Showing papers on "Ceramic published in 1995"

The Science and Engineering of Thermal Spray Coatings

Abstract: Preface to the Second Edition. Preface to the First Edition. Acronyms, Abbreviations and Symbols. 1 Materials Used for Spraying. 1.1 Methods of Powders Production. 1.1.1 Atomization. 1.1.2 Sintering or Fusion. 1.1.3 Spray Drying (Agglomeration). 1.1.4 Cladding. 1.1.5 Mechanical Alloying (Mechanofusion). 1.1.6 Self-propagating High-temperature Synthesis (SHS). 1.1.7 Other Methods. 1.2 Methods of Powders Characterization. 1.2.1 Grain Size. 1.2.2 Chemical and Phase Composition. 1.2.3 Internal and External Morphology. 1.2.4 High-temperature Behaviour. 1.2.5 Apparent Density and Flowability. 1.3 Feeding, Transport and Injection of Powders. 1.3.1 Powder Feeders. 1.3.2 Transport of Powders. 1.3.3 Injection of Powders. References. 2 Pre-Spray Treatment. 2.1 Introduction. 2.2 Surface Cleaning. 2.3 Substrate Shaping. 2.4 Surface Activation. 2.5 Masking. References. 3 Thermal Spraying Techniques. 3.1 Introduction. 3.2 Flame Spraying (FS). 3.2.1 History. 3.2.2 Principles. 3.2.3 Process Parameters. 3.2.4 Coating Properties. 3.3 Atmospheric Plasma Spraying (APS). 3.3.1 History. 3.3.2 Principles. 3.3.3 Process Parameters. 3.3.4 Coating Properties. 3.4 Arc Spraying (AS). 3.4.1 Principles. 3.4.2 Process Parameters. 3.4.3 Coating Properties. 3.5 Detonation-Gun Spraying (D-GUN). 3.5.1 History. 3.5.2 Principles. 3.5.3 Process Parameters. 3.5.4 Coating Properties. 3.6 High-Velocity Oxy-Fuel (HVOF) Spraying. 3.6.1 History. 3.6.2 Principles. 3.6.3 Process Parameters. 3.6.4 Coating Properties. 3.7 Vacuum Plasma Spraying (VPS). 3.7.1 History. 3.7.2 Principles. 3.7.3 Process Parameters. 3.7.4 Coating Properties. 3.8 Controlled-Atmosphere Plasma Spraying (CAPS). 3.8.1 History. 3.8.2 Principles. 3.8.3 Process Parameters. 3.8.4 Coating Properties. 3.9 Cold-Gas Spraying Method (CGSM). 3.9.1 History. 3.9.2 Principles. 3.9.3 Process Parameters. 3.9.4 Coating Properties. 3.10 New Developments in Thermal Spray Techniques. References. 4 Post-Spray Treatment. 4.1 Heat Treatment. 4.1.1 Electromagnetic Treatment. 4.1.2 Furnace Treatment. 4.1.3 Hot Isostatic Pressing (HIP). 4.1.4 Combustion Flame Re-melting. 4.2 Impregnation. 4.2.1 Inorganic Sealants. 4.2.2 Organic Sealants. 4.3 Finishing. 4.3.1 Grinding. 4.3.2 Polishing and Lapping. References. 5 Physics and Chemistry of Thermal Spraying. 5.1 Jets and Flames. 5.1.1 Properties of Jets and Flames. 5.2 Momentum Transfer between Jets or Flames and Sprayed Particles. 5.2.1 Theoretical Description. 5.2.2 Experimental Determination of Sprayed Particles' Velocities. 5.2.3 Examples of Experimental Determination of Particles Velocities. 5.3 Heat Transfer between Jets or Flames and Sprayed Particles. 5.3.1 Theoretical Description. 5.3.2 Methods of Particles' Temperature Measurements. 5.4 Chemical Modification at Flight of Sprayed Particles. References. 6 Coating Build-Up. 6.1 Impact of Particles. 6.1.1 Particle Deformation. 6.1.2 Particle Temperature at Impact. 6.1.3 Nucleation, Solidification and Crystal Growth. 6.1.4 Mechanisms of Adhesion. 6.2 Coating Growth. 6.2.1 Mechanism of Coating Growth. 6.2.2 Temperature of Coatings at Spraying. 6.2.3 Generation of Thermal Stresses at Spraying. 6.2.4 Coatings Surfaces. 6.3 Microstructure of the Coatings. 6.3.1 Crystal Phase Composition. 6.3.2 Coatings' Inhomogeneity. 6.3.3 Final Microstructure of Sprayed Coatings. 6.4 Thermally Sprayed Composites. 6.4.1 Classification of Sprayed Composites. 6.4.2 Composite Coating Manufacturing. References. 7 Methods of Coatings' Characterization. 7.1 Methods of Microstructure Characterization. 