Preparation of rare metallic actinides (248Cm,249Bk,249Cf) and investigation of their crystal structure

²⁴⁸Cm and²⁴⁹Bk metals were prepared by thermal reduction of their oxides with thorium and metallic²⁴⁹Cf with metallic lanthanum. These rare actinide samples of 1.0 mg in mass were thin layers on a flat substrate and were investigated by X-ray technique. Dhcp lattice parameters of -Cm, -Bk and -Cf as main phases in X-ray diagrams are presented. The effect of impurities on the -Cm lattice parameters is shown. Fcc lattices for the high temperature form of Cm metal (-Cm) with a=0.4933 nm, and of Cm and Bk monoxides (a=0.502–0.504 nm and a=0.5002 nm, respectively) have been observed. Thermal expansion coefficients for -Cm and -Bk at 80–300 K were calculated. Identification problems of fcc lattices and oxidation features of metals prepared are discussed.     

One-step synthesis of carbon-supported Pd–Pt alloy electrocatalysts for methanol tolerant oxygen reduction

A facile, one-step reduction route was developed to synthesize Pd-rich carbon-supported Pd–Pt alloy electrocatalysts of different Pd/Pt atomic ratios. As-prepared Pd–Pt/C catalysts exhibit a single phase fcc structure and an expansion lattice parameter. Comparison of the oxygen reduction reaction (ORR) on the Pd–Pt/C alloy catalysts indicates that the Pd₃Pt₁/C bimetallic catalyst exhibits the highest ORR activity among all the Pd–Pt alloy catalysts and shows a comparative ORR activity with the commercial Pt/C catalyst. Moreover, all the Pd–Pt alloy catalysts exhibited much higher methanol tolerance during the ORR than the commercial Pt/C catalyst. High methanol tolerance of the Pd–Pt alloy catalysts could be attributed to the weak adsorption of methanol induced by the composition effect, to the presence of Pd atoms and to the formation of Pd-based alloys.     

Simultaneous electrodeposition of actinides

A new system for simultaneous electrodeposition of U, Np, Pu, Am and Cm has been developed. The system consists of (NH₄)₂C₂O₄–H₂SO₄–HCl. The effects on recovery of pH, current density, interfering ions and the amount of added HCl have been studied. The optimum condition for simultaneous electrodeposition of actinides has been recommended. Under the recommended condition recoveries of U, Np, Pu, Am and Cm have been obtained by using²³²U,²³⁷Np,²⁴¹Am,²⁴²Pu and²⁴⁴Cm. The counting sources prepared are uniform, adherent and suitable for -spectrometry.     

Chromatographische Trennung von Curium-242 und Americium-241 und die spektroskopische Überprüfung ihrer α-Aktivität

Zusammenfassung Es wird eine Trennung von²⁴²Cm und²⁴¹Am am Kationenaustauscher Dowex 50 W×8 mittels -Hydroxyisobutyratlösungen beschrieben, wobei Sm und Pm zur Markierung der Elutionspositionen von Cm und Am zugesetzt werden. Die Elemente werden in der Folge Sm–Cm–Pm–Am eluiert.Die Messung der -Aktivitäten mit Halbleiterdetektoren wurde an Tropf- und Molekularplatingproben vorgenommen.Aus etwa 2·10^–6 g²⁴¹Am, welches 400 Stdn. lang bestrahlt wurde, konnten etwa 4·10^–9 g²⁴²Cm, entsprechend 99,5% der beobachteten Gesamtaktivität, gewonnen werden.

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The separation of²⁴²Cm and²⁴¹Am with -hydroxyisobutyric solutions on the ion exchange resin Dowex 50 W×8 is described. Sm and Pm are used as indicators in order to mark the elution positions of Cm and Am. The elements are eluted in the order Sm–Cm–Pm–Am.Drop- and molecular plating samples were prepared for measuring the -activities with semiconductor detectors.About 2·10^–6 g²⁴¹Am yielded on activation for a period of 400 hours 4·10^–9 g²⁴²Cm corresponding to 99,5% of the observed total activity.

