bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements and Simulations of Temperatures in Polyimide During Excimer Laser Ablation
Authors: Brunco D. P. , Thompson Michael O. , Otis C. E. , Goodwint P. M.
Published: March 2011

The temperature at the interface between a thin polyimide film and a quartz substrate was monitored as a function of time during KrF (248 nm) laser-induced heating and ablation using thin film NiSi thermistors. These experimental temperature measurements were coupled with heat flow simulations to obtain time-resolved temperature profiles in the polyimide. Thermal properties of the polyimide were estimated by requiring that the simulations reproduce experimental temperature profiles. The peak surface temperature in the polyimide at the onset of ablation was subsequently estimated from these simulations, producing a value of 1660 ± 100 K at the observed ablation threshold fluence of 36 mJ/cm2. Simulations were also used to explore the role of pulse duration on polyimide ablation.
Deposition of Thin Film SrFeO2.5+x by Pulsed Laser Ablation
Authors: Sanders Brian W. , Post Michael L.
Published: March 2011

Pulsed laser ablation has been used to deposit thin perovskite films based on the formula: SrFeO2.5+x (x = 0 to ≈ 0.5). Good quality films have been deposited on (1102) and AT cut quartz substrates at temperatures ranging from 300 to 1130 K. Films grown below 770 K showed little or no preferential crystallinity. Temperatures around 913 K produced films predominantly oriented (200), while temperatures greater than 1000 K produced films with (110) orientation. Films were grown from pellets of two compositions (SrFeO2.5, and SrFeO≈3). The former had a higher ablation threshold than the latter. The atmosphere during cooling had a greater effect on the film's oxygen content than the growth atmosphere. Films cooled in vacuum had the brownmillerite structure (x=0), whereas films cooled in 53.3 kPa oxygen had the cubic perovskite structure (x≈0.5).
Microanalysis of Calcium-Aluminosilicate Glass Films Grown on α-Al2O3 by Pulsed-Laser Ablation
Authors: Mallamaci Michael P. , Bentley James , Carter C. Barry
Published: March 2011

Pulsed-laser ablation has been used to deposit amorphous calcium-aluminosilicate films on α-Al2O3 single-crystal substrates. The microstructure and composition of each glass film was characterized using analytical electron microscopy (AEM). Composition was dependent on substrate temperature during deposition and thickness of the deposited glass layer.
Laser Ablation Deposition of Germanium Oxide Thin Films
Authors: Wolf Paul J. , Christensen Thomas M. , Coit Nathan G. , Swinford Richard W.
Published: March 2011

Laser pulsed sputtering of GeO2 targets in both vacuum and oxygen environments is us;ed to produce germanium oxide thin films. Infrared transmission and Auger electron spectroscopies are employed to infer compositional information on the films. The films grown in vacuum are oxygen deficient and they show a radial variation in the metal to oxide content. In contrast, the films grown in an oxygen atmosphere appear stoichiometric along the entire film.
Growth of ZnSe Epitaxial Layers and ZnSe/ZnS Superlattices by Pulsed Laser Deposition
Authors: Rajakarunanayake Y. , Luo Y. , Adkins B. T. , Compaan A.
Published: March 2011

We report the successful growth of ZnSe and ZnSe/ZnS superlattices on GaAs by pulsed laser deposition. An XeCl excimer laser operated at 308 nm was used to ablate/evaporate Il-VI bulk targets in an ultra high vacuum enclosure. For typical growth temperatures in the range 350°–450°C we obtained epitaxial layers with excellent optical properties. The laser power and fluence were varied to produce growth rates in the range 0.1–1 Å/pulse. The photoluminescence of the pulsed laser deposited ZnSe layers showed dominant bound and free exciton features. The superlattice samples showed large blue shifts (∼400 meV) in the photoluminescence as the layer thicknesses were varied. These results are consistent with strong quantum confinement of the heavy holes in the ZnSe layers (valence band offset for ZnSe/ZnS ∼ 850±100 meV), while the electrons are not confined to either layer because of very small conduction band offsets Strong exciton photoluminescence exhibited by our samples indicates that pulsed laser deposition is a promising growth technique for the fabrication of iI-VI epitaxial layers and strained layer superlattices for visible light emitter applications.
Laser Processing, Characterization, and Modeling of Epitaxial Si/TiN/Si (100) Heterostructures
Authors: Chowdhury Rina , Chen X. , Jagannadham K. , Narayan J.
Published: March 2011

We have successfully deposited multilayer Si/ITiN/Si(100) epitaxial heterostructures at a substrate temperature of 600°C in a chamber maintained at a vacuum of ∼10−7 torr using pulsed laser (KrF: λ = 248 nm, τ = 25 ns) deposition. This silicon-on-conductor device configuration has potential applications in three-dimensional integrated circuits and radiation hard devices.The two interfaces were quite sharp without any indication of interfacial reaction between them. The epitaxial relationship was found to be <100> Si II<100> TiN II<100> Si. In the plane, four unit cells of TiN matched with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides the mechanism of epitaxial growth in systems with large lattice mismatch. Energetics and growth characteristics of such domain matching epitaxy in the high lattice mismatch Si/TiN/Si(100) system and possible device implications are discussed.
Amorphic Diamond Films Produced by Laser Ablation
Authors: Collins C. B. , Davanloo F. , Lee T. J. , You J. H. , Park H.
Published: March 2011

