Low Ru Content Research Articles

Phase Transformation and Shape Memory Effect in Ru-Based High Temperature Shape Memory Alloys

Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. For both systems, it is interesting to find a way to control the transformation temperatures while keeping the shape memory effect. One way to change the transformation temperatures is to change the composition in the binary alloys; another is to add a ternary element like Fe. The eight investigated alloys show two different space groups at room temperature. The monoclinic alloys undergo two successive displacive transformations on cooling, starting from the high temperature β phase field: β (B2) à β’ (tetragonal) à β’’ (monoclinic). The tetragonal alloys exhibit a single transition from cubic to tetragonal. A multiple twinned microstructure can be found in all alloys. Transformation temperatures decrease with lower Ru content and with the addition of Fe. The β’ à β transformation seems to be the main responsible for the SME. Compression tests performed in the martensitic phase give a quantitative result of the shape memory effect. In the binary alloys, the SME decreases with decreasing Ru content, which is in accordance with the evolution of the lattice parameters of martensites. A lower SME in the ternary alloys can also be linked to the lattice parameters and seems to be quite reliable to predict the evolution of the shape memory effect.

Catalytic decomposition of N2O over highly active supported Ru nanoparticles (≤3 nm) prepared by chemical reduction with ethylene glycol

In the present work we studied the N2O decomposition activity of nano-Ru/γ-Al2O3 catalysts prepared by in situ reduction with ethylene glycol (EG), in comparison to catalysts prepared via typical incipient wetness procedure. The metal content, particle size, dispersion and reduction characteristics of the supported Ru catalysts were studied by means of ICP-AES, XRD, HRTEM, TPR-H2 and TPD-H2. The EG reduction method favored the formation of almost spherical metallic Ru nanoparticles with the size of 1–3nm (HRTEM) and dispersion of 70–35% (TPD-H2), at Ru loading levels of 0.4–1wt.%. The impregnated-calcined catalysts exhibited larger Ru nanoparticles (10–80nm, TEM) with very low degree of dispersion (∼10%). The activity of the EG-prepared catalysts for the decomposition of N2O in oxygen rich feeds and in the absence or presence of NO, H2O, SO2, CO and CO2, was significantly higher compared to that of the impregnated-calcined samples and comparable with that of the most active catalytic systems reported in the literature for the treatment of combustion processes off-gases. The superior activity of the former catalysts, especially of the sample with low Ru content (0.4wt.% Ru, 1–2nm particle size), was attributed both to the high dispersion of Ru (70% dispersion), i.e., the high surface area of Ru metal available for reaction, and to the higher intrinsic activity and lower apparent activation energy of the very small supported Ru nanoparticles prepared by the EG reduction method. The EG-prepared nano-Ru/γ-Al2O3 catalysts could retain their high N2O decomposition activity (higher than 90%) for long time-on-stream by applying intermediate, short term regenerations in reducing atmosphere at moderate temperatures (i.e., 500°C); treatment of the partially deactivated catalysts under reducing (H2/He) atmosphere leads to elimination of Ru(SO4)2 that is usually formed during reaction via reduction of Ru4+ to active Ru metallic phase.

Hydrogenation of Acetophenone in the Presence of Ru Catalysts Supported on Amine Groups Functionalized Polymer

Liquid phase hydrogenation of acetophenone (ACT) is studied over ruthenium catalysts (1-4 wt% Ru) supported on gel-type methacrylate-styrene resin (FCN) functionalized with C=O, –NH, and –NH2 groups. Microscopic studies (SEM, STEM) show that the nature of Ru particles depends on the level of Ru doping. At low Ru content (1–2 wt%) ruthenium nano-clusters are formed, while at 4 wt% Ru, metal crystallites of few nanometers in size are observed. Catalytic reactions are performed at mild conditions (atmospheric pressure of hydrogen, 40 °C) in biphasic isooctane-water (IO/H2O) solvent system, and, for comparison, in a single component solvent (isooctane or ethanol). The use of biphasic IO/H2O solvent system results in a dramatic improvement of selectivity. The hydrogenation of C=O in acetophenone dominates over the hydrogenation of aromatic ring, yielding 1-phenylethanol with ca. 80% selectivity. Ru/FCN catalysts exhibit higher selectivity than the reference Ru/Al2O3. This is tentatively assigned to the steric effects induced by the polymer network on migrating reactant molecules. Advantageous influence of biphasic IO/H2O solvent system has been attributed to the solvation of phenyl ring of acetophenone by non-polar isooctane, which facilitates the interaction with the catalyst surface via carbonyl group and leads to the preferential reduction to 1-phnenylethanol. Liquid phase hydrogenation of acetophenone was studied over ruthenium catalysts (1–4 wt% Ru) supported on diamine group functionalized gel-type polymer (FCN).

