bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical Vapor Deposition of Ruthenium and Osmium Films from Mono- and bis-(Cyclopentadienyl) Complexes as Precursors
Authors: Smart Christopher J. , Gulhati Akshaya , Reynolds Scott K. 
Published: April 2011

AbstractWe have investigated cyclopentadienyl (Cp) complexes of Ru and Os as precursors for low temperature CVD of pure ruthenium and osmium films. Films were grown on a variety of substrates in a warm-walled CVD reactor, equipped with a resistively heated wafer chuck, massflow controllers for carrier gas regulation, and a mechanically-backed oil-vapor diffusion pump. Typical depositions were done under ca. 1 Torr total pressure. Use of air or oxygen as a carrier gas and Cp2M (M = Ru or Os) as precursors gave high purity, conformal films of ruthenium and osmium at temperatures as low as 275°C and 350°C, respectively. Under these conditions, the only observable by-products were CO2 and H2O, indicating that surface-catalyzed, complete oxidation of the ligands was involved in the decomposition process. Growth rates, film purities, resistivities and conformality were measured.
The Chemical Vapor Deposition of Dispersed Phase Composites in the B-Si-C-H-Cl-Ar System
Authors: Moss T. S. , Lackey W. J. , Freeman G. B. 
Published: April 2011

AbstractThe CVD of the coatings in the B-Si-C-H-C1-Ar system was accomplished using a statistically designed experiment. The experimental design used five factor half-fraction factorial with a central composite design that was both rotatable and orthogonal. Deposits were thick and dense and were composed of B13C2 and β-SiC with compositions ranging from 0 to 100%. Response surfaces were generated using multivariate regression for unit cell volumes of B13C2 and β-SiC, %B13C2/%SiC in the coating, and the Si to B ratio in the deposit. These equations could then be used to examine the significant variables in the reaction, as well as for tailoring and optimizing the deposition process.
CVD of Refractory Amorphous Metal Alloys
Authors: Tenhover M. 
Published: April 2011

AbstractIn this work, a novel process is described for the fabrication of multi-metallic amorphous metal alloy coatings using a chemical vapor deposition (CVD) technique. Of special interest in this work are amorphous metal alloys containing Mo and/or Cr which have high crystallization temperatures and readily available low decomposition temperature metal-bearing precursors. The conditions for amorphous alloy formation via CVD are described as well as the chemical properties of these materials. High temperature, aqueous corrosion tests have shown these materials (especially those containing Cr) are among the most corrosion resistant metal alloys known.
Aerosol-Assisted Chemical Vapor Deposition (AACVD) of Binary Alloy Films: Studies of Film Composition
Authors: Xu Chongying , Hampden-Smith Mark J. , Kodas Toivo T. 
Published: April 2011

AbstractThe chemical vapor deposition (CVD) of Cu-Ag and Cu-Pd alloys using aerosol precursor delivery over a range of preheating temperatures, 70∼80 °C and substrate temperatures, 250∼300 °C is described. The precursors used include Cu(hfac)2, (hfac)Ag(Set2) and Pd(hfac)2 dissolved in toluene and 10% H2 in Ar as carrier gas. The films were characterized by SEM, EDS and X-ray diffraction (XRD). The X-ray diffraction results showed the Cu/Ag films were composed of α-and β-phases of Cu-Ag alloys, the Cu/Pd films were Cu-Pd alloy, solid solutions, under these conditions. Compositional variation studies in Cu-Pd and Pd-Ag alloy systems were also conducted by mixing Cu(hfac)2/Pd(hfac)2 and (hfac)Ag(SEt2)/Pd(hfac)2 in toluene solution in different ratios. The films were characterized by X-ray diffraction and the results showed the composition of films was affected by the solution stoichiometry.
Rate of SiC Deposition from Methyltrichlorosilane and Influence of HCL Addition
Authors: Delhaes Christof , Neuschütz Dieter 
Published: April 2011

