Introduction to Drying:
Drying of ceramics is much more complicated than drying many other objects because unfired ceramics typically exhibit shrinkage during drying. This shrinkage can lead to cracking and loss of acceptable quality in production.
(Drying is the process of removing water from an unfired ceramic object or raw material in the green or as-formed state or in the as received state). As such, drying is accomplished by supplying energy to the ceramic in order to accomplish evaporation.
Drying is a process which is used for removing the liquid from the solid material. In standard chemical engineering practice drying of the water (compound A) from the solid (compound C) by evaporating to the flow of overheated air (compound B) is the most com-mon practical example. Drying is relatively complex process combining the heat and the mass transport. In our laboratory dryer the heat transport which is necessary for the evaporation of the water, is realized only by the heat convection from the air to the drying material.
From mass transport point of view, one must understand the drying as a diffusion process. During first period of drying, water which is contained in material evaporates from the material surface to the air flow (by external diffusion). After formation the moisture gradient inside the material second drying period begins. During this period water is transported inside material to the surface (internal diffusion). Rate of the slower process determines overall drying rate. Mass and heat transport proceed together during drying
WATER ADDED TO A DRY CERAMIC POWDER
When water is added to a completely dry ceramic powder,
• First, covers the surface of the particles. (Assuming ideal mixing to prevent agglomeration).
• Second, water fills small capillaries (minimum spaces between particles).
• Third, since most ceramic compositions also contain some large pores (generally ~50– 100 ?m in size) due to imperfect particle packing or gradation, these pores are gradually filled with water.
• Fourth, additional water causes a separation of particles called forming water .
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 .
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