7.1.1 Methods of Chemical Analysis. 7.1.2 Crystallographic Analyses. 7.1.3 Microstructure Analyses. 7.1.4 Other Applied Methods. 7.2 Mechanical Properties of Coatings. 7.2.1 Adhesion Determination. 7.2.2 Hardness and Microhardness. 7.2.3 Elastic Moduli, Strength and Ductility. 7.2.4 Properties Related to Mechanics of Coating Fracture. 7.2.5 Friction and Wear. 7.2.6 Residual Stresses. 7.3 Physical Properties of Coatings. 7.3.1 Thickness, Porosity and Density. 7.3.2 Thermophysical Properties. 7.3.3 Thermal Shock Resistance. 7.4 Electrical Properties of Coatings. 7.4.1 Electrical Conductivity. 7.4.2 Properties of Dielectrics. 7.4.3 Electron Emission from Surfaces. 7.5 Magnetic Properties of Coatings. 7.6 Chemical Properties of Coatings. 7.6.1 Aqueous Corrosion. 7.6.2 Hot-gas Corrosion. 7.7 Characterization of Coatings' Quality. 7.7.1 Acoustical Methods. 7.7.2 Thermal Methods. References. 8 Properties of Coatings. 8.1 Design of Experiments. 8.2 Mechanical Properties. 8.2.1 Hardness and Microhardness. 8.2.2 Tensile Adhesion Strength. 8.2.3 Elastic Moduli, Strengths and Fracture Toughness. 8.2.4 Friction and Wear. 8.3 Thermophysical Properties. 8.3.1 Thermal Conductivity and Diffusivity. 8.3.2 Specific Heat. 8.3.3 Thermal Expansion. 8.3.4 Emissivity. 8.3.5 Thermal Shock Resistance. 8.4 Electric Properties. 8.4.1 Properties of Conductors. 8.4.2 Properties of Resistors. 8.4.3 Properties of Dielectrics. 8.4.4 Electric Field Emitters. 8.4.5 Properties of Superconductors. 8.5 Magnetic Properties. 8.5.1 Soft Magnets. 8.5.2 Hard Magnets. 8.6 Optical Properties. 8.6.1 Decorative Coatings. 8.6.2 Optically Functional Coatings. 8.7 Corrosion Resistance. 8.7.1 Aqueous Corrosion. 8.7.2 Hot-medium Corrosion. References. 9 Applications of Coatings. 9.1 Aeronautical and Space Industries. 9.1.1 Aero-engines. 9.1.2 Landing-gear Components. 9.1.3 Rocket Thrust-chamber Liners. 9.2 Agroalimentary Industry. 9.3 Automobile Industry. 9.4 Ceramics Industry. 9.4.1 Free-standing Samples. 9.4.2 Brick-Clay Extruders. 9.4.3 Crucibles to Melt Oxide Ceramics. 9.4.4 Ceramic Membranes. 9.5 Chemical Industry. 9.5.1 Photocatalytic Surfaces. 9.5.2 Tools in Petrol Search Installations. 9.5.3 Vessels in Chemical Refineries. 9.5.4 Gas-well Tubing. 9.5.5 Polymeric Coatings on Pipeline Components. 9.5.6 Ozonizer Tubes. 9.6 Civil Engineering. 9.7 Decorative Coatings. 9.8 Electronics Industry. 9.8.1 Heaters. 9.8.2 Sources for Sputtering. 9.8.3 Substrates for Hybrid Microelectronics. 9.8.4 Capacitor Electrodes. 9.8.5 Conductor Paths for Hybrid Electronics. 9.8.6 Microwave Integrated Circuits. 9.9 Energy Generation and Transport. 9.9.1 Solid-oxide Fuel Cell (SOFCs). 9.9.2 Thermopile Devices for Thermoelectric Generators. 9.9.3 Boilers in Power-generation Plants. 9.9.4 Stationary Gas Turbines. 9.9.5 Hydropower Stations. 9.9.6 MHD Generators. 9.10 Iron and Steel Industries. 9.10.1 Continuous Annealing Line (CAL). 9.10.2 Continuous Galvanizing Section. 9.10.3 Stave Cooling Pipes. 9.11 Machine Building Industry. 9.12 Medicine. 9.13 Mining Industry. 9.14 Non-ferrous Metal Industry. 9.14.1 Hot-extrusion Dies. 9.14.2 Protective Coatings against Liquid Copper. 9.14.3 Protective Coatings against Liquid Zirconium. 9.15 Nuclear Industry. 9.15.1 Components of Tokamak Device. 9.15.2 Magnetic-fusion Energy Device. 9.16 Paper Industry. 9.16.1 Dryers. 9.16.2 Gloss Calender Rolls. 9.16.3 Tubing in Boilers. 9.17 Printing and Packaging Industries. 9.17.1 Corona Rolls. 9.17.2 Anilox Rolls. 9.18 Shipbuiding and Naval Industries. 9.18.1 Marine Gas-turbine Engines. 9.18.2 Steam Valve Stems. 9.18.3 Non-skid Helicopter Flight Deck. References. Index.