AbstractSuitable feedgas compositions for monophase SiC deposition were determined starting from methyltrichlorosilane-hydrogen-argon mixtures at 1 bar total pressure and H2/MTS ratios between 50 and zero. At temperatures from 900 to 1400°C, only a ratio of 1 at PMTS = 18 mbar gave the desired result. The deposition rate of SiC was determined as a function of MTS and HCl partial pressures, of gas flow rate, and of temperature at a H2/MTS ratio of 1. Two different rate equations were found at [MTS]/[HCI] ≥ 5.8 (region I) and < 5.8 (region II), respectively:where brackets denote gas concentrations. The apparent activation energy was 380 kJ/mol common to both rate equations. A mathematical model taking into account temperature fields at reactor wall and substrate, heat and mass transport in the flowing gas, and heterogeneous reaction rates jSiC(I) and (II) was developed and found to be in very good agreement with the experimental results.
Phase Transformations in Multilayered CVD Mullite Coatings
Authors: Doppalapudi D. , Muipuri R. , Basu S. N. , Sarin V. K. 
Published: April 2011

AbstractMullite (3Al2O3.2SiO2) is an ideal candidate for coatings on SiC due to its toughness, corrosion resistance and coefficient of thermal expansion (CTE) match. We have deposited alternating layers of Al2O3 and SiO2 followed by post deposition heat treatment to induce mullite formation at the interface. We found that the devitrification of silica to cristobalite led to spallation of the multilayered coatings due to the fracture within the crystalline silica layers. To understand this transformation better, we studied the effect of pressure and temperature on devitrification of silica in both bulk and in coating form. We have demonstrated that the difference in specific volumes of the two phases plays a key role in the vitreous to crystalline transformation in silica.
Asymmetric Drainage in Foam Films N4.1
Authors: Joye Jean-Luc , Hirasak George J. , Miller Clarence A. 
Published: April 2011

ABSTRACTDrainage of circular foam films is much more rapid when the drainage is asymmetric. The same basic mechanism is responsible for asymmetric drainage of thin circular films and marginal regeneration. A linear stability analysis showed that these phenomena are caused by a hydrodynamic instability that is produced by a surface-tension-driven flow and stabilized by surface viscosity, surface diffusivity and system length scale. A criterion for the onset of this instability was derived. Experiments performed on small circular films of aqueous solutions of SDS and SDS:l-dodecanol demonstrated the strong stabilizing effect of surface viscosity. Experimental results were found to be in good agreement with the predictions of the linear stability analysis. Finite difference simulations demonstrate the validity of the linear stability analysis for when the radius of curvature of the “barrier ring” is large compared to the transverse wave length of the instability. These simulations also show the circulation cells that relax the surface tension gradient and thus accelerate the drainage of the film.
Optimization of Diffusive Transport to Irregular Surfaces with Low Sticking Probability
Authors: Pfeifer Peter , Sapoval Bernard 
Published: April 2011

ABSTRACTWe study steady-state diffusion to an irregular membrane or catalyst surface which “annihilates” arriving particles by transfer across the membrane or chemical reaction at the surface. For diffusion in two dimensions and an arbitrary given surface, we present a simple algorithm to compute the total flux across the surface (annihilation rate) when the permeability of the membrane or reaction probability at the surface is small. The resulting flux increases with increasing surfaceirregularity and depends nonlinearly on the transport parameters and on the surface area. It predicts an optimal temperature, dependent on the surface irregularity, at which the flux is maximal. We illustrate this for self-similar surfaces, in which case the flux is a power law of the transport parameters and is governed by the fractal dimension of the surface.
Low-Temperature Mobility of Thionine in a Faujasite Cage
Authors: Deeg F. W. , Ehrl M. , Bräuchle C. 
Published: April 2011

ABSTRACTWe have used low-temperature optical spectroscopy to characterize the guest/host interaction of thiazine and oxazine dyes encapsulated in the three-dimensional pore structure of faujasite cages. The system thionine in dehydrated zeolite-Y exhibits a thermal and optical equilibrium between two spectroscopically distinguishable species. Temperature-dependent measurements allow the determination of the energy difference and barrier between these two forms as 170cm−1and 120cm−1, respectively. The two forms are associated with two different locations/conformations of the chromophore within the faujasite pore structure. The degree of freedom responsible for the interconversion of the two forms is extremely sensitive to the relationship between molecular size and form of the void.
Morphology & Exchange Kinetics in Polymer Brushes: The Physical Significance of Hydrodynamic Transitions and Stretched Exponential Evolutional Forms
Authors: Rodgers S. D. , Santore M. M. 
Published: April 2011

