Showing papers on "Sintering published in 1978"

A sintered magnetoelectric composite material BaTiO3-Ni(Co, Mn) Fe2O4

Abstract: Magnetoelectric composite materials have been made by sintering a mixture of a piezoelectric and piezomagnetic phase. This paper deals with the preparation and some properties of the combination BaTiO3-Ni(Co, Mn)Fe2O4, and investigates the influence of the cooling rate after sintering, TiO2 additions, the mole ratio of both phases and the crystallite size of the grains of both phases on some physical properties of the composite material. The maximum value of the conversion factor (δE/δH)max found for this material up till now is about 80 mV cm−1 Oe−1.

Processing of crystalline ceramics

Abstract: Keynote Address.- Some Considerations in the State of the Art in Processing Crystalline Ceramics.- I: Fine Particle Science, Technology and Characterization.- Physical and Chemical Parameters Controlling the Homogeneity of Fine Grained Powders and Sintering Materials.- Ultrafine Powders of Oxide and Non-Oxide Ceramic Materials and Their Sinterability.- Handling and Green Forming of Fine Powders.- The Potential of Fine Particle Technology Applied to Ceramic Raw Materials.- Particle Size and Permeability in Slip Casting.- Chemical Processing for Ceramics (and Polymers).- Ceramics Sintered Directly from Sol-Gels.- Characterization of Ceramic Microprocessing.- Packing and Sintering Relations for Binary Powders.- Stress and Density Distributions in the Compaction of Powders.- Pore Morphography in Ceramic Processing.- II: Solid State Sintering and Grain Growth.- Fundamentals of the Sintering of Ceramics.- Current Paradigms in Powder Processing.- Some Effects of Aggregates and Agglomerates in the Fabrication of Fine Grained Ceramics.- The Sintering of Conductive Rutile: A Model System for Sintering Electronic Ceramics.- Sintering of Mullite.- Rate Controlled Sintering as a Processing Method.- A Multiple-Lognormal Model of a Normal Grain Growth.- III: Liquid Phase Sintering And Post-Firing Technology.- Rearrangement During Liquid Phase Sintering of Ceramics.- Reactivity of Alumina Substrates with High Lead Glasses.- Influence of the Processing Parameters on the Properties of Rapid Fired Porcelain.- Strengthening of Lime-Stabilized Zirconia by Post Sintering Heat Treatments.- Strain and Surface Energy Effects in Ceramic Processes.- Dynamic and Material Parameters in Brittle Fracture in Ceramics.- Processing Induced Sources of Mechanical Failure in Ceramics.- IV: Dielectric and Magnetic Ceramics.- Processing of High Density Piezoelectric Ceramic Compositions.- The Role of ZrO2 Powders in Microstructural Development of PZT Ceramics.- Novel Uses of Gravimetry in the Processing of Crystalline Ceramics.- Deformation Processing of Magnetic Hexaferrites for Hc Maximization Through Grain Growth Control.- Processing and Magnetic Properties of Low-Loss and High-Stability Mn-Zn Ferrites.- Relationship Between Processing Conditions, Oxygen Stoichiometry and Strength of MnZn Ferrites.- Sintering of High Density Ferrites.- V: Energy Related Ceramics I: Fast Ion Conductors MHD, Nuclear and Refractory Ceramics.- Processing and Characterization of Polycrystalline ?"-Alumina Ceramic Electrolytes.- Microstructural Control During Sintering of ?"-Alumina Compositions Through Ceramic Processing Modification.- Transient Eutectics in Sintering of Sodium Beta Alumina.- Microstructural Evolution During the Processing of Sodium ?-Alumina.- Fabrication and Performance of MHD Electrodes.- Fabrication and Property Control of LaCrO3 Based Oxides.- Strontium Containing Perovskites and Related Conductive Electronic Ceramics.- Hot Pressed Composite Ceramic MHD Electrode Development.- Processing Variables Affecting the Thermomechanical Degradation of Monolithic Refractory Concretes.- UO2-Gd2O3 Sintering Behavior.- Processing Requirements for Property Optimization of EU2O3-W Cermets for Fast Reactor Neutron Absorber Applications.- Ceramic Processing of Boron Nitride Insulators.- VI: Energy Related Ceramics II: Non-Oxide Ceramics.- Grain Boundary Engineering in Non-Oxide Ceramics.- The Fabrication of Dense Nitrogen Ceramics.- Ceramics in the Si-Al-O-N System Fabricated by Conventional Powder Processing and Sintering Techniques.- Polytypism in Magnesium Sialons.- Dense Silicon Nitride Ceramics: Fabrication and Interrelations with Properties.- High-Pressure Hot-Pressing of Silicon Nitride Powders.- The Structure of Grain Boundaries in Silicon Nitride Based Alloys.- Evolution of Microstructure in Polycrystalline Silicon Carbide.- Thermal Gradient Deposition of SiC Diffusion Tracers.- Contributors.