Four types of diamond films have been shown to be stable and free from hydrogen: crystalline diamond, amorphic diamond, i-C and defected graphite. Each is significantly harder than other forms of carbon, but only now are quantitative values of hardness being reported. In this work nanoindentation techniques were used on these highly elastic films and linear ranges of plastic response were identified. Values of hardness were extracted from the on-load data for amorphic diamond and crystalline diamond that could not be distinguished from the hardness of naturally occurring diamond. This seems to explain why thin layers of amorphic diamond have been so effective in protecting substrates from the erosive impacts of particles and droplets reported in previous studies.
Cage Breaking Threshold in DLPD of C60
Authors: Hascicek Yusuf S. , Kleinhammes Alfred , Testardi Louis R.
Published: March 2011

Thin film patterns of desired shape or configuration made of about 15 μm - lines were directly written from a disk of C60 by employing a new laser technique called direct laser patterned deposition (DLPD). DLPD is an ambient technique, needing no special environment or material preparation. Since the ablation and deposition are very localized and deposition and patterning are done in one step this is a very cost efficient process. An energy density threshold was found. Above this density resistance of DLPD films dropped sharply indicating that the C60 cage was broken at least in part of the film.
X-Ray Photoelectron Spectroscopy of Polytetrafluoroethylene Thin Films Grown by Pulsed Laser Deposition
Authors: Shah S. Ismat , Blanchet Graciela B.
Published: March 2011

Polytetrafluoroethylene (PTFE) films were prepared by laser ablation of bulk PTFE targets using a Nd-YAG laser (4th. harmonic). Both low and high molecular weight PTFE targets were used. X-ray Photoelectron Spectroscopy of the deposited films indicates that under certain deposition conditions it is possible to transfer the material of correct composition from the target onto the substrate. Films ablated with lower laser fluence were fluorine deficient. Fluorine deficiency leads to the formation of CF, CHF, and crosslinked carbon impurities. The background gas in the deposition chamber does not seem to have much effect on the composition. Films deposited with either Ar or CF4 as the background gas have similar compositions. The oxygen concentration of the films decreases with the increase in the laser fluence. At the highest fluence used, 1.5 J/cm2, the O concentration was less than 1% regardless of the molecular weight of the target material.
Molecular-Dynamics Simulations of Laser-Ablation and Ionassisted Thin Film Deposition
Authors: Feil H. , Kools J.S.C. , Dieleman J.
Published: March 2011

Molecular dynamics simulations are performed of Cu thin film growth on Cu (111). Ion-Assisted Deposition is simulated by bombarding the substrate with Cu+ ions with a kinetic energy of 80 eV, while 1 eV Cu atoms are used for the simulation of Laser Ablation Deposition. It appears that Ion-Assisted Deposition leads to sputtering, enhanced surface mobility, surface disorder, mixing and rather deep damage. This is discussed in some detail. Laser Ablation Deposition, using laser fluences just above the ablation threshold, does not lead to damage and mixing. Sharper interfaces and more perfect heterostructures and superlattices can be produced using Laser Ablation Deposition.
Imaging and Characterization of Plasma Plumes Produced During Laser Ablation of Zirconium Carbide
Authors: Butt Darryl P. , Wantuck Paul J.
Published: March 2011

Laser diagnostic methods are developed and used to characterize the behavior of laser ablated zirconium carbide (ZrC). Emission from zirconium atoms dominates the total emission of the plasma plumes, which are estimated to have excitation temperatures of 9000 to 12,000 K under the conditions studied. Emission from species such as C, C2, and C3 were absent from the spectra due to the inherently low emission intensities of these species compared with that of Zr. Using a CCD camera, images of the plasma plumes are obtained from the emission and through the use of planar laser induced fluorescence of zirconium atoms.
Thermal Properties of Nanocrystalline Silver
Authors: Wu Xijun , Zhang Hongfei , Qin Xiaoying , Chen Lifang , Wang Guanzhong , Fang Rongchuan
Published: March 2011

The thermal properties of the nanocrystalline metal Ag (n-Ag), with the average grain size of 10 run, synthesized by an inert gas condensation and in situ compacting technique under different pressures of 0.2 to 1.5 GPa were studied. The thermal stable temperature for asprepared state is 373K, above which the grain growth appears at different rates. An exothermal peak and an endothermal peak occur on the DSC curves of the n-Ag. The enthalpy of both peaks are dependent upon the compacting pressure. Tht enhancement of the specific heat in going from the polycrystalline to the nanocrystalline state varies between 5.4% and 3.6% in the temperature range of 380K to 540K. The thermal diffusivity at room temperature increases with grain growth, and approaches to the corresponding value of the polycrystalline Ag.
Processing of Chromium Silicide-Silicon Carbide Nanostructured Composite by Thermal Conversion of Spray Dried Precursor Powders
Authors: Luo Ping , Strutt P. I.
Published: March 2011

A new group of nanostructured composites with chromium silicide and silicon carbide has been developed. These composite powders which are about 20-40 rm in size were prepared by the chemical synthesis route and were characterized by UV, DTA/TGA, XRD, FTIR and SEM. Chemical reaction and phase formation versus the processing temperatures have been investigated and discussed. The particle size and the lattice parameter of the synthesized composite have been found to be dependent on the processing temperatures. A possible reaction mechanism of the nanostructured silicon oxide to silicon carbide is proposed.
Preparation and Characterization of Y3Al5O12 (YAG) from An Alkoxide-Derived Polymer
Authors: Jiang Zhiping , Rhine Wendell E.
Published: March 2011

