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Silicon Nitride (silicon + nitride)
Terms modified by Silicon Nitride Selected AbstractsSintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High StrengthINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2008You Zhou Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400°C for 8 h and subsequently postsintering at 1900°C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source] Processing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride: (II) Effects of Magnesium Compound and Yttria AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007Xinwen Zhu The effects of the magnesium compound and yttria additives on the processing, microstructure, and thermal conductivity of sintered reaction-bonded silicon (Si) nitride (SRBSN) were investigated using two additive compositions of Y2O3,MgO and Y2O3,MgSiN2, and a high-purity coarse Si powder as the starting powder. The replacement of MgO by MgSiN2 leads to the different characteristics in RBSN after complete nitridation at 1400°C for 8 h, such as a higher ,-Si3N4 content but finer ,-Si3N4 grains with a rod-like shape, different crystalline secondary phases, lower nitrided density, and coarser porous structure. The densification, ,,, phase transformation, crystalline secondary phase, and microstructure during the post-sintering were investigated in detail. For both cases, the similar microstructure observed suggests that the ,-Si3N4 nuclei in RBSN may play a dominant role in the microstructural evolution of SRBSN rather than the intergranular glassy chemistry during post-sintering. It is found that the SRBSN materials exhibit an increase in the thermal conductivity from ,110 to ,133 (Wm·K),1 for both cases with the increased time from 6 to 24 h at 1900°C, but there is almost no difference in the thermal conductivity between them, which can be explained by the similar microstructure. The present investigation reveals that as second additives, the MgO is as effective as the MgSiN2 for enhancing the thermal conductivity of SRBSN. [source] Effect of Steam Velocity on the Hydrothermal Oxidation/Volatilization of Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006B. Sudhir The hydrothermal oxidation behavior of silicon nitride was studied as a function of vapor velocity in the range of 1,35 cm/s, at atmospheric pressure and ,100% H2O, using a custom-designed hydrothermal apparatus. At lower velocities, silicon nitride showed a marginal weight gain during early exposure times followed by a linear weight loss at longer exposure times. At higher velocities only linear weight loss was seen. The linear weight loss rates were determined from the weight change studies and they showed a square root dependence on velocity at higher flow rates. At the low flow rates a threshold velocity of ,1 cm/s was observed for volatilization to initiate. The weight loss rates obtained in the apparatus at the higher steam velocities were comparable to those obtained in high pressure burner rigs, proving its viability as a good laboratory scale screening method for potential gas turbine materials. [source] Ultrasonic Velocity Technique for Nondestructive Quantification of Elastic Moduli Degradation during Creep in Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003Franti, ek Lofaj The ultrasonic velocity technique was used for nondestructive quantification of creep damage during interrupted tensile creep tests at 1400°C in an advanced silicon nitride to investigate the possibilities of this technique for creep damage monitoring in ceramic components. The longitudinal and shear wave velocities, Poisson's ratio, and Young's, shear, and bulk moduli linearly decreased with strain. Precise density change measurements indicated a linear relationship with a coefficient of proportionality of 0.69 between the volume fraction of cavities and tensile strain. Cavitation was identified as the main creep mechanism in the studied silicon nitride and the reason for ultrasonic velocity and elastic moduli degradation. The measurement of just the longitudinal wave velocity changes was found to be sufficient for quantification of cavitation during creep. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable nondestructive monitoring of creep damage during intermittent creep was demonstrated in silicon nitride. [source] Pulsed Electric Current Sintering of Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Motohiro Suganuma Pulsed electric current sintering (PECS) has been used to densify ,-Si3N4 powder doped with oxide additives of Y2O3 and Al2O3. A full density (>99%) was achieved with virtually no transformation to ,-phase, resulting in a microstructure with fine equiaxed grains. With further holding at the sintering temperature, the ,-to-, phase transformation took place, concurrent with an exaggerated grain growth of a limited number of elongated ,-grains in a fine-grained matrix, leading to a distinct bimodal grain size distribution. The average grain size was found to obey a cubic growth law, indicating that the growth is diffusion-controlled. In contrast, the densification by hot pressing was accompanied by a significant degree of the phase transformation, and the subsequent grain growth gave a broad normal size distribution. The apparent activation energy for the phase transformation was as high as 1000 kJ/mol for PECS, almost twice the value for hot pressing (,500 kJ/mol), thereby causing the retention of ,-phase during the densification by PECS. [source] Elementary Mechanisms behind the High-Temperature Deformation Behavior of Lutetium-Doped Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Giuseppe Pezzotti Intergranular sliding and diffusive mechanisms behind the deformation behavior of a commercially available lutetium-doped silicon nitride were investigated and discussed. A method of locating and separating phenomena critical for mechanical relaxation at elevated temperatures was applied; the method was based on low-frequency forced-vibration damping measurements. The potentiality of lutetium addition for improving the deformation resistance of silicon nitride was clearly reflected in the high-temperature damping behavior of the investigated polycrystal. Softening of intergranular lutetium silicate phases located at multigrain junctions, which resulted in a grain-boundary sliding peak, occurred at remarkably high temperatures (>1725 K). This phenomenon, partly overlapping diffusional flow, was followed by further damping relaxation with the melting of the lutetium silicates. Subsequent grain growth was also detected at temperatures >2100 K. Torsional creep results, collected up to 2100 K, consistently proved the presence of a "locking" effect by lutetium silicates with the sliding of silicon nitride grain boundaries below 1873 K. [source] Silicon Nitride,Silicon Carbide Nancocomposites Fabricated by Electric-Field-Assisted SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Julin Wan Starting with Si-C-N(-O) amorphous powders, and using the electric field assisted sintering (EFAS) technique, silicon nitride/silicon carbide nanocomposites were fabricated with yttria as an additive. It was found that the material could be sintered in a relatively short time (10 min at 1600°C) to satisfactory densities (2.96,3.09 g/cm3) using 1,8 wt% yttria. With decreasing yttria content, the ratio of SiC to Si3N4 increased, whereas the grain size decreased from ,150 nm to as small as 38 nm. This offers an attractive way to make nano-nanocomposites of silicon nitride and silicon carbide. [source] Synthesis of Porous Silicon Nitride with Unidirectionally Aligned Channels Using Freeze-Drying ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2002Takayuki Fukasawa Porous silicon nitride with macroscopically aligned channels was synthesized using a freeze-drying process. Freezing of a water-based slurry of silicon nitride was done while unidirectionally controlling the growth direction of the ice. Pores were generated subsequently by sublimation of the columnar ice during freeze-drying. By sintering this green body, a porous silicon nitride with high porosity (over 50%) was obtained and its porosity was controllable by the slurry concentration. The porous Si3N4 had a unique microstructure, where macroscopically aligned open pores contained fibrous grains protruding from the internal walls of the Si3N4 matrix. It is hypothesized that vapor/solid phase reactions were important to the formation mechanism of the fibrous grains. [source] Development of a Self-Forming Ytterbium Silicate Skin on Silicon Nitride by Controlled OxidationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Seung Kun Lee A dense and uniform polycrystalline ytterbium silicate skin on silicon nitride ceramics was developed by a controlled oxidation process to improve the hot corrosion resistance of silicon nitride. The process consists of purposely oxidizing the silicon nitride by heating it at high temperatures. It was found that the ytterbium silicate phase was formed as an oxidation product on the surface of the silicon nitride when it was exposed to air at temperatures above 1250°C. The volume fraction of ytterbium silicate compared with that of SiO2 on the silicon nitride surface increased with increasing oxidation time and temperature. The formation and growth of ytterbium silicate on the surface of silicon nitride is attributed to a nucleation and growth mechanism. Ultimately, a dense and uniform ytterbium silicate skin with 3,4 ,m of skin thickness was obtained by oxidation at 1450°C for 24 h. The ytterbium silicate layer, formed by oxidation of the silicon nitride, is associated with the reaction of SiO2 on the surface of silicon nitride with Yb2O3 introduced in the silicon nitride as a sintering additive. Preliminary tests showed that the ytterbium silicate skin appears to protect silicon nitride from hot corrosion. No observable evidence of a reaction between the skin and molten Na2SO4 was found when it was exposed to molten Na2SO4 at 1000°C for 30 min. [source] Theoretical Prediction of Post-Spinel Phases of Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002Kazuyoshi Tatsumi New phases of Si3N4 that may be stable at higher pressure than spinel have been searched using a first-principles plane-wave pseudopotential method. The CaTi2O4 -type phase is found to be the prime candidate for the post-spinel phase among six phases selected on the analogy to high-pressure oxides. The phase transformation from the spinel is predicted to occur at 210 GPa. All silicon atoms of the new phase are coordinated by six anions, similar to the case of the high-pressure forms of SiO2 and SiC. Because of its high energy at zero pressure, this new phase may be difficult to quench. The bandgap increases with an increase of pressure when compared in the same polymorph. However, the bandgap and the net charge decrease in the order of ,, spinel, and CaTi2O4 -type phases at zero pressure. The theoretical bulk modulus of the CaTi2O4 -type phase is comparable with that of spinel. [source] Microstructural Control of a 70% Silicon Nitride, 30% Barium Aluminum Silicate Self-Reinforced CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2001Feng Yu The processing response of a 70% silicon nitride,30% barium aluminum silicate (70%-Si3N4,30%-BAS) ceramic-matrix composite was studied using pressureless sintering, at temperatures ranging from 1740°C, which is below the melting point of BAS, to 1950°C. The relationship between the processing parameters and the microstructural constituents, such as morphology of the ,-Si3N4 whisker and crystallization of the BAS matrix, was evaluated. The mechanical response of this array of microstructures was characterized for flexural strength, as well as fracture behavior, at test temperatures up to 1300°C. The indentation method was used to estimate the fracture resistance, and R -curves were obtained from modified compact-tension samples of selected microstructures at room temperature. [source] Effect of Microstructure on High-Temperature Compressive Creep of Self-Reinforced Hot-Pressed Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Martha A. Boling-Risser An experimental self-reinforced hot-pressed silicon nitride was used to examine the effects of microstructure on high-temperature deformation mechanisms during compression testing. At 1575,1625°C, the as-received material exhibited a stress exponent of 1 and appeared to deform by steady-state grain-boundary sliding accommodated by solution-reprecipitation of silicon nitride through the grain-boundary phase. The activation energy was 610 ± 110 kJ/mol. At 1450,1525°C for the as-received material, and at 1525,1600°C for the larger-grained heat-treated samples, the stress exponent was >1. Damage, primarily in the form of pockets of intergranular material at two-grain junctions, was observed in these samples. [source] Texture Development in Silicon Nitride,Silicon Oxynitride In Situ Composites via Superplastic DeformationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Rong-Jun Xie Silicon nitride,silicon oxynitride (Si3N4,Si2N2O) in situ composites have been fabricated via either the annealing or the superplastic deformation of sintered Si3N4 that has been doped with a silica-containing additive. In this study, quantitative texture measurements, including pole figures and X-ray diffraction patterns, are used in conjunction with scanning electron microscopy and transmission electron microscopy techniques to examine the degree of preferred orientation and texture-development mechanisms in these materials. The results indicate that (i) only superplastic deformation can produce strong textures in the ,-Si3N4 matrix, as well as Si2N2O grains that are formed in situ; (ii) texture development in the ,-Si3N4 matrix mainly results from grain rotation via grain-boundary sliding; and (iii) for Si2N2O, a very strong strain-dependent texture occurs in two stages, namely, preferred nucleation and anisotropic grain growth. [source] Comparison of Tensile and Compressive Creep Behavior in Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Kyung Jin Yoon The creep behavior of a commercial grade of Si3N4 was studied at 1350° and 1400°C. Stresses ranged from 10 to 200 MPa in tension and from 30 to 300 MPa in compression. In tension, the creep rate increased linearly with stress at low stresses and exponentially at high stresses. By contrast, the creep rate in compression increased linearly with stress over the entire stress range. Although compressive and tensile data exhibited an Arrhenius dependence on temperature, the activation energies for creep in tension, 715.3 ± 22.9 kJ/mol, and compression, 489.2 ± 62.0 kJ/mol, were not the same. These differences in creep behavior suggests that mechanisms of creep in tension and compression are different. Creep in tension is controlled by the formation of cavities. The cavity volume fraction increased linearly with increased tensile creep strain with a slope of unity. A cavitation model of creep, developed for materials that contain a triple-junction network of second phase, rationalizes the observed creep behavior at high and low stresses. In compression, cavitation plays a less important role in the creep process. The volume fraction of cavities in compression was ,18% of that in tension at 1.8% axial strain and approached zero at strains <1%. The linear dependence of creep rate on applied stress is consistent with a model for compressive creep involving solution,precipitation of Si3N4. Although the tensile and compressive creep rates overlapped at the lowest stresses, cavity volume fraction measurements showed that solution,precipitation creep of Si3N4 did not contribute substantially to the tensile creep rate. Instead, cavitation creep dominated at high and low stresses. [source] Fracture Energy of an Aligned Porous Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2000Yoshiaki Inagaki The fracture energy of a porous silicon nitride with aligned fibrous grains was investigated, using a chevron-notched-beam technique. A crack was constrained to propagate normal to the grain alignment. The obtained fracture energy was ,500 J/m2, which was ,7 times larger than that of a dense silicon nitride with randomly oriented fibrous grains. The large fracture energy was attributable primarily to the sliding resistance associated with interlocking grains. [source] Effect of Atmospheric Humidity on the Fatigue Crack Propagation Behavior of Short Cracks in Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Sotomi Ishihara The effect of the environment on crack-growth processes in silicon nitride was studied by investigating the static and fatigue crack-growth behavior of small surface cracks, as influenced by testing (i) in the ambient environment, (ii) in distilled water, (iii) under vacuum, and (iv) in toluene. A principal finding was that testing under cyclic conditions led to crack-growth rates that were much higher in air than in toluene, whereas testing under static conditions in air or toluene led to minor differences in the rate of static fatigue crack growth. This difference in sensitivity to the environment under static and cyclic loading conditions was attributed, in part, to a much-greater extent of microcracking at the surface ahead of the main crack in air under cyclic conditions, in comparison to that in other environments. This propensity for microcracking at the surface in air under cyclic conditions also was reflected in the aspect ratios of the crack shapes that developed. [source] Theoretical Investigation of the Solid State Reaction of Silicon Nitride and Silicon Dioxide Forming Silicon Oxynitride (Si2N2O) under PressureCHEMINFORM, Issue 49 2003Peter Kroll Abstract For Abstract see ChemInform Abstract in Full Text. [source] Texture Development in Silicon Nitride,Silicon Oxynitride In Situ Composites via Superplastic DeformationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Rong-Jun Xie Silicon nitride,silicon oxynitride (Si3N4,Si2N2O) in situ composites have been fabricated via either the annealing or the superplastic deformation of sintered Si3N4 that has been doped with a silica-containing additive. In this study, quantitative texture measurements, including pole figures and X-ray diffraction patterns, are used in conjunction with scanning electron microscopy and transmission electron microscopy techniques to examine the degree of preferred orientation and texture-development mechanisms in these materials. The results indicate that (i) only superplastic deformation can produce strong textures in the ,-Si3N4 matrix, as well as Si2N2O grains that are formed in situ; (ii) texture development in the ,-Si3N4 matrix mainly results from grain rotation via grain-boundary sliding; and (iii) for Si2N2O, a very strong strain-dependent texture occurs in two stages, namely, preferred nucleation and anisotropic grain growth. [source] Thermal, electrical, and mechanical properties of Si3N4 filled LLDPE compositePOLYMER COMPOSITES, Issue 7 2009Qunli An Silicon nitride (Si3N4) filled linear low-density polyethylene (LLDPE) composite was prepared. The effects of Si3N4 filler content, dispersion, and LLDPE particle size on the thermal conductivity, and Si3N4 filled content on the mechanical and electrical properties of Si3N4 reinforced LLDPE composites prepared using powder mixing were investigated. The results indicate that there existed a unique dispersion state of Si3N4 particles in LLDPE, shell-kernel structure, in which Si3N4 particles surrounded LLDPE matrix particles. With increasing filler content and LLDPE particles size, thermal conductivity increased, and reached 1.42 W/m K at 30 vol% of filler, seven times as that of unfilled LLDPE. Furthermore, the examinations of Agari model demonstrate that larger size LLDPE particles form thermal conductive networks easily compared with smaller ones. The values predicted by theoretical model underestimate the thermal conductivity of Si3N4/LLDPE composites. In addition, the composites still possessed rather higher electrical resistivity and dielectric properties, but the mechanical properties decreased. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Large-Scale Synthesis of Water Dispersible Ceria Nanocrystals by a Simple Sol,Gel Process and Their Use as a Chemical Mechanical Planarization SlurryEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2008Taekyung Yu Abstract Ceria nanocrystals with a cube shape were synthesized from the hydrolytic sol,gel reaction of cerium salt in the presence of oleylamine. The overall synthetic process is very simple and readily applicable to the large-scale synthesis of tens of grams of product in a single reaction in air. These ceria nanocrystals are readily dispersible in aqueous media without the addition of any extra dispersing agent. The aqueous dispersion of the ceria nanocrystals was successfully used as a chemical mechanical polishing slurry, and it exhibited high removal selectivity between silicon oxide and silicon nitride at pH 7.