bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of Diamond-Like Film Growth Using Filament-Assisted Chemical Vapor Deposition
Authors: Gorsuch G. , Jin Y. , Ingle N. K. , Mountziarisi T. J. , Yu W.-Y. , Petrou A. 
Published: April 2011

AbstractA detailed kinetic model of diamond-like film growth from methane diluted in hydrogen using low-pressure, filament-assisted chemical vapor deposition (FACVD) has been developed. The model includes both gas-phase and surface reactions. The surface kinetics include adsorption of CH3· and H·, abstraction reactions by gas-phase radicals, desorption, and two pathways for diamond (sp3) and graphitic carbon (sp2) growth. It is postulated that adsorbed CH2· species are the major film precursors. The proposed kinetic model was incorporated into a transport model describing flow, heat and mass transfer in stagnation flow FACVD reactors. Diamond-like films were deposited on preseeded Si substrates in such a reactor at a pressure of 26 Torr, inlet gas composition ranging from 0.5% to 1.5% methane in hydrogen and substrate temperatures ranging from 600 to 950°C. The best films were obtained at low methane concentrations and substrate temperature of 700°C. The films were characterized using Scanning Electron Microscopy (SEM) and Raman spectroscopy. Observations from our experiments and growth rate data from similar experiments reported in the literature [1] were used to estimate unknown kinetic parameters of surface reactions. The proposed model predicts observed film growth rates, compositions and stable species distributions in the gas phase. It is the first complete model of FACVD that includes gas-phase and surface kinetics coupled with transport phenomena.
TEM Study of Growth Defects in CVD Diamond Films
Authors: Chen Fred Y. , King Alexander H. , Salat Robert F. , Fricano Glenn J. 
Published: April 2011

AbstractTransmission electron microscopy (TEM) has been used to examine defects in diamond films grown by the microwave plasma-enhanced chemical vapor deposition (CVD) method. Graphite was used as the sole carbon source during the CVD process with silicon substrates. Growth defects including twins, stacking faults, dislocations and second-phase precipitates were observed in the films. In plan-view TEM, defect clusters at the centers of diamond grains were observed, where the film is also the thickest. Cross-sectional TEM was carried out to show that the defect clusters fan out from a single nucleation site in each grain, at the diamond-silicon interface. Possible growth mechanisms of the defect clusters in diamond grains are considered.
Organometallic Chemical Vapor Deposition: the Roles of Precursor Design and Growth Ambient in Film Properties
Authors: Rees William S. , Luten Henry A. , Goedken Virgil L. 
Published: April 2011

AbstractExamples of chemical control in CVD of metallic and ceramic films are highlighted. Specific attention is paid to the complexity of precursor design. The effect of reactor environment on growth chemistry is investigated. Examples where reducing or oxidizing atmospheres provide a high level of control over deposit composition are outlined. The system examined centers on yttrium and yttria. These materials are, in general, desired less for their optical or electronic properties and more for their structural properties. Thus, the rigid purity demands of the microelectronics industry are somewhat relaxed. Nevertheless, critical attention must be paid to the issues of vapor pressure and decomposition profile. Where sufficient data is available to justify it, some explaination of the issues relevent to vapor pressure is presented.
Self-Lubricating, TiN-MoS2 Composite Coatings Produced by Simultaneous Deposition from Ti((CH3) 2N)4/NH3/MoF6/H2S GAS Mixtures
Authors: Bae Y. W. , Lee W. Y. , Besmann T. M. , Blau P. J. , More K. L. , Braski D. N 
Published: April 2011

AbstractComposite coatings consisting of discrete phases of TiN and MoS2 were codeposited on graphite substrates from Ti((CH3)2N)4/NH3/MoF6/H2S gas mixtures in a cold-wall reactor at 1073 K and 1.3 kPa. Chemical composition and microstructure of the coatings were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron microscopy. Kinetic friction coefficients of the coatings were determined by a computer-controlled friction microprobe and values less than 0.2 were obtained with a type-440C stainless-steel counterface under ambient condition.
Functionally Gradient Sic Coatings Produced by Chemical Vapor Reaction
Authors: Kowbel W. , Bruce C. , Withers J. C. , Ransone P. O. 
Published: April 2011

