Chapter 5, Problem 5D.5P

(a)

Interpretation Introduction

Interpretation:

The eutectics, congruent and incongruent melting compounds have to be identified.

Concept introduction:

Eutectic points are the lowest melting points of the mixtures.  Congruent melting compounds are those which remain stable upto their melting points.  Incongruent melting compounds are those which decompose into other products before reaching their melting point.

(b)

Interpretation Introduction

Interpretation:

The number of phases and phase composition present in equilibrium when a melt with composition $x_{\text{Si}}=0.20$ at $1500\text{°C}$  is cooled to $1000\text{°C}$ have to be stated.

Concept introduction:

Eutectic points are the lowest melting points of the mixtures.  Congruent melting compounds are those which remain stable upto their melting points.  Incongruent melting compounds are those which decompose into other products before reaching their melting point.

(c)

Interpretation Introduction

Interpretation:

The equilibrium phases observed when a melt with $x_{\text{Si}}=0.80$ is cooled to $1030\text{°C}$ have to be described.  The phases and relative amounts that would be at equilibrium at a temperature (i) slightly higher than $1030\text{°C}$, (ii) slightly lower than $1030\text{°C}$ have to be stated.

Concept introduction:

Eutectic points are the lowest melting points of the mixtures.  Congruent melting compounds are those which remain stable upto their melting points.  Incongruent melting compounds are those which decompose into other products before reaching their melting point.