Ru Phase Research Articles

Explanation of magnetic behavior in Ru-based superconducting ferromagnets

We have investigated RuSr2Eu1.5Ce0.5Cu2O10 Ru-1222 and RuSr2EuCu2O8 Ru-1212 samples by using x-ray diffraction, scanning electron microscopy, dc magnetization, ac susceptibility, and resistivity measurements. Based on the results obtained, we propose an explanation of the magnetic behavior of the Ru-based systems. Our model is capable of describing controversial observations of multiple magnetic transitions on temperature dependent dc magnetization measurements as well as the reentrance of irreversibility in hysteresis loops at high temperatures, which enables the bell-shaped behavior of the coercive field within 90 KT 200 K. The experimental results suggest that Ru-based samples always contain a small amount of at least one additional magnetic phase with its own magnetic behavior, which is similar yet distinct from the main Ru phase. The presence of these phases and the superposition of their magnetic contributions can produce different transport properties and lead to features that are inherent to various magnetic states, such as ferromagnetic, antiferromagnetic, and spin glass, and still exhibit a coexistence of magnetism and superconductivity at low temperatures. This variety of possible states has led to different controversial models proposed in the literature, reflecting one or another feature observed. The model proposed in this work does not contradict but rather unifies the existing scenarios for the Ru-based systems in a common picture.

Catalytic wet-air oxidation of aqueous solutions of formic acid, acetic acid and phenol in a continuous-flow trickle-bed reactor over Ru/TiO2 catalysts

Catalytic wet-air oxidation of aqueous solutions of formic acid, acetic acid and phenol was carried out in a trickle-bed reactor at T=328–523K and total pressures up to 50bar over various Ru/TiO2 catalysts. Complete oxidation of formic acid was obtained at mild operating conditions, and no catalyst deactivation occurred that could be attributed to the dissolution of active ingredient material. It was observed that besides oxidation route thermal decomposition contributes significantly to the removal of formic acid; Ru/TiO2 catalysts could be thus efficiently used for transformation of HCOOH to H2 and CO2 in an inert atmosphere. Liquid-phase oxidation of acetic acid was found to be structure sensitive; the highest catalyst activity was obtained, when Ru phase on the catalyst surface prevailed in zero-valent state. Due to simultaneous oxidation of metallic Ru to RuO2 during the reaction course, correspondingly lower conversion of acetic acid was measured in the reactor outlet. The employed Ru/TiO2 catalysts enable complete removal of phenol and TOC at temperatures above 483K; at these conditions, no carbonaceous deposits were accumulated on the catalyst surface. Apparent catalyst deactivation observed at temperatures below 463K is attributed to strong adsorption of partially oxidized intermediates on the catalyst surface, which can be avoided by conducting the CWAO process at sufficiently high temperatures. The acute toxicity to Daphnia magna and Vibrio fischeri of end-product solutions compared with that of the feed solutions was significantly reduced by oxidative treatment over Ru/TiO2 catalysts.

An investigation of the high-Al part of the Al–Pd–Ru phase diagram at 790–900°C

Abstract Partial isothermal sections of the Al–Pd–Ru phase diagram at 790 and 900 °C are presented. Complex orthorhombic ɛ-phases extending from Al3Pd up to 15 at.% Ru exhibit structural variants including transient irregular structures. The Al3Pd2 phase dissolves up to 2 at.% Ru, Al13Ru4

Pt-Ru catalysts prepared by high energy ball-milling for PEMFC and DMFC: Influence of the synthesis conditions

High energy ball-milling was used to prepare several unsupported Pt-Ru anode catalysts for PEM- and direct methanol fuel cells. Pt and Ru with a 50:50 nominal Pt/Ru ratio were ball-milled at various ball-to-powder weight ratios (from 4/1 to 12/1) and with various Pt:Ru:MgH 2 proportions (from 1:1:2 to 1:1:10), where MgH 2 is a leacheable dispersive agent. The presence of MgH 2 is necessary to obtain unsupported catalysts with a specific surface area of between 50 and 75 m 2 g −1. The ball-milling parameters greatly affected the relative proportions of the three phases constituting the catalysts. These phases are: Pt(Ru) alloy nanocrystallites, unalloyed Ru crystallites and nanocrystallites. The best CO tolerant catalyst is obtained by using a 12/1 ball-to-powder ratio and a 1:1:8 Pt:Ru:MgH 2 proportion of dispersive agent. It is made of 57 at.% of a nanocrystalline (3 nm) Pt 80Ru 20 alloy, 42 at.% of a nanocrystalline (3 nm) Ru phase and 1 at.% of a crystalline (∼40 nm) Ru phase. This catalyst has the lowest Pt/Ru surface ratio (0.9), the highest content in nanocrystalline Ru, and the highest ratio of oxidized/metallic Ru (3.3). Both Pt-Ru alloy and nanocrystalline Ru participate to the CO tolerance. The best CO tolerant catalyst is, however, not the best catalyst in DMFC. The latter is obtained by using a 4/1 ball-to-powder ratio and a 1:1:6 Pt:Ru:MgH 2 proportion. Within the starting 50:50 Pt-Ru nominal atomic ratio, no specific correlation was found between catalyst performance in DMFC and atomic surface Pt/Ru ratio, nor nanocrystalline Ru content, nor oxidized/metallic Ru ratio. Performances of the best ball-milled catalysts are compared to those of commercial unsupported catalysts in PEMFC and DMFC.

