Showing papers on "Ceramic published in 1976"
TL;DR: In this article, the nonlinear relationship between current and voltage in the zinc oxide varistor arises from electrical barriers at the grain boundaries in the polycrystalline ceramic, with Schottky emission becoming more important as the field increases and assists in lowering the barrier.
Abstract: The nonlinear relationship between current and voltage in the zinc oxide varistor arises from electrical barriers at the grain boundaries in the polycrystalline ceramic. At very low fields, thermionic emission accounts for the majority of the current, with Schottky emission becoming more important as the field increases and assists in lowering the barrier. Tunneling through the barrier dominates in the presence of high fields, giving the highly nonlinear behavior. The bismuth (oxide) which segregates at the grain boundries occurs in two forms: an adsorbed layer present on the interfaces between grains, and a discrete phase which is continuous along grain edges. The latter is in the form of triangular prisms which exhibit a dihedral angle of about 60° as they approach a ZnO–ZnO interface, and thus this phase does not completely wet the ZnO grains. The adsorbed layer can account for the electrical barrier. Its chemical thickness is less than 50 A as determined by Auger electron analysis. A depletion layer i...
200 citations
TL;DR: In this paper, a range of property values that are useful for evaluating range of applicability of low-atom ceramics materials is presented, including carbon, SiC, Be2C, B4C, TiC, Al2O3, and BeO.
Abstract: The (low-atomic-number ceramic) materials carbon, SiC, Be2C, B4C, TiC, BN, Si3N4, Al2O3, and BeO provide a range of property values that are useful for evaluating range of applicability of low-atom...
160 citations
Patent•
22 Apr 1976TL;DR: In this article, a method of making a dense silicon carbide ceramic is disclosed involving the steps of homogeneously dispersing silicon carbides with a sufficient amount of a boron containing additive and a carbonaceous additive, forming the powder mixture into a shaped green body and then sintering the body in a controlled atmosphere and in the absence of external pressure at a temperature of about 1900°-2100° C.
Abstract: A method of making a dense silicon carbide ceramic is disclosed involving the steps of homogeneously dispersing silicon carbide with a sufficient amount of a boron containing additive and a carbonaceous additive, forming the powder mixture into a shaped green body and then sintering the body in a controlled atmosphere and in the absence of external pressure at a temperature of about 1900°-2100° C. such that density of the body is at least 85% of the theoretical density of silicon carbide. The complex shaped silicon carbide product formed thereby is also disclosed.
114 citations
107 citations
TL;DR: In this paper, the effect of matrix microcracking on the mechanical and thermal stability of reinforced-ceramic composites is evaluated, and it is concluded that, although the potential applications of such materials are extremely diverse, several important aspects, particularly the effect that matrix micro-cracking may have on the structural stability, must be fully evaluated before ceramic-matrix composites can seriously be considered as useful replacements for more conventional materials.
Abstract: Ceramic materials often exhibit a combination of useful physical and mechanical properties, including high refractoriness, but their applications are restricted due to their brittle behaviour; in an attempt to improve the strength, and particularly the toughness, of brittle ceramics particle-strengthening and fibre-reinforcement have been utilized, with limited success. The factors which affect the mechanical properties of these composite systems are discussed, and the various experimental systems that have been investigated are reviewed. It is concluded that, although the potential applications of such materials are extremely diverse, several important aspects, particularly the effect that matrix microcracking may have on the mechanical and thermal stability of reinforced-ceramic systems, must be fully evaluated before ceramic-matrix composites can seriously be considered as useful replacements for more conventional materials.
106 citations
TL;DR: In this paper, the corrosion behavior of sintered SiC in gaseous environments and alkaline melts was investigated at 900°C, where SiC formed a dense coherent surface film of SiO2 which was not corroded by thin layers of condensed sodium sulfate.
