Showing papers on "Ceramic published in 1996"

High critical current density superconducting tapes by epitaxial deposition of YBa2Cu3Ox thick films on biaxially textured metals

Abstract: A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high‐temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 105 A/cm2 at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high‐Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

High critical current density superconducting tapes by epitaxial deposition of YBa2Cu3Ox thick films on biaxially textured metals

Abstract: A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high‐temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 105 A/cm2 at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high‐Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

Fundamentals of ceramics

Abstract: INTRODUCTION Introduction Definition of Ceramics Elementary Crystallography Ceramic Microstructures Traditional Versus Advanced Ceramics General Characteristics of Ceramics Applications The Future BONDING IN CERAMICS Introduction Structure of Atoms Ionic versus Covalent Bonding Ionic Bonding Ionically Bonded Solids Covalent Bond Formation Covalently Bonded Solids Band Theory of Solids Summary Appendix 2A: Kinetic Energy of Free Electrons STRUCTURE OF CERAMICS Introduction Ceramic Structures Binary Ionic Compounds Composite Crystal Structures Structure of Covalent Ceramics Structure of Silicates Lattice Parameters and Density Summary Appendix 3A: Ionic Radii EFFECT OF CHEMICAL FORCES ON PHYSICAL PROPERTIES Introduction Melting Points Thermal Expansion Young's Modulus and the Strength of Perfect Solids Surface Energy Summary THERMODYNAMIC AND KINETIC CONSIDERATIONS Introduction Free Energy Chemical Equilibrium and the Mass Action Expression Chemical Stability Domains Electrochemical Potentials Charged Interfaces, Double Layers, and Debye Lengths Gibbs-Duhem Relation for Binary Oxides Kinetic Considerations Summary Appendix 5A: Derivation of Eq. (5.27) DEFECTS IN CERAMICS Introduction Point Defects Linear Defects Planar Defects Summary DIFFUSION AND ELECTRICAL CONDUCTIVITY Introduction Diffusion Electrical Conductivity Ambipolar Diffusion Relationships between Self-, Tracer, Chemical, Ambipolar, and Defect Diffusion Coefficients Summary Appendix 7A: Relationship between Fick's First Law and Eq. (7.30) Appendix 7B: Effective Mass and Density of States Appendix 7C: Derivation of Eq. (7.79) Appendix 7D: Derivation of Eq. (7.92) PHASE EQUILIBRIA Introduction Phase Rule One-Component Systems Binary Systems Ternary Systems Free-Energy Composition and Temperature Diagrams Summary FORMATION, STRUCTURE, AND PROPERTIES OF GLASSES Introduction Glass Formation Glass Structure Glass Properties Glass-Ceramics Summary Appendix 9A: Derivation of Eq. (9.7) SINTERING AND GRAIN GROWTH Introduction Solid-State Sintering Liquid-Phase Sintering Hot Pressing and Hot Isostatic Pressing Summary Appendix 10A: Derivation of the Gibbs-Thompson Equation Appendix 10B: Radii of Curvature Appendix 10C: Derivation of Eq. (10.20) Appendix 10D: Derivation of Eq. (10.22) MECHANICAL PROPERTIES: FAST FRACTURE Introduction Fracture Toughness Strength of Ceramics Toughening Mechanisms Designing with Ceramics Summary CREEP, SUBCRITICAL CRACK GROWTH, AND FATIGUE Introduction Creep Subcritical Crack Growth Fatigue of Ceramics Lifetime Predictions Summary Appendix 12A: Derivation of Eq. (12.24) THERMAL PROPERTIES Introduction Thermal Stresses Thermal Shock Spontaneous Microcracking of Ceramics Thermal Tempering of Glass Thermal Conductivity Summary DIELECTRIC PROPERTIES Introduction Basic Theory Equivalent Circuit Description of Linear Dielectrics Polarization Mechanisms Dielectric Loss Dielectric Breakdown Capacitors and Insulators Summary Appendix 14A: Local Electric Field MAGNETIC AND NONLINEAR DIELECTRIC PROPERTIES Introduction Basic Theory Microscopic Theory Para-, Ferro-, Antiferro-, and Ferrimagnetism Magnetic Domains and the Hysteresis Curve Magnetic Ceramics and their Applications Piezo- and Ferroelectric Ceramics Summary Appendix 15A: Orbital Magnetic Quantum Number OPTICAL PROPERTIES Introduction Basic Principles Absorption and Transmission Scattering and Opacity Fiber Optics and Optical Communication Summary Appendix 16A: Coherence Appendix 16B: Assumptions Made in Deriving Eq. (16.24) INDEX *Each chapter contains Problems and Additional Reading.

