Showing papers on "Ceramic published in 1969"

Transparent glass-ceramics

Abstract: Glass-ceramic materials may transmit visible light if either of the following conditions are operative: (i) the crystallites of all species are much smaller than the wavelength of visible light, or (ii) the optical anisotropy (birefringence) within the crystals and refractive index difference between crystals and glass are very small. These conditions are achieved in several aluminosilicate glass-ceramic systems. Solid solutions (ss) of β-quartz, spinel, and mullite are the major crystalline phases in these transparent glass-ceramics. The transparent β-quartz solid solution glass-ceramics can be divided into three areas: ultra-low expansion materials, refractory and colourless materials, and high electrical resistivity—low dielectric loss materials. These three material groups, though chemically distinct, are all characterised by high crystallinity, thermal shock resistance, excellent chemical durability, and susceptibility to mechanical strengthening by ion-exchange techniques. The transparent spinel and mullite glass-ceramics contain considerable glassy phase, but nevertheless are characterised by excellent transparency, even after thermal exposure for long periods above 1000° C.

Preparation of High-Purity Submicron Barium Titanate Powders

Abstract: Simultaneous hydrolytic decomposition of barium bis isopropoxide and titanium tetrakis tertiary amyloxide was used to produce stoichiometric BaTiO3. The particle size range was 50 to 150 A. The purity was 99.98+%, the major contaminant being silicon from the glass apparatus. The homogeneity and stoichiometry of the powder were demonstrated by electron microscopy and wet chemical analysis. X-ray and infrared analyses indicate that the material, as-prepared and helium-dried at 5O°C, has the titanate crystal structure. The powder sinters at 1300°C to a high density, translucent body with a uniform microstructure. The experiments suggest that the alkoxy-based preparation of oxides may provide a broad base for improving the quality and reproducibility of electrical and structural ceramics.

Lead Zirconate‐Lead Titanate Piezoelectric Ceramics with Iron Oxide Additions

Abstract: An investigation of the effects of small additions of Fe2O3 to lead zirconate-lead titanate ceramics with compositions between 45 and 60 mol% lead zirconate has shown that, with 2 moles of PbO to balance each mole of Fe2O3, the solubility of Fe2O3 was about 0.8 wt% in compositions near the tetragonal-rhombohedra1 boundary. The dielectric constant and dissipation factor for both rhombohedra1 and tetragonal materials were decreased by addition of iron oxide, whereas the mechanical quality factor and frequency constant were increased. The dependence of the electromechanical properties on grain size was qualitatively similar for both undoped and iron oxide-doped materials; the presence of iron oxide inhibited grain growth and lowered the limiting grain size below which the electromechanical properties change rapidly with grain size.

Ferroelectric ceramic electrooptic materials and devices

Abstract: Thin polished plates of hot-pressed rhombohedral lead zirconate-lead titanate ceramics possess one of two types of electro-optic properties depending on the nominal grain diameter. In poled coarse-grained ceramics the electrooptic effect of importance for devices is the dependence of the light scattering properties on the orientation of the ceramic polar axis (electrical poling direction). The light scattering properties are essentially independent of the magnitude of electrical poling (ferroelectric remanence state). Poled fine-grained ceramics are birefringent, and their light transmission characteristics are similar to those of optically uniaxial crystals. These materials exhibit orthotropic symmetry with respect to the optic axis, which coincides with the ceramic polar axis. The fine-grained ceramic electrooptic effect of primary importance for devices is the dependence of the effective birefringence on the magnitude of electrical poling as well as on the intensity of the applied biasing electric field. Retardation of a ceramic plate can be varied incrementally by partial switching or continuously by application of a nonswitching bias field. Both coarse- and fine-grained ceramics have the property that localized areas as small as 25 µ by 25 µ can be poled or switched independently without affecting the light transmission characteristics of the surrounding area. The locally switched areas are stable with time, but they can be "erased" by switching them back to their original orientation. Each locally switched area can function as a light shutter, valve, or spectral filter depending on the ceramic material, the switching mode, and the characteristics of the incident light.

