bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Powders and Processing Methods on Microstructure and Properties of Dense Silicon Nitride
Authors: Woetting G. , Feuer H. , Gugel E. 
Published: March 2011

ABSTRACTExperiments with commercially available as well as with specially prepared Si3N4-powders were performed in order to estimate the extent of influence of the powder properties and the homogeneity of the additive distribution on the sintering behaviour, the microstructure and on mechanical properties of the dense sintered materials.The quality of the processing steps was examined by dilatometry which also proved to be a useful tool for deducing appropriate sintering conditions for different Si3N4-powder/additive systems.The effects of compositional variations and processing on microstructure and mechanical properties are discussed with respect to strength, reliability (Weibull analysis) and fracture toughness. Some important factors to be considered for the production of highperformance, reliable silicon nitride materials and components are pointed out.The careful analysis of possible influences on the final ceramic resulted in the production of a high-quality Si3N4-material which is used for engine valves, bearing balls, etc.
Siaun Ceramics: Retrospect and Prospect
Authors: Jack Kenneth H. 
Published: March 2011

ABSTRACTThe future for sialon ceramics is bright. Engine components are slowly increasing in numbers and variety, and applications for wear parts and molten metal handling are set to flourish.Two major developments have been: (i) the production of useful sialon composites; and (ii) the ability to join pieces to make large and complex components.In (i), properties of a′:8′ sialon composites can be varied by processing modifications in ways that are impossible for single-phase materials. Also, densifying additives such as yttria and rare-earth oxides can subsequently be incorporated into the α′-structure to minimize the amount of intergranular glass. The potentialities of other composites including O′:B′, O′:ZrO2, B′:TiN and B′:BN are assessed.In (ii), the joining of sialons follows from an understanding of phase relationships, glass formation and glass-ceramics in the Y-Si-Al-O-N system. Its exploitation has greatly widened the field of sialon applications.
Structural Characterization of Silicon Carbonitride Ceramics from Polymeric Precursors using Nuclear Magnetic Resonance
Authors: Gerardin Corine M. , Taulelle F. , Livage J. 
Published: March 2011

ABSTRACTThe pyrolytic conversion of a polyvinylsilazane precursor to Si-C-N ceramics is studied using solid-state NMR. 13C and 29Si magic angle spinning and 1H static NMR experiments allow us to investigate the structure of the disordered multiphased intermediates formed during the pyrolysis. The Si environments are quantitatively analyzed by 29Si MAS NMR spectra simulations. The relative abundance of SiHCN2, SiC2N2, SiN3C and SiN4 sites at different temperatures are used to calculate elemental compositions that characterize the Si-containing phase. The comparison of these compositions with those obtained from chemical analyses shows evidence of the presence of a free carbon phase.We have also determined the H and C contents in the free carbon phase.
Effect of Powder Processing on Slip Casting Parameters and Sintering of Si3N4-SiO2-Y2O3
Authors: Gilde Gary , Gazza George 
Published: March 2011

ABSTRACTA procedure was developed for slip casting Si3N4-Y2O3 - SiO2 compositions. The silicon nitride was oxidized to supply the silica. The procedure resulted in 65 w/o slips with viscosities of 35 mPa s which when cast, yielded compacts which were 56 % of theoretical density. Slips with 70 w/o solids loading were also prepared having viscosities of 120 mPa.s. The properties of the slips were influenced by the starting silicon nitride powder, dispersant, and milling media. The resulting compacts could be gas pressure sintered to full density, at temperatures as low as 1850 C, using nitrogen pressures as low as 4 MPa. Strengths as high as 750 MPa were achieved and the initial results show good creep resistance at 1350 C.
A Novel Processing Route for the Fabrication of Monolithic and Composite Silicon Nitride
Authors: Raman R. V. , Rele S. V. 
Published: March 2011