AbstractFunctionally gradient coatings have the potential to eliminate sharp interfaces between the coating layer and substrate resulting in a great ability to tailor the thermo-mechanical properties of the coating systems to a variety of substrates. Primary examples of beneficial use of the functionally gradient materials are the crack free CVD C-SiC coatings that were recently produced by a number of researchers on C-C composites. Inherent limitations of the CVD technique make it practically difficult to obtain high deposition rates on very complex and large shapes combined with good coating uniformity. A new process termed Chemical Vapor Reaction (CVR) has been employed to produce virtually crack free SiC coatings on 2–D C–C composites. Properties of this new class of functionally gradient coatings will be presented and discussed.
The Decomposition of Methyltrichlorosilane in Hydrogen and Helium
Authors: Osterheld Thomas H. , Allendorf Mark D. 
Published: April 2011

AbstractExperimental measurements of the decomposition of methyltrichlorosilane (MTS), a common silicon carbide precursor, in a high-temperature flow reactor are presented. Methane, hydrogen chloride, and silicon tetrachloride are observed as products of the decomposition. Trapping experiments with acetylene and ethylene also detected SiCl3 as a decomposition product. Upper limits on the concentrations of any CH3Cl, HSiCl3, H2SiCl2, or H2C=SiCl2 which might form are provided. Quantitative measurements of product branching and MTS decomposition rates are presented. The results suggest a radical-chain mechanism for the decomposition in hydrogen but not in helium.
Understanding and Improving Materials Processing Through Interpreting and Manipulating Predictive Models
Authors: Kee Robert J. , Ting Aili , Spence Paul A. 
Published: April 2011

AbstractMost physically based modeling software accepts input in the form of geometry definition, physical parameters, initial conditions, and boundary conditions; and then, on the basis of solving physical conservation equations, predicts the steady-state or transient behavior of a system or process. There is a growing need to create software tools that can themselves control or manipulate the physically based models in certain ways to enhance the usability of models for equipment design and process optimization. These required tools can be described broadly in the following categories: sensitivity analysis, parameter estimation, inverse problems, dynamic optimization, and real-time control. This paper discusses generally the development and application of such modeling tools, drawing examples from a specific RTP reactor design. These techniques accelerate significantly the optimal design of processes and the concurrent engineering of real-time process-control algorithms.
Intelligent Process Control of Silicon Nitride Chemical Vapor Deposition
Authors: Bowen Paul S. , Phelps Steve K. , Ringermacher Harry I. , Veltri Richard D. 
Published: April 2011

AbstractThe chemical vapor deposition of silicon nitride can be used to protect advanced materials and composites from high temperature, corrosive, and oxidative environments. Desired coating characteristics, such as uniformity and morphology, cannot be measured in-situ by traditional sensors due to the adverse conditions within the high-temperature reactor. A control strategy has been developed which utilizes a process model and an advanced laser-based sensor to measure the deposition rate of the silicon nitride coating in real-time. The control system is based on a three level hierarchical architecture which functionally separates the process control into PID, supervisory and advanced sensor-based control. Optimal setpoint schedules for the supervisory level are derived from a quasi-fuzzy logic inverse mapping of the process model. An advanced sensor utilizing laser ultrasonics provides real-time coating thickness estimates. Model bias is characterized for each reactor and is correlated on-line with the sensor's deposit thickness estimate. Deviations from model predictions may result in parametric changes to the process model. New setpoint schedules are then created as input to the supervisory control level by regenerating the inverse map of the updated process model.
Light Scattering Studies of an Electrorheological Fluid in Oscillatory Shear
Authors: Martin James E. , Odinek Judy 
Published: April 2011

ABSTRACTWe have conducted a real time, two-dimensional light scattering study of the nonlinear dynamics of field-induced structures in an electrorheological fluid subjected to oscillatory shear. We have developed a theoretical description of the observed dynamics by considering the response of a fragmenting/aggregating particle chain to the prevailing hydrodynamic and electrostatic forces. This structural theory is then used to describe the nonlinear rheology of ER fluids.
Anomalous Phase Separation Kinetics Observed in a Micelle System
Authors: Wilcoxon J. P. , Martin J. E. 
Published: April 2011