Ruthenium oxide–niobium hydroxide composites for pseudocapacitor electrodes

A simple solution-based method has been developed to vary the composition of redox active ruthenium oxide with highly proton-conducting niobium hydroxide to create stable, high capacitance electrodes at elevated temperatures. This method presents a dramatic departure from most other ruthenium oxide systems, which are prepared through annealing of hydrous ruthenium oxide. Typically RuO 2 processed at high temperature only exhibits high electrical conductivity and suffers from poor proton conduction, giving low overall capacitances. Here, the optimized Ru/Nb oxide composition can be used to achieve high power densities, high capacitances, and stabilized electrodes while significantly reducing ruthenium content. Extensive materials characterization including high-resolution cross-sectional TEM, elemental mapping, XRD, electrochemical impedance spectroscopy, and proton NMR were used to evaluate the structure of the material system. The electrochemically inert niobium oxide serves as a network former enhancing accessibility to redox active ruthenium oxide. The dispersion of RuO 2 in the NbO(OH) x matrix results in reduced RuO 2 particle size, as observed via TEM and XRD, while also increasing the proton concentration in the material. Interconnected RuO 2 particles provide electrically conducting pathways, even at low Ru contents, where percolation networks remain intact. Ruthenium is more efficiently utilized in the Ru/Nb composites and ruthenium content can be significantly reduced without decreasing capacitive performance. In addition, the composite electrodes, with the fine mixing of Ru and Nb, give higher power performance than for RuO 2 alone.

Surface and structural properties of titania-supported Ru catalysts for hydrogenolysis of glycerol

A series of catalysts with different Ru contents supported on titania were prepared by conventional impregnation (IM) and deposition–precipitation (DP) methods. These catalysts were characterized by X-ray diffraction, temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy and CO chemisorption. The catalysts were evaluated for selective hydrogenolysis of glycerol. The glycerol conversion and the selectivity towards 1,2-propanediol depend on the method of catalyst preparation and on the Ru content. The catalyst with low Ru content exhibited maximum conversion, in turn was related to its dispersion. The catalysts prepared by DP method showed stable activity even with crude glycerol containing alkali salts as impurity. The catalyst exhibited consistent activity upon reuse. The high activity of Ru/TiO 2 catalyst is due to the presence of well-dispersed nano size Ru particles on titania. The low activity of the IM catalyst is because of large domains of Ru and because of the presence of residual Cl − ions.

Influence of complexing agents on the preparation of bimetallic platinum–ruthenium catalysts supported on O-functionalized graphite cloths

Abstract Electrodeposition of bimetallic Pt–Ru catalysts on O-functionalized graphite cloths from H2PtCl6 and RuCl3 solutions containing trisodium citrate (Cit) and disodium dihydrogen ethylenediaminetetraacetate (Na2H2EDTA) was investigated. SEM analysis of the electrode prepared without complexant showed a relatively compact and rough deposit displaying a ‘tree cortex’ structure, whereas uniform size and globular shape particles regularly distributed over the support surface were obtained using citrate and Na2H2EDTA as complexants. In addition, XRD diffraction and EDX analysis revealed that the catalysts prepared using the complexants showed smaller size particles and lower Ru content. Electrocatalytic activity measurements indicated that the most active electrode for methanol oxidation was obtained with Na2H2EDTA as additive.

Electrocatalysts for methanol oxidation with ultra low content of Pt and Ru

We have developed efficient electrocatalysts for methanol oxidation using new synthetic method facilitating deposition of Pt–Ru very thin nanoplatelets on carbon nanoparticles The method involves oxidation of carbon support, adsorption of Pb 2+, its reduction and galvanic displacement of Pb 0 by Pt and/or Ru. The Pt mass activity of this catalyst is about 10 times higher than that of the commercial Pt–Ru/C. The catalyst with the 1:1 Pt/Ru ratio displayed the highest methanol oxidation activity per surface Pt atom. Our results demonstrate the new synthetic method that yields the catalyst with potential for solving the problem of high Pt loading in direct methanol fuel cell anodes.

