bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution of Gas-Phase Reactions to the Deposition of SiC by A Forced-Flow Chemical Vapor Infiltration Process
Authors: Tsai Ching-Yi , Desu Seshu B.
Published: March 2011

A model, incorporating both gas-phase and surface reactions, for simulating thickness profile of SiC, deposited from trichloromethylsilane (TMS), along the longitudinal direction of a single pore is presented in this paper. The transport mechanisms considered include both forced-flow and diffusion. With the nonlinear nature of this model, a finite element model was developed to solve the problem numerically. Simulation results were in good agreement with the reported experimental data by Fedou et al. (1990). Effects of critical parameters, such as deposition temperature, ratio of sticking coefficients of TMS and intermediate species, and forced-flow, on the deposition thickness profile were investigated. Forced-flow effect was found to be small for the chemical vapor infiltration (CVI) processes at high deposition temperatures.
CVD of Silicon Carbide on Structural Fibers: Microstructure and Composition
Authors: Veitch Lisa C. , Terepka Francis M. , Gokoglu Suleyman A.
Published: March 2011

Structural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack.

Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 °C were studied. Silane (SiH4) and propane (C3H8.) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC-coating using electron microprobe. Microstructures for the different conditions were compared. At 1350°C, the microstructures were similar;however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.
The Oxidation Stability of Boron Nitride Thin Films on MgO and TiO2 Substrates
Authors: Qiu Xiaomei , Datye Abhaya K. , Paine Robert T. , Allard Lawrence. F.
Published: March 2011

The stability of BN thin film coatings (2–5 nm thick) on MgO and TiO2 substrates was investigated using transmission electron microscopy (TEM). The samples were heated in air for at least 16 hours at temperatures ranging from 773 K - 1273 K. On MgO supports, the BN thin film coating was lost by 1073 K due to a solid state reaction with the substrate leading to formation of Mg2B2O5. No such reaction occurred with the TiO2 substrate and the BN was stable even at 1273 K. However, the coating appeared to ball up and phase segregate into islands of near-graphitic BN and clumps of TiO2 (rutile). The oxidizing treatment appears to promote the transformation from turbostratic BN to graphitic BN.
Theoretical Study of Gas-Phase Thermodynamics Relevant to Silicon Carbide Chemical Vapor Deiposition
Authors: Allendorf Mark D. , Melius Carl F.
Published: March 2011

Equilibrium calculations are reported for conditions typical of silicon carbide (SiC) deposition from mixtures of silane and hydrocarbons. Included are 34 molecules containing both silicon and carbon, allowing an assessment to be made of the importance of organosilicon species (and organosilicon radicals in particular) to the deposition process. The results are used to suggest strategies for improved operation of SiC CVD processes.
Chemical Vapor Deposition of Copper Oxide Thin Films
Authors: Chang Yuneng , Schrader Glenn L.
Published: March 2011

Copper oxide films were prepared by organometallic chemical vapor deposition of copper acetylacetonate in an oxygen-rich environment. The films were characterized by X-ray diffraction, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. At 360 °C, Cu2O films were formed for an oxygen pressure of 150 torr and a copper acetylacetonate vapor pressure of 0.2 torr). The Cu2O film was polycrystalline, but the orientation was primarily [111]. Differential scanning calorimetry indicated that O2 assists decomposition of the organometallic precursor during pyrolysis.
Therirmochemistry in C.V.D. - on the Choice of Haliide Gas Species
Authors: Bernard C. , Madar R.
Published: March 2011

The production of thin or thick films of metals or ceramics by chemical vapour deposition has often been achieved by the use of halide gas precursors. In certain cases, this choice was made purely for reasons of simplicity: gas cylinder available, gas species already used in another field, etc. Experience has subsequently shown, however, that this choice can give rise to significant changes in the nature and proportions of deposited phases. These are highly dependent upon:

– the value of the oxidiser:reducer ratio in the gas phase,

– the degree of metal oxidation in the halide considered,

– possible competition between two reducing agents designed to reduce the halide.

These factors, among others, strongly influence the thermochemistry of the deposition reaction. Their roles must therefore be clearly understood, interpreted and predicted by the thermochemical analysis. Based on examples relating to silicide, nitride and boride deposits, an attempt will be made to determine the sensitive parameters and to deduce selection criteria.
Deposition of Tungsten Nitride thin Films from (tBuN)2w(NHtBu)2
Authors: Chiu Hsin-Tien , Chuang Shiow-Huey
Published: March 2011

The possibility of growing tungsten nitride thin films from (tBuN)2W(NHtBu)2, a single-source molecular precursor with two nitrogen to tungsten double bonds, by low pressure chemical vapor deposition (LPCVD) was investigated. Deposition of thin films on silicon and glass substrates was carried out at temperatures 500 – 650 °C in a cold-wall reactor while the precursor was vaporized at 60 – 100 °C. Elemental composition of the thin films, studied by wavelength dispersive spectroscopy (WDS), is best described as WNx (x = 0.8 – 1.8). Elemental distribution within the films, studied by Auger depth profiling, is uniform. X-ray diffraction (XRD) studies show that the films have a cubic structure with a lattice parameter a = 4.14 – 4.18 Å. A stoichiometric WN thin film has a lattice parameter a equal to 4.154 Å. Volatile products, trapped at −196°C, were analyzed by nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS). Isobutylene, acetonitrile, hydrogen cyanide and ammonia were detected in the condensable mixtures.
Diamond Deposition by a Nonequilibrium Plasma Jet
Authors: Keil D. G. , Calcote H. F. , Felder W.
Published: March 2011

