Aluminum cathode

Aluminum metal and, to a lesser extent, aluminum alloys are suitable materials for manufacturing industrial cathodes. Actually, pure aluminum metal exhibits a low density (2690 kg.m ) and high thermal conductivity (237 Wm K ), is a good electrical conductor (2.6548 p 2.cm), does not form hydride with nascent hydrogen, and passivates when polarized anodicaUy. All these characteristics, along with a reasonable average cost of 2.734 US /kg (for 99.7 wt.% Al), are major assets for its wide utilization especially in zinc electrowinning. 

Industrial applications. In zinc electrowinning, zinc is directly plated onto aluminum cathodes while oxygen is evolved at the Pb-Ag anode. Once the zinc electrodeposit reaches a desired thickness, the aluminum cathodes are removed from the cells, followed by either manually or automatically stripping the zinc deposit. On the other hand, molten aluminum is used as liquid cathode during the electrowinning of aluminum in the Hall-Heroult process. 

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The electrorefining of many metals can be carried out using molten salt electrolytes, but these processes are usually expensive and have found Httie commercial use in spite of possible technical advantages. The only appHcation on an industrial scale is the electrorefining of aluminum by the three-layer process. The density of the molten salt electrolyte is adjusted so that a pure molten aluminum cathode floats on the electrolyte, which in turn floats on the impure anode consisting of a molten copper—aluminum alloy. The process is used to manufacture high purity aluminum. 

Currem field characteristics measured wiih conjugated polymers sandwiched between an indium-tin oxide (ITO) anode and an aluminum cathode are usually hole dominated and are, consequently, appropriate for testing injection/lransport models for the case of unipolar current How. Data shown in Figure 12-1 refer to injection-limited currents recorded on typically 100 nm thick spin-coated films of derivatives of poly(y d/"fi-phenylenevinylene) (PPV) and a planarized poly(/ /" -pheny-leue) employing a Keilhley source measure unit. The polymers were ... 

Modification of the top electrode may also be achieved. This was done by adding a small amount of surfactant, such as an ether phosphate or an ether sulfate, to the spin-coal solution of the luminescent polymer [89[. The lipophobic ether chains segregate at the surface of the (predominantly) hydrocarbon polymer, becoming available for complexation with the aluminum cathode which is deposited on top. Thus, the dipole in the surfactant points away from the electrode and lowers its work function to improve the injection of electrons. 

Zinc electrowinning takes place in an electrolytic cell and involves running an electric current from a lead-silver alloy anode through the aqueous zinc solution. This process charges the suspended zinc and forces it to deposit onto an aluminum cathode (a plate with an opposite charge) that is immersed in the solution. Every 24 to 48 h, each cell is shut down, the zinc-coated cathodes removed and rinsed, and the zinc mechanically stripped from the aluminum plates. The zinc concentrate is then melted and cast into ingots, and is often as high as 99.995% pure. 

Zinc electrowinning Zinc in a sulfuric acid/ aqueous solution, lead-silver alloy anodes, aluminum cathodes, barium carbonate, or strontium, colloidal additives... 

Although the preparative cathodic reduction of halomethylsilanes has not been investigated extensively, Dunogues and coworkers revealed that the electrochemical reduction of (chloromethyl)dimethylchlorosilane with an aluminum cathode afforded polycarbosilanes [92]. l,1.3,3-Tetramethyl-l,3-disilacyclobutane is also formed under these condition (Scheme 43). 

G. Chimed and F. Masamichi, A lithium carboxylate ultrathin film on an aluminum cathode for enhanced electron injection in organic electroluminescent devices, Jpn. J. Appl. Phys., Part 2, 38 L1348-L1350 (1999). 

BH Cumpston and KF Jensen, Electromigration of aluminum cathodes in polymer-based electroluminescent devices, Appl. Phys. Lett., 69 3941-3943, 1996. 

Cadmium also may be recovered from zinc ores and separated from other metals present as impurities by fractional distillation. Alternatively, the cadmium dust obtained from the roasting of zinc ore is mixed with sulfuric acid. Zinc dust is added in small quantities to precipitate out copper and other impurities. The metal impurities are removed by filtration. An excess amount of zinc dust is added to the solution. A spongy cadmium-rich precipitate is formed which may he oxidized and dissolved in dilute sulfuric acid. Cadmium sulfate solution is then electrolyzed using aluminum cathodes and lead anodes. The metal is deposited at the cathode, stripped out regularly, washed and melted in an iron retort in the presence of caustic soda, and drawn into desired shapes. More than half of the world s production of cadmium is obtained by elecrolytic processes. 

