Showing papers on "Sintering published in 1985"
TL;DR: In this article, the formation of TiSi2 thin films on silicon substrates has been investigated with several transmission electron microscope techniques, and it was shown that a metastable phase (C49 or ZrSi2 structure) forms prior to the equilibrium phase (TiSi2 (C54 structure).
Abstract: The formation of TiSi2 thin films on silicon substrates has been investigated with several transmission electron microscope techniques. For films formed either by reacting titanium with a silicon substrate or by sintering a codeposited (Ti+Si) mixture, electron diffraction patterns show that a metastable phase—TiSi2 (C49 or ZrSi2 structure)—forms prior to the equilibrium phase—TiSi2 (C54 structure). High‐resolution images indicate that the metastable TiSi2‐silicon interface is atomically sharp, with no ‘‘glassy membrane’’ layer present. The annealing temperature required to transform the metastable TiSi2 to the low resistivity, equilibrium TiSi2 increases as the thin‐film impurity content increases. Previous studies of TiSi2 formation are discussed in light of these results.
375 citations
AT&T1
TL;DR: In this article, a classification of sintering processes includes: (a) sinterting of premelted and pulverized glasses; (b) Sintering of chemically treated glass; (c) sinting without melting; (d) sincing with melting; and (e) Sincing without, or simultaneously with, melting.
Abstract: Preparation of glass articles by sintering of glass and amorphous powders is considered. The classification of sintering processes includes: (a) sintering of premelted and pulverized glasses; (b) sintering of premelted chemically treated glasses; (c) sintering without melting; (d) sintering with melting. The most interesting class of processes is sintering without, or simultaneously with, melting and it includes preparation of preforms for optical fibres and the sol-gel route for glass preparation. This last route is reviewed in detail. Two main versions are considered: preparation of gels by hydrolysis and polymerization of alkoxides, and sintering of amorphous colloidal powder compacts. The sol-gel processes represent an embryo of a new technology for the production of high-melting glasses (including quartz glass) at relatively low temperatures.
226 citations
TL;DR: In this paper, the authors compared the sintering behavior of a rigid substrate and a free film, and found that the shear rate of the film is more important than its densification rate when the film was constrained by a substrate.
Abstract: A model is presented in which the sintering behavior of a ceramic film which is constrained by a rigid substrate is contrasted with the sintering behavior of a free film. The problem is made simple by the assumption that the stress field developed in the film is uniform. This simplification allows several closed form solutions to be obtained. The solutions give new insights into the sintering behavior of films supported on a substrate. It is found (1) that the shear rate of the film is more important in the sintering process than its densification rate when the film is constrained by a substrate, (2) that the incompatibility stress is time dependent and reaches its maximum value during the initial stages of sintering, (3) that the magnitude of that maximum stress may be tensile or it may be compressive depending on the shear response of the material, and (4) that if the incompatibility stress is tensile it can lead to the formation of cracks or defects in the ceramic film.
224 citations
TL;DR: Stoichiometric mullite powder (3Al2O3·2SiO2) prepared by spray pyrolysis and sintered at 1650°C attained 95% of theoretical density as mentioned in this paper.
Abstract: Stoichiometric mullite powder (3Al2O3·2SiO2) prepared by spray pyrolysis and sintered at 1650°C attained 95% of theoretical density. The flexural strength was 360 MPa at room temperature and decreased slightly at 1400°C. A fairly high KIc value (2.8 MN/m3/2) was obtained. These mechanical properties can be attributed to the highly homogeneous stoichiometric composition of the raw powder.
192 citations
TL;DR: The microstructure of strontium titanate internal boundary layer capacitors at various stages in their processing was studied by transmission electron microscopy of rapidly quenched and normally cooled samples as discussed by the authors.
