Primary anode

In the 2inc chloride cell, precipitated basic 2inc chloride is the primary anode product because of the low concentration of ammonium chloride in the cell. Water and 2inc chloride are consumed in equations 1 and 7 and must be provided in adequate amounts for the cell to discharge efficiendy. Usually more carbon is used in 2inc chloride cells than in Led an chit cells in order to increase the electrolyte absorptivity of the cathode and thus allow the use of a larger volume of electrolyte. Also, the use of a thin paper separator, which decreases internal resistance, allows less space for water storage than the thick, pasted separator constmction traditionally used in Leclanchn cells. 

Anode Applications. Graphite has been used as the primary material for electrolysis of brine (aqueous) and fused-salt electrolytes, both as anode and cathode. Technological advances, however, have resulted in a dimensionally stable anode (DSA) consisting of precious metal oxides deposited on a titanium substrate that has replaced graphite as the primary anode (38—41) (see Alkali and chlorine products). 

These are anodes that, to reduce costs, use a combination of materials, sometimes coaxially, to extend the life of the primary anode, reduce resistance to earth, improve current distribution, facilitate installation and improve mechanical properties. Often the so-called anode is primarily a means of conducting the current to the more rapidly consumable anode material. These can be classified as follows ... 

Canister anodes consist of a spirally wound galvanised steel outer casing containing a carbonaceous based extender which surrounds the primary anode element which may be graphite, silicon iron, magnetite, platinised titanium, mixed metal oxide-coated titanium or platinised niobium, etc. 

These consist of a number of parallel slots cut into the concrete surface. Each slot is then filled with a secondary anode of carbon/graphite fibres embedded in a conductive polymer grout. The current to each of these secondary anode systems is provided by a primary anode of platinised niobium wire placed in slots filled with conductive polymer which acts as the primary anode, these slots intersecting each slot of graphite fibre/conductive polymer at right angles. 

Conductive paints (resins) have recently been used for the cathodic protection of steel reinforcing bars in concrete, but they are always used in conjunction with a primary anode material, e.g. platinised-niobium or platinised-titanium wire or a conductive polymer rod. 

In recent years, there has been interest in using zinc as a power-impressed anode for the cathodic protection of steel in concrete. The zinc is flame sprayed onto a grit blasted concrete surface to a final film thickness of approximately 250 m. A primary anode is necessary. Early systems used brass plates as the primary anode, but more recent systems used platinised titanium or niobium wire anodes as the primary current conductor. 

The electrochemical oxidation of 2,5-dimethylthiophene in various electrolytes has been investigated (71JOC3673). In non-halide electrolytes such as ammonium nitrate or sodium acetate, the primary anodic process is the oxidation of the thiophene to the cation-radical (159). Loss of a proton, followed by another oxidation and reaction with solvent methanol, leads to the product (160) (Scheme 31). When the electrolyte is methanolic NaCN, however, nuclear cyanation is observed in addition to side-chain methoxylation. Attack by cyanide ion on the cation-radical (159) can take place at either the 2- or the 3-position, leading to the products (161)-(163) (Scheme 32). 

Reaction (89) requires twice as much carbon as reaction (88) for the same quantity of electricity. One might then expect that the problem of the primary anode product could be easily solved by determining the gas composition and the carbon consumption. 

The following equations demonstrate the primary anodic reaction ... 

Electrolytic introduction of sulfur-containing substituents may be performed by anodic thiocyanation. The primary anodic process of an aromatic system in such a reaction is the loss of an electron with formation of a cation radical. This radical may lose a proton or react with a nucleophile to give a neutral radical which again may lose an electron to form a carbonium ion loss of a proton or reaction with a nucleophile may complete the reaction. 

Similar materials were used by Skeldon et al to produce a self-lubricating surface film on aluminium. They first produced a porous alumina film on the surface by anodizing, and then re-anodized in an electrolyte containing 0.01 M ammonium tetrathiomolybdate. They then found that the pores of the primary anodized film contained mainly amorphous molybdenum trisulphide, and this was converted by vacuum annealing to hexagonal molybdenum disulphide. The film gave a marked improvement in wear resistance. 

In early attempts to oxidize hydrocarbons electrochemically, organic solvents and corrosion-resistant electrodes (PbO, C, Pt) were used to overcome low reactant solubility and anode dissolution at extreme potentials, -I-1.8 V and up to 4.5 V (326, 327). The primary anodic reaction was usually oxygen evolution or solvent decomposition. The electrode material, nonetheless, affected the product even at the small attainable yields. Thus, toluene oxidized to traces of aldehydes on PbO2 (333), while on Pt it yielded up to 19% benzaldehyde (326). The catalytic efifect of the anode, however, on rate and selectivity was not realized. 

Other anode systems specially developed are sprayable conductive polymer coatings, metallized zinc coatings, and conductive paints. Typical primary anode for the conductive polymer or paints is platinized niobium wire attached to the concrete prior to application. Estimated cost is 76/m with a service life of five years. 

The first anodes, developed by Stratfull, were silicon iron primary anodes in contact with a conductive coke breeze asphalt overlay (the secondary anode). This design was based upon CP designs for pipelines where a silicon iron anode is embedded in a carbon coke breeze backfill to give a large contact area and low resistance. The anode is then linked, via the transformer rectifier, to the pipeline to be protected. A modified form of the conductive... 

This is a wet sprayed mortar containing nickel plated carbon fibres to achieve conductivity (Figure 7.14). It requires a primary anode, usually the titanium mesh ribbon. This is a proprietary anode and there are no variations. 

I. Thermodynamic Decomposition Voltage for Membrane and Diaphragm Cells. The primary anodic and cathodic reactions associated with the reaction scheme (140) are ... 

Low Resistance Current Paths. An indirect use of zinc for corrosion protection is to provide a low resistance path for impressed current protection of concrete bridge structures with uncoated steel rebar. Electrochemical protection of steel rebar in concrete was developed as a repair technique but is now being promoted also for new structures. Current generated by impressed anodes on the outside of the concrete and a positive electrical contact with the rebar stops the latter from rusting. The primary anode is usually brass or copper. 

The anode process involving the formation of adsorbed COx compounds, associated with a high overvoltage of several hundred millivolts, is reported [7] at normal current densities of about 0.7 A/cm. CO2 is the primary anode product at normal current density, while... 

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