Ceramic Processing and Sintering

Abstract: Ceramic fabrication processes - an introductory overview synthesis of powders powder characterization science of colloidal processing sol-gel processing powder consolidation and forming of ceramics sintering of ceramics - fundamentals theory of viscous sintering grain growth and microstructural control liquid-phase sintering problems of sintering densification process variables and densification practice.

Ferroelectric Polymers : Chemistry: Physics, and Applications

Abstract: Part 1 Ferroelectric Polymers: Polymer Electrets Crystal Structures and Phase Transitions of PVDF and Related Copolymers Ferroelectric, Pyroelectric, and Piezoelectric Properties of Poly(vinylidene Fluoride) PVDF and Its Blends Poly(trifluoroethylene) Ferroelectric Nylons Cyanopolymers Polyureas and Polythioureas Piezoelectricity and Pyroelectricity Ferroelectric Liquid Crystal (FLC) Polymers Polymer-Ferroelectric Ceramic Composites Nonlinear Optical Properties of Ferroelectric Polymers Dielectric Properties of Ferroelectric Polymers. Part 2 Applications Pyroelectric Applications Electromechanical Applications Transduction Applications Ferroelectric Optical Memory Biomedical and Robotic Applications of Ferroelectric Polymers Applications of Ferroelectric Liquid Crystalline Polymers.

