Showing papers on "Ceramic published in 1983"

Ba(Zn1/3Ta2/3)O3 Ceramics with Low Dielectric Loss at Microwave Frequencies

Abstract: The dielectric properties at microwave frequencies of Ba(Zn1/3Ta2/3)O3 ceramics prepared by sintering were investigated. These ceramics had lower density but higher loss quality than ceramics hot-pressed at 1400°C. Loss quality was greatly improved by prolonged sintering. The Q of the ceramics measured by the dielectric resonator method was 14 000 at 12 GHz. The ceramics were investigated by X-ray diffraction analysis. It was found that Q improvement corresponds with increased Zn and Ta ordered structures in the ceramics.

A Molecular Mechanism for Stress Corrosion in Vitreous Silica

Abstract: The mechanical strength of most glasses and ceramics decreases with time under static loading in an ambient environment. This strength loss is associated with slow growth of preexisting surface flaws due to stress corrosion by water from the surrounding environment. We studied stress corrosion in vitreous silica exposed to water and several nonaqueous environments; environments which enhance stress-corrosion crack growth in silica contain active groups with electron donor sites on one end and proton donor sites at the other. These results suggest a detailed chemical model for the interaction of the environment with mechanically strained bonds in the solid at the tip of a crack. The proposed model for stress-corrosion crack growth also has implications for the long-term strength behavior of a wide variety of brittle materials.

Infrared-transparent mullite ceramic

Abstract: Mullite ceramic, transparent in the infrared, was prepared by hot-pressing and hot-isostatically pressing starting materials derived from alkyloxides. A composition with 72.3 wt% Al2O3 yielded transparent, submicrometer grain size bodies at 1630°C, whereas higher temperatures produced glass-containing microstructures. A composition with 76 wt% A12O3 formed precipitates of α-Al2O3 at the consolidation temperature, which could be removed by subsequent annealing between 1800° and 1850°C. Spectral transmittance and absorption coefficients of the bodies are reported. The formation of the second phases was linked to phase equilibria and grain growth that promoted compositional equilibration of the mullite phase. The results suggest adjustments to phase boundaries in the high-temperature segment of the SiO2-Al2O3 phase diagram.

Method of consolidating a metallic body

Abstract: A method of consolidating a metallic body is disclosed. The method comprises the steps of forming an article of manufacture from powdered metal; sintering the article of manufacture so as to increase the strength thereof; coating the article with a sacrificial layer of ceramic; providing a bed of heated, generally spheroidal ceramic particles; compacting the coated article of manufacture embedded in the heated bed under pressure to thereby consolidate the article into a dense, desired shape; and, removing said sacrificial coating such that the surface of the article remains substantially free of process-related imperfections.

Articles containing non-fused aluminum oxide-based abrasive mineral

Abstract: The invention relates to synthetic, non-fused, aluminum oxide-based abrasive mineral having a microcrystalline structure of randomly oriented crystallites comprising a dominant continuous phase of α-alumina and a secondary phase, to a method of making the same employing chemical ceramic technology, and to abrasive articles made with the abrasive mineral.

Recent developments of piezoelectric ceramic products and composites of synthetic rubber and piezoelectric ceramic particles

Abstract: The theory on the dielectric and piezoelectric constants of the composites, with 0–3 connectivity, of synthetic rubber and piezoelectric ceramic particles is derived based on “modified'’cubes model. The dielectric and piezoelectric constants of the composites of chloroprene rubber and ceramic particles of PZT or PbTiO3 are reported. Also the applications of the composites and the piezoelectric ceramic products recently developed at our laboratory are explained.

Dielectric and piezoelectric properties of modified lead titanate zirconate ceramics from 4.2 to 300 K

Abstract: The dielectric and piezoelectric properties (d-p properties) of four kinds of doped lead titanate zirconate piezoelectric ceramics (PZTs) have been measured from 4.2 to 300 K. The d-p properties of the materials converge with decreasing temperature down to liquid helium temperature, even though the properties have large differences at room temperatue. The values of mechanical and electrical quality factors,Q m,Q e, and of the frequency constant,N, of the materials increased at low temperature. It is evident from the freeze out inK′ and the associate temperature: frequency-dependent maxima in tan 5 that the relaxation processes including ferroelectric domain wall motion and thermal defect motion contribute to the d-p properties. The Navy type-III composition has a minimum temperature coefficient of d-p parameters and it is evident that PZT ceramics modified with Fe2O3 can provide good stability and also give the strongest piezoelectric response at liquid helium temperature.

