Showing papers on "Sialon published in 1988"

Ultrastructure processing of advanced ceramics

Abstract: Experimental investigations and applications of advanced ceramics are discussed in reviews and reports presented at the Third International Conference on Ultrastructure Processing of Ceramics, Glasses, and Composites held in San Diego in February 1987. Sections are devoted to precursors and chemistry for ultrastructure processing; sol-gel science and technology; powders and colloids; advanced ceramics; and composites, new materials, and techniques. Particular attention is given to silicon oxynitride and sialon ceramics from organosilicon powders, fluoropolymer-modified silicate glasses, Raman and FTIR spectroscopy of rapid sol-gel processes, a low-temperature route to high-purity Ti/Zr/Hf diboride powders and films, and sol-gel methods for SiO2 optical-fiber coatings. Diagrams, drawings, graphs, micrographs, and tables of numerical data are included.

Ceramic Microstructures '86: Role of Interfaces

Abstract: Progress in the Understanding of Ceramic Microstructures and Interfaces since 1976.- Ceramic Microstructures: The Art of the Possible.- Designing Material Structures.- Purposive Design of Nanocomposites: Entire Class of New Materials.- Design of High Thermal Expansion Glass-Ceramics Through Micros truetura1 Control.- Microdesigning of Ceramic-Metal Composites.- Characterization of Microstructures.- Grain Boundaries and Interfaces: Some Applications of Electron Microscopy and Microanalysis.- Quantitative Characterization of Microstructural Geometry of Interfaces.- Gas Transport as a Tool for Structural Characterization of Inter facial Phases.- Unit Cell Distortion of Pb(Zr,Ti)O3 by Pb(Co,Nb)O3.- Electron Microscopy Studies of BaTiO3~NaNbO3 Ceramics.- Analytical Electron Microscopy of the Glassy Phase in Mullite/Zirconia Composites.- Microstructure Characterization of Basalt Glass-Ceramics.- Interfacial Reaction Between Bioactive Glass and Synthetic Physiological Solution.- Oxidation and Microstructure of Sintered Silicon Nitride.- Origin of Cracking Phenomena Observed in Decomposition Reactions.- Characterization of Interfaces.- Oxide Interfaces: Theory of Oxide-Oxide and Oxide-Metal Interfaces.- Green Function Method for Calculation of Atomistic Structure of Grain Boundary Interfaces in Ionic Crystals.- Comparison of the Energies of Symmetrical and Asymmetrical Grain Boundaries.- The Structure of a Natural Grain Boundary in a Magnetite Bicrystal Studied by XRD Technique.- Interface Morphology in Ceramics.- HREM Study of a Tetragonal ? Monoclinic Martensitic Interface in a Y2O3-Stabilized ZrO2 Alloy.- Control of the Tetragonal to Monoclinic Phase Transformation of Yttria-doped Tetragonal ZrO2 Polycrystals by Annealing in Water.- Grain Boundary Energy of Twisted MgO Bicrystals on (100).- T.E.M. Statistical Characterization of Grain Boundaries in Polycrystalline NiO Scales Obtained by High Temperature Oxidation of Nickel.- Structure of High-Angle Grain Boundaries in NiO.- High-Angle Grain Boundaries in Sheet Silicates (Biotite/Chlorite): A TEM Study.- HRTEM Analysis of Ordered Grain Boundaries in High Purity Alpha-SiC.- Atomic Structure of Interfaces in Sialon Ceramics.- Characterization of Impurity Segregations.- Atomistic Lattice Simulations of the Structure, Energetics and Impurity Segregation Behaviour of Ceramic Boundaries.- Distribution and Influence of Minor Constituents on Ceramic Formulations.- Characterization of Interphase Interfaces.- Diffusion Bonding of Metal/Ceramic Interfaces-A Model Study at the Nb/Al2O3Interfaces.- Ceramic-Metal Reactions and Their Effect on the Interface Microstructure.- The Influence of Surface Roughness on Interface Formation in Metal/Ceramic Diffusion Bonds.- A Reappraisal of Wetting in the System AI-AI2O3 from 750-1000 C.- Microstructural Characterization of Ni/Al203 Diffusion Bonds.- Bonding Ceramic-Metal Interfaces and Joints.- Copper-Glass-Ceramic Interfaces and Composites: Reactions, Microchemistry, and Electrical Properties.- The Study of Microstructures for Pt-Silicide Interfaces after Nd:YAG Laser Irradiation by XRD, SEM, XPS, and RBS.