The controlled hydrolysis of Al(O-sec-Bu)3 and Y(O-iso-Pr)3 or the reaction of Y(OOCCH)3 with partially hydrolyzed Al(O-sec-Bu)3 [AlO0.75(O-sec-Bu)1.5] resulted in the formation of soluble polymeric materials. Pyrolysis of these materials under a flow of oxygen led to the formation of yttrium aluminum garnet (YAG) at 650-1500°C. YAG was the only crystalline phase observed during pyrolysis, and the Al/Y ratio of the pyrolysis products and the starting material was identical. However, infrared spectroscopy indicated that carbonate groups and entrained CO2 existed in the products at temperatures up to 1250°C. The pyrolysis chemistry of the precursors and the microstructure of the products were studied by FT-IR, TGA, XRD, SEM and elemental analyses.
Nanograin-Boundary-Controlled Reordering in Mechanically Disordered Nanocrystalline L12-Type Ni3 Al+Fe
Authors: Yavari A.R.
Published: March 2011

Using mechanical attrition (milling) which also transforms the material into nanocrystalline form, various L12 or γ-type Ni3 A1-Fe alloys have been prepared in metastable-γ form and their magnetisations M(γ) and M(γ) and Curie temperatures Tc(γ) and Tc(γ) measured.

Using magnetic properties we determine isothermal ordering kinetics in the nanocrystalline γstate and find that the ordering reaction cannot propagate across the nanograin boundaries. Each grain must obtain its own γ nucleus thus resulting in a Johnnson-Mehl-Avrami exponent n =1.
Characteristics of Cordierite-ZrO2 Composites Fabricated by The Multiphasic Sol-Gel Route
Authors: Jang Hyun M. , Lim Byung C.
Published: March 2011

Based on the electrokinetic properties of aqueous silica, boehmite, and ZrO2 dispersions, cordierite-ZrO2 composites were fabricated by the multiphasic sol-gel (or nanometer-scale sol mixing) route. The average particle sizes of boehmite and ZrO2 used in this study are 70 nm and 40 nm, respectively. The fabricated composites were characterized by a dense and homogeneous microstructure and by a uniform spatial distribution of submicron-sized tetragonal ZrO2 particles (200 nm) throughout the matrix. The microstructure of the matrix was represented by small-sized grains (< 400 nm) with a highly uniform grain-size distribution. The enhanced fracture toughness with increasing ZrO2 content was partly attributed to the martensitic t → m transformation. The formation of detrimental zircon (ZrSiO4) was avoided by suitably adjusting the heating schedule during sintering.
Hard Coatings for Polymer Films by Biomimetic in situ Precipitation
Authors: Lombardi John L , Calvert Paul
Published: March 2011

Hard siliceous coatings on polyethyleneterephthalate (PET) surfaces have been prepared upon hydrolyzing a tetraisocyanatosilane permeant present in biaxially oriented PET film samples. The structure of these films differs from commercial PET film materials in that silica is present both as a surface layer and as discrete submicron particles dispersed throughout the films. In order to accomplish this, it was found that suitable silica precursors should be chemically compatible with the polymer and have calculated Hildebrand solubility parameter values similar to that for PET.
Thermal Expansion and Relaxation of W-Cu Multilayers
Authors: Chiang Wen-C. , Kim Soo-Kil , Baxter David V.
Published: March 2011

We have studied the structure of W-Cu multilayers with modulation wavelengths between 65 and 110 xsÅ over the temperature range 25-400° C. Using a high temperature diffractometer stage specifically designed for low angle work, thermal expansion coefficients were measured and found to be marginally greater than would be expected from bulk behavior even when interaction with the substrate is taken into account. Upon annealing at temperature as low as 180° C, increased intensity of the low angle superlattice peaks is observed. Heat treatments above 180° C result in an irreversible change in the multilayer associated with the migration of Cu atoms to cracks produced by thermally induced stresses.
Nanocomposite Formation and Combustion Induced by Reaction Milling
Authors: Takacs Laszlo
Published: March 2011

Displacement reactions between a metal oxide and a more reactive metal can be induced by ball milling. In some cases the reaction progresses gradually and a metal/metal-oxide nanocomposite is formed. Ball milling may also initiate a self propagating combustive reaction. The information available about these processes is reviewed. It is argued that the gradual or combustive nature of the reaction depends on thermodynamic parameters, the microstructure of the reaction mixture, and the way they develop during the milling process.
Quantum Size Effects in Zinc Oxide Nanoclusters Synthesized by Reactive Sublimation
Authors: Ying Jackie Y. , Mcmahon Gregory
Published: March 2011

