Anode carbon aluminum dependence

Further improvements in anode performance have been achieved through the inclusion of certain metal salts in the electrolyte, and more recently by dkect incorporation into the anode (92,96,97). Good anode performance has been shown to depend on the formation of carbon—fluorine intercalation compounds at the electrode surface (98). These intercalation compounds resist further oxidation by fluorine to form (CF ), have good electrical conductivity, and are wet by the electrolyte. The presence of certain metals enhance the formation of the intercalation compounds. Lithium, aluminum, or nickel fluoride appear to be the best salts for this purpose (92,98). 

Gokes derived from resids or blends of resids with other petroleum feedstocks give high GTE values and are utilized as fillers for aluminum anodes and certain specialty carbon and graphite products. The remaining properties differ depending on the final appHcation. Alow ash content is required for... 

The electrolytic processing of concentrated ore to form the metal depends on the specific chemical properties of the metallic compound. To produce aluminum about 2 to 6 percent of purified aluminum oxide is dissolved in ciyolite (sodium alumi-no-fliioride, Na AlF ) at about 960°C. The reduction of the alumina occurs at a carbon (graphite) anode ... 

A blackbody is a body that absorbs all radiation and emits none. Experimentally, it is approximated by a "furry box" (a closed box of aluminum, whose interior walls are anodized to form a black surface, or a metal box painted with carbon black) and with a small hole drilled in one face, to allow some radiation generated at any fixed temperature to escape the box. The puzzle in the late nineteenth century was to explain the experimentally observed wavelength dependence and temperature dependence of the radiation (Fig. 5.5). Partial explanations had been obtained by Rayleigh21 and Jeans22 and by Stefan23 and Boltzmann, but the full, exact, correct, and truly revolutionary explanation was obtained in 1901 by Planck,24 who thereby ushered in quantum mechanics. 

The concentration of any of these species depends on the total concentration of dissolved aluminum and on the pH, and this makes the system complex from the mathematical point of view and consequently, difficult to solve. To simplify the calculations, mass balances were applied only to a unique aluminum species (the total dissolved aluminum, TDA, instead of the several species considered) and to hydroxyl and protons. For each time step (of the differential equations-solving method), the different aluminum species and the resulting proton and hydroxyl concentration in each zone were recalculated using a pseudoequilibrium approach. To do this, the equilibrium equations (4.64)-(4.71), and the charge (4.72), the aluminum (4.73), and inorganic carbon (IC) balances (4.74) were considered in each zone (anodic, cathodic, and chemical), and a nonlinear iterative procedure (based on an optimization method) was applied to satisfy simultaneously all the equilibrium constants. In these equations (4.64)-(4.74), subindex z stands for the three zones in which the electrochemical reactor is divided (anodic, cathodic, and chemical). 

A patented process has been developed for the production of electrode binder pitch from petroleum-based materials. Carbon anodes produced from the petroleum-based pitch and coke have been used successfully on a commercial scale by the aluminum industry. One stage of the process involves the pyrolysis of a highly aromatic petroleum feedstock. To study the pyrolysis stage of the process a small, sealed tube reactor was used to pyrolyze samples of feedstock. The progress of the reaction is discussed in terms of the formation of condensed aromatic structures, defined by selective solvent extraction of the reaction product. The pyrolysis of the feedstock exhibits a temperature-dependent induction period followed by reaction sequences that can be described by first-order kinetics. Rate constants and activation energies are derived for the formation of condensed aromatic structures and coke. 

C. Chemical modification of the glued surfaces by the formation of passivating layers. The modification technique depends on the nature of the metal. The parts are most often subjected to acid pickling, e.g. aluminum alloys are anodized in sulfuric and chromic acids. It is preferable to anodize aluminum parts in sulfuric acid followed by treatment of the anodic film in a bichromate. There are several methods of pickling carbon and stainless steels, chemical oxidation of magnesium alloys as well as copper and titanium alloys before gluing [4]. 

J. L. Goldman, A. B. McEwen, Electrochem. Solid-State Lett. 1999, 2, 501-503. EMIIm and EMlBeti on aluminum. Anodic stability dependence on lithium salt and propylene carbonate. 

The different cell technologies for aluminum production depend on the nature of the carbon anodes and the current load. However, the electrolyte composition and the operation of the electrolysis is very similar for all technologies. Information about innovations and performance data related to aluminum electrolysis has traditionally been very open. Figure 3 shows a schematic drawing of a modem prebaked cell. 

In the primary production of aluminum, the electrolyte is cryoHte, with some excess of aluminum fluoride AlFj. The electrolyte is melted in steel pots with dimensions up to 10 m length, 4 m width and 1.5 m depth (Figure 37.2). Each pot is Hned with carbon, acting as a cathode in the electrolytic cell. Carbon anodes are inserted into the electrolyte from the top. The voltage is 5 V, and the amperage very high - depending on the furnace size, the latter can be between 30 000 and 300 000 A. 

The terms soft and hard, very frequently found in the literature, are really not that helpful being based on early working experiences of their physical properties. These terms should be avoided and relegated to the past literature. To use these imprecise physical terms loses sight of the basis of their structures. For example, a baked carbon anode, as used in the aluminum industry, is an extremely hard material, but is graphitizable. The isotropic carbons in their industrial use are selected for their hardness otherwise they would easily degrade to dust. An isotropic carbon, of low HTT of about 600 °C, may be quite soft, depending. The terms should be avoided. 

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