A nonequilibrium plasma jet has been used to deposit diamond films on a number of substrates, including silicon, silicon nitride, alumina, and molybdenum. Hydrogen is passed through a glow discharge and expanded through a supersonic nozzle to produce a highly nonequilibrium jet. Methane is added downstream of the nozzle, where it mixes and reacts with the nonequilibrium concentration of hydrogen atoms. The resulting supersonic jet strikes the substrate surface producing a high quality (determined by laser Raman spectrometry) adherent diamond film. Because of the low jet temperature, substrate cooling is unnecessary. Diamond deposition rates have exceeded 2 mg/kWh and I μm/h averaged over 16 cm2 area; good quality films prepared at substrate temperatures below 600 K. have been
Onset Conditions for Gas Phase Reaction and Nucleation in the CVD of Transition Metal Oxides
Authors: Collins J. , Rosner D. E. , Castillo J.
Published: March 2011

A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No “vapor phase ignition” has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw=1700 K) and further experiments are planned using more reactive feed materials. The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.
Step Coverage Modeling of Thin Films Deposited by CVD Using Finite Element Method
Authors: Tsai Ching-Yi , Desu Seshu B.
Published: March 2011

A two—dimensional finite element model was developed to study the step coverage of submicron trenches with arbitrary shape under chemical vapor deposition processes. Parameters that characterize the step coverage were found to be the surface Damkohler number, ratio of diffusion coefficients inside and outside of the trench, and aspect ratio of the trench geometry. Efforts were concentrated on studying the step coverage of SiO2 film deposited from SiH4/O2 precursors within rectangular shape trenches. The model predictions were found to be in good agreement with reported experimental results.
Surface Chemistry of Fluorine-Containing Molecules Related to CVD Process on Silicon Nitride: SiF4, XeF2, and HF
Authors: Outka Duane A.
Published: March 2011

The reactivity of several fluorine-containing molecules on a polycrystalline silicon nitride (Si3N4) surface is studied under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). The chemistry of fluorine on Si3N4 is of interest in understanding the high temperature chemical vapor deposition (CVD) of Si3N4, which uses SiF4 as a starting material. XeF2 is reacted with a Si3N4 surface to prepare and characterize various surface SiFx (1 ≤ × ≤ 3) species. These are identified by the chemical shift induced by the fluorine atoms in the Si (LMM) Auger peak and by changes in the TPD. Of these species, SiF2 is stable to the highest temperature. SiF2 is also formed by the reaction of SiF4 with a Si3N4. Because SiF2 is so stable, its decomposition is proposed as a rate-determining step in the CVD deposition of Si3N4 from SiF4. Gaseous HF, which is a product of the CVD process, does not dissociate on Si3N4 and is therefore unlikely to cause the etch-like marks on the Si3N4 coating that are observed under certain conditions.
In-Situ Light-Scattering Measurements During the CVD of Polycrystalline Silicon Carbide
Authors: Sheldon Brian W. , Reichle Philip A. , Besmann Theodore M.
Published: March 2011

Light-scattering was used to monitor the chemical vapor deposition of silicon carbide from methyltrichlorosilane. The nucleation and growth of the SiC features caused changes in the surface topography that altered the angular scattering spectrum that was generated with a He-Ne laser. These scattering spectra were then analyzed to obtain information about the nucleation and growth processes that are occurring.
Impurity Gettering in Silicon by Thin Polycrystalline Films
Authors: Hayamizu Y. , Ushio S. , Takenaka T.
Published: March 2011

Capability of impurity gettering by thin polycrystalline films on the backside of silicon wafer was evaluated by minority-carrier diffusion length. Cu was gettered easily during usual cooling after high temperature annealing. On the other hand, intentional slow cooling or low temperature annealing was necessary for effective Fe gettering. The gettering efficiency for Fe increased with lowering the annealing temperature when Fe was diffused sufficiently. From the quantitative consideration of Fe gettering, we propose the model of impurity gettering based on the chemical equilibrium of impurity reaction in polysilicon films. It was also expected that gettering efficiency increased with the thickness of polysilicon film.
Defects Introduced by Plasma Processing of Silicon
Authors: Benton J. L.
Published: March 2011