- High Resolution Electron Microscopy of Silicon Nitride-Metal Bonded Interfaces.- Interfacial Chemistry and Bonding in Fiber Reinforced Glass and Glass-Ceramic Matrix Composites.- Effects of Interfacial Diffusion Barriers on Thermal Stability of Ceramic Fibers.- Solid State Bonding of Alumina and Steel by HIPING.- Thermochemical Analyses of Interface Reactions in Carbon-Fiber Reinforced Glass Matrix Composites.- Interfaces in Heterogeneous Dissolution of Oxides in Molten Ca-Al-Silicates.- Microstructure Development.- Powders, Interfaces, and Processing: Alumina as a Case Study.- The Role of Powder Packing in Sintering.- Effect of Pores on Microstructure Development.- Microstructure Development of Hydrothermal Powders and Ceramics.- The Colloidal Chemistry of Growing Silica Spheres.- Effects of Vapor Transport on Microstructure Development.- Controlling Grain Growth.- The Effects of Grain Growth on the Intergranular Porosity Distributions in Hot-Pressed and Swelled UO2.- Effects of Solutes on the Grain Boundary Mobility of TiO2.- Microstructural Development in Hot Pressed CaO: Density Decrease and Pore Growth During Post Sintering.- Diffusion Induced Interface Migration in Ceramics.- Grain Boundary Diffusion Artefacts in Polycrystalline Nickel Oxide Grown by High Temperature Oxidation.- Variations in Grain Growth of Donor-Doped SrTiO3 with Cation Nonstoichiometry.- The Wetting and Dewetting of Grain Boundaries.- Anion Controlled Microstructures in the Al2O3-AIN System.- Sintering.- Sintering Theory for Crystalline Solids.- Selected Sintering Conditions for SiC and Si3N4 Ceramics.- Colloidal Consolidation and Sintering Behavior of CVD-Processed Mullite Powders.- Sintering of Acicular NiZn-Ferrite Powder.- Continuous SiC Fiber/Glass Composites.- Electrical Properties.- Electrical Conductivity in Ceramics: A Review.- The Crystallographical and Chemical Relationship between Intergranular and Bulk Resistivity in Semi-Conductor Oxides.- Interface Effects in Zinc Oxide Varistors.- The Role of Inter facial Microstructure in ZnO Varistor Materials.- Electrical Properties and Microstructure of ZnO-Nb2O5~MnO Ceramics Sintered in the Liquid Phase.- New Composite PTC Materials Based on PbTiO3-TiO2.- Effects of Microstructure Control on Ferroelectric Ceramics.- Effect of Deviations from Stoichiometry on Microstructure and Magnetic Properties of Ferrites.- Optical Effects of Grain Boundaries in PLZT Ceramics.- Microstructures of High Dielectric Constant Materials.- Interfaces Generated by Electronic Device Development in Beta SiC Thin Films.- Electrical Barriers at Grain Boundaries in Silicon Carbide Materials with BeO Addition.- Microstructural Analysis of Silicon Carbide Materials with BeO Addition.- Mechanical Properties and Behavior.- The New Generation of High Toughness Ceramics.- Influence of Microstructure on Creep Rupture.- Mechanisms of Dynamic Failure in Debased Alumina.- Some Interfacial Related Properties of Transformation Toughened Ceramics.- Precipitation in a (Mg) Partially Stabilized Zirconia during Aging at 1000 C.- High Temperature Mechanical Properties of ZrO2-Based Ceramics.- Microstructure and Mechanical Properties of a Al2TiO5-Mullite-ZrO2 Composite Obtained by Reaction Sintering.- Interfaces in Ceramic Fiber Composites.- Delamination Toughening from Interfacial Cracking in Ceramics and Ceramic Composites.- Development of Structure in Silicon Nitride Grain Boundaries.- The Impact of Compositional Variations and Processing Conditions on Secondary Phase Characteristics in Sintered Silicon Nitride Materials.- Structure and Chemistry of Interfaces in Silicon Carbide-Containing Materials.- Interfaces in Alumina-SiC Whisker Composites.- Creep Performance of Silicon Carbide Whisker-Reinforced Alumina.- Temperature-Dependent Toughening in Whisker-Reinforced Ceramics.- Effect of High Temperature Oxidation on the Microstructure and Mechanical Properties of Whisker-Reinforced Ceramics.- The Role of Interfacial Reactions on the Mechanical Properties of Ceramic Brazements.- Fracture Energies of Ceramic-Metal Interfaces.- On the Fracture Behavior and Microstructure of Metal-to-Ceramic Joints.