ABSTRACTCurrent hot isostatic consolidation methodology used for the fabrication of complex-shaped Si3N4-based components requires the use of an expensive glass encapsulation technique and extended thermal exposure (in hours) of the specimen. An alternative consolidation approach involving the use of solid pressure transmitting media under high pressure, has enabled the consolidation of Si3N4 alloys without the need for glass encapsulation.Characterization of microstructures and mechanical properties of this (MOR, fracture toughness) material has been carried out and will be presented. It has been noted that in Si 3N4/8%Y2O3-4%Al2O3 composition, consolidated using this approach, a significantly larger volume fraction of α phase has been retained compared with typically observed conversion in α⇒ β in hot isostatically pressed material or sintered material.Key issues for addressing densification and microstructure control using this process are presented. This rapid consolidation approach appears to be a promising alternative to hot isostatic pressing for the fabrication of complex-shaped Si3N4 components.
Characterization of HIP'ed, High Purity Si3N4 Grain Boundaries
Authors: Lu Ping , Danforth S.C. , Symons W.T. 
Published: March 2011

ABSTRACTLaser synthesized, ultra-fine, amorphous, Si3N4 powders were densified via HIP'ing without any oxide sintering aids. Exposed samples were made from powder that had been exposed to the atmosphere, thereby picking up an oxide surface layer, and unexposed samples were made from powders processed entirely under glove box conditions, i.e. without oxygen contamination. TEM (and sintering) studies indicate that the exposed samples HIP'ed at temperatures in excess of the melting point of Si02, densified via a solution-reprecipitation mechanism, with a resultant intergranular glassy phase of high purity Si02. In contrast, unexposed samples had to be HIP'ed to 2050°C to achieve a density of ∼70 %p Th. These samples consisted of equiaxed β-Si3N4 grains, with localized high density regions where no inter-granular phase (crystalline or glassy) was detected to within 0.66 nm.
Microstructural Design by Selective Grain Growth of β-Si3N4
Authors: Hirosaki Naoto , Akimune Yoshio , Mitomo Mamoru 
Published: March 2011

ABSTRACTRaw β-Si3N4 powder was gas-pressure sintered with Y2 O3-Nd2O3additives at > 1700ºC. Graingrowth behavior was investigated in relation to sintering conditions. Selective growth of large grains was accomplished by sintering the powder at high temperatures with small amounts of additives. As a result, in-situ composites were obtained from β-powder.The desired material properties have been attained by controlling the microstructural design using large grains. Materials with high reliability, having a Weibull modulus of about 50, were fabricated by maintaining a uniform size and distribution of elongated grains. Tough materials, having fracture toughness of, were developed by increasing the diameter of elongated grains. This method was applied to the sintering of refractory grade powder with the aim of lowering sintered material cost. Fairly good mechanical properties have been obtained even with impure powders.
Grain Morphology and Intergranular Structure of Si3N4 Based Ceramics Formed by Hip
Authors: BjÖrklund H. , Falk L. K. L. , WasÉn J. , Adlerborn J. E. , Larker H. T. 
Published: March 2011

ABSTRACTThe microstructures of unreinforced and reinforced Si3N4 ceramics have been characterized by analytical electron microscopy in combination with quantitative microscopy. Special attention was paid to the effect which different additives, viz. metal oxides and SiC- and β-Si3N4-whiskers, have upon matrix morphology and intergranular microstructure. It was demonstrated that SiC-whiskers may suppress Si3N4 grain growth while an addition of β-Si3N4-whiskers results in a coarser Si3N4 microstructure. The different microstructures have been related to the mechanical properties of the ceramics.
Cavity Evolution During Tensile Creep of Si3N4
Authors: Luecke William , Wiederhorn S. M. , Hockey B. J. , Long G. G. 
Published: March 2011

ABSTRACTWe have characterized the evolution of cavities during tensile creep of a Y2O3-hot isostatically pressed Si3N4, using precision density measurements, small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM). The cavities are bimodally distributed in size. Lenticular, 200 nm-size cavities are common, and lie primarily on two-grain boundaries. Irregularly shaped 500-1000 nm-size cavities are rare and lie at multi-grain junctions, but comprise approximately half of the total volume fraction of cavities. Although the material shows a continuous decrease in strain rate with strain, the cavity volume fraction evolves linearly with strain. Cavities account for approximately 85% of the total strain at any point during creep.
Mechanical Properties of Silicon Carbide Whisker-Reinforced Silicon Nitride Matrix Composites
Authors: Huang Yong , Le Huirong , Li Jianbao , Zheng Longlie , Wu Jianguang 
Published: March 2011

