Showing papers on "Sintering published in 1979"
TL;DR: In this paper, it was shown that platinum catalyzes the reduction of TiO 2 to Ti 4 O 7 and deposits as thin pill-box structures on the surface of the Ti O 7.
284 citations
TL;DR: In this article, solution-grown crystals of hydroxyapatite were sintered into polycrystalline oxyhydroxyapatites, using the range 1050 to 1450°C.
Abstract: Solution-grown crystals of hydroxyapatite were sintered into polycrystalline oxyhydroxyapatite bodies, using the range 1050 to 1450°C. The heat capacity, thermal diffusivity, and thermal conductivity of the sintered bodies were measured by the laser flash method at 130–1000 K. The sintered bodies were 94.4 to 99.4% of theoretical density and 0.8 to 12 μm in grain size. Sintering is accompanied by grain growth and by vacancy formation and cell contraction due to thermal dehydration. Typical values of the heat capacity, thermal diffusivity, and thermal conductivity at room temperature are 0.73 J/g K, 0.0057 cm2/s and 0.013 J/s cm K, respectively. Low-temperature thermal conductivity increased with increasing temperature, similarly to that of amorphous solids. This odd behavior is discussed in terms of phonon mean free path.
162 citations
TL;DR: In this article, the authors analyzed the self-stresses in optical waveguide preforms made by the OVPO process and determined the conditions required for bulk flow in order to produce bulk flow.
Abstract: Variations in viscosity or pore size within a glass body cause uneven contraction during sintering. Consequently, stresses develop which alter the local sintering rate and, in some cases, produce bulk flow. This paper illustrates how these stresses can be analyzed by analogy to thermal stress. As a particular example, sintering of optical waveguide preforms made by the OVPO process is examined in detail. The magnitude of the self-stresses, and the conditions required for bulk flow are determined.
159 citations
TL;DR: In this article, the structure, sintering rates and chemical composition of 20 to 200-A-diameter Pt-O and Pd-O alloys were examined using scanning transmission electron microscopy and energy dispersive X-ray microanalysis.
140 citations
TL;DR: In this paper, a thin layer of γ -Al 2 O 3 upon which Pt is deposited by evaporation is used to study the redispersion of Pt crystallites supported on alumina.
124 citations
TL;DR: In this article, coprecipitation from water solution of chlorides was used to obtain yttria-stabilized zirconia powders and relative densities of +98% theoretical have been achieved at sintering temperature as low as 1300°C.
120 citations
TL;DR: In this article, it is suggested that the driving force for this process is the chemical potential difference between the equilibrium W-Ni alloy and the pure tungsten phase being dissolved.
111 citations
TL;DR: In this article, the electrical conductivity of zirconia electrolyte cells containing Al2O3 and TiO2 sintering aids made by conventional cold pressing and Sintering procedures, and also by the tape process with co-fired electrodes, were compared with the conductivities of undoped material.
Abstract: The electrical conductivity of zirconia electrolyte cells containing Al2O3 and TiO2 sintering aids made by conventional cold pressing and sintering procedures, and also by the tape process with co-fired electrodes, are compared with the conductivities of undoped material
107 citations
TL;DR: In this paper, a mixture of single crystalline spherical W particles of 200-250 μm dia., fine W powder of 10 μm size and fine Ni powder were sintered at 167°C.
100 citations
TL;DR: In this paper, a numerical procedure is described for simulating sintering of model systems based on earlier work by Nichols for surface diffusion transport, simultaneously acting mechanisms (surface and grainboundary diffusion) are treated without simplifying assumptions concerning the neck geometry developed during Sintering.
98 citations
TL;DR: In this article, the variations in toughness of the liquid-phase sintered heavy alloys W-Ni-Fe and WNi-Cu have been examined, and it was found that the toughness was controlled primarily by the strength of the tungsten particlematrix interfaces, which is sensitive to the rate of cooling from the sintering temperature.
