6. Explain electrodeposition technoly of rhodium

High hardness and wear resistance rhodium coating combined with the presence of significant internal stresses that cause the appearance of a grid of cracks in the galvanic deposition of rhodium, especially in the layers with large thickness. Unlike silver rhodium coating does not fade and oxidize during prolonged operation in air and in the presence of aggressive environments, allowing you to keep, the transitional electric resistance of the contacts unchanged. Rhodium coatings have a beautiful appearance, and the reflectance of light waves occupy the second place after the silver (75— 80%), keeping it constant for a long time. Therefore, the rhodium coating is used to protect silver mirrors and reflectors from tarnishing. Of electrolytes for the deposition of rhodium the largest application received sulfate, phosphate, and possible deposition of rhodium from aminocore-tion, barterisation, sulfamic and chloride aqueous electrolytes. For the preparation of the electrolyte be a solution of sulfuric or forstroy acid with a concentration of 50-60 g/l, as provided with the-I composition of the electrolyte, dipped it in rhodium electrodes and consist of an alternating current of industrial frequency, i.e. 50 Hz. Current density for sulphuric acid electrolyte is maintained in the range 15-30 A/dm2, and phosphoric acid — 12 to 20 A/dm2. The current yield is very small and is usually 0,15—0,30%, but the selection of current density, temperature and frequency of the current output current can be increased to 1-3%. This same method can be applied for correction of these electrolyte salts of rhodium. L. I. Kadaner recommends to prepare sulfuric acid solution: in a solution of sulfuric acid with a concentration of 50 g/l is injected 30% solution of hydrogen peroxide in the amount of 1-1,5 g/l. This solution was filled in a U-shaped glass vessel with soldered ¦in the wall. platinum wires. Plate rhodium metal pre-activated in a solution of hydrochloric acid diluted 1:1, at 15-25° C, treating them with alternating current with a frequency of 50 Hz at a current density of 50 A/dm2 for 5-10 min. Then the plate is placed in a U-shaped vessel, are connected as electrodes and lead dissolution at 200C alternating current to the desired concentration of rhodium. The resulting electrolyte is boiled for 3-4 h to remove traces of hydrogen peroxide. Galvanic deposition of rhodium is conducted at 15-25° C and a current density of 1-5 A/dm2 with insoluble anodes of platinum or rhodium and with agitation cathode rod 120-180 times per minute.

7. Explain electrodeposition technoly of osmium.

Concentrated nitric acid dissolves with the formation of osmium acid. So, one of the electrolytes for the deposition of osmium has the following composition (g/l) and mode: Osmium (osmium acid) .......1,8 Trilon B .................10,0 Vinocity potassium-sodium ... 60 Temperature, °C................50-60 The current density, A/dm2...........26 The deposition is produced on the copper with insoluble anodes of platinum. The second electrolyte proposed by L. I. Caminera. For its preparation a metal osmium electrolytically dissolve in hydrochloric acid with the use of alternating current of industrial frequency 50 Hz. After receiving a specified concentration of salt solution was boiled for 10-20 min to obtain the cherry-red color of the solution. For the deposition of osmium adopted the following composition (g/l): Hydrochloric acid salt of osmium in terms of metal is 0.5—10

Hydrochloric acid (density 1,19 g/cm3) . . . 50-200 Ammonium chloride............. 40-200 Ammonia 25%............

pH 1-1,5 The operating temperature can range from 20 to 100° C, and cathode current density from 0.2 to 20 A/dm2.

8. Explain electrochemical deposition methods ruthenium For the galvanic deposition of ruthenium has developed a number of electrolytes, including chloride, sulfamine-tions, nitrosochlorides etc. The most simple method of preparing of chloride electrolytes are developed by L. I. Danara. For the preparation of the electrolyte in a glass tray and poured the calculated amount of powder metal ruthenium and fill it with hydrochloric acid with a concentration of HCl = 35-40 g/l in an amount that corresponds to the given amount of electrolyte. To speed up the process of dissolving a powder of ruthenium is separated into two parts by a glass bulkhead on the bottom of the bath and injected into each of the compartments of the bath on the platinum electrode, immersing them into a powder and securely insulating parts of the electrodes in contact with the electrolyte. The electrodes are connected to a source of alternating current with industrial frequency 50 Hz and electrolytically dissolve ruthenium at a temperature of 25-30° C and a current density of 50 A/dm2. This method provides a high rate of dissolution of ruthenium (up to 8 g/l in terms of metal for 24 h). minimum metal loss by dissolution. It is suitable to dissolve the ruthenium in hydrochloric, sulfuric, sulfamic and other acids. For chloride electrolyte we recommend the following composition (g/l) and mode: Ruthenium chloride in terms of metal . . . 2-3,5 Hydrochloric acid............... 35-40 Temperature, °C...............15-25

9. Explain electrochemical deposition methods indium The coating is indium or its alloys with lead, zinc, and copper used for the production of metal mirrors, and. also as antifriction coating of babbit sliding bearings in internal combustion engines, resistant against the action of the products of oxidation of lubricating oils. Deposition of indium can be produced from chloride, cyanide, sulfate, borgoricco-hydrogen, silicofluoride, phenolsulfonic-o, sulfaminokislotu and other electrolytes. A. A. Kazarian and A. M. loshkariov is recommended to obtain dense, fine-grained and uniform coatings of the following composition (g/l) and mode of operation of the electrolyte: Indium chloride............ 20-40 Sodium chloride.............30-60 Gelatin.................. 2 Thiourea................ 0,5 Temperature, °C ..............15-25 The anode is indium. After deposition of a layer of indium of a given thickness, the working temperature was raised to 157° C, the current is turned off. The electrolyte is prepared, heating the crystalline calcium chloride to dissolve in its water of crystallization, and then administered indium chloride and hydrochloric acid until complete dissolution of the precipitate. Fused coating for a long period of time retain the ability to solder.

Composition (g/l) and mode of operation of the sulfuric acid electrolyte is given below: indium Sulfate ..... 50-70

Sodium sulfate .....10-15 Temperature, °C....15-25

pH ....................2,0—2,7

the current density…….1-2

the current yield, % ...........60-80 Anodes — graphite or indium metal.