Copper belongs to the group of non-ferrous metals. In its pure form, it has high thermal and electrical conductivity, which is why it is mainly used in electrical engineering. Copper is a very ductile material that lends itself well to pressure treatment in cold and hot conditions.
To increase the mechanical, design and operational properties of copper, its compounds are used with other metals. As a result of the fusion process, the structure of the crystal lattices changes, additional bonds between ions and atoms arise. This is what increases the strength of the alloy compared to pure metal.
Why copper is alloyed with nickel
During fusion, nickel acts as the main alloying element. It has corrosion resistance, therefore, it is mainly used for hardening.
When fused with copper, continuous solid solutions are formed. Copper-nickel alloy acquires a number of new properties:
- increases the heat resistance of the material;
- the temperature coefficient of electrical resistance is significantly reduced;
- high corrosion resistance appears, especially in seawater.
Classification
The properties of the copper-nickel alloy depend on the percentage of nickel and other substances in it. Currently, many new special materials with unique characteristics have been created. Depending on the field of application, they are divided into structural and electrical.
- Structural - possess high anticorrosive and strength characteristics. Products from them are resistant to aggressive environments. This cupronickel, nickel silver and kunial. A separate place in this list is occupied by the monel, the composition of which and the proportional ratio of the elements are somewhat different.
- Electrical - characterized by increased electrical resistance and thermoelectric properties, they are used in energy and electrical engineering. These are constantan, manganin and kopel.
Knowledge of the chemical composition and physical characteristics makes it possible to determine a copper-nickel alloy in one of the groups.
Cupronickel
It contains about 80% copper, about 20% nickel, as well as some manganese and iron. A similar alloy was known to people in the III century BC. e. called “white copper” thanks to a light silver color resembling silver. It possesses high anticorrosive properties, as well as a large margin of strength and wear resistance of a copper-nickel alloy.
Melting point is about 1170 ° C. Good ductility allows you to process products from it by pressure. It is used in the manufacture of capacitors; medical instruments, inexpensive jewelry, cutlery, and coins are made from it.
Nickel silver
This is a copper-nickel alloy with the addition of zinc, which has a silver color with a greenish tint. Depending on the brand, it can contain up to 35% nickel and up to 45% zinc, the rest is copper. Such a solid content of zinc significantly reduces the cost of its production. The nickel silver has approximately the same mechanical properties as cupronickel. It is corrosion resistant, durable, plastic enough to handle hot and cold by pressure.
Sometimes it is additionally alloyed with lead for better machining. Basically, parts of devices, watches, medical instruments are made from it. Interestingly, due to its cheapness, it is from it more often than from cupronickel that jewelry, medals and orders are produced. Neusilber is also used in the manufacture of enamels.
Kunial
Consists of copper base, nickel - up to 20%, small additives of aluminum. It fuses at a temperature of 1183 ° C, followed by hardening and aging, which achieves very high strength and low temperature resistance. It is subdivided into brands A (MNA13-3) and B (MNA 6-1.5).
Grade A has two important characteristics - high strength and unique resistance to corrosion in aggressive environments. For example, in sea water it can be used for decades. Therefore, the alloy is used for the manufacture of parts for special purposes (propellers).
Brand B has springy properties, therefore it is widely used for the manufacture of elastic elements for critical purposes. It is also very resistant to kinks in the cold. From it produce structural parts operating in low temperature conditions.
Monel
It contains about two-thirds of nickel and one-third of copper. Melting point - 1350 ° C. The main property of this copper-nickel alloy is corrosion resistance. It has high indicators of mechanical properties - strength and plastic deformation. Monel grade NMZHMts contains about 28% copper, 3% iron, about 3% magnesium, a small amount of cobalt and nickel.
Monel-400 has the same characteristics. It is a brand of Special Metals Corporation and was patented in 1906. Therefore, other manufacturing companies cannot use this name. So another alloy appeared - Nicorros. However, these materials are identical in all chemical and technical characteristics. Since the alloy contains more than half of nickel in a percentage ratio, its cost is quite high. However, there is a technology for the production of copper-nickel alloy using raw materials from natural sulfide ores containing both elements, without preliminary separation into separate components. This allows you to significantly reduce the cost of the final product.
Monel is used for the production of products operated in aggressive environments, under conditions of increased mechanical load. This is shipbuilding, the chemical and oil industries, the manufacture of medical instruments, critical parts of machines and apparatuses.
Constantan
It has a white color with a characteristic yellowish swelling. The composition includes: copper -59%; nickel - 39-41%; Manganese - 1-2%. Melting point 1260 ° C. This copper-nickel alloy got its name due to its main property - thermal stability. It has very good electrical resistance with a low temperature coefficient of expansion. The alloy is used for the manufacture of wire for thermocouples, in the manufacture of measuring instruments, as well as electric heating elements operating at temperatures up to 400-500 degrees.