Ceramic sensors for humidity detection: the state-of-the-art and future developments

Abstract: The possible applications of humidity sensors in automated systems for environmental control encompass many industrial and domestic fields. Very different operating temperatures and a variety of humidity ranges are needed for these purposes. The different humidity-sensing mechanisms and operating principles identified for ceramics are reviewed. Ceramic humidity sensors are divided into ionic, electronic, solid-electrolyte and rectifying-junction types. Examples of the performance of some ceramic sensors are presented. The correlation between the microstructure of ceramic materials and their humidity-sensitive electrical response is discussed. The improvement of the performance of ionic-type humidity sensors by the addition of alkali ions is explained in terms of influence on the microstructure and on the intrinsic impedance. The recent trend towards the miniaturization and integration of sensors on a single chip requires the production of ceramic films. Ceramic thin films prepared by sol-gel or sputtering processes are investigated. The results obtained on the humidity sensitivity of pn semiconducting oxide heterocontacts are also reported.

Ferroelectric/ferroelastic interactions and a polarization switching model

Abstract: Ferroelectric and ferroelastic switching cause ferroelectric ceramics to depolarize and deform when subjected to excessive electric field or stress. Switching is the source of the classic butterfly shaped strain vs electric field curves and the corresponding electric displacement vs electric field loops [1]. It is also the source of a stress—strain curve with linear elastic behavior at low stress, non-linear switching strain at intermediate stress, and linear elastic behavior at high stress [2, 3]. In this work, ceramic lead lanthanum zirconate titanate (PLZT) is polarized by loading with a strong electric field. The resulting strain and polarization hysteresis loops are recorded. The polarized sample is then loaded with compressive stress parallel to the polarization and the stress vs strain curve is recorded. The experimental results are modeled with a computer simulation of the ceramic microstructure. The polarization and strain for an individual grain are predicted from the imposed electric field and stress through a Preisach hysteresis model. The response of the bulk ceramic to applied loads is predicted by averaging the response of individual grains that are considered to be statistically random in orientation. The observed strain and electric displacement hysteresis loops and the nonlinear stress—strain curve for the polycrystalline ceramic are reproduced by the simulation.

Combinatorial synthesis of novel materials

Abstract: Methods and apparatus for the preparation and use of a substrate having an array of diverse materials in predefined regions thereon. A substrate having an array of diverse materials thereon is generally prepared by delivering components of materials to predefined regions on a substrate, and simultaneously reacting the components to form at least two materials. Materials which can be prepared using the methods and apparatus of the present invention include, for example, covalent network solids, ionic solids and molecular solids. More particularly, materials which can be prepared using the methods and apparatus of the present invention include, for example, inorganic materials, intermetallic materials, metal alloys, ceramic materials, organic materials, organometallic materials, non-biological organic polymers, composite materials (e.g., inorganic composites, organic composites, or combinations thereof), etc. Once prepared, these materials can be screened for useful properties including, for example, electrical, thermal, mechanical, morphological, optical, magnetic, chemical, or other properties. Thus, the present invention provides methods for the parallel synthesis and analysis of novel materials having useful properties.

Active‐Filler‐Controlled Pyrolysis of Preceramic Polymers

Abstract: Manufacturing of bulk ceramic components from materials in the system Si-Me-C-N-O (Me = Ti, Cr, V, Mo, Si, B, CrSi2, MoSi2, etc.) from preceramic organosilicon polymers - such as poly(carbosilanes), poly(silazanes), or poly(siloxanes) - has become possible by incorporating reactive filler particles into the liquid or solid polymer pre-cursor. During pyrolytic decomposition of the polymer matrix, the filler particles react with carbon from the polymer precursor or nitrogen from the reaction gas atmosphere to form new (oxy)carbide or (oxy)nitride phases embedded in a nanocrystalline Si-O-C(-N) matrix. The selective expansion encountered in the filler phase reaction can be used to compensate for the polymer shrinkage upon pyrolytic conversion. The formation of a transient pore net-work between 400° and 1000°C is governed by the polymer decomposition as well as the filler particle reaction kinetics. Thus, the properties of the oxycarbonitride composite materials can be tailored by controlling the microstructures of the polymer-derived matrix phase, the filler network, and the residual porosity. Near-net-shape forming of bulk ceramic components, even with complex geometry, is possible, making novel applications of polymer-derived bulk materials in biomedical, electrical, and mechanical fields highly interesting.