Method of firing ceramic articles utilizing microwave energy

Abstract: A PROCESS FOR FIRING CERAMIC ARTICLES IN WHICH THE ARTICLES ARE FED INTO A MICROWAVE CAVITY WHEREIN A PLURALITY OF PARTICLES OF RESISTIVE MATERIALS ARE LOCATED IN A PREDETERMINED FIXED RELATIONSHIP WITH RESPECT TO THE ARTICLES. MICROWAVE ENERGY IS EMITTED TO THE PARTICLES SO AS TO GENERATE A MULTITUDE OF ARCS THERETHROUGH TO THEREBY CONVERT SAID MICROWAVE ENERGY INTO A HIGH REFRACTORY HEAT ENERGY FOR FIRING THE ARTICLES.

Ceramic ferroelectric field effect studies

Abstract: The ferroelectric field effect has been observed in a semiconducting thin film of n-type tin oxide deposited on a ferroelectric lead zirconate-titanate ceramic substrate. The semiconductor was deposited by electron gun evaporation onto a thermally depolarized (randomly oriented) substrate which permitted the carrier concentration of the film to be enhanced or depleted depending on the direction of polarization of the substrate. Typical average resistivity values of 200-A films are approximately 0.1 Ω.cm for the depoled state, 0.01 Ω.cm for the enhanced state, and 100-1000 Ω.cm for the depleted state. "On"-"off" ratios as high as 1.7 \times 10^{5} have been observed in a single device. The transition from enhancement to depletion is quasi-continuous due to the small size and random orientation of the individual crystallites in the ceramic. Conductance measurements during this transition have yielded field effect mobilities in the range 7-10 cm2/V.s; and maximum average carrier densities in the range 0.5-1.0 × 1020carriers/cm 3 . The tin oxide-ceramic devices described here suffer from the long-term drift that is characteristic of many field effect devices. The resistivity of a device stored in the depleted state will decrease from 3 to 4 orders of magnitude in times between 104-105minutes.

Mechanical Properties of a New Carbon Fibre Material

Abstract: WE report here some preliminary measurements of the mechanical properties of a new ceramic material. The material—a pure silica matrix reinforced by carbon fibres—has been made in our laboratory as part of a programme aimed at the manufacture of a ceramic material which, although composed of stiff and brittle components, is itself strong and relatively tough. Such a material forms a good test of current theories for improving the toughness of composite materials, and of reinforced ceramics in particular1.

Ceramic clad flame spray powder

Abstract: A flame spray powder comprises finely-divided core particles of a metal or a metal alloy coated with discrete particles of a ceramic or cermet that remains in solid phase at least 100 DEG F above the fusing or melting temperature of the metal. The average particle size of the ceramic is less than 25 percent of the average particle size of the metal and the amount used is insufficient to totally cover the surface of the metal particles so that on the average in the range of 5 to 75 percent of the surface area of the metal particles is exposed to ambient conditions.

Dense carbide composite bodies and method of making same

Abstract: Hard, dense, composite ceramic bodies of boron carbide, silicon carbide and silicon, particularly useful as ceramic armor, are produced by forming a mixture of granular boron carbide and a temporary binder into a desired shape and setting the binder to obtain a coherent green body which is siliconized by heating it, in an inert atmosphere and in contact with a controlled amount of silicon, to a temperature above the melting point of silicon and in the range of about 1500-2200 DEG C, whereupon the molten silicon infiltrates the body and reacts with some of the boron carbide thereof.

Ceramic CdS Solar Cell

Abstract: This paper describes the properties and the model of ceramic CdS photovoltaic cell made by treating CdS ceramic plate electrochemically in copper ion solution. The compositions and structures were analysed by means of X-ray Ginuie Camera and X-ray microanalyser. It was found that Cu2-xS (0x0.2) is formed along grain boundaries over a range of a several ten microns of the surface layer, and that the photovoltaic junctions exist at grain boundaries in this surface layer. From examinations of the voltage dependence of the barrier capacitance, the junctions could be classified into step junction, graded junction and Mott barrier, according to the prepared method. The spectral response measurement indicates that the origin of the photo-emf of the Mott barrier is mostly impurity photovoltaic effect.