ABSTRACTThis work reexamines equilibrium and kinetic features of polymer brushes end-adsorbed onto solid substrates from solution, providing a new interpretation of previously-published experimental results and insight into the comparison between experiments and existing kinetic models. The study centers on an end-modified polyethylene oxide (PEO) which may adsorb to form a polymer brush on a hydrophobic polystyrene latex, and whose main backbone also exhibits an attraction for the surface. In a previous work, Gao and Ou-Yang claim a sharp pancake-to-brush transition with increasing surface coverage of the samples with the strongest end group attraction to the substrate, and only a delicate increase in the hydrodynamic thickness of layers whose chain ends are weakly attracted to the surface. Our reevaluation of this data, however, collapses all molecular architectures to a single curve describing the hydrodynamic thickness at different surface loadings, and which shows a relatively sharp transition for all samples. Gao and Ou-Yang have also performed kinetic exchange experiments where low molecular weight species replace preadsorbed high molecular species (with the same endgroup-surface adsorption energy), and observed stretched exponential behavior in the evolution of the hydrodynamic thickness of the adsorbed layer. We employed Milner's treatment for brush exchange kinetics, to extract equivalent phenomenological parameters for more direct comparison between fundamental parameters and experiment.
Reaction-Diffusion Model for the A + A → O Reaction
Authors: Lindenberg Katja , Kopelman Raoul , Argyrakis Panos 
Published: April 2011

ABSTRACTWe formulate an approach to the A + A → products reaction based on a reaction-diffusion model. We construct the first equations in a moment hierarchy whose first two members are the global density of A particles and the pair correlation function. We terminate the hierarchy by relating the three-particle correlation function to two-particle correlation functions and thereby obtain a set of coupled equations that turns out to be linear and hence analytically tractable.This approach leads naturally to the proportionality of the rate of the reaction to the pair correlation function evaluated at r=a, where a is the diameter of the reacting particles. It also confirms the relation between anomalous kinetics and the deviation of the pair correlation function from that associated with a random distribution of particles.Numerical simulations in one and two dimensions that support our theory are presented in a companion paper in this session.
Dynamics of Phase Separation of Binary Fluid Mixtures in the Presence of Surfactants
Authors: Laradji Mohamed , Mouritsen Ole G. , Toxvaerd Søren , Zuckermann Martin J. 
Published: April 2011

ABSTRACTThe dynamics of phase separation of binary fluid mixtures in the presence of surfactants is studied via molecular dynamics simulations. In contrast to phase separation in pure binary fluid mixtures, which is characterized by an algebraic time dependence of the average domain size, mixtures containing surfactants exhibit nonalgebraic slow dynamics. At very late times, the average domain size saturates at a value inversely proportional to the surfactant concentration. Despite the fact that these systems only microphase separate, a dynamical scaling was observed at late times.
Thermal Conditions Favoring Buckytube Growth on the Anode
Authors: Koprinarov Nikola , Marinov Miko , Pchelarov George , Konstantinova Mariana , Stefanov Radoslav 
Published: April 2011

ABSTRACTThe most widespread methoid for buckytube synthesis is by arc discharge in an inert gas ambient. At arc discharge the major kind of charge carriers are the electrons generated from the cathode by thermal emission. For this reason up until now the deposit was always obtained on the cathode. By supplementary electrode heating and cooling we studied the effects of the anode-cathode temperature difference and found that it plays a major role in defining the quality and quantity of the deposit obtained. Given appropriate heat-up or cool-down of the electrodes, a state can be reached such that the temperature at the cathode is higher than the temperature at the anode. A deposit was obtained on the anode, observed by a TEM. In our view employing this method yields the most favorable conditions for buckytube growth. Our results show that except buckytubes with a high ratio of their length with respect to their width, a multitude of small size polyhedral carbon systems closed in by spatial carbon nets and thin flat interfering carbon plates were also obtained. When using electrodes of different cross-section, with the deposition of an ever thicker deposit on the anode, its temperature regime changes. The lower initial temperature at the anode begins to grow steadily with time tending towards the temperature at the cathode. Thus, buckytube growth proceeds at the lowest possible rate, at a small temperature difference between the vapor source and growing structure. In our view employing this method yields the most favorable conditions for buckytube growth.
Infrared Spectroscopic Characterization of Sulfide Cluster-Derived Ensembles
Authors: Brenner James R. , Thompson Levi T. 
Published: April 2011