Abstract: The corrosion behavior of sintered SiC in gaseous environments and alkaline melts was investigated at 900°C. In oxidizing atmospheres such as normally exist in a gas turbine, SiC forms a dense coherent surface film of SiO2 which is not corroded by thin layers of condensed sodium sulfate. However, under some conditions, especially when very low oxygen pressures are maintained at the SiC surface or when basic salt melts or slags containing carbonaceous material are present, rapid corrosion of the ceramic can occur. On the other hand, SiC is inert in pure N2, H2, or H2-H2S mixtures at 900°C. These different modes of behavior are discussed in the context of possible high- temperature applications of SiC ceramics.
83 citations
72 citations
Patent•
04 Mar 1976
TL;DR: This ceramic composition is produced from a mixture of yttrium oxide and heavy rare earth oxides having an atomic number of from 64-71 in selected proportions for the construction of crucibles and the lining of molds employed in making castings of reactive metals such as titanium and alloys thereof.
Abstract: This ceramic composition is produced from a mixture of yttrium oxide and heavy rare earth oxides having an atomic number of from 64-71 in selected proportions for the construction of crucibles and the lining of molds employed in making castings of reactive metals, such as titanium and alloys thereof. The elements utilized in the composition impart a minimum of contamination to the molten metal during the melting and casting phases and are produced from an ore with only the refinement steps necessary so as to secure maximum economy and yet insure the production of castings of the highest quality.
71 citations
Patent•
IBM1
TL;DR: In this article, a method for manufacturing a multilayer ceramic which is particularly suitable for carrying semiconductor chips was proposed, which involves depositing a particulate mixture containing a metal and the metal's oxide in a ratio of between 1:1 to 9:1 in a pattern on at least a portion of the plurality of ceramic layers.
Abstract: A method for manufacturing a multilayer ceramic which is particularly suitable for carrying semiconductor chips. In order to join a semiconductor chip to a multilayer ceramic substrate, it is necessary that the projected site for the semiconductor chip be substantially flat. If there is a bulge, it becomes difficult to make a good joint thereto. The method involves depositing a particulate mixture containing a metal and the metal's oxide in a ratio of between 1:1 to 9:1 in a pattern on at least a portion of the plurality of ceramic layers. The patterns are then dried. The plurality of substrates or layers of ceramic are then laminated under substantial pressure and fired at an elevated temperature. The addition of the metal oxide to the metal powder allows the shrinkage of the metallization compound so that it may more nearly match that of the ceramic it is coated upon during the firing step. This matching of the shrinkage during firing prevents cracking of the ceramic.
71 citations
Patent•
15 Apr 1976TL;DR: In this paper, an inner ceramic layer, an outer metal layer and an intermediate interface layer of a low modulus metallic low density structure having a high melting point are secured by an intermediate ceramic-metal composite.
Abstract: A ceramic-metal composite laminate capable of exposure to high temperature differentials without damage, consisting of an inner ceramic layer, an outer metal layer and an intermediate interface layer of a low modulus metallic low density structure having a high melting point. The ceramic layer is secured to the low modulus structure directly or through an intermediate ceramic-metal composite, and the outer metal layer is brazed to the intermediate low modulus layer. Thermal strains caused by a temperature differential between the inner and outer layers are taken up without harmful effect by the intermediate low modulus layer.
70 citations
Patent•
13 Dec 1976
TL;DR: In this paper, continuous silicon carbide fibers composed of aluminum, aluminum alloy or magnesium alloy matrix were used to construct a light metal composite materials reinforced with continuous silicon carbonide fibers.
Abstract: Light metal composite materials reinforced with novel continuous silicon carbide fibers composed of aluminum, aluminum alloy or magnesium alloy matrix and the continuous silicon carbide fibers containing 0.01-40% by weight of free carbon, in which the free carbon is reacted with aluminum or added metal elements in the aluminum alloy or magnesium alloy to form carbides. When the silicon carbide fibers are coated with a metal or ceramics, the wettability of the silicon carbide fibers to said matrix is more improved.
TL;DR: In this article, high-frequency, 106≲f≲2×109 Hz, impedance measurements on ZnO-based ceramic varistors are described and compared with estimates of ρg from high-current (J≳103 A/cm2) data.