Abstract: The variations in toughness of the liquid-phase sintered heavy alloys W-Ni-Fe and W-Ni-Cu have been examined. Toughness was found to be controlled primarily by the strength of the tungsten particle-matrix interfaces, which is sensitive to the rate of cooling from the sintering temperature. Furnace-cooling led to the embrittlement of these interfaces; in the case of W-Ni-Fe transmission electron microscopy identified interfacial precipitation of a W(NiFe) intermetallic compound, and in W-Ni-Cu Auger electron spectroscopy indicated interfacial segregation of the trace elements phosphorus and sulfur. This embrittlement was effectively reduced by solution treating beneath the sintering temperature and quenching
Patent•
26 Mar 1979
TL;DR: In this paper, pressureless sintered silicon carbide ceramic bodies, having an equiaxed microstructure and an alpha crystalline habit, were produced by firing shaped bodies, containing finely divided silicon carbides, boron source such as BORON carbide, carbon source, phenolic resin and a temporary binder, at a sintering temperature of from about 1900° C to about 2250° C.
Abstract: Pressureless sintered silicon carbide ceramic bodies, having an equiaxed microstructure and an alpha crystalline habit can be produced by firing shaped bodies, containing finely divided silicon carbide, boron source such as boron carbide, carbon source such as phenolic resin and a temporary binder, at a sintering temperature of from about 1900° C. to about 2250° C., depending on the sintering atmosphere, under conditions such that a coating of carbon source is maintained on the finely divided silicon carbide, and sufficient boron is maintained within the shaped body during firing. Boron can be maintained within the shaped body by various techniques, such as the use of a "seasoned boat" or graphite container for the body being sintered, which has been saturated with boron by exposure to boron at or about the temperature of sintering. There is also disclosed a process for producing a sintered silicon carbide ceramic body, with or without the equiaxed crystal microstructure, from silicon carbide powders of alpha or beta crystal structure, or amorphous noncrystalline silicon carbide, or mixtures thereof.
TL;DR: In this paper, the role played by surface oxide layer in the kinetics of sintering of metallic particles is analyzed quantitatively and applied to metals with thermodynamically stable oxides.
Abstract: The role played by a surface oxide layer in the kinetics of sintering of metallic particles is analysed quantitatively. Application of the analysis to metals with thermodynamically stable oxides gave results which are consistent with experimental observations. The presence of oxides which tend to dissolve in the metal at the sintering temperatures gives rise to an incubation period before the onset of sintering. Comparison with experimental results indicates that the oxide dissolution process is kinetically controlled at the oxide-metal interface.
TL;DR: In this paper, the reaction sintering of β-sialon (Si4Al2O2N6) from a powder mixture of Si3N4, Al2O3 and AIN was studied to clarify factors affecting the densification.
Abstract: The reaction sintering of β-sialon (Si4Al2O2N6) from a powder mixture of Si3N4, Al2O3 and AIN was studied to clarify factors affecting the densification. The presence of sufficient SiO vapour on the compact and excess oxide with respect toβ-sialon composition was the most important factor. High densityβ-sialon was fabricated by heating the compact at 1800° C under 1 atm. N2. The sintering was carried out with sufficient SiO vapour pressure to prevent thermal decomposition of sintered sialon by packing the compact with a powder mixture of Si3N4 and SiO2. Care was taken to minimize the amount of excess oxide in the starting composition to obtain a high density sialon with a small amount of intergranular X-phase. The maximum density of 3.04 g cm−3 was obtained from the compact with 2 wt % excess Al2O3 in the composition. The strength of the sinteredβ-sialon was 490 MN m−2 at room temperature and 480 MN m−2 at 1200° C. The values are the best among those so far published for sinteredβ-sialons.
TL;DR: In this paper, the authors investigated the kinetics of recrystallization in sintered and hot-pressed boron carbide specimens obtained by pressing powders with particle sizes smaller than 1 μm.
Abstract: An analysis of the crystallochemical structure of boron carbide has shown that, despite strong covalent atomic bonds, directional mass transfer in boron carbide can occur during activated sintering of disperse powders. Dilatometry and electrical conductivity methods were used to investigate the kinetics of densification for boron carbide specimens obtained by pressing powders with particle sizes smaller than 1 μm. The processes that occurred on heating the samples were studied and the mechanisms of mass transfer at various temperatures were identified. The kinetics of recrystallization in sintered and hot-pressed boron carbide were investigated. The process of recrystallization was found to start at temperatures above 1800 °C; at temperatures above 2200 °C grains grew rapidly. Deformation by twinning is characteristic of boron carbide. These twins can be removed very slowly by high temperature annealing.
Patent•
30 Oct 1979
TL;DR: In this article, a novel high strength, high heat resistance sintered body suitable for use as refractory and abrasive materials is proposed, which can be prepared by sintering the powdery mixture of the components at a relatively low temperature of 1800°C.
