Copper: electrical conductivity, properties, features and applications

In many branches of modern industry, a material such as copper is widely used. The electrical conductivity of this metal is very high. This explains the expediency of using it primarily in electrical engineering. From copper, conductors with excellent performance characteristics are obtained. Of course, this metal is used not only in electrical engineering, but also in other industries. Its demand is explained, among other things, by its qualities, such as resistance to corrosion damage in a number of corrosive media, refractoriness, ductility, etc.

Historical reference

Copper is a metal known to man since ancient times. The early acquaintance of people with this material is explained first of all by its wide spread in nature in the form of nuggets. Many scientists believe that it was copper that was the first metal, a man restored from oxygen compounds. Once upon a time, rocks were simply heated on a fire and drastically cooled, causing them to crack. Later, the restoration of copper began to produce on the bonfires with the addition of coal and blowing fur. Improvement of this method eventually led to the creation of a shaft furnace. Still later, this metal began to be produced by the method of oxidative smelting of ores.

Copper: the electrical conductivity of the material

In a quiet state, all free electrons of any metal rotate around the nucleus. When connecting an external source of impact, they are aligned in a certain sequence and become carriers of current. The degree of ability of the metal to pass through the last is called electrical conductivity. The unit of its measurement in the International SI is Siemens, defined as 1 cm = 1 Ω ^-1 .

The electrical conductivity of copper is very high. By this indicator, it exceeds all the non-noble metals known today. Better than her current flows only silver. The indicator of the electrical conductivity of copper is 57x104 cm ^-1 at a temperature of +20 ° C. Due to this property, this metal at the moment is the most common conductor of all used for industrial and domestic purposes.

Copper perfectly withstands constant electrical loads and is also reliable and durable. Among other things, this metal is characterized by a high melting point (1083.4 ° C). And this, in turn, allows copper for a long time to work in a heated state. As prevalence as a current conductor, only aluminum can compete with this metal.

Effect of impurities on the electrical conductivity of copper

Of course, in our time, much more sophisticated techniques are used to melt this red metal than in antiquity. However, even today it is practically impossible to obtain an absolutely pure Cu. In copper there are always various impurities. It can be, for example, silicon, iron or beryllium. Meanwhile, the more impurities in copper, the lower the index of its electrical conductivity. For the manufacture of wires, for example, only a sufficiently pure metal is suitable. According to the standards, copper can be used for this purpose with an amount of impurities not exceeding 0.1%.

Very often this metal contains a certain percentage of sulfur, arsenic and antimony. The first substance significantly reduces the plasticity of the material. The electrical conductivity of copper and sulfur is very different. This impurity does not conduct the current at all. That is, it is a good insulator. However, the electrical conductivity of copper sulfur is not affected in practice. The same applies to thermal conductivity. With antimony and arsenic, the opposite picture is observed. These elements conductivity of copper can reduce significantly.

Alloys

Various kinds of additives can be used and specifically to increase the strength of such a ductile material as copper. They also reduce its electrical conductivity. But their use makes it possible to significantly extend the life of various products.

Most often, Cd (0.9%) is used as an increase in the strength of the copper additive. The result is cadmium bronze. Its conductivity is 90% of the conductivity of copper. Sometimes, instead of cadmium, aluminum is also used as an additive. Conductivity of this metal is 65% of the same index of copper. To increase the strength of wires in the form of additives, other materials and substances can be used, such as tin, phosphorus, chromium, beryllium. The result is bronze of a certain brand. The connection of copper with zinc is called brass.

Alloy Properties

The electrical conductivity of metals can depend not only on the amount of impurities present in them, but also on other indicators. For example, with an increase in the heating temperature, the ability of copper to pass through a current is reduced. Even the way of its manufacture influences the electrical conductivity of such a wire. In everyday life and in production, both soft annealed copper conductors and hard-drawn copper can be used. In the first species, the ability to pass through the current is higher.

However, most of all, of course, the additives used and their quantity affect the electrical conductivity of copper. The table below provides the reader with exhaustive information on the ability to pass current to the most common alloys of this metal.

The electrical conductivity of brass and copper is comparable. However, for the first metal, this figure, of course, is slightly lower. But at the same time it is higher than in bronze. As a conductor brass is used quite widely. It passes the current worse than copper, but it costs less. Most often brass made contacts, clamps and various parts for radio equipment.