Corrosion of uranium and its low content Zr, Nb, and Ru alloys in aqueous solutions

Corrosion of uranium and its alloys with low content (0.5–5.0 at %) of Zr, Nb, and Ru in water and bicarbonate aqueous solutions is studied; the effect of hydrogen peroxide, the main product of radiation processes, on the corrosion rate is elucidated. The rate of the primary corrosion process U +(2 +n)H2O=UO2·nH2O+ 2H2↑ is measured by electrochemical methods in anaerobic and aerobic conditions for uranium metal and its alloys containing 0.5 to 5.0 at % of Zr, Nb, and Ru. It is shown that the corrosion rates for the alloys are lower than that of reactor-grade uranium; however, the difference is rather close to the measurement error. The corrosion mechanism is studied; U(III) is shown to be rather unstable in neutral solutions when uranium(III) hydroxide is precipitated and no significant amount of U(III) and UH3 is present among the products of the metallic uranium corrosion in water. The kinetics of the second corrosion stage U(IV) + O2→U(VI) is studied by spectrophotometric method. It is shown that the reaction of U(IV) oxidation by atmospheric oxygen is similar in weakly acid solutions (pH 1.5–4.0) and in bicarbonate media: in particular, it has an induction period for uranium (IV) accumulation, after which the reaction accelerates; it is formally a first-order reaction with respect to uranium. The reaction mechanisms differ in the two media: in weakly acid solutions, after the appearance of U(VI), the reproportionation reaction proceeds; thus formed U(V) interacts with O2 faster than U(IV). In the bicarbonate medium, the acceleration of the reaction is due to the formation of a [U(IV)ΣU(VI)] complex whose reactivity is higher than that of uranium (IV). In the absence of bicarbonate, of great importance is the formation of a copolymer of U(IV) and U(VI), which at pH≥4 prevents formation of U(V). It is shown that on the introduction of hydrogen peroxide to aqueous solutions, the metallic uranium surface becomes transpassive, which increases the rate of corrosion process by at least an order of magnitude,. The introducing of oxidants and platinum mesh lowers the hydrogen accumulation at 120–150°C and, hence, the hydrogen-explosion danger of the uranium-water-corrosion-products system. Methods of deposition of metal oxide (Tc, Ru, Mo, W) films onto uranium surfaces by immersing uranium metal into Tc(VII), Ru(VI), or Mo and W heteropoly compound solutions are studied.

A simple and practical phase-separation approach to the recycling of a homogeneous metathesis catalyst

The air stable asarone-derived Ru carbene 16, a robust olefin metathesis catalyst, can be easily separated after reaction by deposition on silica gel and reused up to nine times. This procedure provides products of excellent purity with low Ru content.

ON THE ORIGIN OF THE PGE MINERALIZATION IN THE ELATSITE PORPHYRY Cu Au DEPOSIT, BULGARIA: COMPARISON WITH THE BAULA NUASAHI COMPLEX, INDIA, AND OTHER ALKALINE PGE-RICH PORPHYRIES

The Elatsite porphyry-copper deposit contains platinum-group minerals associated with base-metal sulfi des, i.e., merenskyite, moncheite, palladoarsenide and an undetermined Pd–Ag–Te–Bi mineral, all in a magnetite – bornite – chalcopyrite assemblage. Other minerals such as linnaeite, carrollite, siegenite, rammelsbergite, which are uncommon in typical porphyry-copper deposits, indicate a mantle derivation for the specifi c PGE–Co–Ni episode of mineralization. The Pt–Pd-rich facies is characterized by extremely low Os, Ir and Ru contents (respectively <3.0, <0.6 and <1.0 ppb), with up to 349 ppb Pt and 3440 ppb Pd. Mineralization results either from (1) multi-stage events involving a preconcentration of the PGE in magmatic disseminated (Ni–Cu–Co) sulfi des related to a mantle-derived magmatic event, with subsequent selective hydrothermal remobilization, or (more probably) from (2) particular conditions in the partial melting of the mantle and magmatic evolution that rendered the precious metals available in the magma, along with a specifi c evolution that prevented the early formation of the sulfi des whilst the PGE (mainly Pd) were concentrated in the hydrothermal fl uids. This PGE–Co–Ni episode is a very specifi c event in the main mineralizing process giving rise to the massive deposition of the Cu-porphyry system. The characteristics of the PGE mineralization deviate from those of a purely hydrothermal PGE mineralization in a mafi c environment, as exemplifi ed by the Baula–Nuasahi mineralization (India), in that they tend to converge toward (and present striking similarities with) the PGE mineralization in alkaline porphyry deposits, such as are found in British Columbia.

