Showing papers on "Sintering published in 1977"

Preparation of glasses and ceramics from metal-organic compounds

Abstract: The preparation of glass and ceramic systems from metal-organic compounds permits the mixing of the constituents at the molecular level. These mixes form clear glasses or sinter to dense bodies at temperatures considerably lower than the equivalent compositions prepared by classical methods. A significant recent development in this field has been the preparation of monolithic glass and ceramic material without the need of melting or high temperature sintering. Glass-forming reactions, previously achievable only by thermal means, can take place by chemical polymerization at room temperatures. Structural studies indicate that these materials are indeed amorphous or glassy in naturE. Thus, the often used description of glass as a “supercooled liquid” is, in the literal sense, inapplicable for these materials.

Sintering of Low‐Density Glasses: II, Experimental Study

Abstract: Densification rates are reported for 3 classes of porous glass materials: soot preforms made by flame hydrolysis, silica gel, and phase-separated and leached borosilicate glass. Viscosity values obtained by fitting the densification data to the theory of Part I of the present study are in reasonable agreement with viscosity measured by beam bending using fully sintered glass of the same type.

Metallic Borides: Preparation of Solid Bodies — Sintering Methods and Properties of Solid Bodies

Abstract: Powder metallurgy can proceed in two fundamentally different ways for the fabrication of products from powders of refractory borides. One way — conventional sintering — includes molding or compacting of products from the powder (compression in steel die, isostatic compression, injection molding, rolling, slip casting etc.) with subsequent sintering of the compacts. The other way — hot pressing — combines the pressing and sintering processes and is discussed in Chapter C.XIII. For both ways, the raw boride material must previously be milled to a sufficiently fine particle size.

Sintering of Si3N4 Under High Nitrogen Pressure

Abstract: A graphite resistance furnace was used. Si/sub 3/N/sub 4/ specimens were sintered at 1800 to 1950/sup 0/C under N/sub 2/ pressures of 250 to 300 psi with only minimal degradation and 1 to 2% weight loss. CeO/sub 2/ was used as sintering additive. Modulus-of-rupture values up to 63 ksi were obtained. (DLC)

Catalyst and its method of preparation

Abstract: A catalyst comprising 10 to 30 wt.% of nickel as nickel oxide, 20 to 60 wt.% of calcium as calcium oxide, 10 to 70 wt.% of aluminum as aluminum oxide and containing less than 1 wt.% of silicon dioxide. The catalyst is prepared by using: as the starting material for the nickel component, fine particles of nickel oxide obtained by heating a nickel compound which is decomposed to nickel oxide by heating at a temperature in the range of 400° to 800° C in the presence of oxygen; as the starting material for the calcium component, calcium oxide per se or a calcium compound which is decomposed to calcium oxide by heating and; as the starting material for the aluminum component, alumina cement of a high purity. The catalyst is prepared by mixing and kneading the starting materials with water, molding the same, then keeping the catalyst composition under a highly humid atmosphere at a temperature in the range of 5° to 35° C for longer than one day for hydrating and hardening the cement and thereafter sintering the same at a temperature in the range of 550° to 1200° C.

Low temperature fired ceramic capacitors

Abstract: A multi-layer ceramic capacitor is characterized by a ceramic composition including barium titanate and lithium fluoride as essential ingredients resulting in the capability of sintering the composition at temperatures below 1100° C. As a consequence, the electrodes for the capacitor can be formulated from pure silver or a silver palladium composition in which the major component is silver thereby decreasing the expense of such capacitors as compared to those requiring platinum, gold, or mixtures of these precious metals and/or similar precious metals in making up the electrodes.

Submicron beta silicon carbide powder and sintered articles of high density prepared therefrom

Abstract: Shaped silicon carbide ceramic articles of high density, e.g., at least 90 percent of theoretical, are produced by cold pressing and sintering boron-containing high purity, submicron beta silicon carbide powder. The silicon carbide powder is produced preferably by gas phase reaction of silicon halide, e.g., silicon tetrachloride, carbon source reactant, e.g., halogenated hydrocarbon, and boron source reactant, e.g., boron trichloride, with a hydrogen plasma.

Process for producing 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.

Effect of oxygen on sintering of AlN

Abstract: The effect of the oxygen impurity on the densification behaviour of AlN was investigated AlN powders containing different amounts of oxygen were synthesized from alumina and hot-pressed The way in which oxygen accelerates densification is remarkable Contrary to what is expected from the densification equation, the sintering rate decreases during the holding time at temperatures above 1900° C This discrepancy is caused by the liberation of oxygen during the hot-pressing The compression test, conducted on the hot-pressed specimens, shows that oxygen impurity also improves the mechanical strength of sintered AlN The sintered specimens with more than 25 wt % of oxygen have compressive fracture stresses above 150kg mm−2, which are adequate for a refractory material

Preparation and Characterization of Highly Dispersed Electrocatalytic Materials

Abstract: Catalysis can be defined as the science of maximizing chemical reaction rates for the formation of preferred products. Catalysis is achieved by using high-surface-area materials that may have specific surface features (i.e., preferred reaction sites). A secondary area is the study of adsorbed species on the catalytic surface, catalyst deactivation by poisoning, and loss of surface area due to sintering.

Si{hd 3{b N{HD 4 {B formed by nitridation of sintered silicon compact containing boron

Abstract: A polycrystalline silicon nitride body is produced by shaping a particulate mixture of silicon powder and boron into a green body, sintering the body to a density ranging from 60% to 75% of the theoretical density of silicon, said sintered body having pores which are interconnecting and open to the surface of the body, and reacting said sintered body with gaseous nitrogen to convert it to silicon nitride.

Electrical contact material and method for making the same

Abstract: An electrical contact material which is particularly well suited for use in circuit breaker switches consisting essentially of silver in the amount of about 20% to 50% by weight, nickel in the amount of about 2% to 13% by weight, phosphorus in the amount of about 90 ppm to 1000 ppm, and the remainder tungsten. In one embodiment of the contact material forming method provided by the invention, starting particle sizes and liquid phase sintering parameters are selected to yield a relatively coarse grain size in the contact material microstructure with an optimum combination of resistance to oxidation, electrical erosion and distortion associated with high-current interruptions.

Stereological characterization of the interaction between interfaces and its application to the sintering process

Abstract: The degree or extent to which two different types of interfaces,e.g. grain boundaries and the void-solid interface in a sinter structure or grain boundaries and the particle-matrix interface in a dispersion hardened alloy, intersect, is an important factor in many materials. A method is presented here which allows the degree of this interaction to be quantitatively established from simple metallographic measurements made on a planar section through the structure. The results of the application of this technique to a number of copper sinter structures are presented. From these results some insight into the degree of interaction between the grain boundaries and the void-solid interface and its variation during the sintering process is obtained.

Defect structure, thermal and electrical properties of Ti nitride and V nitride powders

Abstract: Nitride powders of titanium and vanadium prepared by vapour phase reactions have been investigated with regard to their defect structure, thermal stability, sinterability and electrical conductivity. Ti nitride and V nitride containing excess of the non-metallic element and with large numbers of vacancies on the metal and non-metal sublattices liberated nitrogen, with the disappearance of vacancies, when held above 600°C under vacuum. The fractional occupancies of both sublattices were near unity at an atomic ratio (N + O) M of 1.00. However, they decreased again when the (N + O) M ratio fell below 1.00. The dissociation pressures of Ti and V nitrides at 1100°C increased sharply when the (N + O) M ratio was close to or above 1.00. The fine powders of Ti and V nitrides (0.03–0.05μm particle size) showed very high sinterabilities. The sintering proceeded rapidly at temperatures of 1000–1300 °C for titanium nitride and 900–1100°C for vanadium nitride without noticeable grain growth. The resistivities of fine powder compacts of Ti and V nitrides were 10−2–10−1 Ω cm and about 10−3 Ω cm, respectively, in the range -173 –400 °C and the temperature dependences were slightly negative.

A reanalysis of the kinetics of neck growth during liquid phase sintering

Abstract: During liquid phase sintering, solid particles make contact and can subsequently coalesce into one particle. This coalescence phenomena can affect the type of microstructure formed and its subsequent coarsening behavior during liquid phase sintering. The mechanism of particle coalescence is assumed to be the liquid state analog of the evaporation-condensation mechanism of sintering. In this work, a detailed study of the geometry appropriate for analysis of the coalescence phenomena during liquid phase sintering is made. It is found that in the early stages of particle coalescence, the neck between the particles acts as a geometrical barrier to diffusion and the neck between the particles grows approximately ast1/5,i.e., the same kinetics appropriate for solid state sintering are obtained. At longer times, the neck area no longer restricts diffusive flow and at1/6 dependency of neck growth is obtained. The use of numerical techniques also allows the analysis to be carried out with fewer geometrical restrictions than in the original analysis of the evaporation-condensation mechanism.

