固体材料中的扩散.ppt

重点内容:
1、固体中质点扩散的特点和扩散动力学方程:扩散第一、第二定律、扩散方程的求解;
2、扩散驱动力及扩散机制:间隙扩散、置换扩散、空位扩散;
3、扩散系数、扩散激活能、影响扩散的因素。
第7章固体材料中的扩散
water
adding dye
partial mixing
homogenization
time
扩散现象(diffusion)
原子或离子迁移的微观过程以及由此引起的宏观现象。
半导体掺杂
固溶体的形成
离子晶体的导电
固相反应
相变
烧结
材料表面处理
扩散
•表面硬化:
--Diffuse carbon atoms
into the host iron atoms
at the surface.
--Example of interstitial
diffusion is a case
hardened gear.
• Result: The "Case" is
--hard to deform: C atoms
"lock" planes from shearing.
--hard to crack: C atoms put
the surface pression.
8
扩散的应用(1)
•在硅中掺杂磷制备N型半导体:
• Process:
9
1. Deposit P rich
layers on surface.
2. Heat it.
3. Result: Doped
semiconductor
regions.
SEM images and dot maps
扩散的应用(2)
在稳态扩散中,单位时间内通过垂直于给定方向的单位面积的净原子数(称为通量)不随时间变化,即任一点的浓度不随时间变化。
扩散定律
稳态扩散与非稳态扩散
在非稳态扩散中,通量随时间而变化。
Adolf Fick, Created the Contact Lens
Adolf Fick, a German physiologist and inventor,
was born on August 3rd, 1829, in Kassel,
Germany.
In 1855, he introduced “Fick’s Law of Diffusion”
which described the dispersal of gas as it passes
through a fluid membrane.
An astigmatism in his eyes led Fick to explore the idea of a contact lens, which he essfully created in 1887.
His other research resulted in the development of a technique to measure cardiac output. Adolf Fick’s work served as a vital precursor in the studies of biophysics, cardiology, critical care medicine, and vision.
Fick的经典实验
Solid NaCl
Fresh Water
饱和溶液
浓度为0
单位:扩散通量,J,atoms/(m2·s)或kg/(m2·s)
扩散系数,D,m2/s;
浓度梯度, ,atoms/(m3·m)或kg/(m3·m)
扩散通量
浓度梯度
扩散系数
1855年
菲克第一定律(Fick’s First Law)
在稳态扩散的条件下,单位时间内通过垂直于扩散方向的单位面积的扩散物质量(通称扩散通量)与该截面处的浓度梯度成正比。
“-”号表示扩散方向为浓度梯度的反方向,即扩散由高浓度向低浓度区进行。