Bioactive glass-ceramics
They are polycrystalline ceramics made by controlled crystallization of glasses using heat treatment resulting in the nucleation and growth of crystal phases within the glass. The resulting glass-ceramic consists of at least one glass phase and one crystal phase and superior mechanical properties to those of the base glass from which it was formed. The reason for this is that, unlike glass which is amorphous, crystalline ceramics contain structural discontinuities or grain boundaries at points where the crystals meet, which act as an impediment for fracture propagation by causing deflection, branching, or splitting of cracks that lead to increase the fracture toughness and make glass-ceramics more suitable than glass for bone load bearing applications.
The nucleation of glass is carried out at temperatures much lower than the melting or glass transition temperature, in order to obtain a more crystallized material, the glass is further heated to a temperature at which maximum crystal growth can be attained without deformation of product or phase transformation within the crystalline phases or redissolution of some of the phases. Crystallization is usually more than 90% complete when grain sizes are 0.1 to 1 ?m, which are much smaller than in conventional ceramics. Figure 4 is a schematic representation of the temperature–time cycle for a glass-ceramic.
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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