Showing papers on "Ceramic published in 1988"

Better Ceramics Through Chemistry

Abstract: The ultrastructural control of materials through sol-gel processes offers significant promise for the achievement of reliable performance in ceramics, glass and composites. Several examples of new structural, optical and electromagnetic materials with superior and unique properties are presented based on maximal homogeneity or heterogeneity attained through understanding of the fundamental chemistry. New concepts such as ceramic molecular composites and optically active gels have been derived through polymer, physical and synthetic chemistry. Scaling calculations based on molecular orbital calculations for prediction of the silanol polymerization mechanism, and hierarchical clustering predictions for the sol-gel derived ultrastructures are presented. The application of polymeric network theory to the design of gel ultrastructures is presented.

Introduction to the Principles of Ceramic Processing

Abstract: Introduction to Principles of Ceramic Processing is an undergraduate text book for an introductory course in ceramic engineering. Covering how products are formed from natural and synthetic minerals, techniques of heat treatment, and their inherent characteristics, the book introduces the student and engineer to ceramics such as glass, porcelain, enamels, abrasives and refractories. A systematic development of the scientific principles involved in ceramic processing is presented, together with an explanation of principles such as packing, mixing, separation, granulation, forming, molding, casting, drying etc. The book also explains causes and prevention of product defects, and offers detailed explanations of material characterization and materials specifications, functions and nature of additives.

Metal matrix composites

Abstract: A ceramic-reinforced aluminum matrix composite is formed by contacting a molten aluminum-magnesium alloy with a permeable mass of ceramic material in the presence of a gas comprising from about 10 to 100% nitrogen, by volume, balance non-oxidizing gas, e.g., hydrogen or argon. Under these conditions, the molten alloy spontaneously infiltrates the ceramic mass under normal atmospheric pressures. A solid body of the alloy can be placed adjacent a permeable bedding of ceramic material, and brought to the molten state, preferably to at least about 700° C., in order to form the aluminum matrix composite by infiltration. In addition to magnesium, auxiliary alloying elements may be employed with aluminum. The resulting composite products may contain a discontinuous aluminum nitride phase in the aluminum matrix and/or an aluminum nitride external surface layer.

Abrasive grits formed of ceramic containing oxides of aluminum and rare earth metal, method of making and products made therewith

Abstract: Ceramic abrasive grits comprising alpha alumina and at least about 0.5 percent by weight rare earth metal oxide are prepared by combining alumina hydrate and rare earth metal oxide or its precursors to produce a blend, drying the blend to produce a dried solid, crushing the dried solid to produce grits, calcining the dried grits to substantially remove bound volatile materials, and firing the grits to produce a ceramic material. The rare earth metal is selected from the group consisting of praseodymium, samarium, ytterbium, neodymium, lanthanum, gadolinium, cerium, dysprosium, erbium, and mixtures of one or more rare earth metal.

The use of dense alumina-alumina ceramic combination in total hip replacement.

Abstract: The purpose of this article was to review the laboratory and clinical performances since 1970 of a total hip prosthesis using alumina–alumina combination. The chemical and physical properties of dense alumina ceramic were studied in relation to biocompatibility, mechanical strength, and surface properties. Through the examination of 35 retrieved implants, it was found that the long-term success of alumina–alumina total hip replacement depends on both the ceramic microstructure (small grain size with uniform distribution, minimum porosity, absence of inclusions) and implant geometry (sphericity deviation ±1 μm, radius tolerance between components 7–10 μm). Alumina component wear and fractures have disappeared with the use of high-performance materials and severe manufacturing quality control. Examination of human biopsies from well-fixed prostheses showed that alumina particles deposits increase with time with only a low-grade macrophagic reaction. When loosening occurred, an inflammatory reaction appeared; this reaction was less striking than with loose metal–polyethylene prostheses, however. The long-term behavior of cementless alumina cup fixation depends upon initial positioning and stability; survivorship analysis of the cemented ceramic cups showed an 88% survival probability after 8 years with a 1.6% average annual probability of revision. The percentage of surviving was 100% after 8 years in patients who were less than 50 years old. Aseptic loosenings occurring at the cup–cement interface were assumed to be related to stress protection secondary to the high rigidity of the ceramic leading to a weakening of the spongious bone supporting the cement mantle. Good bone stock quality as well as high-quality ceramic appear to be the prerequisites for durable fixation of alumina sockets.

