36.7 Reaction Diffusion Diffusion in Multiple Phase Zone I Course of reaction di ffus ion diffusion phase change
§6.7 Reaction Diffusion (Diffusion in Multiple Phase Zone) ◆ Ⅰ. Course of reaction diffusion diffusion phase change
IB C C +d (a) (b) (c) y相变为a相
1. There have no two-phases area in diffusion area, every layer is single-phases 2. Phase' s interface moves according to parabola law 3. Phase's width
1. There have no two-phases area in diffusion area, every layer is single-phases. 2. Phase’s interface moves according to parabola law. 3. Phase’s width
Ⅱ. Basic features: 1. Diffusion is accompanied by reaction or phase transformation. In general, diffusion is rate-determining step while reaction take place instantaneously 2. For diffusion in binary systems there appear only a series of single phase, one adjacent to another, while mixed phase zone doesnt appear 3. Concentrating changes abruptly at phase boundary 4. The phase boundaries and the width of each phase change parabolic ally with time
Ⅱ.Basic features: 1. Diffusion is accompanied by reaction or phase transformation. In general, diffusion is rate-determining step while reaction take place instantaneously. 2. For diffusion in binary systems there appear only a series of single phase, one adjacent to another, while mixed phase zone doesn’t appear. 3. Concentrating changes abruptly at phase boundary. 4. The phase boundaries and the width of each phase change parabolic ally with time
ll Reaction Di ffus i on dynamics 1. Speed of interface aC C、 (DO)Ba(D.aB dt =(CBa-CaB)dx OX aC dx (D) aB-(d)Ba ax dt Ba B xX let dc OX d
◆ Ⅲ.Reaction Diffusion dynamics ( ) ( ) d = ( − )d 1 − − − t C C x x C D x C D d 1 d let ( ) ( ) d d C x t C t x C C x C D x C D t x = = − − = 1. Speed of interface