Showing papers on "Ceramic published in 1974"

A New BaO-TiO2 Compound with Temperature-Stable High Permittivity and Low Microwave Loss

Abstract: The dielectric properties of ceramics in the TiO2-rich region of the BaO-TiO2 system were investigated. In the composition range between BaTi4O9 and TiO2, another compound, Ba2Ti9O20, can be obtained when calcining and sintering conditions are controlled carefully. When dense and single-phase, this ceramic has excellent dielectric and physical properties. At 4 GHz, the dielectric K= 39.8, Q= 8000, and τK (temperature coefficient of dielectric constant) =−24 ± 2 ppm/°C.

Slow crack growth in brittle materials under dynamic loading conditions

Abstract: The failure of materials due to slow crack growth, under dynamic loading conditions, is analyzed in terms of crack velocity, stress intensity relationships. It is shown that this type of analysis can fully describe the failure characteristics for both constant strain-rate and constant stress-rate loading. The analysis is used to predict the variations of strength and subcritical crack growth with strain-rate and stress-rate. Application of the analysis to several ceramic systems give data which are entirely consistent with available experimental data.

Grain-size effects on properties of some ferroelectric ceramics

Abstract: Hot-pressed ceramics of the lead titanate zirconate system with different grain sizes were prepared and some of their electrical properties measured. The values of the dielectric and piezoelectric properties were analysed together with information on barium titanate ceramics already published in the literature. Many similarities were found between both systems. There are two main contributions to the properties; the single-crystal single-domain intrinsic effect and the contribution of the wall motion. The intrinsic effect is analysed considering the grains as monodomains. A model is developed which proposes that each grain has a different transition temperature Tc. The Tc values are taken as following a Gaussian distribution and the behaviour of the dielectric constant against temperature is computed and checked with experimental results. All the results can be explained qualitatively with the model; a connection between findings and the idea of diffuse phase transitions is outlined.

Light scattering by pores in polycrystalline materials: Transmission properties of alumina

Abstract: The in‐line transmission of polycrystalline high‐density ceramics is discussed in terms of light scattering by pores. The Mie theory for light scattering is applied to calculate scattering coefficients using generalized parameters. Results are shown for scattering by spherical pores with uniform size and with a lognormal size distribution. Specific examples are given of the calculated transmission of alumina in the wavelength region 0.4–5 μm. Experimentally determined transmission curves of normally sintered and of hot‐pressed alumina are compared with calculated curves. The porosity, the position of the maximum, and the width of the lognormal distribution are treated as variables in the calculation. Good agreement with the experimental data is obtained.

Effect of ion bombardment during deposition on thick metal and ceramic deposits

Abstract: Energetic ion bombardment of metal and ceramic deposits during deposition is shown to affect the morphology, structure, stochiometry, and physical properties of the resulting deposit. The bombardment of the growing deposit tends to eliminate the columnar growth morphology normally encountered in thick-crystalline deposits. Generally, in metals it is found that internal stress, density, and gas content increase with increasing ion bombardment energy, but in some cases there is a decrease at high energies, possibly due to heating. In the case of sputter-deposited glass films, it is found that ion bombardment affects the stoichiometry, the coefficient of thermal expansion, and the strain point of the glass. Specific data are presented for thick (> 1 μ) rf sputter-deposited Corning 1720 glass and also sputter-deposited and electron-beam ion-plated chromium deposits with both a dc and a rf substrate bias.

Preparation and casting of metal-particulate non-metal composites

Abstract: A new process for the preparation and casting of metal-particulate non-metal composites is described. Particulate composites of ceramic oxides and carbides and an Al-5 pet Si-2 pct Fe matrix were successfully prepared. From 10 to 30 wt pct of A12O3, SiC, and up to 21 wt pct glass particles, ranging in size from 14 to 340 ώ were uniformly distributed in the liquid matrix of a 0.4 to 0.45 fraction solid slurry of the alloy. Initially, the non-wetted ceramic particles are mechanically entrapped, dispersed and prevented from settling, floating, or agglomerating by the fact that the alloy is already partially solid. With increasing mixing times, after addition, interaction between the ceramic particles and the liquid matrix promotes bonding. Efforts to mix the non-wetted particles into the liquid alloy above its liquidus temperature were unsuccessful. The composite can then be cast either when the metal alloy is partially solid or after reheating to above the liquidus temperature of the alloy. End-chilled plates and cylindrical slugs of the composites were sand cast from above the liquidus temperature of the alloy. The cylindrical slugs were again reheated and used as starting material for die casting. Some of the reheated composites possessed “thixotropy.” Distribution of the ceramic particles in the alloy matrix was uniform in all the castings except for some settling of the coarse, 340ώ in size, particles in the end-chilled cast plates.