Thermal Barrier Coating Life Prediction Model Development

Abstract: A methodology is established to predict thermal barrier coating life in a environment similar to that experienced by gas turbine airfoils. Experiments were conducted to determine failure modes of the thermal barrier coating. Analytical studies were employed to derive a life prediction model. A review of experimental and flight service components as well as laboratory post evaluations indicates that the predominant mode of TBC failure involves thermomechanical spallation of the ceramic coating layer. This ceramic spallation involves the formation of a dominant crack in the ceramic coating parallel to and closely adjacent to the topologically complex metal ceramic interface. This mechanical failure mode clearly is influenced by thermal exposure effects as shown in experiments conducted to study thermal pre-exposure and thermal cycle-rate effects. The preliminary life prediction model developed focuses on the two major damage modes identified in the critical experiments tasks. The first of these involves a mechanical driving force, resulting from cyclic strains and stresses caused by thermally induced and externally imposed mechanical loads. The second is an environmental driving force based on experimental results, and is believed to be related to bond coat oxidation. It is also believed that the growth of this oxide scale influences the intensity of the mechanical driving force.

Behavior of ceramic particles at the solid- liquid metal interface in metal matrix composites

Abstract: Directional solidification results were obtained in order to investigate particle behavior at the solid-liquid interface in Al-2 pct Mg (cellular interface) and Al-6.1 pct Ni (eutectic interface) alloys. It is found that particles can be entrapped in the solid if adequate solidification rates and temperature gradients are used. Model results showed critical velocity values slightly higher than those obtained experimentally.

Surface and near-surface chemistry of oxide materials

Abstract: 1. The Theory of Ceramic Surfaces (A.M. Stoneham, P.W. Tasker). 2. Electronic and Geometric Structure of Defects on Oxides and their Role in Chemisorption (V.E. Henrich). 3. Selected Experimental Methods in the Characterization of Oxide Surfaces (H. Hirschwald). 4. Surface Reactivity of Oxide Materials in Oxidation-Reduction Environment (T. Seyama). 5. Metal Oxide Overlayers and Oxygen Induced Chemical Reactivity Studied by Photoelectron Spectroscopy (M.W. Roberts). 6. Surface Segregation in Metal Oxides (P. Wynblatt, R.C. McCune). 7. Work Function of Oxide Ceramic Materials (J. Nowotny, M. Sloma). 8. Photoeffects on Metal Oxide Powders. (J. Cunningham). 9. The Role of the Surface on Bulk Physical Properties of Glasses (A.A. Kruger). 10. Segregation in Oxide Surfaces Solid Electrolytes and Mixed Conductors (A.J. Burggraaf, A.J.A. Winnubst). 11. Grain Size and Grain Boundary Effects in Passive Electronic Components (D. Hennings). 12. Reactions at Phase Boundaries during Metal/Ceramic Bonding (H.J. de Bruin). 13. Oxide Surfaces in Solution (R.L. Segall et al.). 14. Metals on Oxides: Formation, Characterization and Properties (L.C. Dufour, M. Perderau). 15. Electronic Structure and Transport Properties of Interfaces in Metal Oxides (M.H. Sukkar, H.L. Tuller). 16. High T c Oxide Superconductors. Possible Effect of Interfaces (J. Nowotny, M. Rekas, D.D. Sarma, W. Weppner). Subject Index. Formula Index.