The electrical and optical properties of defects introduced by Reactive Ion Etching (RIE) in the near surface region of Si after dry etching with various gases and plasma conditions is studied with spreading Resistance (SR), photoluminescence (PL), and capacitance-voltage profiling (C-V). Plasma etching in chlorine and fluorine based gases produce donors at the surface in both n-type and p-type, Czochralski and float-zone silicon. Isochronal annealing reveals the presence of two distinct regions of dopant compensation. The surface damage region is confined to 1000 Å and survives heat treatment at 400°C, while the defect reaction region extends ≥ 1 μm in depth and recovers by 250°C. A comprehensive picture of the interstitial defect reactions in RIE silicon is completed. The interstitial defects, Ci and Bi, created in the ion damaged near surface region, undergo recombination enhanced diffusion caused by the presence of ultraviolet light in the plasma, resulting in the long range diffusion into the Si bulk. Subsequently, the interstitial atoms are trapped by the background impurities forming the defect pairs, CiOi, CSCi, or BiOi, which are observed experimentally. The depth of the diffusion-limited trapping and the probability of forming specific pairs depends on the relative concentrations of the reactants, oxygen, carbon or boron, present in the bulk material.
Defect Formation by Ion Implantation in Cz-Si Studied by a Monoenergetic Positron Beam
Authors: Uedono A. , Ujihira Y. , Wei L. , Tabuki Y. , Tanigawa S. , Sugiura J. , Ogasawara M. , Tamura M.
Published: March 2011

Vacancy-type defects in ion implanted Si were studied by a monoenergetic positron beam. The depth-distributions of the defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. The results showed that a size of vacany-clusters introduced by 150-keV P+-ion implantation was found to be smaller than that introduced by 2-MeV P+-ion implantation. This was attributed to an overlap of collision cascades in low-energy (150 keV) ion implanted specimens. From isochronal annealing experiments for 80-keV B+- and 150-keV P+-ion implanted specimens, the defected region was removed by 1200 °C annealing, however, for 2-MeV P+-implanted specimen, two-types of oxygen-vacancy complexes were found to coexist even after 1200 °C annealing.
Generation of Defects and Strain by Ion Implantation in Ge (100) Single Crystals, and in Pseudomorphic GexSi1-x Films Grown on Si (100)
Authors: Lie D. Y. C. , Vantomme A. , Eisen F. , Nicolet M. -A. , Arbet-Engels V. , Wang K.L.
Published: March 2011

We have studied the damage and strain produced in Ge (100) single crystals by implantation of various doses of 300 keV 28Si ions at room temperature. The analyzing tools were x-ray double-crystal diffractometry, and MeV 4He channeling spectrometry. The damage induced by implantation produces positive strain in Ge (100). The maximum perpendicular strain and maximum defect concentration rise nonlinearly with increasing dose. These quantities are linearly related with a dose-independent coefficient of ∼ 0.013 for Ge (100) single crystals implanted at room temperature. The results are compared with those available for Si (100) self-implantation. We have also monitored the strain and defects generated in pseudomorphic Ge0.1Si0.9/Si (100) films induced by room temperature 28Si ion implantation. It is found that the relationship between the strain and defect concentration induced by ion implantation is no longer a simple linear one.
Dopant Dependent Extended Defect Nucleation and Growth Kinetics in Silicon During 1 Mev Electron Irradiation
Authors: Romano-Rodriguez Albert , Vanhellemont Jan
Published: March 2011

In this paper results of a study of electron irradiation induced extended defect generation in doped silicon is presented. The irradiations are performed in-situ with 1 MeV electrons in a high voltage transmission electron microscope. Preferential generation of extended defects is observed in certain areas of the sample which can be correlated with well defined dopant concentration levels. The defect growth kinetics is studied as a function of the irradiation temperature and dose and the type and concentration of dopant.

After the first irradiation experiment some of the samples received a second electron irradiation, during which shrinkage and even complete annihilation of the previously generated defects can be observed. The observed results are interpreted on the base of point defect reactions.
Formation of End-of-Range Defects in Silicon at Low Temperatures
Authors: Seibt M. , Imschweiler J. , Heftier H. -A.
Published: March 2011

We have used high resolution transmission electron microscopy to study the formation of end- of- range defects after pre- amorphization due to Ge+ - implantation and subsequent furnace annealing at temperatures below 550 C. It is shown that depending on the annealing conditions two types of extrinsic stacking faults (SFs) are formed, i.e. {113}- defects or Frank- type {111} SFs. We present a scheme allowing the controlled deposition of Si self- interstitials into {113}- defects, which can be removed more easily than Frank type SFs during subsequent RTA under constraints of low thermal budget.
Ion Implantation Defect Characterization by High-Resolution X-Ray Diffraction
Authors: Klappe Jos G.E. , Bársony István , Ryan Tom W.
Published: March 2011

High-energy ion-implantation is one of the roost critical processing steps regarding the formation of defects in mono-crystalline silicon. High- as well as low-doses implanted at various energies can result in relatively high residual defect concentrations after post-implantation annealing.

Before annealing, the crystal lattice strain is mainly caused by the point defects. After annealing, the accommodation of substitutional impurities is the main origin of the residual lattice strain. High-Resolution X-ray Diffraction (HRXD) has been frequently used for the characterization of these structures. Dislocation loops formed during the high temperature step, however, cause enhanced diffuse X-ray scattering, which can dominate the measured X-ray intensity in conventional HRXD.

