Showing papers on "Ceramic published in 1972"

Ceramics based on the Si-Al-O-N and Related Systems

Abstract: TSUGE et al.1 have shown that β -Si3N4 can accommodate up to about 60% by weight Al2O3 in solid solution without major change of crystal structure but with increasing a and c unit-cell dimensions as the Al2O3 concentration increases. The products, obtained by sintering the mixed powders at 1,700 and 1,770° C, are undoubtedly similar to a new phase observed by Oyama and Kamigaito2 in mixtures of Si3N4, Al2O3 and Li2CO3 hot-pressed at 1,750° C. We report here a variety of ceramic materials built up of (Si,Al)(N,O)4 tetrahedra joined by sharing corners just as the silicate structures are built up of SiO4 and (Si,Al)O4 units.

Energy storage in ceramic dielectrics

Abstract: An evaluation has been made of the energy storage capabilities of ceramic dielectrics that were considered likely to provide high energy/volume efficiency on the basis of their expected permittivity-field characteristics. Data for fields up to 400 kV/cm are presented for a strontium titanate, and for a barium titanate ceramic. The materials were in thick-film form and bonded with a small amount of glass. At the maximum fields, energy storage in the barium titanate ceramic was close to that reported earlier for glass-bonded lead zirconate (approx. 2.0 J/cm3), but was about 30% lower in the strontium titanate material.

Synthesis and Mechanical Properties of Stoichiometric Aluminum Silicate (Mullite)

Abstract: Highly dense translucent polycrystalline bodies of stoichiometric aluminum silicate (mullite) were obtained by vacuum-hot-pressing of high-purity submicron mixed oxide powders. The powders were prepared by the hydrolytic decomposition of mixed metal alkoxides. X-ray diffraction and electron microscopy indicated that the initially amorphous needlelike fine particulates transform into highly crystalline orthorhombic mullite at ∼1200°C. Optimum hot-pressing conditions were 5 kpsi and 1500°C for 30 min. Densities within experimental error of the theoretical value of 3.19 g/cm3 were obtained. A typical microstructure consisted of fine interlocking needlelike grains arranged in an overall mosaic or “jigsaw” pattern. Microprobe traverses across the samples indicated homogeneous dispersion of SiO2 in the AlO3 matrix. Room-temperature mechanical properties were measured and correlated with the microstructure and crystal structure of the ceramic compact. A slightly higher melting temperature than has been previously reported was observed for the 3Al2O3·2SiO2 studied. All specimens exhibited a smooth surface finish and excellent thermal-shock resistance from 1200°C to room temperature.

Carbon fibre composites with ceramic and glass matrices

Abstract: A description is given of the microstructure and mechanical properties of alumina, sodalime glass, borosilicate glass and a lithia alumino-silicate glass-ceramic containing continuous, high modulus carbon fibres. Strengths up to 680 MNm−2 were obtained in glass samples containing 40 vol % of fibre whereas unreinforced glass had a strength of 100 MNm−2. Works of fracture were typically 3 kJm−2 compared to 3 Jm−2 for unreinforced glass. The results are discussed in terms of volume fraction of fibre, fibre damage, matrix critical strain and stresses generated by a mismatch in the thermal expansion coefficients of the matrix and the fibres.

Carbon fibre composites with ceramic and glass matrices: Part 1 Discontinuous fibres

Abstract: The fabrication, microstructure and some of the mechanical and thermal properties of a series of composites are described. The systems investigated were magnesia, alumina, soda-lime glass, borosilicate glass and a lithia alumino-silicate glass-ceramic incorporating high modulus, chopped carbon fibres and magnesia containing chopped, stabilized zirconia fibres. Fracture strengths were increased when the fibres were partially aligned, but decreased when the fibres were randomly oriented. In all cases, however, a substantial increase in work of fracture was observed compared to the non-reinforced matrices. The observed effects are discussed in terms of the volume fraction of fibre, the mismatch of thermal expansion coefficients between matrix and fibre and the nature of the interface.

Recent improvements in the optical and electrooptic properties of plzt ceramics

Abstract: Continuing studies on the improvement of the optical quality of lanthanum modified lead zirconate titanate (PLZT) ceramics have shown that (1) bulk residual porosity and (2) chemical inhomogeneity are primary factors contributing to optical losses in thick plates of the material. This paper describes methods by which both of these major faults in the ceramic can be virtually eliminated. In addition, the optical and electrooptic properties of the improved material are presented and compared with those of previously available materials. Successful methods of eliminating residual porosity and enhancing chemical homogeneity resulted from studies which led to improved hot-pressing techniques and chemical preparation of the PLZT powders. Essentially all of the residual porosity was eliminated by introducing an oxygen atmosphere during the hot-pressing process. Chemical homogeneity was improved significantly by using high purity liquid solutions for preparing the PLZT powders. A combination of lead oxide and sol...

Cold‐Pressing and Low‐Temperature Sintering of Alkoxy‐Derived PLZT

Abstract: Multiorganometallic compounds were used to prepare high-purity submicron-size lead lanthanum zirconate-titanate (PLZT) powders which can be consolidated at low sintering temperatures to high-density piezoelectric and electrooptic ceramic bodies. Simultaneous hydrolytic decomposition of lead isoamyloxide, lanthanum isopropoxide, and zirconium and titanium tertiary amyloxides produced quaternary titanate powders with particle sizes of 75 to 300 A and analyzed purity of 99.92%; the major contaminant was Na from an intermediate reaction product. Homogeneity and stoichiometry of the powders before and after processing were demonstrated by electron microscopy and chemical analysis. High-temperature X-ray diffraction indicated an amorphous material up to ∼600°C, where the crystalline phase was first observed. Powders prepared in this manner sintered to high-density fine-grained transparent bodies with uniform microstructure. The experimental results suggest that less rigorous consolidation methods are required with high-purity homogeneous precursor materials with fine particle size.

Carbon Fibers Obtained by Thermal Decomposition of Vaporized Hydrocarbon

Abstract: Carbon fibers are successfully grown on ceramic and/or graphite substrates through thermal decomposition of vaporized hydrocarbons at temperatures from 1100°C to 1300°C. The diameter ranges from 3 to 100 µm and the length 10 to 25 cm. Appropriate conditions for the growth of such long fibers are described. Some branched and crossed structures were observed in the fibers. Morphological and structural studies are made by means of optical microscope, scanning electron microscope, and X-ray diffraction. It leads to a conclusion that these carbon fibers are composed of cylindrical layers and scrolls of thin aromatic films aligned parallel to the fiber axis. There are two kinds of fibers with smooth and rough surfaces as illustrated in the accompanying photographs. The electrical resistivity, the tensile strength and the Young's modulus are found to be 1–2×10-3 ton-cm2, 4–34 ton/cm2 and 2–4×103 ton/cm2 respectively.

Dielectric Constant and Loss Data

Abstract: : This report includes data on high temperature organic crystals, ceramics, and glasses Additional sections include plastic materials with less heat resistance (PS-PL)

Effects of Additives on Piezoelectric and Related Properties of PbTiO 3 Ceramics

Abstract: Effects of additives Li2CO3, Ag2O, NiO, Cr2O3, Fe2O3, Gd2O3, Bi2O3, TiO2, MnO2, Nb3O5 and WO3 on piezoelectric and related properties of PbTiO3 ceramics are studied. Additives partly dissolve in lattice and the rest segregate at grain boundary. These additives act as grain growth inhibitors and binders. Additions of Li2CO3, NiO, Fe2O3 and MnO2 are most effective for densification. The additives Gd2O3, Bi2O3, Nb2O5 and WO3 give high resistivity probably by compensating Pb vacancies. Many piezoelectric and related properties depend on species and content of additives. Grain size is a main factor influencing these properties. The specimens with Cr2O3 and MnO2 characterized by coarse grain have small e*, small dissipation factor, short poling time, large coupling factors, high mechanical Q and small elastic compliance. These features may be explained by diminishing of stress between grains, decrease of interfacial polarization and large binding force at grain boundary.

Method of making gradient ceramic-metal material

Abstract: A ceramic-metal material system is fabricated by cold compressing separate adjacent volumes of different ceramic material or different particle sizes to form a porous ceramic compact; infiltrating each separate volume of the compact with a molten metal, the first separate volume of the compact being infiltrated with a metal having a higher melting point than the metal which infiltrates the second separate volume and forms an interface with the first infiltrated metal.

Method of prepairing porous ceramic structures by firing a polyurethane foam that is impregnated with inorganic material

Abstract: The invention disclosed is for ceramic foam structures prepared by reacting an isocyanate capped polyoxyethylene polyol reactant with large amounts of an aqueous reactant containing finely divided sinterable ceramic material. The resultant foams having the sinterable ceramic material dispersed thereon are heat treated to decompose the carrier foam under firing conditions which sinter the ceramic particles resulting in a rigid ceramic foam structure.

Hot pressed silicon carbide

Abstract: A dense silicon carbide having improved properties is disclosed which is prepared by the addition of a carbonaceous additive to a boron doped silicon carbide and hot pressing the mixture at a sufficient temperature and pressure whereby a dense substantially nonporous ceramic is formed.

The Strength of Glass

Abstract: The search for new high strength materials has always been one of the more active areas in the materials sciences, and while glass is not normally catagorized with high strength metallic alloys and crystalline ceramics, it does have particular properties which will warrant, or necessitate, its use in many new applications.

Development of ceramic and ceramic composite devices for maxillofacial applications

Abstract: Ceramic and ceramic composite materials and devices were developed for specific maxillofacial applications. These applications included: (1) Replacement of hard tissue voids in low stress areas with a phosphate-bonded alumina-foamed ceramic and a calcium aluminate-bonded alumina foam; (2) development of porous ceramic-coated metallic devices for stabilization of mandibles with avulsed segments; (3) development of implantable ceramic tooth roots onto which more or less conventional crowns may be mounted. Efforts to date have been rewarding. Using the rhesus monkey for all experimental implant work, incorporation of porous ceramic foam prostheses to eliminate maxillary defects has been accomplished. Also, we have succeeded in stabilizing the mandible where segments of from 3 to 8 mm were removed. Bridging of the gap with new bone occurred within 6 weeks resulting in a total regeneration of the resected area with restoration of normal mandibular function. Finally, implantable tooth roots were developed. Three different surface treatment techniques have been used on a basic high-density alumina core. The first is a high-density matt finish which can only permit a fibrous tissue attachment or bony approximation but no ingrowth. The second is a porous alumina coating intended to permit bone ingrowth. The third is a rough surface consisting of particles of alumina sintered to the surface to maximize the bone/ceramic interface shear strength potential. Implantations of both anterior and posterior tooth roots with all three surface configurations have been successful for periods of up to six months.

Ceramic-metal reaction welding

Abstract: In bonding ceramic oxides to metals, two reaction mechanisms have been utilized. These are (1) a surface or microscopic reaction, between close-packed ceramic oxides, quartz, and glasses and the noble metals (e.g. Pt, Pd, Au, Ag), maintaining a sharp discontinuity at the interface, (2) a bulk or macroscopic reaction between the same oxides and other transition metals (e.g. Fe, Co, Ni) producing a diffusional type interface. Both have common reaction conditions and occur: (a) below the melting point of the lowest melting component, (b) in any atmosphere compatible with all components at the operating temperature, (c) under little or no pressure, and (d) without deformation.

Production of porous ceramic materials

Abstract: Porous ceramic materials are made by impregnating a foam with a slurry of finely divided ceramic material, drying and firing the foam. Prior to impregnating the foam it is treated so that the particulate material of the slurry will adhere to the foam.

Electrical elements operable as thermisters, varisters, smoke and moisture detectors, and methods for making the same

Abstract: Electrical elements comprising a metal substrate, a ceramic semiconductor applied thereon and an outer conductive coating. The metal substrate may be a ferrous metal, preferably stainless steel, and may also be a non-ferrous metal, such as aluminum. A bonding agent, such as nickel aluminide is applied to ferrous metal substrates by plasma spraying. The ceramic semiconductor material is also applied to the metal substrate by plasma spraying, and the preferred ceramic semiconductor material for use with a ferrous metal substrate is aluminia titania. The ceramic semiconductor material is coated with a plasma sprayed conductive layer of copper-glass frit to which terminals may be easily soldered. In one configuration, the metal substrate is a long thin rod and the bonding agent, ceramic semiconductor, and copper-glass frit are applied thereto to form cylindrical coatings. Smaller elements are made by cutting the coated rod into short lengths. One terminal is soldered to the copper-glass frit, and the other terminal is the central wire. This configuration displays some polarity. A second configuration comprises grinding away strips of the copper-glass frit wherein two isolated terminals may be attached thereto. The resultant electrical element has the characteristics of a resistance drop in response to either an increase in temperature or humidity, and may be included in a resistance-sensitive alarm circuit. It is desirable to coat electrical elements used as temperature sensors with a water proof coating, so that they do not respond to changes in humidity.