ABSTRACTWe report a real-time, two-dimensional light scattering study of the evolution of structure of a two component nonionic micelle system undergoing phase separation. The micelles act like molecular slug-a-beds whose domain growth is pathetically lathargic (i.e. slower than the cube root of time prediction for simple binary fluids). In fact, the growth kinetics can be empirically described as a stretched exponential approach to a pinned domain size. Although the kinetics are not yet understood, this anomalous behavior may be due to the ability of the spherical micelles to reorganize into more complex structures.
Experimental Study of Electrokinetics in Porous Media
Authors: Pengra David B. , Shi Liang , Li Sidney Xi , Wong Po-Zen 
Published: April 2011

ABSTRACTIn brine-saturated porous media the existence of a space-charge layer at the solid/liquid interface leads to a coupling between fluid and electric currents. This coupling is seen as a streaming potential (STP) across a porous plug when the fluid flows through it, or conversely, as electroosmosis (ELO) of the fluid when an electric field is applied. The magnitude of these electrokinetic effects depends on the thickness of the space-charge layer relative to the pore size, which in turn depends upon the salinity of the brine. From electrokinetic measurements one can obtain an effective hydraulic radius Reff and an effective zeta-potential at the slipplane ζeff. We have developed a high-sensitivity AC technique that can detect these small coupling effects, and have measured them in a suite of natural and artificial rock samples. We find that Reff and ζeff depend on salinity in ways which may be attributed to the roughness of the pore surfaces.
Reorientational Dynamics of a Nematogenic Liquid in Porous Sol-Gel-Glasses: Surface and Pore Size Effects
Authors: Deeg F. W. , Schwalb G. 
Published: April 2011

ABSTRACTTime-resolved transient grating optical Kerr effect experiments on a nanosecond timescale were used to investigate the reorientational dynamics of pentylcyanobiphenyl (5CB) confined in the nanometer lengthscale pores of silica glasses. Pore size dependent studies (25 Å ≤ d ≤ 100 Å) over a large temperature range from the bulk phase transition temperature Tni, = 35.2 ° C up to 115 ° C demonstrate a drastic influence of geometrical restriction on the cooperative reorientational motion in the nematogenic liquid. At temperatures far above the phase transition (T ≥ 70 °C) a bulk phase and a distinct surface layer with different dynamic properties are observed. With pore size reduction to 25 Å, a decrease of the surface layer thickness and an increase of the surface layer relaxation time are found. This is associated with the modification of the surface layer structure by geometrical factors, e.g., the pore curvature. Measurements at lower temperature in the range Tni ≤ T ≤ Tni = 30 ° C show a drastic decrease of the mean relaxation time τ of the order parameter fluctuations compared to the bulk. The relaxation dynamics exhibit a pronounced pore size dependence which can be explained by a crude correlation length cutoff model as well as a modified LandaudeGennes ansatz. However, these approaches cannot reproduce the nonexponentiality of the observed decays suggesting the importance of interporous interactions.
An Undercooling Effect in Porous Glass: From Bulk to the Confined
Authors: Xue Y. , Mu R. , Henderson D. O. , Frazier D. O. 
Published: April 2011

ABSTRACTThe Thermodynamic properties of TNT physically confined in 5, 10, and 20 nm pores were investigated by Differential Scanning Calorimetry (DSC). Depending upon the pore size and the sample condition, different aspects of the thermodynamic properties of the confined TNT were illustrated. The freezing transition of the confined TNT in 10, 20 nm pores can be triggered by excess bulk TNT on the outer surface. The sharp freezing transition of the TNT in 20 nm pores without the presence of the bulk suggests that the confined TNT maintains its interconnectivity during the transition. The confined TNT in 10 nm pores without bulk on surface failed to freeze during the cooling run up to 100 K with cooling rates ranging from 10 K/min. - 1 K/min. However, a sharp crystallization peak was observed upon heating. When the TNT is confined in 5 nm pores, the confined TNT is incapable of freezing.
Phase Separation Studies of Confined Thin Film Polymer Blends
Authors: Pan Q. , Composto R. J. 
Published: April 2011