Triple axis diffractometry is used in this study to analyze the size, type and location of defects in a boron implanted and rapid thermally annealed silicon sample.
Uniform Low-Temperature Deposition of Optical Layers by Plasma-Activated CVD
Authors: Lydtin Hans , Ritz Arnd
Published: March 2011

Plasma activated CVD in a remote operation mode is applied to the deposition of dielectric layers on extended substrates. Layer thickness uniformity of ±1% over areas of 80mm diameter is demonstrated. The microwave applicator sustaining the plasma source of condensable species is compared in its deposition characteristic to conventional evaporation sources. Deposition efficiencies up to 70% are reached. The layer materials used are SiO2 and TiO2. Multilayer structures are prepared and optically characterized.
Measurement of Microwave Induced Forces
Authors: Watkins John L. , Jackson H. W. , Barmatz M.
Published: March 2011

Electrically polarizable materials in an inhomogeneous electric field experience a dielectrophoretic force which is proportional to the gradient of the square of the electric field. For high frequency radiation, the time averaged electromagnetic field provides a dc force. The force exerted on a sapphire and a metal sphere by the microwave field in a single mode resonant cavity has been measured. The force measurements have been made at equally spaced points along three orthogonal axes centered in a cylindrical cavity operating in the TE111 mode using 20 watts of microwave power at about 4.84 GHz. These data are compared to the simple theory of dielectrophoresis on a small sphere and verify that, for this mode and in the absence of other forces, there is a unique and stable equilibrium position at the center of the cavity. Measurements of the quality factor of the cavity provide a means of making an absolute check to the theory. The TE111 mode is one of an infinite set of modes predicted to have stable equilibrium positions that exist away from the cavity walls. It is proposed that dielectrophoresis in a microwave resonant cavity can be used to position samples for material processing applications in a microgravity environment. Knowledge of these forces may also be important for interpreting thermogravimetric measurements made in a microwave oven.
Interaction between Gyrotron Radiation and Powder Materials
Authors: Sklyarevich V. , Detkov A. , Shevelev M. , Decker R.
Published: March 2011

To capitilize on the special advantages of gyrotron radiation for fast and continuous materials processing, surface and interface layers are ‘alloyed’ with lossy chemicals and fine-disperse powders. The principles and practical uses are described herein.
Fabrication of Hydroxyapatite Ceramics by Microwave Processing
Authors: Agrawal Dinesh. K. , Fang Y. , Roy D. M. , Roy R.
Published: March 2011

Various hydroxyapatite (HAp) ceramics were fabricated by microwave processing. By carefully selecting the starting material and controlling the processing conditions, regular HAp ceramics with density up to 97% of the theoretical density, porous HAp ceramics with porosity up to 76%, and fully densified transparent HAp ceramics were obtained by using a 2.45 GHz, 500W microwave oven. These ceramics were characterized for density, microstructure, strength, and phase composition, and the results were compared with the conventionally processed ceramics.
Microwave Sintering of Oxide Ceramics
Authors: Brandon J.R. , Samuels J. , Hodgkins W.R.
Published: March 2011

The activities of EA Technology in microwave processing of oxide ceramics are reviewed. Comparative sintering rate measurement techniques have been used to demonstrate microwave enhanced densification of oxide ceramics. Temperature distributions within microwave and conventionally heated ceramics are simulated. Based on these simulations a method for firing large components has been developed which achieves uniform microstructures and low thermal stresses by careful control of temperature distribution.
Processing Aerosols and Filaments in a TM010 Microwave Cavity at 2.45 GHz
Authors: Vogt Gerald J. , Unruh Wesley P.
Published: March 2011

As part of the development of generic microwave processes for spray-drying of homogeneous complex metal oxide powders and for inorganic fiber processing, we have investigated the use of 2.45 GHz microwaves in a high-Q single-mode TM010 cavity coupled directly to aerosols and fibers. Aqueous and ethanol aerosols of ferric nitrate solutions have been successfully dried at 1.8 kW of cavity power for a loaded Q greater than 6000 in flowing nitrogen gas. Similarly, we have observed extremely rapid heating rates in the TM0l0 cavity for small-diameter confined cylinders of water and lossy inorganic fibers. These observations suggest using 2.45 GHz microwave power for drying, calcining, and sintering extruded ceramic filaments. Droplet modeling indicates that the large dielectric shielding for spherical droplets can significantly limit the coupling of 2.45 GHz microwave with spherical aerosols, but not with fibers. Experimental observations on the microwave interactions with ferric nitrate aerosols and with ceramic filaments in the TM010 cavity are described.
Nitridation of Non-Isothermal Silicon Compacts
Authors: Thomas Jeffrey J. , Jesse Renee R. , Johnson D. Lynn , Jennings Hamlin M.
Published: March 2011

The use of microwave heating for the processing of reaction-bonded silicon nitride offers at least two advantages over conventional heating methods. First, the reaction can be made to proceed preferentially in the interior of the reacting compact by maximizing the temperature gradient resulting from microwave heating. This helps maintain the flow of nitrogen into the compact during the later stages of the reaction, when the overall porosity is reduced. Second, the reaction rate can be controlled by changing the power, which gives better control over the processing than can be obtained using conventional heating.
Characterization of Sintered Reaction-Bonded Silicon Nitride Processed by Microwave Heating
Authors: Kiggans J. O. , Tiegs T. N.
Published: March 2011