Nanostructured PtRu/C as Anode Catalysts Prepared in a Pseudomicroemulsion with Ionic Surfactant for Direct Methanol Fuel Cell

Nanostructured PtRu/C catalysts have been prepared from a water-in-oil pseudomicroemulsion with the aqueous phase of a mixed concentrated solution of H(2)PtCl(6), RuCl(3), and carbon powder, oil phase of cyclohexane, ionic surfactant of sodium dodecylbenzene sulfonate (C(18)H(29)NaO(3)S), and cosurfactant n-butanol (C(4)H(10)O). Two different composing PtRu/C nanocatalysts (catalyst 1, Pt 20 wt %, Ru 15 wt %; catalyst 2, Pt 20 wt %, Ru 10 wt %) were synthesized. The catalysts were characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and thermogravimetric analysis, and the particles were found to be nanosized (2-4 nm) and inherit the Pt face-centered cubic structure with Pt and Ru mainly in the zero valance oxidation state. The ruthenium oxide and hydrous ruthenium oxide (RuO(x)()H(y)()) were also found in these catalysts. The cyclic voltammograms (CVs) and chronoamperometries for methanol oxidation on these catalysts showed that catalyst 1 with a higher Ru content (15 wt %) has a higher and more durable electrocatalytic activity to methanol oxidation than catalyst 2 with low Ru content (10 wt %). The CV results for catalysts 1 and 2 strongly support the bifunctional mechanism of PtRu/C catalysts for methanol oxidation. The data from direct methanol single cells using these two PtRu/C as anode catalysts show the cell with catalyst 1 has higher open circuit voltage (OCV = 0.75 V) and maximal power density (78 mW/cm(2)) than that with catalyst 2 (OCV = 0.70 V, P(max) = 56 mW/cm(2)) at 80 degrees C.

Promoted Ru–hydroxyapatite: designed structure for the fast and highly selective oxidation of alcohols with oxygen

Ru-containing hydroxyapatite (HAp) catalysts have been developed for the oxidation of alcohols with molecular oxygen in an organic solvent. The working hypothesis has been that fine-tuning of the location and surroundings of the active Ru species would provide outstanding performance. The highest oxidation activity was achieved when (i) the contact time between the metal salt solution and HAp was limited to a few minutes to minimize restructuring via dissolution–redeposition, (ii) low Ru content was applied, (iii) Co 2+ and Pb 2+ promoters were incorporated to occupy the poorly accessible “hidden” sites in HAp before the introduction of Ru 3+, thus facilitating egg-shell-type Ru distribution in the particles, and (iv) after Ru incorporation the catalysts were dried at moderate temperature to avoid restructuring induced by dehydration of the active sites and their neighborhood. It is assumed that the active sites are Ru(OH) 2+ species stabilized by the phosphate O atoms and adsorbed (H-bonded) water. Various methods have been used for characterization of these catalysts, including XPS, DRIFT spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), XRD, thermogravimetry combined with mass spectroscopy (pulse thermal analysis), and nitrogen adsorption. One of the two best catalysts (RuCoHAp-10min) was used in the partial oxidation of benzylic, allylic, aliphatic and cycloaliphatic alcohols. Most carbonyl compounds were produced in excellent yields without the formation of any detectable by-product. The catalytic activity seems to be higher than that of other Ru-based solid catalysts developed for the aerobic oxidation of alcohols.

Effects of thermal activation on the oxidation pathways of methanol at bulk Pt–Ru alloy electrodes

Abstract The competition between pathways that lead to adsorbed CO and CO 2 during the electrochemical oxidation of 1.0 M methanol in 0.1 M HClO 4 on two bulk Pt–Ru alloys (10 at.% Ru ( X Ru ≈0.1) and 90 at.% Ru ( X Ru ≈0.9)) was investigated for temperatures in the range of 25–80°C. On the high Ru content alloy studied ( X Ru ≈0.9), the dissociative chemisorption of methanol was inhibited below 70°C; the faradaic current for methanol oxidation was low, and only small quantities of adsorbed CO and CO 2 were detected with infrared spectroscopy between 0.2–0.8 V (vs. RHE). At 80°C, strong infrared bands from CO 2 and adsorbed, atop coordinated CO were observed over the potential ranges of 0.4–0.8 V and 0.2–0.8 V, respectively. The infrared measurements are consistent with the observation that bulk, high Ru content alloy electrodes appear passivated toward methanol oxidation below 70°C. On the low Ru content alloy studied ( X Ru ≈0.1), the methanol surface chemistry was similar to that of pure, polycrystalline Pt, but the electrode was more poison resistant than Pt. For both alloys, the persistence of strong adsorbed CO bands and rapid CO 2 production between 0.4–0.8 V suggests CO functions as a reactive species with high steady-state coverages at these potentials.

