Platinum, electrolytic production

Most metals can be electrolytically deposited from water-free melts of the corresponding metal salts. It is well known that aluminum, lithium, sodium, magnesium, and potassium are mass produced by electrolytic deposition from melts. Industrial processes for the melt-electrolytic production of beryllium, rare earth metals, titanium, zirconium, and thorium are also already in use. Pertinent publications [74, 137, 163] describe the electrolytic deposition of chromium, silicon, and titanium from melts. Cyanidic melts are used for the deposition of thick layers of platinum group metals. It is with this technique that, for instance, adhesion of platinum layers on titanium materials is obtained. Reports concerning the deposition of electrolytic aluminum layers [17, 71-73, 94, 96, 102, 164, 179] and aluminum refinement from fused salts [161] have been published. For these processes, fused salt... 

Use Hardener for platinum and palladinum in jewelry, electrical contact alloys, catalyst, medical instruments, corrosion-resistant alloys, electrodeposited coatings, nitrogen-fixing agent (experimental), solar cells (experimental) the oxide is used to coat titanium anodes in electrolytic production of chloride the dioxide serves as an oxidizer in photolysis of hydrogen sulfide. 

Electrocatalysis can modify the composition of the electrode surfaces and the nature of the electrolytic products. The perchlorate decomposition (cathodic production of chloride) on platinum catalysts is one of the examples [57] and the IrCT decomposition during the sodium chlorate production [58]. The electropolymerization of the organic substances is critically dependent on the type of the electronic/ionic conductors, electrolyte characteristics, and the electrolysis resident time of the monomer [59]. 

The calculated value E° = +1.23 V for the O2, 4H /2H20 electrode implies that electrolysis of water using this applied potential difference at pH 0 should be possible. Even with a platinum electrode, however, no O2 is produced. The minimum potential for O2 evolution to occur is about 1.8V. The excess potential required ( 0.6V) is the overpotential of O2 on platinum. For electrolytic production of H2 at a Pt electrode, there is no overpotential. For other metals as electrodes, overpotentials are observed, e.g. 0.8 V for Hg. In general, the overpotential depends on the gas evolved, the electrode material and the current density. It may be thought of as the activation energy for conversion of the species discharged at the electrode into that liberated from the electrolytic cell, and an example is given in worked example 16.3. Some metals do not liberate H2 from water or acids because of the overpotential of H2 on them. 

Gaston Plante was very active in the field of electrochemistry. He replaced the then used platinum electrode with lead electrode in the process of reproduction of full-relief figures in galvanoplastics. This method was employed for the fabrication of the sculptures decorating the front of the Opera house in Paris. In 1866, Gaston Plante explored the electrolytic production of ozone. He came to the conclusion that production of ozone should be performed using lead electrodes instead of platinum. 

Bunsen s electrolytic researches included the electrodeposition of chromium from chromous chloride solution, in which the great influence of the current density was observed with amalgamated platinum wire cathodes even metallic barium and calcium were deposited from hot concentrated solutions of the chlorides. He described (after Deville) the electrolytic production of aluminium from fused NaAlCl4. Bunsen and Matthiessen described the preparation of lithium by electrolysis of the fused chloride. 

The electrolytic processes for commercial production of hydrogen peroxide are based on (/) the oxidation of sulfuric acid or sulfates to peroxydisulfuric acid [13445-49-3] (peroxydisulfates) with the formation of hydrogen and (2) the double hydrolysis of the peroxydisulfuric acid (peroxydisulfates) to Caro s acid and then hydrogen peroxide. To avoid electrolysis of water, smooth platinum electrodes are used because of the high oxygen overvoltage. The overall reaction is... 

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

Reduction of vanillin by means of platinum black in the presence of ferric chloride gives vanillin alcohol in excellent yields. In 1875, Tiemann reported the reduction of vanillin to vanillin alcohol by using sodium amalgam in water. The yields were poor, however, and there were a number of by-products. High yields of vanillin alcohol have been obtained by electrolytic reduction. 

By-Product Recovery. The anode slime contains gold, silver, platinum, palladium, selenium, and teUurium. The sulfur, selenium, and teUurium in the slimes combine with copper and sUver to give precipitates (30). Some arsenic, antimony, and bismuth can also enter the slime, depending on the concentrations in the electrolyte. Other elements that may precipitate in the electrolytic ceUs are lead and tin, which form lead sulfate and Sn(0H)2S04. 

Potassium cyanide is primarily used for fine silver plating but is also used for dyes and specialty products (see Electroplating). Electrolytic refining of platinum is carried out in fused potassium cyanide baths, in which a separation from silver is effected. Potassium cyanide is also a component of the electrolyte for the analytical separation of gold, silver, and copper from platinum. It is used with sodium cyanide for nitriding steel and also in mixtures for metal coloring by chemical or electrolytic processes. 

Suitable starting materials for the Kolbe electrolytic synthesis are aliphatic carboxylic acids that are not branched in a-position. With aryl carboxylic acids the reaction is not successful. Many functional groups are tolerated. The generation of the desired radical species is favored by a high concentration of the carboxylate salt as well as a high current density. Product distribution is further dependend on the anodic material, platinum is often used, as well as the solvent, the temperature and the pH of the solution." ... 

Ruthenium, iridium and osmium The use of a fused cyanide electrolyte is the most effective means for the production of sound relatively thick coatings of ruthenium and iridium, but this type of process is unattractive and inconvenient for general purposes and does not therefore appear to have developed yet to a significant extent for industrial application. This is unfortunate, since these metals are the most refractory of the platinum group and in principle their properties might best be utilised in the form of coatings. However, several interesting improvements have been made in the development of aqueous electrolytes. 

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