Rhodium, deposition

In view of the high cost, when tarnish resistance of the surface is the only requirement it is customary to use the thinnest possible coatings of rhodium (0-000 25-0-000 5 mm). Since rhodium deposits in this thickness range, like thin electrodeposits of other metals, show significant porosity, readily corrodible metals, e.g. steel, zinc-base alloys, etc. must be provided with an undercoating deposit, usually of silver or nickel, which is sufficiently thick to provide a fairly high level of protection to the basis metal even before the final precious metal deposit is applied, and, in this way, to prevent accelerated electrochemical corrosion at pores in the rhodium deposit. 

Silver is often preferred as an undercoat for rhodium by reason of its high electrical conductivity. A further advantage of silver in the case of the thicker rhodium deposits (0-0025 mm) applied to electrical contacts for wear resistance is that the use of a relatively soft undercoat permits some stress relief of the rhodium deposit by plastic deformation of the under-layer, and hence reduces the tendency to cracking , with a corresponding improvement in protective value. Nickel, on the other hand, may be employed to provide a measure of mechanical support, and hence enhanced wear resistance, for a thin rhodium deposit. A nickel undercoating is so used on copper printed connectors, where the thickness of rhodium that may be applied from conventional electrolytes is limited by the tendency of the plating solution to attack the copper/laminate adhesive, and by the lifting effect of internal stress in the rhodium deposit. 

We have undertaken a series of experiments Involving thin film models of such powdered transition metal catalysts (13,14). In this paper we present a brief review of the results we have obtained to date Involving platinum and rhodium deposited on thin films of tltanla, the latter prepared by oxidation of a tltanliua single crystal. These systems are prepared and characterized under well-controlled conditions. We have used thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and static secondary Ion mass spectrometry (SSIMS). Our results Illustrate the power of SSIMS In understanding the processes that take place during thermal treatment of these thin films. Thermal desorption spectroscopy Is used to characterize the adsorption and desorption of small molecules, In particular, carbon monoxide. AES confirms the SSIMS results and was used to verify the surface cleanliness of the films as they were prepared. 

The above studies concerning rhodium deposition provide evidences of the crucial importance of surface chemistry on the final quality of the deposit. Purity can be controlled by addition of reactive components that assist the expected loss of ligands, which otherwise would leave contaminants such as halides, carbides or oxides on the deposits. 

Einaga H., Futamura S., Ibusuki T. (2001) Improvement of Catalyst Durability in Benzene Photooxidation by Rhodium Deposition on Ti02, Chem. Lett. 582-583. 

How a catalytic converter works A typical catalytic converter consists of particles of platinum and rhodium deposited on a ceramic structure that is like a honeycomb. The platimun and rhodium catalyze reactions that remove pollutants such as nitrogen monoxide (NO), carhon monoxide (CO), and unhurned hydrocarbons. When nitrogen monoxide binds to the rhodimn surface, it breaks down to oxygen and nitrogen. The bound oxygen reacts with carbon monoxide, which has also become bound to the rhodimn surface. The reaction produces carbon dioxide. The oxidation of unburned hydrocarbons produces carbon dioxide and water. 

In order to evaluate the interaction between platinum and rhodium deposited on the alumina-lanthanum oxide, the different catalysts were characterized by temperature programmed reduction and measure of the activity for the reaction of propane-propene oxidation. 

The comparison of metallic monohths directly fabricated by nucronaachining of rhodium and of rhodium deposited on micromachined Fecralloy monohths exhibited superior WGS activity and thus higher hydrogen yield for the deposited rhodium system [12]. This could be explained by the higher surface area of rhodium on the additional alumina support on Fecralloy prepared by annealing at 1000 °C. 

Brylev O, Sarrazin M, Belanger D, Roue L (2006) Rhodium deposits on pyrolytic graphite substrate physico-chemical properties and electrocatalytic activity towards nitrate reduction in neutral medium. Appl Catal Environ 64 243-253... 

Faraday s laws. Rhodium was plated from an aqueous solution containing Rh + for 2.00 hours with a current of 0.0650 A. The rhodium deposit on the cathode weighed 0.1664 g. What is the charge of the rhodium ion ... 

Heterogeneous hydrogenation catalysts typically involve finely divided platinum, palladium, nickel, or rhodium deposited on the surface of powdered carbon (charcoal). Hydrogen gas introduced into the atmosphere of the reaction vessel adsorbs to the metal by a chemical reaction where unpaired electrons on the surface of the metal pair with the electrons of hydrogen (Fig. 7.10a) and bind the hydrogen to the surface. The collision of an alkene with the surface bearing adsorbed hydrogen causes adsorption of the alkene as... 

Union Carbide Corporation was working on a low-pressure hydroformylation process as early as 1967, and used a rhodium carbonyl catalyst modified with a triphenyl phosphine ligand. " The ligand dramatically improved the normal/iso-aldehyde ratio of the product when compared to the free metal carbonyl. Reduced operating temperatures and pressures, low by-product formation, and the elimination of metallic rhodium deposition were also achieved. By 1975, a plant was operating using this catalyst, and the process was being licensed for the hydroformylation of propylene. 

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