bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modification of Optical Surfaces Employing CVD Boron Carbide Coatings
Authors: Lowden Richard A. , Riester Laura , Akerman M. Alfred 
Published: March 2011

AbstractNon-reflective or high emissivity optical surfaces require materials with given roughness or surface characteristics wherein interaction with incident radiation results in the absorption and dissipation of a specific spectrum of radiation. Coatings have been used to alter optical properties, however, extreme service environments, such as experienced by satellite systems and other spacecraft, necessitate the use of materials with unique combinations of physical, chemical, and mechanical properties. Thus, ceramics such as boron carbide are leading candidates for these applications. Boron carbide was examined as a coating for optical baffle surfaces. Boron carbide coatings were deposited on graphite substrates from BCl3, CH4, and H2 gases employing chemical vapor deposition (CVD) techniques. Parameters including temperature, reactant gas compositions and flows, and pressure were explored. The structures of the coatings were characterized using electron microscopy and compositions were determined using x-ray diffraction. The optical properties of the boron carbide coatings were measured, and relationships between processing conditions, deposit morphology, and optical properties were determined.
Fiber-Reinforced Tubular Composites by Chemical Vapor Infiltration°
Authors: Stinton D. P. , Lowden R. A. , Besmann T. M. 
Published: March 2011

AbstractA forced-flow thermal-gradient chemical vapor infiltration process has been developed to fabricate composites of thick-walled tubular geometry common to many components. Fibrous preforms of different fiber architectures (3-dimensionally braided and filament wound) have been investigated to accommodate components with different mechanical property requirements. This paper will discuss the fabrication of tubular, fiber-reinforced SiC matrix composites and their mechanical properties.
The CVD of Ceramic Protective Coatings on SiC Monofilaments
Authors: Choy K. L. , Derby B. 
Published: March 2011

AbstractThe TiB2, TiC and TiN coatings were studied as potential protective coatings for SiC fibre reinforced titanium alloys. These coatings were deposited by a CVD technique on resistively heated SiC monofilament fibres at reduced pressure in a cold wall reactor. The deposition conditions that are required to coat each of these materials were determined. The morphology, microstructure, phase composition and nature of the coatings were examined. The comparison and evaluation of the effectiveness and potential of these as protective coatings were carried out by incorporating the coated fibre into Ti-6A1–24V using the diffusion bonding method at 1100°C under 10 MPa for 1 hour.
Chemoical Vapor Deposotdoo of Tungsten and Molybdenum Folms From m(η3–C3H5)4 (M=Mo, W)
Authors: Kirss Rein U. , Chen Jian , Hallock Robert B. 
Published: March 2011

AbstractChemical vapor deposition using tetra(allyl) tungsten and molybdenum precursors yielded amorphous tungsten and molybdenum carbide films on pyrex substrates. The films were characterized by Auger, ESCA, SEM, XRD and resistivity measurements. Volatile pyrolysis products consisted primarily of propene, C3H6.
Advanced Dielectrics Deposited by LPCVD
Authors: Lane Andrew P. , Chen Arthur , Sandier Neal P. , Freeman Dean W. , Page Barry S. 
Published: March 2011

AbstractTa2O5 and Nb2O5 films were deposited using the Lam Research Integrity™ reactor. The chemical precursors used were pentaethoxides of Ta and Nb. Typical films were deposited at a rate of 4 nm/min with uniformities of <1.5% lσ in the presence of O2 at 470°C. Annealing the Ta2O5 films did not change the O/Ta ratio. Annealing the Nb2O5 films increased the O/Nb ratio to 2.5/1 at 850°C. Interfacial SiO2 grew to 4 nm after annealing at 850°C for both Ta2O5 and Nb2O5. The as-deposited films were amorphous, but became crystalline above 600°C and 700°C for the Nb2O5 and Ta2O5 films respectively. The TEM observations on crystallization is supported by x-ray diffraction data.
Pyrolytic Carbon Deposition on Graphitic Surfaces
Authors: Ismail Ismail M. K. 
Published: March 2011