Process for densifying polycrystalline articles

Abstract: A polycrystalline article is densified to provide either a nonporous body or a body with controlled interconnected porosity. A mixture of fine powders of the polycrystalline material and a sintering aid is compacted and outgassed under reduced pressure. The outgassed compact is then subjected to a permeation anneal step in which it is heated in a closed chamber to a temperature sufficient to form a liquid of the sintering aid, but under pressure conditions which inhibit evaporation of the sintering aid. The sintering aid can then be leached out to provide a densified article having interconnected porosity. Alternatively, the sintering aid can be leached out at elevated temperature, further densifying the compact to form a substantially nonporous body. Alternatively, the sintering aid can be removed by subjecting the densified article to an evaporation anneal step in which the article is heated to evaporate the sintering aid, further densifying the compact to form a substantially nonporous article. Apparatus is provided containing interconnected sections to accomplish the foregoing process. When applied to magnesium fluoride, a transparent polycrystalline body is obtained as a new article of manufacture which is substantially uniformly transparent to infrared radiation throughout the entire range of 0.7-8 microns.

AL/Si and Al/Poly‐Si Contact Resistance in Integrated Circuits

Abstract: This paper presents results on the effects of sintering temperature, sintering time, and contact geometry on Al/Si and Al/poly‐Si contact resistance. At sintering temperatures >450°C the resistance of p‐type contacts is virtually constant and independent of time. The resistance of n‐type contacts, particularly to poly‐Si, increases with increasing sintering temperature for . This is attributed to the precipitation of a p‐type (Al‐doped) layer on n‐contacts during sintering. The interface resistance of both Al/Si and Al/poly‐Si contacts is independent of the length of the contact and inversely proportional to the width of the contact.

Sintering of silicon nitride using Be additive

Abstract: A particulate dispersion of silicon nitride and beryllium additive is formed into a green body and sintered at a temperature ranging from about 1900° to about 2200° C in a sintering atmosphere of nitrogen at superatmospheric pressure producing a sintered body with a density ranging from about 80 to about 100%.

Method of manufacturing an object of silicon nitride

Abstract: A method for manufacturing an object of silicon nitride by isostatic pressing of a preformed body of silicon nitride powder utilizing a pressure medium at a temperature sufficiently high to sinter the silicon nitride. The preformed body is subjected to a degassing operation before isostatic pressing. An inner porous layer of a first material and then an outer porous layer of a second material are applied on the preformed powder body. The inner porous layer is transformable, at a temperature below the sintering temperature for silicon nitride, into a pressure medium impermeable layer. The outer porous layer is also transformable into a pressure medium impermeable layer, but at a temperature which is lower than the temperature when the inner porous layer is converted into its pressure medium impermeable form. Thus, the preformed body is first subjected to a degassing and to a heating to the temperature for transforming the outer porous layer into a pressure medium impermeable layer while the inner porous layer is maintained in a porous form. Thereafter the preformed body and the surrounding layers are heated further to the temperature for converting the inner porous layer into its pressure medium impermeable form while a pressure greater than the gas pressure inside the layers is maintained on the outside of the layers. The isostatic pressing of the preformed object is then carried out.

Spray dried silica for chromatography

Abstract: A process for preparing a low-cost silica packing for chromatography is disclosed. The process involves spray-drying an aqueous silica sol containing from 5 to 60 weight percent silica, to form porous micrograins having a dense packing, acid-washing the porous micrograins, and sintering to effect a 5 to 20% loss in surface area.

Method of manufacturing {60 -alumina

Abstract: A method of manufacturing alpha -alumina with a degree of purity of at least 98% which has a high sintering activity. The alpha -alumina contains at least 98% alpha -Al2O3 and not more than 0.1% Na (calculated as Na2O), and not more than 0.1% Ti (calculated as TiO2). The alpha -alumina also contains between 0.03% and 2% of Fe2O3 and/or Cr2O3. The alpha -alumina is formed by first fine grinding and then calcining, preferably at a temperature between about 1120 DEG C and 1350 DEG C, an aluminum hydroxide and/or hydrated aluminum oxide. The alpha -alumina is then cooled and finely ground to provide an alpha -alumina having excellent sintering activity.

High temperature resistant cermet and ceramic compositions

Abstract: Cermet compositions having high temperature oxidation resistance, high hardness and high abrasion and wear resistance, and particularly adapted for production of high temperature resistant cermet insulator bodies, comprising a sintered body of particles of a high temperature resistant metal or metal alloy, preferably molybdenum or tungsten particles, dispersed in and bonded to a solid solution formed of aluminum oxide and silicon nitride, and particularly a ternary solid solution formed of a mixture of aluminum oxide, silicon nitride and aluminum nitride. Also disclosed are novel ceramic compositions comprising a sintered solid solution of aluminum oxide, silicon nitride and aluminum nitride. The cermet compositions are designed particularly to provide high temperature resistant refractory coatings on metal substrates, preferably molybdenum or tungsten substrates.