Zinc also may be produced by electrolysis of zinc sulfate solution. The zinc oxide in the roasted concentrate is leached with sulfuric acid. The oxide is converted to soluble zinc sulfate. Impurity metals, such as iron, copper, cadmium, arsenic, tin, and cobalt are removed by precipitation, floe formation, and other methods. The purified zinc sulfate solution is electrolyzed using aluminum cathodes and lead anodes. Zinc is deposited on the cathode. 

A standard solution of B-5 fixative containing a concentration of mercuric chloride of 60 g/1 was plated for 8 hours and yielded 60% recovered mercury metal. Two liters of solution were plated, thus a total of 120 g of mercuric chloride were processed. The stoichiometric amount of mercury metal from the reduction of 120 g of mercuric chloride equals 88 g. The recovered mercury metal totaled 53 g, thus demonstrating a 60% recovery efficiency. During the eight hour process the aluminum cathodes were changed once. The solution pH was between 3.6-3.8. 10 g of calcium chloride were added in order to... 

Nearly pure cadmium sponge is precipitated by the addition of high-purity. lead-free zinc dust. The cadmium sponge then is redigested in spent cadmium electrolyte, alter which the cadmium is deposited by electrolysis onto aluminum cathodes. The metal is then stopped from the electrodes, melted, and cast into various shapes. Reactions which occur during the electrolytic process are (Roasting) ZnS +1,0 — — ZnO +... 

Zinc is extracted from the purified solution in cells using lead/silver alloy anodes and aluminum cathodes at a current density of 38-60 amperes/square foot (400-650 amperes/square meter) The product is normally SHG zinc, particularly if strontium carbonate is added and/or lead/silver anodes of greater than 0.596 silver content are used. After deposition of 24 to 72 horns, the cathodes are removed from the cells and the zinc is stripped by automatic machines in modem plants, melted, and cast for market. The move to automated handling of large cathodes was a major factor in lowering the overall labor requirement in producing zinc. 

A single-layer OLED with [Er(acac)3phen] doped into a 80-nm thick film of PVK (see fig. 117) prepared by spin-coating and deposited on an ITO electrode, and with a 100-nm lithium-doped (0.1%) aluminum cathode has also been tested and shows an onset voltage of about 12 V for electroluminescence (Sun et al., 2000). [Er(dbm)3bath] has a photoluminescence quantum yield of 0.007% in dmso-7fl at 1 mM concentration the OLED based on this compound and similar to the one described above for Ndm has a NIR external electroluminescence efficiency of 1 x 10-6 (Kawamura et al., 2001). 

At aluminum cathode, hydrogen gas is released according to the following reaction ... 

Electroluminescence (EL) spectra of P-l-P-4 are given in Fig. 6 [29,30]. The EL spectra of the polymers were obtained for the light-emitting diodes (LEDs) fabricated between the indium-tin oxide (ITO) coated glass anode and the aluminum cathode. For P-l-P-3, their organic soluble precursor polymers were coated onto the ITO-coated glass and they were subjected to thermolysis at 270 °C for 12 h to convert them into the final polymers. And then aluminum cathode was vacuum deposited on the polymer films. P-4 obtained by base-catalyzed polymerization of the bis-bromomethyl monomer was organic soluble and, thus,... 

The most used liquid metal pool electrode is the aluminum cathode (m.p. 660°C) in the Hall-Heroult aluminum extraction cell. Alkali metals and alkaline-earth metals are also used as liquid cathodes in their molten salt extraction processes. 

Fig. 4.11. Left (a) Optical microscope image of an OLED working at a luminance of 100 cd/m2 under water vapor atmosphere. Non-emitting dark spots can be seen clearly, (b) SEM image of the bubbles formed on the aluminum cathode in the dark spot area, (c) Correlation between dark spot growths (taken from the increase in diameter) and total current density [110]. Right (a) Shown here is the random pattern of carbonized areas on the surface of the cathode after operation, shown in wide field, (b) At higher resolution, the structure of one of these areas becomes more apparent, (c) and (d) show nanoscale views of carbonized areas with the extrusion of the polymer through the cathode and the resulting void underneath [111].

The separation of the flocculated sludge formed by EC process can be accomplished by precipitation or flotation (Yavuz 2007 Szpyrkowicz 2007). However, preliminary experiment showed that the hydrogen gas produced at the aluminum cathode in an electrocoagulation cell was not so fine that could float only about 60% of the total solids. In our research group, a combinative bipolar EC-EF process was developed to treat laundry wastewater (Ge et al. 2004). 

Chaudry and Bhide [57] demonstrated a process for cleaning metallic surfaces contaminated by a spent-fuel radioactive wastewater stream. Using an aluminum cathode and tapwater as the electrolyte, a current density of 15 pA/cm on a contaminated pipe wrench made of mild steel (rendered anodic) reduced the radioactivity from 26 pGy/h to 0.26-0.39 pGy/h in 15 min. Similar results were obtained when studies were performed on contaminated aluminium plates. 

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