Showing papers on "Ceramic published in 1973"

Direct chemical bond of bioactive glass-ceramic materials to bone and muscle

Abstract: The objective of this research is to achieve direct chemical bonding of structurally strong implant materials with hard and soft tissues. This objective has been achieved through the development of a series of surface-active bioglasses and bioglass-ceramics. A controlled release of Ca, P, and Na ions from the surface of the materials produces an alkaline pH and nutrient constituents at a time when the body can incorporate the ions into newly formed tissues. Optical and electron microscopy of in-vivo implants in rat femurs and muscles show the development of stable chemically bonded physiological interfaces after 6 weeks. Microstructure and crystallinity of the materials do not influence the bonding achieved. Mechanical measurements of the bond strength in bone show that the bone fractures before the interface does. In-vitro studies of protein epitaxy, hydroxyapatite crystallization, and solubility kinetics correlate with the proposed interfacial bonding theory.

Effects of Grain Size and Porosity on Electrical and Optical Properties of PLZT Ceramics

Abstract: A group of transparent ferroelectric hot-pressed (Pb0.92La0.08)-(Zr0.65Ti0.35)0.98O3 specimens with controlled grain size and constant porosity and a group of similar specimens with controlled porosity and constant grain size were prepared. The electrical and optical constants and polarization-reversal properties of these ceramics were determined as functions of grain size and porosity. When poled PLZT ceramics were aged, the polarization-reversal characteristic was quite asymmetric, apparently because a space-charge field, E8p, was generated during aging. From a detailed study of the behavior of the E8p, including its (1) generation with increasing aging time, (2) relaxation with repeated polarization reversals, (3) relaxation by heat depolarization, and (4) grain-size and porosity dependence, it is concluded that the space-charge layer is present inside every domain. This layer also explains the grain-size dependencies of the remanent polarization, piezoelectric constants, and Curie point.

Polycrystalline ceramic lasers

Abstract: A method of making a laser body from a high density yttria-based ceramic material is provided. The method involves forming an aqueous solution containing water soluble salts of yttrium, thorium and neodymium, coprecipitating the cations from solution with oxalic acid, recovering the oxalate precipitate in the form of a purified dried powder, calcining the powder to convert the oxalates to the oxides, particulating the oxides in a rubber-lined ball mill, pressing the powdered oxides into a "green body", sintering the "green body" in a hydrogen atmosphere and rapidly cooling the sintered body to form an improved lasing ceramic material.

Fabrication of Transparent Electrooptic PLZT Ceramics by Atmosphere Sintering

Abstract: PLZT electrooptic ceramics were fabricated by a unique atmosphere sintering technique. The ceramics produced were significantly more transparent than those obtained by ordinary O2 sintering methods; in fact, they were comparable in transparency to those obtained by hot-pressing. To achieve good transparency, the powder must be batched with excess PbO, which at the sintering temperature is present as a liquid phase at the grain boundaries. Sintering was conducted at 1200°C for 60 h in an atmosphere containing O2 and a relatively high partial pressure of lead oxide.

Refractory metal hot-junction thermocouple

Abstract: The invention relates to a refractory metal hot junction thermocouple comprising conducting wires insulated by ceramic beads protected by a metal sheath. The hot junction between the wires is obtained by crimping a noble-metal crimping element on the twisted hot junction which is then secured in the metal sheath. The crimping element is preferably made of niobium or rhenium.

Graded metal-to-ceramic structure for high temperature abradable seal applications and a method of producing said

Abstract: Abradable seal composite structure having a porous, abradable ceramic surface layer which is resistant to high temperature oxidation and a metallic bottom layer capable of being bonded to a metallic substrate, with at least two intermediate layers consisting of ceramic/metal mixtures. The intermediate layer next to the ceramic layer has the highest ceramic content, with the remaining intermediate layers having progressively lower ceramic content and correspondingly higher metallic contents. The composite is made by laying up the layers in wet paste form and then drying them, after which the composite can be heated to bond it to the metallic substrate.

Electrical Properties of ZnO‐Bi2O3 Ceramics

Abstract: The nonlinear volt-ampere characteristics and small-signal ac capacitance and resistance of sintered ZnO containing 0.5 mol% Bi2O3 were measured. Many of the electrical properties are related directly to the microstructure, which consists of conductive ZnO grains separated by a continuous amorphous Bl2O3, phase. The origin of the nonlinear conduction in the intergranular phase was confirmed by experiments with evaporated thin films. The proposed conduction mechanism in varistors containing ZnO and Bi2O3 is a combination of hopping and tunneling in the amorphous phase.

