aluminum, 97 per cent. A handsome color.

II.—A silver aluminum that is easily worked into various articles contains about one-fourth silver and three-fourths of aluminum.

«Aluminum-Tin.»—Bourbon metal is composed of equal parts of aluminum and tin; it solders readily.

«Aluminum-Tungsten.»—A new metal alloy consisting of aluminum and tungsten is used of late in France in the construction of conveyances, especially carriages, bicycles, and motor vehicles. The French call it partinium; the composition of the new alloy varies according to the purposes for which it is used. It is considerably cheaper than aluminum, almost as light, and has a greater resistance. The strength is stated at 32 to 37 kilograms per square millimeter.

«Aluminum-Zinc.»—Zinc, 3 per cent; aluminum, 97 per cent. Very ductile, white, and harder than aluminum.

AMALGAMS: See Fusible Alloys.

«Anti-Friction Bearing or Babbitt Metals.»—These alloys are usually supported by bearings of brass, into which it is poured after they have been tinned, and heated and put together with an exact model of the axle, or other working piece, plastic clay being previously applied, in the usual manner, as a lute or outer mold. Soft gun metal is also excellent, and is much used for bearings. They all become less heated in working than the {51} harder metals, and less grease or oil is consequently required when they are used.

I.—An anti-friction metal of excellent quality and one that has been used with success is made as follows: 17 parts zinc; 1 part copper; 1 1⁠/⁠2 parts antimony; prepared in the following way: Melt the copper in a small crucible, then add the antimony, and lastly the zinc, care being taken not to burn the zinc. Burning can be prevented by allowing the copper and antimony to cool slightly before adding the zinc. This metal is preferably cast into the shape desired and is not used as a lining metal because it requires too great a heat to pour. It machines nicely and takes a fine polish on bearing surfaces. It has the appearance of aluminum when finished. Use a lubricating oil made from any good grade of machine oil to which 3 parts of kerosene have been added.