Hoofdstuk 7: Binaire fazendiagrammen
– Evenwichtstoestanden A, B bij zeer langzame afkoeling of opwarming
– f(T,%) p = cte
-> fazen
7.1) Evenwicht in vloeibare toestand
-> maximale concentratie B
a: A.X 1 =% B ; B.X 1= % A -> maximale concentratie A
b: A.X 2= % B ; B.X 2= % A
c: A.X 3= % B ; B.X 3=% A
oplosbaarheid daalt met dalende temperatuur
HEFBOOMREGEL: bepaling ma en mb in c (m = totale massa in c)
B voor =B na
m.A.X 3 =m I . A . X 1 m II . A . X 2
m I m II . A . X 3 =m I . A . X 1 m II . A . X 2
A.b - A.c
m I A X 2 – A X 3 b.c
= =
m II A X 3 – A X 1 a.c
A.c – A.a
- liquiduslijn (begintemperatuur van de stolling)
- soliduslijn (eindtemperatuur stolling)
tussen beide lijnen: ontmengingsgebied
stollingsverloop: (figuur 7.5)
- boven a alles vloeibaar
- in a eerste kiemen (zeer kleine hoeveelheid: samenstelling b)
- na verdere afkoeling: kiemen -> dendriste
in Y: twee fasen smelt fase: v%
vaste fase: u%
- in C: laatste oneindig kleine hoeveelheid vloeistof (d%) stolt.
bij verdere afkoeling naar e: geen samenstellingsverandering mengkristallen
behouden samenstelling X
diffusie: inmengkristallen kunnen de moederatomen en de opgeloste atomen
bewegen van plaatsen met hoge concentratie naar plaatsen met lage concentratie
in praktijk: diffusie steeds onvolledig.
-> in gestolde korrels: steeds samenstellingsgradiënt
=> fenomenen: microsegratie (figuur 7.6)
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