Fundamentals of inorganic membrane science and technology

Abstract: Preface. List of contributors. 1. General Overview, Trends and Prospects (A.J. Burggraaf, L. Cot). 2. Important Characteristics of Inorganic Membranes (A.J. Burggraaf). 3. Adsorption Phenomena in Membrane Systems (Y.H. Ma). 4. Methods for the Characterisation of Porous Structure in Membrane Materials (A. Julbe, J.D.F. Ramsay). 5. Ceramic Processing Techniques of Support Systems for Membranes Synthesis (A. Larbot). 6. Preparation of Asymmetric Ceramic Membrane Supports by Dip-coating (B.C. Bonekamp). 7. Sol-Gel Chemistry and its Application to Porous Membrane Processing (C. Guizard). 8. Fundamentals of Membrane Top-Layer Synthesis and Processing (A.J. Burggraaf). 9. Transport and Separation Properties of Membranes with Gases and Vapours (A.J. Burggraaf). 10. Dense Ceramic Membranes for Oxygen Separation (H.J.M. Bouwmeester, A.J. Burggraaf). 11. Current Developments and Future Research in Catalytic Membrane Reactors (J. Sanchez, T.T. Tsotsis). 12. Transport and Fouling Phenomena in Liquid Phase Separation with Inorganic and Hybrid Membranes (C. Guizard, G. Rios). 13. Applications of Ceramic Membranes in Liquid Filtration (C.A.M. Siskens). 14. Feasibility of the Application of Porous Inorganic Gas Separation Membranes in some Large-Scale Chemical Processes (H.M. van Veen, M. Bracht, E. Hamoen, P.T. Alderliesten). Subject Index.

A silicoboron carbonitride ceramic stable to 2,000°C

Abstract: CERAMICS based on silicon nitride and carbide are strong and stable at high temperatures, and are therefore under investigation for the fabrication of motor and turbine parts1–3. But silicon nitride decomposes at about 1,400 °C in vacuum and 1,775 °C in 0.1 MPa nitrogen4,5, limiting the high-temperature range of its technological uses. Here we describe a boron-containing silicon nitride/carbide ceramic that does not degrade at temperatures up to 2,000 °C even in nitrogen-free environments. We synthesize the material in a polymer-to-ceramic transformation6 from a single polymeric polyborosilazane precursor. On heating at 1,000 °C in argon we obtain a ceramic with the composition Si3.0B1.0C4.3N2.0. The ceramic begins to convert to a polycrystalline composite of silicon nitride and carbide (with some non-crystalline boron nitride) at 1,700 °C, a process that is completed (without substantial change in elemental composition) at 2,000 °C.

Physical Ceramics: Principles for Ceramic Science and Engineering

Abstract: Structure of Ceramics. Defects in Ceramics. Mass and Electrical Transport. Phase Equilibria. Microstructure. Index.

