electrical conductivity

Nevertheless, electric conductivities of numerous materials at high pressures have been documented. The principal classes of solids—insulators, semiconductors, metals, and superconductors—are distinguished on the basis of electric conductivity and its variation with temperature. Insulators, which include most rock-forming oxides and silicates, have been investigated extensively by…

Since then, shipboard electrical conductivity systems have become widely used. Salinity-Temperature-Depth (STD) and the more recent Conductivity-Temperature-Depth (CTD) systems have greatly improved on-site hydrographic sampling methods. They have enabled oceanographers to learn much about small-scale temperature and salinity distributions.

Electrical conductivity involves a flow or current of free electrons through a solid body. Some materials, such as metals, are good conductors of electricity; these possess free or valence electrons that do not remain permanently associated with the atoms of a solid but instead form…

…measured, notably by determining the electrical conductivity of the solution (its ability to carry an electrical current), a quantitative measure of the acidity or alkalinity of the solution is provided. Moreover, the equations developed to express the relationships between the various components of reversible reactions can be applied to acid…

Ordinarily, ceramics are poor conductors of electricity and therefore make excellent insulators. Nonconductivity arises from the lack of “free” electrons such as those found in metals. In ionically bonded ceramics, bonding electrons are accepted by the electronegative elements, such as oxygen, and donated by the electropositive…

Some ceramics, however, are excellent conductors of electricity. Most of these conductors are advanced ceramics, modern materials whose properties are modified through precise control over their fabrication from powders into products. The properties and manufacture of advanced ceramics are described in the article advanced ceramics. This article offers a survey…

Electrical conductivity σ is the inverse of resistivity and is measured in units of ohm-metre⁻¹. Electrical current is produced by the motion of charges. In crystals, electrical current is due to the motion of both ions and electrons. Ions move by hopping occasionally from site…

…ferromagnetic metals, they have low electric conductivity, however. In alternating magnetic fields, this greatly reduces the energy loss resulting from eddy currents. Since these losses rise with the frequency of the alternating field, such substances are of much importance in the electronics industry.

Although most glasses contain charged metallic ions capable of carrying an electric current, the high viscosity of glass impedes their movements and electrical activity. Thus, glass is an efficient electrical insulator—though this property varies with viscosity, which in turn is a function of…

…a metallic glass causes its electrical conductivity to be lower than the conductivity of the corresponding crystalline metal, because the structural disorder impedes the motion of the mobile electrons that make up the electrical current. (This lower electrical conductivity for the amorphous metal can be an advantage in some situations,…

The electrical conductivity of a metal (or its reciprocal, electrical resistivity) is determined by the ease of movement of electrons past the atoms under the influence of an electric field. This movement is particularly easy in copper, silver, gold, and aluminum—all of which are well-known conductors…

…which tend to be good electrical conductors, quasicrystals conduct electricity poorly. For alloys of aluminum-copper-ruthenium these conductivities differ by as much as a factor of 100. As the perfection of the quasicrystalline order grows, the conductivity drops. Such behaviour is consistent with the appearance of a gap in the electronic…

…a material with a high electrical conductivity. These materials (5–8 percent Y₂O₃ in ZrO₂) are excellent oxygen sensors. They are used to determine the oxygen content in the air and to control the rich-to-lean ratio in automobile fuels.

The electrical nature of a material is characterized by its conductivity (or, inversely, its resistivity) and its dielectric constant, and coefficients that indicate the rates of change of these with temperature, frequency at which measurement is made, and so on. For rocks with…

The calculated electrical conductivity of Saturn’s outer core of fluid metallic hydrogen is such that if slow circulation currents are present—as would be expected with the flow of heat to the surface accompanied by gravitational settling of denser components—there is sufficient dynamo action to generate the planet’s…

) Figure 1 shows the conductivities σ (and the corresponding resistivities ρ = 1/σ) that are associated with some important materials in each of the three classes. Insulators, such as fused quartz and glass, have very low conductivities, on the order of 10⁻¹⁸ to 10⁻¹⁰ siemens per centimetre; and conductors,…

Because silver has the highest electrical conductivity of all metals, it is used in alloyed form for electrical contacts. Palladium and nickel improve the metal’s chemical resistance to oxidation and sulfidation as well as its resistance to corrosion.

…particular type of charged particle moves through a solid material under the influence of an electric field. Such particles are both pulled along by the electric field and periodically collide with atoms of the solid. This combination of electric field and collisions causes the particles to move with an average…

…proportionality constant σ_J is the conductivity of the material. In a metallic conductor, the charge carriers are electrons and, under the influence of an external electric field, they acquire some average drift velocity in the direction opposite the field. In conductors of this variety, the drift velocity is limited by…

…conductivity for both heat and electricity. Conduction of both in metallic crystals is attributable to their ordered structure. The more perfect the structure, the better is the conduction. Frenkel defects, generated by irradiation, therefore decrease both conductivities. In extreme cases conductivity decrease of orders of magnitude has been observed. With…

Conductivity is the reciprocal of resistivity, and it, too, characterizes materials on the basis of how well electric current flows in them. The metre-kilogram-second unit of conductivity is mho per metre, or ampere per volt-metre. Good electrical conductors have high conductivities and low resistivities. Good…