ABSTRACTUsing video-optical microscopy and image analysis software, the morphological development of phase separation of polystyrene (PS) and poly(vinyl methyl ether) (PVME) blends is monitored for film thickness ranging from 200 to 700nm's. In the current studies, films are confined between glass slides. For blends having a PS volume fraction of 0.30 (the critical composition), the area fraction of the PS-rich minority phase, A, decreases more rapidly as film thickness decreases. At long times, the final A achieves a constant value which is less than the bulk value. The correlation length of concentration fluctuations increases more rapidly than the bulk scaling prediction, which suggests that wetting plays a significant role in the phase separation kinetics of thin films. Because of confinement, the shape of the PS-rich phase is anisotropic, flattened along the film direction. The confinement restricts the phase growth perpendicular to the film plane, and thus hinders the development of phase separation at very late stages.
A Spectroscopic and Thermodynamic Investigation of Mercuric Iodide Physically Confined in Porous Glass Hosts
Authors: Henderson D. O. , Mu R. , Ueda A. , Burger A. , Chen K. T. , Frazier D. O. 
Published: April 2011

ABSTRACTRaman and electronic spectra and results from differential scanning calorimetry (DSC) are reported for mercuric iodide (HgI2) confined in four different pore-sized glass hosts. The Raman spectra reveal peaks at 39 and 141 cm−1 that indicate the confined HgI2 is stabilized at 300 K in a modified orthorhombic (yellow) β-phase which is observed at 400 K for the bulk material. An additional band begins to appear at 145 cm−1 for pore radii smaller than 3.75 nm suggesting the presence of new phase of confined HgI2. The DSC measurements show the melting and freezing transitions of confined β-HgI2 are depressed from values reported for the bulk material and the depression increases as the pore size decreases. No transition is observed in the DSC measurement which could be attributed to the α→β transition for the confined material. Evidence supporting the new phase of HgI2 is observed in the electronic spectra of the confined HgI2 by the appearance of an energy gap transitions located at 2.7 eV.
Monte Carlo Studies of a Coupled ‘Elementary’ Reaction-Diffusion System in One Dimension
Authors: Lin Anna , Kopelman Raoul 
Published: April 2011

ABSTRACTThe anomalous rate laws of diffusion limited elementary reactions in low dimensions have garnered attention over the past decade as researchers have become aware that the mean field approximation utilized in traditional kinetic rate equations is not valid in low and fractal dimensions. We use Monte Carlo simulations to study a diffusion limited system simultaneously undergoing A+B-->0 and A+A--> 0 reactions, a common situation in photochemistry. We are studying how this coupled system affects the attenuation of local fluctuations and thus the rate laws of the system in low dimensions and how these results compare to the mean field rate laws. Our results give useful guidelines for studying this type of reaction system experimentally.
Ceramic-Like Materials from Waste Industrial Gypsum
Authors: Herling E. , Cyrkiewicz Marceli , Kleszewski Jacek 
Published: April 2011

ABSTRACTThis paper presents a new method for preparing composites of phosphogypsum, a chemical industry waste, and synthetic (polyester, epoxide and vinyl ester) resins. These composites, after thermal improvement of the phosphogypsum, are called CLM (ceramic-like materials). They are characterized by highly desirable physical, chemical, mechanical and strength-related properties which enable there usage as anti-corrosive coatings for storage tanks and as durable floor coatings in many branches of industry.
Local Field Effects Near Surfaces of Small Systems
Authors: Beaglehole David 
Published: April 2011

ABSTRACTThe interaction of light with a system of molecules depends upon the polarisation induced by an external electric field, which depends not only upon the external field but also upon the local fields due to neighboring polarised molecules. These local fields result in the traditional Clausius-Mossotti (CM) dielectric constant for a molecule deeply imbedded in a medium. Near the surface the local fields are altered, and the dielectric constant becomes anisotropic and dependent upon depth into the medium. The local fields are shape dependent in small systems and differ substantially from the CM value.A self-consistent computer calculation of the local fields has been implemented, and these effects will be shown using molecule positions and polarisabilities typical of liquids and crystals. The shape dependence of small systems, the reflection of light from liquids with fluctuating surfaces, and the effect of supporting substrates will be described.
Design and Preparation of Heterogeneous Catalysts by Controlled Chemical Reactions with Oxygen and Hydrogen
Authors: Cocke David L. , Naugle Donald G. , Hess Thomas R. 
Published: April 2011

