Showing papers on "Ceramic published in 1986"

Process for durable sol-gel produced alumina-based ceramic abrasive grain and abrasive products

Abstract: A sol-gel process of producing durable alpha alumina-based ceramic particularly useful as abrasive grain from alpha alumina monohydrate is improved by the addition of a nucleating agent. Improved abrasive products containing the durable ceramic abrasive grains are also provided.

Solidification, structures, and properties of cast metal-ceramic particle composites

Abstract: Solidification synthesis of cast metal-ceramic particle composite materials by dispersing hard or soft ceramic particles (including microballoons) and short fibres in molten alloys before solidification is described. Microstructures synthesized using a variety of casting techniques such as gravity or pressure die casting, centrifugal casting, and squeeze casting are discussed. Techniques to obtain a selected distribution of dispersed particles in cast alloy matrices by controlling solidification parameters and inducing melt particle wettability are reviewed. These cast metal-ceramic particle composites represent low cost, high performance, tailor made substitute materials for a variety of automotive and electromechanical applications such as pistons, cylinder liners, bearings, and current collectors, resulting in savings of material and energy.

Formation of LanxideTMa) ceramic composite materials

Abstract: An overview is given of a new process that has been used successfully to make numerous ceramic/metal composite materials by directed oxidation of molten metallic precursors. As an example, the formation of A12O3/A1 composites from Al is discussed in detail.

Fiber reinforced glasses and glass-ceramics for high performance applications

Abstract: The development of fiber reinforced glass and glass-ceramic matrix composites is described The general concepts involved in composite fabrication and resultant composite properties are given for a broad range of fiber and matrix combinations It is shown that composite materials can be tailored to achieve high levels of toughness, strength, and elastic stiffness, as well as wear resistance and dimensional stability

Tension and flexural strength of silicon carbide fibre-reinforced glass ceramics

Abstract: The use of silicon carbide-type fibres to reinforce lithium aluminosilicate glass ceramics results in composites with exceptional levels of strength and toughness. It is demonstrated that composite strength and stress-strain behaviour depend onin situ fibre strength, matrix composition, test technique and atmosphere of test. Both linear and non-linear tensile stress-strain curves are obtained with ultimate strengths at 22° C approaching 700 MPa and failure strains of 1%. Flexure tests performed at up to 1000° C in air are compared with data obtained in argon to demonstrate a significant dependence of strength and failure mode on test atmosphere. Finally, glass ceramic matrix composite performance is compared with a silicon carbide fibre-reinforced epoxy system to demonstrate the importance of matrix failure strain on strength and stress-strain behaviour.

Ceramic materials for electronics: Processing, properties, and applications

Abstract: Addressed to professionals who develop, design, and fabricate electrical ceramic parts, or who use such parts in designing electronic devices. Also suitable as a text for a senior undergraduate engineering course. Considers a wide range of ceramic materials such as piezoelectrics, ferroelectrics, in