ABSTRACTThe transition metal sulfide clusters (MeCp)2Mo2(μ-SH)2(μ-S)2, (MeCp)2Mo2Co2(μ3-S)2(μ4-S)(CO)4 [MoCoS], and (MeCp)2Mo2 Fe2 (μ3-S)2(CO)8, (MeCp = methylcyclopentadienyl) were used to prepare γ-Al2O3-supported catalysts. For comparison, a series of supported materials was also prepared using conventional incipient wetness impregnation. Infrared spectroscopy of adsorbed species was used to characterize the sites in the clusterderived and conventionally prepared catalysts. Nitric oxide chemisorbed onto the MoCoS/A catalyst was associated initially only with Co sites and then upon gentle heating shifted to the Mo sites, indicating that Co and Mo were in close proximity. In contrast, NO adsorbed onto both Co and Mo sites in the conventionally prepared materials and desorbed independently from these two types of sites. Infrared spectra of adsorbed thiophene and pyridine were similar for the clusterderived and conventionally prepared catalysts. Thiophene reacted at 100 °C to produce both olefinic species. The most abundant products from thiophene HDS were 1-butene, cis-2-butene, and trans-2-butene. Displacement studies showed that thiophene, pyridine, and NO adsorbed to the same site. The most active sites for HDS and HDN contained both Mo and a late transition metal. The HDN product distributions suggested that Mo was selective for C=N bond cleavage while the late transition metals were more active for C=C hydrogenolysis.
Heteropoly Compounds: Efficient Superacid Catalysts
Authors: Misono Makoto , Okuhara Toshio 
Published: April 2011

ABSTRACTOur recent studies on the acidity and acid catalysis of heteropoly compounds are described, together with a brief introduction of the background. High catalytic activities were observed due to the combination of their superacidity, pseudoliquid behavior, acid-base bifunctionality and/or high surface concentration of proton. It was also shown how the acid strength and the number of acid sites as well as their tertiary structure were controlled by the constituent elements (heteroand addenda-atoms and counter cations), and how those properties were correlated with the catalytic activities
Catalytic Implications for Keggin and Dawson Ions: A Theoretical Study of Stability Factors of Heteropolyoxoanions
Authors: Wang Shu-Hsien , Jansen Susan A. 
Published: April 2011

ABSTRACTHetreropolyoxoanions(HPAs) have received wide spread attention due to their unique oxidation-reduction properties in catalysis. Two main structural motifs groups of HPAs have been described by Keggin and Dawson. The first is composed of twelve distorted, octahedrallycoordinated metal atoms forming trimeric and tetrameric subunits connected such that a closed shell results. The second is formed by fusing two Keggin units. The most common Keggin ions(XM12O40n−,) with Td symmetry and the Dawson ions(X2M18O62n−) with D3h symmetry are the α-isomers; while the β-isomers are generated by rotating one trimer 60° along its C3 axis, thus producing the Cs, symmetry for β-Keggin ions and D34 symmetry for β-Dawson ions. Here, M is the framework metal atom, usually Mo, W, and X is the central heteroatom which can be the metal or nonmetal. From our previous studies, the instability of β-isomers caused by the “rotated” trimer can not be compensated by other coordination effects within the cluster and therefore defect states are retained between the HOMO-LUMO gap relative to the α-isomer. This enhances catalytic properties and causes thermal/photo lability. The catalytic function of a-Keggin ions are well studied; however, related research reports about Dawson ions are rare. The α-Dawson ion possesses stronger oxidizing ability and higher activities in oxidative dehydrogenation and oxygen addition reactions than the α-Keggin ions; the β-isomers have a greater tendency to be reduced than the α-isomers. Most of the characterization methods applied have not yielded the electronic or the structural requisites for the catalytic properties of the HPAs. In this work, the theoretical analysis is done through the application of crystal/tight binding theory coupled with the extended HMckel methodology. The stability trends and the redox behaviors provided by this work reliably trace the experimental data. In addition, the intrinsic instability and the redox effects in the β-isomers with respect to the α-isomers is assessed and a rationale for the observed catalytic and electronic develpoment of structrual function is also offered.
New Nanophase Iron-Based Catalysts for Hydrocracking Applications
Authors: Matson Dean W. , Linehan John C. , Darab John G. , Camaioni Donald M. , Autrey S. Thomas , Lui Eddie G. 
Published: April 2011