Molten-salt corrosion of silicon nitride. I - Sodium carbonate. II - Sodium sulfate

Abstract: An experimental study of the corrosion of Si3N4 under thin films of Na2CO3 at 1000 C has been conducted using both pure Si3N4 and Si3N4 with various additives. The reaction mechanism is shown to consist of: (1) the decomposition of Na2CO3 and the formation of Na2SiO3; (2) rapid oxidation; and (3) the formation of a protective silica layer below the silicate. In the second part, the corrosion mechanism of Si3N4 + Na2SO4/O2 at 1000 C was studied for both pure and additive-containing Si3N4. The reaction of Si3N4 + Na2SO4 was found to involve an initial period of slow weight loss (due to Na2SO4 vaporization and oxidation-dissolution) followed by further oxidation or the near termination of the reaction, depending on the Si3N4 additive.

Sialon cutting tool composition

Abstract: A sialon ceramic material comprising a ceramic core selected from alpha-prime-sialon, beta-prime-sialon, and an intergranular phase and, optionally substantially substantially inert refractory phases. The sialon ceramic material has an alloyed surface layer with a substantially increased aluminum and oxygen content.

Sialons from natural aluminosilicates

Abstract: The synthesis of the high-temperature material sialon (Si{sub 6{minus}z}Al{sub z}O{sub z}N{sub 8{minus}z}) by carbothermic reduction followed by nitridation has been examined. Kaolin, sillimanite, and pyrophillite can be converted to {beta}{prime}-sialon having z values of 2, 2.5, and 0.8, respectively. Other phases that appear in small quantities along with the sialon are mainly alumina and mullite, and trace amounts of AlN and the AlON spinel phase also form. The carbon content at {ge}90% theoretical is very sensitive to nitrogen uptake and phase composition. The uniform mixing of carbon with clay is equally important. Fireclay without an Fe{sub 2}O{sub 3} catalyst produces the same product that does kaolin with an Fe{sub 2}O{sub 3} catalyst.

Rotating body for molten metal

Abstract: PURPOSE:To decrease wear and to eliminate generation of cracks so as to extend the life of the titled rotating body using nonoxide type ceramics having a specific thickness or below to form rotary vanes for removing impurities in a molten metal of aluminum, etc., and a rotating body of a rotary pump. CONSTITUTION:The rotary vanes 1 for removing the impurities in the molten metal of aluminum, etc., and the rotating body 3 of the rotary pump are formed of the nonoxide type ceramics such as silicon carbide, silicon nitride and SIALON. Grooves etc., 1a, 3b are provided thereto and the max. thickness thereof is specified to <=30mm. Since the rotating bodies 1, 3 are ceramics, the wear in the molten metal is decreased and since the thickness is small, the generation of the cracks by heat shock is obviated. The excellent rotating body for the molten metal having a long life is thus provided.