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Mit 2 Abbildungen     

Studies on the stereochemistry of diphenyl diketone monothio-semicarbazone and its transition metal complexes

Summary The stereochemistry and complexation behaviour of diphenyl diketone monothiosemicarbazone (DKTS) with Cu^II, Co^II, Ni^II, Cd^II, Zn^II, Pd^II, Pt^II, Ru^III, Rh^III and Ir^III have been investigated by means of chemical, magnetic and spectral (i.r., Raman, ¹H- and ¹³C-n.m.r. and electronic) studies. The ligand forms complexes of the M(DKTS)₂ type with Ni^II, Cu^II and Co^II having a distorted octahedral geometry. The absence of a v(M—X) band in the i.r. spectra, coupled with their 1:1 electrolytic conductances, suggests that Ru^III, Rh^III and Ir^III form octahedral complexes of the [M(DKTS)₂]Cl type. A four-coordinate structure involving bridging halides is proposed for the Zn^II, Cd^II, Pd^II and Pt^II complexes, which have relatively low v(M—X) vibration modes.     

Selective Oxidation of Glucose to Gluconic Acid over Bimetallic Pd–Me Catalysts (Me = Bi,Tl, Sn,Co)

Catalytic properties of bimetallic Pd–Bi, Pd–Tl, Pd–Sn, and Pd–Co catalysts supported on C (from plum stones) and SiO₂ were studied in the reaction of glucose oxidation to gluconic acid. Catalysts modified with Bi show the best selectivity and activity. The results obtained from research on 5% Pd–5% Bi/C and 5% Pd–5% Bi/SiO₂ catalytic systems were compared with the results for a commercial catalyst containing 1% Pt–4% Pd–5% Bi supported on active carbon (Degussa). For both Pd–Bi/support catalysts and 1% Pt–4% Pd–5% Bi/C, similar selectivity in the reaction of glucose oxidation was observed. XRD studies proved the presence of intermetallic compounds BiPd and Bi₂Pd, which probably increase the selectivity of PdBi/SiO₂ catalysts.     

Self-irradiation induced structural changes in the transplutonium pyrochlores An2Zr2O7 (An=Am, Cf)

We have pursued the fundamental chemistry of actinide pyrochlore oxides, An₂Zr₂O₇ (An=Am, Cm, Bk, and Cf), using X-ray diffraction as well as optical spectroscopy. One recent facet of our studies has been to observe the structural changes of these materials under self-irradiation as a function of time. It has been reported that both titanate and silicate materials transform from a crystalline to an amorphous state under irradiation. With the Zr-based actinide pyrochlores studied here, we have observed a phase change from a pyrochlore structure to a fluorite-type structure with the retention of crystallinity. We focus here on the impact of α-radiation (²⁴³Am and ²⁴⁹Cf), rather than that from neutrons (²⁴⁸Cm) or β-radiation (²⁴⁹Bk), on the An₂Zr₂O₇ pyrochlore structures. As a result of this phase change, the local coordination environments of both the actinide and zirconium atoms are altered. We consider a defect/ion deficiency driven mechanism and also address the occurrence of oxidation of the trivalent actinides during the self-irradiation process as being potential mechanisms responsible for the observed phase change.     

Ag–Pt alloy nanoparticles with the compositions in the miscibility gap

Silver platinum binary alloys with compositions between about Ag₂Pt₉₈ and Ag₉₅Pt₅ at < 400 °C have largely not been observed in bulk due to the large immiscibility between these two metals. We present in this paper that Ag–Pt alloy nanostructures can be made in a broad composition range. The formation of Ag–Pt nanostructures is studied by powder X-ray diffraction (PXRD) and energy-dispersive X-ray (EDX). Our results indicate that lattice parameter changes almost linearly with composition in these Ag–Pt nanomaterials. In another word, lattice parameter and composition relationship follows the Vegard's law, which is a strong indication for the formation of metal alloys. Our transmission electron microscopy (TEM) study shows that the silver-rich Ag–Pt alloy nanostructures have spherical shape, while the platinum-rich ones possess wire-like morphology. The stability and crystal phase are investigated by annealing the alloy nanostructures directly or on carbon supports.     