Manufacture of porous ceramic materials

Abstract: Permeable ceramic structures are made by impregnating an organic foam with a slurry of finely divided ceramic material, the slurry containing a high concentration of anti-foaming agent, and drying and firing the so-impregnated foam.

Method for prestressing a body of ceramic material

Abstract: Thermal prestressing methods using unit and selective heating of tendons incorporated in a ceramic or cermet body to selectively elongate the tendon with respect to the body and soften the latter. Upon cooling an anchorage bond is formed between the body and the ends of the tendons, which bond develops a tension in the tendon and prestress in the body upon further cooling. Bodies are also prestressed by forming a bond between the tendon and the body and then heating the body in use so as to elongate the tendon relative to the body, the tendon having a greater coefficient of expansion than the material of the body.

Ion Scattering Spectrometry

Abstract: A sensitive method of surface composition analysis is obtained through monitoring the binary scattering of low energy noble gas ions from surface atoms. Such analyses have been shown to be accomplished with simplified instrumentation and to be primarily sensitive to the first atomic surface layer. The technique has been extended to include the direct examination of electrically insulating surfaces, and examples of surface compositions obtained from ceramic and glass will be presented. With the capability of examining surfaces irrespective of their electrical conductivity, multilayer thin film structures become a prime example of the dual utilization of the probe ion beam to both analyze and simultaneously controllably remove surface atoms. Such a depth composition profile will be shown for a TiO2 thin film sandwich in which interface contamination was found. Quantitative aspects of the technique will be shown in the SiOx system. Diverse applications of surface analyses will also be shown on metal, semicon...

Preparation and Properties of Pyrolysis of Vanadium Oxide Films

Abstract: Vanadium oxide films (, , ) were obtained by the pyrolysis of vanadium acetylacetonate in controlled atmosphere. The influence of deposition parameters on the film composition is studied. It was revealed that the composition of the gas carrier is the main factor determining the film composition. Electron diffraction and electron microscopy analysis of films are carried out. Temperature dependence of resistance was studied. films deposited on glazed ceramic and sapphire change resistance by factor 103 at about 340°K. films had an activated conductivity.

A Study of the Mechanisms of Cermet Electrodeposition

Abstract: SummaryThe paper describes work on the mechanism by which solid ceramic particles are transferred from suspension in a plating electrolyte and occluded in a cathodic metal electrodeposit. Investigation was mainly on the system silicon carbide/copper, the copper bath being acid sulphate. The changes of the electrokinetic (zeta) potential with electrolyte concentration and composition were studied by a streaming potential method: it was found that the change of zeta potential with electrolyte concentration was an ionic strength effect, and was not specific-ion dependent. Deposition experiments were carried out to show the distribution of ceramic in the metal matrix: this was found to be related to the surface roughness, being highest where the surface was most rough and irregular. The mechanism of transport is seen to be a combination of hydrodynamic transport of particle to the cathode surface (followed possibly by electrophoretic transport through the double layer) and subsequent attachment and mechanical...

Ceramic tile panel construction

Abstract: A prefabricated ceramic tile building panel includes a pre-grouted sheet of ceramic tile and a layer of rigid plastic foam. The plastic is foamed in place on the tile sheet to provide a unitary, light weight, self supporting, water proof panel. For additional strength, a fiber-reinforced paper backing sheet is provided along the rear surface of the foam layer. A novel panel mounting arrangement permits the rapid installation of the prefabricated panels by those unskilled in tile installation.

Characteristics of rf Sputtered Barium Titanate Films on Silicon

Abstract: The physical and electrical properties of barium titanate films approximately 1 μm thick, prepared by rf sputtering onto silicon substrates in both pure argon and 95% argon–5% oxygen glow discharges were investigated. The argon-oxygen mixture was used to minimize oxygen deficiencies in the films resulting from the possible decomposition of the barium titanate in the glow discharge. Sputtering was carried out in a standard diode system with a water-cooled target of ceramic BaTiO3 at power densities of up to 1.6 W/cm2, at a gas pressure of 7–8×10−3 Torr, and in a magnetic field of 20 G. The substrate holder could be heated to about 650°C during deposition. The deposition rate was typically 100 A/min and was dependent on the sputtering power density and the substrate temperature. The films were deposited on clean n-type silicon wafers of approximately 5 and 0.01 Ω⋅cm resistivity. Some samples were subjected to a post-deposition heat treatment in nitrogen or oxygen ambients at 1000°C. The deposition rate, cry...