We explain what electrical conductivity is and based on what it varies. Electrical conduction of metals, water and soil.
What is electrical conductivity?
Electrical conductivity is the ability of matter to allow the flow of electric current through its particles. This capacity depends directly on the atomic and molecular structure of the material, as well as other physical factors such as the temperature at which it is found or the state in which it is (liquid, solid, gaseous).
The electrical conductivity is the opposite of resistivity that is, the resistance to the passage of electricity of the materials. There are then good materials and bad electrical conductors, to the extent that they are more or less resistant.
The symbol for conductivity is the Greek letter sigma (σ) and Its unit of measurement is the siemens per meter (S/m) or 𝛀-1⋅ m-1. For its calculation, the notions of electric field (E) and conduction current density (J) are also usually taken into account, as follows:
J = σE, from which: σ = J/E
conductivity varies depending on the state in which the matter is found. In liquid media, for example, it will depend on the presence of salts dissolved in them that generate positively or negatively charged ions, and are the electrolytes responsible for conducting the electric current when the liquid is subjected to an electric field.
On the other hand, solids have a much more closed atomic structure with less movement, so the conductivity will depend on the cloud of electrons shared by the valence bands and the conduction band, which varies depending on the atomic nature of the matter: metals are good electrical conductors and non-metals, on the other hand, are good resistors (or insulators, like plastic).
See also: Thermal conductivity
water conductivity
Water in general terms is a good electrical conductor. However, this capacity Depends on your Total Dissolved Solids (TDS) margin since the presence of salts and minerals in water forms electrolytic ions that allow the passage of electric current. Proof of this is that distilled water, from which all the ions dissolved in it are removed (using distillation and other methods), does not conduct electricity.
This way, The conductivity of salt water is greater than that of fresh water. The increase in the conductivity rate can be recorded as ions dissolved in the liquid are added, until a maximum ionic concentration is reached in which pairs of ions are formed, positive with negative, which annul their charge and prevent the conductivity. increases more.
Soil conductivity
Soils, in general, have different electrical conductivity, depending on various factors such as water irrigation or the amount of salts they present. Just as in the case of water, More saline soils will be better electrical conductors than less saline ones and this distinction is often determined by the amount of water they receive (since water can “wash” salts from the soil).
This level of salinity often confused with soil sodicity (the presence of sodium), when in reality salinity refers to the abundance of sodium cations (Na+), potassium (K+), calcium (Ca2+) and magnesium (Mg2+), along with chlorine cations (Cl–), sulfate (SO42-), bicarbonate (HCO3–) and carbonate (CO32-).
Thus, in many cases, techniques such as washing are used (for very saline soils) or the injection of other neutralizing elements (such as sulfur) for very basic soils. This can often be determined by electrical conduction testing.
Conductivity of metals
Metals are, in general terms, excellent electrical conductors. This is because the atoms of this type of material combine by forming metallic bonds. In metals, the electrons remain around the metal like a cloud, moving around the closely bonded atomic nuclei, and they are what allow electrical flow.
When the metal is applied to an electric field, electrons flow freely from one end of the metal to the other, as also happens with heat, of which they are also good transmitters. That is why copper and other metals are used in power lines and electronic devices. The following figure schematically represents the flow of electrons (in red) when an electric field is applied to a metal:
