Showing papers on "Ceramic published in 1985"

Dielectric properties of fine‐grained barium titanate ceramics

Abstract: Dielectric properties, lattice‐ and microstructure of ceramic BaTiO3 showing grain sizes of 0.3–100 μm were studied. At grain sizes <10 μm the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter. The decreasing width of the domains can be theoretically explained by the equilibrium of elastic field energy and domain wall energy. The smaller the grains, the more the dielectric and the elastic constants are determined by the contribution of 90° domain walls. The permittivity below the Curie point shows a pronounced maximum er ≊5000 at grain sizes 0.8–1 μm. At grain sizes <0.7 μm the permittivity strongly decreases and the lattice gradually changes from tetragonal to pseudocubic.

Introduction to materials science for engineers

Abstract: 1. Materials for Engineering. I. THE FUNDAMENTALS. 2. Atomic Bonding. 3. Crystalline Structure-Perfection. 4. Crystal Defects and Noncrystalline Structure-Imperfection. 5. Diffusion. 6. Mechanical Behavior. 7. Thermal Behavior. 8. Failure Analysis and Prevention. 9. Phase Diagrams-Equilibrium Microstructural Development. 10. Kinetics-Heat Treatment. II. THE STRUCTURAL MATERIALS. 11. Metals. 12. Ceramics and Glasses. 13. Polymers. 14. Composites. III. THE ELECTRONIC, OPTICAL AND MAGNETIC MATERIALS. 15. Electrical Behavior. 16. Optical Behavior. 17. Semiconductor Materials. 18. Magnetic Materials. IV. MATERIALS IN ENGINEERING DESIGN. 19. Environmental Degradation. 20. Materials Selection.

Electronic properties of materials

Abstract: Part I: Fundamentals of Electron Theory: Introduction. Wave Properties of Electrons. The Schroedinger Equation. Solution of the Schroedinger Equation for Four Specific Problems. Energy Bands in Crystals. Electrons in a Crystal.- Part II: Electrical Properties of Materials: Electrical Conduction in Metals and Alloys. Semiconductors. Electrical Properties of Polymers, Ceramics, Dielectrics and Amorphous Materials.- Part III: Optical Properties of Materials: The Optical Constants. Atomistic Theory of the Optical Properties. Quantum Mechanical Treatment of the Optical Properties. Applications.- Part IV: Magnetic Properties of Materials: Foundations of Magnetism. Magnetic Phenomena and Their Interpretation - Classical Approach. Quantum Mechanical Considerations. Applications.- Part V: Thermal Properties of Materials: Introduction. Fundamentals of Thermal Properties. Heat Capacity. Thermal Conduction. Thermal Expansion.- Appendices.- Index.

Strength, fracture toughness and Vickers hardness of CeO2-stabilized tetragonal ZrO2 polycrystals (Ce-TZP)

Abstract: Dense Ce-TZP ceramics containing about 7 to 16 mol% CeO2 were fabricated using fine powders prepared by the hydrolysis technique. The mechanical properties of these ceramics were evaluated. The bending strength of sintered bodies with 10 to 12 mol% CeO2 content and small grain-size was about 800 MPa. Fracture toughness was measured by two different methods; a micro-indentation technique and the chevron notched beam technique. A high fracture toughness was obtained for sintered bodies with 7 to 10% CeO2 content and large grain-size. Fracture toughness and hardness were dependent on CeO2 content and grain-size. These mechanical properties are discussed on the basis of the stability of the metastable tetragonal phase depending on CeO2 content and grain-size.

Sintering Behavior of Ceramic Films Constrained by a Rigid Substrate

Abstract: A model is presented in which the sintering behavior of a ceramic film which is constrained by a rigid substrate is contrasted with the sintering behavior of a free film. The problem is made simple by the assumption that the stress field developed in the film is uniform. This simplification allows several closed form solutions to be obtained. The solutions give new insights into the sintering behavior of films supported on a substrate. It is found (1) that the shear rate of the film is more important in the sintering process than its densification rate when the film is constrained by a substrate, (2) that the incompatibility stress is time dependent and reaches its maximum value during the initial stages of sintering, (3) that the magnitude of that maximum stress may be tensile or it may be compressive depending on the shear response of the material, and (4) that if the incompatibility stress is tensile it can lead to the formation of cracks or defects in the ceramic film.

