Iridium determination

Ionization chamber pulses, 51, 59, 60 Ionization chambers, 49-52, 93 Ion pairs, 48-50 Ion tubes, characteristics, 3, 4 Ion yield in counter tubfes, 50, 51 Iridium, determination by x-ray emission spectrography, 328 Iron, determination by x-ray emission spectrography, 222, 328 in cements, 260, 261 in domestic ores, 200, 202, 203 in hi h-temperature alloys, 179-183 in solution, 185, 255... 

Figure 8.1 Comparison of sample pretreatment steps required for iridium determination in photographic emulsions via ICP-IDMS and TI-IDMS [6],...

In analogy with the investigations for 400 keV the values for 100, 200 and 300 keV, Iridium-192 and Cobalt-60 were determined (Table I, [1,3]). For Co-60 the equivalent value for film could not be reached with lead foils. Sandwich sPuctures of steel foils and lead foils were necessary. For instance, with 0,5 mm steel and 1 mm lead one could only attain about 80 % of the film value referred to 1/(1+k). The necessary equivalent value is estimated to be 0,5 mm steel and 1,5-2,0 mm lead, but we are still short of determining the precise value. 

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. 

Electrochemical reduction of iridium solutions in the presence azodye (acid chrome dark blue [ACDB]) on slowly dropping mercury electrode is accompanied by occurrence of additional peaks on background acetic-ammonium buffer solutions except for waves of reduction azodye. Potentials of these peaks are displaced to cathode region of the potential compared to the respective peaks of reduction of the azodye. The nature of reduction current in iridium solutions in the presence ACDB is diffusive with considerable adsorptive limitations. The method of voltamiuetric determination of iridium with ACDB has been developed (C 1-2 x 10 mol/L). 

For comparison, Battles et al. (15) determined the partial heats of sublimation of Pu02(g) and Pu0(g) above PuOi.33 over the temperature range 1937 to 2342 K by means of mass spectrometric measurements with Iridium effusion cells. The absence of Iridium oxides or Iridium species In the vapor phase Indicated that Iridium was nonreducing toward plutonia. The partial heats of sublimation calculated from the slopes of the temperature dependency data yielded values of 127.1 1.2 and 138.8 1.6 kcal/mol for Pu0(g) and Pu02(g) ... 

The five-coordinate iridium complexes may be protonated by glacial acetic acid, yielding [Ir(PPh3)2(CNR)3H] + the structure of this complex is determined by PMR measurements to be (XXIX). However, in the analogous HCl reaction [Ir(PPh3)2(CNR)2Cl2] is obtained. The reaction of [Ir(PPh3)2(CNR)3] with methanol also proved quite out of the ordinary. 

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. 

The iridium phosphine complex [IrC PEt,),] 39b can also activate O-H bonds of carboxylic acids. The stoichiometric reaction with a,(o-alkynoic acids RC=C(CH2)2 CO2H (R = Me, Ph) gave cis-hydrido(carboxylato)iridium(III) complexes 92 (Eq. 6.26), and the molecular structure of 92a was determined crystallographically [59]. 

The ionic iridium(III) carbene complex (47) is prepared from the reaction of IrHCl(03SCF3)-(CO)(PPh3)2] with [RC=NMe](03SCF3).61 Addition of Na(barf) (barf = B(3,5-C6H3 (CF3)2)4) to [Ircp (PMe3)(CH3)(0S02CF3)] in CH2C12 yields the structurally determined species... 

The number of protons extracted from the film during coloration depends on the width of the potential step under consideration. As can be seen in the formulation of Fig. 26 an additional valence state change occurs at 1.25 Vsce giving rise to another proton extraction. The second proton exchange may explain the observation by Michell et al. [91] who determined a transfer of two electrons (protons) during coloration. Equation (5) is well supported by XPS measurements of the Ir4/ and Ols levels of thick anodic iridium oxide films emersed at different electrode potentials in the bleached and coloured state. Deconyolution of the Ols level of an AIROF into the contribution of oxide (O2-, 529.6 eV) hydroxide, (OH, 531.2 eV) and probably water (533.1 eV) indicates that oxide species are formed during anodization (coloration) on the expense of hydroxide species. The bleached film appears to be pure hydroxide (Fig. 27). 

These spectra show even fewer features than those of the palladium catalysts. Absorption takes place almost exclusively in the region 2000-2100 cm-1. There are some weak bands below 2000 cm-1, but our experimental method did not allow us to determine their frequencies with reasonable accuracy. It is clear that also with the iridium catalysts the particle size has an effect on the spectra. The spectrum of Ir-8 shows only one intense band at 2048 cm-1, whereas the other two have additional bands at higher frequencies. There is also a marked dependence of the intensity of the 2048 cm-1 band on the CO pressure, especially in the case of Ir-37 and Ir-100. We shall not try to interpret the CO spectra of the iridium samples, as we consider the data available insufficient for the purpose. 

Whereas determination of chemisorption isotherms, e.g., of hydrogen on metals, is a means for calculating the size of the metallic surface area, our results clearly demonstrate that IR studies on the adsorption of nitrogen and carbon monoxide can give valuable information about the structure of the metal surface. The adsorption of nitrogen enables us to determine the number of B5 sites per unit of metal surface area, not only on nickel, but also on palladium, platinum, and iridium. Once the number of B5 sites is known, it is possible to look for other phenomena that require the presence of these sites. One has already been found, viz, the dissociative chemisorption of carbon dioxide on nickel. 

The surface areas of the iridium and palladium catalysts were determined by chemisorption of hydrogen and carbon monoxide, respectively, the monolayer volume being determined from an adsorption isotherm taken at 20°C. 

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