Abstract: High‐frequency, 106≲f≲2×109 Hz, impedance measurements on ZnO‐based ceramic varistors are described. Our studies indicate that the ZnO grain resistivity ρg is less than 1 Ω cm for GE‐MOVR varistors at room temperature. The high‐frequency measurements are compared with estimates of ρg from high‐current (J≳103 A/cm2) data and the difference observed is explained in terms of the varistor ceramic microstructure.
Patent•
26 Jan 1976
TL;DR: In this article, a layer of ceramic having completely imbedded therein a metal grid is described, which is used as a liner for a metal wall which is cast with the liner in situ and is disclosed as having a hollow shape about which the cast wall extends in a manner having particular utility for insulated components of internal combustion engines.
Abstract: The composite of the present invention comprises a layer of ceramic having completely imbedded therein a metal grid, such composite having been made by coating a metal grid with a viscous ceramic slurry and thereafter firing to form the ceramic to a unitary structure At the temperature to which the composite is fired to form the unitary structure the metal grid is in an expanded condition because of its high coefficient of thermal expansion, and upon cooling the metal grid is put into tension thereby putting the ceramic in compression The composite is used as a liner for a metal wall which is cast with the liner in situ and is disclosed as having a hollow shape about which the cast wall extends in a manner having particular utility for insulated components of internal combustion engines
Patent•
22 Sep 1976
TL;DR: The electroconductive composite ceramics as mentioned in this paper are composed of an independent phase conglomerates having a particle diameter of at least 20μ and a continuous phase connecting mutually the independent phase of conglomerates.
Abstract: The electroconductive composite ceramics composed of an independent phase conglomerates having a particle diameter of at least 20μ and a continuous phase connecting mutually the independent phase of conglomerates. Particularly, electroconductive composite ceramics composed of (A) 50-98% by weight of an independent phase of conglomerates having a particle diameter of at least 20 which consists essentially of a phase of insulating or semiconductive ceramics having a high melting point or a mixture thereof and (B) 50-2% by weight of a continuous phase of an electroconductive substance connecting mutually the independent phase of conglomerates. The electroconductive composite ceramics exhibit stable electroconductivity-temperature characteristics at a temperature of 1000° C. or higher and have excellent thermal shock resistance, mechanical strength and chemical resistance.
TL;DR: In this paper, the correlation of physical ferroelectric properties of polycrystalline materials and their many applications is discussed, and the materials discussed here are all oxides based on BaTiO3 and Pb(Ti, Zr)O3 with perovskite structure.
Abstract: During the last few years ferroelectric ceramics have attained increasing importance as materials for electronic devices. Present world production of such devices is more than 1010 per year. Since the suitability of these materials is due to their ferroelectric nature, this paper will mainly discuss the correlation of their physical ferroelectric behaviour and their many applications.As compared to single crystalline materials, polycrystalline ceramics are preferred firstly because of their lower cost and secondly because of the possibility of preparing doped mixed crystals of almost any composition with optimum properties. On the other hand certain disadvantages are present in ceramics: the physical effects in single crystals can only partially be exploited in ceramics. Furthermore ceramics suffer from characteristic instabilities.The materials discussed here are all oxides based on BaTiO3 and Pb(Ti, Zr)O3 with perovskite structure. The large variation of their physical properties, which is very convenie...
Patent•
29 Jan 1976
TL;DR: Si 3 N 4 ceramics exhibiting densities and modulus of rupture values heretofore obtainable only by hot pressing are produced by pressureless sintering of powder compacts of partly amorphours, partly crystalline Si 3 n 4 powder containing between 5 and 60 percent by weight of crystalline material as mentioned in this paper.
Abstract: Si 3 N 4 ceramics exhibiting densities and modulus of rupture values heretofore obtainable only by hot pressing are produced by pressureless sintering of powder compacts of partly amorphours, partly crystalline Si 3 N 4 powder containing between 5 and 60 percent by weight of crystalline material.
Patent•
27 Dec 1976
TL;DR: A process for the production of ceramic-metal assemblies which are joined by a graded layer of a metal-ceramic mixture is described in this article, where the effect of the processing sequence is to vary the prestress between the metal and ceramic components.