Abstract: The microstructure of strontium titanate internal boundary layer capacitors at various stages in their processing was studied by transmission electron microscopy of rapidly quenched and normally cooled samples. Compositions containing excess TiO2, Al2O3, and SiO2 have a completely wetting liquid phase at the sintering temperature; during cooling TinO2n−1, Magneli phases precipitate at multiple grain junctions. Diffused metal oxides and flux (Bi2O3, PbO, CuO, and B2O3) rapidly penetrate as a liquid phase along boundaries in postsintering heat treatment. This liquid phase disappears during slow cooling.
174 citations
TL;DR: In this paper, two analyses for the sintering kinetics of a porous glass layer on a rigid substrate were presented, one using a continuum model, with constitutive equations and the free strain rate derived from an appropriate microstructural model.
Abstract: Two analyses are presented for the sintering kinetics of a porous glass layer on a rigid substrate. The first treatment uses a continuum model, with constitutive equations and the free strain rate derived from an appropriate microstructural model. Predictions are obtained for the sintering kinetics and the magnitude of the tensile stress in the layer. During sintering, shrinkage is not permitted in the plane of the substrate, but the resulting microstructural anisotropy is ignored by the model. A second treatment represents the sintering layer by tubes whose axes are normal to the substrate. The densification kinetics of this model are in reasonable agreement with the results of the continuum model. Therefore, the effects of microstructural anisotropy (pore orientation) are likely to be small, and either model can be used
171 citations
01 Dec 1985
TL;DR: In this paper, the simultaneous creep and densification of glass powder compacts was studied as a function of low applied uniaxial stress, temperature, and particle size, and it was shown that the ratio of the creep rate to the densification rate is almost independent of both termperature and density.
Abstract: The simultaneous creep and densification of glass powder compacts was studied as a function of low applied uniaxial stress, temperature, and particle size. The creep rate can be expressed as the sum of the contribution from the applied stress that varies linearly with stress, and a contribution due to anisotropic densification that varies linearly with the densification rate. For a constant applied stress, the ratio of the creep rate to the densification rate is almost independent of both termperature and density. While these observations are consistent with the model of Scherer for the viscous sintering of glass, other observations show significant deviations from the model. Both the densification rate and the creep viscosity, which has an exponential dependence on porosity, show much stronger dependence on density compared with theoretical predictions.
144 citations
TL;DR: In this article, the authors found that the reduction in density resulted from the nucleation and growth of grain-boundary pores, which had diffused down the grain boundaries from the ambient, to form CO/CO2 and SO2 gas at high pressures.
Abstract: Fully dense aluminas, prepared by hot-pressing, were found to swell during annealing at 1600°C in air, but not during annealing in a reducing atmosphere (po2= 10-7 Pa). The reaction followed the relation p - po = -K log t, where po and p are the initial and final densities, respectively, t is the time, and AT is a constant. The rate of swelling was enhanced by MgO solute. The reduction in density resulted from the nucleation and growth of grain-boundary pores. Pore formation was attributed to the reaction of carbon and sulfur impurities at the boundaries with oxygen, which had diffused down the grain boundaries from the ambient, to form CO/CO2 and SO2 gas at high pressures. Preliminary results indicate that this reaction can be avoided by preannealing powders in flowing oxygen prior to hot-pressing. The consequences of internal gas-forming reactions to other processes such as high-temperature creep and sintering are also discussed.
139 citations
TL;DR: In this article, the effects of formulation and aging on the dynamic oxygen storage capacity (OSC) of three-way catalysts (TWC) were determined by surface redox reaction using CO and O 2 pulses.
132 citations
TL;DR: Si3N4 is a suitable material for high temperature radome applications because of its good thermomechanical and dielectric properties The process parameters employed in pressureless sintering to obtain high density material were investigated as discussed by the authors.
117 citations
TL;DR: The microstructure of a ZnO varistor material has been investigated by a combination of X-ray diffractometry and analytical electron microscopy (SEM, TEM, STEM, EDX) as discussed by the authors.