Tailoring Multiphase and Composite Ceramics

Abstract: Processing and Fabrication of Multiphase Ceramics.- Sintering of Multiphase Ceramics.- The Morphological Stability of Continuous Intergranular Phases.- Role of Shear in the Sintering of Composites.- HIP of Liquid Phase Sintered Ceramic Composites.- Sinterable Yttria-Doped Zirconia Powders Chemically Coprecipitated in Non-Aqueous Medium.- Microstructural and Chemical Aspects of a Strontia Sintering Aid on Mg-PSZ.- Phase Relationships in Y-Si-A1-O-N Ceramics.- The Fabrication of Composite O'-B' Sialon Ceramics.- Ceramic Eutectic Composites.- Nickel Oxide-Based Aligned Eutectics.- Imperfections in the Directionally Solidified Structure of NiO-CaO Eutectic.- CVD-Processing of Ceramic-Ceramic Composite Materials.- CVD Fabrication of In-situ Composites of Non-oxide Ceramics.- Preparation of Boron Nitride/Boron Carbide Ceramics by Pyrolysis of Boric Acid-Glycerin Condensation Product.- Porous and Dense Composites for Sol-Gel.- Non-Equilibrium Surface Conditions and Microstructural Changes Following Pulsed Laser Irradiation and Ion Beam Mixing of Ni Overlayers on Sintered Alpha-SiC.- Structure-Property Relations in Multiphase Ceramics.- Quantitative Microstructural Characterization and Description of Multiphase Ceramics.- Displacive Transformation Mechanisms in Zirconia Ceramics and Other Non-Metals.- On Precipitate Morphology in ZrO2 ?-Al2O3, FeTiO3 Matrices.- Particle Toughening in Partially Stabilized Zirconia Influence of Thermal History.- Fabrication and Properties of Transformation-Toughened Sodium Beta"-Alumina.- Phase Transformation and Toughening in MgO Dispersed with ZrO2.- Effect of Impurities on Microstructure and Mechanical Properties of Si3N4-TiC Composites.- On the Microstructure and Hardness Characteristics of Composite Ceramics for Tool Applications.- Mechanical Properties and Wear Resistance of Silicon Nitride-Titanium Carbide Composites.- The Structure and Properties of Interfaces in Reaction-Bonded Silicon Carbides.- Some Factors Affecting Mechanical and Microstructural Anisotropy in Reaction-Bonded Silicon Carbides.- Microstructure-Mechanical Property Relationships in 94% Alumina Ceramics.- New Low Expansion Magnetic Materials-A Composite Approach.- Multiphase Electroceramics.- Electroceramic Composites.- Finite Element/Difference Modeling of Electroceramics.- Multiphase Interaction for Seeking Exotic Phenomena.- Processing of Heterogeneous Ceramics for Dielectric Applications.- Dielectric and Electrical Properties of BaTiO3 Composites.- Composite Piezoelectric Sensors.- Wave Absorption in Piezoceramic-Polymer Composites.- Structured Macrovoids in Ceramic PZT.- Composite Thermistors.- Grain Resistivity and Conduction in Metal Oxide Varistors.- Influence of Microstructure and Chemistry on the Electrical Characteristic of ZnO Varistors.- Influence of Chemical Composition on the Barrier Height in Zn Varistors.- Polycrystalline H3O+-?/?" Alumina: A Designed Composite for Steam Electrolysis.- Fiber and Whisker Reinforced Composites.- The Development of Fiber Reinforced Glasses and Glass Ceramics.- Interfacial Characterization of Glass and Glass-Ceramic Matrix/Nicalon SiC Fiber Composites.- Fatigue Behavior of Silicon Carbide Fiber Reinforced Lithium-Alumino-Silicate Glass-Ceramics.- Fiber Reinforced Composites Via the Sol/Gel Route.- Fiber-Matrix Interactions in Carbon Fiber/Cement Matrix Composites.- Morphological and Mechanical Characterization of Ceramic Composite Materials.- Toughness Anisotropy of a SiC/SiC Laminar Composite.- Whisker Reinforced Ceramic Composites.- Whisker-Reinforced Zirconia-Toughened Ceramics.- Si3N4-SiC Whisker Composite Material.- Mechanical Properties of SiC Fiber-Reinforced Reaction-Bonded Si3N4 Composites.- Surface Energy as an Indicator of Interfacial Mechanical Response.- High Temperature Multiphase Ceramics.- Prospects for Ultra-High-Temperature Ceramic Composites.- Microstructural Engineering of Ceramics for High-Temperature Application.- Tailoring of the Thermal Transport Properties and Thermal Shock Resistance of Structural Ceramics.- Creep Rupture of Siliconized Silicon Carbide.- High Temperature Mechanical Properties of Siliconized Silicon Carbide Composites.- Contributors.