Crystal Phases of Nonohmic Zinc Oxide Ceramics

Abstract: The crystal phases of nonohmic ZnO ceramics, having Bi2O3, Sb2O3, Co2O3, MnO2 and Cr2O3 as additives, have been investigated by classifying and clarifying them as a function of the amounts of the additives and sintering temperature, and synthesizing their single phases. These ceramics consist of ZnO phase dissolving Co and Mn components, spinel phase of Zn7Sb2O12 dissolving Co, Mn and Cr components, and Bi-rich phases (B, C, D or B'). The B-phase is a δ-Bi2O3 type phase (a=5.59 A) having a fundamental composition of 12Bi2O3Cr2O3. The C-phase is a tetragonal phase (a=7.76 A, c=5.75 A) having a fundamental composition of 14Bi2O3Cr2O3. The D-phase is a β-Bi2O3 type tetragonal phase (a=10.93 A, c=5.62 A) dissolving a large amount of Zn component and a small amount of Sb component. The B'-phase is also a δ-Bi2O3 type phase (a=5.48 A) formed in the system Bi2O3–ZnO–Sb2O3. A solid solution between B and B'-is formed. The nonohmic property of ZnO ceramics is improved with the changes of phases, B→C→D or D+B', by raising the sintering temperature. The extinction of the nonohmic property caused by the change in the amounts of additives and sintering temperature corresponds to that of ZnO or Bi-rich phases in the ceramics.

Impurity-Induced Exaggerated Grain Growth in Mn-Zn Ferrites

Abstract: The effects of 20 oxide dopants on the microstructure development of Mn-Zn ferrite during sintering were investigated by diffusion-couple-like experiments. Nine oxides enhanced grain growth in ferrite; the effects of TiO2 dopant were studied in detail. The TiO2-induced exaggerated grain growth shows a parabolic time dependence, as was also true for the diffusion of Ti into ferrite as shown by X-ray spectrometry. For samples sintered at a given temperature but for different times, the Ti concentrations at the growth fronts of the exaggerated grains are identical. Exaggerated grain growth kinetics and Ti diffusivities have similar activation energies. Furthermore, the mobility of the exaggerated grains is reduced to that of the matrix grains after the TiO2 layer is removed, showing that the exaggerated grain growth is sustained by Ti diffusion into ferrite. Probable mechanisms for TiO2-promoted exaggerated grain growth are proposed. Some self-consistent arguments are presented for the observed effects of other dopants. Grain boundary mobilities of undoped Mn-Zn ferrite were measured and are in good agreement with those reported in the literature.

Coarsening of tungsten grains in liquid nickel-tungsten matrix

Abstract: In sintered W-Ni alloys with 1,7, and 30 wt pct Ni the tungsten grain growth in liquid matrix at 1540°C was investigated. The observed grain size distributions and growth rate are compared with the theoretical predictions of Wagner, Lifshitz and Slyozov, Lay, and Ardell. In the 70 pct W-30 pct Ni alloy the tungsten particles settled to the bottom of the specimens immediately upon melting of the matrix, but the spherical grain shape is maintained during the initial stage of annealing. In these specimens the linear intercept distribution of the grains agrees with the prediction of the LSW (Lifshitz, Slyozov, and Wagner) theory for the reaction controlled growth mechanism. On the other hand the growth rate appears to follow the t1/3 law predicted for the diffusion controlled mechanism. These results are consistent with Lay and Ardell's theory in which the concentration gradient around grains is inversely proportional to the average grain size in the limit of small matrix fraction. In the alloys with 1 and 7 pct Ni a meaningful comparison of the observed linear intercept distribution of the grains with theoretical predictions is difficult because of grain contact flattening due to densification. The grain growth is larger with less matrix fraction in the specimens and this result provides an evidence for the diffusion controlled grain growth during the liquid phase sintering of this alloy.

Simulation of spherical powder sintering by surface diffusion

Abstract: The surface diffusion-controlled sintering of monosized spheres is studied by a computer simulation process. The simulation is used to determine the variations in neck size and surface area as functions of both sintering time and powder packing density. Both morphology parameters are shown to be complex functions of the sintering time, contrary to numerous models. This work shows that the exponent method is not sufficient for identifying the dominant sintering mechanism.

Method for the manufacture of tools, machines or parts thereof by composite sintering

Abstract: Described herein is a method for the manufacture of materials such as tools, machines or parts thereof composed of at least two sections joined together by composite sintering from sintered alloys with an iron, nickel or cobalt base wherein at least two powdered metallic mixtures having differing metal carbide contents are separately prepared and poured, one after the other, into a mold and then formed into a pressed body; the pressed body is then sintered at the lowest temperature sufficient to cause alloy formation in the mixture having the lowest sintering temperature, and then hot-pressed to complete alloy formation in the pressed body and achieve maximum density

β'-Sialon sintered body and a method for manufacturing the same

Abstract: This invention provides a method for manufacturing said sintered body, comprising preparing a starting material by adding 10 to 1,000 wt. parts of metal silicon powder to 100 wt. parts of mixed powder composed of 20 to 80 wt. % silica powder and 80 to 20 wt. % aluminium powder and mixing said powders thoroughly, further adding, if required, a refractory fine powder of alumina, silicon nitride, aluminium nitride, β'-sialon, aluminium nitride polytype sialon, or silicon carbide, molding the resultant mixture into a green compact, and then sintering said green compact in a nitrogeneous nonoxidative gas atmosphere at a temperature of 1,200° to 1,550° C. This invention further provides a compact sintered body which will be prepared by the above mentioned method.

Strength improvement of cemented carbides by hot isostatic pressing (HIP)

Abstract: HIP treatment after sintering increases the strength of the investigated cemented carbide alloy by a factor of two whereas hardness, fracture toughness, and work of fracture remain unchanged. HIP does not affect the microstructural parameters of the carbide skeleton and the binder phase, but the residual pores are eliminated entirely. Failure of both the as-sintered and post-densified material occurs by a pure Griffith mechanism. The strength-flaw size relationship is established experimentally and is shown to obey exactly Griffith's basic strength equation. The strength is controlled by the largest microstructural defects, i.e. pores in the as-sintered material, and coarse WC grains and inclusions in the HIP-treated specimens.

Process for the production of dense sintered shaped articles of polycrystalline boron carbide by pressureless sintering

Abstract: A method of producing dense shaped articles of pure boron carbide that optionally contain 0.1 to 8% by weight of free carbon in the form of graphite is disclosed involving the steps of homogeneously mixing boron carbide in submicron powder form with small quantities of a carbon containing 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 2100°-2200° C. The shaped articles thus obtained are polycrystalline and, insofar as they correspond to the stoichiometric composition B 4 C, single-phase; they have an average grain size of not more than 10 μm, a density of at least 90% of the theoretical density of boron carbide and a flexural strength of at least 300 N/mm 2 . The fracture mode of the sintered articles is completely transcrystalline.

Heterodiffusion model for the activated sintering of molybdenum

Abstract: Sintering studies were conducted on a 2.2 μm Mo powder in the temperature range 1000–1350°C. The influence of thirteen transition metal additions on the sintering kinetics was determined by shrinkage measurements. On the basis of a grain boundary heterodiffusion model it is shown that Ni and Pd are the best sintering activators when present as coatings approximately 10 monolayers thick on the powder surface. Calculated activation energies are in reasonable agreement with the experimental values. In addition, the sintering of pure Mo was found to be controlled by a volume diffusion process with an apparent activation energy of 405 ± 20 kJ mol −1 .

Copper-boron carbide composite particle and method for its production

Abstract: A process for manufacturing radiation shield structures of the type consisting of neutron absorbing boron carbide particles embedded in a copper matrix The material comprises a multiplicity of particles comprising a core of boron carbide, a film of electroless copper bonded to the carbide, and a relatively thick electrodeposited copper layer bonded to the film The particles are then consolidated to produce shield structures by hot rolling or hot pressing, with or without sintering

Method of producing dense sintered silicon carbide body from polycarbosilane

Abstract: A method of producing a dense sintered silicon carbide body, which is high in flexural strength, purity and strength at an elevated temperature, from polycarbosilanes is disclosed. This method comprises the following steps of: A. polymerizing organosilicon compounds to obtain insoluble and unmeltable polycarbosilane of which the melting or softening temperature lies higher than its thermal decomposition temperature; B. grinding this insoluble and unmeltable polycarbosilane to powder; C. decomposing this powder thermally in the range of 600° to 2200° C. in a nonoxidizing atmosphere to obtain silicon carbide; D. molding this silicon carbide powder; and E. sintering the thus molded body in a nonoxidizing atmosphere.