Histochemical responses at a biomaterial's interface

Abstract: A series of nonporous glasses and glass materials designed with controlled surface ion activities to allow chemical bonding to bone are described Surface reactivities of these materials in vitro are correlated with biological activities in vivo and in tissue culture Direct chemical bonding of the materials to bone is demonstrated The mechanism for development of this bond is through the production of an amorphous ion surface gel on the bioglass This gel induces osteogenesis by a chemotactic response of osteoblasts

Translucent Sintered MgAl2O4

Abstract: A translucent polycrystalline MgAl2O4 ceramic was prepared from finely divided coprecipitated spinel in which a small amount of CaO added as a sintering aid was uniformly distributed. The CaO promotes densification through the formation of a liquid phase at the sintering temperatures. Depending on the sintering treatment, the relative density of the sintered spinel was 99.7 to ∼100% of theoretical. The in-line optical transmission was > 10% from 0.3 to 6.5 μm. Total transmission in the visible region was between 67 and 78%.

Interfacial bonding and the toughness of carbon fibre reinforced glass and glass-ceramics

Abstract: The work of fracture of four different carbon fibre reinforced glass and glass-ceramic composites has been measured to determine the effects of the different properties of the components on fracture behaviour. Differences in fracture energies can be explained in terms of the fibre pull-out model and differences in the fibre-matrix interfacial shear bond. The work of fracture of the glass-ceramic is independent of crack velocity while that of the Pyrex matrix composite decreases with increasing velocity at low velocities, the decrease stopping at higher velocities. Work of fracture values agree well with linear elastic fracture mechanics toughness values.

Electrical conductivity in ceramics and glass

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Dense polycrystalline silicon carbide

Abstract: A dense silicon carbide material having improved electrically conducting properties is disclosed which is prepared by forming a homogeneous dispersion of silicon carbide, a sufficient amount of boron nitride, and optionally a boron containing additive and hot pressing the dispersion at a sufficient temperature and pressure whereby a dense substantially nonporous ceramic is formed. The silicon carbide material can be machined by electrical discharge machining or by electrochemical machining.

Laser drilling mechanics

Abstract: Many laser drilling applications require that the shape of the drilled hole be carefully controlled. In order to successfully do this it is necessary to understand the laser drilling process. This paper reports on a quantitative model which predicts the depth and shape of a hole drilled in alumina ceramic by a ruby laser. Both experimental and theoretical results indicate that the predominant drilling mechanism for this application is not one of surface absorption and conduction inward, but one in which laser energy is absorbed throughout the bulk of the ceramic. The depth and shape of holes drilled in ceramic have been accurately predicted from the measured beam energy density distribution. Finally, it is shown that the radiation pressure of the focused beam plays an important role in the romoval of molten material from the heated region.

Improved polycrystalline ceramic lasers

Abstract: Improved polycrystalline ceramic laser rods, composed of cubic solid solutions of 89–96.5 mole% Y2O3, 10–2.5% ThO2, and 1% Nd2O3, were synthesized by a conventional sintering process. This material, called Nd‐doped Yttralox (NDY) ceramic, was produced with laser threshold energies lower than that of the best commercially available Nd:glass laser rod and with a lasing efficiency ∼94% that of laser glass at 40 J of input energy under pulsed mode conditions. In a similar operating mode a NDY rod, containing 5 mole% ThO2 and having dimensions 7.6×0.46 cm, delivered 0.41 J of optical energy when using an input energy of 162 J, a pump pulse of 150 μsec, and output mirror reflectivity of 70%. The lasing efficiencies depended strongly on the method of powder preparation and processing, composition, and the cooling rate from the sintering temperature. The dependence of the fluorescent linewidth on the NDY composition provides a means of appreciably varying the material gain coefficient. Active attenuation coeffici...

Molten metal filter

Abstract: The present invention resides in an improved molten metal filter and a method of preparing same and a method of filtering molten metal therethrough. The filter is an open cell ceramic foam material having a plurality of interconnected voids surrounded by a web of said ceramic.

Fracture Mechanics Determinations

Abstract: Techniques for the evaluation of fracture mechanics parameters are described The selection of techniques for various ceramic applications is discussed, emphasizing the particular problems encountered with these measurements in ceramic systems Finally, the application of fracture mechanics parameters to problems in both materials development and failure prediction in ceramic systems is described

Methods for producing oxygen-sensing element, particularly for use with internal combustion engine exhaust emission analysis

Abstract: Methods for making an exhaust-gas-sensing element which is an oxygen concentration cell having a solid electrolyte with an electron-conductive surface on the side exposed to the reference air and a catalytic electron-conductive layer containing micro pores which extend through to the solid electrolyte on the other surface which is adapted to be exposed to the exhaust gases The electron-conductive catalytic layer is covered with a porous protective layer The method comprising applying the catalytic layer by means of thin layer techniques and then heating to form the micro pores; or by applying a paste comprising ceramic particles, catalytic particles and a thinning oil and sintering

Sensor device and method of manufacturing same

Abstract: An oxygen sensing device particularly suited as a sensor for the exhaust gases of internal combustion engines, the sensing device comprising an electrically insulative ceramic element having bonded on the surface thereof a layer of an oxygen sensing metal oxide, preferably titania, and a pair of electrical leads for the oxygen sensing metal oxide, the device also having a layer of electrical resistance heating material adjacent to the layer of oxygen sensing metal oxide but separated therefrom by a layer of the electrically insulative ceramic, a pair of electrical leads for the electrical resistance heating material, and a layer of ceramic covering the layer of electrical resistance heating material.