Abstract: The microstructure of a ZnO varistor material has been investigated by a combination of X-ray diffractometry and analytical electron microscopy (SEM, TEM, STEM, EDX). The material was found to consist of: ZnO grains (doped with manganese, cobalt and nickel); smaller spinel grains which hinder the growth of ZnO grains during sintering; intergranular Bi-rich phases (namely α-Bi2O3, pyrochlore and an amorphous phase); and a small proportion of ZnO-ZnO interfaces which did not have any intergranular film but to which bismuth had segregated. The intergranular microstructure is largely a result of processes which occur during liquid phase sintering and subsequent cooling to room temperature.
TL;DR: In this article, the kinetics of grain growth in fully dense Al2O3 with and without MgO solute additions were measured for high-purity samples containing no liquid phases.
Abstract: The kinetics of grain growth in fully dense Al2O3 with and without MgO solute additions were measured for high-purity samples containing no liquid phases. The MgO was found to suppress the grain-boundary migration rate by a factor of 50. Compensating lattice defects are suggested to play a role in grain-growth inhibition. Implications of these results to the sintering of Al2O3 are discussed.
TL;DR: In this paper, very small aggregates appear to be the smallest microstructural units which determine the ultimate packing situation after compaction, and the sintering process is seen to proceed via several stages of micro-structural development.
Abstract: Ultra-fine stabilized zirconia powders, which only contain extremely small aggregates were prepared. The control of agglomerates and aggregates in these powders is of utmost importance in order to obtain highly sinter-reactive ceramics. The very small aggregates appear to be the smallest microstructural units which determine the ultimate packing situation after compaction. Resulting green microstructures and sintering behaviour were studied extensively. The sintering process is seen to proceed via several stages of micro-structural development. During the most important stage, where the ceramic material approaches full density, the observed occurrence of abnormal grain growth strongly influences the ultimate grain size. The extent of abnormal growth is highly dependent on aggregate sizes present in the starting powder.
TL;DR: In this article, the effects of compaction pressure, sintering temperature, and powder particle size on dimensional changes of sintered compacts are reported, with anisotropy of dimensional change occurring, with expansion in the radial and contraction in the axial direction.
Abstract: Ti–Ni specimens of the equiatomic composition have been processed by conventional powder metallurgy techniques. The effects of compaction pressure, sintering temperature, and powder particle size on dimensional changes of sintered compacts are reported. During sintering, anisotropy of dimensional change occurs, with expansion in the radial and contraction in the axial direction. Densities decrease during sintering. From metallographic evidence it is suggested that these observations are connected with the difference in interdiffusion rates of Ti and Ni and the segregation of powder particles in the green compacts. The sintered compacts demonstrate a well defined shape memory behaviour, with martensite nucleation being enhanced by the presence of pores. PM/0358
TL;DR: In this article, the lattice parameter measurements showed that the tetragonal and rhombohedral unit cells of the two ferroelectric phases depend on the sintering temperature.
Abstract: Pb(Zr /SUB 0.525/ Ti /SUB 0.475/ )O3 piezoceramics, both unmodified and doped with 2 wt% Bi2O3 or Nb2O5, were prepared by the usual techniques, using sintering temperatures from 900 to 1250C. The microstructural data showed that the sintering temperature which produces minimum porosity is altered by the oxide additions. X-ray diffraction demonstrated the coexistence of both ferroelectric phases. The lattice parameter measurements showed that the tetragonal and rhombohedral unit cells of the two ferroelectric phases depend on the sintering temperature.
NEC1
TL;DR: A new aluminum nitride (AIN) substrate has been developed using the hot press sintering technique, which has high thermal conductivity of 160 W/mK at room temperture as discussed by the authors.
