A theory is presented which describes the development of surface grooves at the grain boundaries of a heated polycrystal. The mechanisms of evaporation‐condensation and surface diffusion are discussed with the use of the Gibbs‐Thompson formula and the assumption that the properties of an interface do not depend on its orientation. For the idealized case in which only one of the mechanisms is operative, the groove profile is shown to have a time‐independent shape whose linear dimensions are proportional to t½ for evaporation‐condensation, and to t½ for surface diffusion. The proportionality constants are evaluated, and criteria are developed which permit one to estimate which process predominates in practice. Order of magnitude agreement is obtained with estimates of actual grooving speeds and profiles.

Theory of Thermal Grooving

Sintering is the process whereby interparticle pores in a granular material are eliminated by atomic diffusion driven by capillary forces. It is the preferred manufacturing method for industrial ceramics. The observation of Burke and Coble that certain crystalline granular solids could gain full density and translucency by solid-state sintering was an important milestone for modern technical ceramics. But these final-stage sintering processes are always accompanied by rapid grain growth, because the capillary driving forces for sintering (involving surfaces) and grain growth (involving grain boundaries) are comparable in magnitude, both being proportional to the reciprocal grain size. This has greatly hampered efforts to produce dense materials with nanometre-scale structure (grain size less than 100 nm), leading many researchers to resort to the 'brute force' approach of high-pressure consolidation at elevated temperatures. Here we show that fully dense cubic Y2O3 (melting point, 2,439 degrees C) with a grain size of 60 nm can be prepared by a simple two-step sintering method, at temperatures of about 1,000 degrees C without applied pressure. The suppression of the final-stage grain growth is achieved by exploiting the difference in kinetics between grain-boundary diffusion and grain-boundary migration. Such a process should facilitate the cost-effective preparation of other nanocrystalline materials for practical applications.

Sintering dense nanocrystalline ceramics without final-stage grain growth

The applications and interest in thermal analysis and calorimetry have grown enormously during the last half of 20th century. The renaissance in these methods has been fueled by several influences, not least of which has been the revolution in instrumentation resulting from computer automation. Our ingenuity and vision have also expanded to recognize the tremendous versatility of these techniques. They have long been used to characterize materials, decompositions, and transitions. We now appreciate the fact that these techniques have greatly increased their utility in studying many processes such as catalysis, hazards evaluation, etc., or to measuring important physical properties quickly, conveniently, and with markedly improved accuracy. Consequently, thermal analysis and calorimetry have grown in stature and more scientists and engineers have become, at least part time, practitioners. It is very desirable that those who are new to the field can have a source of information describing the basic principles and current state of the art. Examples of the prevailing applications of these methods are also essential to spur recognition of the potential for future uses. The use of these methods is highly interdisciplinary and any adequate description must encompass a range of topics well beyond the interests and capabilities of any single investigator. To this end, a convenient four-volume compendium of such information has been prepared by recognized experts in various aspects of the topic. The editorial team has chosen authors with great care in an effort to produce a readable, informative handbook on this broad topic. The chapters are not intended to be a comprehensive review of the specific subject. The purpose is that they will enable the reader to glean the essence of the subject and form the basis for further critical reading or actual involvement in the topic. The goal of the editorial team is to spur the imagination to recognize the potential application of these methods to specific goals and efforts. In addition it is hoped to anticipate and answer questions, to guide the reader in the selection of appropriate techniques, and to help him perform them in a proper and meaningful manner.

Handbook of thermal analysis and calorimetry

Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

Liquid phase sintering (LPS) is a process for forming high performance, multiple-phase components from powders. It involves sintering under conditions where solid grains coexist with a wetting liquid. Many variants of LPS are applied to a wide range of engineering materials. Example applications for this technology are found in automobile engine connecting rods and high-speed metal cutting inserts. Scientific advances in understanding LPS began in the 1950s. The resulting quantitative process models are now embedded in computer simulations to enable predictions of the sintered component dimensions, microstructure, and properties. However, there are remaining areas in need of research attention. This LPS review, based on over 2,500 publications, outlines what happens when mixed powders are heated to the LPS temperature, with a focus on the densification and microstructure evolution events.

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Review: liquid phase sintering

Sintering and Related Phenomena

Two particles in mutual contact form a system which is not in thermodynamical equilibrium, because its total surface free energy is not a minimum. If such a system is left for a certain period of time, the bonding of the two particles will take place in order to decrease the total surface area, even though the temperature is lower than the melting point. This phenomenon of bonding of two or more particles with the application of heat only and at temperatures below melting point of any component of the system will be called sintering, although the powder metallurgists use this term in a broader sense, including the presence of molten phase and pressure. It is the objective of this paper to study this process and the mechanisms involved in it.

Self-diffusion in sintering of metallic particles

It has been shown experimentally that the mechanism of sintering of spherical glass particles is that of viscous flow. The viscosities of the investigated glass were determined for a range of temperatures from 575°C to 744°C. These viscosities remain in good agreement with those obtained by other methods.

Study of the Sintering of Glass

Sintering and Catalysis

Models and Mechanisms.- 1. The Sintering of Monodisperse TiO2.- 2. A Cell Model for Microstructural Evolution during Sintering.- 3. Analysis of Initial Stage Sintering by Computer Simulation.- 4. Channel Network Decay in Sintering.- 5. The Applicability of Herring's Scaling Law to the Sintering of Powders.- 6. On the Mechanism of Pore Coarsening.- 7. The Influence of Green Density Upon Sintering.- 8. An Overview of Enhanced Sintering Treatments for Iron.- Effect of Atmosphere and Pressure.- 9. Vapor Transport and Sintering of Ceramics.- 10. Effects of Oxygen Pressure and Water Vapor on Sintering of ZnO.- 11. Microstructure Development of Fe2O3 in HCL VaPor.- 12. Microstructure Evolution in SnO2 and CdO in Reducing Atmospheres.- 13. Reactive Sintering of Diamond-Titanium System Under High Pressure.- Sintering of Catalysts.- 14. Application of X-Ray Diffraction Techniques to Study the Sintering of Catalysts.- 15. The Effect of Interactions Among Metal, Support and Atmosphere on the Behaviour of Supported Metal Catalysts.- 16. Sintering and Redispersion of Conventional Supported Metal Catalysts in Hydrogen and Oxygen Atmospheres.- Non-Isothermal Sintering and Chemical Reactions.- 17. Ultra-Rapid Sintering.- 18. Characterization and Initial Sintering of a Fine Alumina Powder.- 19. Sintering Behavior of Overcompacted Shock-Conditioned Alumina Powder.- 20. Sintering of LiF Fluxed SrTiO3.- 21. Influence of Bismuth Oxide Additions on Cadmium Oxide Sintering.- 22. Sintering of Combustion-Synthesized Titanium Carbide.- 23. Activated Sintering of Chromium and Manganese Powders with Nickel and Palladium Additions.- 24. Reactive Phase Calsintering of Dolomite.- 25. A Contribution to the Study of Consolidation of Precipitation Strengthened Materials.

G. C. Kuczynski

Papers

Sintering and Related Phenomena

Self-diffusion in sintering of metallic particles

Study of the Sintering of Glass

Sintering and Catalysis

Sintering and Heterogeneous Catalysis