Sintered reaction-bonded silicon nitride (SRBSN) tiles were fabricated using microwave and conventional heating. Materials from both processes were analyzed at various stages in their fabrication. Microwave processing resulted in a SRBSN material of higher density and strength than the conventionally processed material.
Mechanica and Physical Properties of Microwave Sintered Si3N4
Authors: Patterson M.C.L. , Apte P.S. , Kimber R.M. , Roy R.
Published: March 2011

Microwave energy at 2.45 GHz has been used to sinter silicon nitride in times of between 30 and 120 minutes to form a dense product with an average grain size of 0.35 μm and substantially improved uniformity of properties over all commercial silicon nitrides and sialons investigated.

A comparison between microwave and conventionally sintered parts of the same density showed the average mechanical properties to be the same for both sintering techniques, but revealed an improvement in the uniformity of mechanical properties of the microwave sintered products.

Silicon nitride components with 5% Al2O3 and 5% Y2O3 as sintering aids, has been sintered to a density of approximately 97% of theoretical. Hipping of these components at 1800 °C for 60 minutes, resulted in the complete removal of residual porosity. Dense components were evaluated in machining tests against commercial ceramic cutting tools. The results show a reduction in wear rate of batter than 10% for microwave sintered Sl3N4 in turning and milling operations on cast iron at a cutting speed of 2000 surface feet per minute.
Microwave Sintering of Si3N4 Ceramics
Authors: Zhang Jinsong , Cao Lihua , Xia Fei
Published: March 2011

The Si3N4 ceramics(91wt%Si3N4+5wt%Y2O3+4wt%Al2O3) of room temperature strength 620--760 MPa and fracture toughness 7 MPa-m½ were prepared by microwave sintering and their microstructure and mechanical properties were studied.The experiment results show that the higher N2 pressure (>4atm) is very necessary for microwave sintering of Si3N4 ceramics; microwave sintering can greatly decrease the sintering temperature to 1500* C, and increase the transformation rate of α to β-Si3N4,and reduce the total sintering time to about 1 hour. The mechanical properties of the Si3N4 ceramics sintered by microwave are better than that by conventional pressureless sintering.
Polymethyl Methacrylate Binder Removal from an Alumina Compact: Microwave Versus Conventional Heating
Authors: Moore Edmund H. , Clark David E. , Hutcheon Ronald
Published: March 2011

Compact samples of alumina and polymethyl methacrylate have been heated in a 2.45 GHz microwave cavity and by conventional heating in an electric furnace. Various heating schedules have been used to effect the removal of the polymeric binder by thermal decomposition. Dielectric properties, porosity and other physical properties have been investigated in order to better understand the binder removal process in a microwave field. Results of the study emphasize the amount of carbon residuals remaining in the bulk.
Surface Modification of Ceramics Using Microwave Energy
Authors: Fathi Z. , Clark D.E. , Hutcheon R.
Published: March 2011

Sodium alumino-silicate glasses having a constant concentration of alkali ions (15mol%) were prepared. The interdiffusion of potassium ions, K+, for sodium ions, Na+, in the glass composition having AI/Na= 1 was investigated in the presence and absence of a microwave field. Characterization consisted of dielectric loss measurements, electron microprobe analysis (EMP), and microhardness indentation.
Electron Microscopy Study on Zirconia and Alumina Ceramic Powders Synthesized by Microwave Plasma Pyrolysis
Authors: Sickafus Kurt E. , Vollath Dieter , Varma Ravi
Published: March 2011

Morphology, chemistry and microstructure of zirconia and alumina based ceramic powders synthesized by microwave plasma pyrolysis were studied by transmission electron microscopy. Electron diffraction was used to determine the phases present, while conventional bright field and dark field imaging were used to characterize grain size and density variations. Materials analyzed in this study were either pure zirconia, pure alumina, or a ternary zirconia-yttria-alumina oxide. Solid spheres, hollow spheres, and fragments of hollow spheres were observed. All three modifications of zirconia were observed in the pure zirconia powder. In alumina, the predominant phase was cubic, gamma alumina. In the ternary oxide, most structures exhibited cubic zirconia diffraction patterns. Energy dispersive x-ray spectroscopy revealed chemical inhomogeneities in the ternary oxide powder.
Microwave Processing of Aluminum-Silicon Carbide Cermets
Authors: Bescher Eric P. , Sarkar Urmimala , MacKenzie John D.
Published: March 2011

Electromagnetic radiation in the microwave range has been utilized for the fabrication of SiC particulates-reinforced aluminum matrix cermets. Powder mixtures with compositions ranging from 70 wt% Al - 30wt% SiC to 100 wt% Al were placed and processed under protective nitrogen atmosphere in a 750 W multimode cavity operating at 2.45 GHz. Temperatures larger than 800°C have been achieved in a time varying with the mixture composition. Microstructures and some physical properties of the composites are presented.
Synthesis of Nanocrystalline Powders for Oxide Ceramics by Microwave Plasma Pyrolysis
Authors: Vollath Dieter , Varma Ravi , Sickafus Kurt E.
Published: March 2011