Shear vs. Tensile Bond Strength of Resin Composite Bonded to Ceramic

Abstract: Since the mode of failure of resin composites bonded to ceramics has frequently been reported to be cohesive fracture of either ceramic or resin composite rather than separation at the adhesive interface, this study was designed to question the validity of shear bond strength tests. The reasons for such a failure mode are identified and an alternative tensile bond strength test evaluated. Three configurations (A, conventional; B, reversed; and C, all composite) of the cylinder-on-disc design were produced for shear bond strength testing. Two-dimensional finite element stress analysis (FEA) was carried out to determine qualitatively the stress distribution for the three configurations. A tensile bond strength test was designed and used to evaluate two ceramic repair systems, one using hydrofluoric acid (HF) and the other acidulated phosphate fluoride (APF). Results from the shear bond strength tests and FEA showed that this particular test has as its inherent feature the measurement of the strength of the ...

Ceramic Composites of Monazite and Alumina

Abstract: A new family of high-temperature, oxidation-resistant, ceramic composites, with (La)-monazite (LaPO{sub 4}) serving as a weakly bonded interphase, is proposed. Monazite is stable and phase-compatible with alumina at temperatures at least as high as 1,750 C in air. Especially important for use in high-toughness composites, the monazite-alumina interface is shown to be sufficiently weak that interfacial debonding prevents cracks from growing from monazite into alumina. Observations of fracture responses of fibrous and laminar reinforcements are presented.

Dense ceramic membranes for partial oxidation of methane to syngas

Abstract: Several perovskite-type oxides (ABO3) containing transition metals on the B-site show mixed (electronic/ionic) conductivity. These mixed-conductivity oxides are promising materials for oxygen-permeating membranes that can operate without electrodes or external electrical circuitry. Oxides in the system LaSrFeCoO permeate large amounts of oxygen, and extruded tubes of these materials have been evaluated in a reactor operating at ca. 850°C for direct conversion of methane into syngas (CO + H2) in the presence of a reforming catalyst. Methane conversion efficiencies of > 99% were observed, and some of the reactor tubes have been operated for over 1000 h. Membrane tubes were fabricated from calcined powders by a plastic extrusion technique. Ceramic powders in the LaSrFeCoO system were made by solid-state reaction of the constituent carbonates, oxides, and/or nitrates. The chemical-phase behavior of the ceramic powders with varying stoichiometries were studied by high-temperature in-situ X-ray diffraction (XRD) as a function of oxygen partial pressure. The sintered extruded tubes were also characterized by XRD and scanning electron microscopy.

Review: aqueous tape casting of ceramic powders

Abstract: Slurry formulations and processing parameters of the water-based tape casting of ceramic powders are reviewed. Additives include binders, like cellulose ethers, vinyl or acrylic-type polymers; plasticizers, like glycols; and dispersants, like ammonium salts of poly(acrylic acids). Mostly alumina powders have been employed. Hydrophobing of ceramic powders permits the aqueous processing even of water-reactive powders, like aluminium nitride. Non-toxicity and non-inflammability of water-based systems represent an alternative to organic solvent-based ones. Aqueous slurries are, on the other hand, complex multiphase systems, very sensitive to process variations. Statistical design of experiments was used for the improvement of the process.

A covalent micro/nano-composite resistant to high-temperature oxidation

Abstract: ADVANCED ceramic materials that can withstand high temperatures (over 1,500 °C) without degradation or oxidation are needed for applications such as structural parts for motor engines, gas turbines, catalytic heat exchangers and combustion systems1,2. Hard, oxidation-resistant ceramic composites and coatings are also in demand for use on aircraft and spacecraft. Silicon nitride (Si3N4) and silicon nitride/carbide (Si3N4 /SiC) composites are good candidates for such high-temperature applications2,3. Commercial Si3N4 parts can be used in oxidizing environments up to 1,200–1,300 °C (ref. 4), but are oxidized at still higher temperatures. Here we describe the synthesis of a covalent ceramic composite which is resistant to oxidation at temperatures up to 1,600 °C. The composite is formed from an amorphous silicon carbonitride, which crystallizes at high temperature into a composite of α-Si3N4 microcrystals and α-SiC nanocrystals. The oxidation resistance stems from the formation of a passivating surface layer of SiO2 a few micrometres thick.

