Electric current alternating

Both chemical and physical environmental variables affect corrosion. The chemical influence of the environment depends on its composition and the presence of impurities such as heavy metal ions. Physical variables are tenq>erature, degree of movement and agitation, and pressure. Another physical variable that can cause corrosion of aluminum is the presence of stray electrical currents (alternating or direct). 

Stray-current corrosion, or stray-current electrolysis, is different fixim natural corrosion because it is caused by an externally induced electrical current (alternating, ac, or direct current, dc) and is basically independent of such environmental factors as oxygen concentration or pH. Environmental factors can enhance other corrosion mechanisms invcdved in the total corrosion process, but the stray-current corrosion portion of the mechanism is unaffected. 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

Induction furnaces utilize the phenomena of electromagnetic induction to produce an electric current in the load or workpiece. This current is a result of a varying magnetic field created by an alternating current in a cod that typically surrounds the workpiece. Power to heat the load results from the passage of the electric current through the resistance of the load. Physical contact between the electric system and the material to be heated is not essential and is usually avoided. Nonconducting materials cannot be heated directiy by induction fields. 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Electrodialysis. In electro dialysis (ED), the saline solution is placed between two membranes, one permeable to cations only and the other to anions only. A direct electrical current is passed across this system by means of two electrodes, causiag the cations ia the saline solution to move toward the cathode, and the anions to the anode. As shown ia Figure 15, the anions can only leave one compartment ia their travel to the anode, because a membrane separating them from the anode is permeable to them. Cations are both excluded from one compartment and concentrated ia the compartment toward the cathode. This reduces the salt concentration ia some compartments, and iacreases it ia others. Tens to hundreds of such compartments are stacked together ia practical ED plants, lea ding to the creation of alternating compartments of fresh and salt-concentrated water. ED is a continuous-flow process, where saline feed is continuously fed iato all compartments and the product water and concentrated brine flow out of alternate compartments. 

Alternating-current motors are classified as induction motors or synchronous motors. Faraday found that a stationaiy wire in a magnetic field produced no current. However, when the wire continues to move across magnetic lines of force, it produces a continual current. When the motion stops, so does the current. Thus Faraday proved that electric current is only produced from relative motion between the wire and magnetic field. It is called an induced current—an electromagnetic induction effect. 

Consider requirements for electrical isolation in order to restrict the spread of protective current. Alternatively assess extra current allowance for unrestricted spread. 

As with alternating electrical currents, phase-sensitive measurements are also possible with microwave radiation. The easiest method consists of measuring phase-shifted microwave signals via a lock-in technique by modulating the electrode potential. Such a technique, which measures the phase shift between the potential and the microwave signal, will give specific (e.g., kinetic) information on the system (see later discussion). However, it should not be taken as the equivalent of impedance measurements with microwaves. As in electrochemical impedance measurements,... 

For pyroelectric measurements, we used two A1 electrodes on both sides of the alternating LB film as shown in Figure 14. The electric current generated on linearly heating the LB film was measured by a picoammeter in the temperature range from -30° to 60 °C. The pyroelectric coefficient p is calculated from the observed pyroelectric current/ by... 

A thermocouple as radiation detector converts the alternating IR beams from the sample and reference cell into an alternating electric current. 

A well-known fact of fundamental solution science is that the presence of ions in any solution gives the solution a low electrical resistance and the ability to conduct an electrical current. The absence of ions means that the solution would not be conductive. Thus, solutions of ionic compounds and acids, especially strong acids, have a low electrical resistance and are conductive. This means that if a pair of conductive surfaces are immersed into the solution and connected to an electrical power source, such as a simple battery, a current can be detected flowing in the circuit. Alternatively, if the resistance of the solution between the electrodes were measured (with an ohmmeter), it would be low. Conductivity cells based on this simple design are in common use in nonchromatography applications to determine the quality of deionized water, for example. Deionized water should have no ions dissolved in it and thus should have a very low conductivity. The conductivity detector is based on this simple apparatus. 

Crystalline selenium is a p-type semiconductor. It acts as a rectifier that can change electric current from alternating current (AC) to direct current (to DC). It has photovoltaic proper-... 

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