Microcrystalline alumina-based ceramic articles

Abstract: Microcrystalline alpha-alumina based ceramic articles comprising at least 60% alumina by weight in which substantially all the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites with an average crystallite size less than 0.5 micrometer and a density greater than 90% theoretical are disclosed. Ceramic articles particularly useful as high modulus refractory fibers, among other shaped bodies such as beads, flakes, coatings, and shaped or randomly-shaped abrasive particles, are produced from a unique sol-gel process wherein hydroxy iron polymers are utilized to nucleate the alpha alumina transformation. An inherent advantage of the unique process disclosed is the resulting fine grained microstructure which is essential if a ceramic article such as an alpha alumina fiber is to have reasonable strength.

Ceramic coatings for carbon-carbon composites

Abstract: Protection des composites carbone-carbone contre l'oxydation: revetements a base de SiC et de Si 3 N 4 , revetements resistants a plus de 1800°C

High oxide ion conductivity in Ca 12 Al 14 O 33

Abstract: Oxide ion conducting solids have much potential for use in fuel cells, sensors, oxygen pumps and gauges. Existing oxide ion conductors are essentially confined to a small group of ceramic oxides with structures related to fluorite, the most important examples being ZrO2- and Bi2O3-related materials. There is a clear need for new oxide ion conductors with improved properties. We report measurements of the conductivity of Ca12Al14O33, which indicate it to be an oxide ion conductor with bulk conductivity only 8–10 times less than that of yttria-stabilized zirconia. The structure of Ca12Al14O33 is unrelated to the fluorite structure. The reasons for the high conductivity are not well understood but may be associated with the fact that the structure contains a mixture of anions, a three-dimensional aluminate framework and essentially free oxide ions.

Electrochemical synthesis of ceramic films and powders

Abstract: Ceramic precursor compositions, such as metal hydroxides and oxides, are electrochemically deposited in a biased electrochemical cell. The cell typically generates hydroxide ions that precipitate metallic or semimetallic ions to form insoluble solids that may be separated from the cell, then dried, calcined and sintered to form a ceramic composition.

Abrasive grits formed of ceramic, impregnation method of making the same and products made therewith

Abstract: Ceramic abrasive grits are formed by an impregnation process that involves preparing an alumina hydrate sol, drying the sol to form a porous solid, crushing the solid to produce particles, calcining the dried particles, preparing a mixture of an additive metal oxide or its precursor in a liquid vehicle, impregnating the mixture into the calcined particles, drying the impregnated particles, calcining the dried impregnated particles, and firing the particles to produce ceramic abrasive grits. The concentration of the modifying additive metal is greater at or near the surface of the grit than at the interior of the grit.

Development and Microstructural Characterization of High‐Thermal‐Conductivity Aluminum Nitride Ceramics

Abstract: The effect of several additives, such as CaC2, CaO, Y2O3, and C, on thermal conductivity of hot-pressed AlN ceramics was investigated. The addition of CaC2 reductant was found to be useful for achieving high thermal conductivity of 180 W/(m·K) at room temperature. The characterization of AlN ceramics with CaC2 additive was performed by chemical analysis of Ca, C, and O and microstructural analysis using transmission electron microscopes equipped with an energy-dispersive X-ray analyzer and an electron energy loss spectrometer. The major influence on high thermal conductivity is the disappearance of a thermal barrier caused by oxygen impurities at the grain boundary.

Development of a new continuous Si−Ti−C−O fibre using an organometallic polymer precursor

Abstract: A polytitanocarbosilane, which is useful as the precursor polymer for ceramic fibre, was synthesized using polydimethylsilane, polyborodiphenylsiloxane and titanium tetraisopropoxide. The polytitanocarbosilane was melt-spun and using the continuous heat-treatment process from the polymer fibre to ceramic fibre, flexible Si-Ti-C-O fibre was produced. The density, tensile strength and Young's modulus of this amorphous ceramic fibre were found to be 2.35 g cm−3, 3.0±0.2 and 220±10 GPa, respectively. The Si-Ti-C-O fibre retained its high tensile strength to higher temperatures (about 1200° C). The specific resistance of this ceramic fibre covered a wide range of 107 to 10−1ωcm. This ceramic fibre is considered to be useful as reinforcement fibre for composites.