Anomalies in Heat Capacity Measurements of RuO2-TiO2 System

DSC was used for heat capacity measurements of pure RuO2 in the temperature range from 300 to 1170 K of solid solutions corresponding to the compositions of (Ti1−x Rux )O2 (x ≤0.15 and x ≥0.85) and in the temperature range from 300 to 1550 K of pure TiO2. The analysis of experimental data obtained within ±2% of accuracy has shown that the characteristic temperatures representing the harmonic lattice vibrations do not strongly depend on the chemical composition x . It was demonstrated that non-harmonic heat capacity is strongly correlated to x. The existence of additional excess heat capacity was observed with the mixed oxide solid solution samples of low Ru content and explained by the defect formation model.

SULFUR ENRICHMENT VIA VOLATILE-RICH METASOMATISM IN MONTFERRIER XENOLITHS (SOUTHERN FRANCE): CONSEQUENCES FOR HIGHLY SIDEROPHILE ELEMENTS IN THE SUB-CONTINENTAL MANTLE

Sulfides are the main hosts for highly siderophile elements (HSE); therefore the mantle S content is a crucial datum for geochemical studies relevant to platinum-group element abundances or Re-Os systematics. The estimated S content of the primitive mantle is about 250±50 ppm. Although S contents of fertile peridotite from orogenic massifs support this estimate, peridotites hosted in alkali basalt commonly contain only a few tens of ppm S, whatever their fertility (Lorand, 1990). Some xenoliths from southern France, i.e. Montferrier volcano (Herault) have very high sulfide abundances (up to 0.2 wt.%) with intergranular sulfides predominating over enclosed sulfides (Lorand and Conquere, 1983). The process responsible for such high sulfide modal abundances and its possible effect on HSE abundances are not clear. To shed some light on this process we have carried out an extensive study of 21 xenoliths from this locality, involving major elements and lithophile trace element data, chalcogenide (S, Se) geochemistry, platinum-group element analyses and Re-Os systematics. Montferrier xenoliths are either breccia-hosted or lavahosted. The former have a yellowish color indicating weathering, while the lava-hosted have a fresh green color and do not show obvious alteration features. Some xenoliths display disseminated Ti-pargasite (up to 6%) regardless of their host. Montferrier peridotites are characterized by a strongly deformed porphyroclastic microstructure giving them a mylonitic appearance. It has been shown that this deformation took place at low temperature (900-750°C), probably during an uplift on the nearby Cevennes lithospheric shear zone (e.g., Fabries et al., 1987). They also display very fertile compositions. Most of the studied samples contain between 3.0 and 4.5% Al2O3 and the least fertile still contains 2.0 wt.% Al2O3. The S concentration range (7 - 592 ppm) is the highest reported for basalt-hosted peridotite xenoliths. S contents are uncorrelated with fertility indices (e.g., Al2O3%). Breccia- hosted xenoliths have the lowest S contents ( 10). Ba and Rb enrichments are determined by amphibole. The second end-member is strongly enriched in LREE (La/SmN > 1). This LREE enrichment, is accompanied by large ion lithophile elements (Sr, U, Th...), but without concomitant enrichment of the high field strength elements (Nb, Ta, Zr, Hf). In contrast to the depleted type, the U/Th ratios are chondritic. Such enriched patterns are commonly ascribed to mantle metasomatism by carbonated and/or volatile-rich small volume melts. The positive correlation of figure 1B indicates that large amounts of S have been added by this metasomatism. In thin sections, the xenoliths containing more than c.a. 200 ppm S show numerous large intergranular sulfide blebs (up to 700 µm in maximum dimension) much richer in Fe and Cu than those from the depleted samples. Contrary to S, Se contents increase only moderately from 17-48 ppb in depleted samples to 50- 63 ppb in enriched xenoliths. The most S-rich samples may show markedly higher than chondritic S/Se ratios (104) which are inconsistent with a simple addition of immiscible sulphides during metasomatism. This observation suggests that S was a dissolved species in the volatile-rich metasomatic fluid whose effects are indicated by the trace element studies. Apart from the most refractory lherzolite which is unusually poor in PGE (total PGE = 5.2 ppb), the 8 xenoliths analyzed for the PGEs show a narrow PGE concentration range (20-28.2 ppb) independant of their fertility indices and S contents. Ru/Ir and Rh/Ir ratios are remarkably constant and slightly higher than chondritic. Pd/Ir ratios (1.37-2.26) are suprachondritic, as reported for Pyrenean orogenic lherzolites (Pattou et al., 1996) and some abyssal peridotites (Snow and Schmidt, 1998, Luguet et al., this volume). Pd/Ir ratios are correlated with S contents, mostly because the enriched samples have low Ir and Ru contents. Whole-rock fractionated Pd/Ir ratios are reflected in the pattern of the sulphides (LA-ICP-MS data). Os/Ir varies sympathetically with Pd/Ir, increasing from nearly chondritic values (1.1) in the depleted sample to suprachondritic (1.99) in the most S-rich xenolith. 187Os/188Os shows a similar increase from DMM-like values (0.128) in the depleted samples to highly radiogenic values (0.175) in the most S-rich sample. Our study provides further evidence that metasomatic process(es) involving volatile-rich small melt fractions may significantly alter the HSE relative abundances and Os isotopic composition of the lithospheric mantle (cf Gutierez Narbonna et al., this volume). Such parallel variations of Os, Pd and S are consistent with the experimentally-demonstrated affinity of these elements for S-bearing vapor phases at magmatic temperatures.