Process for sintering reaction bonded silicon nitride

Abstract: Sintered silicon nitride articles are prepared from a silicon nitride compact by forming a silicon powder containing one or more sintering additives for silicon nitride into a compact having at density of at least 1.3 g/cm3, said additives being present in the powder in an amount such as to ensure an additive content of from 0.5 to 20 wt. % in the silicon nitride compact, nitriding the silicon compact by heating under nitrogen gas blanket at a temperature not exceeding 1500° C., to convert said silicon into reaction bonded silicon nitride, and sintering the reaction bonded silicon nitride compact by heating in a nitrogen gas atmosphere at a temperature of at least 1500° C.

Process for producing an apatite powder having improved sinterability

Abstract: A sintered apatite body obtained by molding and sintering an apatite powder, Ca 5 (PO 4 ) 3 OH, containing 0.01 to 20% by weight of (Ca,Mg) 3 (PO 4 ) 2 . The sintered apatite body has high mechanical strength and good affinity with living tissues and cells, and is suitable as medical implant materials such as prosthetic teeth or bones.

Process for preparing titanium carbide-tungsten carbide base powder for cemented carbide alloys

Abstract: A process comprises the steps of molding a mixture of usual TiC powder material having a combined carbon content lower than the theoretical value, a required amount of binder metal and a suitable amount of WC powder, sintering the molded mixture at a high temperature of about 1550° to 2500° C. to dissolve the WC particles in the TiC particles, and maintaining the sintered product at the high temperature, whereby the combined carbon content is increased to the highest possible value approximate to the theoretical value and the binder metal is fully effectively fused to the surface of the TiC particles. The resulting product is readily crushable to a powder having greatly improved amenability to sintering.

Sintered rare earth-iron Laves phase magnetostrictive alloy product and preparation thereof

Abstract: A sintered rare earth-iron Laves phase magnetostrictive alloy product characterized by a grain oriented morphology. The grain oriented morphology is obtained by magnetically aligning powder particles of the magnetostrictive alloy prior to sintering. Specifically disclosed are grain oriented sintered compacts of Tbx Dy1-x Fe2 and their method of preparation. The present sintered products have enhanced magnetostrictive properties.

Ionic conductivity and crystal structure of magnesium- and cobalt-doped sodium-beta-alumina

Abstract: The effect of cobalt as a dopant for sodium-beta-alumina has been studied in polycrystalline materials prepared from a mixed oxide precursor. Two materials have been examined; one containing a small amount of cobalt as well as magnesium as a dopant and the other magnesium alone to produce the same molar quality of divalent dopant. The sintering behaviour, microstructure and phase composition are shown to be related to the measured ionic conductivity.

Rate Controlled Sintering as a Processing Method

Abstract: Rate controlled sintering (RCS) has been under development at this University since 1965. It has emerged as an optimizable laboratory procedure which offers a rational alternative to the up-and-hold conventional temperature sintering (CTS) profiles commonly employed for the densification of kiln-fired crystalline ceramics.

Surface Area Reduction Kinetics During Intermediate Stage Sintering

Abstract: The surface-area reduction kinetics for the intermediate stage of sintering was analyzed. The high sintering rate in the initial stage results from the initially large curvature gradients. In the intermediate stage these gradients are reduced and the surface-area reduction kinetics shift to a dependence on the mass transport rate associated with grain growth. This is a much slower process. (FS)

Process for producing a metastable precursor powder and for producing sialon from this powder

Abstract: There is disclosed a process for producing a metastable precursor powder having about 20 to 60 percent of the silicon thereof in the nitride form. This process includes a controlled nitriding step using silicon, alumina, and either aluminum or aluminum nitride as starting materials. There is also disclosed a process for producing sialon from this precursor powder. This process includes the steps of doping the precursor powder, cold pressing or slip casting the doped powder, and then carrying out a controlled sintering step under a nitrogen atmosphere.

Activation of ruthenium on silica hydrogenation catalysts

Abstract: Activation of RuCl3-impregnated silica by nitrogen-hydrogen tratment at high temperature, up to 700 °C, is superior to calcination of the material prior to reduction. Sintering hardly occurs. In addition, activity measurements, based on the liquid phase hydrogenation of benzene, and thermogravimetric analysis suggest a favorable (chemical) interaction between ruthenium and silica.