Dielectric and optical properties of a quasi-ferroelectric PLZT ceramic

Abstract: Certain compositions within the quaternary lead-lanthanum-titanate-zirconate (PLZT) system exhibit neither a "true" ferroelectric nor a "true" paraelectric behavior and are therefore best characterized as quasi-ferroelectric. The dielectric, hysteresis, and optical properties of quasi-ferroelectric PLZT ceramics have been investigated for the representative 9/65/35 composition which was prepared as a transparent ceramic by means of a two-stage sintering-densification process. The results of these studies suggest that the quasi-ferroelectric behavior of PLZT compositions between their Curie temperature and a transition temperature T p is brought about by the existence of polar distorted microregions (polar short-range order). By applying an electric field a transition to a macroscopic ferroelectric (FE) state (polar long-range order) is enforced which is, however, not stable at zero field at T > T p . This concept, which explains the experimental observations, is compared with the possibility of a FE to anti-FE phase transition at T p . Attention is drawn to the quasi-static memory behavior of this type of material that can be realized by disconnecting the sample in its ON state from the voltage source and which might enlarge the scope of applications of quasi-ferroelectric PLZT ceramics.

Application of Glass-Ceramics for Electronic Components and Circuits

Abstract: Ceramic materials of interest for electronic components, such as ferroelectrics, ferrites, and transition metal oxides have no natural glass-forming habit. A rapid cooling of their melt is required to obtain homogeneous glasses. This is the most important requirement for controlling crystallization and phase dispersion, as required for Various applications. Materials and methods used for making disk and multilayer capacitors are discussed and their properties are described for normal and high voltage applications, and for hybrid circuits. Other application areas to be discussed are cryogenics, thermistors, varistors, and magnetics.

Biological activity and histocompatibility of dense Al2 O3/MgO ceramic implants in rats

Abstract: Three types of dense alumina oxide ceramic (Al2O3) 99.7%, MgO 0.3%; density more than 3.9 g/cm3 differing only in their average grain size (5–15μ) and stainless steel (V4A) plates were implanted into the left femur of male Wistar rats 6 months old. Light and scanning electron microscopic techniques were used to investigate tissue reaction and the ceramic surface. Both ceramic and stainless steel plates were surrounded by a soft tissue layer that differed greatly depending on the implant type in respect to the fiber/cell ratio. While the body tended to enclose the metal plate with a small more or less avascular tissue mostly composed of fibers and some inactive fibrocytes, around the ceramic implants a highly cellulated soft tissue of mesenchyme character developed with signs of osteoblast and chondrocyte metaplasia. Adjacent to this mesenchyme a dense cuff of newly formed woven bone arose, showing numerous active osteocytes. Both metaplastic tendency of the newly formed messenchyme and osteocyte activity in the surrounding bone did not decrease remarkably towards the end of the experiment (70 weeks after operation), while the tissue around metal implants reached a steady relatively reactive state 12–24 weeks after operation. Intimate ceramic surface-mesenchyme contacts without foreign body reactions supported the idea that alumina oxide ceramic tends to be incorporated into the body's physiological environment while metals are “excluded” by fibrous tissue layers of low biological activity. Corrosion on the ceramic surface was not detectable.

Current-voltage characteristics and capacitance of single grain boundaries in semiconducting BaTiO3 ceramics

Abstract: Specimens were prepared of doped ceramic barium titanate in the form of bars which, between their metallized ends, contained only one high-resistance grain boundary running across the entire cross-section. The measurements covered the differential capacitance of these individual grain boundaries, under bias, and their d.c. current-voltage characteristics. The results can be described quite well by a model in which a layer of a second phase present between the barium titanate grains is assumed to possess, firstly, acceptor character and, secondly, a dependence of its permittivity on the temperature and the electric field strength.

Fibrous insulation and process for making the same

Abstract: An insulative material comprises a random network of ceramic fibers and a binder for holding the fibers together. In addition, it may include a filler material composed of hollow ceramic spheres which locate at the interstices of the fibrous network and increase the strength of the network. The insulative material can withstand extremely high temperatures and thermal shock without degradation, has an extremely low density, has excellent insulating properties, and has reasonably high compressive strength. The material is formed by making a slurry which contains the ceramic fibers, with or without the filler, and the binder; felting the slurry; subjecting the felt so formed to microwave energy for drying; and firing the dried felt at 2300°-3200°F. to increase its strength.

