Showing papers on "Ceramic published in 1982"

Diffuse Ferroelectric Phase Transitions in Ba(Ti1-yZry)O3 Ceramics

Abstract: Very high and broad Curie maxima are observed in ceramic Ba(Ti1-yZry)O3 mixed crystals, which are often used for the preparation of ceramic dielectrics The ferroelectric-to-paraelectric phase transition of ceramic Ba(Ti1-yZry)O3 was studied using dielectric measurements, quantitative DTA, X-ray diffraction, and determination of the remanent polarization At higher Zr concentrations, it was found that ferroelectric and paraelectric phases coexist in a wide temperature region Up toy =016, the phase transition remains first order The diffuse character is promoted by the small energy difference between the ferroelectric and paraelectric phases appearing at higher Zr content It can be best described by a normal distribution of Curie temperatures using the phenome-nological theory of Devonshire and the Newton-Raphson mathematical approximation

Stability of Tetragonal ZrO2 Particles in Ceramic Matrices

Abstract: The stability of tetragonal ZrO2 particles in ceramic matrices was considered, with particular reference to Al2O3-ZrO2 composites and to partially stabilized ZrO2. In both systems, particles above a “critical” size transform martensitically to monoclinic symmetry on cooling to room temperature. The critical factors that could affect the size dependence of the transformation temperature—surface and strain energy effects, the chemical free energy driving force, and the difficulty of nucleating the martensitic transformation—were considered. Nucleation arguments are probably the most important.

A molecular interpretation of stress corrosion in silica

Abstract: The mechanical strength of many glasses and ceramic materials decreases with time under static loading and ambient environments. This strength loss is associated with slow growth of pre-existing surface flaws due to a stress-corrosion process. To make long-term strength predictions for ceramic components, it is important to understand the stress-corrosion mechanism. We have studied stress corrosion in vitreous silica exposed to water and several non-aqueous environments and report here that environments which enhance stress corrosion are composed of molecular 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 also has implications for the long-term strength behaviour of a wide variety of brittle materials.

Sinterable Ceramic Powders from Laser-Driven Reactions: I, Process Description and Modeling

Abstract: A novel process is discussed for producing a wide variety of ceramic powders with unique physical and chemical characteristics. Silicon, Si3N4, and SiC powders were produced from CO2 laser-heated gas-phase reactants; a detailed description of this laser-driven process is presented. The physical, chemical, and crystalline nature of the resultant powders and the effect of process variables are discussed in Part II. In this process, reactant gases are rapidly heated by CO2 laser radiation and decompose, causing particles to nucleate and grow rapidly. Analytical models of fluid flow, heat transfer, heating rates, and powder-formation mechanisms are discussed. The powders produced in this process are very fine (<0.1μm), spherical, nearly monodispersed in size, extremely pure, and loosely agglomerated.

Improving the linearity of piezoelectric ceramic actuators

Abstract: It is shown that the linearity of a piezoelectric ceramic actuator may be greatly improved if the applied electric charge, rather than the applied voltage, is varied to control the extension. Hysteresis is virtually eliminated.

Ba(Mg 1⁄3 Ta 2⁄3 )O 3 Ceramics with Temperature-Stable High Dielectric Constant and Low Microwave Loss

Abstract: A dense ceramic with an ordered perovskite structure with chemical formula Ba(Mg1/3Ta2/3)O3 is prepared, aiming at materials for a dielectric resonator with temperature-stable high dielectric contsant and low loss at microwave frequency. A small amount of Mn ion is doped to the sample to complete the sintering. The dielectric constant and unloaded Q are 25 and 16800 at 10.5 GHz respectively. The temperature coefficient of resonant frequency is estimated as 2.7 ppm/°C in the vicinity of room temperature. The value of Q we obtained is the highest among those reported so far on ceramics having a similar characteristic.