AbstractThe present study outlines the importance of carbon active sites in controlling the kinetics of pyrolytic carbon deposition on a graphitized pitch fiber at 1025°C. Blockage of active sites with chemisorbed hydrogen retards deposition rates substantially. Removal of the chemisorbed hydrogen from the occupied sites raises deposition rates to the normal values noted on a fresh “clean” surface. The effect of surface activation prior to deposition is discussed. Activating the surface generates additional active sites and enhances the rates. However, not all the newly developed sites contribute to the kinetics. After the deposition of the first carbon layer, a fraction of those newly developed sites is instantaneously blocked and does not further contribute to subsequent deposition. The remaining fraction, along with the original sites available before activation, keeps replicating during the remaining course of deposition. That is, the disappearance of one active site after carbon deposition is associated with the generation of a new site. This trend continues up to the deposition of 60 carbon layers.
H States, Impurity Passivation and Gettering Studies in H-Implanted Si Crystals
Authors: Mukashev Bulat N. , Tokmoldin Serikbol Zh. 
Published: March 2011

ABSTRACTIR and DLTS studies of H-implanted Si crystals are performed. It is shown that H is a bistable impurity: it has an equilibrium site at a T-site for H+ and H- and at a BC-site for H°. The mechanisms of H-passivation of defects and shallow and deep impurities are discussed.
Studies of the Effects of Ion-Implantation and Electron Beam Irradiation on CuInSe2 Single Crystals
Authors: Mullan C. A. , Kiely C. J. , Rockett A. , Imanieh M. , Yakushev M. V. , Tomlinson R. D. 
Published: March 2011

ABSTRACTA series of CuInSe2 single crystals which were grown by the vertical Bridgman technique have been implanted with oxygen and xenon ions. These implants tend to cause a change from n to p-type conductivity and an enhancement of the photoconductivity. We present HREM and SIMS characterisation of the microstructural effects caused by high dose ion implants on CuInSe2. We also correlate our data with calculated ion implant profiles. In addition, we show that CuInSe2 thin foils can undergo significant degradation under the electron beam irradiation conditions which are commonly encountered in electron microscopes.
Studies of Nonthermal Effects During Intense Microwave Heating of Crystalline Solids
Authors: Booske John H. , Cooper Reid F. , McCaughan Leon , Freeman Sam , Meng Binshen 
Published: March 2011

ABSTRACTReports of enhanced sintering rates associated with microwave heating may be due to nonthermal lattice fluctuation statistics. Recent theoretical analyses reviewed in this paper confirm the feasibility of this phenomenon for a wide variety of situations involving very different microwave absorption mechanisms. For materials with weak microwave absorption coefficients, the effect is expected to be uniformly distributed throughout the volume. For strongly absorbing materials, however, the effect is expected to be concentrated near the material surface, with a characteristic exponential penetration depth of Lnt ∼ 10 - 100 μm. An “observable” nonthermal effect depends on the relative magnitude of the microwave electric field strength |E| and the lattice ion energy relaxation rate γ with the most pronounced effects occurring for larger values of |E| and smaller values of γ.
Microwave Processing of Ceramics: Guidelines Used at the Oak Ridge National Laboratory
Authors: Janney Mark A. , Kimrey Hal D. , Kiggans James O. 
Published: March 2011

ABSTRACTTo make meaningful comparisons between conventional and microwave processing of materials, one must conduct experiments that are as similar as possible in the two environments. Particular attention must be given to thermal conditions, sample parameters, and furnace environment. Under thermal conditions, one must consider temperature measurement (pyrometer or thermocouple, sheath type, and arcing of thermocouples), thermal history (heating and cooling rates, thermal gradients), and exothermic reactions. Regarding sample parameters, one must. consider sample size, and packing powders and insulation systems. With respect to furnaces, one must consider differences in atmosphere, impurities, and uniformity of heating. Examples will be drawn from diffusion, grain growth, sintering, nitridation, and drying experiments conducted at the Oak Ridge National Laboratory (ORNL) over the past six years.
Ceramic Powders Generated by Metallorganic and Microwave Processing
Authors: Willert-Porada M. , Krummel T. , Rohde B. , Moormann D. 
Published: March 2011