Mechanical Properties of Ceramic Materials

Abstract: The strength and fracture behaviour of ceramics are considered with particular reference to oxides. Ceramics fracture in a brittle manner and the strength of most materials is about two orders of magnitude less than the theoretical strength. Strength is discussed conveniently in terms of a modified Griffith equation and the important variables are an effective surface energy and an initial crack size. Both these variables can be related to microstructural features. The effective surface energy is relatively insensitive to structure. The Griffith crack size is more dependent on structure but the controlling factors are only partly understood. Further advances require more detailed information about the role of grain and phase boundaries and the relationship to Griffith cracks.

Determination of the Firing Temperature of Ancient Ceramics by Measurement of Thermal Expansion

Abstract: THE thermal expansion method for determining firing temperatures1–3 is based on the assumption that, when clays are fired, shrinkage occurs as a result of various sintering processes such as vitrification. Consequently when a clay ceramic is heated up from room temperature (see Fig. 1) it typically exhibits a reversible expansion, characteristic of its mineralogical composition, until temperatures comparable with the original firing temperature are reached. With continued increase in temperature the ceramic begins to contract because superimposed on the reversible expansion there is an irreversible shrinkage associated with resumption of sintering (that is, the firing of the ceramic is being continued beyond the point reached during the original firing). The temperature (Ta) at which a net shrinkage is first observed should therefore provide an indication of the original firing temperature (Te) of the ceramic.

Improvements in or relating to fibrous insulating materials

Abstract: IN A METHOD OF MAKING A FIBROUS INSULATING MATERIAL CONSISTING OF, FOR EXAMPLE, CERAMIC FIBRES, A MASS OF FIBROUS FILAMENTS IS FIRST TREATED TO THE ACTION OF A BINDING AGENT SUCH AS A SILICA SOL AND THEREAFTER A PART OR THE WHOLE OF THE SURFACE OF THE MATERIAL IS SPRAYED WITH AN ADHERENT COATING OR LAYER OF A METAL OXIDE SUCH AS ALUMINA

Powder compacting press

Abstract: AN ISOSTATIC POWDER PRESS FOR COMPRESSING CERAMIC POWDERS TOGETHER TO FORM A TOILET BOWL SECTION, SAID PRESS INCLUDING ONE OR MORE DEFORMABLE MEMBRANES SUBJECTABLE TO FLUID PRESSURE TO UNIFORMLY COMPRESS THE POWDERS TO A SUBSTANTIALLY CONSTANT DENSITY THROUGHOUT.

Ferroelectric electrooptic ceramics with reduced scattering

Abstract: Ferroelectric lead zirconate-titanate ceramics appear promising for use as electrically controlled retarders because both conventional electrooptic and nonvolatile incremental retardation changes can be induced in areas as small as 25 µ on a side. One particular composition, Pb 0.97 La 0.02 Zr 0.65 Ti 0.35 O 3 , has so far proved superior to all other rhombohedral lead zirconate-titanates when judged by either the conventional electrooptic retardation variation with applied bias voltage, or the nonvolatile incremental retardation change with remanent polarization state of the ceramic. Furthermore, this same lanthanum-doped composition exhibits a marked decrease in undesirable light scattering when compared with extensive data on the same composition with bismuth doping. Scattering also decreases with increasing wavelength λ, and the ceramic transmittance is greater than 85 percent for 3 µ<λ<8 µ with sample thickness less than 50 µ. This increased transmittance now makes feasible the construction of multistage ceramic electrooptic systems.