High energy ball-milled Pt and Pt–Ru catalysts for polymer electrolyte fuel cells and their tolerance to CO

High energy ball milling, an industrially amenable technique, has been used to produce CO tolerant unsupported Pt–Ru based catalysts for the oxidation of hydrogen in polymer electrolyte fuel cells. Nanocrystalline Pt0.5–Ru0.5 alloys are easily obtained by ball-milling but their performances as anode catalysts are poor because nanocrystals composing the material aggregate during milling into larger particles. The result is a low specific area material. Improved specific areas were obtained by milling together Pt, Ru and a metal leacheable after the milling step. The best results were obtained by milling Pt, Ru, and Al in a 1:1:8 atomic ratio. After leaching Al, this catalyst (Pt0.5–Ru0.5 (Al4)) displays a specific area of 38 m2g−1. Pt0.5–Ru0.5 (Al4) is a composite catalyst. It consists of two components: (i) small crystallites (∼4 nm) of a Pt–Al solid solution (1–3 Al wt%) of low Ru content, and (ii) larger Ru crystallites. It shows hydrogen oxidation performance and CO tolerance equivalent to those of Pt0.5–Ru0.5 Black from Johnson Matthey, the commercial catalyst which was found to be the most CO tolerant one in this study.

Structural and electrochemical properties of Ti–Ru–Fe–O alloys prepared by high energy ball-milling

The structural and electrochemical properties of the Ti–Ru–Fe–O system have been studied over the whole ternary metal compositional range, keeping constant the oxygen content at 30 at.%. The phase diagram was explored systematically by varying the composition of the material along one of the following axes: (i) constant Ru content of 16 at. %; (ii) constant Ti/Ru ratio of 2; (iii) constant Ti/Fe ratio of 1.6. For O/Ti ratios equal or below unity, the most prominent peaks observed in the x-ray diffraction patterns belong to a B2 structure. For O/Ti ratio larger than unity, stable titanium oxide phases are formed, which coexist with a cubic Fe-like or hcp-Ru like phases depending on the Fe/Ru ratio. Powder compositions with stoichiometry close to Ti2RuFeO2 are of interest due to good electrocatalytic properties, long-term stability, and low Ru content.

