材料科学基础
Fundamental of Materials
Prof,Tian Min Bo
Tel,62795426, 62772851
E-mail,tmb@mail.tsinghua.edu.cn
Department of Material Science and Engineering
Tsinghua University,Beijing 100084
Lesson twenty-nine
§ 6.7 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 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.
? Ⅲ,Reaction Diffusion dynamics
1d)(d)()( ?????????? ??????? xCCtxCDxCD ????????
?
?
????
????
d
d1
le t
)()(
d
d
C
tx
C
t
x
CC
x
C
D
x
C
D
t
x
?
?
?
?
?
?
?
?
?
?
??
1,Speed of interface
tBxxW jjjjjj ??? ??,11,
????? xxW ??
t
A
t
x
t
x
t
W ?????? ???
d
d
d
d
d
d
tBW ?? ?
)(
1
)(
1
)
d
d
()
d
d
(
d
d
CKtx
t
CK
tCC
t
C
D
t
C
D
t
x
????
??
?
?
??
????
????
2,Phase width
3,Rule of phase appearing
? Ⅳ.Discussion
1,Phases that can appear
2,Growth law,in general
in special cases,～
(1) is tenable in volume (lattice) diffusion
? ?1)(2 tCKW ?
41)( ?? ntCKx n
factors influencing growth,
a,Diffusion path (lattice grain boundaries pore surface).
b,Relative rate of diffusion and reaction
Examples and Discussions
1,F-N
2,F-C
Exercise
Thank you !
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