Effect of Microstructure on the Properties of TiB2 Ceramics

Abstract: Samples of a TiB2 ceramic containing 0 to 10 wt% Ni were fabricated by hot-pressing. Several properties, including fracture strength, indentation fracture toughness, and thermal expansion (between 25° and 1000°C) were measured. Resulting data were correlated with sample microstructure and composition.

A Biaxial-Flexure Test for Evaluating Ceramic Strengths

Abstract: An improved test fixture for biaxial-tension strength testing of ceramics featuring uniform pressure loading of disks was developed and qualified. Biaxial data were obtained for an alumina ceramic, along with comparable uniaxial data from three- and four-point flexure tests. Weibull statistics provided a good description of the size effect on data from the two uniaxial tests, but underestimated the effect of stress biaxiality. The biaxial strengthening observed in the alumina ceramic is consistent with that observed previously in a glass-ceramic.

Experimental Ridge Augmentation With Porous Hydroxyapatite Implants

Abstract: A new hydroxyapatite ceramic implant material for restoration of atrophic edentulous ridges was tested in a canine animal model The structure of this material is unique, in that it is produced from the skeleton of a coral, and in that it is penetrated by a uniform network of interconnected pores. Results indicate that bone penetrates its structure to a greater degree than had been observed with similar implants constructed of different materials. Implant insertion through a simple surgical technique involving minimal morbidity is a viable method of placement.

Barium Titanate Perovskite Sintered with Lithium Fluoride

Abstract: The sintering of barium titanate with, respectively, 1 and 2 wt% LiF for two stoichiometries, Ti/Ba=1 and 0.975, was studied using two calcined powders. One was pure barium titanate; the other contained BaTi03 plus BaC03 and TiO2 that did not react when burning. The sintering chronology—intermediate phases, appearance, and disappearance of a liquid phase that has been pointed out for the first time—is directly dependent on the used calcined powder, on the LiF amount, and on the firing schedule. In the same way, the obtained perovskite symmetry varies during sintering from tetragonal to cubic and then to a second tetragonal form, whereas most of the Li and F disappear from the ceramic with two different kinetics.

Controlled Flaws in Ceramics: A Comparison of Knoop and Vickers Indentation

Abstract: Application of indentation fracture analysis to Knoop and Vickers indentation is examined, with particular emphasis on determining the limitations of the point force representation for the residual stress field. Deviation from the point force approximation is insignificant for crack-size/plastic-zone-size ratios 1.3. The Vickers deformation/fracture configuration in brittle materials invariably conforms to this requirement, whereas the Knoop configuration does not (except at very high indentation loads). However, stable crack growth during a failure test extends the crack sufficiently that the strength degradation for both types of indentation is well described by the point force approximation.

Metallic glasses as novel catalysts

Abstract: Metallic glasses are nonequilibrium amorphous metal alloys which combine the metallic electronic structure with a disorered atomic structure usually reserved for ceramic and polymeric materials. Amorphous silicon-based structures have already been shown to be effective in semiconductor1,2 and photovoltaic applications3, where single crystal structures were previously thought to be required. The properties of metallic glasses have been reviewed recently by Gilman4 and Turnbull5. Recent reports demonstrate that metallic glasses are indeed both catalytically active6 and uniquely selective7. Here we disclose the nature of this unique selectivity. We report observations of glassy Pd–Si and Pd–Ge alloys which exhibit different selectivity in catalysis of hydrogen reactions than their crystalline Pd systems. We also observe an increase in the activity of these amorphous catalysts when partial crystallization occurs.

Activated carbon formed body and method of producing the same

Abstract: This disclosure relates to a formed body having activated carbon granules bondedly carried by an inorganic substance body consisting of a sintered body or fused body of inorganic substance powder. The formed body preferably is of a honeycombed structure. The formed body is not only high in strength, excellent in absorbing ability, long in service life, but also permits of molding into various shapes fit for uses. The invention also relates to a method of producing the formed body of the type described above. The method essentially follows the conventional ceramic firing art or ceramic production art.

