Copper: electrical conductivity, properties, features and applications

In many branches of modern industry, material such as copper is very widely used. The electrical conductivity of this metal is very high. This explains the feasibility of its use primarily in electrical engineering. Conductors with excellent performance are made from copper. Of course, this metal is used not only in electrical engineering, but also in other industries. It is explained by its relevance, including its qualities such as resistance to corrosion damage in a number of aggressive environments, refractoriness, ductility, etc.

History reference

Copper is a metal known to man from ancient times. The early acquaintance of people with this material is explained, first of all, by its wide distribution in nature in the form of nuggets. Many scientists believe that it was copper that was the first metal reduced by man from oxygen compounds. Once the rocks were simply heated at the stake and sharply cooled, as a result of which they cracked. Later, copper recovery began to be made on bonfires with the addition of coal and blowing furs. The improvement of this method ultimately led to the creation of a shaft furnace. Even later, this metal began to be obtained by the method of oxidative smelting of ores.

Copper: conductivity of the material

In a calm state, all free electrons of any metal revolve around the nucleus. When an external source of influence is connected, they line up in a certain sequence and become current carriers. The degree of ability of a metal to pass through itself the latter is called electrical conductivity. The SI unit of measurement is Siemens, defined as 1 cm = 1 ohm ^-1 .

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

Copper withstands constant electrical loads and is also characterized by reliability and durability. In addition, this metal is also characterized by a high melting point (1083.4 ° C). And this, in turn, allows copper to work for a long time in a heated state. In terms of prevalence, only aluminum can compete with this metal as a current conductor.

The effect of impurities on the conductivity of copper

Of course, in our time, much more advanced techniques are used for smelting this red metal than in antiquity. However, today it is almost impossible to obtain completely pure Cu. Different types of impurities are always present in copper. It can be, for example, silicon, iron or beryllium. Meanwhile, the more impurities are in copper, the lower is its conductivity index. For the manufacture of wires, for example, only sufficiently pure metal is suitable. According to the regulations, 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 ductility of the material. The electrical conductivity of copper and sulfur varies greatly. This impurity does not conduct current at all. That is, it is a good insulator. However, sulfur does not affect the conductivity of copper in any way. The same goes for thermal conductivity. With antimony and arsenic, the opposite is observed. These elements can significantly reduce the conductivity of copper.

Alloys

Various additives can also be used specifically to increase the strength of a plastic material such as copper. They also reduce its electrical conductivity. But their application can significantly extend the service life of various products.

Most often, Cd (0.9%) is used as a copper strength improver. 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. The conductivity of this metal is 65% of the same indicator of copper. To increase the strength of wires in the form of additives, other materials and substances can also be used - tin, phosphorus, chromium, beryllium. The result is bronze of a certain brand. The combination of copper and zinc is called brass.

Alloy characteristics

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 increasing heating temperature, the ability of copper to pass current through itself decreases. Even the method of its manufacture affects the conductivity of such a wire. In everyday life and in production, both soft annealed copper conductors and solid ones can be used. In the first variety, the ability to pass current through itself is higher.

However, of course, the additives used and their amount affect copper conductivity most of all. The table below provides the reader with comprehensive information on the ability to pass current of 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 that of bronzes. Brass is used quite widely as a conductor. It passes current worse than copper, but it also costs less. Most often, contacts, clamps and various parts for radio equipment are made of brass.

High Resistance Copper Alloys

Such conductive materials are mainly used 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) is 0.48-0.52 μΩ / m.

Relationship to thermal conductivity

The specific electrical conductivity of copper is 59 500 000 S / m. This indicator, as already mentioned, is true, however, only at a temperature of +20 . There is a definite connection between the thermal conductivity coefficient of any metal and the specific conductivity. Establishes his law of Wiedemann - Franz. 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 specific conductivity, k is the Boltzmann constant, e is the elementary charge.

Of course, there is a similar relationship with a metal such as copper. Her thermal conductivity and electrical conductivity are very high. In second place after silver, it is in both of these indicators.

Connection of copper and aluminum wires

Recently, electrical equipment of ever higher power has begun to be used in everyday life and industry. In Soviet times, wiring was made primarily of cheap aluminum. Unfortunately, its operational characteristics no longer meet the new requirements. Therefore, today in everyday life and in industry, very often aluminum wires are replaced by copper. The main advantage of the latter, in addition to refractoriness, is that during the oxidation process their conductive properties do not decrease.

Often when upgrading electrical networks, aluminum and copper wires have to be connected. You cannot do this directly. Actually, the electrical conductivity of aluminum and copper does not differ too much. But only these metals themselves. The oxidizing films of aluminum and copper have different properties. Because of this, the conductivity at the junction is significantly reduced. Oxidation film in aluminum is characterized by much greater resistance than in copper. Therefore, the connection of these two varieties of conductors should be carried out exclusively through special adapters. These can be, for example, clamps containing a paste that protects metals from the appearance of oxide. This type of adapter is usually used when connecting wires on the street. In rooms, branching clamps are more often used. Their design includes a special plate that eliminates direct contact between aluminum and copper. In the absence of such conductors in the domestic environment, instead of twisting the wires, it is directly recommended to use a washer and nut as an intermediate “bridge”.

Physical properties

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

Chemical properties

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

• propensity for complexation;

• ability to give colored compounds and insoluble sulfides.

The most characteristic of copper is the divalent state. There are practically no similarities with alkali metals. Its chemical activity is also low. In the presence of CO ₂ or moisture, a green carbonate film forms on the surface of the copper. All copper salts are toxic substances. In the mono- and divalent state, this metal forms very stable complex compounds. Of greatest importance for industry are ammonia.

Scope of use

The high thermal and electrical conductivity of copper determines its widespread use in a wide variety of industries. Of course, most often this metal is used in electrical engineering. However, this is far from the only sphere of its application. Among other things, copper can be used:

• in jewelry;

• in architecture;

• during the assembly of plumbing and heating systems;

• in gas pipelines.

For the manufacture of various kinds of jewelry, an alloy of copper with gold is mainly used. This allows you to increase the resistance of jewelry to deformation and abrasion. In architecture, copper can be used for cladding roofs and facades. The main advantage of this finish is durability. For example, the sheets of this metal are sheathed the roof of a well-known architectural landmark - the Catholic Cathedral in the German city of Hildesheim. The copper roof of this building has reliably protected its interior for nearly 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 are able to withstand a much greater load than steel. The only drawback of copper pipelines is their high cost.