Rhodium plating

Sodium nitrite has been synthesized by a number of chemical reactions involving the reduction of sodium nitrate [7631-99-4] NaNO. These include exposure to heat, light, and ionizing radiation (2), addition of lead metal to fused sodium nitrate at 400—450°C (2), reaction of the nitrate in the presence of sodium ferrate and nitric oxide at - 400° C (2), contacting molten sodium nitrate with hydrogen (7), and electrolytic reduction of sodium nitrate in a cell having a cation-exchange membrane, rhodium-plated titanium anode, and lead cathode (8). 

For ruthenium, electrolytes based on ruthenium sulphamate or nitrosyl-sulphamate have been described, but the most useful solutions currently available are based on the anionic complex (H2 0 Cl4 Ru N Ru-Cl4-OH2) . The latter solutions operate with relatively high cathode efficiency to furnish bright deposits up to a thickness of about 0-005 0 mm, which are similar in physical characteristics to electrodeposited rhodium and have shown promise in applications for which the latter more costly metal is commonly employed. Particularly interesting is the potential application of ruthenium as an alternative to gold or rhodium plating on the contact members of sealed-reed relay switches. 

Rhodium compounds, 19 644-648 synthesis of, 19 646 uses for, 19 646-648 Rhodium oxide, 10 42 Rhodium plating, 9 822 19 648 Rhodium-platinum alloys, 19 602 Rhodochrosite, 15 540 Rhodochrosite ore, 15 589 Rhodococcus, as a host system for gene expression, 12 478 Rhodonite, 15 540 color, 7 331 Rhodopsin, 9 512 Rhoeadine, 2 90 Rhoedales... 

Only three of the metals, rhodium, palladium and platinum, need be considered. Of these only rhodium plating is of significant commercial importance, but the relatively low cost of palladium has made it attractive for contacts and printed circuits. Electrodeposited platinum is harder than the annealed bulk metal and finds applications in jewellery, the plating of scientific instruments, standard weights and parts of electrical apparatus. 

Rhodium-plated reflectors, on account of their resistance to heat and oxidation, are particularly suited for searchlight and cinema projectors. Rhodium black has been used for producing a black colour in the decoration of pottery. 

The reaction between cobalt atoms and diazomethane proceeds spontaneously to yield methane and MeCoH when these reactants and dihydrogen are co-condensed with argon onto a rhodium-plated copper surface at 12 K. Wavelength-dependent photolysis of this reaction gave evidence for a cobalt-methane complex formation [15] ... 

A piece of metal that measures 1.3 cm by 0.83 cm will have a coating of rhodium plated on its surface to serve as a mirror. The rhodium thickness will be 0.00030 mm, and the electrolyte contains Rh + ions. If the operating current of the electrolysis is... 

Deposits from the sulfate or phosphate are hard (900 to 1000 Knoop), highly reflective, extremely corrosion-resistant, and highly conductive (resistivity is 4.51 pi/cm). Rhodium plate is used where a low-resistance, long-wear, oxide-free contact is required. In addition, rhodium as a deposit on nickel for edge connectors has been replaced by gold.This is due to difficulty in bath control problems with organic and metallic contaminants, as weU as cost. Table 29.12 shows details of rhodium plating. 

Silver alloy electrodes made in this manner are usually rhodium-plated (tips) and then platinized. They serve well in registering fast transients and exhibit a noise figure close to the theoretical limit for their equivalent resistance. 

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