Homework 9 Solutions

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Homework 9 Solutions
Question 5.3 Write the Arrhenius rate equation in the (a) exponential and (b) common logarithmic forms.
Answer 5.3
Question 5.6 Write the equation for Fick’s first law of diffusion, and define each of the terms in SI units.
Answer 5.6
Question 5.7 What factors affect the diffusion rate in solid metal crystals?
Answer 5.7
The diffusion rate in solid metal crystals is affected by five factors:
1.Type of diffusion mechanism;
2.Temperature of diffusion;
3.Concentration of the diffusion species (concentration gradient);
4.Type of crystal structures;
5.Type of crystal imperfections present.
Question 5.12 (a) Calculate the equilibrium concentration of vacancies per cubic meter in pure silver at 750°C. Assume that the energy of formation of a vacancy in pure silver is 1.10eV. (b) What is the vacancy fraction at 700°C?
Answer 5.12
Question 5.13 Determine the diffusion flux of zinc atoms in a solid solution of zinc in copper between two points A and B, µm apart, at 500°C. C A=1026 atoms/m3 and C B=1024 atoms/m3.
Answer 5.13
Question 5.16
Answer 5.16
Question 5.20
Answer 5.20
Question 5.24
Answer 5.24
Question 4.3 In the solidification of a pure metal, what are the two energies involved in the transformation? Write the equation for the total free-energy change involved in the transformation of liquid to produce a strain-free solid nucleus by homogeneous nucleation. Also illustrate graphically the energy changes associated with the formation of a nucleus during solidification.
Answer 4.3
Question 4.5 During solidification, how does the degree of under cooling affect the critical nucleus size? Assume homogeneous nucleation.
Answer 4.5
In general, the greater the degree of under cooling of a liquid melt, the smaller the critical radius of the nuclei formed.
Question 4.6 Distinguish between homogeneous and heterogeneous nucleation for the solidification of a pure metal.
Answer 4.6
In homogeneous nucleation of a liquid metal, the nuclei are formed from atoms of the metal solidifying. In heterogeneous nucleation, impurity atoms or container surfaces act as nucleating agents.
Question 4.32 Calculate the size (radius) of the critically sized nucleus for pure platinum when homogeneous nucleation takes place.
Answer 4.32
Question 4.33 Calculate the number of atoms in a critically sized nucleus for the homogeneous nucleation of pure platinum.
Answer 4.33
Question 8.21 Consider an alloy containing 70 wt% Ni and 30 wt% Cu
a.At 1350°C make a phase analysis assuming equilibrium conditions. In the
phase analysis include the following:
(i)What phases are present?
(ii)What is the chemical composition of each phase?
(iii)What amount of each phase is present?
b.Make a similar phase analysis at 1500°C.
c.Sketch the microstructure of the alloy at each of these temperatures by using
circular microscopic fields.
Answer 8.21
Question 8.48 Derive the lever rule for the amount in weight percent of each phase in two-phase regions of a binary phase diagram. Use a phase diagram in which two elements are completely soluble in each other.
Answer 8.48。