Pyrolytically prepared ceramic powders usually exhibit excellent homogeneity and small grain sizes. The energy efficiency of those methods for synthesis is, particularly in systems heated electrically, very poor. The situation can be improved drastically using a microwave plasma as a source of energy. This has been confirmed by the synthesis of alumina- and zirconia-based ceramic powders for which an efficiency of more than 80% was found. Aqueous solutions of nitrates of zirconium, yttrium, and aluminum were used as starting materials. Electron microscopy revealed that, through proper selection of the experimental conditions, it is possible to obtain nanocrystalline powders with cubic structure. Because of the extreme conditions during synthesis, it is possible to prepare solid solutions in systems without solubility.
Microwave-Assisted Organic Synthesis
Authors: Giguere Raymond J.
Published: March 2011

A concise overview of the use of microwave heating in organic synthesis is presented. The role of solvents and representative examples from the relevant literature are discussed to illustrate the significant impact this non-conventional heating mode continues to have in this area of materials research.
RF Processing of Thermoset and Thermoplastic Composites
Authors: Pearce John A. , Faulkner Carl M.
Published: March 2011

Graphite fiber-thermoset epoxy resin composite materials are frequently used in aerospace and related industries. Electromagnetic heating may have some advantages over the present autoclave techniques, especially for large objects. However, the loss factor of graphite composites at microwave frequencies (915 MHz and 2.45 GHz) is so high that the depth of penetration is no more than about 0.1 mm. Arcing may be encountered at high heating rates due to strong transverse E-fields. Also, since the curing process is exothermic and the surface is at elevated temperature, thermal runaway may be encountered in the interior spaces and result in over-cured (thermally damaged) material.

We have investigated the heating obtained at radio frequency (nominal 27 MHz) in magnetic induction fields in both experiments and numerical models. Inductive coupling has the advantage that arcing is virtually eliminated, even at high heating rates, for typical cylindrical geometries. Also, induction heating easily accomplishes lap seam welds in thermoplastic composites owing to favorable electric field boundary conditions. Transient temperatures were recorded during heating by optical fiber probes and heating distribution was measured, where possible, using thermographic imaging. Finite difference electrical and thermal model results illustrate the dominance of conduction heat transfer in these materials.
Microwave Dynamic Dielectric Analysis of Curing Neat Resins
Authors: King Ray J. , Werner Michael J. , Mayorga Guillermo D.
Published: March 2011

Microwave reflection resonator sensors have been developed to monitor the dynamic, in situ real and imaginary dielectric components (ε′, ε″) of thermoset polymer matrix composites and thermoplastics. These reusable and noninvasive sensors are conformably mounted in the autoclave mold in such a manner that the EM fields are strongly coupled to the resin. Tracking of (ε′, ε″) during the cure provides information about the chemical kinetics such as timing the point of minimum viscosity and monitoring the relative cure index. The sensor is readily adjustable for optimum coupling to the type of material being tested and is rated for temperatures up to 250°C (480*F). The technique is complementary to other analysis techniques such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). A prototype software and electronics package has been developed to support the sensor.
Preliminary Comparison of Microwave Heating of Complex-Shaped Composites Reinforced with Conductive and Nonconductive Fibers
Authors: Fellows Larry A. , Travis Susannah , Hawley Martin C.
Published: March 2011

The microwave heating of composites with complex shapes has been studied. A V-shaped mold was used to fabricate samples which do not lie parallel to the electric field produced in a 7-in. cylindrical microwave applicator operating at 2.45 GHz.

A polyester/glass composite and a polyester/graphite fiber composite were produced for comparison. Heating profiles were made more uniform by applying mode-switching techniques to the processing. Mode-switching is the application of more than one electromagnetic mode to achieve uniform heating.

The samples were tested for heating patterns in different geometric and fiber orientations within a single-frequency, cylindrical microwave applicator operating at 2.45 GHz. The temperature profile for each mode was recorded. Mode-switching provided better temperature profiles than single modes. Modeswitching techniques were more successful with the graphite fiber reinforcement.
Finite-Difference Time-Domain (FDTD) Simulation of Microwave Sintering in Multimode Cavities
Authors: Smith Ray L. , Iskander Magdy F. , Andrade Octavio , Kimrey Hal
Published: March 2011

Microwave sintering of ceramics in multimode cavities, particularly the use of picket-fence arrangements, has recently received considerable attention. Various types of ceramics have been successfully sintered and, in some cases, a desirable and unique “microwave effect” has been observed.

At present, various aspects of the sintering process such as sample sizes and shapes, types of insulations, and the desirability of including a process stimulus such as SiC rods are considered forms of art and highly dependent on human expertise. The simulation of realistic sintering experiments in a multimode cavity may provide a better understanding of critical parameters involved and allow for the development of guidelines towards the optimization of the sintering process.