A wire made from constantan is subjected to special heat treatment, as a result of which a metal forms a thin oxide film on the surface. Due to this, the product does not need additional varnishing or protective coating. Konstantan is very plastic. This property allows its use in welding copper-nickel alloys.
The disadvantage of constantan is its rather high EMF - about 43 μV. This eliminates the use of wire and tape from it in high-precision measuring instruments.
Manganin
Contains approximately 5% nickel, 12% manganese and a copper base. Melting point - 960 ° C. Interestingly, the manganin was invented by the American Edward Vanston around 1888 on the basis of the constantan he invented as a special material for the windings of electrical measuring instruments. It really has a high electrical resistivity, as well as an extremely low EMF paired with copper (not more than 1 μV), which compares it favorably with constantan.
In order to reduce the temperature coefficient of resistance, the manganese wire is annealed at temperatures of about 600 degrees in vacuum, then slowly cooled. This technology allows you to increase the temperature at which the material retains its electrical properties, up to 200 ° C. The wire already wound in coils is additionally heated repeatedly to 150 ° C. This achieves the effect of artificial aging, after which changes in the crystal structure of the metal are minimized.
The main area of application of manganin as a material with stable electrical resistivity is the manufacture of a variety of high-precision instruments for measuring electric current (current, voltage, power).
Kopel
Another special alloy. Contains copper, 43% nickel, some iron and manganese. Melting point 1290 ° C. Due to the optimal ratio of stably low resistivity and high TED together with various metals, the alloy is used for the manufacture of wire for thermocouples and electrodes. The TEDS of the material increases in proportion to the working temperature:
- at 100 degrees Celsius - 6.95V;
- at 600 - up to 49V.
Kopel is very heat-resistant - without violating the basic properties it withstands heating up to 600 degrees and is resistant to corrosion.
Copel is used in thermocouples of instrument sensors for non-contact temperature measurement. They use thermocouples with a maximum TED - with chromium, copper or iron. These elements are positive electrodes, and the copel is negative. The copel-chromel thermocouple is mainly used in pyrometry for constant temperature control in the range from 200 to 600 degrees in industrial and laboratory installations.
Smelting process
In the production of copper-nickel alloys adhere to relatively similar technologies. Cupronickel, nickel silver, kunial, constantan, manganin are first melted in induction furnaces under a layer of calcined charcoal. Adding waste to the charge is allowed up to 80%.
The smelting process begins with copper and nickel. As they melt, the waste is added in large pieces, then small. Zinc is the last to be loaded. After the final melting of the mixture, deoxidation is performed with manganese and silicon (nickel silver), or with silicon and manganese (constantan and cupronickel). After that, all slag is removed from the surface of the melt and more charcoal is added. The hot mass is heated to a temperature of about 1300 ° C, if necessary, manganese chloride is added for refining.
The cooking technology of the couniales is slightly different, since they contain aluminum. Before introducing aluminum into the melt, 0.1% manganese is necessarily added for deoxidation. And after dissolution of aluminum, the surface of the melt is sprinkled with flux. If this is not done, films are formed, from which the melt becomes unsuitable for pouring.
Chemical, physical and structural properties determine the destination of various copper-nickel alloys. GOST 492–73, GOST 5063–73, GOST 5187–70, GOST 5220–78, GOST 17217–79, GOST 10155–75 are the main standards in their production.
Coin minting
Around the end of the century before last, coins from a copper-nickel alloy began to be minted everywhere.
Its composition was very different at different mints. But mainly it contained up to 30% nickel, a minor iron impurity and copper as the basis. Since metal for ordinary coins should be primarily plastic, malleable, wear-resistant and inexpensive, the composition of the coin alloy was determined in a practical way. Subsequently, cupronickel was especially popular for making coins.
Modern Russian coins are made of various alloys. In particular, coins issued before 2009 consist entirely of cupronickel. Steel coins in denominations of one and five kopecks and five-ruble copper coins are covered with a thin layer of cupronickel. Such material is called "bimetal." Thus, the cost of manufacturing metal money is decreasing more and more.
Alloys of copper and nickel are little susceptible to oxidation in air. Therefore, its signs can be found only on old coins, or those that have long been in an aggressive environment. Connoisseur-treasure hunters and numismatists use various means to clean valuable copies of coins - from folk recipes to advanced technologies.
Cleaning with a soapy solution removes only greenish copper oxides well. Olive oil, acetic acid, Goya paste are also used. It must be borne in mind that these funds can not only remove plaque, but also react with the alloy itself, causing harm to the coin. The most effective, gentle and fast is the cleaning of coins from a copper-nickel alloy using electrolysis.