Abstract: A process for the production of ceramic-metal assemblies which are joined by a graded layer of a metal-ceramic mixture is described. The effect of the processing sequence is to vary the prestress between the metal and ceramic components. The assemblies are produced by heating at elevated temperatures and the process of the invention involves preferential cooling of the metal portion of the assembly.
TL;DR: In this paper, the results of a collaborative study of the ferroelectric-ferroelectric transition in rhombohedral lead zirconate-titanate are described.
Abstract: The results of a collaborative study of the ferroelectric-ferroelectric transition in rhombohedral lead zirconate-titanate are described. Firstly, experimental evidence for the first-order nature of the transition is given together with an explanation of this in pure single crystals. Secondly, the use of bismuth-doped ceramic material in pyro-electric detection is discussed. By applying an electric field on the cooling cycle, thermal hysteresis can be reduced to a minimum.
TL;DR: Ionic conductivity measurements on LiAlSiO/sub 4/ glass and glass-ceramic showed these materials to be good lithium ion conducting solid electrolytes at high temperatures as discussed by the authors.
Abstract: Ionic conductivity measurements on LiAlSiO/sub 4/ glass and glass-ceramic showed these materials to be good lithium ion conducting solid electrolytes at high temperatures This composition crystallizes in the beta-eucryptite structure which is attractive for solid electrolyte applications because of its low thermal expansion The glasses were prepared by quenching from the melt and were annealed to remove strain The glass-ceramic (beta-eucryptite) samples were crystallized (aided by TiO/sub 2/ and ZrO/sub 2/ nucleating agents) by using a heat treatment determined through differential thermal analysis The conductivity (sigma) was measured (to 650/sup 0/C) with a variety of techniques, including 2-terminal ac, 3-terminal guarded ac, 4-terminal ac, 2-terminal dc, and a pulsed method Vapor-deposited Cr contacts were used Different sample geometries, contact geometries, and measurement circuitries were employed All results are in excellent agreement, and the a-c techniques appear to be the most versatile and accurate of the methods examined In these materials the conductivity is thermally activated (sigma = sigma/sub 0/e/sup -E/kT/) with typical values of sigma/sub 0/ = 19 x 10/sup 2/ (ohm-cm)/sup -1/ and E approximately 068 eV for the glasses, and sigma/sub 0/ = 21 x 10/sup 4/ (ohm-cm)/sup -1/ and E approximately 105 eV for the glass-ceramics Themore » TiO/sub 2/ and ZrO/sub 2/ nucleating agents (concentrations up to 28 mole percent) did not appear to influence the ionic conductivity Data were also taken on a (beta-eucryptite) glass-ceramic with a composition near the beta-eucryptite/beta-spodumene phase boundary The ionic conductivity of this material is lower than that of the LiAlSiO/sub 4/ materials Data are also provided on beta-spodumene material 8 figures, 35 references (auth)« less
TL;DR: In this paper, a 2-SCR-3-diode controlled bridge was used as a 2hp dc motor speed control for a 2.5-DOF DC motor.
Abstract: A new technique of bonding copper directly to ceramic, employing the copper-copper oxide eutectic melt, is described. Scanning electron micrographs (SEM) and EDAX are used to study the details of this bond. A specific utilization of these techniques is portrayed in a 2-SCR-3-diode controlled bridge. This bridge is used as a 2-hp dc motor speed control. The advantages of using these techniques over previous methods (thick film or moly-manganese) lie in the ability to bond almost any thickness of high-conductivity copper to ceramics (Al 2 O 3 , BeO, BN, ZnO, etc.) silica, dissimilar metals, or to copper itself. Incidental benefits, described in the report, include bonding copper lead frames instead of screen printing, lack of high thermal and electrical resistivity interface layers, and simplicity of manufacture. Ceramic properties found to influence bond quality were: 1) Topology in terms of a fractured surface due to lapping and/or die sticking. 2) Degree of intergranular bond strength. 3) Cleanliness of surface and degree of unbonded particulate matter (powder) on the surface. 4) Grain size. The bonding agent is characterized as a field of bonded Cu 2 O nodules precipitated from the Cu-Cu 2 O eutectic melt with a density much higher than expected from the 4.7-percent Cu 2 O (by volume) contained in the eutectic mixture. Mechanisms to explain this behavior are described. The bond strength is noted to depend on the nodule density and the bond strength of the Cu 2 O to copper and is higher than any other bonding method.