Bone bonding behavior of three kinds of apatite containing glass ceramics

Abstract: We have produced three kinds of apatite-containing glass ceramics of the same chemical composition: MgO (4.6), CaO (44.9), SiO2 (34.2), P2O5 (16.3), CaF2 (0.5) (in weight ratio). They contain different crystal combinations and have different mechanical properties. The first glass ceramic (A–;GC) was prepared by heating a glass plate to 870°C. It contains only oxy- and fluoroapatite (35 wt%). The second glass ceramic (A–W–GC), and the third (A–W–CP–GC), were prepared by heating glass powder compacts to 1050°C and 1200°C, respectively. A–W–GC contains oxyapatite and fluoroapatite (Ca10(PO4)6(O,F2)) (35 wt%) and β-wollastonite (40 wt%). A–W–CP–GC contains oxyapatite and fluoroapatite (20 wt%), β-wollastonite (CaO·SiO2) (55 wt%), and β-whitlockite (3CaO·P2O5) (15 wt%). The bending strengths of A–;GC, A–W–GC, and A–W–CP–GC were 88MPa, 178MPa, and 213MPa, respectively, in air. Rectangular ceramic plates (15mm × 10mm × 2mm) were implanted into a rabbit tibia. Ten and 25 weeks after implantation, the segment of tibia with implant was excised for examination. The segment was held by a special jig and the traction breaking load (failure load) was measured by an autograph. A–;GC showed a lower load than A–W–GC and A–W–CP–GC. The loads for A–W–GC and A–W–CP–GC were almost equal. The failure loads did not change significantly between 10 and 25 weeks for any of the materials. The interface was examined by Giemsa surface staining, contact micro-radiography, and SEM-EPMA. Giemsa surface staining and CMR revealed direct bonding between the materials and the bone for all the three materials. SEM-EPMA showed that Si and Mg content decreased, Ca content did not change, and P content increased at the reaction zone between all three glass ceramics and bone. This was observed at 10 weeks, as well as at 25 weeks, after implantation. The reaction zone was narrowest with A–;GC, wider with A–W–GC, and widest with A–W–CP–GC.

Mechanical properties of toughened ZrO2-Y2O3 Ceramics

Abstract: Tetragonal zirconia polycrystals were produced from high purity powders containing 1.5 to 5.0 mol% Y/sub 2/O/sub 3/ by cold isostatic pressing and sintering, hot-pressing, and hot isostatic pressing. The mechanical properties and microstructures of these resulting materials were examined, with emphasis on the relation between strength and fracture toughness.

On the Conductivity of Polycrystalline Materials

Abstract: Expressions for the conductivity and impedance of polycrystalline materials are given for a greatly simplified grain distribution topology. We include not only contributions from the bulk and the proper grain boundary, but also series and parallel contributions from the space charge regions surrounding the grain boundaries. The relations obtained are applied to conductance measurements of bicrystalline and of ceramic ionic conductors (silver halides). - It is shown that the space-dependent grain boundary conductivity can be taken account of to a first approximation by introducing effective charge carrier concentrations and an effective width, and thus normal resistor-elements. The experiments give evidence for both the presence of highly conductive space charge layers adjacent to the grain boundaries (manifesting in the high frequency impedance semi-circle) and the presence of less conductive core regions (manifesting in the low frequency circle) in the silver halides.

Ceramic-metal composites

Abstract: A reinforced composite structure is disclosed comprising a heat resistant chemically-bonded layer of a ceramic composition mechanically attached to a metallic substrate. The structure includes a metallic anchoring matrix characterized by a plurality of spatially and cooperably arranged reinforcing elements, the matrix being attached to the substrate and projecting from the surface thereof with the spatially arranged reinforcing elements of the matrix collectively defining a ceramic-occupiable zone of finite thickness adjacent to and following the surface configuration of said substrate, the zone having at least confined therein the heat resistant chemically-bonded ceramic in intimate contact with the reinforcing elements. A method for fabricating said composite structure is also disclosed.