Ceramic foam filter

Abstract: An improved ceramic foam filter for filtering molten metal, in particular iron and iron alloys, is prepared from a ceramic slip containing silicon carbide and a colloidal silicon dioxide binder The ceramic filter has a solid matter content of at least 50% silicon carbide and at least 3% silicon dioxide

The effect of plasma‐sprayed calcium phosphate ceramic coatings on the metal ion release from porous titanium and cobalt‐chromium alloys

Abstract: Bone tissue ingrowth in porous materials is enhanced by the deposition of bioactive calcium phosphate ceramic linings onto the pore walls. These bioactive coatings can be deposited using several methods which yield a variety of coating efficiencies and thereby influence the mechanisms and kinetics of ion release from the metal. We analyzed the effect of plasma-spraying hydroxyapatite onto titanium and cobalt-chromium alloys by measuring the release of Ti, Al, V, Co, and Cr in vitro. Plasma-sprayed coatings significantly reduced the Ti and Al release from titanium-based alloy specimens. The tendencies of release from the cobalt-based specimens are less pronounced. The data substantiate that neither localized enhanced passive dissolution of metal ions nor ceramic shielding of the metal occurs. The Scanning Auger Electron Microprobe Spectroscopic data suggest that the dissipation of thermal and kinetic energy of the ceramic particle at the time of impact can produce compositional and structural changes in the metal surfaces. The resulting effects are significant for the titanium alloy but less significant for the Co-Cr alloy system.

Properties of ceramic KNO3 thin-film memories☆

Abstract: We have measured electrical and spectroscopic properties of thin films (d = 75–500 nm) of ferroelectric ceramic potassium nitrate and developed a mean field theory which explicitly incorporates film thickness effects. Variations of Tc(d) are observed as are changes in the shape of Ps(T) with thickness. Comparisons with earlier work on TGS are made.

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.

Liquid phase sintering of silicon carbide

Abstract: Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1600° C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase.

Effect of Pore Distribution on Microstructure Development: II, First‐ and Second‐Generation Pores

Abstract: A sintering model has been developed to predict the consequences of independently varying the grain growth rate in alumina during final-stage sintering of a microstructure containing both small (first-generation) and large (inter-agglomerate second-generation) pores. The model shows that although it may be thermodynamically favorable to increase the grain growth rate, the kinetics of densification are such that it almost always pays to inhibit grain growth. This conclusion was verified by experiments on undoped, MgO-doped, and ZrO2-doped alumina impregnated with model spherical large pores produced by the burnt-out latex sphere method. A new type of ceramic processing map has also been developed to aid in the selection of the optimum processing conditions for the sintering of ceramics containing large pores.

Sintering of Si3N4 with the Addition of Rare-Earth Oxides

Abstract: The effect of rare-earth oxide additives on the densification of silicon nitride by pressureless sintering at 1600° to 1700°C and by gas pressure sintering under 10 MPa of N2 at 1800° to 2000°C was studied. When a single-component oxide, such as CeO2, Nd2O3, La2O3, Sm2O3, or Y2O3, was used as an additive, the sintering temperature required to reach approximate theoretical density became higher as the melting temperature of the oxide increased. When a mixed oxide additive, such as Y2O3–Ln2O3 (Ln=Ce, Nd, La, Sm), was used, higher densification was achieved below 2000°C because of a lower liquid formation temperature. The sinterability of silicon nitride ceramics with the addition of rare-earth oxides is discussed in relation to the additive compositions.

Fiber reinforced ceramic matrix laminate

Abstract: Tough ceramic products can be prepared without exotic pressure fabricating techniques by use of a matrix laminate comprising a continuous fiber ceramic reinforcement in tow or woven form for strength, stiffness, and toughness and a ceramic matrix generally comprising (a) a filler, such as mullite; (b) ceramic reinforcing whiskers, such as silicon nitride or silicon carbide, for fine-scale interlaminar shear resistance (c) a binder, such as colloidal silica; and (d) an activator, such as a trona-like material including sodium and carbonate. The matrix is brushed into the fiber reinforcement, which is then laid up, dried, and cured. Tandem ceramic composites can be fabricated.