Nanostructured ZnO materials were synthesized by a novel reactive sublimation process, followed by cluster consolidation. The zinc oxide nanometer-sized grains were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoacoustic Fourier-transform infrared spectroscopy (PA-FTIR). These techniques illustrate the crystallization and grain growth of the ZnO nanostructured materials in a sequence of heat treatments. Peak sharpening and red-shifting of the phonon band in PA-FTIR spectra of ZnO nanoclusters demonstrate the reduction of finite crystal size effects during annealing. The high surface area and adsorbed species in ZnO nanoclusters were eliminated after sintering at a low temperature of 800 °C. The nanometer-sized ZnO particles have promising electronic and optical properties associated with the quantum size effects.
Silicon Nitride Powder from Carbothermal Reaction
Authors: Hofmann Heinrich , Vogt U. , Kerber A. , van Dijen F
Published: March 2011

The synthesis of silicon nitride powder by the reaction between silica, carbon and nitrogen is the economically most interesting route. Only this route makes possible the use of very cheap raw materials as well as the use of a simple production process. On the other side, the properties of the powders are within the limit of the technical requirements of the ceramic part manufacturer. The aim of this paper is to show that an optimized carbothermal Si3N4 powder synthesis leads to a product which fulfills the economical (low price) as well as the technical requirements. After a short introduction regarding the economical requirements, an overview of the carbothermal synthesis will be given. The influence of raw material, conditions of synthesis and removal of excess carbon on the powder properties will be discussed. Also, the properties of the powder as well as the sintering behaviour of Si3Ns4 powders, produced by Si-direct nitridation, Si-diimide process and the carbothermal route, will be compared in detail.
Status of Research and Development on Materials for Ceramic Gas Turbine Components
Authors: Matsui Minoru
Published: March 2011

Aggressive research and development has raised structural ceramics to a level where they are now of practical use as an alternative to metal. Major applications include use in automobile engine components, such as turbocharger rotors [1].
Perplastic SiAION—A Bird's Eye View of Silicon Nitride Ceramics
Authors: Chen I-Wei , Hwang Shyh-Lung
Published: March 2011

Superplastic Sialons have very fine microstructures containing submicron grains and transient phases. Fabrication of these materials requires processing at relatively low temperatures. As a result, different stages of phase evolution, including oxide melt formation, nitride dissolution, a′ and β′-SiAlON nucleation, and Sialon growth with and without concurrent deformation, can be captured in the development of these materials. In addition, only very low flow stresses are required for large strain deformation which, in turn, allows grain boundary and liquid phase processes to be manifested in the deformation behavior. Highlights of investigation of these aspects are reviewed here to shed light on the phase relationship, microstructural development, and grain boundary characteristics of silicon nitride.
Fabrication and Characterization of β-SiAION Components from Polymeric Precursors
Authors: Soraru G.D. , Sglavo V. M. , Vulcan F. , Babonneau F.
Published: March 2011

This paper reports on the fabrication of microcrystalline β-SiAlON components by direct nitridation of polymeric green compacts. The preceramic material was obtained from a polycarbosilane modified with an aluminum alkoxide. The microstructural transformation from the polymeric bodies to the final dense ceramic components was monitored by several techniques such as BET, XRD and dilatometry. Mechanical characterization, performed by indentation at various stages of the conversion process, will also be presented.
Microwave Nitrudation of Silicon Compacts Utilizing a Temperature Gradient
Authors: Thomas Jeffrey J. , Jennings Hamlin M. , Johnson D. Lynn
Published: March 2011

Silicon compacts nitrided utilizing the temperature gradient inherent to microwave heating were more fully converted to silicon nitride than was possible with similar compacts nitrided isothermally. Although nitrogen depletion prevented the reaction rate in the center from exceeding that at the surface, the temperature gradient partially counteracted the effect of nitrogen depletion. Thus the microwave-heated specimens could be nitrided fully before the reduction in porosity that accompanies the reaction eliminated the diffusion of nitrogen into the compact.
Sintered Reaction-Bonded Silicon Nitride by Microwave Heating
Authors: Tiegs Terry N. , Kiggans James O. , Ploetz Kristin L.
Published: March 2011

Sintered silicon nitride has many desired properties, however, for most applications these materials are too expensive to compete with metal parts. Sintered reaction-bonded silicon nitride (SRBSN) is more economical, with raw material costs <27% those of comparable high-purity materials, making it competitive with metal parts. Conventional processing of SRBSN requires long nitridation times and a two-step firing process. Microwave (MW) heating reduces the reaction times and is performed in a one-step process, thereby simplifying the operation. The flexural strength of the MW-SRBSN is equivalent to the strength of some materials made from higher-cost powders. Thus, these materials may be appropriate for a number of applications.
Progress in Silicon Nitride Ceramics in Japan
Authors: Komeya K.
Published: March 2011

Progress in silicon nitride ceramics in Japan is reviewed. It is historically divided into three stages. Through these stages, basic experimental research and innovations have progressed along with industrial applications, and the government project on fine ceramics in 1981-1992 has contributed much to the acceleration in the development of silicon nitride ceramics. Focus in this paper is mainly on materials development including raw powder synthesis and exploration for applications. The future prospect of utilizing silicon nitride as an engineering material, however, is seen to depend on cost reduction and reliability improvement.
Microstructural Design of Si3N4 Based Ceramics
Authors: Hoffmann M.J. , Petzow G.
Published: March 2011

