Showing papers on "Ceramic published in 1987"

Ceramics ductile at low temperature

Abstract: It is generally recognized that ceramics frequently offer advantages over metals in their use, such as chemical resistivity, hardness, wear resistance, high melting temperature, low density and low price. However, the use of ceramics has so far been hampered by their brittleness at low temperature. Here we report observations that could open a way to remove these limitations. We observed that conventionally brittle ceramics became ductile permitting large (~100%) plastic deformations at low temperature if a polycrystalline ceramic was generated with a crystal size of a few nm. The ductility seems to originate from the diffusional flow of atoms along the intercrystalline interfaces.

On the Equilibrium Thickness of Intergranular Glass Phases in Ceramic Materials

Abstract: The fundamental question as to whether thin intergranular films can adopt an equilibrium thickness in polycrystalline ceramics is addressed. Two continuum approaches are presented, one based on interfacial energies and the other on the force balance normal to the boundary. These indicate that there will exist a stable thickness for the intergranular film and that it will be of the order of 1 nm. The origin of an equilibrium thickness is shown to be the result of two competing interactions, an attractive van der Waals-disperson interaction between the grains on either side of the boundary acting to thin the film and a repulsive term, due to the structure of the intergranular liquid, opposing this attraction. As both of these interactions are of short range (

Role of H2O on the degradation process of Y-TZP

Abstract: Yttrium-doped tetragonal zirconia (Y-TZP) is expected to be a good structural ceramic material because of its high strength, high toughness and wear resistance. However, the instability (degradation) of Y-TZP around 150 to 400° C in air and above 100° C in water during ageing is a severe problem which must be solved before the direct application of this material.

High TC superconductors—composite wire fabrication

Abstract: Commercially useful, bulk superconductors typically require stabilization using a normal metal cladding for reasons of electrical, thermal, and mechanical protection and, in general, need to be drawn into fine fibers and wound into a magnet configuration. The recent discovery of high‐TC superconductor materials such as Ba2YCu3O7 stimulated worldwide interest in the subject, however, with much concern about fabricability of such brittle ceramic materials into desirable fine wire geometry. In this letter, we report preliminary success in the fabrication of fine‐wire, composite superconductors consisting of a high‐conductivity normal metal shell such as Ag or Cu/Ni/Au and a superconducting core of Ba2YCu3O7 oxide. The wire is would into a coil, and then heat treated to produce the desired chemistry in a dense structure. The resistivity of the composite wire is measured to be zero at ≊90 K (in zero field) with a zero‐field critical density of ≊175 A/cm2. Microscopy and x‐ray analysis show that the superconduc...

Layered surgical biocomposite material

Abstract: Biocomposite material that is especially suitable for bone surgical applications, containing: at least one bioceramic piece (1) (bioceramic component) and at least one material component (2). The material component (2) comprises at least reinforcement elements which have been manufactured of essentially resorbable material like polymer, copolymer, polymer mixture and/or ceramic material.

New strong cement materials: chemically bonded ceramics.

Abstract: New cements developed in recent years have strengths that are greater by an order of magnitude than those of conventional hydraulic cements. These low-temperature materials, whose strengths approach those of many traditional high-temperature ceramics, are termed chemically bonded ceramics. The different routes to generating strong cementitious materials, including warm pressing, chemical modification, high-shear mixing with polymer additions, and the making of fiber and particulate composites, are reviewed. Strength, toughness, durability, impermeability, and abrasion resistance of these new materials have been greatly improved, as have certain electrical and acoustical properties.

Multilayer ceramics from hydrogen silsesquioxane

Abstract: This invention related to materials produced by diluting in a solvent a hydrogen silsesquioxane resin solvent solution which is applied to a substrate and ceramified by heating. One or more ceramic coatings containing silicon carbon, silicon nitrogen, or silicon carbon nitrogen can be applied over the ceramified SiO₂ coating. A CVD or PECVD top coating can be applied for further protection. The invention is particularly useful for coating electronic devices.

Growth of YBa2Cu3Ox single crystals

Abstract: We report a set of conditions for crystal growth of the high‐temperature superconductor YBa2Cu3Ox. The as‐grown single crystals have critical temperatures up to 85 K. Preliminary studies have shown that the transition temperatures can be increased by thermal annealing in oxygen, as in ceramic samples. The crystals are in suitable dimensions for definitive magnetic, optical, and transport measurements.

Multilayer ceramic coatings from silicate esters and metal oxides

Abstract: This invention relates to materials produced by diluting in a solvent a preceramic mixture of a partially hydrolyzed silicate ester and a metal oxide precursor selected from the group consisting of an aluminum alkoxide, a titanium alkoxide, and a zirconium alkoxide. The preceramic mixture solvent solution is applied to a substrate and ceramified by heating. One or more ceramic coatings containing silicon carbon, silicon nitrogen, or silicon carbon nitrogen can be applied over the ceramified SiO₂/metal oxide coating. A CVD or PECVD top coating can be applied for further protection. The invention is particularly useful for coating electronic devices.

Porous ceramic bed supports for fused silica packed capillary columns used in liquid chromatography

Abstract: Porous ceramic bed supports for fused silica packed capillary columns utilized in liquid chromatography were prepared by polymerizing solutions containing potassium silicate in-situ within a column to create a mechanically stable, rugged, and easily constructed termination. The effect of the bed support length on efficiency, and comparisons to glass wool bed supports, were considered in terms of column efficiencies and hydrodynamic variables. Results obtained indicate better performance for the ceramic bed support.