Controls on Platinum-Group Elemental Distributions of Podiform Chromitites: A Case Study of High-Cr and High-Al Chromitites from Chinese Orogenic Belts

A study of podiform chromite deposits from the Asiatic Orogenic Belt and the Qilian-Qiangling-Kunlun-Himalaya Tectonic Domain provides new insights into the geochemistry of the PGEs in podiform chromite deposits and the genesis of the deposits themselves. The bulk of deposits, which occur in mantle peridotites of ophiolites, have typical ophiolitic PGE patterns that are depleted in Pt and Pd relative to the average upper mantle and have negatively sloping distributions on mantle-normalized diagrams. Type I (high-Cr) chromitites have higher Os, Ir, Ru, and Rh contents than Type II (high-Al) chromitites, although both have similar Pd and Pt. Most of the Type I and II chromite deposits have lower Pd and Pt contents than the upper mantle peridotites in which they occur. Podiform chromitites are essentially products of melt/rock interaction in the upper mantle; their Cr and PGEs were contributed by not only the invading magmas but also by the upper mantle host; the chromite deposits are, in part, metasomatic replacement bodies. The Type I (high-Cr) chromitite PGE patterns were produced by interaction between S-undersaturated boninitic magmas and depleted harzburgites, whereas the Type II (high-Al) chromitite PGE patterns were formed by interaction between initially S-saturated tholeiitic magmas and depleted harzburgites. The low to very low Pd and Pt contents of both Type I and Type II chromitites require that the mantle assemblage in which the chromite deposits were formed had lost their sulfides, and hence Pd and Pt, prior to formation of the chromite deposits; in addition, no or little Pd and Pt were deposited by the invading magma which either remained S-undersaturated (boninite) or became (MORB) S-undersaturated due to interaction with the S-depleted harzburgitic mantle. It is suggested that the very low Ir, Os, and Ru contents of boninites in general might be due to loss of Ir during the formation of podiform chromitites. It is suggested that podiform chromitites with Type I PGE patterns were formed in an island arc environment, whereas those with Type II PGE patterns were formed in a back-arc setting.

Chemical Ordering Along the Growth Direction in Epitaxial [0002] Co1−xRux Alloy Thin Films

AbstractThe occurrence of metastable long range order (LRO) along the growth direction with a periodicity twice that of a disordered alloy is now a well established result in epitaxial hcp [0002] Co-Ru and Co-Pt alloy thin films. We first present a review of previous results obtained in Co-rich Co1−xRux alloy thin films (x = 0.25) prepared at various growth temperatures (TG) and the diffusive model developed to account for the observed behavior. This model which takes into account the competition between surface and bulk interactions and surface and bulk diffusion during the growth time reproduces the TG dependence of the LRO parameter (η) and of the lattice constants. Then we present new results on the occurrence of this LRO in Co1−xRux films for higher Ru concentrations (0.22 ≤ x ≤ 0.78) prepared at the optimal temperature for the occurrence of this LRO (570-595 K). Chemical ordering is observed over the whole explored concentration range and it is found to be in agreement with results obtained in a previous series prepared at 610 K with lower Ru content. The LRO parameter deduced from the difference in composition between two successive planes normalized with respect to the concentration of the minonty element displays a nearly symmetric dependence with concentration characterized by a maximum around x = 0.2 and a minimum around the equiatomic composition. These results are qualitatively discussed in terms of a balance between the different energetic contributions to the surface segregation that arise from the release of the elastic energy and the difference in the wetting energy of each element. The important role played by the quality of the substrate in determining the value of η is outlined.

Performing CO Tolerant Anode Catalyst for Polymer Electrolyte Fuel Cells

High energy ball-milling of Pt, Ru, and Al in a 1:1:8 atomic ratio has been used to produce CO tolerant unsupported Pt-Ru based catalysts for the oxidation of hydrogen in polymer electrolyte fuel cells. After leaching Al, this catalyst [Pt 0.5 -Ru 0.5 (Al 4 )] displays a specific area of 38 m 2 /g. It shows hydrogen oxidation performance and CO tolerance equivalent to those of Pt 0.5 -Ru 0.5 Black from Johnson Matthey, the commercial catalyst which was found to be the most CO tolerant one in this study. Pt 0.5 -Ru 0.5 (Al 4 ) is a composite catalyst. It consists of two components: (i) small crystallites (∼ 4 nm) of a Pt-Al solid solution (1-3 Al wt%) of low Ru content, and (ii) larger Ru crystallites. The providers of oxygenated species necessary for the electrochemical oxidation of CO on Pt are either oxidized Al or Ru. The latter may be either on the surface of the Pt-Al (+Ru) alloy crystallites or at the surface of the larger Ru crystallites. Pt 0.5 -Ru 0.5 (Al 4 ) provides a stable current under H 2 + 100 ppm CO.