Thermodynamics of Cm(III) in Concentrated Salt Solutions: Carbonate Complexation in NaCl Solution at 25°C

The carbonate complexation reactions of Cm(III) were studied by time-resolved laser fluorescence spectroscopy in 0–6 m NaCl at 25°C. The ionic strength dependence of the stepwise formation constants for the carbonato complexes Cm(CO₃) _n ^3–2n with n = 1, 2, 3, and 4 is described by modeling the activity coefficients of the Cm(III) species with Pitzer's ion-interaction approach. Based on the present results and literature data for Cm(III) and Am (III), the mean carbonate complexation constants at I = 0 are calculated to be: log ₁₀₁ ^o =8.1 ±0.3, log ₁₀₂ ^o =13.0 ± 0.6, log ₁₀₃ ^o =15.2 ± 0.4, and log ₁₀₄ ^o =13.0 ± 0.5. Combining these equilibrium constants at infinite dilution and the evaluated set of Pitzer parameters, a model is obtained, that reliably predicts the thermodynamics of bivalent actinide An(III) carbonate complexation in dilute to concentrated NaCl solution.     

Synthesis and characterization of some octahedral transition metal complexes with phenyl-2-picolylketone thiosemicarbazone

Summary A series of transition metal complexes with phenyl-2-picolylketone-thiosemicarbazone, LH, of the general formula [ML₂]Cl_nmH₂O, (M=Cr³⁺, Mn²⁺, Fe²⁺, Rh³⁺, Ir³⁺ or Ru³⁺; n=0 or 1 and m=1,2 or 3) have been prepared and characterized. Magnetic and spectral (electronic and vibrational) data are commensurate with an octahedral ligand field for all complexes. The variable temperature magnetic moment shows that the iron(II) complex exists in a temperature-dependent high-spinlow-spin equilibrium. The far i.r. spectra show that the strength of the M–S bond follows the order: Mn²⁺ 2+3+3+3+3+. The various ligand field parameters, Dq, B' and are calculated.     

O2-adsorption and (O2?H2)-titration on electron deficient platinum in reforming catalysts

Behavior of supported Pt in O₂ chemisorption and (O₂–H₂) titration has been studied. In Pt/SiO₂, Pt/-Al₂O₃ and Pt/-Al₂O₃ Pt^o catalysts are characterized by the following stoichiometric coefficients of oxygen adsorption (X), hydrogen adsorption (Y) and oxygen-hydrogen titration (Z) X:Y:Z=1:1:1.5. The co-efficients differ for Pt–Cl/-Al₂O₃ reforming catalysts. This is explained by the presence of electron deficient platium (Pt) with a coefficient ratio of X:Y:Z=0.5:2:1.5.     

Rapid anion-exchange separation of berkelium with mineral acid-methyl alcohol mixtures

Adsorption behaviour of Bk/III/ on anion-exchange resin in mineral acid-methyl alcohol mixtures has been investigated. Berkelium was successively separated with a HCl–CH₃OH mixture at elevated temperatures within 5 min from an Al catcher foil collecting the recoil products of the⁴He+²⁴¹Am reaction. The counting source of Bk was immediately prepared for alpha- and X-ray spectrum measurements. Rapid separation of Bk from Ce was also performed by the use of a HNO₃–CH₃OH mixture.     

Preparation of actinide targets for the synthesis of the heaviest elements

The heaviest elements are synthesized in heavy-ion induced hot fusion reactions with various actinide targets. Because the actinide material is often available only in very limited amounts, a deposition method with high yields (~90 %) is needed. We report on the production of ²⁴⁴Pu, ²⁴³Am, ²⁴⁸Cm, ²⁴⁹Bk, and ²⁴⁹Cf targets on thin Ti backings by molecular plating. Different chemical purification steps using ion chromatographic techniques were applied for the purification of ²⁴⁹Cf and ²⁴⁴Pu. The deposition procedure applied for the production of ~0.4–0.8 mg/cm² thick targets is described. The deposition yield was determined either by α-particle or γ-ray spectroscopy. Furthermore, neutron activation analysis has been applied in the case of ²⁴⁴Pu, ²⁴³Am, and ²⁴⁸Cm. Information about the spatial distribution and homogeneity of the target layer was obtained by radiographic imaging.     

