Showing papers on "Sintering published in 1975"

The Sintering of Supported Metal Catalysts

Abstract: Metal catalysts are commonly employed in the form of metal dispersed as small crystallites on high surface area supports. The use of these supported metal catalysts increases the utilization of the metal as a catalyst since a large fraction of the metal atoms are at the surface of the small metal crystallites. Another important function of the support is to physically separate the small metal crystallites and thereby hinder the agglomeration of the small metal crystallites into larger crystallites. This agglomeration would decrease the number of surface metal atoms per unit mass of metal, and thereby decrease the utilization of the metal and the activity of the catalyst.

Pressureless sintering of Si3N4

Abstract: An investigation of the pressureless sintering of Si3N4 powder with the addition of 5 wt % MgO revealed that shrinkage by a liquid phase mechanism and bulk decomposition are two countervailing processes. Within the temperature range studied, i.e. between 1500 and 1750° C, high densities can be achieved when sintering is performed either for long periods at low temperatures or short periods at higher temperatures. A model is presented showing that pore growth due to decomposition causes a decrease in the driving force for sintering and causes shrinkage to cease.

High resistivity BaTiO3 ceramics sintered in CO-CO2 atmospheres

Abstract: A barium titanate ceramic containing 13.5 mol % calcium zirconate was doped with up to 3 mol % of oxides of various metals that were considered likely on the basis of ionic size and valence to enter the small cation lattice with charge less than 4+. It was hoped in this way to compensate electrically for loss of oxygen during sintering in CO-CO2 mixtures, so as to obtain high resistivity dielectrics and allow the use of base metal electrodes in a monolithic capacitor. Doping with approximately 0.5 mol % Mn, Co, or Mg produced the highest resistivities, and dielectrics with nickel electrodes and relative permittivity up to 10 000 were obtained with resistivity in excess of 1012 Ω cm at room temperature. When the doped ceramic sintered in contact with nickel, the grain structure and permittivity-temperature characteristics depended on the oxygen partial pressure of the sintering atmosphere, apparently influenced by dissolution of Ni into the ceramic.

Sintering of Silicon Carbide

Abstract: The absence of densification during sintering of pure SiC is the result of its high grain boundary to surface energy ratio. Whenever this ratio exceeds a certain critical value, a solid will fail to densify without external pressure as there is not enough energy available to extend the grain boundaries.

Method for producing a sintered silicon nitride base ceramic and said ceramic

Abstract: A silicon nitride based ceramic is formed of silicon nitride and at least two metal oxides of such a type that when the metal oxides are heated separately they form a spinel. Combination of said metal oxides and said silicon nitride as fine powders and sintering same at a specified temperature for a specified period of time results in a silicon nitride based ceramic having improved mechanical and chemical properties.

Process for fabricating articles of tungsten-nickel-iron alloy

Abstract: A high density W--Ni--Fe alloy of composition 85-96% by weight W and the remainder Ni and Fe in a wt. ratio of 5:5-8:2 having enhanced mechanical properties is prepared by compacting the mixed powders, sintering the compact in reducing atmosphere to near theoretical density followed by further sintering at a temperature where a liquid phase is present, vacuum annealing, and cold working to achieve high uniform hardness.

Sintering in the Presence of Liquid Phase

Abstract: In recent years considerable progress in materials development has been achieved by applying the methods of liquid phase sintering well known from heavy alloy and hard metal production Sintering of cobalt rare earth magnets (1–4), hot pressing of silicon nitride structural ceramics in the presence of a liquid phase (5–8), supersolidus sintering of superalloys (9–12), accelerated diffusion alloying for powder forging (13) or the development of hardenable cemented carbides (14–16) may be listed here as the most prominent examples These technological achievements, however, were for a long time hardly matched by the scientific work which is necessary not only for a basic understanding of liquid phase sintering but also for an improvement of the materials made by this method

Theory of the Dependence of Densification on Grain Growth During Intermediate-Stage Sintering

Abstract: A semiempirical model for intermediate-stage sintering is developed based on simultaneously occurring volume and grain-boundary diffusion mechanisms of mass transport and explicitly incorporating the effects of grain growth. The sintering equation derived depends strongly on the reduction of pore number density associated with grain growth and is independent of the mechanism of grain growth. The time and temperature dependencies of densification predicted by the equation, which are tested using data for metal and ceramic powders, agree well with observations. The data indicate that grain-boundary diffusion contributes negligibly to densification.

