Copper Compounds and Alloys

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What are the alloys and compounds of copper? What is brass and bronze? Information on the copper alloys and compounds and their properties, uses.

Copper Compounds and AlloysCopper Compounds and Alloys;

When a metal is alloyed (or dissolved) with a second metal, an improvement in certain properties of the metals is sometimes obtained. A great deal of research and development has been undertaken to understand the ways in which specifically desired properties can be influenced and hence obtained by specific alloying treatments.

Brass and Bronze. A few copper alloys were known since ancient times to have superior properties, and these properties were extensively exploited; the art of metallurgy preceded the science of metallurgy. For example, bronze (an alloy of tin and copper) was produced in King Solomon’s mines on the Sinai Peninsula. Since those early days, however, extensive research has been undertaken to obtain a useful understanding of alloy properties and how they can be controlled.

Undoubtedly one of the more important groups of copper alloys is the one formed by the combination of copper with zinc; this alloy is known as brass. The composition of zinc in brass alloys is variable, and many of the properties of the material vary accordingly—in some cases, with highly favorable improvements. One of the striking property changes which accompanies increasing additions of zinc to copper is the gradual transition of colors. The typical salmon pink of pure unoxidized copper changes to a rich bronze (90% copper, 10% zinc), to golden (85% copper, 15% zinc), followed by yellow (70% copper, 30% zinc), until finally a reddish yellow is reached (60% copper, 40% zinc).

The addition of zinc to copper results in an alloy which is easily machined, much stronger than the base metal, and far more corrosion-resistant than copper. Some typical applications of brass include plumbing fixtures and tubing, and decorative items such as brass urns and bases for lamps. However, most brass in the United States is used in industrial applications.

Another well-known alloy employing copper as a base metal is bronze, which involves the addition of tin. This alloy was known to the ancients; indeed, the dawn of modern civilization is often called the Bronze Age. As with the zinc in brass, the exact percentage of tin in bronze is variable, and various resultant properties accompany the different compositions. Many uses are known for bronze, although the total production of the alloy is small compared to brass alloys.

Other Alloys. Copper is often alloyed with other elements to obtain specifically desired properties. Among these properties is increased corrosion resistance. A classic example of such an alloy is Monel metal, which contains 60% copper and 40% nickel. The commercial product is very corrosion resistant, in some instances more so than stainless steel, and despite its higher cost Monel metal quite often is substituted advantageously for stainless steel in applications which require extreme resistance to corrosion.

A large number of additional alloys of copper with various elements have been developed for special applications. These include alloys with arsenic, beryllium, silver, silicon, aluminum, phosphorus, lead, and manganese. (If ternary -three-member—or still more complex combinations are also considered, the number of possible copper alloys is amazingly large.) The alloy system of copper and beryllium, for example, has interesting and useful properties. The alloy is used quite often in very special springs, since the hysteresis of springs made from this material—that is, their lag in response to the exertion or release of forceáis extremely small. This property is very important in highly sensitive electrical instruments such as galvanometers.

Copper is also used as an alloying element in a wide variety of applications in which it is a minor constituent of the resultant alloy. One such industrially important alloy involves the reaction of copper precipitated from solid solution in a matrix of aluminum. The alloy, which also contains small amounts of magnesium and manganese, is known as duralumin. The industrial and commercial importance of aluminum arose when it was shown by the German metallurgist Alfred Wilm in 1911 that aluminum could be strengthened by this process. Before that time, wrought products of aluminum were too soft for most industrial applications.

Chemical Compounds. Copper forms a very large number of chemical compounds. The compounds vary from fungicides and insecticides to catalysts in chemical cracking processes, and are used in the refining of copper itself. However, the volume of copper used in such applications is very small compared with the production of the metal itself, amounting to 1% of the total.

The following are only some of the more important copper compounds.

Copper acetate—Cu( C2H3O2) . H2O—is used as a fungicide, as a catalyst in some organic reactions such as the aging of rubber, and as a chemical in textile dyeing. Copper arsenate— Cu3( ASO4 )2 . 4H2O—is also used as an insecticide, in snail control, and as a wood preservative. The copper oxides Cu2O and CuO are used in the coloring of glass and, more important, as a catalyst in many chemical processes. Copper sulfate or blue vitriol—CuSO4—is used extensively in agriculture, principally as a pesticide and as a required trace element in the feeding of plants and animals. Copper sulfide—Cu2S—is one of the most important mineral sources of copper, and is given the name chalcocite. This list of compounds, while by no means complete, illustrates the variety of uses that man has found for copper.

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