Silicon carbide whisker reinforced ceramic composites and method for making same

Abstract: The present invention is directed to the fabrication of ceramic composites which possess improved mechanical properties especially increased fracture toughness. In the formation of these ceramic composites, the single crystal SiC whiskers are mixed with fine ceramic powders of a ceramic material such as Al2 O3, mullite, or B4 C. The mixtures which contain a homogeneous dispersion of the SiC whiskers are hot pressed at pressures in a range of about 28 to 70 MPa and temperatures in the range of about 1600° to 1950° C. with pressing times varying from about 0.75 to 2.5 hours. The resulting ceramic composites show an increase in fracture toughness of up to about 9 MPa.m1/2 which represents as much as a two-fold increase over that of the matrix material.

Properties of thermal barrier coatings

Abstract: A variety of mechanisms which degrade thermal barrier coatings are outlined. Some are specific to the bondcoat, others to the ceramic. Material properties which influence the rates of degradation, and so determine the useful life of the coating system, are outlined.MST/288

Novel ceramic materials and methods for making same

Abstract: Novel self-supporting ceramic structures are produced by the oxidation reaction of a molten metal precursor with a vapor-phase oxidant to form an oxidation reaction product. Molten metal is drawn through the oxidation reaction product towards the oxidant to cause continued growth of the product at the interface between oxidant and previously formed product. This reaction or growth is continued to form a thick, self-supporting ceramic body. The resulting ceramic material of the polycrystalline growth product consists essentially of an oxidation reaction product and, optionally, one or more non-oxidized constituents of the metal precursor.

Ceramic spheroids having low density and high crush resistance

Abstract: Ceramic spheroids having: A a core made by firing raw materials comprising about: 50-998 parts by weight mineral particulates; 01 to 50 parts by weight silicon carbide; and 01 to 15 parts by weight binder (eg bentonite); and B an outer shell comprising Al 2 O 3 or MgO More alumina or magnesium oxide is contained in the outer shell than in the core The core of the ceramic spheroid has closed cell microporosity The inventive spheroids are characterized by a density less than 22 g/cc and can be readily made to have a density less than 1 g/cc These ceramic spheroids combine high strength (due to the tough outer shell) with low density (due to the closed cell microporosity) and have applications (among others) as buoyant water filtration media and low density fillers

Method of making piezoelectric composites

Abstract: Piezoelectric ceramic polymer matrices, piezoelectric composites, and methods of make the matrices and composites are disclosed.

Transparent non-vitreous zirconia microspheres

Abstract: TRANSPARENT NON-VITREOUS ZIRCONIA MICROSPHERES Abstract of the Disclosure Solid, transparent, non-vitreous, zirconia and zirconia-silica ceramic microspheres, useful as lens elements in retroreflective pavement markings. The microspheres are characterized by: (a) containing at least one additive metal oxide selected from alumina, magnesia, yttria and mixtures thereof; (b) an index of refraction greater than 1.6; and (c) being virtually free of cracks. These microspheres are formed by a sol-gel technique of extractive gelation (extracting carboxylic acid away from zirconyl carboxylate) of a sol in liquid medium such as hot peanut oil. The microspheres of this ceramic composition have been made with relatively large diameters, (e.g.200-1000 micrometers) making them quite useful as lens elements in pavement marking sheet materials.

Glow plug for diesel engine

Abstract: There is disclosed glow plug for a diesel engine provided with an elongated ceramic heater retained by an opening end of a hollow holder with one end of said ceramic heater being projected toward the outside The ceramic heater comprises an insulating tubular section of an insulating ceramic material, and a heating body as a continuous conductive section formed so as to cover the outer peripheral portion, the outermost portion and the hollow portion of the insulating tubular section with a conductive ceramic material, the heating body being formed in a manner that the thickness of at least the outer peripheral portion of the insulating tubular member in the vicinity of said one end of the ceramic heater is thinner than that of other portions thereof The insulating tubular section and the heating body constituting the ceramic heater are integrally formed with the ceramic material which can select insulating property and conductive property by adjusting an amount of titanium nitride added into β-sialon or a sialon consisting of a mixture of α- and β- sialons Thus, there is provided a glow plug provided with a ceramic heater which exhibits a function as a heater of the rapid heating type and provide a self-temperature saturation characteristic such that its heating characteristic can be improved to attain after glow for a long time

Maxwell-wagner relaxation and degradation of SrTiO3 and BaTiO3 ceramics

Abstract: Ceramics of undoped SrTiO3 and BaTiO3 (at T > Tc) show a pronounced Maxwell-Wagner relaxation at ultra low frequencies. This indicates thin nonconducting barrier layers at the grain boundaries and some residual conductivity in the grain. Degradation of the ceramic starts when the electrical field, which develops at the grain boundaries, exceeds breakdown strength.

