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 timeⅡ.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