In this paper, we utilize the FDTD technique to model various geometrical arrangements and material compatibility aspects in multimode microwave cavities and to simulate realistic sintering experiments. The FDTD procedure starts with the simulation of a field distribution in multimode microwave cavities that resembles a set of measured data using liquid crystal sheets. Also included in the simulation is the waveguide feed as well as a dielectric loading plate placed at the base of the cavity. The FDTD simulation thus provides realistic representation of a typical sintering experiment. Aspects that have been successfully simulated include types of insulation, role of SiC rods on the uniformity of the resulting fields, problems that may result from presence of thermocouples, and the possible shielding effects that may result from excessive use of SiC. These results as well as others showing the electromagnetic fields and power-deposition patterns in multiple ceramic samples are presented.
Immobilization of ASH by Microwave Melting
Authors: Morita Kazuki , Nguyen Vinh Q. , Nakaoka Ron , Mackenzie John D.
Published: March 2011

Non-radioactive ash was immobilized via microwave melting. The ash composed mainly of silica (SiO2), titania (TiO2), calcia (CaO), alumina (Al2O3), and carbon (C). The ash was melted with various additives, such as magnetite (Fe3O4), lithium carbonate (Li2CO3), sodium carbonate (Na2CO3), and boron oxide (B2O3) by using a 2.45 GHz, 750 W microwave oven. Samples with different ash and additive concentrations were melted when subjected to microwave radiation. Ease of melting was dependent on the carbon and magnetite concentrations. Melted samples were characterized by X-ray diffraction and scanning electron microscopy (SEM), and subjected to the Toxicity Characteristic Leaching Procedure in regard to lead (Pb) immobilization. Melted samples with more than 30 wt% additives has an undetectable leaching rate of less than 0.1 ppm of lead for TCLP test, which was found to be due to the reduction and evaporation of the lead during melting. More than 80 % of the lead was lost through evaporation leaving less than 0.1 wt% Pb in the melted glass.
High Temperature Broadband Dielectric Properties Measurement Techniques
Authors: Andrade Octavio M. , Iskander Magdy F. , Bringhurst Shane
Published: March 2011

This paper discusses theoretical and practical aspects of the development and implementation of various measurement techniques for high-temperature broadband microwave characterization of materials at the University of Utah. Objectives include materials measurements in the frequency range from 45 MHz to 12 GHz and for temperatures as high as 1000°C.
General Purpose High Temperature Microwave Measurement of Electromagnetic Properties
Authors: Batt John A. , Rukus Robert , Gilden Meyer
Published: March 2011

An efficient general purpose method has been developed for implementing a variety of broad band microwave measurement techniques at high temperature. Central to these techniques has been the development of a “dual-waveguide” test fixture. These techniques have been selected, out of necessity, to cover a variety of material types and geometries such as slabs, posts and sheets. These include measurement of complex permittivity and permeability using a modified Nicolson-Ross technique for slabs and Marcuwitz' algorithm for posts. In the implementation of the dual-waveguide, two adjacent and symmetric X-band waveguides are machined from a single block of Inconel alloy 601*, one serving as a test waveguide, the other as a reference waveguide. The dual-waveguide is surrounded by a programmable clam-shell furnace. The reference waveguide provides data which is used to compensate for electrical and dimensional thermal changes in the test section. Combined with commonly used HP 8510 Network Analyzer methods, automated test procedures have been developed to accommodate the various measurement types and sample shapes. Prototypical data will be presented illustrating the effectiveness of some of these techniques. The methods discussed are most useful for rapid data generation over temperatures ranging from room temperature to 2000 degrees F (1093 degrees C) and at frequencies defined by the waveguide dimensions. This paper highlights developments in the dual waveguide system since its construction over one year ago.
Microwave Heating and Characterization of Machinable Ceramics
Authors: Xi Weiguo , Tinga W.R.
Published: March 2011

The dielectric properties of three types of machinable ceramics have been investigated using an automatic microwave dielectrometer system from 300°C to 1600°C at 3GHz. The system setup and techniques are described, and results are presented.
Complex Permittivity Studies of Polyaniline
Authors: Buckley Leonard J. , Dudeck Kenneth E.
Published: March 2011

A study of the complex dielectric properties at microwave and millimeterwave frequencies on several polyanilines was performed. The polymers investigated were based on emeraldine salts. The chemically synthesized emeraldine base was protonated with acids of various pH levels. Aqueous HCI (pH range 0.12 to 1.07) and Tosylic (pH range 0.22 to 1.13) were used. Complex permittivities of the emeraldine base and salts were determined at X-band and R-band using waveguide measurements. Characterization techniques were developed to reduce the measurement error. This included the electrical determination of the sample holder length and sample position. The real component of the dielectric constant was found to vary from 4 to 107 at Xband and from 3.8 to 926 at R-band. The dielectric loss spanned 3 orders of magnitude at X-band and 4 orders of magnitude at Rband. The frequency dependence was relatively level within each band with a slight decrease in each permittivity component with increasing frequency. The DC conductivity ranged from 10−4 S/cm to 10−1 S/cm for the emeraldine salts. The time dependence of the complex permittivity and DC conductivity was examined.
Observed Trends in The Dielectric Properties of Minerals at Elevated Temperatures
Authors: Holderfield Sonya P. , Salsman J. B.
Published: March 2011

Researchers at the U.S. Bureau of Mines' Tuscaloosa Research Center have measured the dielectric properties of over 60 minerals. Thirty-eight of these minerals have been identified as containing elements such as Co, Pt, and Ni, which are considered to be critical and strategic to the Nation. The dielectric properties were measured over the temperature range of 25° to325° C and microwave frequencies of 300 MHz to 3 GHz.