Hard metal body

Abstract: A sintered hard metal body is provided with a thin wear-resistant surface coating consisting of an outer layer of ceramic oxide and an intermediate layer of carbide or/and nitride.

Porous ceramics-exhaust oxidation catalyst

Abstract: Method of preparing temperature resistant exhaust oxidation catalysts suitable for use in land vehicle exhaust systems comprising a porous ceramic base impregnated with suitable oxidizing agents and the resulting catalysts. The porous ceramic base is prepared from a ceramic powder filled, plasticized polyolefin.

Gas sensor and method of manufacture

Abstract: A gas sensor, and its method of manufacture, particularly useful as an exhaust gas sensor for an internal combustion engine air/fuel ratio system, is disclosed. The sensor is comprised of a sintered ceramic body of transition metal oxide, such as titania, and includes a pair of spacedapart electrodes. As the partial pressure of oxygen in the gas being sensed varies in response to variations in the inlet air/fuel mixture ratio, the resistance of the ceramic material varies. The active portion of the sensor body is a substantially uniform body of porous ceramic material having a density of less than about 85% of theoretical density and a modulus of rupture in excess of 11,000 psi. The sensor is fabricated from a very pure transition metal oxide powder having a very fine and highly uniform particle size. The transitional metal oxide is selected so that the operating temperature of the resulting device is less than about 75% and preferably less than about 50% of the melting temperature of the metal oxide.

Pore size control in cordierite ceramic

Abstract: Coarse porosity is imposed in fired ceramic bodies containing cordierite (2MgO.2Al 2 O 3 .5SiO 2 ) primary phase by substituting pyrophillite, kyanite, quartz, or fused silica in the batch composition in place of the usual raw talc or clay or a portion thereof.

Formation of new oxide glasses by laser spin melting and free fall cooling

Abstract: Glass spherules have been made by laser spin melting and free fall cooling techniques from ceramic rods. Thus, the materials were not in contact with a container at any time. Glasses of 100 to 800 μm diameter were formed from at least 80 wt% of the oxides Al2O3, Ga2O3, In2O3, La2O3, ZrO2, HfO2, Nb2O5 and Ta2O5 with 20 or less weight percent of CaO + SiO2. The best glass formers were in the Nb2O5- and Ta2O5-based systems. The indices of refraction of most of the glasses and Abbe numbers of many were measured.

Electrical interconnection for metallized ceramic arrays

Abstract: Metal such as gold used for electroplating small metallized ceramic pieces is conserved by providing arrays of such pieces in which electrical interconnections crossing lines of separation of the pieces completely connect all parts to be plated in the array but are severed when the pieces are separated.

Ceramic-lined combustion chamber and means for support of a liner with combustion air penetrations

Abstract: A gas turbine power plant metal combustion chamber cylinder is lined on its inside with two layers of ceramic material. The radially innermost layer is an interlocking, tile-like structure of dense ceramic material providing good thermal shock resistance. The intermediate layer which is disposed between the metal cylinder and the innermost layer is a low density ceramic material providing high thermal insulation. The layers of ceramic material are supported by ceramic tubes extending from the outer metal cylinder of the combustor through the intermediate wall and the inner wall. The tubes are also used to direct cooling air into the combustion chamber and increase the turbulence of the burning fuel and air within the chamber.

Process for forming thin walled articles or thin sheets

Abstract: A process for forming thin walled articles or thin sheets by applying a casting composition to a substrate, drying the composition on the substrate, and separating the article so formed from the substrate, said casting composition consisting essentially of (a) at least about 95 percent of a combination of three constituents: (1) from 65-92 percent by weight of glass, glassceramic, or sinterable ceramic particles having a mean particle size of from 0.2 to 12 microns and a maximum particle size of about 100 microns; (2) from about 5 to 35 percent by weight of an aqueous acrylic polymer emulsion binder containing from about 40 to about 60 percent by weight of water and; (3) up to about 15 percent by weight of water, and (b) the balance being a small amount of one or more surfactants to inhibit foaming and to promote dispersion of the particulate material in the binder. The composition has excellent properties for forming thin walled articles and thin films which are flexible and have sufficient green strength so that they can be handled easily. Upon sintering, the flexible articles or films form dense glass, glass-ceramic, or sintered ceramic articles or sheets, which sheets, for example, form excellent substrates or dielectrics for electrical capacitors or other electrical devices.

