An alloy of 70 atomic % arsenic and 30 atomic % gallium is produced, and the all

Question

An alloy of 70 atomic % arsenic and 30 atomic % gallium is produced, and the alloy is heated to 1250°C to thoroughly melt the mixture. The alloy is then slowly cooled so that it is always close to equilibrium. Answer the following about the alloy (use the graph shown):
a) At what temperature does a solid first form?
b) What is the chemical composition of the first solid to form?
c) Below what temperature is the alloy completely solid?
d) At room temperature (23°C), what phases are present, what are their chemical compositions, and what is the atom fraction of each phase present?

Explanation / Answer

a) At what temperature does a solid first form?

A solid first formed at 1200 oC

b) What is the chemical composition of the first solid to form?

Solid first formed is GaAs with 50% atomic percentage of Ga and 50% atomic percentage of As.

c) Below what temperature is the alloy completely solid?

Below 825 oC the alloy is completely solid.

d) At room temperature (23°C), what phases are present, what are their chemical compositions, and what is the atom fraction of each phase present?

The phases present are GaAs and As

i) GaAs – 50 Atom% of As

fGaAs = (100-70)/(100-50) = 0.6

ii) As – 100 Atom% of As

fAs = 1-0.6 = 0.4

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