Dielectric properties of donor-doped polycrystalline SrTiO3

Abstract: Various donor dopants such as Y3+ and Nb5+ were incorporated in SrTiO3 in amounts ⩽25 mol % during sintering in air at 1450° C for ⩽ 15 h Dense ceramic materials with grains of optimum uniformity and largest size were obtained when the cation stoichiometry was adjusted to allow for charge compensation of the donor ions by strontium vacancies For donor levels ≳ 03 mol%, the dielectric constant measured at 25° C and 1 kHz was up to two orders of magnitude higher than that of undoped strontium titanate The increase in permittivity, however, was dependent on grain size, was influenced by the method of electrode application, and was suppressed by the presence of ≲ 01 mol% Mn in the ceramic These observations, together with data obtained from electrical measurements at other temperatures and frequencies, were consistent with interpretation of the anomalously high dielectric constant as a boundary-layer effect resulting from semiconducting grains and weakly insulating grain-surfaces It is suggested that donor doping influences the electrical properties of SrTiO3 mainly by increasing the volatility of oxygen from the grains during sintering, and by decreasing the rate of re-oxidation during cooling

Radiation damage in crystalline insulators, oxides and ceramic nuclear fuels

Abstract: Studies of radiation damage in crystalline insulators usually originate from problems connected with heavy ion impact during ion bombardment, from neutron irradiation with and without fission in nuclear reactors, or from α-decay with the resulting damage due to recoil daughter atoms of the decaying nuclei of actinide compounds. The materials involved cover a broad range of compounds, e.g. from BeO to CmO2 for oxides, for which most work has been done. The damage studied ranges from production of isolated Frenkel pairs to complete amorphization of the crystalline compound (metamictization). The available knowledge is discussed. Emphasis is put on simple binary oxides and on ceramic nuclear fuel materials, i.e. oxides, carbides and nitrides of U and Pu. Recent work on irradiated glasses is also briefly discussed since these glasses are considered as promising media for safe storage of radioactive waste for long periods of time.

Sinterable Ceramic Powders from Laser‐Driven Reactions: II, Powder Characteristics and Process Variables

Abstract: Si, Si3N4, and SiC powders which possess a unique set of characteristics were produced by a laser-driven gas-phase synthesis process. The powders have a fine particle size (<0.1 μm), are spherical, have a narrow range of particle sizes, are free of hard agglomerates, have a high degree of phase purity, and have a high absolute purity (<0.1% including oxygen). A detailed analysis of the physical, chemical, and crystalline characteristics of Si and Si3N4 is presented. A brief discussion of our initial work with SiC is also included. The dependence of particle characteristics on the various process parameters (laser power, cell pressure, gas composition) is discussed and related to a model of the powder-synthesis process.

History and principles of the sol-gel process, and some new multicomponent oxide coatings

Abstract: Certain historical facts are discussed regarding the principles of the sol-gel process and some new applications are mentioned. Forty years ago Geffcken and Bergen prepared single oxide coatings by the sol-gel process and Schroeder developed a thin film physics. The first products appeared on the market in 1953 and large scale production in 1959 with automotive rear-view mirrors, later anti-reflection coatings and sunshielding windows were introduced using TiO 2 and SiO 2 . Dislich and Hinz elaborated the chemical basis for the preparation of multicomponent oxides, glasses, glass ceramics and crystalline substances in 1969 and published their results in 1971. So from 1971 on it was known that any type of multicomponent oxide can be synthesized using the alkoxides of the different elements by the sol-gel process. Of the three steps; complexation, hydrolysis, polycondensation, it is the first step that has been newly introduced. The first product on the market now for some years is a silicate phosphate layer which improves the hydrolytic stability of optical glasses, used in laser protective filters manufactured by the Deutsche Spezial Glas AG. An 8-component glass ceramic (Si, Al, P, Li, Mg, Na, Ti, Zr) and a crystalline cadmium stannate layer (Cd 2 SnO 4 have been prepared.

Microstructural Analysis of Sintered High-Conductivity Zirconia with Al203 Additions

Abstract: Transmission electron microscopy (at 100 and 1000 kV potential) and analytical scanning transmission electron microscopy were used to study α-Al203 second-phase particles and their interactions with grain boundaries in two high-conductivity Y203/Yb203 stabilized zirconia ceramics containing deliberate additions of the alumina as a sintering aid. Most of the Al203 particles were intragranular and microanalysis showed that they contained inclusions rich in Zr or Si plus Zr. Al2O3 particles at grain boundaries were frequently associated with amorphous cusp areas rich in Si and Al. The results suggest that the Al203 acts as a scavenger for SiO2, removing it from grain-boundary localities. A model is proposed whereby this process occurs as the boundaries meet the second-phase particles, assisted by rapid grain-boundary diffusion. Such an ZrO2-Al2O3-SiO2 interaction and partitioning is predicted thermodynamically and offers a possible explanation for the improvements in ionic conductivity brought about by Al2O3 additions, as reported in the literature.

