Showing papers on "Ceramic published in 1985"
TL;DR: In this article, the authors studied the dielectric properties, lattice and microstructure of ceramic BaTiO3 showing grain sizes of 0.3-100 μm and showed that at grain sizes <10 μm the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter.
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.
1,742 citations
Book•
01 Jan 1985
TL;DR: In this paper, the authors present an overview of the materials for engineering, including the following: 1. Materials for Engineering. 2. Materials Selection. 3. Materials selection. 4. Failure analysis and prevention. 5. Diffusion. 6. Thermal Behavior.
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.
734 citations
TL;DR: The Ina Tile Company found that increasing the content of lime in the tile formulation from 1% to 5% reduced the tile size variation by a factor of ten as discussed by the authors, which was a breakthrough for the tile industry.
Abstract: A Japanese ceramic tile manufacturer knew in 1953 that is more costly to control causes of manufacturing variations than to make a process insensitive to these variations. The Ina Tile Company knew that an uneven temperature distribution in the kiln caused variation in the size of the tiles. Since uneven temperature distribution was an assignable cause of variation, a process quality control approach would have increased manufacturing cost. The company wanted to reduce the size variation without increasing cost. Therefore, instead of controlling temperature distribution they tried to find a tile formulation that reduced the effect of uneven temperature distribution on the uniformity of tiles. Through a designed experiment, the Ina Tile Company found a cost-effective method for reducing tile size variation caused by uneven temperature distribution in the kiln. The company found that increasing the content of lime in the tile formulation from 1% to 5% reduced the tile size variation by a factor of ten. This discovery was a breakthrough for the ceramic tile industry.
580 citations
Book•
01 Jan 1985
TL;DR: In this paper, the authors present an approach for the treatment of the optical properties of materials based on Quantum Mechanical Treatment of the Optical Properties of Materials (QMT) and Magnetic Phenomena and their interpretation.
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.
378 citations
TL;DR: In this article, the transformation, microstructural development, and densification of an α-alumina-seeded boehmite sol-gel was studied, and α-Alumina particles are shown to act as nuclei for the trans-formation of θ- to α- alumina and to result in an increase in the transformation kinetics and lowering of the transformation temperature by as much as 170°C.
Abstract: The transformation, microstructural development, and densification of an α-alumina-seeded boehmite sol-gel was studied. α-Alumina particles are shown to act as nuclei for the trans- formation of θ- to α-alumina and to result in an increase in the transformation kinetics and lowering of the transformation temperature by as much as 170°C. By increasing the seed concentration (i.e., nucleation frequency), a submicrometer aggregate-free microstructure develops, rather than the vermicular microstructure that usually characterizes the α-alumina transformation. As a result, the transformed α-alumina sinters to full density with a submicrometer grain size at 1200°C. It is believed that seeding may represent a unique method for microstructure control in the many ceramic systems that transform by nucleation and growth.
342 citations
TL;DR: In this article, the fracture toughness of dense Ce-TZP ceramics containing about 7 to 16 mol% CeO2 was evaluated using fine powders prepared by the hydrolysis technique.
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.
338 citations
TL;DR: In this paper, the authors compared the sintering behavior of a rigid substrate and a free film, and found that the shear rate of the film is more important than its densification rate when the film was constrained by a 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.
224 citations
TL;DR: In this article, the residual stresses that develop during cooling of a metal/ceramic strip are calculated analytically, and 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.
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.
223 citations
Book•
01 Jan 1985
218 citations
Patent•
24 Jun 1985
TL;DR: In this paper, a chemical vapor deposition method for the production of a composite body with one or more polycrystalline diamond layers, essentially free of intercrystaline binder phase, on a substrate of one of: (a) metalbonded hard material 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.
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.
TL;DR: The sol-gel process is a technique which is applicable for forming ceramic materials as discussed by the authors, where liquid precursor materials are reacted to form a sol which then polymerizes into an inorganic polymeric gel.
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.
Patent•
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TL;DR: 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, was produced by a paper-forming method from a slurry of alumino-silicate fiber and fire clay as discussed by the authors.
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.
Patent•
11 Feb 1985TL;DR: In this paper, a ceramic fiber composite material comprised of boron nitride coated cera fibers embedded in a ceramic matrix is presented, which limits both physical bonding and chemical reaction between the fibers and matrix to improve both strength and toughness.
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.
TL;DR: In this article, the authors provide and discuss microstructural design strategies which may enable ZrO2-toughened ceramics to be applied to higher temperatures.
Journal Article•
TL;DR: Preparation des ceramiques et verres par le procede sol-gel: cas des alcoolates polymerises and des sols colloidaux as discussed by the authors, i.e.
Abstract: Preparation des ceramiques et verres par le procede sol-gel: cas des alcoolates polymerises et des sols colloidaux
TL;DR: In this article, an in situ TEM experiment on martensitic nucleation was performed using sub-micron ZrO2 particles which were initially defect free Extrinsic, spontaneous and heterogeneous nucleation is induced by introducing dislocation loops with a strong shear component and Hertzian contact stresses into selected particles.
TL;DR: In this paper, the creep behavior of such a composite was studied and the introduction of silicon carbide whiskers significantly improved the creep resistance of polycrystaline alumina, which is a type of ceramic composites with enhanced fracture toughness properties.
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.
Patent•
28 Mar 1985
TL;DR: In this article, a method for depositing a coating of a dense ceramic material is disclosed, where a starting material is melted and refined by heating with an electron beam in vacuum.
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.
Patent•
3M1
TL;DR: In this paper, solid, transparent, non-vitreous, ceramic particles are used 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.
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.
Patent•
3M1
TL;DR: A two-phase ceramic particulate useful as a proppant in hydraulic fracturing operations which comprises a vitreous matrix phase containing a crystalline alumina phase is described in this paper.
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.
TL;DR: In this article, the lattice parameter measurements showed that the tetragonal and rhombohedral unit cells of the two ferroelectric phases depend on the sintering temperature.
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.
Patent•
07 Feb 1985TL;DR: In this article, a process for producing ultra-fine ceramic particles with the particle size of less than 1000 A is described. But the process is not suitable for high dimensional materials.
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.
TL;DR: The only commercial coating processes practised have been the thermochemical diffusion techniques termed boronizing or boriding, whereby borone is diffused into, and combines with, the substrate material forming a single or double phase metal boride layer at, and adjacent to, the surface.
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...
Patent•
06 May 1985TL;DR: Hard, tough, lightweight boron-carbide-reactive metal composites, particularly BCA-aluminum composites as discussed by the authors, have been used to form a variety of structural elements.
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.
TL;DR: In this article, a hot-pressed silicon-nitride-based ceramic has been used for cutting cast irons at high speeds (10−16.75 m s−1 (600−1000 m min−1) and rates (about 1.0 mm rev−1), where conventional tools cannot be used.
Patent•
17 Jul 1985
TL;DR: In this article, a method to produce a self-supporting ceramic structure by oxidation of a liquid phase parent metal with a vapor phase oxidizing environment is described. But this method requires the parent metal to become 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.
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.
TL;DR: In this paper, graphite fibers are grown on a suitably nucleated ceramic surface by passing a methane gas stream over the surface at an elevated temperature, where the methane concentration in the gas stream is adjusted to between 5 and 15 volume percent to form microscopic carbon filaments.
Patent•
27 Nov 1985
TL;DR: In this article, a continuous graded metallic-ceramic layer and an outer layer of abradable ceramic material are applied to a metal substrate and a metallic bond coat is applied to maintain low stress to strength ratios across the depth of the graded layer.
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.