The determination of platinum-group elements (PGE) by nickel sulfide fire-assay: Coexisting PGE-phases in the nickel sulfide button

The chemical composition of phases in buttons obtained by nickel sulfide fire-assay during the determination of platinum-group elements (PGE) has been investigated by electron microprobe analysis. Different PGE-containing phases, due to varying flux constituents and species of added PGE, have been detected. By using sodium tetraborate as flux constituent and adding PGE as chlorides, in a cryptocrystalline Ni₃S₂ matrix with low PGE (mainly Rh and Ru) contents, Rh- and Ru-bearing nickel sulfides ((Ni_7.68–7.80Ru_0.84–0.90Rh_0.35–0.43)₉S₈) and Ir alloys ((Ir,Pt,Os)_0.56–0.62(Ru,Rh)_0.25–0.28Ni_0.12–0.19) are found. Treatment with lithium tetraborate leads to a Ni₃S₂ matrix exhibiting slightly higher Rh and Ru contents, with inclusions of nickel-rhodium sulfides (Ni₈Rh₄S₉) and platinumnickel alloys (Pt_0.45Ni_0.36–0.39Ru_0.11–0.14Rh_0.05). Finely dispersed metallic colloidals from an automobile catalyst, with platinum and rhodium as main components, have given only platinum-nickel alloys (Pt_1–xNi_x). Considerable losses of PGE during analytical steps following the fire assay are expected when their contents in sulfidic phases, which are more likely to be dissolved, are high.     

2-Mercapto-benzothiazole as an analytical reagent

Summary The reagent 2-mercapto-benzothiazole quantitatively precipitates palladium at a PH 5.6 to 10.2. The red coloured compound, Pd(C₇H₄NS₂)₂, is diamagnetic and is stable up to a temperature of 388 C. Palladium is separated from alkalis, alkaline earths, Mg, Fe³⁺, Cr, Th, Zr, Ti, UO₂ ²⁺, Be, rare earths, Ce³⁺, Ce⁴⁺, Zn, Mn, Co, Ni, Pb, Bi, Sb³⁺, As³⁺, Sn⁴⁺, Tl+, Cu²⁺, Cd, Ir⁴⁺, Rh³⁺, Ru³⁺, Os⁴⁺, CrO₄ ^2–, MoO₄ ^2–, WO₄ ^2–, VO₃ ^–, PO₄ ^3– and AsO₄ ^3– at apH 6–8 in presence of EDTA and tartaric or citric acid. Besides Pb, Ag and Hg²⁺ are kept in solution with potassium iodide and Au in a limited quantity forms a soluble complex with thiosulphate. The palladium complex is either weighed after drying and determined gravimetrically or dissolved in an excess of cyanide and determined volumetrically by back titrating the latter with silver nitrate.     

Bismuthiol I as an analytical reagent

Summary Bismuth and palladium have been determined volumetrically after precipitation as bismuthiol I complexes. From 0.1 N hydrochloric acid solutions they are separated from Fe²⁺, Al, Cr, Ce³⁺, Zr, Ti, Zn, Th, UO₂ ²⁺, Be, Mg, Mn, Co, Ni, alkalis, alkaline and rare earths.A mixture of tartrate or citrate and EDTA has been found to be useful for the separation of palladium at a p_H 3.5–8.5 from As, Zn, Bi, Sn⁴⁺, Sb, Fe³⁺, Tl⁺, Cu²⁺, Cd, Pb, Ru³⁺, Os⁴⁺, PO₄ ^3–, Ce⁴⁺, Ir⁴⁺, Rh³⁺, VO₃ ^–, CrO₄ ^2–, AsO₄ ^3–, WO₄ ^2–, MoO₄ ^2– and from all the other ions referred to above. Potassium iodide at p_H 6.0–8.0 and thiosulphate at 6–7 keep Ag, Pb, Hg²⁺ and Au³⁺, Ir⁴⁺, Os⁴⁺ respectively in solution and thus allow a selective precipitation of palladium.Hg²⁺, Pb, Cu²⁺, Ag, Tl⁺, Cd and Pd when present along with bismuth are first removed by the reagent and from the filtrate bismuth is estimated. Sn²⁺, Sb³⁺, Fe³⁺, F^–, VO₃ ^–, PO₄ ^3–, AsO₄ ^3– and CrO₄ ^2– interfere in bismuth determination while only Sn²⁺, Pt⁴⁺ and CN^– interfere in palladium estimation.     