ABSTRACTCarbon-carbon bond cleavage catalysts produced in situ at reaction conditions from nanocrystalline hydrated iron oxides, show high activity and selectivity in model compound studies. Two highly active catalyst precursors, ferric oxyhydroxysulfate (OHS) and 6-line ferrihydrite, can be produced by a flow-through hydrothermal powder synthesis method, the Rapid Thermal Decomposition of precursors in Solution (RTDS) process. Model compound studies indicate that both catalyst precursors are active at a 400°C reaction temperature, but that there are significant differences in their catalytic characteristics. The activity of 6-line ferrihydrite is highly dependent on the particle (aggregate) size whereas the activity of the OHS is essentially independent of particle size. These differences are attributed to variations in the crystallite aggregation and particle surface characteristics of the two catalyst precursor materials. Catalytic activity is retained to lower reaction temperatures in tests using OHS than in similar tests using 6-line ferrihydrite.
Mixed Metal Oxide Interfaces: An Experimental and Theoretical Assessment of Secondary Metal Influences in Metal Impregnated Aluminas
Authors: Malaty M. , Singh D. , Schaeffer R. , Jansen S. , Lawrence S. 
Published: April 2011

ABSTRACTStudies of the mixed-metal interface in metal impregnated alumina have indicated the possibility of much metal-metal and metal-substrate interaction. Studies were carried out on NiCu/Al2O3 system which was evaluated to develop a better understanding of the forces that drive modification of the catalytic selectivity of Ni in the presence of Cu. Electron Paramagnetic Resonance (EPR), Powder X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD) and theoretical calculations were carried out on this bimetallic system, using Ni,Ag/Al2O3 as a reference as Ni shows negligible electron perturbation on co-adsorbance with Ag onto alumina. XRD results indicate that gross modification of the electronic fields of Ni and Cu are due to direct coupling and intercalation into the alumina matrix. As a result of this phenomena, these materials may form a good base for the development of novel ceramics based on mixed-metal interactions where the intermetallic perturbations are driven by the substrate effects.
Perovskite Catalysts: High-Surface Area Powders Synthesis, Monoliths Shaping and High-Temperature Applications
Authors: Sadykov Vladislav A. , Isupova L.A. , Tikhov S.F. , Kimkhai. O.N. 
Published: April 2011

ABSTRACTMonolith perovskite catalysts of honeycomb structure for high-temperature applications are elaborated. Problems of powdered perovskites synthesis by efficient plasmochemical and mechanochemical methods as related to real structure and reactivity of these compounds are discussed. Pilot testing in reactions of fuels combustion, ammonia oxidation, methane conversion and sulphur dioxide reduction proved high activity and stability of these catalysts.
Advances in the Design of Pillared Clay Catalysts by Surfactant and Polymer Modification
Authors: Pinnavaia T. J. , Butruille Jean-Rémi , Michot Laurent J. , Guan Jingie 
Published: April 2011

ABSTRACTThe catalytic properties of pillared clays for organic chemical conversions, especially those occurring in liquid media, can be substantially improved by surfactant modification of the pore structure during the pillaring reaction. For instance, the incorporation of a non-ionic surfactant, such as the alkylated polyethylene oxide C12–14H25–29O(CH2CH2O)5H, in the synthesis of alumina pillared montmorillonite results in a dramatic increase in the interparticle (textural) mesoporosity of the final calcined products. These surfactant-modified mesoporous pillared clays are exceptionally active as catalysts for the diffusion controlled liquid phase alkylation of biphenyl. The enhanced mesoporosity facilitates access of the reactants to the active acid sites in the interlayer nanopores of the pillared clay tactoids. Organic polymeric molecules also can be used to mediate the pore structure of pillared clay materials. The reaction of aluminum chlorohydrate oligomers with Na+ rectorite in the presence of polyvinyl alcohol as a pillaring precursor affords a supergallery alumina pillared rectorite with a basal spacings of 52 Å and a corresponding gallery height of 33 Å under air- dried conditions. A stable gallery height of 23 Å is observed even after treatment with 100% steam at 800°C for 17 hour. The new supergallery intercalate is characterized by a surface area, pore volume, and catalytic cracking activity superior to conventional alumina pillared rectorite and related smectites with 9 Å gallery heights.