ABSTRACTIn the present paper, the effect of La2O3-Y2O3-Al2O3 (LYA) and La2O3-Y2O3-MgO (LYM) additives on the mechanical properties of hot pressed SiC whisker-reinforced Si3N4 matrix composites and the relationship between whisker content and additive content were investigated in detail. The results show obvious strengthening in the case of LYA additives containing ≤2.4 wt% Al2O3. When the Al2O3 content of the additive was > 1.2 wt%, the fracture toughness decreased accompanied by decreased interfacial debonding and whisker pull-out. With LYM additives containing 2.4 wt% MgO, both the room temperature strength and toughness increased. A combination of Y2O3 + MgO (YM) with LYA additives produced substantial improvements in strength and toughness, up to 1050 MPa and ∼11 MPa√m, respectively. The Weibull modulus of a SiC whisker-reinforced composite was found to be greater than that of either the unreinforced Si3N4 or Si3N4 containing SiC particles. The experiments also demonstrated that in order to achieve full density the additive content had to be increased with increased whisker content. Preliminary but encouraging results on strength retention at elevated temperatures were also reported.
The Mechanical Properties of a Novel Si3N4-Amorphous Si3N4 Composite
Authors: Reimanis Ivar E. , Petrovic J. J. , Suematsu H. , Mitchell T. E. , Leung O. S. 
Published: March 2011

ABSTRACTThe hardness and fracture toughness of a model two-phase composite consisting of crystalline Si3N4 particles in a matrix of amorphous Si3N4 are examined. The composite is created by heat treating high purity, partially amorphous CVD Si3N4 in N2 for various times and temperatures in order to induce crystallization of the a phase. Microindentation tests at temperatures up to 1200 °C are conducted to evaluate the high temperature hardness and fracture toughness. The role of the microstructure is examined using optical and transmission electron microscopy. Finally, the relationship between the microstructure and the mechanical properties is discussed.
New Grain-Boundary Phases for Nitrogen Ceramics
Authors: Thompson Derek P. 
Published: March 2011

ABSTRACTThe drive for improved refractoriness in nitrogen ceramics, which has motivated the removal of residual glass from grain-boundaries by heat-treatment at sub-solidus temperatures, has resulted in the discovery of a wide range of crystalline oxynitride phases. Generally, these phases are oxygen-rich, and can be classified in the same way as the mineral silicates, in which oxygen atoms are coordinated to a maximum of two silicon atoms, with SiO4 tetrahedra joined at either 0,1,2,3 or 4 corners to other tetrahedra. However, the field of oxynitride crystal chemistry is wider than this, because nitrogen in SiN4 tetrahedra commonly occurs coordinated to three silicon atoms, and an additional range of structures exist with nitrogen in this coordination.Oxynitride analogues of mineral silicates are well known in neso-, soro- and cyclostructure types; new structures have recently been reported which belong to the pyroxene family (ino-silicates), and information on their preparation and crystal chemistry is reported here. The sialon U-phase (typical composition Ln3Si3Al3O12N2, Ln = La,Ce,Nd,Sm), is an example of an oxynitride with a structure intermediate between layer (phyllo-) and framework (tecto-) types. Sialon W-phase (approximate composition Ln4Si9Al5O30N, Ln = La,Ce,Nd) has not been completely characterized, but appears to have a structure related to the amphibole group of double-chain silicates.Comments are made on the many oxynitride structures which are still uncharacterized. The suitability of all these oxynitrides as grain-boundary phases in silicon nitride and sialon ceramics is discussed.
Rheology and Microstructure of Concentrated Zirconia-Alumina Suspensions for Gelcasting Composites
Authors: Bleier A. , Omatete O. O. 
Published: March 2011