Parameters controlling the size and aspect ratio of elongated Si3N4 grains are discussed, based on the assumption that only pre-existing β-Si3N4 particles of the starting powder grow. Powder mixtures of α-rich and β-rich Si3N4 were prepared In order to study the microstructural development. The resulting microstructures were analyzed by quantitative microstructural analysis determining the distribution of the length and aspect ratio of the Si3N4 grains. Subsequently, the Influence of the sintering conditions on grain growth was analyzed In relation to mechanical properties. A high Weibull modulus and the non-catastrophic failure during thermal shock of coarse-grained materials Is attributed to an R-curve behaviour. Finally, the influence of sintering additives on the mechanical properties was studied. The Importance of phase relationships between the matrix and the grain boundary phase Is discussed for Si3N4 with Yb2O3 additives. It Is demonstrated that the oxygen content of Si3N4 powder must been taken Into account In order to devitrify defined secondary phases and to achieve a high degree of crystallization. A reduction in the amount of additives does not necessarily Improve the properties as high temperature strength and creep data Indicate.
Nucleation and Growth of Cvd Polycrystalline Si3N4 Films at Low Temperatures
Authors: Lauten Frederick S. , Rankin Janet , Sheldon Brian W.
Published: March 2011

Silicon nitride films were deposited from silane and ammonia onto single crystal silicon substrates at a total pressure of 4.7 kPa. At temperatures below 1200° C, continuous films of polycrystalline Si3N4 deposited within a narrow region of low SiH4 partial pressures but at relatively high growth rates, for example, > 10 μm/hr at 1170° C. The early stages of crystalline film growth were studied with a combination of analytical techniques: FT-IR spectroscopy, x-ray and electron diffraction and electron microscopy. During deposition faceted Si3N4 grains nucleate on a growing nanocrystalline/amorphous interlayer.
Silicon Nitride Containing Rare Earth Silicate Intergranular Phases
Authors: Nunn Stephen D. , Tiegs Terry N. , Ploetz Kristin L. , Walls Claudia A. , Bell Nelson
Published: March 2011

Si3N4 ceramics prepared with refractory grain boundary phases to improve high temperature properties are difficult to densify by conventional sintering methods. Gas-pressure sintering may be used to promote densification and development of acicular grains for improved fracture toughness. The current study examined rare earth silicate sintering aids with the composition M2Si2O7, where M is a trivalent cation (Y, La, Nd). M2O3 and Si02 additions were varied to develop a number of compositions in the Si3N4—Si2N2O—M2Si2O7 ternary phase field. Pressureless sintering and gas-pressure sintering were used to densify the samples. Densification, microstructure development, oxidation resistance, and mechanical properties were evaluated and compared with respect to compositional variations and processing conditions.
Chemically Induced Defects in Oxynitride Glasses
Authors: Messier Donald R. , Patel Parimal J.
Published: March 2011

The ultimate usefulness of oxynitride glasses and fibers depends upon the minimization or elimination of metallic defects that arise during processing. Despite this, the origins and chemistry of such defects in oxynitride glasses have received scant attention in the literature. The defects reduce glass transparency and cause oxynitride glass fibers to fail at relatively low stress levels. The same types of defects undoubtedly occur in the grain boundary glass phase of sintered Si3N4with unknown effects on material properties.

Exampls are shown of Si-rich metallic defects in oxynitride glasses, and their effects on glass and fiber properties are discussed. Chemical reactions that produce the defects are considered, as are chemical analysis results supporting the proposed reaction mechanisms.
Evaluation of Tensile Static, Dynamic, and Cyclic Fatigue Behavior for A Hiped Silicon Nitride at Elevated Temperatures
Authors: Lin Chih-Kuang Jack , Jenkins Michael G. , Ferber Matitison K.
Published: March 2011

Tensile fatigue behavior of a hot-isostatically-pressed (HIPed) silicon nitride was investigated over ranges of constant stresses, constant stress rates, and cyclic loading at 1150-1370°C. At 1150°C, static and dynamic fatigue failures were governed by a slow crack growth mechanism. Creep rupture was the dominant failure mechanism in static fatigue at 1260 and 1370°C. A transition of failure mechanism from slow crack growth to creep rupture appeared at stress rates ≤10−2MPa/s for dynamic fatigue at 1260 and 1370°C. At 1 150-1370°C, cyclic loading appeared to be less damaging than static loading as cyclic fatigue specimens displayed greater failure times than static fatigue specimens under the same maximum stresses.
Crack Growth Resistance of Ceramic Composite
Authors: Hayashi Seijiro , Baba H. , Suzuki A.
Published: March 2011

Fracture process zone in SiCw/Si3N4 ceramic composite was studied by a hybrid experimental-numerical analysis employing moire interferometry and finite element analysis. A chevron-notched, wedge-loaded double cantilever beam specimen was used to obtain a stable crack growth. The relation between crack closure stress and crack opening displacement which govern fracture process zone was obtained.
Mechanical Properties of Sic Whisker Reinforced β-SiAION Composites
Authors: Yamagishi C. , Hakoshima J. , Nakajoh S. , Miyata N. , Tsukamoto K.
Published: March 2011

The mechanical properties of SiC whisker, SiCw, reinforced β-Sialon composite were investigated. β-Sialon with 20 vol% SiCw showed excellent high temperature strength, 610 MPa at 1350°C, and fracture toughness, 5.3 MPa √m (Chevron Notched Beam, CNB, method). This fracture toughness value was an improvement of 75% over that of β-Sialon (monolithic material). This composite also showed excellent oxidation-resistance; the weight gain due to oxidation after 200 hr at 1350°C in dry air was 0.3 mg/cm2, and after oxidation the high temperature strength, 1350°C, was 683 MPa, an improvement over the pre-oxidation value. Also, in high temperature creep testing (200 hr at 1350°C and 300 MPa) deformation of the SiCw reinforced β-Sialon composite, SiCw/β-Sialon was 66% smaller than that of β-Sialon.
Silicon Nitride Ceramics—Alloy Design
Authors: Tien Tseng-Ying
Published: March 2011

Properties of silicon nitride ceramics depend on the phases present and their microstructure. In order to obtain ceramics with optimum properties, knowledge of phase relationships in silicon nitride-metal oxides systems and the mechanism and kinetics of microstructure development are necessary.

