Volta effect

Let us now investigate the Volta effect more quantitatively. When equilibrium is established, there will be a difference of potential between the empty space outside the two metals. The potential energy of an electron in this space will then be as in Fig. XXVIII-2. The jump in potential at the surface of each metal is as in Fig. XXVIII-1, but now the potential varies from one metal to another. Since metal b is negatively charged, the potential in its neighborhood is less than near metal a, and the potential energy of an electron, which is — e times the electrostatic potential, will be greater. The difference of potential between empty... 

Chemical Chemo luminance Explosion reaction Exothermal reaction Volta effect Chemical reaction... 

Two-stage batteries in which decay energy goes into the generation of a charge-free carrier (batteries with the p-n junction, Volta effect, secondary electron emission). 

Chemical Hygrometer Electrodeposition cell Photoacoustic effect Calorimeter Thermal conductivity cell Potentiometry Conductimetry Amperometry Flame ionization Volta effect Gas-sensitive field effect Nuclear magnetic resonance (Emission and absorption) spectroscopy Chemiluminiscence ... 

When certain materials are bonded together, electrons tend to transfer from one to the other. This is called the Volta effect. If two such materials are joined together with two junctions at the same temperature, the plus Volta emf at one junction will be balanced by a minus emf at the other and no current will flow. However, if the two junctions have different temperatures, a current will flow from one junction to the other. This is called the Seebeck effect, and is the basis of the thermocouple. Figure 11.1 (a) shows a thermocouple with a small voltmeter in series with two thermocouple wires (iron and 60 Cu-40 Ni constantan). The emf will be proportional to (T2 - Tj). Figure 11.1 (6) gives the calibration curve for an iron-constantan couple. Thermocouples are used to measure very high (furnace) temperatures, and when the upper range of an iron-constantan thermocouple is reached, a platinum-rhodiiun couple [also shown in Fig. 11.1(6)] may be employed. 

Figure 5.7. Schematic representation of the definitions of work function O, chemical potential of electrons i, electrochemical potential of electrons or Fermi level p = EF, surface potential %, Galvani (or inner) potential

Volta discovered that when he used different metals in his pile some combinations had a stronger effect than others. From that information he constructed an electromotive series. How would Volta have ordered the following metals, if he put the most strongly reducing metal first Fe, Ag, Au, Zn, Cu, Ni. Co, Al ... 

The Volta pile was of extraordinary significance for developments both in the sciences of electricity and electrochemistry, since a new phenomenon, a continuous electric current, hitherto not known, could now be realized. Soon various properties and effects of the electric current were discovered, including many electrochemical processes. In May of 1800, William Nicholson and Sir Anthony Carlisle electrolyzed... 

During the next decades after the appearance of the Volta pile and of different other versions of batteries, fundamental laws of electrodynamics and electromagnetism were formulated based on experiments carried out with electric current supplied by batteries Ampere s law of interaction between electrical currents (1820), Ohm s law of proportionality between current and voltage (1827), the laws of electromagnetic induction (Faraday, 1831), Joule s law of the thermal effect of electric current, and many others. 

With higher ion concentrations or electron-conductive liquids, the effect of the zeta potential is essentially superseded by electrolytic (galvanic) or volta potentials, respectively. Although these potentials are of the order of 1 V while zeta potentials are one or two orders of magnitude lower, the high conductivities of the more conductive liquids make it normally impossible to build up the high streaming potentials that are possible with low conductivity liquids by virtue of the zeta potential. 

The ready availability of electricity following the invention by Alssandro Volta of his famous pile in 1800 prompted, from an early date, the study of its effects on condensed matter and, most particularly, the decomposition of water by electrolysis involving chemical reactions at the electrodes. Work developed to the point where, by the middle of the second half of the nineteenth century, well-established industrial processes for the manufacture of aluminium and chlorine gas operated by electrolysis. 

The main effect of crystal orientation is caused by different barrier heights on different crystal faces. It is well known that Volta-potential differences are dependent on crystal orientation because the surface dipole differs for different faces. In the case of a semiconductor electrode this means that the flat band potential which can be determined experimentally depends... 

The effects of the crystallographic face and the difference between metals are evidence of the incorrectness of the classical representations of the interface with all the potential decay within the solution (Fig. 3.13a). In fact a discontinuity is physically improbable and experimental evidence mentioned above confirms that it is incorrect, the schematic representation of Fig. 3.136 being more correct. This corresponds to the chemical models (Section 3.3) and reflects the fact that the electrons from the solid penetrate a tiny distance into the solution (due to wave properties of the electron). In this treatment the Galvani (or inner electric) potential, (p, (associated with EF) and the Volta (or outer electric) potential, ip, that is the potential outside the electrode s electronic distribution (approximately at the IHP, 10 5cm from the surface) are distinguished from each other. The difference between these potentials is the surface potential x (see Fig. 3.14 and Section 4.6). 

The crucial point is that the difference of potential available to effect electrode reactions and surmount activation barriers is not simply the difference between the Galvani potential (i.e. the Fermi energy) and the potential in solution. On the side of the solid it is the Volta potential and on the side of the solution it is the potential at the inner Helmholtz plane, where species have to reach to in order for electron transfer to be possible. Corrections to rate constants for the latter are commonly carried out using the Gouy-Chapman model of the electrolyte double layer and will be described in Section 6.9. 

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