ABSTRACTA novel approach to synthetic ceramic powders based on microwave heating of metallorganic ceramic precursor compounds or mixtures of such compounds with a appropriate matrix material is described.Numerous oxides as well as nonoxide powders with high specific surface area were obtained. Pyrolysis as well as enhanced reactivity is observed with microwave heating at lower temperatures than in conventional heating.
Microwave Processing of Tantalum Capacitor Anodes
Authors: Lauf R. J. , Hamby C. , Holcombe C. E. , Vierow W. F. 
Published: March 2011

ABSTRACTPorous tantalum anodes were sintered at temperatures from 1600 to 1900°C using a conventional high-vacuum furnace as well as both 2.45 GHz fixed-frequency and 4-8 GHz variable-frequency microwave furnaces. Various insulation and casketing techniques were used to couple the microwave power to the tantalum compacts. Several types of tantalum powder were used to assess the effect of microwave processing on sintered surface area and impurity levels.Some microwave sintered anodes have an unusual surface rippling not seen on conventionally fired parts. The rippling suggests that a microscopic arcing or plasma might have been generated. Two important effects could be exploited if this phenomenon can be controlled. First, the effective tantalum surface area could be increased, yielding higher capacitance per volume. Second, surface impurities might be cleaned away, allowing the formation of a better dielectric film during the anodization process and, ultimately, higher working voltage.
An Experimental Investigation of Hybrid Convective/Microwave Drying of Electrical Porcelain
Authors: Hendrix Walter A. , Martin Tom 
Published: March 2011

ABSTRACTThe drying of electrical porcelain using a combination of convection and microwave heating has been experimentally studied. To date, a total of 58 individual tests have been conducted to evaluate the effect of a range of microwave and convection conditions on the drying behavior of both solid and cavity core bodies. Preliminary indications are that order of magnitude reduction in drying time may be achieved. Furthermore, improved control over quality problems appears to be possible because of the ability of microwave heating to minimize the amount of convective surface heating.
Microwave Processing of Glass Fiber/Vinyl Ester-Vinyl Toluene Composites
Authors: Ramakrishna Dhulipala , Travis Susannah , Hawley Martin C. 
Published: March 2011

ABSTRACTMicrowave processing has been investigated as an alternative to the conventional processing of polymers and polymer matrix composites. Different studies have demonstrated its viability and advantages, but various aspects related to its industrial applicability are still being investigated.Two aspects related to the microwave curing of glass fiber/vinyl ester-vinyl toluene composites have been studied. A qualitative evaluation was done to determine the reproducibility of heating patterns of these laminates in different modes of a microwave resonant cavity. The samples were prepared to similar physical and chemical specifications and heated in different single modes of the cavity.Another evaluation was done to compare the mechanical properties of microwave and thermally cured laminates subjected to flexural load. The samples were processed using similar cure cycles. The microwave samples were cured using a mode-switching technique and the thermal samples were cured in a temperature controlled oven. The void fractions of the samples were evaluated to develop pre-consolidation conditions that yield samples with low void fraction. Results of these two evaluations are discussed.
Microwave Processing of Foam Materials
Authors: Loock W. Van 
Published: March 2011

ABSTRACTThe distinct phases in the production process of a foam material are foaming, curing and drying. Cellular materials are insulators to conventional heat. This paper discusses the effectiveness of microwave or high frequency energy for processing a layer of foam material on for example a conveyor belt. The emphasis is on the thermal and drying time constants and on the specific energy consumption. It is demonstrated that a limit is set on time gain when using microwaves.A case study for applying microwaves in an industrial production line of foam rubber for mattresses according to the above principles is presented.
Microwave Treatment of Hazardous Wastes: Physical Chemical Mechanisms
Authors: Dauerman Leonard , Windgasse Gabriele , Zhu Naihong , He Yaoll 
Published: March 2011

ABSTRACTThe objective Is to develop processes to treat hazardous waste streams using microwave treatment. First, physical chemical mechanisms have been posited for a variety, of such waste streams including: soils contaminated with organics, and toxic heavy metals; “spent” GAC; organics in the gas phase. Second, feasibility tests are being carried out to determine if on-site field testing is warranted. In the case of microwave-induced steam distillation of volatile and semivolatile organics, pilot plant stuides indicate that the incident power cost is not prohibitive: that fear of prohibitive power costs has been thought to be the major drawback for micrwave treatment to become a competitive technology in this market.
Rapid High Temperature Measurement of Microwave Dielectric Properties
Authors: Tinga W.R. 
Published: March 2011