There are four major stable silicon nitride phases in the Si3N4-metal oxides systems: β-Si3N4, α′-SiAlON, AIN-polytypoids and silicon oxynitride. The morphologies of these phases are different. The β-Si3N4 grains are elongated hexagonal rods; the α′-SiA1ON grains are equiaxed; the A1N-polytypoids are platelets; and the silicon oxynitride are equiaxed. Ceramics with combinations of these phases would have different microstructures and properties. The system Si3N4-SiO2-AIN-Al2O3-YN-Y2O3 will be used to demonstrate the concept of the alloy design. Kinetics of microstructural development will also be discussed.
High-Resolution Electron Microscopy Observations of Grain-Boundary Films in Silicon Nitride Ceramics
Authors: Kleebe H.-J. , Cinibulk M. K. , Tanaka I. , Bruley J. , Cannon R. M. , Clarke D. R. , Hoffmann M. J. , Rühle M.
Published: March 2011

Characterization of silicon nitride ceramics by transmission electron microscopy (TEM) provides structural and compositional information on intergranular phases necessary to elucidate the factors that can influence the presence and thickness of grain-boundary films. Different TEM techniques can be used for the detection and determination of intergranular-film thickness, however, the most accurate results are obtained by high-resolution electron microscopy (HREM). HREM studies were applied, in conjunction with analytical electron microscopy, to investigate the correlation between intergranular-phase composition and film thickness. Statistical analyses of a number of grain-boundary films provided experimental verification of a theoretical equilibrium film thickness. Model experiments on a high-purity Si3N4 material, doped with low amounts of Ca, suggest the presence of two repulsive forces, a steric force and a force produced by an electrical double layer, that may act to balance the attractive van der Waals force necessary to establish an equilibrium film thickness.
Low Strain Shear Behaviour of Cement Slurries at Quasi-static Rates.
Authors: Pafitis D. G. , Meeten. G. H.
Published: March 2011

The response of a freshly mixed oil-field cement slurry to an imposed shear strain has been experimentally studied using a method based upon concentric cylinders rheometry. At various stages of the reaction of cement with water, the slurry was deformed at quasi-static rates and the resultant shear stresses calculated. In an attempt to reduce errors due to wall slip, porous coated bobs which allow some infiltration of the slurry have been used. Stress-strain curves for the cement have been produced and the variation of yield stress with time after mixing evaluated. The experimentally determined stress-strain curves exhibited three characteristic regions. Firstly, a region of negligible stress increase at very low strain. A region of rapid linear increase in stress with strain, and finally, a post-yield strain softening region. The low strain (<0.01) response of cement slurries has been compared to that of suspensions of polyethylene beads in water with similar solids volume fraction and mean particle size. A number of similarities in the stress versus strain curves of these two granular suspensions have been observed.
Flow Response and Microstructure of Polymers Reinforced with Discontinuous Fibers
Authors: Davidson Theodore , Huang T. A. , Brizzolara J. P. , Sebastian D. H.
Published: March 2011

The reinforcement of plastics with fibers has been practiced for many years. Only recently have long discontinuous fibers been compounded with thermoplastics by the method of pultrusion which preserves fiber length while promoting wetting of each fiber by the matrix polymer. Reinforcement of linear polymers with high strength fibers enhances physical properties and creates formable thermoplastic composites. Conventional compounding of fiber and polymer in a pelletizing extruder creates pellets. These are typically cylindrical, about 3 × 3 mm; containing fibers with a length distribution averaging 0.3 mm (but always > 3 mm). In distinction to such “short fiber” (SF) materials, greater fiber length can be achieved by the process of pultrusion. In this technology, continuous tows of fiber are wetted by molten polymer, “pultruded” through a die; and chopped to any desired length. The resulting pellets are typically 3 mm diameter, 12 mm long, and contain 30 to 60 weight percent of fibers with l/d ≥ 700. These long fiber (LF) pellets can be processed e.g. by injection molding, to give parts with net shape and good dimensional tolerances, high stiffness, tensile, and impact strength.1−3

In order to understand the distribution of discontinuous fibers in molded parts, and to comprehend the flow behavior of these non-Newtonian fiber-filled suspensions,4−8we have examined the melt rheology of short and long fiber reinforced thermoplastics.
A two Roll Mill as a Rheomer for Pastes
Authors: Adams Michael J. , Biswas Sanjay K. , Briscoe Brian J. , Sinha Sujeet K.
Published: March 2011