The fabrication of O′-sialon ceramics by pressureless sintering

Abstract: Low-porosity ceramics with O′-sialon as the major crystalline phase have been successfully fabricated by pressureless sintering. Densification at 1400 to 1800° C is interpreted using Kingery's liquid-phase sintering model. Particle rearrangement accounts for a significant proportion of the overall densification and is closely related to the amount and viscosity of the liquid present. The oxidation resistance of fabricated samples is good but, at temperatures above 1300° C, decreases with increasing alumina content in the starting mix. Modulus of rupture values of about 420 MPa at room temperature are high enough to encourage further work.

α‐β Sialon Ceramics Made from Different Silicon Nitride Powders

Abstract: Etude du frittage d'une ceramique de sialon α-β a partir de cinq poudres differentes de Si 3 N 4 , les parametres variant etant la teneur en silicium «libre», la teneur en fer, le rapport α/β et la grosseur de grain

Corrosion and strength degradation of Si3N4 and sialons in K2CO3 and K2SO4 melts

Abstract: Si3N4-based ceramics, such as hot isostatically pressed Si3N4, hot-pressed Si3N4, hot-pressed sialons containing 0, 30, 60 and 100% a phase, were corroded by K2SO4 and K2CO3 melts at 1150 to 1300 and 925 to 1150° C, respectively. The surface chemical reaction-controlled shrinking core model adequately described the relationship between the weight loss of the specimen and time for the corrosion reactions in both K2SO4 and K2CO3 melts, and the apparent activation energies were 380 to 608 and 157 to 344 kJ mol−1, respectively. The corrosion rate in K2CO3 melt decreased with increasing content of aluminium and yttrium ions in the specimens, but no systematic relation was observed for the reaction in K2SO4 melts. The fracture strength of the specimens corroded by K2SO4 and K2CO3 melts degraded to 2/3 to 2/5 of the original values up to a 2% weight loss, and then was almost constant up to 30% weight loss.

Heat ray reflecting plate having visible light permeability

Abstract: PURPOSE: To enhance visible light permeability and also enhance heat ray reflecting ability by providing a heat ray reflecting layer consisting of a noble metal on a basement with visible light permeability and providing thereon a coating layer consisting of aluminum or aluminum nitride or nitrogen oxide. CONSTITUTION: The heat ray reflecting plate 1 is made up of the heat ray reflecting layer 3 consisting of the noble metal formed on the basement 2 having visible radiation permeability and the coating layer 4 consisting of metal nitride or nitrogen oxide contained mainly with Al or Al and Si formed on the heat ray reflecting layer 3. Between the basement 2 and the heat ray reflecting layer 3, a transparent dielectric layer 5 consisting of metal oxide, nitride or nitrogen oxide is formed and a transparent dielectric layer 6 consisting of metal oxide is also formed on the coating layer 4. As a basement 2, glass or plastic or the like is used and as a noble metal constituting the heat ray reflecting layer 3, silver, gold, copper, palladium, rhodium or the like is used. And as alloy oxide or nitrogen oxide of Al or Al and Si constituting the coating layer 4, aluminum nitride, sialon or the like is given and the thickness of the coating layer 4 is above 10Å. COPYRIGHT: (C)1989,JPO&Japio

Oxidation of nonoxide ceramics by water vapor at high temperatures.

Abstract: Nonoxide ceramics of hot-pressed AlN, hot-pressed Si3N4, sintered Si3N4, hot-pressed sialon and hot-pressed B4C were oxidized in wet nitrogen and/or wet air atmosphere at 1.5 to 20kPa of water vapor pressure and in dry air at 900-1400°C. All specimens were oxidized by both dry air and water vapor at high temperatures. AlN formed α-Al2O3 film on the surface above 1150°C. The oxidation rate of AlN increased with increasing water vapor pressure. The oxidation rate of AlN in wet nitrogen was much greater than that in wet air. Si3N4 and sialon formed oxide films consisting of SiO2, Y2Si2O7 and YAlO3. The oxidation kinetics obeyed the usual parabolic law. The oxidation rate in wet nitrogen, however, was unaffected by water vapor pressure and increased with increasing Y2O3 content. The apparent activation energy for the oxidation of Si3N4 based ceramics was about 800kJ/mol. On the other hand, since the oxidation of B4C by water vapor and dry air above 900°C resulted in weight loss, the formation of BO or HBO2 seemed to be the main reaction. The oxidation rate of B4C by water vapor above 900°C could be expressed by the surface chemical reaction controlled kinetics with the apparent activation energy of 200kJ/mol.