ABSTRACTChemical reactions of metals and strongly interacting alloys such as Cu-Mn, Ni-Ti, Ni-Hf and Ni-Zr with oxygen and hydrogen play important roles in the preparation, activation, and regeneration of many important heterogeneous catalytic systems involving supported and unsupported metals and alloys. Recent advances in the understanding of metal and alloy oxidation is bringing new insight into the reactive design and activation of bi- and multi-metallic catalysts. By surface studies of oxidation, thermal annealing and reduction of selected alloys and their thin films and reaction layers and products we have been able to delineate the factors which are most important to the oxide formation processes and the oxide reduction processes. Reaction models developed from these results are permitting the design of new catalyst systems and providing long sought understanding to explain specific aspects of well established metallic catalysts.
The Preparation and Characterization of Pt/Fe Electrocatalyst for Direct Methanol Oxidation
Authors: Ma Chaoying , Kowalak A. D. , Sung Changmo 
Published: April 2011

ABSTRACTPt/Fe electrocatalysts (Pt/Fe) supported on Vulcan XC-72 carbon black were prepared by chemical method. The formation of Pt/Fe clusters was confirmed by transmission electron microscopy (TEM) and energy dispersive x-ray spectrometry (EDXS). The electrochemical efficiency and durability of the catalysts for direct methanol oxidation were compared with the catalyst containing Pt only (Pt) under the same reaction conditions of 1 M CH3OH in 0.1 M H2SO4 electrolyte solution. The current density for the Pt/Fe is three times of that of the Pt catalyst. Effects of various factors on the behavior of the catalysts, such as reaction time during preparation, order of the addition of the chemicals into the reaction system, methanol concentration, activation per unit Pt, scan rate for cyclic voltammograph, were examined.
Activity and Structure of Supported Molybdenum Nitride Hydrotreating Catalysts
Authors: Dolce Gregory M. , Colling Craig W. , Thompson Levi T. 
Published: April 2011

ABSTRACTMolybdenum nitrides have been shown to be active hydrotreating catalysts. We explored the hydrotreating activities of supported Mo nitrides. It was observed that the hydrodenitrogenation and hydrodesulfurization activities were inverse functions of the molybdenum loading. By using oxygen chemisorption and carbon monoxide temperature programmed desorption, we were able to characterize the particle morphology of the nitrides.
Interaction of Ni(II,III) and Sol-Gel Derived ZrO2 in Ni/ZrO2 Catalyst System
Authors: Zeng H.C. , Lin J. , Teo W.K. , Loh F.C. , Tan K.L. 
Published: April 2011

ABSTRACTNiO/ZrO2 catalyst has a selectivity for producing higher hydrocarbons, whereas NiO on classical supports gives rise to methanation of CO + H2 mixture. In this study, tetragonal and monoclinic ZrO2 gel carriers have been synthesized using sol-gel method. The interaction of nickel ions with a sol-gel derived catalyst support has been investigated using FTIR, DTA, and XPS. It is found that the nickel ions diffuses into the ZrO2 continuously over 400 to 600°C for both tetragonal and monoclinic ZrO2, and forms a thermodynamically stable Ni/ZrO2 solid solution at elevated calcination temperatures. Higher nickel surface contents are observed in tetragonal ZrO2. In addition to Ni2+, Ni3+ ions are also detected in Ni/ZrO2 system. Cation ratio of Ni2+/Ni3+ peaks at 700°C in the tetragonal ZrO2. In the monoclinic case, the ratio remains constant at different elevated temperatures. The diffusion activation energy for Ni(II,III) on both tetragonal and monoclinic in ZrO2 is 0.40 eV.
Cellular Ceramic Substrates
Authors: Williams Jimmie L. , Lachman Irwin M. , Patil M.D. , Guile Donald L. 
Published: April 2011

ABSTRACTCeramic materials in monolithic honeycomb form offer the advantage of low pressure drop for automotive & stationary emissions control reactors, catalytic oxidation, adsorption, separation, and other applications. The ceramic materials can be extruded into cellular monoliths or coated onto a cellular ceramic substrate using conventional “washcoat” processes. Both extruded and coated ceramic substrates are prepared with a binder to promote interparticle adhesion and strength. For many applications it is advantageous to control pore structure, density, strength and surface area.In this paper composition, fabrication and physical properties of cellular monolithic substrates will be reviewed. Emphasis will be on extruded materials used as catalytic supports for automotive, DeNOx and oxidation reactions.