Previous work involving the squeeze-film flow of a model paste substance, a mixture of clay particles and mineral oil commonly known as ‘Plasticine’, has suggested that it behaves as a simple Herschel-Bulkley fluid which exhibits little strain history. However, tensile measurements, which are naturally limited to small strains by the onset of necking, indicate that this material shows strain hardening. A two roll-mill is employed here to investigate the influence of larger extensional strains. The data are analysed using an available first order engineering plasticity solution. The results confirm that this material exhibits both extensional strain and strain rate hardening. This observed strain hardening effect, which is not observed in the squeeze-film experiments, is attributed, in part, to the more homogeneous deformation fields induced during rolling and tensile extension.
The Simulation of Aggregated Colloids Under Flow
Authors: Melrose John R.
Published: March 2011

An overview is given of theories of aggregates under flow. These generally assume some sort of structural breakdown as the shear rate is increased. Models vary with both the rigidity of the bonding and the level of treatment of hydrodynamics. Results are presented for simulations of a Rouse model of non-rigid, (i.e. central force) weakly bonded aggregates. In large scale simulations different structures are observed at low and high shear rates. The change from one structure to another is associated with a change in the rate of shear thinning. The model captures low shear rate features of real systems absent in previous models: this feature is ascribed to agglomerate deformations. Quantitatively, the model is two orders of magnitude out from experiment but some scaling is possible.
Viscoelastric Properties of Confined Polymer Layers
Authors: Costello Bernard A. , Luckham Paul F.
Published: March 2011

The viscoelastic properties of thin films of graft copolymers of poly (hydroxy stearic acid)/poly (methyl methacrylate) adsorbed on mica surfaces have been investigated by oscillating one surface sinusoidally using a piezoelectric crystal and monitoring the response of the other on a piezo bimorph. Two distinct regions were found. At low separations the viscous response was negligible, although equilibrium force / distance profiles clearly showed that fluid could be squeezed from the intersurface gap. This was ascribed to hydrodynamic effects, the time scale of the dynamic experiments being much shorter than the equilibrium experiments. Several ways of investigating these effects further have been proposed. At larger separations the viscosity of the medium achieved its bulk value, as expected.
Rheological Properties of Dense Silica Suspensions
Authors: Chappuis J. , Guinot D. , Leture P.
Published: March 2011

The rheological properties and microstructure of concentrated suspensions of silica particles in water have been studied. Two typical pH conditions, the effect of the addition of CaCl2 and different mixing procedures have been investigated. When CaCl2 is added, the suspensions become very thick only if the pH is far from the point of zero charge.
Laser-Induced Photodeposition of Fe Films From Iron Carbonyl
Authors: Love P. J. , Loda R. T. , La Roe P. R. , Green A. K. , Rehn Victor
Published: March 2011

Excimer laser photodecomposition of Fe(CO)5 has been used to produce large-area (≳ 1 cm2) Fe films on insulating and semiconducting substrates. Films were deposited in an ultrahigh vacuum system at room temperature or 77 K. Film composition and morphology were examined with Auger-depth profiling, scanning electron microscopy, x-ray fluorescence, and resistivity measurements. At appropriate laser power densities and Fe(CO)5 pressures, adherent metallic films were obtained. These films were typically less than 500 Å thick and contained less than 13% bulk oxygen and carbon contamination.
Laser Investigations of the Dynamics of Molecule-Surface Interaction
Authors: Hager J. , Walther H.
Published: March 2011

The internal energy distribution of NO molecules scattered from different solid surfaces (Pt(111), graphite, and Pt(111) covered with various adlayers) was investigated by the laser-induced fluorescence method. In the case of the NO/graphite system, moreover, the velocity distribution of the scattered molecules could be measured in a time-offlight experiment. The rotational energy distribution, which can always be described as a Boltzmann distribution, exhibits only partial accommodation to the surface temperature for all surfaces investigated. The measurements of the velocity of the NO molecules scattered from the graphite surface show only a small influence of the surface temperature on the average velocity and on the velocity distribution. Furthermore, the measured velocity distribution is independent of the final rotational state of the scattered molecules. On the basis of these results, a rather complete description of the behavior of the NO molecules during the scattering process can be presented.
Spectral Widths in the Rate Equations for Photodesorption by Laser Infrared
Authors: Heidberg Joachim
Published: March 2011

Desorption and evaporation from solid surfaces are induced with high yield and wavelength selectivity by excitation of internal adsorbate vibrations with resonant laser infrared. Simple rate equations describe essential features of the process and relate the photoreaction rate and yield to the intensity, the duration of laser-solid surface interaction and molecular properties of the adsorbate. The significance in photodesorption of the experimentally determined spectral widths is shown. Considering the spectral widths in the theory brings the order of the calculated photo-desorption rates for CH3 F-NaCl and the measured rates (also yields) in better concert.
Effects of Surfaces on the Melting/Freezing Behavior of Fluids in Derivatized- and Nude-Porous Silica
Authors: Malhotra V. K. , Mu R. , Natarajan A.
Published: March 2011