Residual Stresses in Machined Ceramic Surfaces

Abstract: Residual surface stresses generated in ceramic materials by diamond grinding were studied. The stresses are characterized both by X-ray measurements of stress magnitudes and by line forces (product of stress and layer thickness) obtained from the bending of plates that were machined on one side. The line forces tend to increase with the hardness of the material but are insensitive to the rate of material removal during grinding (over a limited range of variation). Residual stress measurements are compared with measurements of strengths of the ground surfaces.

Electronic packaging of components incorporating a ceramic-glass-metal composite

Abstract: The present invention is directed to components and the process of forming the components for housing semiconductor devices. The components are formed of a unique ceramic-glass-metal composite material comprising ceramic particles, metallic particles and a glass matrix with said ceramic and metallic particles dispersed throughout. Metal elements can be embedded into the material to enable simplified fabrication of devices such as semiconductor packaging.

Influence of toughness on Weibull modulus of ceramic bending strength

Abstract: It is demonstrated both theoretically and experimentally that fracture toughness does not directly influence the Weibull modulus of ceramic bending strength for materials that obey the Griffith criterion for crack propagation. Weibull modulus remains unchanged as toughness is increased. However, toughness variations with crack length do affect the Weibull modulus. Thus materials that display R-curve behavior or Dugdale character give an increased Weibull modulus and appear more reliable.

Inadequacy of Coulomb's friction law for particle assemblies

Abstract: Wherever powders are manipulated by mechanical means, adhesive and frictional forces act between the solid grains. For two centuries, these forces have been described by Coulomb's law1, a law which originally proved useful in designing civil engineering structures, and which has since been profitably extended to the understanding of the powder flows in chemical plants2. However, we have now found that Coulomb's law is not adequate to explain the compaction of fine powders in the manufacture of ceramic articles, where it has been observed that friction appears to increase for smaller particles. This apparent increase in friction is explained by considering in detail the contact of loaded, adhesive, elastic spheres.

Ceramics from Hydridopolysilazane

Abstract: The Advanced Ceramics Based on Polymer Processing Program is sponsored by the Defense Advanced Research Projects Agency (Materials Science Division). The objectives of the program include development of a family of Si-C, Si-N, and Si-C-N ceramic fibers which may be used for reinforcement in ceramic, metal and plastic matrices, and development of economical process technology for fabricating ceramic matrix composites with high fracture toughness, high temperature performance and no inherent limitations to forming complex shapes. Attainment of these objectives would circumvent two limitations of existing ceramic material technology - lack of design reliability due largely to catastrophic failure related to brittleness, and inability to fabricate complex shapes [1].

Ceramic membrane for hydrocarbon conversion

Abstract: The invention relates to a novel mixed ion and electron conducting catalytic ceramic membrane and to its use in hydrocarbon oxidation and or dehydrogenation processes, the membrane consists of two layers, layer 1 which is an impervious mixed ion and electron conducting ceramic layer and layer 2 which is a porous catalyst-containing ion conducting ceramic layer.

Process for forming metal-ceramic composites

Abstract: A method is taught for the in-situ precipitation of ceramic materials in a metal matrix. By means of the solvent assisted reaction, metal-ceramic composites having highly superior properties may be obtained. The invention involves the reaction of the ceramic forming constituents in a metal solvent medium to provide very finely-dispersed ceramic particles in the metal matrix. Exemplary materials include titanium diboride in an aluminum matrix.