Abstract: A novel high strength, high heat resistance sintered body suitable for use as refractory and abrasive materials is proposed. The sintered body comprises from 99.99 to 70% by weight of a combination of at least two kinds of metal diborides selected from the group consisting of diborides of Ti, Ta, Cr, Mn, Mo, Y, V, Hf, Nb, Al and Zr and from 0.01 to 30% by weight of a metal boride or borides selected from the group consisting of borides of nickel, iron and cobalt. The sintered body of the invention can be prepared by sintering the powdery mixture of the components at a relatively low temperature of 1800° C. or lower and has a bending strength as high as 190 kg/mm 2 and a Vickers hardness of 3300 kg/mm 2 at room temperature and 2400 kg/mm 2 at 1000° C.
TL;DR: In this paper, the effects of temperature, time, initial distribution, and nickel concentration on sintering of nickel on silica were studied. But the results were interpreted as particle migration, and they did not consider the influence of pore-size distributions.
TL;DR: In this paper, two different experimental procedures were used to investigate the sintering characteristics of coal ashes on heating, and the results are consistent with a sintered model based on the precept that the development of a Sinter bond between the particles is accompanied by the external shrinkage of the ash compact and by the increase of the conductance.
Abstract: Two different experimental procedures were used to investigate the sintering characteristics of coal ashes on heating. First, the Leitz heating microscope was used to record the shrinkage of an ash pellet and the electrical conductance was measured by inserting two platinum wire electrodes into the sample carrier. Another furnace assembly was also constructed where the shrinkage of the ash compact was monitored by a linear displacement transducer, and the conductance of the sample was measured between two platinum disc electrodes. Usually the results are consistent with a sintering model based on the precept that the development of a sinter bond between the particles is accompanied by the external shrinkage of the ash compact and by the increase of the conductance.
01 Jan 1979
TL;DR: In this paper, theoretical consideration of sintering of metal po powders is discussed, as well as the effects of different types of sintered materials, such as metaux, oxydes etc.
Abstract: 1. Sintering - Theoretical consideration - 2. Sintering of metal po powders 3. Sintering of oxides and oxides systems - 4. Activated and liquid phase sintering - 5. New types of sintered materials - Frittage. Materiaux frittes : metaux, oxydes etc...
Patent•
24 Sep 1979TL;DR: In this article, a method of densifying a reaction-bonded silicon nitride article is described, in which a densification aid is incorporated into a reaction bonded silicon oxide article, and the powder mixture associated therewith, is subjected to a nitrogen gas pressure sufficient to prohibit a significant volatilization of silicon oxide at a sintering temperature.
Abstract: A method of densifying a reaction bonded silicon nitride article is disclosed. In accordance with the broadest principles disclosed, a densification aid is incorporated into a reaction bonded silicon nitride article. The so-made reaction bonded silicon nitride article is enclosed in a chamber which also contains a mixture of silicon nitride powder and powder the same as the densification aid incorporated into the reaction bonded silicon nitride article. The reaction bonded silicon nitride article, and the powder mixture associated therewith, is subjected to a nitrogen gas pressure sufficient to prohibit a significant volatilization of silicon nitride at a sintering temperature. The reaction bonded silicon nitride article, the powder mixture and nitrogen gas associated therewith are heated to a temperature above 1700° C. for a time sufficient to permit sintering of that article whereby the strength of the reaction bonded silicon nitride article is increased. In accordance with preferred teachings, the densification aid can be selected from the group of materials consisting of magnesium oxide, yttrium oxide, cerium oxide and zirconium oxide.
TL;DR: In this article, the authors demonstrate that small amounts of porosity, even 1 or 2%, can cause drastic reduction of the mechanical properties in tungsten heavy alloys, and large irregular pores are formed with a sharp decrease of strength and ductility.
Abstract: W–Ni–Fe heavy alloy tensile specimens were sintered at 1450°C for various times up to 44h. The W content varied between 90 and 96 wt-%, and the Ni to Fe weight ratio was 1:1. The specimens are fully densified after 15 min to 1 h of sintering and show high strength and ductility. During the tension test, cracks are formed at the interface between tungsten grains when the grain deformation reaches critical levels. The number of these intergranular cracks increases with deformation until the specimens fracture. When the specimens are over-sintered for 4 and 8 h, large irregular pores are formed with a sharp decrease of strength and ductility. Upon further sintering, the porosity decreases again with a recovery of the mechanical properties. The results demonstrate that small amounts of porosity, even 1 or 2%, can cause drastic reduction of the mechanical properties in tungsten heavy alloys.
