The Science and Engineering of Materials (MindTap Course List)
The Science and Engineering of Materials (MindTap Course List)
7th Edition
ISBN: 9781305076761
Author: Donald R. Askeland, Wendelin J. Wright
Publisher: Cengage Learning
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Chapter 4, Problem 4.1P

Gold has 5.82 × 10 8 v a c a n c i e s / c m 3 at equilibrium at 300 K. What fraction of the atomic sites is vacant at 600 K?

Expert Solution & Answer
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To determine

The fraction of atomic sites which are vacant in gold.

Answer to Problem 4.1P

The vacant fraction of atomic sites in gold at 600 K is 0.00091 .

Explanation of Solution

Given information:

At 300 K ,

The number of vacancies is 5.82×108 vacancies/cm3 .

Final temperature is 600 K .

Concept used:

Write the expression for the number of vacancies.

  nv=n×exp(QvRT) ...............(1)

Here,Qv is the energy required in cal/mol , n is the number of atoms per unit volume, T is the temperature in Kelvin and R is the universalgas constant.

Calculation:

Use FCC lattice parameter for goldas 4.065 A˙ .

For 1 cell, the number of gold atoms per cm3

is calculated as follows:

  n=4 atoms/cell ( 4.065× 10 8  cm )3=5.95×1022 atoms/cm3

The temperature is given as 300 K .

Universal gas constant is 1.987 calmolK .

Calculate the activation energy for goldusing equation (1) as follows:

  nv=n×exp( Q v RT)5.82×108 vacancies cm3=(5.95× 10 22  atoms cm 3 )exp( Q v ( 1.987  cal molK )( 300 K ))0.978×1014=exp( Q v ( 1.987 )( 300 ))Qv=8351.159 cal/mol

Calculate the fraction of vacant atomic sites (nv/n) in gold at 600 K

by using value of activation energyas follows:

  nvv=exp( Q v RT)=exp( Q v RT)=exp( 8351.159 cal/mol ( 1.987  cal molK )( 600 K ))=0.00091

The vacantfraction of atomic sites in gold at 600 K is 0.00091 .

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Chapter 4 Solutions

The Science and Engineering of Materials (MindTap Course List)

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