Electric conductivity field

Carbon nanotubes are a new allotropic form of caibon and possess interesting physicochemical properties. Their chance discovery was a result of an enormous interest in fullerenes. Carbon nanotubes are built of graphene layers and can assume single- or multi-wallet structures [23,25,35]. Chemical modifications of nanotubes in both open terminated areas and on outer and inner walls create many possibilities. Prospective and present applications of nanotubes depend on their physicochemical properties, such as density, resistance to stretching and bending, thermal and electrical conductivity, field emission, as well as resistance to temperature. Good adsorption properties of nanocarbon materials contribute to their extensive practical application. 

Fluids influenced by external force fields are best exemplified by systems in which electrically conducting fields play a role (for example, magnetohydrodynamics). In such cases,... 

The intensity of the magnetic field produced by eddy current is depended on electrical conductivity and magnetic permeability of the studied area. In case of a uniform structure, when the conductivity of the material is high, the intensity of the induced magnetic field is big and signal received by probe Hp is small. 

Measurement by Electromagnetic Effects. The magnetic flow meter is a device that measures the potential developed when an electrically conductive flow moves through an imposed magnetic field. The voltage developed is proportional to the volumetric flow rate of the fluid and the magnetic field strength. The process fluid sees only an empty pipe so that the device has a very low pressure drop. The device is useful for the measurement of slurries and other fluid systems where an accumulation of another phase could interfere with flow measurement by other devices. The meter must be installed in a section of pipe that is much less conductive than the fluid. This limits its appHcabiHty in many industrial situations. 

The electrical conductivity O of a gas is defined as the ratio of the current to the field, ie, from the most general form of Ohm s law. Neglecting ion mobihty, this becomes equation 16, which can be written in terms of the current density components ... 

Disadvantages associated with some organic solvents include toxicity flammabiHty and explosion ha2ards sensitivity to moisture uptake, possibly leading to subsequent undesirable reactions with solutes low electrical conductivity relatively high cost and limited solubiHty of many solutes. In addition, the electrolyte system can degrade under the influence of an electric field, yielding undesirable materials such as polymers, chars, and products that interfere with deposition of the metal or alloy. 

The absence of an electron from a covalent bond leaves a hole and the neighboring valence electron can vacate its covalent bond to fill the hole, thereby creating a hole in a new location. The new hole can, in turn, be filled by a valence electron from another covalent bond, and so on. Hence, a mechanism is estabUshed for electrical conduction that involves the motion of valence electrons but not free electrons. Although a hole is a conceptual artifact, it can be described as a concrete physical entity to keep track of the motion of the valence electrons. Because holes and electrons move in opposite directions under the influence of an electric field, a hole has the same magnitude of charge as an electron but is opposite in sign. 

A general observation, verified for nearly all soHds, is a proportionality between current density and field strength, known as Ohm s law. The electrical conductivity is this proportionality constant and is defined as... 

Electrical conduction ia glasses is mainly attributed to the migration of mobile ions such as LE, Na", K", and OH under the influence of an appHed field. At higher temperatures, >250° C, divalent ions, eg, Ca " and Mg ", contribute to conduction, although their mobiUty is much less (14). Conduction ia glass is an activated process and thus the number of conducting ions iacreases with both temperature and field. The temperature—resistivity dependence is given... 

This article addresses the synthesis, properties, and appHcations of redox dopable electronically conducting polymers and presents an overview of the field, drawing on specific examples to illustrate general concepts. There have been a number of excellent review articles (1—13). Metal particle-filled polymers, where electrical conductivity is the result of percolation of conducting filler particles in an insulating matrix (14) and ionically conducting polymers, where charge-transport is the result of the motion of ions and is thus a problem of mass transport (15), are not discussed. 

Ebbesen[4] was the first to estimate a conductivity of the order of lO fim for the black core bulk material existing in two thirds of tubes and one third of nanoparticles. From this observation, it may naturally be inferred that the carbon arc deposit must contain material that is electrically conducting. An analysis of the temperature dependence of the zero-field resistivity of similar bulk materials[14,15] indicated that the absolute values of the conductivity were very sample dependent. 

The early pioneers also include Benjamin Franklin and Charles de Coulomb. Franklin studied the effect of point electrodes in drawing electric currents. Coulomb discovered that a charged object gradually loses its charge i.e., he actually discovered the electrical conductivity of air. Coulomb s importance for the development of electrostatic air-cleaning methods is great, mainly because the present theories about electric charges and electric fields are based on his work. 

These quantum effects, though they do not generally affect significantly the magnitude of the resistivity, introduce new features in the low temperature transport effects [8]. So, in addition to the semiclassical ideal and residual resistivities discussed above, we must take into account the contributions due to quantum localisation and interaction effects. These localisation effects were found to confirm the 2D character of conduction in MWCNT. In the same way, experiments performed at the mesoscopic scale revealed quantum oscillations of the electrical conductance as a function of magnetic field, the so-called universal conductance fluctuations (Sec. 5.2). 

Fig. 3. Electrical conductance of an MWCNT as a function of temperature at the indicated magnetic fields. The solid line is a fit to the data (see ref. 10). The dashed line separates the contributions to the magnetoconductance of the Landau levels and the weak localisation [10].

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