TL;DR: The influence of additives on the sintering behavior of Cr2O3 was studied in this article, where the authors found that adding ∼ 1 wt% TiO2 increased the densification rate.
Abstract: The influence of additives on the sintering behavior of Cr2O3 was studied. The oxygen pressure and temperature at which the sintering rate becomes significant are dramatically altered by adding ∼ 1 wt% TiO2; the sintering temperature decreases, whereas the oxygen pressure for appreciable densification increases. At temperatures as low as 1280°C, densities of 92% of theoretical were obtained. Densification was examined as a function of temperature, oxygen pressure, and TiO2 concentration. Several other transition metal oxides were tested for their ability to enhance sintering; none was successful.
Patent•
26 Feb 1979
TL;DR: In this article, the authors provided shaped polycrystalline silicon carbide having densities of at least 97% and improved mechanical properties particularly at high temperatures, said articles consisting of at at least 95.4% by weight of.alpha.-silicon carbide, about 0.1 to 2.0% of additional carbon, about 2.2 to 3.5% of nitrogen, and about 0 to 0.9% of oxygen.
Abstract: OF THE DISCLOSURE There are provided shaped articles of polycrystalline silicon carbide having densities of at least 97% and improved mechanical properties particularly at high temperatures, said articles consisting of at least 95.4% by weight of .alpha.-silicon carbide, about 0.1 to 2.0% by weight of additional carbon, about 0.2 to 2.0% by weight of aluminium, about 0 to 0.5% by weight of nitrogen, and about 0 to 0.1% by weight of oxygen, the .alpha.-silicon carbide being in the form of a homogeneous micro-structure with an average grain size of less than 10 µm. There is also provided a process for the preparation of such articles by pressureless sintering submicron powder compacts consisting of .alpha.-silicon carbide and aluminium- and carbon containing additives as sintering aids.
TL;DR: In this paper, the concurrent rates of reaction and densification during hot-pressing of mixtures of alumina and zircon powders were measured in terms of a liquid-phase sintering model and evidence was presented for separable stages of particle rearrangement, diffusion-controlled densification and residual reaction subsequent to attainment of zero porosity.
Abstract: Measurements have been made of the concurrent rates of reaction and of densification during the hot-pressing of mixtures of alumina and zircon powders. The results can be interpreted in terms of a liquid-phase sintering model and evidence is presented for separable stages of particle rearrangement, diffusion-controlled densification and residual reaction subsequent to attainment of zero porosity.
TL;DR: In this article, the sintering behavior of poly(methyl methacrylate) (PMMA) particles was studied by photographic, means and mechanical testing, and it was suggested that the flow mechanisms involved in the Sintering process are viscoelastfc flow in lower temperature range and shorter times and non-Newtonian viscous flow in the higher temperature range.
Abstract: The sintering behavior of poly(methyl methacrylate) (PMMA) particles was studied by photographic, means and mechanical testing. Interpretation of the data gives the sequence of events taking place during high temperature sintering (without pre-compaction). Optical observations, show essentially two main sintering regions while mechanical studies also give an intermediate transition zone separating these two regions. It is suggested that the flow mechanisms involved in the sintering process are viscoelastfc flow in the lower temperature range and shorter times and non-Newtonian viscous flow in the higher temperature range and longer times.
TL;DR: In this paper, the authors propose to embed the powder compacts in a loose powder mixture to control both the decomposition of the Si3N4 and the loss by volatilization of the MgO.
Abstract: Silicon nitride with the addition of MgO as a sintering aid can be sintered at atmospheric pressure by embedding the powder compacts in a loose powder mixture. By choosing a suitable composition of the powder in the bed it is possible to control both the decomposition of the Si3N4 and the loss by volatilization of the MgO. In this way one can obtain homogeneously sintered articles of complex shapes of density >3.0 Mg m−3.
TL;DR: In this paper, reaction-bonded silicon nitride (RBSN) is used as the starting material for a post-densification process carried out at about 1800°C in nitrogen at atmospheric pressure.