Refractory ceramic material and preparation thereof

Abstract: A refractory material composed of conventional fused or tabular alumina grains, bonded by a novel bonding phase that shows X ray diffraction lines characteristic of both sialon and silicon oxynitride, with the latter predominating, has a modulus of rupture at 1450 C of more than 350 bars and good thermal shock resistance. The material can be made by mixing appropriate amounts of silicon metal powder, fine reactive alumina, and a fine silica source such as bentonite clay with the alumina grains and a binder and dispersant liquid to form a refractory mass suitable for shaping, then shaping, and heating the shaped body in a nitrogen atmosphere.

Method for the production of beta-sialon based ceramic powders

Abstract: Disclosed is a method to obtain β′-sialon-based ceramic powders through carbo-thermal reduction in a nitrogen atmos­phere at 13OO-15OO°C of pre-mullitic material with high specific surface and reactivity; the latter material ha­ving a crystalline phase with a formula of 3Al₂O₃, 2SiO₂ and a proportion of displaced amorphous silica, and the overall proportion of Al₂O₃/SiO₂ ranges from O.5 to 1.5 giving specific surfaces that are always higher than 5O m²/g. The product obtained has a major phase of β′-sialon with a formula of Si 6-z Al z N 8-z O z (where z=2.7-4.O) and small proportions or traces of other phases such as α-Al₂O₃, β-Si₃N₄ and polytypes.

The U-phase in heat-treated sialon ceramics

Abstract: On etudie une nouvelle phase, designee comme «U», qui est observee lors du traitement thermique a 1000-1350°C apres frittage d'une ceramique de sialon additionnee de Y 2 O 3 comme agent densifiant

High temperature fracture toughness and fractographic study of reaction-sintered SiAlON and liquid-phase-sintered SiAlON

Abstract: Fracture toughness of reaction-sintered SiAlON and liquid-phase-sintered SiAlON by the single-edge-notched bending (SENB) technique was determined in the range from room temperature to 1400°C. Reaction-sintered SiAlON with a higher density and a predominantly elongated grain structure showed better KIc characteristics. Liquid-phase-sintered SiAlON with a higher density, a higher morphological aspect ration of elongated grains and a lower liquid phase content showed better KIc characteristics. Liquid-phase-sintered SiAlON containing yttrium had a better KIc. For all materials, KIc determined by the SENB technique was 1.42 times higher than that determined by the indentation method. Scanning electron microscopy of fracture surfaces offered qualitative estimation of fracture initiating flaws.

Composition for metallizing a surface of ceramics, a method for metallizing, and metallized ceramics

Abstract: A metallizing composition essentially consists of given amounts of Ni, Nb, Cr, C, Si, Zr, SiC and W and is used for metallizing the surface of ceramics such as Si 3 N 4 , SIALON, A1N, high purity alumina and so on. This composition forms a metallized layer having an excellent bonding strength to the ceramic surface.

Process for the preparation of sialon products

Abstract: The invention relates to a process for the preparation of sialon products by mixing zeolites with carbon or a carbon-containing compound and subjecting the obtained mixture to a carbothermic reduction in a nitrogen containing, flowing gas at a temperature in the range of 1350-1700 °C and to sialon products, having an average nitrogen content in the bulk of 25-31% by weight and an active surface of 1-15 m²/g (measured according to the BET method) and to shaped ceramic materials and catalyst carriers therefrom.

