Iridium concentrations

Dichloro-tetrammino-iridium Chloride, [Ir(NH3)4Cl2]Cl.H20, is produced when dinitrito-tetrammino-iridium chloride is heated with ammonium chloride and concentrated hydrochloric acid for several hours. A yellow liquid is obtained, from which on evaporation a yellow crystalline precipitate separates containing the chloro-compound mixed with ammonium chloride. This is collected, dissolved in warm water, filtered, and allowed to crystallise on the addition of hydrochloric acid. It separates in yellow needles and prisms which are impure, but are purified on further reerystallisation from warm water containing acid. It loses water on heating, and finally leaves a residue of iridium. Concentrated hydrochloric acid does not attack the salt. 

Because of the extent to which the gold and iridium concentrations seem related to ore sources, objects were grouped according to these con-... 

Figure 3. Histogram of iridium concentrations relative to silver in all silver objects analyzed. The distribution of iridium concentrations in shells of plates with external rim lines only are represented by dark columns.

Although such detailed information has been obtained for a few transition metals and heavy metals, initial measurements of the oceanic concentrations and distributions need to be made for elements such as Ti, Ga, Ru, Pd, Ir, Pt, Au, Re Te, Zr, and FIf in many ocean basins before simple vertical and horizontal profiles can be constructed. Using newly developed analytical techniques, researchers have begun to obtain initial data on these metals. For example, the first concentration data on iridium in sea water (North Pacific) have been reported. Iridium concentrations ranged from 0.5 x 10 moll in North Pacific surface waters and increased with depth to a maximum of 0.8 x 10 molD near the bottom. 

Analysis of rock specimens by NAA is helpftil to geochemists in research on the processes involved in the formation of different rocks through the analysis of the rare earth elements and other trace elements. For example, the discovery of anomalously high iridium concentrations in 65-miIlion-year old limestone deposits from Italy and Demnark have been accomphshed by NAA. The NAA findings support the theory that extinction of the dinosaurs occurred soon after the impact of a large meteorite with the earth. The study of low concentration of U in stony and meteorites and trace elements in Apollo-II lunar rocks (Ganapathy et al. 1970) have been imdertaken through NAA. Detection... 

Nitric acid reacts with all metals except gold, iridium, platinum, rhodium, tantalum, titanium, and certain alloys. It reacts violentiy with sodium and potassium to produce nitrogen. Most metals are converted iato nitrates arsenic, antimony, and tin form oxides. Chrome, iron, and aluminum readily dissolve ia dilute nitric acid but with concentrated acid form a metal oxide layer that passivates the metal, ie, prevents further reaction. 

The PGM concentrate is attacked with aqua regia to dissolve gold, platinum, and palladium. The more insoluble metals, iridium, rhodium, mthenium, and osmium remain as a residue. Gold is recovered from the aqua regia solution either by reduction to the metallic form with ferrous salts or by solvent-extraction methods. The solution is then treated with ammonium chloride to produce a precipitate of ammonium hexachloroplatinate(IV),... 

Kinetic mles of oxidation of MDASA and TPASA by periodate ions in the weak-acidic medium at the presence of mthenium (VI), iridium (IV), rhodium (III) and their mixtures are investigated by spectrophotometric method. The influence of high temperature treatment with mineral acids of catalysts, concentration of reactants, interfering ions, temperature and ionic strength of solutions on the rate of reactions was investigated. Optimal conditions of indicator reactions, rate constants and energy of activation for arylamine oxidation reactions at the presence of individual catalysts are determined. 

Significant distinction in rate constants of MDASA and TPASA oxidation reactions by periodate ions at the presence of individual catalysts allow to use them for differential determination of platinum metals in complex mixtures. The range of concentration rations iridium (IV) rhodium (III) is determined where sinergetic effect of concentration of one catalyst on the rate of oxidation MDASA and TPASA by periodate ions at the presence of another is not observed. Optimal conditions of iridium (IV) and rhodium (III) determination are established at theirs simultaneous presence. Indicative oxidation reactions of MDASA and TPASA are applied to differential determination of iridium (IV) and rhodium (III) in artificial mixtures and a complex industrial sample by the method of the proportional equations. 

Iridium (IV) chloride hydrate (hexachloroiridic acid) [16941-92-7 (6H2O) 207399-11-9 (XH2O)] M 334.O+H2O. If it contains nitrogen then repeatedly concentrate a cone HCl solution until free from nitrogen, and dry free from HCl in a vac over CaO until crystals are formed. The solid is very hygroscopic. [J Am Chem Soc 53 884 1931 Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Vol II 1592 7965.]... 

As already noted (p. 1073), the platinum metals are all isolated from concentrates obtained as anode slimes or converter matte. In the classical process, after ruthenium and osmium have been removed, excess oxidants are removed by boiling, iridium is precipitated as (NH4)2lrCl6 and rhodium as [Rh(NH3)5Cl]Cl2. In alternative solvent extraction processes (p. 1147) [IrClg] " is extracted in organic amines leaving rhodium in the aqueous phase to be precipitated, again, as [Rh(NH3)5Cl]Cl2. In all cases ignition in H2... 