An investigation of the high-Al part of the Al–Pd–Ru phase diagram at 1000 and 1100 ºC

An investigation of the high-Al part of the Al–Pd–Ru phase diagram at 1000 and 1100 ºC

Al-rich region of Al–Pd–Ru at 1000 to 1100°C

Abstract Partial isothermal sections of the Al–Pd–Ru phase diagram at 1000, 1050 and 1100 °C are presented here. The Al–Pd orthorhombic ɛ-phases dissolve up to ∼15.5 at.% Ru, Al 13 Ru 4 2 Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C ( P m 3 ¯ , a = 0.7757 nm), C 1 ( I m 3 ¯ , a = 1.5532 nm) and C 2 ( F m 3 ¯ , a = 1.5566 nm) were revealed. An additional complex cubic structure with a ≈ 3.96 nm was found to be formed at compositions close to those of the icosahedral phase.

Synthesis of nano-crystalline RuAl by mechanical alloying

Nano-crystalline RuAl was synthesised by mechanical alloying. The evolution of the nano-crystalline RuAl phase during the mechanical alloying process using ruthenium and aluminium powders was studied. During the milling process, the peaks corresponding to reflections from the aluminium planes disappeared. The variation of crystallite size and microstrain with milling time was evaluated using X-ray diffraction (XRD) patterns. though the XRD results showed the formation of a RuAl phase after 7h of milling, scanning electron microscopy studies revealed that the RuAl phase was formed after 2h of milling. The analysis revealed that average crystallite sizes of 17 and 120 nm were obtained for RuAl and Ru phases, respectively, during the milling process. Density value of 97 % of the theoretical value was obtained for the milled powder mixture after cold compaction and sintering.

CHROMIAN SPINEL COMPOSITION AND THE PLATINUM-GROUP MINERALS OF THE PGE-RICH LOMA PEGUERA CHROMITITES, LOMA CARIBE PERIDOTITE, DOMINICAN REPUBLIC

The Loma Peguera chromitites are located in the central part of Loma Caribe peridotite in the Cordillera Central of Dominican Republic. The chromitite bodies are hosted in typical mantle peridotites, have small size (less than a few meters across) and show massive textures. Primary chromite composition is Cr-rich (0.74 < Cr# < 0.78) and exhibits systematically high Ti (average value: 0.84 wt% TiO2) and Fe3+ (average value: 7.82 wt% Fe2O3). The total PGE concentrations vary from 1.82 to 2.04 ppm, and show an enrichment in Os + Ir + Ru relative to Rh + Pd + Pt. Among the latter group, a positive anomaly of Pt (249–269 ppb) is present as a result of the appearance of Pt-bearing alloys. The PGM assemblage comprises Ru, Os, Ir and Pt-rich phases, including laurite, irarsite, unknown Ru3As2, Ru–Os–Ir–Fe oxides, unknown Pt–Ir–Ni–Fe and Ru–Os–Ir–Pt–Fe–Ni alloys, native Ru and Ru-rich Ni–Fe alloy. The Loma Peguera chromitites are rather unusual in chemical composition compared with those commonly occurring in the Moho transition zone or from mantle harzburgites in ophiolites, but bear some similarity to chromitites from Uralian–Alaska-type complex. The Al2O3 and TiO2 contents of the calculated composition of the melt in equilibrium with the Loma Peguera chromitites are similar to those from island-arc magmas and to some oceanic plateau basalts.