Transparent glass ceramics for 1300 nm amplifier applications

Abstract: The properties of an oxyfluoride glass ceramic that possesses high transparency after ceramming are described. Approximately 25 vol % of this material is comprised of cubic, fluoride nanocrystals and the remainder is a predominantly oxide glass. When doped with Pr+3, the fluorescence lifetime at 1300 nm is longer than in a fluorozirconate glass, suggesting that a significant fraction of the rare‐earth dopant is preferentially partitioned into the fluoride crystal phase. This material has the added advantage of being compatible with ambient air processing.

Bonding to glass infiltrated alumina ceramic: Adhesive methods and their durability

Abstract: Resin bonding to a glass-infiltrated aluminum oxide ceramic (In-Ceram) cannot be achieved by the methods commonly used for conventional silica-based dental caramics. This study evaluated the durability of alternative methods of adhesive bonding to In-Ceram ceramic. The tensile bond strength of six bonding systems to In-Ceram ceramic was tested after up to 150 days of storage in isotonic artificial saliva solution and theramal cycling. Sandblasting alone or additional use of a silane did not result in a durable bond of a conventional BIS-GMA composite resin to In-Ceram ceramic. A durable bond to In-Ceram ceramic was achieved with a combination of tribochemical silica coating and conventional BIS-GMA composite resin or with the combination of sandblasting and a composite resin modified with a phosphate monomer. These two chemomechanical bonding methods appeared suitable for clinical bonding of In-Ceram ceramic restorations. A delayed degradation in bond strength was recorded for the combination of thermal silica coating and a conventional BIS-GMA composite resin; no reduction was found after 30 days, but there was a pronounced decrease after 150 days. This degradation indicated that extended storage in a wet environment was needed in laboratory tests to evaluate the durability of chemical bonds.

The Influence of the Microstructure on the Properties of Ferroelectric Ceramics

Abstract: Conventional ferroelectric perovskite type ceramics have dielectric, piezoelectric and elastic properties which depend on grain size and on domain configuration. Very fine grained ceramic is not splitted in domains. This causes strong elastic stress fields in the grains which counteract ferroelectricity. Tetragonal fine grained ceramic has a simple laminar domain structure and high elastic stress fields inside the grain and at the grain boundaries. These stress fields cause very high permittivity. In coarse grained ceramics the stress fields inside the grain are eliminated by a three-dimensional network of domains. In fine and in coarse grained ceramics the domain walls contribute considerably to the dielectric, piezoelectric and elastic constants at frequencies below a relaxation frecuency which is between 200 and 1000 MHz. At low temperatures, however, the domain wall contributions freeze in. Acceptor doping lowers the domain wall contributions and shifts the relaxation frequency to higher values. The properties of the conventional ceramics will be compared wiht properties of thin firms and with properties of relaxor ceramics.