Structural quality of parts processed by fused deposition

Abstract: Commercial solid freeform fabrication (SFF) systems, which have been developed for fabrication of wax and polymer parts for form and fit and secondary applications, such as moulds for casting, etc., require further improvements for use in direct processing of structural ceramic and metal parts. Defects, both surface as well as internal, are undesirable in SFF processed ceramic and metal parts for structural and functional applications. Process improvements are needed before any SFF technique can successfully be commercialized for structural ceramic and metal processing. Describes process improvements made in new SFF techniques, called fused deposition of ceramics (FDC) and metals (FDMet), for fabrication of structural and functional ceramic and metal parts. They are based on an existing SFF technique, fused deposition modelling (FDM) and use commercial FDM systems. The current state of SFF technology and commercial FDM systems results in parts with several surface and internal defects which, if not eliminated, severely limit the structural properties of ceramic and metal parts thus produced. Describes systematically, in detail, the nature of these defects and their origins. Discusses several novel strategies for elimination of most of these defects. Shows how some of these strategies have successfully been implemented to result in ceramic parts with structural properties comparable to those obtained in conventionally processed ceramics.

Ceramic‐reinforced polymers and polymer‐modified ceramics

Abstract: The composites discussed in this review are prepared using techniques similar to those used in the new sol-gel approach to ceramics. Organometallics such as silicates, titanates, and aluminates are hydrolyzed in the presence of polymer chains (for example polysiloxanes and polyimides) that typically contain hydroxyl or amino groups. The functional groups are used to bond the polymer chains onto the silica, titania, or alumina being formed in the hydrolysis, thus forming organicinorganic composites. When the polymer chains are present in excess, they constitute the continuous phase, with the ceramic-type material appearing as reinforcing particles. When present in smaller amounts, the polymer is dispersed in the continuous ceramic phase, to give a polymer-modified ceramic. Under some conditions, bicontinuous systems are obtained. The composites thus prepared are characterized by electron microscopy, X ray, and neutron scattering intensities, density determinations, and stress-strain and impact-strength measurements.

Chapter 10 Dense ceramic membranes for oxygen separation

Abstract: Publisher Summary This chapter reviews the recent developments in the area of mixed ionic-electronic conducting membranes for oxygen separation, in which the membrane material is made dense—that is, free of cracks and connected-through porosity, being susceptible only for oxygen ionic and electronic transport. Emphasis is on the defect chemistry, mass transport, and the associated surface exchange kinetics. The basic elements of mixed ionic and electronic transport through dense ceramic membranes are focused. The chapter discusses mixed-conducting acceptor-doped perovskite and perovskite-related oxides and gives examples to illustrate the fundamental factors determining the oxygen fluxes through dense ceramic membranes. A key factor in the possible application of oxygen ion conducting ceramics is that, for use as solid electrolyte in fuel cells, batteries, oxygen pumps or sensors, their electronic transport number should be as low as possible. Stimulated by the search for candidate materials for electrodes in solid oxide fuel cells (SOFC) and oxygen separation membranes, researchers have explored the possibility of introducing electronic conductivity in oxygen-ion conducting fluorite-type matrices by doping with multi-valent dopants.

Oxidation protection for carbon fibre composites

Abstract: Carbon fibre-reinforced ceramic matrix composites are promising candidate materials for high-temperature structural applications such as gas turbine blades. In oxidizing environments at temperatures above 400°C, however, carbon fibres are rapidly oxidized. There is, therefore, a need to coat the composite in order to protect it against oxidation. This review identifies the requirements of an effective oxidation protection system for carbon fibre-reinforced ceramics and summarizes the work which has been carried out towards this goal over the last 50 years. The most promising coatings are those composed of several ceramic layers designed to protect against erosion, spallation and corrosion, in addition to possessing a self-healing capability by the formation of glassy phases on exposure to oxygen.

Inorganic ceramic/polymer ferroelectric composite electrets

Abstract: Ferroelectric composites are now an established alternative to conventional ferroelectric ceramic materials and to the more recently discovered ferroelectric polymers. These materials due to their unique blending of polymetric properties of mechanical flexibility, formability and low cost with high electro-active properties have been been suggested to be a viable alternative both in piezoelectric and pyroelectric transducer applications. This review is devoted to the piezoelectric and pyroelectric properties exhibited by these type of composites with a special reference to those made of ceramic particles embedded in a polymer matrix (i.e. 0-3 connectivity type composite). A review of models predicting the electro-active properties of 0-3 composites is presented together with a proposal for a new mixed connectivity cubes model to be applicable to the case of high ceramic loading and/or when the ceramic grain size incorporated in the polymer matrix is comparable to the thickness of the sample. A review of the experimental results of the piezo- and pyroelectric properties of various ferroelectric composite materials, reported by several workers, is also presented in this paper. Special reference is made to composites made from calcium modified lead titanate and poly(vinyldene fluoride-trifluorethylene) emphasizing their advantages in the poling process which is a critical phase in the process of obtaining successful electro-active 0-3 composite electrets.