Pressure transmitting medium and method for utilizing same to densify material

Abstract: A quantity of material (10), which is at less than a predetermined density, is disposed within a sealed container (12) which is, in turn, encapsulated in a pressure-transmitting (18) medium which is, in turn, placed within a pot die (20) of a press where it is restrained as a ram (24) enters the pot die (20) and applies a force to the pressure-transmitting medium (18) to densify the material within the container into a compact (10') of predetermined density The pressure-transmitting medium (18) is characterized by a rigid interconnected ceramic skeleton structure (26) which is collapsible in response to a predetermined force and fluidizing glass (28) capable of fluidity and supported by and retained within the skeleton structure (26) The glass (28) becomes fluidic and capable of plastic flow at temperatures utilized for compaction whereas the ceramic skeleton (26) retains its configuration and acts as a carrier for the fluidic glass (28) As external pressure is applied by coaction between the pot die (20) and ram (24), the ceramic skeleton structure (26) collapses to produce a composite (18') of ceramic skeleton structure fragments (26') dispersed in the fluidizing glass (28) with the composite (18) being substantially fully dense and incompressible and rendered fluidic and capable of plastic flow at the predetermined densification of the material being compacted within the container Accordingly, the ceramic skeleton structure (26) is dominant to provide structural rigidity and encapsulation and retainment of the fluidic glass (28') until the skeleton structure (26) is collapsed under ram (28') becomes dominant to provide omni-directional pressure transmission to effect the predetermined densification of the material being compacted within the container (12)

Semiconductor device including an alpha-particle shield

Abstract: The present invention relates to a semiconductor device having a semiconductor element which is sealed by a ceramic package, wherein a shielding member is provided near it from upper surface of the semiconductor element to shield the alpha-particles radiated from the package.

Ba(Zn 1⁄3 Nb 2⁄3 )O 3 –Sr(Zn 1⁄3 Nb 2⁄3 )O 3 Solid Solution Ceramics with Temperature-Stable High Dielectric Constant and Low Microwave Loss

Abstract: Solid solution ceramics in the Ba(Zn1/3Nb2/3)O3(BZN)–Sr(Zn1/3Nb2/3)O3 (SZN) system have been studied with a view to finding materials for use as dielectric resonators at microwave frequency. The relative dielectric constant and the unloaded Q at 10 GHz are respectively 41 and 5400 for BZN, and 40 and 2000 for SZN. The temperature coefficient of the resonant frequency is estimated as 30 ppm/°C for BZN and -38 ppm/°C for SZN. The dielectric constant of 0.3 BZN–0.7 SZN ceramic is nearly independent of temperature, which gives a very small estimated temperature coefficient of the resonant frequency of -5 ppm/°C.

Piezoelectric 3–3 composites

Abstract: Piezoelectric composites of PZT and polymers were prepared by mixing tiny plastic spheres with PZT powder in an organic binder and firing the mixture to give a ceramic skeleton. After cooling, the skeleton was back-filled with polymer and poled. Dielectric and piezoelectric properties were measured on samples ranging from 30 to 70 volume % PZT, and compared with a rectangular skeleton model for 3–3 composites. Composites containing 50% PZT-50% silicone rubber appear especially useful for hydrophone applications with dhgh products a hundred times larger than PZT.

Flux-sintered BaTiO3 dielectrics

Abstract: BaTiO3 modified with BaZrO3 or SrZrO3 was sintered at 1100° C with the aid of various fluxes. The objective was to identify compositions in the system CdO-Bi2O3-PbO-B2O3 that would permit growth of the ceramic grains during sintering to produce dielectric constants greater than 5000 at room temperature. By studying binary, and then ternary flux systems initially, the roles of the flux components were identified and classified according to their solubility and mode of substitution in the titanate crystal lattice. This, together with close control of cation stoichiometry, resulted in the discovery of flux systems with other oxides substituting for CdO, Bi2O3 or B2O3 that produced similar results.

