bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Expansion and Relaxation of W-Cu Multilayers
Authors: Chiang Wen-C. , Kim Soo-Kil , Baxter David V. 
Published: March 2011

ABSTRACTWe 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

ABSTRACTDisplacement 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

ABSTRACTNanostructured 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

ABSTRACTThe 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.
Perplastic SiAION—A Bird's Eye View of Silicon Nitride Ceramics
Authors: Chen I-Wei , Hwang Shyh-Lung 
Published: March 2011

ABSTRACTSuperplastic 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

ABSTRACTThis 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

ABSTRACTSilicon 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

ABSTRACTSintered 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

ABSTRACTProgress 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

ABSTRACTParameters 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

ABSTRACTSilicon 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

ABSTRACTSi3N4 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

ABSTRACTThe 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

ABSTRACTTensile 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

ABSTRACTFracture 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

ABSTRACTThe 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

ABSTRACTProperties 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

ABSTRACTCharacterization 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

AbstractThe 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.1−3In 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

AbstractPrevious 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

AbstractAn 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

AbstractThe 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

AbstractThe 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

ABSTRACTExcimer 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.