Bioresorbable ceramic composites

Abstract: A composite material is provided including a strongly bioresorbable, poorly crystalline apatitic calcium phosphate composite and a supplementary material. The poorly crystalline apatitic calcium phosphate is characterized in that, when placed in an intramuscular or subcutaneous site, resorption of at least 1 g of the material is complete within one year. The supplementary material is in intimate contact with the hydroxyapatite material in an amount effective to impart a selected characteristic to the composite. The supplemental material may be biocompatible, bioresorbable or non-resorbable.

Sintered alumina with low dielectric loss

Abstract: Low dielectric loss materials are required for applications in radio‐frequency and microwave communications. Aluminium is the second most abundant element in the Earth’s crust and aluminium oxide (alumina) is one of the commonest ceramics. Single crystals of aluminium oxide, i.e., sapphire, possess one of the lowest dielectric losses of any material. Polycrystalline alumina has a higher loss due to extrinsic factors. The dielectric loss of sintered alumina is studied in an attempt to determine the causes of extrinsic loss. Impurities are shown to play an important role, but the microstructure also is a key factor. High‐purity aluminas, sintered to near theoretical density, are found to display very low loss, tan δ=2.7×10−5 at 10 GHz. Doping alumina with titanium dioxide was found to reduce the tan δ=2×10−5.