ABSTRACTPractical high temperature (above 500°C) dielectric measurement techniques are reviewed stating both advantages and limitations of known methods. Details of a new and practical dual frequency microwave high temperature dielectrometer are discussed. This dielectrometer technique is capable of measurements beyond 2000°C. Both heating of the small samples and the measurement of their complex dielectric constant is done simultaneously using both a medium power (60W) microwave source and a low power scalar network analyzer. Good accuracy is obtained and the measurement is capable of being totally automated. Presently, a measurement and heating cycle time of about 20 s is needed to completely characterize the sample's microwave dielectric response from 300°C to 1600°C. A second high temperature dielectrometer technique is discussed which requires only one microwave source of medium power level (60W). This method requires only the reflected power to be monitored during the microwave heating of the sample to obtain the complex permittivity versus temperature curve.
Polybenzene, A Predicted New Low Energy Form of Carbon
Authors: Adams Gary B. , O'Keeffe Michael , Sankey Otto F. , Page John B. 
Published: March 2011

ABSTRACTWe have used a first principles molecular dynamics technique to find the relaxed atomic geometry and the corresponding electronic structure of a simple novel form of threecoordinated solid carbon, which we name polybenzene. The polybenzene structure is found to have a substantially lower energy per atom (by 0.23 eV) than C60, yet contains only 24 atoms per unit cell. In addition we have calculated the zero wavevector vibrational spectrum for this novel carbon structure.
Electronic Structure of Doped Buckminsterfullerene
Authors: RosÉn Arne , Östling Daniel 
Published: March 2011

ABSTRACTMolecular cluster calculations within the local density approximation have been performed in a study of the electronic structure of the C60 molecule - “Buckminsterfullerene” doped with K, B and N. Calculations for the KC60 molecule, with the K atom located at the centre of the cage as well as at different positions inside or outside the cage, show how the valence 4s electron is transferred to the LUMO state of the bare C60 molecule. Doping with a B or N atom located at the centre of the cage creates a molecule with a partly occupied level of 2p character in the HOMO and LUMO gap, similar to donor and acceptor levels in the band gap of traditionally doped semiconductors. Doping by substitution of one or two of the carbon atoms in the cage with X = B or N, as modelled with the C59 X1 or C58X2 clusters, gives a different structure with a splitting of the HOMO and LUMO levels in the pure C60 molecule and with the creation of acceptor and donor levels with the substitution of B and N, respectively.
Electron-Phonon Coupling in Superconducting Alkali-Metal Doped Fullerenes
Authors: Jishi R.A. , Dresseliiaus M.S. 
Published: March 2011

ABSTRACTThe dimensionless electron-phonon coupling parameter in alkali metal-doped fullerenes isevaluated in a model whereby the electrons are treated within a tight binding formalism.The phonon mode frequencies and eigenvectors are obtained from a lattice dynamical modelwhich accurately fits all available experimental data on these modes. It is shown that the electrormphonon interaction can account for the relatively high values of the superconducting transition temperatures in alkali-metal fullerenes.
Synthesis of Fullerols from an Aqueous Acid Method
Authors: Chiang Long Y. , Swirczewski John. W. , Hsu Chang S. , Chowdhury S. K. , Cameron Steve , Creegan Andkathy 
Published: March 2011

ABSTRACTAn efficient aqueous acid chemistry for the preparation of fullerols, consisting of 14-15 hydroxyl moieties in an average structure, from C60 molecules is described.
Carbon Aerogels and Xerogels
Authors: Pekala Richard W. , Alviso Cynthia T. 
Published: March 2011

