diffusion coefficient D remains constant and the concentrations of the
diffusing atoms at the surface (cs) and at large distance (x) within the
material (c0) remain unchanged. Fick’s second law can also assist us in
designing a variety of materials processing techniques, including
carburization and dopant diffusion in semiconductors as described in the
following examples
The surface of a 0.1% C steel gear is to be hardened by carburizing. In gas
carburizing, the steel gears are placed in an atmosphere that provides 1.2%
C at the surface of the steel at a high temperature (Figure 5-1). Carbon then
diffuses from the surface into the steel. For optimum properties, the steel
must contain 0.45% C at a depth of 0.2 cm below the surface. Design a
carburizing heat treatment that will produce these optimum properties.
Assume that the temperature is high enough (at
least 900°C) so that the iron has the FCC structure.
SOLUTION
Since the boundary conditions for which Equation 5-7 was derived are
assumed to be valid, we can use this equation:
Any combination of D and t with a product of 0.0198 cm2 will work. For
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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