Thermodynamics in material science questions.(pdf file is attached)
(Question 1) Construct the Kroger Vink diagram for the Cu2O where the principal defects are Schottky defects that can be singly ionized in the case of copper vacancies and doubly ionized in the case of oxygen vacancies.
(Question 2) We usually define the activity of oxygen as a_0=P_(O_2)^(1/2)
A common reference state for oxygen gas is 1atm pressure at the temperature of interest. Consequently,〖〖(a〗_0)〗_(P_(O_2 )=1) = P_(O_2)^(1/2)
When a metal is oxidized we can write M+1/2 O_2=MO, K=1/(a_M P_(O_2)^(1/2) )
At the metal oxide interface a_M=1 and K=1/〖(P_(O_2)^(1⁄2))〗_(M⁄MO)
Write an expression for the activity of oxygen where 〖(P_(O_2)^(1⁄2))〗_(M⁄MO) is taken as our reference state where a_0=1. Relate this activity to the activity of oxygen where the reference state is P_(O_2 )=1atm.
(Question 3) Some alloys can become hot short when one phase, often a liquid, wets the grain boundaries of a metal or alloy. In the case of nickel, when the sulfur concentration is high, liquid NiS can be formed.
Given σ_GB (nickel)=2σ_(Ni/NiS), would you expect to have hot shortness in nickel when the sulfur concentration is high enough to form NiS?
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