Impurities electrical resistivity

Piebaked anodes aie produced by molding petroleum coke and coal tar pitch binder into blocks typically 70 cm x 125 cm x 50 cm, and baking to 1000—1200°C. Petroleum coke is used because of its low impurity (ash) content. The more noble impurities, such as iron and siUcon, deposit in the aluminum whereas less noble ones such as calcium and magnesium, accumulate as fluorides in the bath. Coal-based coke could be used, but extensive and expensive prepurification would be required. Steel stubs seated in the anode using cast iron support the anodes (via anode rods) in the electrolyte and conduct electric current into the anodes (Fig. 3). Electrical resistivity of prebaked anodes ranges from 5-6 Hm anode current density ranges from 0.65 to 1.3 A/crn. ... 

Total electrical resistivity of 99.999% pure or purer bulk silver. Impurities increase resistivity. 

The total electrical resistance at room temperature includes tire contribution from scattering of conduction electrons by the vacancies as well as by ion-core and impurity scattering. If the experiment is repeated at a number of high temperarnre anneals, then the effects of temperarnre on tire vacancy conuibu-tion can be isolated, since the other two terms will be constant providing that... 

However, the intra-atomic Coulomb interaction Uf.f affects the dynamics of f spin and f charge in different ways while the spin fluctuation propagator x(q, co) is enhanced by a factor (1 - U fX°(q, co)) which may exhibit a phase transition as Uy is increased, the charge fluctuation propagator C(q, co) is depressed by a factor (1 -H UffC°(q, co)) In the case of light actinide materials no evidence of charge fluctuation has been found. Most of the theoretical effort for the concentrated case (by opposition to the dilute one-impurity limit) has been done within the Fermi hquid theory Main practical results are a T term in electrical resistivity, scaled to order T/T f where T f is the characteristic spin fluctuation temperature (which is of the order - Tp/S where S is the Stoner enhancement factor (S = 1/1 — IN((iF)) and Tp A/ks is the Fermi temperature of the narrow band). 

A heliarc-welded, all-nickel can of 850-mL volume was filled with an intimate mixture of NiF, (290 g, 3 mol) and anhyd KF (52 g, 9 mol). The can was valved to a tank of F2 gas and a vacuum pump and was heated by an electric-resistance furnace. The can was heated slowly to 500 C under 10 atm of F2 and then cooled to 250 C, while still under several atm of F2. Several such cycles were carried out before using the device for the regeneration of F2. For the regeneration of F2, the salt was fluorinated at 250 C until no more F2 was taken up. The can was then cooled to 225 C and evacuated to remove the excess F2 and any volatile impurities. The temperature was then raised until the desired F, pressure (at 400 C, 25 atm) was achieved. 

Ad a. The set may be discrete, e.g. heads or tails the number of electrons in the conduction band of a semiconductor the number of molecules of a certain component in a reacting mixture. Or the set may be continuous in a given interval one velocity component of a Brownian particle (interval — oo, +00) the kinetic energy of that particle (0, 00) the potential difference between the end points of an electrical resistance (— 00, + 00). Finally the set may be partly discrete, partly continuous, e.g., the energy of an electron in the presence of binding centers. Moreover the set of states may be multidimensional in this case X is often conveniently written as a vector X. Examples X may stand for the three velocity components of a Brownian particle or for the collection of all numbers of molecules of the various components in a reacting mixture or the numbers of electrons trapped in the various species of impurities in a semiconductor. 

Copper from the reduction of ores must be purified for use in making electrical wiring because impurities increase its electrical resistance. The method used is electrorefining (Figure 18.19), an electrolytic process in which copper is oxidized to Cu2+ at an impure copper anode, and Cu2+ from an aqueous copper sulfate solution is reduced to copper at a pure copper cathode. The process is described in Section 18.12. 

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