2-Mercapto-benzimidazole as an analytical reagent

Summary Palladium is quantitatively precipitated at aPH 5.0 to 10.1 by 2-mercapto-benzimidazole and the complex, Pd(C₇H₅N₂S)₂, which is found to be diamagnetic, is stable up to a temperature of 447 C. In presence of EDTA and tartrate or citrate and at aPH between 6 and 8, it is separated from alkalis, alkaline earths, Mg, Fe³⁺, Cr, Th, Zr, Ti, UO₂ ²⁺, Be, Ce³⁺, Ce⁴⁺, rare earths, Zn, Mn, Ni, Co, Pb, Bi, As, Sb³⁺, Sn⁴⁺, Tl⁺, Cu²⁺, Cd, Ir⁴⁺, Rh³⁺, Ru³⁺, Os⁴⁺, CrO₄ ^2–, MoO₄ ^2–, WO₄ ^2–, VO₃ ^–, PO₄ ^3– and AsO₄ ^3–. Pb, Ag and Hg²⁺ are kept in solution by potassium iodide while a small amount of Au³⁺ by thiosulphate. The palladium complex is either weighed after drying at 110 C or dissolved in a cyanide solution and determined volumetrically by back titrating the excess cyanide with a standard silver nitrate solution.     

Oxidation of Methanol on Pt,Pt–Ru,and Pt–Ru–Mo Electrocatalysts Dispersed in Polyaniline: An in situ Infrared Reflectance Spectroscopy Study

The electrochemical oxidation of methanol was investigated on a Pt–Ru–Mo catalyst with an in situ infrared reflectance spectroscopy. The electrocatalysts were prepared by an electrochemical deposition and dispersed in a conducting three-dimensional matrix of polyaniline (PAni). We observed that CO₂ is produced from methanol oxidation at 350 mV vs. RHE on PAni/Pt–Ru–Mo, which is 100 mV less negative than on PAni/Pt–Ru and 200 mV less than on PAni/Pt. The results suggest that Pt–Ru–Mo is less sensitive to CO_ADS poisoning than Pt–Ru and much more sensitive than Pt. Large differences are observed concerning the average wavenumber of _ADS between Pt–Ru–Mo, Pt–Ru, and Pt.     

Cyclic voltammetric behavior of Pd–Pt–Rh ternary alloys

The electrochemical behavior of Pd–Pt–Rh alloys has been investigated using cyclic voltammetry (CV). The alloys were prepared by electrochemical codeposition as limited volume electrodes (less than 1 m in thickness). The morphology of the alloy surface and bulk compositions were examined by the SEM/EDAX method. Surface oxides generation (oxygen adsorption) and oxides reduction (oxygen desorption) currents together with hydrogen adsorption and hydrogen absorption signals can be distinguished on CV curves. During potential cycling through the full hydrogen–oxygen potential range Rh and Pd are preferentially dissolved, which is reflected in a dramatic transformation in the voltammogram shape. The composition changes involve not only the surface but also some atomic layers beneath the surface.     

X–Ray Photoelectron Spectra and Electronic Energy Structure of Tetragonal Cu x Ni1-xTi Alloys

The electronic energy structure (EES) of Cu_0.8Ni_0.2Ti and Cu_0.6Ni_0.4Ti alloys, stoichiometric CuTi compound with a tetrahedral CuTi–type crystal lattice, and cubic NiTi was studied experimentally and theoretically. The experimental study of valence band EES was carried out by Xray photoelectron spectroscopy (XPS). The EES of both the stoichiometric compounds and the alloys was calculated using the cluster version of multiple scattering theory in a selfconsistent field approximation. The calculation and experimental results are in good agreement. The major contribution to XPS of the studied compounds is from the d states of copper and nickel. The specifics of chemical bonding in the compounds are discussed. The EES of tetragonal Cu—Ni—Ti alloys is modeled.