Armour plate composite with ceramic impact layer

Abstract: The preferred embodiment of the armor plate composite according to the invention is composed of four main components, viz. the ceramic impact layer, the sub-layer laminate, the supporting element and the backing layer. The ceramic impact layer is excellently suitable for blunting the tip of a projectile. The sub-layer laminate of metal sheets alternating with fabrics impregnated with a viscoelastic synthetic material is perfectly suitable to absorb the kinetic energy of the projectile by plastic deformation, sufficient allowance for said plastic deformation being provided by the supporting honeycomb shaped layer. The backing layer away from the impact side and consisting of a pack of impregnated fabrics still offers additional protection. The optimum combination of said four main components gives a high degree of protection of the resulting armour plate at a limited weight per unit of surface area.

Microstructure and material properties of SiC-TiB/sub 2/ particulate composites

Abstract: The effects of TiB/sub 2/ addition to ..cap alpha..-SiC on mechanical, thermal, and electrical behavior were determined. The reliability of ceramics for structural applications is, in general, limited by variability in mechanical strength and low toughness. Property variability is normally attributed to processing- or microstructure-related flaws. Examples of microstructural flaws are exaggerated grain growth, voids and inclusions, while processing-related flaws can include impurities and nonuniform sintered material densification. These flaws can exert significant influence on nominal mechanical properties and their associated time-dependent behavior.

Crack resistance by interfacial bridging: Its role in determining strength characteristics

Abstract: An indentation-strength formulation is presented for nontransforming ceramic materials that show an increasing toughness with crack length (T curve, or R curve) due to the restraining action of interfacial bridges behind the crack tip. By assuming a stress-separation function for the bridges a microstructure-associated stress intensity factor is determined for the penny-like indentation cracks. This stress intensity factor opposes that associated with the applied loading, thereby contributing to an apparent toughening of the material, i.e., the measured toughness in excess of that associated with the intrinsic cohesion of the grain boundaries (intergranular fracture). The incorporation of this additional factor into conventional indentation fracture mechanics allows the strengths of specimens with Vickers flaws to be calculated as a function of indentation load. The resulting formulation is used to analyze earlier indentation-strength data on a range of alumina, glass-ceramic, and barium titanate materials. Numerical deconvolution of these data determines the appropriate T curves. A feature of the analysis is that materials with pronounced T curves have the qualities of flaw tolerance and enhanced crack stability. It is suggested that the indentation-strength methodology, in combination with the bridging model, can be a powerful tool for the development and characterization of structural ceramics, particularly with regard to grain boundary structure.

Dielectric Characteristics of Several Complex Oxide Ceramics at Microwave Frequencies : F: Ferroelectric Materials

Abstract: Dielectric characteristics of several complex-oxide compounds have been investigated. The materials investigated are those with rutile- or rutile-like crystal structure, and the complex-oxides related to TiO2. Some candidates for microwave resonator materials are shown.

Methods for weld repairing hollow, air cooled turbine blades and vanes

Abstract: A mask particularly useful in the weld repair of air cooled gas turbine blades and vanes contains a mixture of ceramic particles in a liquid carrier. The mask is applied onto the surface of the blade or vane, and into the cooling holes. Following a sintering treatment, an inert, thermally stable, electrically nonconductive ceramic mask is produced, which is easily removed after welding.

Behavior of thermal barrier coatings for advanced gas turbine blades

Abstract: The work reported herein deals with a plasma-sprayed zirconia-yttria ceramic coating with a nickel-chromium-aluminum bond coat on a super- alloy substrate. This investigation has as its principal objective the quantitative determination of stress states in a model thermal barrier coating as it cools in air. The effects associated with an idealized rough ceramic-bond interface were investigated. The influence of bond coat oxidation was also determined, together with the impact of initial cracking within the coating. An improved understanding of these coating behaviors is expected to lead to the discovery of coating failure mechanisms which can greatly benefit the designer. In this investigation the powerful finite element method was employed to model the coating which is assumed to be elastic for this initial effort. To obtain the necessary accuracy a very fine finite element grid was developed, utilizing generalized plane-strain elements to model a cylindrical coated specimen. The model which is named TBCOC contains 1316 nodal points and 2140 elements. Using a generic code called MARC, numerical results were obtained from this model. The actual calculations were performed on a CRAY-1S supercomputer. Detailed stress distributions in the coating were obtained to reflect the effects of thermal expansion mismatch and the material properties. Results to date have pinpointed the existence (and location) of large radial tensile stresses in the ceramic layer adjacent to the rough ceramic- bond interface. The effects of oxidation on the stresses are shown together with the influence of initial cracking at specific locations near the ceramic-bond interface. A preliminary failure mechanism for thermal barrier coatings is proposed on the basis of these numerical results and published experimental work.

Method of making multilayered ceramic structures having an internal distribution of copper-based conductors

Abstract: The present invention provides a method for producing multilayered ceramic structures having copper-based conductors therein, wherein the onset of sintering of the copper-based conductor can be adjusted to approach or match that of the ceramic portion of the structure. In addition, methods are provided whereby the polymeric binder resin used in formation of the ceramic portion of the structure can be removed or burned-off, using oxygen-containing ambients, wherein the oxygen content is greater than 200 ppm, without oxidation of the copper-based conductors therein.

Controlled pore size ceramics particularly for orthopaedic and dental applications

Abstract: The present invention provides a ceramic composite having an open porous network and a controlled pore size comprising a plurality of ceramic particles having a fused glass coating and a method for producing the same. The ceramic particles are enveloped by and bonded to adjacent ceramic particles at their interfaces by the glass coating.