MSE 230 Assignment 7 Fall 2013 due 10 10 10 11 Problems with an by them will not be graded but solutions will be provided 1 Callister Problem 5 6 The purification of hydrogen gas through a palladium sheet was discussed in Section 5 3 Compute the number of kilograms of hydrogen that pass per hour through a 5 mm thick sheet of palladium having an area of 0 20 m2 at 500 C Assume a diffusion coefficient of 1 0 x 10 8 m2 s that the concentrations at the high and low pressure sides of the plate are 2 4 and 0 60 kg of hydrogen per cubic meter of palladium and that steady state conditions have been attained 2 Which element would you expect to diffuse through iron more rapidly carbon or chromium Which element would have the higher activation energy for diffusion Please explain your answer 3 On the same graph sketch qualitatively correct plots of ln D vs 1 T for i carbon diffusing through BCC iron and ii radioactive iron diffusing through BCC iron Please provide reasons for any differences between the two plots this is a follow up from problem 2 4 The steady state diffusion flux through a metal plate is 5 4 x 10 10 kg m2s at a temperature of 727 C 1000K and when the concentration gradient is 350 kg m4 Calculate the diffusion flux at 1027 C 1300 K for the same concentration gradient and assuming an activation energy for diffusion of 125 000 J mol 5 Problem 5 15 in Callister For a steel alloy it has been determined that a carburizing heat treatment of 10 h duration will raise the carbon concentration to 0 45 wt at a point 2 5 mm from the surface Estimate the time necessary to achieve the same concentration at a 5 0 mm position for an identical steel and at the same carburizing temperature 6 The wear resistance of a steel shaft is to be improved by hardening its surface This is to be accomplished by increasing the nitrogen content within an outer surface layer as a result of nitrogen diffusion into the steel the nitrogen is to be supplied from an external nitrogen rich gas at an elevated and constant temperature The initial nitrogen content of the steel is 0 0025 wt whereas the surface concentration is to be maintained at 0 45 wt For this treatment to be effective a nitrogen content of 0 12 wt must be established at a position 0 45 mm below the surface Specify an appropriate heat treatment in terms of temperature and time for a temperature between 475 C and 625 C The preexponential and activation energy for the diffusion of nitrogen in iron are 3 x 10 7 m2 s and 76 150 J mol respectively over this temperature range 7 Several samples of a ductile metal are subject to 50 cold work using a rolling mill The samples are then given recrystallization heat treatments at temperatures ranging from 0 40 to 0 70 of Tm the melting temperature of the metal Sketch a qualitative plot of recrystallization time y axis versus recrystallization temperature x axis for the samples Please explain your answer
View Full Document
Unlocking...