文档介绍：材料科学基础 Fundamental of Materials Lesson twenty-nine Lesson twenty-nine § Reaction Diffusion (Diffusion in Multiple Phase Zone) ?Ⅰ. Course of reaction diffusion diffusion phase change 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 panied 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. ??ⅢⅢ. .Reaction Diffusion Reaction Diffusion dynamics dynamics 1d)(d)()(?????????????????xCCtx CDx CD ??????????????????d d1 let )()(d dCt x C t x CDx CDt x???????????? 1. Speed of interface 1. Speed of interface tBxxW jjjjjj?????,11, ?????xxW??t At xt xt W ?????????d dd dd dtBW ???)( 1)( 1 )d d()d d(d dCKtx t t CDt CDt x?????????????????? 2. Phase width 2. Phase width 3. Rule of phase appearing 3. Rule of phase appearing ?Ⅳ.Discussion that can appear law: in general in special cases: ~ (1) is tenable in volume (lattice) diffusion ?? 1)( 2tCKW?41)(??ntCKx n factors influencing growth: factors influencing growth: a. a. Diffusion path (lattice grain boundaries pore surface). Diffusion path (lattice grain boundaries pore surface). b. b. Relative rate of diffusion and reaction Relative rate of diffusion and reaction Examples and Discussions 1. F-N