TL;DR: Raman spectra of powdered samples of tungsten trioxide have been obtained over the temperature range 80-300 K as discussed by the authors. But no discontinuous or major changes in the spectra are observed, indicating that the transition at 233 K to the ferroelectric phase is inhibited for this form of sample, presumably because of perturbations to the long range electrostatic forces.
Abstract: Raman spectra of powdered samples of tungsten trioxide have been obtained over the temperature range 80–300 K. No discontinuous or major changes in the spectra are observed, indicating that the transition at 233 K to the ferroelectric phase is inhibited for this form of sample, presumably because of perturbations to the long range electrostatic forces.
Patent•
06 Jul 1976
TL;DR: In this paper, a process for the preparation of a metallic and metal-ceramic and/or ceramic sponge with a three-dimensional cellular structure of filiform morphology, starting from a plastic sponge, which has been preliminarily metallized while maintaining substantially unaltered the initial geometrical shape.
Abstract: A process is disclosed for the preparation of a metallic and/or metal-ceramic and/or ceramic sponge with a three-dimensional cellular structure of filiform morphology, starting from a plastic sponge with a three-dimensional cellular structure of filiform morphology, which has been preliminarily metallized while maintaining substantially unaltered the initial geometrical shape, said process being characterized in that said metallized sponge is coated with a metallic and/or metal-ceramic and/or ceramic material, the coating with said metallic and/or metal-ceramic material being carried out by molten-spray deposition, galvanic co-deposition, evaporation under vacuum, or reactive sputtering, while the coating with the ceramic material is carried out by molten-spray deposition, reactive sputtering or chemical vapor deposition. The starting plastic sponge is foamed polyurethane preferably having a number of pores not exceeding 30 pores/inch, and a thickness not exceeding 25 mm. The metal-ceramic material consists essentially of one or more metal components selected from the class consisting of chromium and nickel associated with one or more ceramic compounds selected from the class consisting of Al2 O3, MgO, ZrO2 and Cr3 C2, and the ceramic material is selected from the class consisting of ZrO2, Al2 O3, MgO.Al2 O3, 3Al2 O3.2SiO2, CaZrO3, MgZrO3, WC, TaC, MoC, TiC, ZrC and Cr3 C2. The sponges per se as well as supporting structures for catalysts in heterogenous catalytic processes are also claimed.
Patent•
02 Sep 1976TL;DR: In this article, a sintered mixture of a main component consisting essentially of chromium oxide and at least one metal oxide selected from the group consisting of BeO, MgO, CaO, SrO, BaO, FeO, NiO, CuO, ZnO, CdO and PbO is obtained by sintering a mixture having the above composition with a glass frit binder.
Abstract: Humidity sensitive ceramic resistor having a high humidity activity, a low electrical resistance and a high stability with respect to time, temperature, humidity and electric load and suited for use in humidity-controlling devices is provided by a sintered mixture of a main component, which consists essentially of chromium oxide and at least one metal oxide selected from the group consisting of TiO 2 , ZrO 2 , HfO 2 , SnO 2 , Nb 2 O 5 , Ta 2 O 5 , WO 3 , MnO 2 , MoO 2 , CeO 2 , DyO 2 , VO 2 , SiO 2 and GeO 2 , and an addition of at least one metal oxide selected from the group consisting of BeO, MgO, CaO, SrO, BaO, FeO, NiO, CuO, ZnO, CdO and PbO. Furthermore, humidity sensitive thin layer ceramic resistor having an improved quick response to humidity is obtained by sintering a mixture having the above composition with a glass frit binder.
01 Sep 1976
TL;DR: In this paper, thermal barrier ceramic coatings of stabilized zirconia over a bond coat of Ni Cr Al Y were tested for durability on air cooled turbine rotor blades in a research turbojet engine.