Residual Stresses in Meta/Ceramic Bonded Strips

Abstract: Residual stresses that develop during cooling of a metal/ ceramic strip are calculated analytically. It is shown that the metal may behave elastically or plastically (with full or partial plasticity) depending on the mechanical properties, the thickness of the two constituents, and the mismatch in thermal expansion. Residual stresses are also calculated for a sequence consisting of constrained undercooling, removal of the constraint, and reheating. It is demonstrated that reheating, which results in elastic stress relaxation, may be used to eliminate the residual stress. The optimum undercooling and reheating conditions needed to produce a stress-free strip, at the operational temperature, are calculated, and specific results are presented for the system Cu/A2, O2.

Method for making a composite body coated with one or more layers of inorganic materials including CVD diamond

Abstract: A chemical vapor deposition method for the production of a composite body with one or more polycrystalline diamond layers, essentially free of intercrystalline binder phase, on a substrate of one of: (a) metalbonded hardmaterial compound; (b) ceramic material; or (c) a metal or an alloy, whereby the heated substrate is contacted with a gaseous mixture of hydrocarbon or hydrogen, which mixture has been activated by passing it over a tantalum heater heated to a temperature of 1500°-2500° C. Also disclosed is the use of the compound body in tools subjected to mechanical operations.

Sol-gel-derived PbTiO 3

Abstract: The sol-gel process is a technique which is applicable for forming ceramic materials. In this process, liquid precursor materials are reacted to form a sol which then polymerizes into an inorganic polymeric gel. Advantages of this process over standard powder preparation of ceramics are: purity, homogeneity, control of macro- and micro-structures, and low processing temperatures. In our laboratory the sol-gel process has been used to form lead titanate. We detail a procedure which has produced dried monolithic gels up to 1.5 cm in diameter. The as-dried gels have not been exposed to temperatures above 40‡ C and are X-ray amorphous. Samples of the gels were crushed into powder and heated at 8‡ C min−1 to various temperatures up to 500‡ C, held for a variety of times, and then cooled to room temperature. After certain annealing procedures crystalline phases were observed. The initial crystalline phase to emerge has not yet been identified. Upon further annealing this phase transforms to tetragonal PbTiO3.

Exhaust gas filter

Abstract: An exhaust gas filter for diesel particulates, comprising a row of a plurality of channels of honeycomb structure of porous sintered ceramic fiber composite sheet, the ceramic fiber composite sheet being produced by a paper-forming method from a slurry of alumino-silicate fiber and fire clay. The honeycomb structure of the ceramic fiber composite sheet is formed by stacking plane sheets and corrugated sheets one atop the other. The filter exhibits low pressure drop yet highly efficient operation by having a bulk density of the ceramic fiber composite sheet in the range of 0.1 g/cm3 to 0.8 g/cm3.

BN coating of ceramic fibers for ceramic fiber composites

Abstract: A ceramic fiber composite material comprised of boron nitride coated cera fibers embedded in a ceramic matrix. The boron nitride coating limits both physical bonding and chemical reaction between the fibers and matrix to improve both strength and toughness of the composite material.

Creep Deformation of an Alumina Matrix Composite Reinforced with Silicon Carbide Whiskers

Abstract: Whisker-reinforced ceramic composites with enhanced fracture toughness properties are being developed. The creep behavior of such a composite was studied. The introduction of silicon carbide whiskers significantly improves the creep resistance of polycrystaline alumina.

Adherent ceramic coatings

Abstract: A method for depositing a coating of a dense ceramic material is disclosed. The coating may be an oxide or other refractory ceramic material. A ceramic starting material is melted and refined by heating with an electron beam in vacuum. The refined material is evaporated and deposited on a heated substrate to form a dense ceramic coating. In particular, a durable ceramic thermal barrier coating on a superalloy turbine part may be formed by coating the part with a metal layer which is oxidized to form alumina and depositing a dense ceramic layer followed by an overcoating of a columnar ceramic material.