Laser enhanced etching in KOH

Abstract: We have used a focused laser beam to perform localized etching on 〈111〉 Si and several ceramic materials submerged in an aqueous potassium hydroxide solution. The etching process is accompanied by localized melting of the material whenever high material removal rates are observed. Mil sized blind holes, through holes, and slots have been fabricated. Instantaneous etch rates as high as 200 μm/s have been observed in alumina/TiC ceramic for 1‐W of incident laser power (∼106 W/cm2). An average rate of a 15 μm/s has been observed in the etching of through holes in 10‐mil silicon with 15 W of incident laser power (∼107 W/cm2).

Rare-earth-doped yttria-gadolinia ceramic scintillators

Abstract: Rare-earth-doped, polycrystalline yttria-gadolinia ceramic scintillators with high density, optical clarity, uniformity, cubic structure and which are useful in the detection of X-rays, include one or more of the oxides of rare-earth elements Eu, Nd, Yb, Dy, Tb, and Pr as activators. The oxides of elements Zr, Th, and Ta are included as transparency-promoting densifying agents. Any decrease in scintillator light output, due to the addition of transparency promoting additives, may be partially restored by the addition of either calcium oxide (CaO) or strontium oxide (SrO). Sintering, sintering combined with gas hot isostatic pressing, and hot pressing methods for preparing the ceramic scintillators are also described.

Developments in fabrication of piezoelectric ceramics

Abstract: First, the progress in the piezoelectric ceramic compositions after Pb(Zr, Ti)O3 is briefly described with newly developed materials both of the ternary compositions and of PbTiO3 families. Second, the effects of porosity on the electric and piezoelectric properties are discussed for PZT samples with controlled porosities and pore shapes and the electric and piezoelectric properties of porous Pb(Zr, Ti)O3 with the good connectivity of structure are discussed. Third, the relationship between the defect structure and the electrical properties are discussed for pore-free (Pb, La) (Zr, Ti)O3 ceramics especially prepared by the two-stage processing. Fourth, recent results in the grain-oriented ceramics with an anisotropic structure such as bismuth layer-type compounds are reviewed.

Process for making sintered glasses and ceramics

Abstract: Glass or ceramic products including glass optical waveguides are produced by a vapor phase oxidation process wherein β-diketonate complexes of selected metals having significant vapor pressures at some temperature below their decomposition temperatures are vaporized, transported to an oxidation site in the vapor phase, and reacted in the vapor phase to form particulate metal oxide soot After capture, this soot can be consolidated by sintering to form eg clear glass of a purity suitable for drawing into glass optical waveguide fiber

Compliant interface for ceramic turbine blades

Abstract: The present invention provides a ceramic turbine blade having a ceramic root flange and a metallic compliant layer which is electroformed to the ceramic root flange and then machine-formed to the geometry required for attachment to the turbine disk. Because of its intimate bond to the surface of the ceramic root flange and because of its compliant nature, the metallic compliant layer serves to uniformly distribute stresses induced by the attachment of the blade to the turbine disk. The present invention also envisions the attachment and use of a fir tree root section to an otherwise complete ceramic blade without risk of stress fracture or modification of the turbine disk.

Application of Auger line shapes and factor analysis to characterize a metal‐ceramic interfacial reaction

Abstract: A factor analysis of Auger line shapes selected from a compositional depth profile can determine the presence and number of new chemical states formed at a solid interface. A technique known as target transformation is used to extract the Auger spectrum of an unidentified interfacial component from mixed spectra. Quantitative information is also provided by factor analysis and target transformation. The procedures described in this work are superior to other methods of interpreting Auger line shape and depth profile data, such as visual inspection, spectral stripping or peak area measurements. Auger line shape analysis was used to study the sputter deposition of Pt onto a zirconia ceramic. Under some sputtering conditions, a platinum–zirconium intermetallic is formed at the solid interface.