Abstract: A new aluminum nitride (AIN) substrate, which has high thermal conductivity of 160 W/mK at room temperture, has been developed using the hot press sintering technique. The new AIN substrate has the following excellent characteristics. 1) The thermal conductivity is eight times as high as that of AI 2 O 3 at room temperature and is almost equal to that of 99.5 percent BeO at 150°C. 2) The thermal expansion coefficient is smaller than that of AI 2 O 3 and BeO, and is close to that of a silicon semiconductor chip. 3) The electrical properties are almost as good as those for AI 2 O 3 and BeO in the wide frequency range. 4) It not only has higher mechanical stength but also easier machinable property than AI 2 O 3 . It is characterized by its light transparency from visible light to the infrared wavelength region. It was proved that the new AIN substrate is able to be metallized with good adhesion strength by the conventional evaporating method and the conventional sputtering method. The new AIN was found to be applicable to three kinds of semiconductor devices: 1) silicon epitaxial transistor, 2) GaAIAs light emitting diode, and 3) InGaAsP laser diode. Also, another AIN substrate was developed using the normal sintering technique, which has high thermal conductivity of 140 W/mK at room temperature.
TL;DR: A review of studies of the synthesis and densification of mullite ceramics suggests that reaction sintering could be the best way to obtain high purity, dense mullite from common materials (amorphous silicon dioxide and α-aluminum oxide) as discussed by the authors.
TL;DR: In this article, the hydrogen properties of a mechanically alloyed 2Mg + Ni mixture have been investigated and compared with those of the Mg2Ni alloy prepared by melting and sintering.
TL;DR: In this paper, the surface area loss of gamma and theta alumina at high temperatures (800-1100°C) was investigated and the cause was shown to be sintering, neck formation between crystallites via surface diffusion.
TL;DR: In this article, an analysis of isothermal sintering data reveals that the viscosity of a sintered glass increases with time and if the experiment is continued long enough, a limiting value of viscosities, η (final), is reached at each temperature.
Abstract: Analysis of isothermal sintering data reveals that the viscosity of a gel increases with time. If the experiment is continued long enough, a limiting value of viscosity, η (final), is reached at each temperature. The increase in viscosity is attributed to two concurrent processes: condensation of hydroxyl groups and structural relaxation. Analysis of heat capacity ( C p ) data permits an estimate of the viscosity (η) of the sintered glass. The results are in good agreement with η (final) from the sintering data. The approximate dependence of viscosity on hydroxyl content ([OH]) was established using η obtained from ( C p ) data and [OH] from IR transmission spectra. The results indicate that structural relaxation contributes significantly to the rise in η during sintering.
TL;DR: The fracture toughness of these cellular materials per unit weight is similar to that of bulk glass but is not translated into strength because of the relatively large flaw sizes in the final microstructure as discussed by the authors.
Abstract: Lightweight ceramics with densities in the range 8 to 24% of theoretical were fabricated by sintering hollow glass spheres. The densification behavior, which was complex, involved uniform shrinkage of the spheres, local densification, deformation of the spheres, and coarsening of the cells. A major flaw population was found to be relatively large areas which were devoid of spheres. There was a distinct difference in the mechanical behavior and fracture path for the low- and high-density materials. The behavior of the high-density materials appeared to agree well with existing micromechanical models in terms of Young's modulus, fracture toughness, and density. The fracture toughness of these cellular materials per unit weight is similar to that of bulk glass but is not translated into strength because of the relatively large flaw sizes in the final microstructure.
Patent•
16 Nov 1985
TL;DR: In this article, an ''Alnico(R)'' permanent magnet having superior magnetic characteristic as well as high density sintering property was obtained by kneading a raw material powder composed of 6-12% Al, 10-28% Ni, 5-36% Co and 0-7% Cu, 0-8% Ti and balance Fe.