Fundamentals of ceramic powder processing and synthesis

Abstract: Part I: Introduction: History, Raw Materials, Ceramic Powder Characterization. Ceramic Powder Processing History and Discussion of Natural Raw Materials. Ceramic Powder Characterization. Part II: Ceramic Powder Synthesis. The Population Balance. Comminution and Classification of Ceramic Powders. Ceramic Powder Synthesis with Solid Phase Reactant. Liquid Phase Synthesis by Precipitation. Powder Synthesis with Gas Phase Reactants. Other Ceramic Powder Fabrification Processes. Part III: Ceramic Paste Formation - Mise-En Pte. Wetting, Deagglomeration, and Adsorption. Colloid Stability of Ceramic Suspensions. Colloidal Properties of Ceramic Suspensions. Part IV: Green Body Formation - Mise en Forme. Mechanical Properties of Dry Ceramic Powders and Wet Ceramic Suspensions. Ceramic Green Body Formation. Part V: Presintering Heat Treatments of Drying and Binder Burnout. Green Body Drying. Binder Burnout. Part VI: Sintering and Finishing. Sintering. Finishing. Appendixes. SubjectIndex.Part I: Introduction: History, Raw Materials, Ceramic Powder Characterization. General Concepts of Ceramic Powder Processing. Ceramic Powder Processing History and Discussion of Natural Raw Materials: Objectives. Historical Perspective. Raw Materials. Selecting a Raw Material. Ceramic Powder Characterization: Objectives. Introduction. Powder Sampling. Particle Size. Particle Morphology. Powder Density. Surface Area. Particle Size Distributions. Comparison of Two-Powder Size Distributions. Blending Powder Samples. Summary. Part II: Ceramic Powder Synthesis: The Population Balance: Objectives. Microscopic Population Balance. Macroscopic Population Balance. Population Balances Where Length, Area, and Volume are Conserved. Population Balances on a Mass Basis. Summary. Comminution and Classification of Ceramic Powders: Objectives. Communition. Classification of Ceramic Powders. Communition and Classification Circuits. Summary. Ceramic Powder Synthesis with Solid Phase Reactant: Objectives. Introduction. Thermodynamics of Fluid Solid Reactions. Oxidation Reactions. Reduction Reactions. Nitridation Reactions. Thermodynamics of Multiple Reaction Systems. Liquid Solid Reactions. Fluid Solid Reaction Kinetics. Fluid Solid Reactors. Solid Solid Reactions. Summary. Liquid Phase Synthesis by Precipitation: Objectives. Introduction. Nucleation Kinetics. Growth Kinetics. Crystal Shape. Size Distribution Effects - Population Balance and Precipitator Design. Coprecipitation of Ceramic Powders. Summary. Powder Synthesis with Gas Phase Reactants: Objectives. Introduction. Gas Phase Reactions. Reaction Kinetics. Homogeneous Nucleation. Collisional Growth Theory. Population Balance for Gas PhaseSynthesis. Dispersion Model for Gas Synthesis Reactors. Population Balance with Aggregation. Quenching the Aggregation. Particle Shape. Summary. Other Ceramic Powder Fabrification Processes: Objectives. Spray Drying. Spray Roasting. Metal Organic Decomposition for Ceramic Films. Freeze Drying. Sol Gel Synthesis. Melt Solidification. Summary. Part III: Ceramic Paste Formation - Mise-En Pte: Wetting, Deagglomeration, and Adsorption: Objectives. Wetting of a Powder by a Liquid. Deagglomeration. Adsorption onto Powder Surfaces. Chemical Stability of a Powder in a Solvent. Summary. Colloid Stability of Ceramic Suspensions: Objectives. Introduction. Interaction Energy and Colloid Stability. Kinetics of Coagulation and Flocculation. Colloid Stability in Ceramic Systems. Summary. Colloidal Properties of Ceramic Suspensions: Objectives. Introduction. Sedimentation. Brownian Diffusion. Solution and Suspension Colligative Properties. Ordered Suspensions. Summary. Part IV: Green Body Formation - Mise en Forme: Mechanical Properties of Dry Ceramic Powders and Wet Ceramic Suspensions: Objectives. Introduction. Equations of Motion. Ceramic Suspension Rheology. Mechanical Properties of Dry Ceramic Powders. Summary. Ceramic Green Body Formation: Objectives. Introdution. Green Body Formation with Ceramic Suspensions. Extrustion and Injection Molding of Ceramic Pastes. Green Body Formation with Dry Powders - Dry Pressing. Green Body Characterization. Summary. Part V: Presintering Heat Treatments of Drying and Binder Burnout: Green Body Drying: Objectives. Introduction. Sphere and Cylinder Drying. Drying of Flat Plates. Warping and Cracking during Drying. Characterization of Ceramic Green Bodies. Summary. Binder Burnout: Objectives. Introduction. Thermal Degradation of Polymers. Oxidative Polymer Degradation. Kinetics of Binder Burnout. Stresses Induced during Binder Burnout. Summary. Part VI: Sintering and Finishing: Sintering: Objectives Introduction. Solid State Sintering Mechanisms. Grain Growth. Reactive Sintering. Pressure Sintering. Cool Down after Sintering. Summary. Finishing: Objectives. Introduction. Ceramic Machining. Coating and Glazing. Quality Assurance Testing.Nondestructive Testing. Summary. Appendixes. Subject Index.

Optimization of energy storage density in ceramic capacitors

Abstract: A theoretical treatment, based on the Devonshire theory of ferroelectrics, is presented to describe the storage of electrostatic energy in ferroelectric and paraelectric materials at very high field strengths. In all cases, optimal energy density is achieved by using compositions with Curie temperatures well below the operating temperature. The theory is applied to barium - strontium titanate ceramics and optimal compositions are deduced for energy storage at given working fields. The theory is supported by experimental data showing energy densities up to 8 J at 100 kV .