Pyroelectric effect in barium titanate ceramic

Abstract: Pyroelectric coefficient extrema measurement at constant stress in barium titanate ceramic at various temperature ranges for various transition points

Self-cleaning cooking apparatus

Abstract: A self-cleaning, abrasion-resistant surface for a cooking apparatus comprising a three-layer coating on a metal surface, each of the first two layers comprising a mixture of a ceramic and a catalytically active material, with, preferably, increased amounts of catalyst in the second coating layer, and an interrupted layer of ceramic above the two-layer coating. Improved bond between the three-layer coating and the base structure of the cooking apparatus can be achieved through the use of a sandwiched ceramic layer.

Ferroelectric ceramic materials

Abstract: An electrooptic ferroelectric ceramic material of a lead lanthanum zirconate titanate solid solution having about 5 to 25 atom percent lanthanum with the ratio of zirconium to titanium varying from about 5/95 to about 95/5, hot-pressed, having an optical transmittance throughout the visible spectrum of about 100 percent for optically polished plates about 0.25 millimeters thick, with an effective birefringence of from about -0.003 to 0.03 at saturation remanence polarization to near zero as the remanent polarization is switched to electrical zero, and an effective electrooptic coefficient at saturation remanence from about 1 X 10 2 to 5 X 10 2 m2/C, and for memory applications a coercive field from about 2 to 10kV/cm.

The strengths of cements reinforced with glass fibres

Abstract: Synopsis Fibrous composite materials utilizing ceramic fibres and inorganic cements offer a potential source of new lightweight, strong and durable materials. Commercial glass fibres now available are not durable in an alkaline medium of the kind present in most hydrating cements; a new alkali-resistant glass has been developed at the Building Research Station to surmount this difficulty. Because this has renewed interest in the subject, and to provide a yardstick for the effectiveness of the new glass, composites made with commercially available glass fibres and various inorganic binders were studied to find suitable methods of fabrication and to establish the behaviour of the material. This paper describes the influence of type of matrix, age and glass content upon the impact, tensile and bending strengths of composites fabricated by a simple spray-suction technique. On the basis of the properties developed before chemical interaction between glass and cement becomes dominant, it can be foreseen that, g...

Laminated ceramic structure for containing a semiconductor element

Abstract: A package having a bottom plate comprises by laminating at least two ceramic plates, in which a semiconductor substrate including an integrated circuit is fixed on the principal surface of said bottom plate and a conducting layer with low resistivity is extended between said ceramic plates, an operating current being supplied to said integrated circuit through the conducting layer, thus the ohmic loss is reduced at the time of supplying the operating current.

Evaporation from a Simulated Soil Shrinkage Crack

Abstract: A simulated soil shrinkage crack, 46 cm wide and 62 cm deep, was constructed in such a manner that depth could be varied by 15.2-cm increments and width could be adjusted between 10 and 70 mm by 20-mm intervals. The walls of the crack were lined with porous ceramic plates connected to a water supply maintained at −5 mb potential. The simulated crack was installed in the floor of a laboratory wind tunnel located in a controlled environment room maintained at 24.0 ± 1.5C air temperature and 43 ± 3% relative humidity. Evaporation from the simulated crack walls (ceramic plates) was determined for all combinations of four crack widths (10, 30, 50, and 70 mm), three crack depths (30, 45, and 60 cm) and five windspeeds (0, 2.2, 4.5, 6.7, and 8.9 m sec⁻¹). Total water loss (evaporation) from the walls of the simulated crack increased as any one or all of the three variables (windspeed, crack depth, or crack width) increased. These three variables accounted for 99.1% of the variability in total evaporation from the crack walls. Turbulent air movement within the simulated crack was the major factor affecting the evaporation. Both straw and gravel mulches reduced evaporation from the crack walls 85 to 90% with no wind and about 60% at 8.9 m sec⁻¹ windspeed. The results suggest that evaporation from soil shrinkage cracks may be reduced by closer plant or row spacing or by surface residues such as trash and clod mulches. Total evaporation from a simulated crack 60 cm deep varied from 0.5 cm³ hr⁻¹ (10 mm wide, 0 m sec⁻¹ windspeed) to 18 cm³ hr⁻¹ (70 mm wide, 8.9 m sec⁻¹ windspeed). In simulated cracks 60 cm deep and 30–70 mm wide, 50–60% of the total evaporation occurred below 15 cm and 30–40% occurred below 30 cm.