Method of producing aggregated abrasive grains

Abstract: A method of producing aggregated abrasive grains for cutting tools and the like, comprising sintering a mixture of abrasive material powders and metal or alloy powders together with 5 to 10% by weight of the metal powders of an adhesion-active agent, to obtain a cake which is subsequently crushed. The sintering takes place in a loose state so that the cake has a porous structure which by crushing forms aggregated abrasive grains which break along the voids.

Copper coated, iron-carbon eutectic alloy powders

Abstract: A mechanical mixture of selected powders is subjected to compressive forces to define a pre-compact, the pre-compact then being subjected to liquid phase sintering for producing a raw alloy steel product which is more economical and has enhanced physical properties, particularly tensile strength as compared to sintered compacts produced by the prior art to date. The improvement in physical properties and processing technique results principally from the use of a mechanical mixture consisting of a base iron powder and a coated alloyed additive powder having selected alloying ingredients (such as manganese, nickel, molybdenum, in an iron-carbon system); the particles of the alloyed powder have a thin flash coating of a low melting metal, such as copper, to control carbon diffusion into the base iron powder during liquid phase sintering.

Heat insulating particles

Abstract: The present invention relates to improved heat insulating particles with a high heat insulating effect and high mechanical strength. The particles are smooth cells formed around hollow or solid grains of a low heat-conducting material such as silica, alumina, glass, or a synthetic resin like nylon or teflon, which are coated with a material that can readily reflect the heat radiation such as aluminum, copper, gold, silver, stainless steel or titanium. The cells thus-formed are bound together by sintering in the form of a block or any other desirable shape so that the metallic surface cells are bonded together at their points of contact through molecular dispersion of the metal molecules of the respective surfaces.

The sintering of open and closed porosity in UO2

Abstract: High green density UO2 powder compacts were annealed over a range of temperatures to establish the sintering mechanisms for open and closed porosity. During the intermediate stage of sintering the interconnected porosity was found to sinter at a rate consistent with a volume diffusion process dependent on the instantaneous grain size. The apparent activation energy for open pore sintering was significantly higher than that for volume or grain boundary diffusion, this being attributed to systematic differences resulting from the grain growth process. The fraction of closed porosity increased to a maximum with the collapse of the open porosity then decreased during the final stage of sintering.

Effect of additional alloying elements on the properties of sintered manganese steels

Abstract: Sintered alloys based on the Fe-Mn system have been investigated by using single-pressing and double-pressing techniques. Fe-Mn (Mn up to 8 wt.-%) and Fe-Mn-C (C up to 1·4 wt.-%) alloys were prepared both with manganese as an electrolytic powder and with a Fe-Mn master alloy. The influence of sintering temperature and sintering time on mechanical properties and homogenization is discussed. The effect of the additional alloying elements Cr, Mo, eu, and of their combinations on mechanical properties has been determined. Further investigations were carried out with a Fe-Mn-Cr-Mo-C master alloy. The optimum single-pressed and double-pressed alloy (Fe with Mn 0·8, Cr 0·8, Mo 0·8, and total C 0·6%) has a tensile strength (σB) of >700 N/mm2. Optimum alloys of all investigated systems were hot-forged and their mechanical properties are compared with those of single- and double-pressing techniques. The alloys were heat-treated and their tempering behaviour determined. Jominy standard tests were carried out...

The Development of Pressure Sintering Maps

Abstract: The several mechanisms which contribute to the densification of a powder compact during pressure sintering are described, and equations are listed for the rates of densification that each, acting alone, would yield. The equations are used to construct pressure sintering diagrams. These identify the dominant mechanism, for a given temperature, pressure and density. They further display contours indicating the rate of densification and the time to Teach a certain density. Their use in the design and interpretation of experiments is discussed, and their application to practical problems is illustrated by a case study of the pressure sintering of ice.