Method of sealing by brazing of a metal part on a ceramic part

Abstract: The present invention relates to a method of brazing a fluidtight sealing joint between a metal part and a part of ceramic material, of the kind in which, before the actual brazing is carried out, the said ceramic part is first metallized by the application of a metallization product containing at least one metallic derivative, and sintering the said product, followed by nickelling of the ceramic part thus metallized, the operations of metallization being repeated twice, said method comprising the further steps of effecting the metallization of said ceramic part by applying said metallization product and effecting two successive nickelling operations on the ceramic part thus metallized, a first nickelling operation being effected chemically by the application of a nickelling product and reduction of said product under heat, while a second nickelling operation is carried out by an electrolytic process. The invention finds a particular application in the brazing of joints sealing a metallic conductor into a bore passing through a ceramic part.

Capacitors with nickel containing electrodes

Abstract: Metallizations for formation of conductors on substrates, comprising (1) nickel or nickel-containing base metal alloys, and (2) noble metals, e.g., palladium, palladium/gold, platinum/palladium/gold, and palladium/silver, wherein the ratio of nickel or nickel-containing alloy to noble metal is up to 1/1 (by weight). The metallization are used as conductors on ceramic substrates and for ceramic capacitors.

High strength composite ceramic structure

Abstract: A hot pressed ceramic body is formed of a sandwich comprising an interior layer of a ceramic material having a given coefficient of thermal expansion and two outer surface layers formed of a ceramic material having a lower coefficient of thermal expansion When the product is formed as a unitary sandwich by hot pressing at elevated temperature the outer layers are put under compression as the body is cooled to room temperature A preferred form of the invention involves a central layer of a mixture of silicon carbide and silicon nitride and the external layers are pure silicon nitride

Method of producing a matched parameter acceleration cancelling hydrophone

Abstract: A seismic cable having minimum response to speed changes is provided. The cable includes a plurality of miniature seismic pressure sensitive detectors coupled one to another in such a manner so as to minimize through cancellation undesired electrical disturbance resulting from speed changes. Each detector includes transducers of the ceramic piezoelectric crystal type having matched geometric and physical property parameters. Each ceramic piezoelectric crystal is provided with metal electrodes such as, for example, gold, nickel, platinum, or rhodium which, in addition to being corrosion resistant and inactive as to the constituents in the ceramic material, are insoluble in liquids encountered by the detector in its use environment to avoid dendrite type growth of the metal through minute cracks developing in the ceramic which causes short circuits in the piezoelectric element.

Method of making ceramic sintered body

Abstract: A method of making a ceramic sintered body, comprising preparing a powder-mixture consisting of 40 to 80 percent by weight of alumina with or without replacing not more than 2 percent by weight by a grain growth inhibitor, 16 to 40 percent by weight of titanium carbide and 4 to 20 percent by weight of metallic titanium, the total being 100 percent by weight, and hot-pressing said mixture. The mixture is not subjected to a calcination in nonoxidizing atmosphere at a temperature of 600*C to 1,000*C as previously proposed by the inventors, but it is directly subjected to hot-press forming at a high temperature under a high pressure.

A Method for Counting Ceramic Rim Sherds

Abstract: Abstract Archaeologists rely upon the sherd count to quantify creamic data. A simple method for counting rim sherds uses the percentage of a vessel's orifice represented by each sherd. This technique can be used to estimate the minimum number of vessels represented by the sherds in any specific category.

Laser diode package formed of ceramic and metal materials having high electrical and thermal conductivity

Abstract: A laser diode package which has little inherent induction at high frequency, due to its size and geometry, and allows operation of the diode at reduced temperature without affecting the temperature of the optically coupled medium.

Electrical cooker unit for a ceramic glass plate type electrical cooker

Abstract: An electrical cooker unit for use in the type of cooker in which a ceramic glass plate is placed above the electrical heating elements. The cooker unit consists of a cylindrical metal tray, the base and side wall of which is lined with electrical and thermal insulating material formed from particulate microporous thermal insulating material which has been consolidated into block form. The base layer of insulating material has a flat planar upper surface and the electrical heating element consists of a helically coiled uncovered wire laid out in the form of a flat spiral on such upper surface and secured solely by metal staples which engage in the base layer for part of the depth thereof. The ceramic glass plate rests upon the upper edge of the side wall of the thermal insulation, leaving a space between the under side of the plate and the electrical element.