Ceramic combustion liner

Abstract: A liner for a gas turbine combustion apparatus has a ceramic side wall made up of a number of axially-aligned rings. These are retained between a metal dome and a metal outlet fitting which are connected together by tie rods and maintained at proper axial spacing by sleeves disposed around the tie rods. A T-section metal ring is disposed between each adjacent pair of liner wall segments to align the segments with each other. A resilient compressive connection is disposed between the upstream ring and the dome. These arrangements accommodate differential thermal expansion of the metal and ceramic parts of the liner.

Thermoelectric exhaust gas sensor

Abstract: An extremely durable and high output thermoelectric sensor for detecting the quantitative content of combustibles in the exhaust gases of an internal combustion engine. A U-shaped ceramic body of doped titanium dioxide is mounted in an exhaust system with ends of leg portions on the body outside of the exhaust gas flow. Chromel wires are embedded into these ends to form two thermocouple junctions with the ceramic body. Platinum coated alumina particles fill an opening in an area of the ceramic body exposed to the exhaust gas flow near one junction. Heat generated by an incompletely burned exhaust gas oxidizing on the platinum makes the nearby junction hotter than the other junction. The difference in output between the two junctions is proportional to the concentration of combustibles in the exhaust gases.

High Performance Ceramics

Abstract: Within the past several years, the field of ceramic technology has seen the development of a number of significant achievements in materials processing and application.

Recessed metallurgy for dielectric substrates

Abstract: A ceramic green sheet material is metallized by laminating a thin organic material, preferably MYLAR, to a ceramic green sheet surface, and then employing an electron beam to define a predetermined pattern of openings extending through the organic material and selectively into and through the green sheet. The resulting channels and via holes are then filled with a metal paste. The organic mask is removed by peeling subsequent to the metal paste deposition step.

Silicon carbide resistance igniter

Abstract: A monolithic ceramic resistance igniter of simple configuration is composed essentially of polycrystalline silicon carbide adapted for use in gas and liquid fuel burning systems. As a result of the combination of its sintered silicon carbide composition, its microstructure, controlled density and large cross-sectional area, the igniter possesses an unusually high degree of physical ruggedness. The igniter will attain a temperature of about 1,000*C in well under 20 seconds drawing a maximum of 6 amps at 132 volts, with a room temperature resistivity of 0.10 to 1.70 ohm centimeters and a resistivity at about 1000*C of from 0.06 to 0.26 ohm centimeter. The igniter also has a physical construction such that a high percentage of its hot surface area radiates directly to the environment.

Method for bonding metal to ceramic

Abstract: An improved method of bonding metal to a ceramic is described in which the metal is shaped, surface treated, and curved prior to heating the metal to form a eutectic bond between the metal and the ceramic. The surface treatment comprises heating the metal in a reactive atmosphere, e.g., in an oxidizing atmosphere to produce an oxide layer. The surface treatment is carried out at a temperature lower than the metal-metal oxide eutectic temperature.

Vibrational modes in (Pb,La)(Zr,Ti)O3 ceramics

Abstract: Results are presented for the Raman spectra, the far‐infrared reflectivity spectra, and the radio‐frequency dielectric constant of several selected PLZT ceramics. Vibrational modes are assigned by comparing these results with previous Raman and infrared measurements on single‐crystal PbTiO3, and the PZT and PLT mixed ceramic systems. The mode responsible for the temperature variation of the low‐frequency dielectric constant was not observed but is shown to be below 65 cm−1.

Ceramic Manufacturing Technology for the High Performance PTC Thermistor

Abstract: The roles and the effects of transition elements and other additives on the resistivity and the ratio of the resistivity rise of the semiconducting barium titanate ceramics are presented. The variety of the typical experimental data are illustrated to explain that the exact controlling up to ppm order of the small amount components including both impurities and additives as well as the controlling of the characteristics attributing to the powder, is very important technology for the industrial manufacturing of the high performance positive temperature coefficient (PTC) thermistor. The importance of the exact controlling of the whole firing program is also discussed, indicating the existence of particular temperature ranges at high temperature regions, both in the heating and cooling processes.

Effects of grain size on the electrical properties of PLZT ceramics

Abstract: A group of transparent hot-pressed ferroelectric (Pb0.92La0.08)(Zr0.65Ti0.35)098O3 ceramics with controlled grain size from 1 to 14 μm and with few pores, less than 0.2% at most, were prepared from the oxide powders by applying a hot-pressing procedure including atmosphere control. The electrical and optical constants of these ceramics were determined as a function of grain size. The effect of grain size on each measured constant, χ, was expressed by a simple equation, χ = A + B/√GS . Polarization-reversal properties were also measured and the switching time related with the space charge effects were discussed.