Factors Affecting DMFC Fuel Cell Performances and Commercialization Consideration

. By combining novel platinum and ruthenium chemistry, we have succeeded in developing a new process for making thoroughly mixed Pt:Ru alloy with minimum undesirable phases at all loadings, as evidenced by XRD analysis. XRD analysis indicated that most other commercial PtRu products have oxide impurities (RuO2 xH2O), or unalloyed Ru phase. Correlation of RDE (rotating disk electrode) results and XRD spectra indicates these phases are ineffective for catalysis. These phases reduce the electronic interaction for weakening Pt-CO bond and the bimolecular reaction rate for CO removal. A good PtRu catalyst should have thorough atomic mixing with large surface area. Oxygen cathodes are also crucial for DMFC performance. Newly developed high performance Pt black cathode catalysts possess high surface areas. 60%-80% Pt on carbon shows similar performance and is easier to process. DMFC anode structure needs to reach a compromise between catalyst access by methanol and cross-over; cathode structure needs to find the compromise between catalyst wetting and proton conduction.

Selective oxidation of naphthalene derivatives with ruthenium catalysts using hydrogen peroxide as terminal oxidant

The selective oxidation of naphthalene and its derivatives to give naphthoquinones has been investigated in detail. The reaction can be carried out effectively in the presence of a catalytic amount of Ru complexes (0.2 mol%) and phase transfer catalysts (PTC) using H 2O 2 as the terminal oxidant and water as the solvent. The effect of different ruthenium complexes, phase transfer catalysts, and the concentration of hydrogen peroxide were studied. Compared to previous procedures for this type of reactions, acidic solvents and high concentration of hydrogen peroxide are not necessary, which makes the reaction more environmentally friendly.

Preparation of AlRu intermetallic compounds by mechanical alloying

The formation of Al6Ru intermetallic compounds using high-energy ball milling was investigated. High-purity Al and Ru crystalline powders, in the relative (molar) ratio of 6:1, were milled for periods up to 30h. Samples of the milled materials were annealed at different times and temperatures. The microstructures of the annealed samples were compared to those of the as-milled samples. It was found that the obtained alloys have compositions that are in accord with the Al–Ru phase diagram. However, the X-ray analysis of a 10h milled sample, annealed at 873K for 30min, showed evidence of the formation of a quasicrystalline icosahedral alloy mixed with the crystalline Al6Ru. Scanning electron microscopy showed that the microstructures are similar to those obtained by other sample preparation techniques.

Binary Mixtures of Carbon Supported Pt and Ru Catalysts for PEM Fuel Cells

AbstractCommercially available carbon‐supported pure Pt and pure Ru catalysts were heat treated in order to modify their individual particle sizes, mixed in a mortar and tested for their suitability as anode catalysts in polymer electrolyte fuel cells (PEMFCs). The procedure chosen for mixing monometallic catalysts should bring more flexibility to the preparation of catalysts, which could thus be easily adjusted to the working conditions. The catalyst mixtures were structurally characterized using a combination of X‐ray diffraction (XRD) and transmission electron microscopy (TEM), and indicated an increase in particle size with heat treatment temperature, while the size distribution remained sufficiently narrow. The particle size effect on the resulting activity of the catalyst mixtures was investigated by current‐voltage measurements (U/i curves) in single cell fuel cells. A mixture of the as‐received platinum and ruthenium gave the best results, which was almost comparable to a commercial Pt‐Ru alloy catalyst purchased from E‐TEK inc. Only a minor decrease in cell performance was seen during long term operation. Following operation, the X‐ray diffraction patterns show reflections of the Pt fcc phase, but not the hcp Ru phase. This may be explained by leaching of the pure ruthenium catalysts and re‐decoration on Pt nanoparticles, or by formation of an amorphous Ru oxide or, less likely, Pt‐Ru alloy during operation. However, these structural changes do not seem to significantly affect the cell performance.

Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts

Pt, Ru and Pt/Ru nano-particles, synthesized in ethylene glycol solutions, are studied using infrared (IR) spectroscopy and high resolution transmission electron microscopy (HRTEM). The synthesis method allows the control of the mono- and bi-metallic catalyst particle sizes between 1 and 5.5 nm. The IR spectra of CO adsorbed (CO ads) on the Pt, Ru and bi-metallic Pt/Ru colloids are recorded as a function of the particle size. The stretching frequency of CO ads depends on the particle size and composition. Strong IR bands due to the stretching vibration of CO ads are observed between 2010 and 2050 cm −1 for the Pt nano-particles, while two IR bands between 2030 and 2060 cm −1 for linear bonded CO ads, and at lower wavenumbers between 1950 and 1980 cm −1 for bridged bonded CO ads, are found for the Ru particles. The IR spectra for the Pt/Ru nano-sized catalyst particles show complex behaviour. For the larger particles (>2 ± 0.5 nm), two IR bands representative of CO ads on Ru and Pt–Ru alloy phases, are observed in the range of 1970–2050 cm −1. A decrease in the particle size results in the appearance of a third band at ∼2020 cm −1, indicative of CO ads on Pt. The relative intensity of the band for CO ads on the Pt–Ru alloy vs. the Pt phase decreases with decreasing particle size. These results suggest that Ru is partially dissolved in the Pt lattice for the larger Pt/Ru nano-particles and that a separate Ru phase is also present. A Pt–Ru alloy and Ru phase is observed for all Pt/Ru particles prepared in this work. However, a decrease in particle size results in a decrease of the number of Pt and Ru atoms in the Pt–Ru alloy phase, as they are increasingly present as single Pt and Ru phases.