To a solution of 1.0 g (0.003 mole) of iridium tetrachloride in 0.5 ml of concentrated hydrochloric acid is added 15 ml of trimethylphosphite. This solution is added to a solution of 7.7 g (0.05 mole) of 4-/-butylcyclohexanone in 160 ml of isopropanol in a 500-ml flask equipped with a reflux condenser. The solution is refluxed for 48 hours, then cooled, and the isopropanol is removed on a rotary evaporator. The residue is diluted with 65 ml of water and extracted four times with 40-ml portions of ether. The extracts are dried with anhydrous magnesium sulfate, filtered, and the ether is removed on the rotary evaporator. The white solid residue is recrystallized from 60 % aqueous ethanol affording cis alcohol of greater than 99% purity, mp 82-83.5°. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

As well as increasing the reaction rate and catalyst stability, at all-important low water concentrations and low CO partial pressures, the iridium system also produces lower levels of by-products. These improvements combine to give the CATIVA process the following advantages ... 

Because of- the similarity in the backscattering properties of platinum and iridium, we were not able to distinguish between neighboring platinum and iridium atoms in the analysis of the EXAFS associated with either component of platinum-iridium alloys or clusters. In this respect, the situation is very different from that for systems like ruthenium-copper, osmium-copper, or rhodium-copper. Therefore, we concentrated on the determination of interatomic distances. To obtain accurate values of interatomic distances, it is necessary to have precise information on phase shifts. For the platinum-iridium system, there is no problem in this regard, since the phase shifts of platinum and iridium are not very different. Hence the uncertainty in the phase shift of a platinum-iridium atom pair is very small. 

From results on interatomic distances derived from analysis of EXAFS data, one can draw some conclusions about the structure of platinum-iridium clusters (13,17). If the clusters were truly homogeneous, the interatomic distance characteristic of the platinum EXAFS should be identical to that characteristic of the iridium EXAFS. When we analyze EXAFS data on the clusters, however, we do not find this simple result. We find in general that the distances are not equal. The data indicate that the clusters are not homogeneous in other words,the environments about the platinum and iridium are different. We conclude that the platinum concentrates at the surface or boundary of the clusters. In the case of very highly dispersed platinum-iridium clusters on alumina, the clusters may well have "raft-like" two dimensional structures, with platinum... 

There appears to be concentration of rhodium in the surface of the iridium-rhodium clusters, on the basis that the total number of nearest neighbor atoms about rhodium atoms was found to be smaller than the nunber about iridium atoms in both catalysts investigated. This conclusion agrees with that of other workers (35) based on different types of measurements. The results on the average compositions of the first coordination shells of atoms about iridium and rhodium atoms in either catalyst Indicate that rhodium atoms are also incorporated extensively in the interiors of the clusters. In this respect the iridium-rhodium system differs markedly from a system such as ruthenium-copper (8), in which the copper appears to be present exclusively at the surface. 

The EXAFS results suggested that the iridium-rhodium clusters dispersed on alumina differed in size and/or shape from those dispersed on silica, based on the result that the total coordination nunbers of the iridium and rhodium atoms in the clusters were very different (7 and 5 in the alumina supported clusters vs. 11 and 10 in the silica supported clusters). These coordination numbers suggested that the clusters dispersed on alumina were smaller or that they were present in the form of thin rafts or patches on the support. The possibility of a "raft-like" structure in the case of the alumina supported clusters suggests an interaction between the metal clusters and the support which is much more pronounced for alumina than for silica. If the clusters on the alumina were present as rafts with a thickness of one atomic layer, one could have a situation in which the rhodium concentration at the perimeter of the raft was greater... 

The iridium complex 35 has been also used as catalyst for the transfer hydrogenation of substituted nitroarenes [34]. Good to very good conversions were observed (2.5 mol%, in refluxing isopropanol, 12 h). A mixture of two products was obtained, the relative ratio of which depends on the concentration of added base (KOH) and catalyst. (Scheme 2.5)... 

Figure 5.33. Impurity and Th concentrations on intergranular and transgranular areas of an iridium alloy containing 6000 ppm Th and (a) 5000 ppm Fe, (b) 4000 ppm Al, (c) 3000 ppm Ni, (d) 5000 ppm Cr and (e) no added impurities. (After Heatherly and George 2001).

The magnitudes of the rate constants for the iridium catalyst were close to those obtained for rhodium 3 and osmium 5 based catalyst systems at similar conditions. However, the unusual dependence on catalyst concentration affects its general utility in comparison to other homogeneous catalysts for the hydrogenation of NBR. 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

Actually, a similar approach was used in studying the oxidative addition of methane to an iridium complex. Hydrocarbon solvents would have reacted faster than methane with the photochemically produced unsaturated iridium species, therefore J.K. Hoyano et al chose perfluorinated hexane as being an inert solvent. The elevated pressure was necessary in order to increase the concentration of the methane in the solution sufficiently to shift equilibrium (15) to the right /20/. 

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