Steel cathode

Steel additive Steel anode Steel bearings Steel cans Steel cathodes Steel, decaiburized Steel drums Steel grit... 

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). 

Fig. 4. The Norsk Hydro cell. Refractory material, A graphic anode, B steel cathode, C refractory cover, D metal oudet, E metal, F partition wall, G ...

United States, LaSalle, IH. 1918 continuous Hquid-phase oxidation (since ca 1961) K MnO separation from Hquid phase is without prior dilution continuous electrolysis of filtered electrolyte in bipolar ceUs Monel anodes, mild steel cathodes, vacuum crystallization 14,000 ... 

Other Metals. AH the sodium metal produced comes from electrolysis of sodium chloride melts in Downs ceUs. The ceU consists of a cylindrical steel cathode separated from the graphite anode by a perforated steel diaphragm. Lithium is also produced by electrolysis of the chloride in a process similar to that used for sodium. The other alkaH and alkaHne-earth metals can be electrowon from molten chlorides, but thermochemical reduction is preferred commercially. The rare earths can also be electrowon but only the mixture known as mischmetal is prepared in tonnage quantity by electrochemical means. In addition, beryIHum and boron are produced by electrolysis on a commercial scale in the order of a few hundred t/yr. Processes have been developed for electrowinning titanium, tantalum, and niobium from molten salts. These metals, however, are obtained as a powdery deposit which is not easily separated from the electrolyte so that further purification is required. 

New Synthesis. Many attempts have been made to synthesize oxaUc acid by electrochemical reduction of carbon dioxide in either aqueous or nonaqueous electrolytes (53—57). For instance, oxaUc acid is prepared from CO2 as its Zn salt in an undivided ceU with Zn anodes and stainless steel cathodes ia acetonitrile containing (C4H2)4NC104 and current efficiency of >90% (53). Micropilot experiments and a process design were also made. 

Fig. 2. Downs cell A, the steel shell, contains the fused bath B is the fire-brick lining C, four cylindrical graphite anodes project upward from the base of the cell, each surrounded by D, a diaphragm of iron gau2e, and E, a steel cathode. The four cathode cylinders are joined to form a single unit supported on cathode arms projecting through the cell walls and connected to F, the cathode bus bar. The diaphragms are suspended from G, the collector assembly, which is supported from steel beams spanning the cell top. For descriptions of H—M, see text.

The most favorable conditions for equation 9 are temperature from 60—75°C and pH 5.8—7.0. The optimum pH depends on temperature. This reaction is quite slow and takes place in the bulk electrolyte rather than at or near the anode surface (44—46). Usually 2—5 g/L of sodium dichromate is added to the electrolysis solution. The dichromate forms a protective Cr202 film or diaphragm on the cathode surface, creating an adverse potential gradient that prevents the reduction of OCU to CU ion (44). Dichromate also serves as a buffering agent, which tends to stabilize the pH of the solution (45,46). Chromate also suppresses corrosion of steel cathodes and inhibits O2 evolution at the anode (47—51). 

Table 4. Electrical Energy Requirement for a Chlorate Cell Using Steel Cathodes and Pt—Ir Anodes ...

For mild steel cathodes maximum hardness is 2 ppm. Some brines contain up to 20 ppm. 

Mild steel cathodes are used extensively in chlor-alkah and chlorate cells. Newer activated cathode materials have been developed that decrease cell voltages about 0.2 V below that for cells having mild steel cathodes. Some activated cathodes have operated in production membrane cells for three years with only minor increases in voltage (17). Activated cathodes can decrease the energy consumption for chlorine—caustic production by 5 to 6.5%. 

Chlora.tes. Sodium chlorate is produced by the electrolysis of sodium chloride at pH 6.5—7.5 in a one-compartment cell. DSA anodes and steel cathodes are generally used in chlorate cells. The electrolysis products, hypochlorous acid, and hypochlorite ions, react chemically to produce chlorate (eq. 

Sodium metal is produced commercially on the kilotonne scale by the electrolysis of a fused eutectic mixture of 40% NaCl, 60% CaCh at 580°C in a Downs cell (introduced by du Pont, Niagara Falls, 1921). Metallic Na and Ca are liberated at the cylindrical steel cathode and rise through a cooled collecting pipe which allows the calcium to solidify and fall back into the melt. Chlorine liberated at the central graphite anode is collected in a nickel dome and subsequently purified. Potassium cannot be produced in this way because it is too soluble in the molten chloride to float on top of the cell for collection and because it vaporizes readily... 

Similar effects to those shown in Fig. 1.65 have been observed by Pryor and Keir in certain bimetallic couples having steel cathodes. Figure 1.66... 

Fig. 1.66 Effect of area of steel cathode on the polarisation curves of the AI-Fe couple in I 0 NNaCl at 25°C using 100 cm of aluminium (potential vs. S.H.E.) (after Pryor and Keir )...

Fig. 1.67 Effect of mild-steel cathode on the weight loss of aluminium and zinc anodes (100 cm area) and on the number of coulombs flowing in the aluminium-mild steel and zinc-mild steel couples over a 96 h period in 1 -0 n NaCl at 25°C (after Pryor and Keir )...

FIGURE 12.15 In the Downs process, molten sodium chloride is electrolyzed with a graphite anode (at which the Cl ions are oxidized to chlorine) and a steel cathode (at which the Na4 ions are reduced to sodium). The sodium and chlorine are kept apart by the hoods surrounding the electrodes. Calcium chloride is present to lower the melting point of sodium chloride to an economical temperature. 

FIGURE 14.17 A diaphragm cell tor the electrolytic production of sodium hydroxide from brine (aqueous sodium chloride solution), represented by the blue color. The diaphragm (gold color) prevents the chlorine produced at the titanium anodes from mixing with the hydrogen and the sodium hydroxide formed at the steel cathodes. The liquid (cell liquor) is drawn off and the water is partly evaporated. The unconverted sodium chloride crystallizes, leaving the sodium hydroxide dissolved in the cell liquor. 

FIGURE 14.24 In the Hall process, aluminum oxide is dissolved in molten cryolite and the mixture is electrolyzed in a cell with carbon anodes and a steel cathode. The molten aluminum flows out of the bottom ot the cell. 

The nature of the cathode material is not critical in the Kolbe reaction. The reduction of protons from the carboxylic acid is the main process, so that the electrolysis can normally be conducted in an undivided cell. For substrates with double or triple bonds, however, a platinum cathode should be avoided, as cathodic hydrogenation can occur there. A steel cathode should be used, instead. 

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