Transparent non-vitreous ceramic particulate

Abstract: Solid, transparent, non-vitreous, ceramic particles useful as lens elements in retroreflective pavement markings characterized by having: A. at least one metal oxide phase; and B. an average minimum dimension of more than 125 micrometers. These particles are formed by various sol gel techniques, one example of which is the chemical gelation of titania sols by first mixing with glacial acetic acid, then with ammonium acetate, followed by formation of microspheres in 2-ethylhexanol. Microspheres of this ceramic composition can have relatively large diameters (e.g. over 200-1000 micrometers) making them quite useful as retroreflective lens elements in pavement marking sheet materials.

Particulate ceramic useful as a proppant

Abstract: A two-phase ceramic particulate useful as a proppant in hydraulic fracturing operations which comprises a vitreous matrix phase containing a crystalline alumina phase. The new ceramic particles are characterized by: (i) a concentration gradient of alumina which increases from very low in the centre to relatively high near the surface of the particles; (ii) a fired density less than about 2.9 g/cc; and (iii) closed cell microporosity. Certain embodiments of the inventive ceramic particulate are also characterized by a Krumbein roundness of at least 0.8 and are chemically stable. The ceramic is made by a process comprising the steps of: (a) mixing and pelletizing, with the aid of water, the dry raw materials including a mineral particulate such as nepheline syenite and a binder such as bentonite; (b) drying the wet pelletizer product; (c) mixing the dried pellets with a parting agent; and (d) firing the mixture of pellets and parting agent at sufficient temperature and for sufficient time to cause vitrification to occur.

Structural Dependence on Sintering Temperature of Lead Zirconate‐Titanate Solid Solutions

Abstract: Pb(Zr /SUB 0.525/ Ti /SUB 0.475/ )O3 piezoceramics, both unmodified and doped with 2 wt% Bi2O3 or Nb2O5, were prepared by the usual techniques, using sintering temperatures from 900 to 1250C. The microstructural data showed that the sintering temperature which produces minimum porosity is altered by the oxide additions. X-ray diffraction demonstrated the coexistence of both ferroelectric phases. The lattice parameter measurements showed that the tetragonal and rhombohedral unit cells of the two ferroelectric phases depend on the sintering temperature.

Process for producing ultra-fine ceramic particles

Abstract: A process for producing ultra-fine ceramic particles with the particle size of less than 1000 A, which comprises the steps of forming powdered dust cloud of metal powder such as Si constituting a portion of aimed ceramic particles in a reaction gas containing the other portion of said aimed ceramic particles, igniting said powdered dust cloud to cause explosive burning and synthesizing said aimed ceramic particles and gathering said resulting ceramic particles. By the process, ceramics particles such as Al 2 O 3 , MgO, SiO 2 , TiO 2 , TiN having particle size of 10 - 100 nm can be produced.

Engineering the Surface with Boron Based Materials

Abstract: Boron, boron carbide, boron nitride, and transition metal borides have many attractive properties, including high melting point and hardness, good wear and corrosion resistance, excellent electrical conductivity, and resistance to attack by molten metals. There therefore appears to be significant scope for enhancing surface properties of metals and ceramics by applying coatings constituted from these materials. Currently, the only commercial coating processes practised have been the thermochemical diffusion techniques termed boronizing or boriding, whereby boron is diffused into, and combines with, the substrate material forming a single or double phase metal boride layer at, and adjacent to, the surface. This review not only describes the various media used for such treatments and their limitations, but attention is also given to the lesser known processes, not yet commercially practised, which provide for the deposition of a wide variety of boron based materials. Such processes, like PVD and CVD...

Boron-carbide-aluminum and boron-carbide-reactive- metal cermets

Abstract: Hard, tough, lightweight boron-carbide-reactive metal composites, particularly boron-carbide-aluminum composites, are produced. These composites have compositions with a plurality of phases. A method is provided, including the steps of wetting and reacting the starting materials, by which the microstructures in the resulting composites can be controllably selected. Starting compositions, reaction temperatures, reaction times, and reaction atmospheres are parameters for controlling the process and resulting compositions. The ceramic phases are homogeneously distributed in the metal phases and adhesive forces at ceramic-metal interfaces are maximized. An initial consolidation step is used to achieve fully dense composites. Microstructures of boron-carbide-aluminum cermets have been produced with modulus of rupture exceeding 110 ksi and fracture toughness exceeding 12 ksi√in. These composites and methods can be used to form a variety of structural elements.