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Harald Schmidt Abstract The investigation of self-diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1,nm and below at corresponding low self-diffusivities between 10,25 and 10,20,m2 s,1. Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non-equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron. [source] Numerical and experimental investigation of mixed-mode fracture parameters on silicon nitride using the Brazilian disc testFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2010G. LEVESQUE ABSTRACT Engineering applications of ceramics can often involve mixed-mode conditions involving both tensile and shear loading. Mixed-mode fracture toughness parameters are evaluated for applicability to ceramics using the Brazilian disc test on silicon nitride. Semi-elliptical centrally located surface flaws are induced on the disc specimens using Vickers indentation and compression loaded to fracture with varying levels of mode mixity. The disc specimens are modelled via 3D finite element analysis and all three modes of stress intensity factors computed along the crack front, at failure load. We present a numerical and experimental investigation of four widely used mixed-mode fracture criteria and conclude that the critical strain energy release rate criterion is simple to implement and effective for silicon nitride under mixed-mode conditions. [source] Flaking failure originating from a single surface crack in silicon nitride under rolling contact fatigueFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2005K. KIDA ABSTRACT Flaking failure caused by surface cracks of silicon nitride ceramic bearings has been investigated from the viewpoint of the ring crack model. However, the relation between surface and subsurface cracks under rolling contact fatigue is not fully understood. In this investigation subsurface cracks branching from an initial surface crack were observed in detail, and the process of flaking failure was investigated. The specimens were observed prior to the separation of the surface layers and it was found that the initial surface cracks grew vertically to the surfaces and did not curve as predicted by the ring crack model. Subsurface cracks branched from the single surface cracks and grew in a direction parallel to the surface. They grew in both the same and the opposite directions to the ball movement, with small upward and downward branches. These subsurface cracks grew prior to the semi-circular surface cracks. From these observations it was concluded that the flaking failures are not caused directly by the surface cracks, but by the subsurface cracks that branch from them. [source] Vertical Transistor with Ultrathin Silicon Nitride Gate DielectricADVANCED MATERIALS, Issue 44 2009Maryam Moradi Nanoscale vertical thin-film transistors (VTFTs) are fabricated employing a new ultrathin silicon nitride (SiNx) gate dielectric for applications in high-resolution active matrix flat panel electronics. Illustrated are the cross-section schematic and SEM image of a 500,nm channel length VTFT with a 50,nm thick SiNx gate dielectric. The device demonstrates excellent gate control with gate leakage as low as 0.1,nA cm,2. [source] Properties of Porous Si3N4/BN Composites Fabricated by RBSN TechniqueINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2010Ji-Xuan Liu Reaction bonding of silicon nitride (RBSN) technique combined with slip-casting shaping process was used to fabricate porous Si3N4/BN ceramic composites. Si/BN slurry with chemical stability, good dispersibility, and viscosity was prepared using glycerol trioleate (GTO) covering on Si surface and poly(acrylic acid) (PAA) as dispersant. The hydrolysis of Si was strongly prevented by GTO coating. The dispersibility of covered Si and BN suspensions were improved by PAA dispersant. Twenty volume percent covered Si/BN slurries with low viscosity were successfully casted. The cast bodies were dried at room temperature, debindered at 750°C and nitrided below 1450°C. The nitrided samples mainly consist of ,-Si3N4, ,-Si3N4, and h-BN. The composites exhibit homogeneous microstructure consisting of faceted particles, ,-Si3N4 nanowires and a large amount of pores. The porosity is 52.64% and the pore size is in the range of 60,300 nm. The composites show compressive strength of 16.6±1.5 MPa. The dielectric constant of the composite is about 3.1 and the dielectric loss is below 0.5% under different frequencies. [source] Sintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High StrengthINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2008You Zhou Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400°C for 8 h and subsequently postsintering at 1900°C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source] Highly Durable Ceramic Thermometer for Molten MetalINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2006Hideki Kita It was shown that a silicon nitride (SN)/boron nitride (BN) composite laminate provides excellent thermal shock resistance, and to improve the corrosion resistance of the SN pipe against molten metals, the Mo/ZrB2 film was effective for molten cast iron. The authors have developed a thermocouple that yields high durability and good response using an SN/BN composite laminate as an external