Copper alloys of high resistance

Such conductor materials are used mainly in the manufacture of resistors, rheostats, measuring instruments and electric heating devices. Most often, copper alloys of constantan and manganin are used for this purpose. The resistivity of the first (86% Cu, 12% Mn, 2% Ni) is 0.42-0.48 μΩ / m, and the second (60% Cu, 40% Ni) 0.48-0.52 μΩ / m.

Relationship with the coefficient of thermal conductivity

The specific electrical conductivity of copper is 59 500 000 S / m. This index, as already mentioned, is correct, but only at a temperature of + 20 ° C. There is a definite relationship between the thermal conductivity of any metal and the conductivity. Establishes its Wiedemann-Franz law. It is performed for metals at high temperatures and is expressed in the following formula: K / γ = π 2/3 (k / e) ² T, where y is the conductivity, k is the Boltzmann constant, and e is the elementary charge.

Of course, there is a similar connection with a metal such as copper. Thermal conductivity and electrical conductivity are very high. In second place after silver, it is on both these indicators.

Connection of copper and aluminum wires

Recently, electrical equipment of ever higher power began to be used in everyday life and industry. In Soviet times, the wiring was mainly made from cheap aluminum. Unfortunately, its performance characteristics do not correspond to new requirements. Therefore today in everyday life and in industry very often aluminum wires are changed to copper ones. The main advantage of the latter, in addition to the refractory properties, is that their conductive properties do not decrease with an oxidizing process.

Often, when upgrading the electricity network, aluminum and copper wires have to be connected. You can not do this directly. Actually, the electrical conductivity of aluminum and copper does not differ very much. But only the metals themselves. Oxidation films of aluminum and copper properties are not the same. Because of this, the conductivity at the junction is significantly reduced. Oxidizing film in aluminum is much more resistant than copper. Therefore, the connection of these two types of conductors must be made exclusively through special adapters. It can be, for example, clamps containing a paste that protects metals from the appearance of oxide. This version of the adapter is usually used when connecting wires on the street. In the premises, branching clamps are often used. Their design includes a special plate, which eliminates direct contact between aluminum and copper. In the absence of such conductors in domestic conditions, instead of twisting the wires, it is recommended to use the washer and nut as an intermediate "bridge".

Physical properties

Thus, we found out what is the electrical conductivity of copper. This indicator can vary depending on the impurities included in the composition of this metal. However, the demand for copper in the industry is determined by its other useful physical properties, information on which can be obtained from the table below.

Chemical properties

For such characteristics, copper, the electrical conductivity and thermal conductivity of which is very high, occupies an intermediate position between the elements of the first triad of the eighth group and the alkaline ones of the first group of the periodic table. Its main chemical properties include:

• Propensity to complex formation;

• The ability to give colored compounds and insoluble sulfides.

The most characteristic for copper is the bivalent state. Similarities with alkali metals, it has virtually no. Its chemical activity is also low. In the presence of CO ₂ or moisture, a green carbonate film forms on the copper surface. All copper salts are poisonous substances. In the single and divalent state, this metal forms very stable complex compounds. The most important for the industry are ammonia.

Scope of use

The high thermal and electrical conductivity of copper determines its wide application in a wide variety of industries. Of course, most often this metal is used in electrical engineering. However, this is not the only sphere of its application. Among other things, copper can be used:

• In the jewelry business;

• In architecture;

• When assembling plumbing and heating systems;

• In gas pipelines.

For the manufacture of various kinds of jewelry, a copper alloy with gold is used. This allows you to increase the resistance of jewelry to deformation and abrasion. In architecture, copper can be used for facing roofs and facades. The main advantage of this finish is durability. For example, the sheets of this metal are covered with the roof of a well-known architectural landmark - the Catholic Cathedral in the German city of Hildesheim. The copper roof of this building reliably protects its interior space for almost 700 years.

Engineering Communication

The main advantages of copper water pipes are also durability and reliability. In addition, this metal is able to give water special unique properties, making it useful for the body. For the assembly of gas pipelines and heating systems, copper pipes are also ideally suited - mainly due to their corrosion resistance and ductility. With an emergency increase in pressure, such lines can withstand a much greater load than steel. The only drawback of copper pipelines is their high cost.