AbstractThe relationships among colloidal stability, suspension rheology, and solids loading are elucidated for zirconia-alumina mixtures containing 20 vol% ZrO2, based on solids. The lower colloidal stability of ZrO2 limits the rheological properties of this system. If the zeta potential of ZrO2 is less than 49 mV, high degrees of pseudoplasticity, high yield stress, high viscosity, and long relaxation times characterize the binary suspensions. These effects occur, despite the fact that ZrO2 is the minor ceramic constituent. If the zeta potential of ZrO2 is maintained above 49 mV, suspensions with high solids loading (55 vol%) can be prepared which behave as Newtonian fluids over the 0-to-200 s−1 shear rate range and as an elastic solid at higher rates. As the solids loading of a highly stable binary suspension is increased, the rheological properties change. They evolve from those of a near Newtonian-like fluid with nearly independent particles (40 vol%) to those of a pseudoplastic fluid with a weakly interacting particle network (50 vol%) to those of an elastic-like solid composed of crowded, strongly repulsive particles (55 vol%). Low-shear conditions for suspension-transport and mold-filling operations that ensure a homogeneous arrangement of ZrO2 and A12O3 particles in a gelcast ceramic seem promising.
Characterization of Ceramic Batch Via Capillary Rheometry
Authors: Janas Victor F. , Malarkey Christopher J. , Treacy David R. , Zak Michael E. 
Published: March 2011

AbstractRheological testing has been developed to predict the extrudability of ceramic pastes. Inorganic batches containing cellulosic binders were mixed in a twin screw extruder prior to characterization in a capillary rheometer. Various die lengths were used to separate viscosity from wall slip parameters. A power law model was fit to the paste viscosity. The wall shear stress, assuming 100% slip, was a linear function of the wall velocity. The resulting rheological models were used in fluid flow finite element analysis for determination of extrusion pressure, and the evaluation of binders.
The Role of Rheological Characterization of Ceramic Dopes in Predicting Fiber Spinning Performance
Authors: Subramanian G. , Bike S. G. , Baskaran S. , Popovic D. , Halloran J. W. 
Published: March 2011

AbstractWe have previously shown that suspension dry spinning of green ceramic fibers can produce continuous fibers of alumina in an ethyl methacrylate binder. The spinning behavior of the dope and the particle packing in the dried fiber are highly dependent on the interparticle interactions in the dope prior to spinning. In particular, the interactions between the ceramic powder and both the dispersant and the binder are critical in determining the processability and spinnability of the dope. We have used rheological techniques to probe these interactions in alumina dispersions in methyl ethyl ketone employing ethyl methacrylate as the binder and a phosphate ester as the dispersant. Measurements of the viscosity of the dispersion as a function of dispersant concentration demonstrate that there is an optimum dispersant concentration to achieve a minimum viscosity at a given binder concentration. In addition, the relative viscosity (viscosity of the dispersion relative to that of the dispersing medium) is found to decrease significantly with increasing binder concentration. These results highlight the importance of characterizing the power-binder-dispersant interactions to fully understand the stability and ultimate spinnability of a ceramic dope. In addition, this work illustrates the general applicability of rheological characterization in ceramic fiber spinning.
On the Development of Rheological Properties of Cement Paste During the Induction Period
Authors: Yang Ming , Jennings H. M. 
Published: March 2011

AbstractAlthough chemical reactions in cement slurries are very slow during the first few hours (induction period), the viscosity increases continuously. Relationships between various mixing methods, structure, and rhcology of cement paste throughout the induction period are being investigated, and some results are reported in this paper.
Surface-Enhanced Raman Spectroscopy from Colloids at High Pressures
Authors: Bradley Michael , Krech John , Efrima Shlomo 
Published: March 2011

AbstractHigh pressure surface enhanced Raman (SERS) spectra are reported for a highly dense silver colloidal suspension, termed a MEtal Liquid-Like Film or MELLF. Comparison is made with the SERS spectrum of a dilute organosol. Raman signals due to adsorbed molecules and the solvent dichloromethane reveal appreciable frequency shifts as the colloidal environment is influenced by temperature, pressure, and packing. The C-Cl stretch of neat dichloromethane near 705 cm−1 shifts 1.7 cm −1 blue in a MELLF. Raman signals due to the adsorbed anisic acid in MELLFs blue shift about 2 cm −1 as 4 kilobars of pressure are applied; the solvent peaks shift blue only about 1 cm −1. Temperature influences the MELLF in two ways: desorption of anisic acid and formation of agglomerated particles.
Equilibrium-State Density Profiles of Centrifuged Cakes of Flocculated Suspensions
Authors: Shih Wei-Heng , Shih Wan Y. , Kim Seong-Il , Aksay Ilhan A. 
Published: March 2011