Effects of Treatment and Storage Conditions on Ceramic/Composite Bond Strength

Abstract: During the past few years, the interest in using ceramic inlays and veneers has increased. New materials and methods have been introduced to bond these restorations to resinous materials. Since our knowledge of how to optimize such bonding is limited, the objective of this study was to test the hypothesis that various surface treatment variables and combinations of these variables affect the strength of the ceramic/composite interphase of ceramic inlays differently. The influences of material composition, surface-roughening method, silane treatment, silane heat treatment, and storage condition on bond strength were investigated. Three ceramics (Dicor, Mirage, Vitabloc), three surface-roughening methods (etching, sandblasting, grinding), three silane treatments (gamma-methacryloxypropyltrimethoxysilane [MPS], MPS+paratoluidine, vinyltrichlorosilane), two heat treatments (20 degrees C for 60 s, 100 degrees C for 60 s), and two storage conditions (24-hour dry, one yr in water at 37 degrees C) were studied. For each of the 108 combinations, five specimens were tested. Ceramic cylinders were treated according to group assignment and bonded to blocks of the same ceramic material with a dual-cured resin. The shear bond strength was determined, and the experimental factors were evaluated by analysis of variance. The results showed that surface-roughening method had the strongest effect on bond strength, while ceramic selection had the least significant effect. Of the surface-roughening methods, etching was associated with higher bond strength values than either sandblasting or grinding.(ABSTRACT TRUNCATED AT 250 WORDS)

Overview of Fine-Scale Piezoelectric Ceramic/Polymer Composite Processing

Abstract: In the past two decades, piezoelectric ceramic/polymer composites with different connectivities have been developed for transducer applications such as hydrophones, biomedical imaging, nondestructive testing, and air imaging. Recently, much attention has been given to fine-scale piezoelectric ceramic/polymer composites. These composites allow higher operating frequencies, and thus increased resolution, in medical imaging transducers. In this review, methods for processing fine-scale piezoelectric ceramic/polymer composites are discussed. The current capabilities, strengths, and weaknesses of each method are compared. The importance of spatial scale in composite performance is also reviewed. Several of the processing methods have demonstrated composites with fine-scale ceramic phases (<50 μm), and others have potential to form composites with a ceramic scale of under 20 μm.

Fatigue of ceramic matrix composites

Abstract: Fatigue in ceramic matrix composites typically occurs when matrix cracks are present. It proceeds by cyclic degradation of the sliding resistance of the interface. The basic mechanisms are discussed and a methodology is developed that enables fatigue life predictions to be made, based on a minimum number of experimental measurements. The methodology relies on analysis of hysteresis loops. Changes in modulus upon cyclic loading as well as the permanent strains are predicted, as well as the fatigue threshold and the S-N curve.

Low thermal expansion glass ceramics

Abstract: 1. Overview 2. The Scientific Basis 3. Transparent and Tinted Glass Ceramics for Household Appliances 4. Zerodur(R) - A Low Thermal Glass Ceramic for Optical Precision Applications

Relative fracture toughness and hardness of new dental ceramics

Abstract: Dental ceramics can fail through growth of microscopic surface flaws that form during processing or from surface impact during service. New restorative dental ceramic materials have been developed to improve resistance to crack propagation. Eleven of these improved materials with the common feature of a considerable amount of crystalline phase in the glassy matrix were evaluated. The ceramic materials studied included fluormica-, leucite-, alumina-, and zirconia-reinforced glasses. The relative hardness and fracture toughness were determined by indentation technique. Aluminareinforced materials resulted in the highest fracture toughness values, whereas the fluormica- and leucite-reinfoced materials showed more moderate but statistically significant greater values compared with those of control materials. The hardness values of ceramic materials with improved fracture toughness were both substantially higher or lower than those of the control groups and suggested a lack of direct correlation between these two properties. Selection of appropriate restorative materials depends on clinical application and requires consideration of several physical properties including fracture toughness.

Grain Size Dependence of Hardness in Dense Submicrometer Alumina

Abstract: Pressureless sintered alumina compacts with a submicrometer microstructure exhibit a hardness that approaches or even exceeds the level of advanced hot-pressed composites of Al{sub 2}O{sub 3} + 35 vol% TiC, whereas the strength of both ceramics is approximately the same. The combination of reduced dislocation mobility (due to the small grain size), high density, and density homogeneity are the prerequisites for the surprisingly high hardness. Quasi-conventional powder processing is used to produce these outstanding alumina bodies.