Abstract: Thermal barrier ceramic coatings of stabilized zirconia over a bond coat of Ni Cr Al Y were tested for durability on air cooled turbine rotor blades in a research turbojet engine. Zirconia stabilized with either yttria, magnesia, or calcia was investigated. On the basis of durability and processing cost, the yttria stabilized zirconia was considered the best of the three coatings investigated.
TL;DR: In this paper, a theoretical analysis is performed to determine the intrinsic variables which affect the green strength of ideal dry bodies held together by organic binders, including types of bonds formed, the amount of binder, the density of the ceramic, the packing density, and the cohesive or adhesive strength of the binder.
Abstract: A theoretical analysis is performed to determine the intrinsic variables which affect the green strength of ideal dry bodies held together by organic binders. The parameters which influence strength (i.e. types of bonds formed, the amount of binder, the density of the ceramic, the packing density, and the cohesive or adhesive strength of the binder) are determined.
Patent•
18 Oct 1976
TL;DR: In this article, a heat-resistant composite material reinforced with continuous silicon carbide fibers is produced by forming a powdery ceramics matrix and the fibers into a composite, and pressing and heating the composite into a sintered composite.
Abstract: A heat-resistant composite material reinforced with continuous silicon carbide fibers is produced by forming a powdery ceramics matrix and the fibers into a composite, and pressing and heating the composite into a sintered composite. The composite material is excellent in the mechanical strength at a high temperature, heat resistance, oxidation resistance and corrosion resistance.
Patent•
05 Apr 1976
TL;DR: In this article, a thermo-electric generator of the kind making use of beta alumina ceramic through which sodium is circulated to produce an electric potential between the two surfaces of the ceramic has the ceramic in the form of a tube closed at its upper end and with its open end extending into liquid sodium.
Abstract: A thermo-electric generator of the kind making use of beta alumina ceramic through which sodium is circulated to produce an electric potential between the two surfaces of the ceramic has the ceramic in the form of a tube closed at its upper end and with its open end extending into liquid sodium. A heat pipe extends into the ceramic tube and there is an external tubular casing around the ceramic tube forming a closed structure for housing sodium in liquid and vapor form both inside and outside the ceramic tube. The heat pipe may be arranged either as a heat source or heat sink for the sodium inside the ceramic tube, the housing forming the heat sink in the former case of the heat source in the latter. The ceramic tube may, at its open end, be sealed to the housing and a pump used for pumping the sodium from the cold face to the hot face of the ceramic or capillary means may be used to circulate the sodium.
Patent•
05 Apr 1976TL;DR: In this article, an inner ceramic layer, an outer metal layer and an intermediate interface layer of a low modulus metallic low density structure having a high melting point are secured by an intermediate ceramic-metal composite.
Abstract: A ceramic-metal composite laminate capable of exposure to high temperature differentials without damage, consisting of an inner ceramic layer, an outer metal layer and an intermediate interface layer of a low modulus metallic low density structure having a high melting point. The ceramic layer is secured to the low modulus structure directly or through an intermediate ceramic-metal composite, and the outer metal layer is brazed to the intermediate low modulus layer. Thermal strains caused by a temperature differential between the inner and outer layers are taken up without harmful effect by the intermediate low modulus layer.
TL;DR: In this paper, the variation of a number of physical properties of a glass-ceramic composition as a function of the crystallization heat-treatment temperature are reported, including mechanical strength, modulus of elasticity, electrical properties and linear coefficient of thermal expansion.
Abstract: The variation of a number of physical properties of a glass-ceramic composition as a function of the crystallization heat-treatment temperature are reported. The properties studied include mechanical strength, modulus of elasticity, electrical properties and linear coefficient of thermal expansion. It is shown that several of the properties are dependent on microstructural effects. This dependence is especially marked for modulus of rupture and is also apparent for electrical properties such as conductivity and loss tangent. For the latter, however, compositional changes in the residual glass phase also exert a significant influence. For other properties, such as indentation hardness, the microstructural dependence is less well defined.