Comparative differential scanning calorimetry (DSC) measurements were made at 200 K < T < 310 K on geometrically restricted cyclohexane and n-decane in nude-, trimethyl derivatized-, and hexyl derivatized-porous (Rp = 4 nm) silica with a view to determine how the surface structure of the confining media affects the thermodynamic behavior of the restricted fluid. Our results suggest that, irrespective of the fact that both trimethyl derivatized- and hexyl derivatized-silica have methyl terminal groups, the freezing or melting transition of cyclohexane is much more depressed in trimethyl derivatized-silica than in hexyl derivatized- or nude-silica. This is not the case for n-decane where the depression in the melting transition is consistent with the fact that the effective pore radius of the hexyl derivatized-silica is smaller than the trimethyl derivatized- or nude-silica.
NMR Studies of Fluid Diffusion in Confining Geometries
Authors: Jerosch-Herold Michael , Thomann Hans , Thompson A. H.
Published: March 2011

Diffusion dynamics for fluids in sandstone rocks were studied by CPMG and pulsed field gradient (PFG) NMR measurements. Stretched exponential decays of the transverse magnetization were observed while varying the interpulse spacing, τ, in the CPMG experiment which sets the time for diffusion. A crossover from free to restricted diffusion is evident in the dependence of both T2 and the stretch exponent, β2, on the diffusion time τ. The T2(τ) data is fit to a model which interpolates between free and restricted diffusion and has only one free adjustable length scale despite the fact that the sandstone rocks are characterized by a pore size distribution. This NMR derived length scale correlates with a characteristic length derived from Hg injection experiments at the percolation threshold. We compare these results from the CPMG experiment with stimulated echo PFG-NMR diffusion measurements. This provides a complementary method of probing the diffusion dynamics since the longitudinal magnetization is insensitive to the dephasing effects of diffusion in internal field gradients.
Dipolar Energy Transfer and Knudsen Diffusion Inside Disordered Porous Media: Interfacial Geometry and Chord Distributions.
Authors: Levitz P.
Published: March 2011

The interfacial geometry of a disordered porous medium strongly influences Knudsen diffusion of gases and interfacial dipolar energy transfer. Some interesting comparison can be made between these two transport processes, involving statistical properties of chords belonging either to the solid matrix or to the pore network. A quantitative analysis of these two mechanisms is proposed, based on a chord distribution model. In a first part, we discuss how chord distribution functions contribute to the stastistical characterization of a porous medium. We show that a direct connection between imaging techniques and small angle scattering provides, in many cases, a reliable description of theses functions. In a second part, interfacial direct energy transfer is analyzed. This one step excitation transfer strongly relies on the interfacial autocorrelation function φ2s(r). An analytic expression of φ2s(r) is given and theoretical predictions compared with available experiments. In a third part and following the seminal work of Derjaguin on the Knudsen diffusion, we critically examine how the self diffusion coefficient can be related to the two first moments of the pore chord distribution. A direct comparison with experimental results and numerical simulations is presented in the case of a model porous medium: the random packing of hard spheres. Finally, we analyze a trapping reaction where an excited gas molecule, diffusing in the Knudsen regime, relaxes primarily by wall effects. We show how the chord distribution of the pore network permits to compute the survival probability of the tagged molecules. Two situations are more closely analyzed: the strong and the very weak wall quenching efficiency.
Energy Transfer, Nanometer Crystals and Opfical Nano-probes
Authors: Tan Weihong , Kopelnan Kopelman
Published: March 2011

Nanometer light and exciton sources and probes have been prepared by adding various inorganic and organic crystals and molecularly doped polymers to micropipettes and nanofabricated optical fiber tips. Specifically, a new nanotechnology, near-field photonanofabrication, has been developed, leading to a thousandfold miniaturization of immobilized Fiber Optical Chemical Sensors and to a billionfold decrease in necessary sample volume. The response time has also been shortened by a factor of at least 100. Applications of these subwavelength probes include biological single cell analysis, supertip development, Förster-energy transfer and Kasha quenching phenomena at the interface between the positionally controlled nanocrystal tip and its photoactive environment. Practically, this leads to enhanced sensitivity of optical probes, nano-optical chemical sensors and near-field exciton light sources.
Dynamics of Polystyrene in Confining Geometry: Transition from Dilute to Semidilute
Authors: Teraoka Iwao , Langley Kenneth H. , Karasz Frank E.
Published: March 2011

Dynamics of polystyrene molecules inside controlled pore glasses, a typical confining geometry, was studied by dynamic light scattering over a wide range of concentrations of polystyrene in solutions in equilibrium with the porous glasses. Index-matching of the solvent to the silica glasses effectively facilitates the acquisition of information on the dynamics of polymer chains inside the pore without compromising that information by multiple light scattering. When the concentration outside the pore is much smaller than the overlap concentration v*, the apparent diffusion coefficient Dporc of polymers within the pore shows little dependence on concentration. As the outside concentration increases and approaches v*, Dporc rapidly increases. This tendency is more pronounced for polystyrene samples that have higher molecular weights and are predicted to have a lower concentration inside the pore. With further increases of concentration beyond v*, Dporc approaches the apparent diffusion coefficient outside the pore. Moreover, Dporc becomes almost the same for the three different molecular weights of polystyrene fractions studied and depends primarily on the weight concentration of the solute outside the pore. These features are typical of a semidilute solution regime for flexible polymers. The rapid increase in Dporc, is ascribed to a drastic increase of the polymer concentration inside the pore, which results from an equilibration of the chemical potential of the polymer molecule between the interior of the pore and the exterior. Thus, a rapid increase in the osmotic pressure outside the pore drives the polymers into pore channels even at the expense of reduced entropy. We present a quantitative analysis of this highly nonlinear partitioning of polymer molecules.