Sintered silicon carbide ceramic body

Abstract: Pressureless sintering of silicon carbide to produce ceramic bodies having 75% and greater theoretical densities, can be accomplished 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 2500° C.

Open mesh, random fiber, ceramic structure, monolithic catalyst support

Abstract: The present invention provides a novel cellular ceramic catalyst support. The support consists of a random-fiber ceramic framework having a high surface area. The support is fabricated by flocking an organic sponge with wood or textile fibers, and impregnating the flocked sponge with a high alumina slurry containing a silicone resin and a flux. The impregnated organic sponge is sintered at a high temperature to burn out the organic sponge material. A fired high-silica glaze can be applied to the sintered article, followed by a second sintering step. A second glaze containing from 10-25 parts by weight CuO and from 10-25 parts by weight ZrO 2 , can be applied, followed by a 2000° F. sintering step. The high temperature causes recrystallization of the CuO onto the surface of the catalyst support thereby increasing the surface area. The glazed surface can be plated with copper or nickel and combinations thereof to function as a reducing unit in a catalytic converter. In addition, other reduction catalysts and oxidation catalysts, e.g., platinum are compatible with the support.

Influence of MgO on the Evolution of the Microstructure of Alumina

Abstract: Small amounts of additives can have a great influence on the sintering of ceramic powders. The most extensively studied example is, without doubt, the effect of dopants especially MgO, on the sintering behaviour of Al2O3. In spite of all these studies many questions are still unsolved since Coble1 reported that the addition of 0.25 wt % MgO inhibits discontinuous grain growth and allows nearly theoretical densities to be achieved.

Process for forming high density silicon carbide

Abstract: High density sintered silicon carbide articles are formed by first forming a green blank or billet out of powdered silicon carbide, heat treating the billet to cause it to lightly sinter and become partially densified, shaping the billet to the desired final dimensions and configuration, and fully sintering and densifying the partially sintered shape by heat alone or by heat in the presence of silicon. The product of the process possesses high mechanical strength and may be very fine grained.

Sintered silicon nitride base ceramic and said ceramic

Abstract: A silicon nitride based ceramic is formed of silicon nitride and at least two metal oxides of such a type that when the metal oxides are heated separately they form a spinel. Combination of said metal oxides and said silicon nitride as fine powders and sintering same at a specified temperature for a specified period of time results in a silicon nitride based ceramic having improved mechanical and chemical properties.

Process for the manufacture of articles of translucent alumina

Abstract: Final sintering of an alumina powder containing a small portion of magnesia, baryta, lanthana, yttria, or salts of magnesium, barium, lanthanum or yttrium, in a non-oxidizing carbon monoxide atmosphere at a temperature above 1700° C produces a translucent alumina article.

Polycrystalline silicon carbide with increased conductivity

Abstract: Polycrystalline silicon carbide with increased electrical conductivity at room temperature is produced by shaping a particulate mixture of β-silicon carbide, boron additive, beryllium carbide and a carbonaceous additive into a green body and sintering the body producing a sintered body having a density of at least about 85% of the theoretical density of silicon carbide.

High-alumina content compositions containing BaO-MgO-SiO2 glass and sintered ceramic articles made therefrom

Abstract: The compositions of the present invention comprise alumina and minor proportions of a ternary glass sintering aid from the system: BaO-MgO-SiO2. The compositions can be sintered in a reducing atmosphere to provide ceramics which find particular utility in electrical devices, e.g., in multilayer ceramic sandwiches. The compositions are particularly amenable to formation by doctor blade slip casting techniques.

Direct observation of liquid-phase sintering in the system iron-copper

Abstract: The hot-stage of a scanning electron microscope has been used to observe liquid-phase sintering in the system iron-copper. The densification behaviour of compacts of Fe and Cu particles were determined. The influence of particle size of both components and the amount of liquid phase developed were investigated. In samples with about 20 vol % liquid phase, the densification kinetics as observed by direct observation shows that no rearrangement takes place. In samples with 40 vol % liquid phase and particle sizes of 10 to 20 µm, some rearrangement was observed.