The data were analyzed to determine if trends could be detected in the dielectric properties of minerals having the same crystalline structure and/or mineralogical classification. Such trends would make possible realistic assumptions about how these classes of minerals would be affected by microwave energy without specific knowledge of their dielectric properties.
Dynamic Model for Calculating Heating Patterns During Microwave Sintering
Authors: Tucker James , Smith Ray , Iskander Magdy F. , Andrade Octavio M.
Published: March 2011

Analysis of dynamic development of heating patterns during microwave sintering provides vital information on the evolution of the heating process and the contributions from the various components in a complex sintering arrangement (picket fence) to the heat-transfer mechanism. Measured heating patterns often provide overall effects, and it is difficult to isolate and control the various contributions. To this end, results from numerical simulation may be significant.

In this paper we describe a thermal model that calculates the temperature distribution in ceramic samples and insulation under realistic sintering conditions. The calculation process involves a two-step procedure. The first step is to calculate the microwave power deposition in the sample and surrounding insulation. 3D FDTD calculations described in a companion paper are used for this purpose [1] The other step involves calculation of the temperature distribution using a 3D finite-difference heat-transfer program developed in our department.Results illustrating the effect of thickness of insulation and the placement of SiC rods in picket-fence arrangement are presented. Also, the need to measure additional parameters such as thermal conductivity and density of green samples as a function of temperature during sintering is discussed.
High Temperature Dielectric Measurements on Ceramics
Authors: Aral M , Binner J G P , Carr G E , Cross T E
Published: March 2011

The use of microwave frequency radiation as an alternative energy source for processing materials is currently receiving considerable worldwide attention. The ability of a material to extract energy from the microwave field depends upon its dielectric properties, however these change as the material heats. There is, therefore, a need for obtaining measurements of the microwave dielectric properties at elevated temperatures. This paper outlines some of the current work on high temperature dielectric measurements which is in progress at the University of Nottingham as part of the Materials and Microwave Processing Group initiative and some results on engineering ceramics are presented.
Multikilowatt Variable Frequency Microwave Furnace
Authors: Bible D. W. , Lauf R. J. , Everleigh C. A.
Published: March 2011

We describe a new type of microwave processing furnace in which the frequency can be varied continuously from 4 to 8 GHz and the power level varied from zero up to 2.5 kW. The extraordinary bandwidth of this furnace is achieved by using a traveling wave tube (TWT) amplifier originally developed for electronic warfare applications. The TWT is a linear beam device characterized by a traveling electromagnetic wave that continuously extracts energy longitudinally along the path of an electron beam. The TWT, unlike other microwave tubes such as the magnetron, klystron, gyrotron, and others, does not depend upon resonant RF fields and is therefore capable of wide bandwidth operation.
Structural Studies of Submonolayers of Carbon Atoms on Graphite
Authors: Ge M. , Sattler K. , Xhie J. , Venkateswaran N.
Published: March 2011

Submonolayer coverages of carbon adsorbed on highly-oriented pyrolytic graphite were examined by scanning tunneling microscopy under ultra-high vacuum condition. Linear carbon wires were found on atomically flat graphite surfaces. The wires had different thicknesses, from single atomic width to about lnm. The long wires extended to over several hundred nanometers. Two directions, graphite β-β direction and 30° rotated, were preferred for the long wire orientation. Parallel wire alignment, with several nanometers of inter-wire spacings were observed. Carbon particles, from 0.7 to 2 nm in diameter were found to be attached to the carbon wires. Particles from different wires formed parallel linear chains about perpendicular to the wire direction.
One- and Two-Dimensional Carbon Clusters: Isomers, Structures and Isomer Abundances.
Authors: Helden Gert von , Hsu Ming-Teh , Kemper Paul R. , Bowers Michael T.
Published: March 2011

The new technique of ion structural chromatography is applied to carbon clusters. The results indicate that C5+ and C6+ are purely linear but C7+, C8+, C9+ and C1O+ have both linear and monocyclic ring structures. From C11+ to C20+ only monocyclic ring structures are observed. At C21+, a new family of planar ring structures appears. The first 3 dimensional structure occurs at C29+ and the first fullerene at C30+. Isomer structure is verified by the comparison of experimental mobilities with those derived from theory for the various structures. For C20+ only the monocyclic ring is observed experimentally but electronic structure calculations suggest more compact structures might be lower in energy. The results are discussed in terms of possible growth mechanisms for C60.
Favorable Structures for Higher Fullerenes
Authors: Schmalz T. G. , Klein D. J. , Liu X.
Published: March 2011

Methods have been developed for the systematic generation of all fullerene isomers and for screening them to identify potentially stable structures. Some structural features associated with stable fullerenes are identified.