The thermal treatment of a powder or compact samples at a temperature below the melting point of the main constituent, for the purpose of converts the weak green sample into a strong article of low porosity, and increasing its strength by bonding together of the particles.
General fabrication patterns of sintered parts. Figure- 1
Types of Sintering process
1- for solid phase sintering: only solid phases are present at the sintering temperature, the quantity of liquid is zero or is at least too low to be detected. Consolidation and elimination of the porosity require a disruption of the granular architecture, after the sintering grains of the polycrystalline are generally much larger than the particles of the starting powder and their morphologies are also different. Solid phase sintering requires very fine particles (micrometric) and high treatment temperatures; it is reserved for demanding uses, for example, transparent alumina for lamps.
2- for liquid phase sintering: the quantity of liquid formed is too low (a few vol.%) to fill the inter-particle porosities. However, the few quantity of liquid contributes to the movements of matter, particularly thanks to phenomena of dissolution followed by reprecipitation. The partial dissolution of the particles modifies their morphology and can lead to the development of new phases. A number of technical ceramics (refractory materials, alumina for insulators, BaTiO3-based dielectrics) are sintered in liquid phase.
3- Reactive sintering: there is an abundant liquid phase (for example, 20 vol.%), resulting from the melting of some of the starting components or from products of the reaction between these components. This liquid fills the spaces between the non-molten particles and consolidation occurs primarily by the penetration of the liquid into the interstices due to capillary forces, then final
Sintering -------------------------Lecture(1&2)
2
solidification during cooling, to give crystallized phases or amorphous glass. This type of sintering is the rule for silicate ceramics, for example, porcelains. However, the quantity of liquid must not be excessive, and its viscosity must not be too low, otherwise the object would collapse under its own weight and would lose the shape given to it.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
|