AbstractMany advanced ceramics are formed by colloidal consolidation using techniques such as sedimentation, centrifugation, or pressure filtration. In all these, the minimization of density variations of various colloidally-consolidated cakes has not been examined systematically until recently. Schilling et al. used γ-ray densitometry to study the density variations in a sedimented cake and showed that the sediment of a flocculated alumina suspension exhibited significant density variations within the cake whereas the sediment of a dispersed alumina suspension showed a constant density profile. Auzerais et al. used a medical X-ray computer tomography (CT) to study the settling of dispersed and flocculated silica suspensions and obtained similar results: The sedimented cake of a dispersed silica suspension was fairly uniform whereas those of flocculated silica suspensions exhibited significant density variations. However, Shih et al. examined pressure-filtered cakes of flocculated alumina suspensions with γ-ray densitometry and showed that the density profiles of pressure-filtered cakes of flocculated alumina suspensions were uniform, in contrast to their sedimentation counterparts which showed significant density variations. These studies illustrate that how the local density varies within a consolidated cake depends not only on the suspension conditions but also on how the suspensions are consolidated, e.g., the consolidation pressure.
Coarsening of a Quiescent Electrorheological Fluid II: Theory
Authors: Halsey Thomas C. 
Published: March 2011

AbstractThe coarsening observed orthogonal to the field lines in light scattering studies of a quiescent electrorhcological fluid during the “liquid-solid” phase transition can be qualitatively understood using the thermal mechanism of chain interaction proposed by Halsey and Toor. By analyzing fluctuations in the interaction between chains, we predict a power-law increase of the column width with time, with a time constant that decreases as a power of the electric field. Lubrication forces between the particles may control the time scale of these fluctuations. These predictions are in good accord with light scattering measurements.
Limiting and Enhancement Effects in Laser Chemical Vapor Deposition
Authors: Allen S. D. , Jan R. Y. , Mazuk S. M. , Shin K. J. , Vernon S. D. 
Published: March 2011

ABSTRACTLaser chemical vapor deposition (LCVD) is a modification of conventional CVD using a laser heat source. The film growth characteristics differ considerably from conventional CVD in several ways, however. The use of an optical heat source means that the optical properties of the film/substrate system must be considered, e.g., for metals deposited on absorbing substrates, the film thickness and diameter may “self-limit” in some cases because the deposited film reflects most of the laser energy. On the other hand, the small area heated in LCVD results in a different diffusion geometry and access to higher surface temperatures than are achievable when large areas are heated. For favorable reactant systems, these enhancement effects can yield fast deposition rates and line deposition scan speeds greater than 10 cm/sec. This paper will review results of pulsed and cw LCVD of predominantly metal films using visible and infrared lasers.
Photochemical Vapor Deposition of Amorphous Silicon Using Mercury Photosensitization of Disilane
Authors: Tarui Yasuo , Aota Katsumi , Sugiura Takashi , Saitoh Tadashi 
Published: March 2011

ABSTRACTHigh-rate deposition of amorphous silicon films using the mercury-photosensitized reaction of disilane gas is described. The deposition rate depends upon reactant pressure, light intensity, and concentration of mercury atoms. A maximum rate of 100 nm/min is attained at a 250°C substrate temperature and a disilane pressure of 200 Pa. This rate is about 3 times higher than that for monosilane gas.Generally, the optical gap of the deposited films range from 1.7 to 1.8 eV, although the value decreases slightly with increasing substrate temperature. Photoconductivity under AM1 irradiation is 2×10−4 mho·cm−1 at a 250°C substrate temperature and the ratio of photoconductivity to dark is around 104. From the infrared data, amorphous silicon films are found to include only an SiH bond at substrate temperatures of 200° to 300°C. Hydrogen content is 10 to 13%. These data suggest that silicon films can be used in thin-film electronic device fabrication.
Recent Advances in UV Laser Photodeposition
Authors: Tsao J. Y. , Ehrlich D. J. 
Published: March 2011

ABSTRACTTechniques for laser-photochemically depositing localized thin films are reviewed. A comparison is made between techniques relying on gas-phase and surface-phase photochemistry. New photoreactions, confined entirely to surface phases, are described, including multimolecular reactions based on methyl methacrylate, and multicomponent reactions based on mixtures of trimethylaluminum and titanium tetrachloride. Recent developments in the use of surface photochemistry to nucleate subsequent growth by pyrolytic chemical vapor deposition are also reported.