Abstract: PURPOSE:To obtain an ''Alnico(R)'' permanent magnet having superior magnetic characteristic as well as high density sintering property by kneading a raw material powder composing ''Alnico(R)'' permanent magnet with a binder consisting of methyl cellulose as the component, then applying binder removing, sintering and heat treatment. CONSTITUTION:Well known ''Alnico(R)'' magnet, e.g. the raw material powder composed of 6-12% Al, 10-28% Ni, 5-36% Co, 0-7% Cu, 0-8% Ti and the balance Fe is prepared. Said powder is kneaded with methyl cellulose aqueous solution as the binder at about room temp., then said material is injection formed in mold space by injection molding machine. Next, said formed body obtained by rising temp. of the mold to >=70 deg.C, is made uniform accompanying with the gelling of methyl cellulose. Next, obtained formed body free from flaws and cracks is subjected to binder removing, sintering and heat treatment to obtain the aimed ''Alnico(R)'' permanent magnet.
TL;DR: In this article, the microstructures of the grain boundaries in an Fe77Nd15B8 permanent magnet have been examined by high-resolution electron microscopy, in samples quenched from the sintering temperature of 1350 K and in sample quENched and then annealed at 870 K.
Abstract: The microstructures of the grain boundaries in an Fe77Nd15B8 permanent magnet have been examined by high-resolution electron microscopy, in samples quenched from the sintering temperature of 1350 K and in samples quenched and then annealed at 870 K. The coercivities of the quenched and the quenched-and-annealed samples were 500 and 1000 kA/m, respectively. Thin layers of a bcc phase were observed over the surfaces of most of the Fe14Nd2B grains in both samples. In the quenched sample, the interfaces between the bcc phase and the Fe14Nd2B grains were not so distinct, and many thin platelets of the bcc phase were found to extend from the interfaces to the inside of the Fe14Nd2B grains of which the surrounding lattice is compressed locally. In the annealed sample, the platelets disappear completely and the interfaces between the bcc phase and the Fe14Nd2B grains become very sharp and distinct. It is concluded that the morphology of the bcc phase, particularly the microstructure of its interface with Fe14Nd2B grains, controls the coercivity mechanism of Fe77Nd15B2.
TL;DR: In this paper, a ternary eutectic has been used to sinter Si2N2O ceramics to nearly the theoretical density without the application of pressure.
TL;DR: In this article, a spray-pyrolysis technique was used to extract magnesium, aluminate spinel powders from a corresponding nitrate solution, which were characterized by poor crystallinity, large specific surface area, and hollow spheres 1-20μm in size.
TL;DR: In this paper, it was shown that the coherency strain energy in a diffusion layer in the retreating grain is the driving force for boundary migration in liquid phase sintered 95Mo-5Ni alloy.
TL;DR: In this article, the effect of MgO and ZnO addition on the sintering behavior and thermal expansion characteristics of Ca0.5Zr2P3O12 was investigated.
TL;DR: In this paper, the effect of adding B, Al, and B + Al on the pressureless sintering of β-Sic was examined, and the influence of the Sintering atmosphere and heating schedule on densification behavior, polytype transformation, and microstructure development was also studied.
Abstract: The effect of additions of B, Al, and B + Al on the pressureless sintering of β-Sic was examined. The influence of the sintering atmosphere and heating schedule on densification behavior, polytype transformation, and microstructure development was also studied. High densities were obtained at 1940°C by the simultaneous addition of B and Al. The decrease in the sintering temperature is attributed to the presence of a liquid phase which results in the formation of platelets (up to 200 # in size) of an α-polytype, predominantly 4H and 6H. Polytype transformation and exaggerated grain growth could be prevented by annealing the compact at 1650° to 18500°C for 0.5 to 1 h. This procedure results in a better redistribution of the sintering aids, giving a fine-grained microstructure, constituted primarily of the cubic 3C polytype.
TL;DR: In this article, the role of strong chemical interactions between gas, crystallite, and substrate in the behavior of supported metal crystallites is examined in some detail, and it is suggested that because of these interactions the interfacial tension between crystallite and substrate can be decreased enormously (it may even become negative under nonequilibrium conditions).