Methods of making self-supporting ceramic materials

Abstract: A method to produce a self-supporting ceramic structure by oxidation of a liquid phase parent metal with a vapor phase oxidizing environment includes applying a layer having at least one dopant material to at least a portion of a parent metal of the type having an oxide skin which is normally impervious to an oxiding atmosphere. Upon temperature elevation, the parent metal becomes molten and due to the dopant material in the layer, is caused to migrate through the oxide skin and layer so as to be exposed to the oxidizing atmosphere whereupon an oxide of the parent metal is formed. Migration of the parent metal continues through the formed parent metal oxide to grow layer upon layer of parent metal oxide to thus achieve a self-supporting oxide structure.

Method of applying continuously graded metallic-ceramic layer on metallic substrates

Abstract: Methods of coating metallic substrates with continuously graded metallic-ceramic material are disclosed. The method maintains low stress to strength ratios across the depth of the graded layer when the graded layer is under subsequent operative conditions. In one particular structure, the coating is applied to a metal substrate and includes a metallic bond coat a continuously graded metallic-ceramic layer and an outer layer of abradable ceramic material. Modulation of the metal substrate temperature during the coating process establishes a desired residual stress pattern in the graded layer.

Glasses and glass-ceramics from gels

Abstract: The present state and the future of glasses anf glass-ceramics synthesized by the sol-gel method from metal alkoxides have been critically reviewed and discussed. Glasses and glass-ceramics can be prepared in forms of bulk, fiber, sheet, coating film and particulate. Advantages and disadvantages in applying the sol-gel method for each form are discussed. It is shown that this method is very prospective and many materials will be manufactured by this method in the year 2004.

Residual Stresses and Cracking in Metal/Ceramic Systems for Microelectronics Packaging

Abstract: Residual stresses that develop in a metalkeramic system due to thermal expansion mismatch were calculated for a workhardening metal. The calculations were conducted for a cylindrical configuration, pertinent to certain microelectronics packaging systems. Experimental measurements of the stress have also been made on a Cukordierite ceramic system, using an indentation technique. It is shown that porosity in the metal can plastically expand and provide a mode of dilatational relaxation. Porosity in the metal thus emerges as an important stress-relaxing mechanism.

Abrasive surfaced article for high temperature service

Abstract: Abrasive Surfaced Article for High Temperature Service Abstract A very thin abrasive material on a substrate is comprised of ceramic particulates contained within a metal matrix. The particulates extend fully through the matrix from the substrate surface to the machined free surface of the abrasive. In a representative 0.38 mm abrasive the particulates are sized nominally at 0.42-0.50 mm and have an aspect ratio of less than 1.9 to 1. This enables a high density of particulates, in the range 33-62 per cm2, while at the same time ensuring good bonding in that most of the particulates are fully surrounded by matrix. When the abrasive is applied to the tip of a superalloy gas turbine engine blade, about 10-50% of the matrix metal is removed after machining. This allows the machined ceramic particulates to project into space and to thus better interact with ceramic abradable seals. In the preferred practice of the invention the particulates are alumina coated silicon carbide contained in a nickel superalloy matrix.

Ceramic Matrix for Large Scale Animal Cell Culture

Abstract: A ceramic matrix having a high degree of surface area per unit volume is shown to have significant utility in the large scale culture of animal cells. The surfaces of the ceramic provide for the adhesion and growth of a wide variety of cells to densities equal to or greater than obtained with other methods such as roller bottles or microcarriers. Utilizing an automated system controlling pH and dissolved oxygen, scale-up from 0.9 m2 to 18.5 m2 of surface area was accomplished with no losses in efficiency of surface utilization. The density of Vero cells after 7–8 days culture under standard conditions averaged 6.6 × 105 cells/cm2 for each size of ceramic. Methods providing continuous monitoring of the culture through analysis of the cellular oxygen consumption rate and complete cell harvesting are described.