ABSTRACTThe aqueous polycondensation of resorcinol with formaldehyde proceeds through a sol-gel transition and results in the formation of highly crosslinked, transparent gels. If the solvent is simply evaporated from the pores of these gels, large capillary forces are exerted and a collapsed structure known as a xerogel is formed. In order to preserve the gel skeleton and minimize shrinkage, the aforementioned solvent or its substitute must be removed under supercritical conditions. The microporous material that results from this operation is known as an aerogel. Because resorcinol-formaldehyde aerogels and xerogels consist of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon monoliths. The resultant porous materials are black in color and no longer transparent, yet they retain the ultrafine cell size (< 50 nm), high surface area (600-800 m2 /g), and the interconnected particle morphology of their organic precursors. The thermal, acoustic, mechanical, and electrical properties of carbon aerogels/xerogels primarily depend upon polymerization conditions and pyrolysis temperature. In this paper, the chemistry-structure-property relationships of these unique materials will be discussed in detail.
Diamond Growth in an Oxy-Acetylene Flame by an Alternating Gas Ratio Technique
Authors: Sivazlian F. R. , von Windheim J. A. , Glass J.T. 
Published: March 2011

ABSTRACTDiamond films were grown using a computer controlled oxy-acetylene torch that allowed precise programming of O2 and C2H2 gas profiles. This enabled more accurate control of the diamond growth chemistry. With this torch, systematic and complex variations in gas chemistry were applied during growth and the resulting film morphology and film quality was investigated. Plan view scanning electron microscopy (SEM) revealed predominately (111) faceting as a result of a sawtooth variation in the O2:C2H2 gas ratio from 0.97 to 1.00. Raman spectroscopy indicated mostly sp3 bonding, with little non-diamond component present. Furthermore, crosssectional SEM showed small grains during normal growth (O2:C2H2 = 0.97), whereas grain size increased significantly after onset of a sawtooth variation in the gas ratio.
Scanning Atomic Force Microscopy and Scanning Electron Microscopy Study of Diamond Thin Films Grown by Microwave Plasma Enhanced Chemical Vapour Deposition
Authors: Ahn Jaeshin , Tan F.H. , Tan H.S. , Zhu W. 
Published: March 2011

ABSTRACTThe early stages of diamond thin film growth under various growth conditions have been investigated using Scanning Atomic Force Microscopy and Scanning Electron Microscopy. A series of experiment with various source gas combinations, substrate surface preparation methods and different substrates have been carried out to determine the effect on the diamond nucleation. The highest early nucleation density was obtained with CH4(1%)/H2 process among other gas combinations used. It is suggested that the atomic oxygen content should be kept minimum during the initial nucleation period of CVD diamond. It has been observed that diamond nucleation does not necessarily require diamond seeding dust. The silicon substrate polished with alumina powder showed diamond nucleation along the alumina scratched lines. In the process of diamond crystal growth, screw dislocations and stacking faults have been observed.
The Role of Heavy Hydrocarbons in Cvd Diamond Growth
Authors: Wu Ching-Hsong , Potter T. J. , Tamor M. A. 
Published: March 2011

ABSTRACTA mass spectrometric analysis of heavy hydrocarbons (HHCs) during hot-filament CVD diamond growth was performed together with in situ monitoring of the growth rate. Many HHCs were detected and tentatively identified. Of all HHCs studied, only diacetylene shows good correlation with the diamond growth rate under various deposition conditions. Its possible role is discussed.
Chemical and Structural Effects on Diamond C(111)-(2×1) Surface Exposed to F, H and Hydrocarbon Species
Authors: Yramada Taro , Chuang T.J. , Seki H. 
Published: March 2011

ABSTRACTAdsorption and subsequent surface processes of hydrogen and hydrocarbon species on the diamond C(111)-(2×1) bare surface have been investigated by AES, XPS, LEED, TDS and laser non-linear spectroscopies (SHG and SFG) under ultrahigh vacuum condition. Extremely low coverage of atomic II causes the transition of the hare (2×1) surface to the (1×1) structure. Exposure of the. bare (2×1) surface to CIIx species from hot filament activated methane leads to the formation mainly of CH3 species. The conversion of the surface structure from (2×1) to (1×1) with exposure does take place but not as easily as for hydrogen. These studies are now being extended to adsorption of F by exposures to XeF2 There arc two stages of saturation for 17 adsorption on the C(111)-(2×1) surface. This is interpreted to indicate that there are at least two adsorption sites for the F atoms. Whereas adsorption of II atoms at coverages less than 5% of a monolayer causes the surface lattice transition from (2×1) to (1×1) structure, the (2×1) structure is retained at all levels of fluorine adsorption. However the C(111) (1×1) surface with over half a monolayer of II adsorption behaves quite differently with respect to F adsorption.