A critical test of ab initio and CALPHAD methods: The structural energy difference between bcc and hcp molybdenum

Ab initio calculations of the enthalpy of formation of bcc, fcc, and hcp Ru–Mo alloys have been performed for random, ordered, and partially ordered structures. The lattice stability of the bcc and hcp forms of Mo is isolated in order to compare the hcp–bcc difference calculated by ab initio and CALPHAD methods with experimental measurements of the enthalpy of formation of Ru–Mo alloys. The significance of this comparison in calculating the Mo–Ru phase diagram is illustrated. The results of these considerations suggest a rational method for coupling ab initio and CALPHAD techniques might be utilization of the ab initio methods for calculation of the isostructural energies of formation for binary bcc, hcp, and fcc solutions while retaining the CALPHAD lattice stabilities in the calculation of phase diagrams.

Chemical vapor deposition of ruthenium and ruthenium oxide thin films for advanced complementary metal-oxide semiconductor gate electrode applications

A low-temperature (320–480 °C) metal-organic chemical vapor deposition (MOCVD) process was developed for the growth of ruthenium and ruthenium oxide thin films. The process used bis(ethylcyclopentadienyl)ruthenium [Ru(C5H4C2H5)2] and oxygen as, respectively, the ruthenium and oxygen sources. Systematic investigations of film formation mechanisms and associated rate limiting factors that control the nucleation and growth of the Ru and RuO2 phases led to the demonstration that the MOCVD process can be smoothly and reversibly modified to form either Ru or RuO2 through simple and straightforward modifications to the processing conditions–primarily oxygen flow and substrate temperature. In particular, films grown at low oxygen flows (50 sccm) exhibited a metallic Ru phase at processing temperatures below 480 °C. In contrast, films grown at high oxygen flow (300 sccm) were metallic Ru below 400 °C. Above 400 °C, a phase transition was observed from Ru to RuOx (0 &lt; x &lt; 2.0) to RuO2 as the processing temperature was gradually increased to 480 °C.

Study of phase states and oxidation of B2-structure based Al–Ni–Ru–M alloys

Phase states and oxidation resistance of B2-structure based Al–Ni–Ru–M alloys have been investigated on equilibrium alloys and by the diffusion couple approach. The isothermal cross-sections of the Al–Ni–Ru phase diagram have been partially defined in a range of Al<70 at.% at 900 and 1100 °C. The existence of a miscibility gap between AlRu (β1) and AlNi (β2) phases in the Al–Ni–Ru ternary system has been clearly established. The following phase equilibria have been experimentally identified: β1-AlNi 3, β1–β2, β2-Al 2Ru, Al 2Ru–AlNi 3–Al 13Ru 4 at 900 °C and β1–β2, β2-Al 2Ru at 1100 °C. The high temperature properties of B2-structure based Al–Ni–Ru–M alloys are presented. All the studied samples display high melting points up to more than 2100 °C. Oxidation of Al–Ni–Ru–M B2 alloys in laboratory air has been found to follow parabolic law at 950 and 1050 °C and it is slower than that of a commercial MCrAlY alloy. There is no remarkable difference of oxidation mechanisms of the B2 structure based Al–Ni–Ru–M alloys at 950 and 1050 °C. Protective α-Al 2O 3 scale develops already after 100–150 h of oxidation. The protective α-Al 2O 3 scale (i) is mono-phased (α-Al 2O 3), (ii) is dense, (iii) does not contain remarkable amount of Ni and Ru and (iv) has good adhesion to bulk alloy. A dense continuous Ru underlayer forms between the α-Al 2O 3 film and the bulk alloy for compositions with Ru>25 at.%. The Ru layer can contain considerable amounts of Cr or Ir and exhibits good adhesion to both the scale and the bulk alloy. Physical properties of the B2 structure based Al–Ni–Ru–M alloys make them good candidates for oxidation resistant coatings in different high temperature industrial applications.