Diesel particulate filter apparatus

Abstract: According to the present invention, a filter body for collecting particulates is constituted of a fiber laminate material produced by laminating a fiber material comprising a core material in the form of a fiber, and a covering layer of a material different from that of the core material formed around the outer periphery of the core material by coating. The core material of the fiber material is selected from among inorganic fibers such as glass or ceramic fibers containing alumina, and heat-resistant alloy fibers each made of a heat-resistant alloy selected from among Ti-Al alloys, Fe alloys containing at least one of Mo, Cr and Ni, and Fe-Cr-Al-Y alloys. The covering layer is made of a material selected from among silicon carbide ceramics respectively derived from polytitanocarbosilane, polysilazane and polycarbosilane, thermoplastic materials, silicon carbide ceramics such as Si-C, Si-Ti-C-O and Si-C-O or silicon nitride ceramics such as Si-N-C-O, alumina ceramics, and zirconia ceramics.

Giant magnetoresistive cobalt oxide compounds

Abstract: Methods and apparatus for the preparation and use of a substrate having an array of diverse materials in predefined regions thereon. A substrate having an array of diverse materials thereon is generally prepared by delivering components of materials to predefined regions on a substrate, and simultaneously reacting the components to form at least two materials. Materials which can be prepared using the methods and apparatus of the present invention include, for example, covalent network solids, ionic solids and molecular solids. More particularly, materials which can be prepared using the methods and apparatus of the present invention include, for example, inorganic materials, intermetallic materials, metal alloys, ceramic materials, organic materials, organometallic materials, non-biological organic polymers, composite materials (e.g., inorganic composites, organic composites, or combinations thereof), etc. Once prepared, these materials can be screened for useful properties including, for example, electrical, thermal, mechanical, morphological, optical, magnetic, chemical, or other properties. Thus, the present invention provides methods for the parallel synthesis and analysis of novel materials having useful properties.

Optical properties of transparent glass-ceramics in K2ONb2O5TeO2 glasses

Abstract: Transparent glass-ceramics consisting of a cubic crystalline phase with crystallites having diameters between 20 and 40 nm in the composition of 15K2O15Nb2O570TeO2 (mol%) have been fabricated. A phase with cubic structure is formed by post-heat-treatment at around 390°C for 1 h and transforms into a stable phase at temperatures above 450°C. The glass-ceramics consisting of a stable crystalline phase are opaque. The transparency of glass-ceramics is attributed to a small particle size (average radius: 10–20 nm) of the cubic crystalline phase. The optical and dielectric properties for the transparent glass-ceramics obtained by heat-treatment at 425°C for 1 h are: refractive index, n = 2.11 ± 0.02; relative permittivity (1 kHz, 300 K), ϵr = 44 ± 1 and third-order non-linear optical susceptibility, χ(3) = 3.3 × 10−13esu. These values are larger than those for the original base glass, i.e. n = 2.02 ± 0.02, ϵr = 28 ± 1 and χ(3) = 0.9 × 10−13esu. Second-harmonic generation is clearly observed in transparent glass-ceramics. These transparent glass-ceramics have a potential as a new type of non-linear optical material.

Methane to syngas via ceramic membranes

Abstract: Long tubes of La[sub 0.2]Sr[sub 0.8]Fe[sub 0.6]Co[sub 0.4]O[sub x] (LSFC) membrane have been fabricated by plastic extrusion. Thermodynamic stability of the tubes was studied as a function of oxygen partial pressure by high-temperature XRD. Mechanical properties were measured and found to be adequate for a reactor material. Performance of the membrane strongly depended on the stoichiometry of the material. Fracture of certain LSFC tubes was the consequence of an oxygen gradient that introduced a volumetric lattice difference between the inner and outer walls. However, tubes made with LSFC-2 provided methane-conversion efficiencies of >99% in a reactor. Some of these reactor tubes have operated for up to 500 h. A thin-wall membrane ceramic material could prevent both fracture and chemical decomposition of the tubes.