제 3 장 2성분계 상평형

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제 3 장 2성분계 상평형

3.1 2성분계

① 화합물을 만들지 않는 2개의 성분을 혼합시키는 경우

② Gibbs의 상률 F = C - P + 2 ( F: 자유도, C : 화학성분의 수, P : 상의 수) ③ 2성분계의 상률

- C = 2, P = 1, F = 3

- 압력, 온도 및 조성을 자유로이 선택 - 상태도 ( 3차원 상태도 )

- 압력을 상압으로 하는 상태도 (빗금친 부분) F = ( )

A와 B 조성을 가진 두 개의 고상과 액상이 공존할 경우 (( ) : 온도 TM과 조성 C) C = ( ), P = ( ) --> F = ( )

1. At X Point X lies within the liquid field,

o P = 1 - Liquid

o C = 2 - two components A and B

o F = 2 - two degrees of freedom, giving a divariant area.

o To maintain equilibrium, i.e. to keep the single phase Liquid stable, T and X may be varied independently.

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2. At Y Point Y lies on the boundary curve between the fields of Liquid and A + Liq.

o P = 2 - Solid A and Liquid

o C = 2 - two components A and B,

o F = 1 - one degree of freedom yielding a univariant curve.

o To maintain equilibrium, i.e. to stay on the boundary curve, Fixing T automatically fixes X.

3. At E Point E is the eutectic, the point where the liquidus and solidus intersect.

o P = 3 - Solid A, Solid B and Liquid, o C = 2 - two components A and B,

o F = 0 - no degrees of freedom, an invariant point.

o No degrees of freedom, all 3 phases coexist in equilibrium, changing either temperature or compostion from the point represented by E will cause one or more of the phases to disappear, thus changing the value for P in the phase rule equation.

④ Phase Equilibria : Solubility Limit

㉠ Introduction

- Solutions - solid solutions, single phase - Mixtures - more than one phase

㉡ Solubility Limit ( ) : Max concentration for which only a single phase solution occurs

㉢ Question: What is the solubility limit at 20°C? → Answer : ( )wt% sugar If Co < 65 wt% sugar : syrup

If Co > 65 wt% sugar : syrup + sugar.

⑤ Components and Phases

㉠ Components ( ) : The elements, compounds or solutions which are present in the mixture

㉡ Phases ( ) : The physically and chemically distinct material regions (e.g., α and β).

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β (lighter phase)

⑥ Effect of T & Composition (Co)

Changing T can change # of phases : path A to B.

Changing Co can change # of phases : path B to D.

water-sugar system

⑦ Conode (or Tie Line)

For a particular temperature,

the straight line connecting the composition of two equilibrium with each other.

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⑧ Examples