The effect of carbide and nitride additives on the oxidation resistance of silicon nitride ceramics

Abstract: The mechanism of high temperature oxidation in air (up to 1500°C) for silicon nitride materials containing SiC, TiN, TiC0.5N0.5, ZrN and EN was investigated. The effect of non-oxide refract...

Production of silicon carbide brick having sialon linkage

Abstract: PURPOSE: To obtain the title brick excellent in heat shock resistance with little change in volume and physical properties in an oxidative or reducive atmosphere by press forming of a mixture comprising SiC aggregate, metallic Si powder and metallic Al powder followed by sintering in a N 2 atmosphere. CONSTITUTION: Firstly, 100 pts.wt. of silicon carbide aggregate is homogeneously mixed with 15-20 pts.wt. of a blend comprising 67.5-88.8wt.% of metallic silicon powder, 3.4-8.5wt.% of metallic aluminum powder and 3-24wt.% of aluminum oxide powder. Thence, the resultant mixture is put to press forming and sintered in a nitrogen atmosphere at 1300-1500°C thus obtaining the objective brick. The sintering atmosphere is required to be a nitrogen one in order to develop SIALON linkage during the sintering process. If 1500°C, SIALON is rapidly formed on the surface of the sintered form to effect densification of said form; hence, a nitrogen gas cannot diffuse deep into the sintered form, therefore being unfavorable. COPYRIGHT: (C)1990,JPO&Japio

Skate and skate-blade

Abstract: A skate for ice-skaing has a skate-blade (2), consisting wholly of ceramic material which may be fibre-reinforced. The hardness and low thermal conductivity of ceramic material gives improved skating performance. Suitable materials are aluminium titanate, aluminium zirconate, zirconia silicon nitride, silicon carbide and sialon.

Joining stress buffer alloy of ceramics and metal and joined body of ceramics and metal formed by using said buffer alloy

Abstract: PURPOSE: To prevent exfoliation and breakage of joint surfaces by thermal stresses of heating and cooling by interposing joining stress buffer alloy layers essentially consisting of W between ceramics and metal which are largely different in coefft. of thermal expansion, then brazing and the ceramics and the metal at the time of joining both. CONSTITUTION: The joining stress buffer alloy 1 consisting of >60wt.% W and the balance ≥1 kinds among Fe, Ni, Cu, and Cr as a sintering assistant and the metal layers 2, 3, 4 consisting of Ni, Fe, Nb, 'Cobal(R)', Cu or W alloy are laminated and dispersed between the ceramics 10 such as silicon nitride or sialon and the metal 20 such as heat resisting steel at the time of joining both. The respective end faces 11, 1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b, 21 of these laminated materials are soldered by brazing filter metals 5W9 having compositions consisting of 70% Ag, 25% Cu and 5% Ti. The joined body a of the ceramics 10 and the heat resisting steel 20 has excellent durability to the heat history of about ≥250°C temp. difference. COPYRIGHT: (C)1989,JPO&Japio

Production of ceramic-metallic composite body

Abstract: PURPOSE:To obtain the titled composite body in which fine pores are almost uniformly distributed all over by eluting porous forming powders away from the molded and sintered body of ceramic powders and the porous forming powders elutable by acid and pressurizing and packing the molten metals into said sintered body. CONSTITUTION:The ceramic powders consisting of the single or mixed powders such as Si3N4, SIALON, SiC, etc., having <=20mum diameter and the porous forming powders elutable by the acid are mixed and molded. As said porous forming powders, e.g., Al2O3-Na2O-B2O3-SiO2 powders, etc., having 1-5mum diameter are used. The above-mentioned molded body is then sintered at 800-2,200 deg.C and the obtd. sintered body is immersed into the acid soln. of the single acid of HCl or HNO3, or the mixed acid of those at 30-60 deg.C and the porous forming powders are eluted away. The ceramic sintered body after the acid elution is furthermore calcined at 1,700 deg.C and the metals such as Al, Mg, Zr, Cu, etc., are pressurized and packed thereto as melted. By this method, the desired ceramic-metallic composite body having excellent wear resistance, heat resistance, etc., is obtd.