sleeve and film-coated SN protection tube. According to the results of repeated temperature measurement tests for molten metals, it was demonstrated that the thermometer thus designed had high durability, e.g., 360 times measurement to life was achieved for molten cast iron. [source] Development of the powder reaction moulding processJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2009Lei Zhao Abstract BACKGROUND: The powder reaction moulding process uses a reactive monomer as carrier and binder for the moulding of metal or ceramic powders. De-binding is achieved using thermal depolymerisation which is followed by sintering to give the finished component. Binder can be recovered for re-use. RESULTS: Moulding compounds, with various powder volume fractions, have been prepared using stainless steel, silicon nitride and alumina with n-butyl cyanoacrylate as binder, and the stability of the compounds established. Rheological properties of the compounds have been measured using both pressure flow and drag flow methods. Compounds are strongly pseudoplastic. Comparison of experimental results with theoretical models, describing suspension flow behaviour shows that experimental maximum volume fractions are close to the theoretical volume fraction of 0.42 for silicon nitride, 0.68 for alumina and 0.7 for stainless steel. Differential scanning calorimetry and thermogravimetry have been used to simulate de-binding and show a rapid loss of binder through depolymerisation. Post-sintering porosity of the ceramic materials is high but this is thought to arise from the low pressure moulding techniques used. Porosity of the stainless steel mouldings is much lower. CONCLUSIONS: The results validate the powder reaction moulding idea and demonstrate applicability to three widely different powder materials. Copyright © 2008 Society of Chemical Industry [source] Atomic force microscopy study of the role of LPS O-antigen on adhesion of E. coliJOURNAL OF MOLECULAR RECOGNITION, Issue 5 2009Joshua Strauss Abstract The O-antigen is a highly variable component of the lipopolysaccharide (LPS) among Escherichia coli strains and is useful for strain identification and assessing virulence. While the O-antigen has been chemically well characterized in terms of sugar composition, physical properties such as O-antigen length of E. coli LPS have not been well studied, even though LPS length is important for determining binding of bacteria to biomolecules and epithelial cells. Atomic force microscopy (AFM) was used to characterize the physicochemical properties of the LPS of eight E. coli strains. Steric repulsion between the AFM tip (silicon nitride) and the E. coli cells was measured and modeled, to determine LPS lengths for three O157 and two O113 E. coli strains, and three control (K12) strains that do not express the O-antigen. For strains with an O-antigen, the LPS lengths ranged from 17,±,10 to 37,±,9,nm, and LPS length was positively correlated with the force of adhesion (Fadh). Longer lengths of LPS may have allowed for more hydrogen bonding between the O-antigen and silanol groups of the AFM silicon nitride tip, which controlled the magnitude of Fadh. For control strains, LPS lengths ranged from 3,±,2 to 5,±,3,nm, and there was no relationship between LPS length and adhesion force between the bacterium and the silicon nitride tip. In the absence of the O-antigen, we attributed Fadh to electrostatic interactions with lipids in the bacterial membrane. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis of silicon nitride based ceramic nanoparticles by the pyrolysis of silazane block copolymer micellesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2006Kozo Matsumoto Abstract Diblock copolymer poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane)- block- polystyrene (polyVSA- b -polySt) and triblock copolymer poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane)- block- polystyrene- block -poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane) (polyVSA- b -polySt- b -polyVSA), consisting of silazane and nonsilazane segments, were prepared by the living anionic polymerization of 1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane and styrene. PolyVSA- b -polySt formed micelles having a poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane) (polyVSA) core in N,N -dimethylformamide, whereas polyVSA- b -polySt and polyVSA- b -polySt- b -polyVSA formed micelles having a polyVSA shell in n -heptane. The micelles with a polyVSA core were core-crosslinked by UV irradiation in the presence of diethoxyacetophenone as a photosensitizer, and the micelles with a polyVSA shell were shell-crosslinked by UV irradiation in the presence of diethoxyacetophenone and 1,6-hexanedithiol. These crosslinked micelles were pyrolyzed at 600 °C in N2 to give spherical ceramic particles. The pyrolysis process was examined by thermogravimetry and thermogravimetry/mass spectrometry. The morphologies of the particles were analyzed by atomic force microscopy and transmission electron microscopy. The chemical composition of the pyrolysis products was analyzed by X-ray fluorescence spectroscopy and Raman scattering spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4696,4707, 2006 [source] | |||||||||||||||||||||||||||||||