Thermal stability of RuSr 2GdCu 2O 8, Ru 1 − xSr 2GdCu 2O 8 − y, RuO 2

Thermal stability of RuSr 2GdCu 2O 8, Ru 0.9Sr 2GdCu 2O 8 − y , and RuO 2 powders in oxygen has been studied by thermogravimetry. Decomposition of RuSr 2GdCu 2O 8 and Ru 0.9Sr 2GdCu 2O 8 − y samples in 0.85 bar of oxygen appears as a solid phase process at ∼1050 °C. This is followed by peritectic decomposition with onset starting at ∼1110 °C for the stoichiometric sample and at ∼1090 °C for the Ru deficient one. We observed that sublimation of ruthenium oxide in 0.85 bar of oxygen starts at ∼850 °C and sample's humidity significantly increases a sublimation rate. Enhanced sublimation above 1060 °C was observed for powder mixtures (RuO 2 + xCuO), x=0.1, 0.2, 0.5. Analysis of the sublimation process of these mixtures suggests existence of an unknown compound in Ru–Cu–O system with approximate composition Ru 1 − x Cu x O 2 − y , x⩽0.1. Various aspects of a synthetic route of rutenates and, in particular RuSr 2GdCu 2O 8 phase, eliminating Ru off-stoichiometry and phase separation, are discussed.

Size-selected synthesis of PtRu nano-catalysts: reaction and size control mechanism.

A rapid synthesis method for the preparation of PtRu colloids and their subsequent deposition on high surface area carbons is presented. The reaction mechanism is shown to involve the oxidation of the solvent, ethylene glycol, to mainly glycolic acid or, depending on the pH, its anion, glycolate, while the Pt(+IV) and Ru(+III) precursor salts are reduced. Glycolate acts as a stabilizer for the PtRu colloids and the glycolate concentration, and hence the size of the resulting noble metal colloids is controlled via the pH of the synthesis solution. Carbon-supported PtRu catalysts of controlled size can be prepared within the range of 0.7-4 nm. Slow scan X-ray diffraction and high-resolution transmission electron microscopy show the PtRu catalysts to be crystalline. The Ru is partly dissolved in the face-centered cubic Pt lattice, but the catalysts also consist of a separate, hexagonal Ru phase. The PtRu catalysts appear to be of the same composition independent of the catalyst size in the range of 1.2-4 nm. Particular PtRu catalysts prepared in this work display enhanced activities for the CH(3)OH electro-oxidation reaction when compared to two commercial catalysts.

Preparation and Characterization of RuOx Thin Films by Liquid Delivery Metalorganic Chemical Vapor Deposition

RuOx films were deposited by liquid delivery metalorganic chemical vapor deposition method using a new Ru(C8H13O2)3 precursor for the advanced capacitor electrode in Gbit-scale dynamic random access memory. Deposition was carried out on a TiN barrier layer in the range of 250–400°C and the ratio of the O2 flow rate to the total flow rate of Ar and O2 was varied from 20 to 80%. RuOx thin films were annealed at 650°C for 1 min with Ar, N2 or NH3 ambient. Film characterization was performed in terms of resistivity, crystal structure, surface morphology, microstructure and film purity. The resistivity depended on the impurity, grain density and crystalline structure of the film. The oxygen used to form Ru the oxide was found to eliminate the carbon and hydrogen elements in an organic source. The O2 flow ratio that changes the crystal structure of the films from Ru to RuO2 was found to be 40%. The metallic Ru phase forming a RuO2/Ru bilayer at the RuO2/TiN interface was observed at O2 flow ratios of 50% and 60%. The X-ray diffraction results indicate that the RuO2 phase and the silicidation are not observed regardless of the ambient gases. Ar was more effective than N2 and NH3 as an ambient gas for the postannealing of the Ru films.

Phase equilibrium in the vicinity of the Al–Ni–Ru decagonal phase

The Al-rich part of the Al–Ni–Ru phase diagram was re-investigated with respect to the existence of stable quasicrystalline phases. The thermodynamic stability of the ternary decagonal phase with a 1.6 nm periodicity was confirmed in a small compositional range around Al 73.1Ni 15.7Ru 11.2 and at temperatures below 1050 °C. The partial 900 °C isothermal section of Al–Ni–Ru is presented. Apart from the decagonal phase, two ternary crystalline compounds are stable at this temperature. The results are compared to those in Al–Ni–Fe.