Metallurgical and ceramic protective coatings

Abstract: Introduction. Electroplating of refractory metals from molten salts. Electroplating of refractory compounds from molten salts. Laser assisted surface coatings. Sol-gel derived ceramic films: fundamentals and applications. Solid phase cladding. Thermal barrier coatings. Pack cementation of diffusion coatings. Thermal spray coatings. Degradation of coatings by high temperature atmospheric corrosion and molten salt deposits. Measurement of coating adhesion.

Glass-ceramic sealants for solid oxide fuel cells: Part I. Physical properties

Abstract: A family of sealant materials has been developed for use in the solid oxide fuel cell (SOFC) and in other applications in the temperature range of 800–1000 °C. These materials are based on glasses and glass-ceramics in the SrO–La2O3–Al2O3–B2O3–SiO2 system. The coefficients of thermal expansion (CTE) for these materials are in the range of 8–13 × 10−6/°C, a good match with those of the SOFC components. These sealant materials bond well with the ceramics of the SOFC and, more importantly, form bonds that can be thermally cycled without failure. At the fuel cell operating temperature, the sealants have viscosities in the range of 104–106 Pa-s, which allow them to tolerate a CTE mismatch of about 20% among the bonded substrates. The gas tightness of a sample seal was demonstrated in a simple zirconia-based oxygen concentration cell.

Film bulk acoustic wave device

Abstract: Embodiments of the present invention provide a small and well-characterized bulk acoustic wave device by fabricating a filter having a wide band width or a resonator having a wide oscillation frequency range together with a semiconductor circuit. In embodiments of the present invention, a bulk acoustic wave device comprises a semiconductor substrate having a dielectric substance layer thereon, the dielectric substance layer has a ground conductor layer thereon, the ground conductor layer has a piezoelectric ceramic thin film thereon and the piezoelectric ceramic thin film has a conductive electrode pattern thereon. The thickness of the piezoelectric ceramic thin film is more than ten times the thickness of the ground conductor layer, and the wave number of acoustic waves that propagate in a direction parallel to a surface of the piezoelectric ceramic thin film multiplied by the thickness of the piezoelectric ceramic thin film is less than 2.

Ceramic structural body

Abstract: Ceramic structural body having improved material properties of a sealing member, such as adhesion properties at room temperature and high temperature, and having an improved durability. The ceramic structural body comprises an assembly of plural united ceramic members each having a plurality of through-holes arranged side by side along a longitudinal direction, in which end faces at either side of these through-holes are closed in a checkered pattern so as to have a reverse relation of open and close between gas inlet side and gas outlet side and adjacent through-holes are permeable to each other through porous partition walls. A plurality of the ceramic members are integrally adhered by interposing a sealing member of an elastic material comprising at least inorganic fibers, an inorganic binder, an organic binder and inorganic particles and mutually bonded three-dimensionally intersected organic fibers and inorganic particles through the inorganic binder and organic binder between the mutual ceramic members.

Three-dimensional degradable porous polymer-ceramic matrices for use in bone repair

Abstract: A degradable polymer-ceramic matrix for use as a bone graft material is described. The fabrication method used produces 3-dimensional macroporous matrices which are structurally similar to cancellous bone in their porosity, mechanically similar to cancellous bone in compressive elastic modulus and chemically comparable to the mineral matrix of bone in that they contain hydroxyapatite (HA). A 50:50 copolymer of poly(lactide/ glycolide) (PLAGA) reinforced by a particulate calcium phosphate ceramic, HA, was used to create a matrix composed of polymeric microspheres. The channels between these spheres were pores approximately 100 μm in diameter. Four polymer/ceramic ratios were used in matrix fabrication: 1:0, 1:1, 2.5:1, and 5 : 1. The mechanical behavior of the material was found to vary with ceramic content. Increased levels of HA resulted in increased compressive elastic moduli. Prior to polymer degradation, moduli ranged from a high of 1459 MPa (50% HA) to a low of 293 MPa (0% HA). Degradation studies ov...

Ceramic femoral head fractures in total hip arthroplasty.

