Carbon anode

Hardee, K. Brown, Jr., C. (2003) Mesh-on-Lead anodes for copper electrowinning. JOM, 55(7), 46-48 

Isfort, H. (1985) State of the art after 20 years experience with industrial hydrochloric acid electrolysis. DECHEMA Monographien, 98,141-155. 

Gardiner, W.C. (1946) Hydrochloric Acid Electrolysis at Wolfen. Field Information Agency, Technical (FIAT) Report No. 832, US Office of Military Government for Germany. 

Holemann, H. (1962) The hydrochloric acid electrolysis. Chem. Ing. Techn., 34,371-376. 

Gallone, P. Messner, G. (1965) Direct electrolysis of hydrochloric acid. Electrochem. Technol., 3(11-12), 321-326. 

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Fluorine cannot be prepared directly by chemical methods. It is prepared in the laboratory and on an industrial scale by electrolysis. Two methods are employed (a) using fused potassium hydrogen-fluoride, KHFj, ill a cell heated electrically to 520-570 K or (b) using fused electrolyte, of composition KF HF = 1 2, in a cell at 340-370 K which can be electrically or steam heated. Moissan, who first isolated fluorine in 1886, used a method very similar to (b) and it is this process which is commonly used in the laboratory and on an industrial scale today. There have been many cell designs but the cell is usually made from steel, or a copper-nickel alloy ( Monel metal). Steel or copper cathodes and specially made amorphous carbon anodes (to minimise attack by fluorine) are used. Hydrogen is formed at the cathode and fluorine at the anode, and the hydrogen fluoride content of the fused electrolyte is maintained by passing in... 

Lithium fluoride is an essential component of the fluorine cell electrolyte 1% LiF in the KF 2HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cells to depolarize (18). Thermoluminescent radiation dosimeters used in personnel and environmental monitoring and in radiation therapy contain lithium fluoride powder, extmded ribbons, or rods (19). 

Fluorocarbons are made commercially also by the electrolysis of hydrocarbons in anhydrous hydrogen fluoride (Simons process) (14). Nickel anodes and nickel or steel cathodes are used. Special porous anodes improve the yields. This method is limited to starting materials that are appreciably soluble in hydrogen fluoride, and is most useflil for manufacturing perfluoroalkyl carboxyflc and sulfonic acids, and tertiary amines. For volatile materials with tittle solubility in hydrofluoric acid, a complementary method that uses porous carbon anodes and HF 2KF electrolyte (Phillips process) is useflil (14). 

The electrolytic decomposition of alumina yields oxygen which reacts with the carbon anode for an overall cell reaction ... 

Fused-salt electrolysis of K2NbFy is not an economically feasible process because of the low current efficiency (31). However, electrowinning has been used to obtain niobium from molten alkaU haUde electrolytes (32). The oxide is dissolved in molten alkaU haUde and is deposited in a molten metal cathode, either cadmium or zinc. The reaction is carried out in a ceramic or glass container using a carbon anode the niobium alloys with the cathode metal, from which it is freed by vacuum distillation, and the niobium powder is left behind. 

Alternative Processes for Aluminum Production. In spite of its industrial dominance, the HaH-HAroult process has several inherent disadvantages. The most serious is the large capital investment requited resulting from the multiplicity of units (250 —1000 cells in a typical plant), the cost of the Bayer aluniina-puriftcation plant, and the cost of the carbon—anode plant (or paste plant for Soderberg anodes). Additionally, HaH-HAroult cells requite expensive electrical power rather than thermal energy, most producing countries must import alumina or bauxite, and petroleum coke for anodes is in limited supply. 

Industrial carbon anodes and artificial graphites are not a single material but are rather members of a broad family of essentially pure carbon. Fortunately, artificial graphites can be tailored to vary widely in their strength, density, conductivity, pore structure, and crystalline development. These attributes contribute to their widespread applicability. Specific characteristics are imparted to the fmished product by conti ollmg the selection of precursor materials and the method of processing [19]... 

Freshly assembled lithium/carbon coin cells typically have voltages between 2.8 and 3.4 volts. The cells are in their fully charged state which means that no lithium is inserted in the carbon anode. Then the coin cells are tested with computer-controlled constant-current cyclers having currents stable to 1%. The cells are placed in thermostats at a particular set temperature v/hich is stable to 0.1°C during the test. Most of our cells were tested at 30°C. 

Many metals are extracted from their compounds, as found in ores, by electrolytic processes. By far the most important is the Hall-Heroult process, invented in 1886, for producing aluminium from alumina, itself refined from bauxite ore. Alumina is dissolved in molten cryolite, Na3Alp6, and electrolysed, using carbon anodes and the aluminium itself as cathode. While various details are being steadily improved, the basic process is still the same today. 

On carbon anode baking furnaces (ring furnaces) for removal of carbon particles, tar mists, and SO2,... 

Fig. 10. (a) Raman spectra (T = 300 K) of arc-derived carbons from a dc arc cobalt was absent (dotted line) and cobalt was present (solid line) in the carbon anode, (b) the difference spectrum calculated from (a), emphasbjng the contribution from Co-catalyzed nanolubes, the inset to (b) depicts a Lorentzian fit to the first-order spectrum (after ref. [27]). 

The corrosion product is predominantly carbon dioxide, but considerable amounts of free oxygen are produced at the anode surface, particularly in fresh-water applications, and can attack both the carbon and any organic binders used to reduce its porosity. For this reason carbon anodes for underground service are used in conjunction with a carbonaceous backfill. 

In general, lithium-ion batteries are assembled in the discharged state. That is, the cathode, for example LqCoC, is filly intercalated by lithium, while the anode (carbon) is completely empty (not charged by lithium). In the first charge the anode is polarized in the negative direction (electrons are inserted into the carbon) and lithium cations leave the cathode, enter the solution, and are inserted into the carbon anode. This first charge process is very complex. On the basis of many reports it is presented schematically [6, 74, 76] in Fig. 5. The reactions presented in Fig. 5 are also discussed in Sec. 6.2.1, 6.2.2 and 6.3.5. 

It was concluded [93, 94J that, on long cycling of the lithium-ion battery, the passivating layer on the carbon anode becomes thicker and more resistive, and is responsible, in part, for capacity loss. 

Xing and Dahn recently reported [70] that <2 R for disordered carbon and MCMB 2800 can be markedly reduced from about 180 and 30mAhg l to less than 50 and lOmAhg-1 respectively, when the carbon anode and cell assembly are made in an inert atmosphere and never come in contact with air. This indicates that these carbons contain nanopores that... 

The SEI is formed by parallel and competing reduction reactions and its composition thus depends on i0, t], and the concentrations of each of the electroactive materials. For carbon anodes, (0 also depends on the surface properties of the electrode (ash content, surface chemistry, and surface morphology). Thus, SEI composition on the basal plane is different from that on the cross—section planes. 

We did not feel any of these methods would work reliably on a commercial scale at current densities in the range of 300 mA cm"2 or for commercial periods (at least 4000 hr). Rudge s work9,10 with porous carbon anodes was a very elegant solution to the problem (and formed the basis for the Phillips Electrochemical Fluorination process), but the high electrical resistance of the porous carbon limited it to small anodes at high current densities or lower current densities on large anodes. 

Figure 8. Section through an incipient fluorine cell incorporating a fresh carbon anode with grooves.

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