Solid state SiC/Ni alloy reaction

Abstract: The solid state reaction between silicon carbide and a model superalloy consisting of 70 at. pct Ni, 20 at. pct Cr, and 10 at. pct Al was studied between 700 °C and 1150 °C for times ranging from “0” hours to 330 hours. Reaction couples consisting of SiC/Ni, SiC/Cr, and SiC/NiCr were also studied. The reactions were carried out in air with the materials, in the shape of discs, maintained in contact under a pressure of 7 MPa. A reaction was detected with SiC and the model alloy at all temperatures studied, and the reaction was diffusion controlled with an activation energy of 184 kJ/mole. In the ceramic the reaction was dominated by the diffusion of Ni into the ceramic forming a banded structure consisting of alternating layers of δ-Ni2Si and a two phase mixture of graphite and δ. On the metal side, the reaction was very dependent on the presence of alloying elements, with pure Ni reacting to the greatest extent, followed by the binary NiCr alloy, and finally by NiCrAl. The growth and presence of the phases detected in these reactions is consistent with phase equilibria concepts.

Aluminum titanate-mullite ceramic articles

Abstract: This invention is directed to the production of sintered ceramic articles wherein aluminum titanate and mullite constitute the predominant crystal phases and wherein the microstructure thereof evidences grain boundary and intracrystalline microcracking. The articles have base compositions encompassed within the area I, J, K, L, M, I of the drawing to which 0.5-5% Fe 2 O 3 and/or 0.5-5% rare earth metal oxide may be added.

High Temperature Reactions and Microstructures in the Al2O3-AlN System

Abstract: The potential utilization of nitride and oxynitride ceramics in high and low temperature structural engineering systems has focused much interest on these materials. These new efforts have revealed many problems concerned with the formation, stability and sintering of single or multi-phase materials based on compositions in these systems. One of the keys to producing materials with controlled micro structures and optimized properties is an understanding of the phase equilibria. In particular, the phase diagram should include liquid and vapour phases if they occur.

Siloxanes, silanes, and silazanes in the preparation of ceramics and glasses

Abstract: The use of selected organosilicon compounds for the preparation of silicon based ceramic materials is discussed in terms of processing microstructure-property relationships. The mechanisms operative in the formation of gel derived silicate glasses and glass ceramics are reasonably well understood, but this is not true for silicon carbide/nitride based ceramics. The properties of organosilicon precursors and the mechanism of pyrolysis affect the microstructural features of the ceramic. Reaction mechanisms are proposed and the microstructural features and properties of organosilazane derived ceramics discussed.

Internal electrode piezoelectric ceramic actuator

Abstract: A piezoelectric ceramic actuator element with multilayer internal electrodes has been investigated. It was fabricated by multilayer ceramic capacitor techniques. An individual internal electrode has the same area as the element cross section area. It has no piezoelectric inactive part, so that it shows original strain/field characteristics in the material. It can be driven by a relatively low votlage (< 200V) and has a semi-permanent life under successive voltage pulse application. Typical properties of the element using 0·65Pb(Mg1/3Nb2/3)O3-0·35PbTiO3 ceramics are 8·7 × 10−4 strain, over 3·5 × 107 N/m2 force, within 100 μsec response time and 70% electromechanical couplig factor driven by 1 × 106 V/m field.

Smoke and heat barrier

Abstract: A heat insulative barrier for use in isolating potential fire zones relative to expansion joint voids which comprises the use of a sealed sheet of ceramic felt material secured across an expansion void and including one or more refractory cloth sheets sealingly secured contiguous to the ceramic felt sheet on one or both sides thereof and adjacent to the potential fire zone.

Ceramic fiber reinforced piston for high performance diesel engines

Abstract: A Ceramic Fiber Reinforced Aluminum Matrix Composite has been developed that has excellent wear resistance, seizure resistance against cast iron, good thermal conductivity and high strength at elevated temperatures. By strengthening top land and top ring groove of piston with the Aluminum Matrix Composites, a newly designed Diesel Engine attained excellent performance without sacrificing manufacturing cost and productivity.

Method of consolidating a metallic or ceramic body

Abstract: A method of consolidating a metallic or ceramic body is disclosed. The method comprises the steps of forming an article of manufacture from powdered metal; sintering the article of manufacture so as to increase the strength thereof; providing a bed of heated, generally spheroidal ceramic particles which have been coated with a thermally stable lubricant; and compacting the article of manufacture embedded in the heated bed under pressure to thereby consolidate the article into a dense, desired shape.