Low-expansion, low-melting zinc phosphovanadate glass compositions

Abstract: Low-melting, low-expansion, lead-free glass compositions are provided for sealing ceramics parts and encapsulating ceramic substrates. In addition to having a thermal expansion matching that of alumina, the glass compositions provide for the formation of a glass-to-alumina seal in the 380 DEG to 450 DEG C. temperature range.

Foamed ceramic comprising fly ash and phosphoric acid

Abstract: A LIGHTWEIGHT FOAMED CERAMIC CONTAINING FLY ASH, AN ACIDIC PHOSPHATE AND A FILLER WHICH SETS HYDRAULICALLY WITH THE PHOSPHATE WITHOUT HEATING.

The design and operating characteristics of a 1200-element ferroelectric-electroluminescent display

Abstract: A 1200-element matrix addressed ferroelectric-electroluminescent display has been built with doctor-bladed Pb 0.99 [(Zr 0.50 Sn 0.50 ) 0.86 Ti 0.14 ] 0.98 Nb 0.02 O 3 ferroelectric ceramic. Each display element comprises a diode and a three-cell ferroelectric control circuit which stores the video information and drives an associated electroluminescent cell. The characteristics of the three-cell circuit are described in terms of the pertinent properties of the doctor-bladed ceramic. A design procedure based on the properties of the ferroelectric and electroluminescent materials is given for determining the cell dimensions and the driving voltage needed to obtain a specified maximum brightness, transfer characteristic, and contrast ratio. The 6- by 8-inch display panel, driven from a vidicon camera source, has been operated with high reliability for approximately 40 hours spread over a year. Subjective tests have shown that satisfactory gray scale, moving images can be obtained which are comparable to those of a conventional TV receiver. The average power dissipated is 175 watts. The measured variation in the transfer characteristics and the highlight brightness (16 ± 4 fL) was found to be due primarily to variations in the ferroelectric coercive voltage. These variations are due to nonuniformities in thickness caused by differential shrinkage during the firing of the 60 doctor-bladed strips (4- by 0.5- by 0.003-inch nominal) used in the display. Techniques exist for reducing these variations.

Ceramic gate valve

Abstract: A gate valve having the gate member and valve seating portions constructed from a ceramic material for hardness and density qualities and extremely high resistance to chemical action and resistance to high temperatures. The valve gate member is particularly designed and constructed to maintain the ceramic material under compression at all times to assure excessive strength for the valve. In addition, the coaction between the ceramic gate and ceramic-seating members provides an optimum coefficient of static friction during operation of the valve for facilitating opening thereof.

Process for increasing the strength and electrical conductivity of graphite or carbon articles and/or for bonding such articles to each other to ceramic articles or to metals

Abstract: An impregnating composition for increasing the strength and electrical conduction of graphite and carbon articles, comprises 60-90 percent by volume furfurol or furfuryl alcohol, 5-20 percent by volume anthracene oil, and as a catalyst either 2 to 25 percent by volume phosphoric acid or 5 to 35 percent by volume of titanium ethyl ester. A bonding composition for impregnating and bonding graphite and carbon articles to each other and to ceramic articles and metals, comprises this impregnating composition in an amount 20 to 80 percent by weight, 1 to 15 percent by weight of boric acid or boric oxide, and the rest a filler, which can be TiC, TiB2, SiC, B4C, BN, CaO, Al2O3, powdered coke, graphite or a mixture thereof. To impregnate or bond, the impregnating composition or bonding composition is applied and the articles are heated at 80 to 250* C. for 2 to 10 hours, and then carbonized at 300* to 1,500* C.