Abstract: A failure analysis was performed of 4341 alumina ceramic heads articulating with 2693 alumina ceramic and 1464 polymer sockets implanted over 20 years (1974 to 1994). From 1974 to 1982, a mushroom shaped head with ceramic neck was used in 1069 cases, and from 1982 to 1994 a ball type head was used in 3272 cases. In the ceramic/ceramic cases, the average followup was 11 years, and in the polymer pairing cases, the average followup was 6 years. In ceramic self pairing with the mushroom shaped head, the fracture rate was 0.4% (5 of 1069). With the ball type head, the fracture rate was 0.06% (1 of 1763). In articulation with polymer sockets, only 1 head fracture occurred (0.07%). In the group of cases with ceramic/ceramic pairing, the reason for fracture was direct trauma in 4 cases, recurrent neck impingement in 2 cases, and fatigue failure in 1 case. The only case with ceramic head fracture in polymer pairing also was caused by direct trauma. Fractures of the alumina ceramic heads cannot be avoided, but the use of ball type neckless heads brought the fracture rate close to 0. Under the aspect of material safety, it seems to be possible to use the great advantage of the superior low wear of the alumina/alumina couple with negligible fracture risk.

Comparison of physical property-porosity behaviour with minimum solid area models

Abstract: An extensive survey of the porosity dependence of (room temperature) physical properties shows that mechanical properties and electrical and thermal conductivity, i.e. properties dependent on the local flux or fields in the material, follow minimum solid area models. This is shown extensively for elastic properties and tensile (flexure) strength, but consistency with other properties, e.g. compressive strength, hardness, electrical and thermal conductivity is also shown. Although data for ceramics is most extensive, data for rocks, metals, and carbon are included, since the consistency of these, especially of metals with ceramics, provides important support for the minimum solid area concept. While porosity characterization is generally minimal, expected model trends with pore character are corroborated by correlating processing and resultant expected pore character with porosity-property results. It is argued that properties dependent on mass should be better fit by a linear, i.e. rule of mixture, relationship between such properties and porosity. Support for this is shown in dielectric constant-porosity data.

Thermal barrier coating resistant to erosion and impact by particulate matter

Abstract: A thermal barrier coating adapted to be formed on an article subjected to a hostile thermal environment while subjected to erosion by particles and debris, as is the case with turbine, combustor and augmentor components of a gas turbine engine. The thermal barrier coating is composed of a metallic bond layer deposited on the surface of the article, a ceramic layer overlaying the bond layer, and an erosion-resistant composition dispersed within or overlaying the ceramic layer. The bond layer serves to tenaciously adhere the thermal insulating ceramic layer to the article, while the erosion-resistant composition renders the ceramic layer more resistant to erosion. The erosion-resistant composition is either alumina (Al 2 O 3 ) or silicon carbide (SiC), while a preferred ceramic layer is yttria-stabilized zirconia (YSZ) deposited by a physical vapor deposition technique to have a columnar grain structure.

Thermal behavior of (organosilicon) polymer-derived ceramics. V: Main facts and trends

Abstract: Extensive investigations of polymer-based ceramic materials taken within the Si-C-N-O-(H) system have been performed and previously published as Parts I – IV. This paper reports the main results, facts, trends and conclusions which can be drawn from them, regarding the physical and chemical behavior of these materials submitted to an increasing thermal treatment. Both similarities and discrepancies are described and explained, whatever the chemical composition of the ceramic, (i.e. containing Si-C or Si-C-N, Si-C-O, Si-C-N-O). Emphasis is made on the mechanisms, and the role of various parameters, either intrinsic (e.g. the role of compositional C, O, or N) or extrinsic (e.g. influence of the atmosphere), is examined. The overall results indicate, among others, that excess carbon (relative to the SiC stoichiometry) is always beneficial both to the structural stability of the ceramic and the mechanical properties (when measurable), while heteroatoms (O, N) are always finally detrimental. They thus sustain the current efforts to develop ceramic fibers from chemical systems as simple as possible, using oxygen-free curing processes. More generally, they provide guidelines for understanding, and somewhat predicting, the thermochemical behavior of any related materials.