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Materials Assignement 6 Attempt 2

Materials Assignement 6 Attempt 2 - WebCT Quiz Homepage...

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WebCT Quiz Homepage http://webct.mcmaster.ca/SCRIPT/MATLS_1M03_T2_06_newRestore/s... 1 of 4 31/03/2006 5:43 PM View Results Assignment 6 (Ch 10, 11, 14 & 15) Name: BRYCE JONES Attempt: 2 / 3 Out of: 9 Started: March 31, 2006 5:38pm Finished: March 31, 2006 5:43pm Time spent: 5 min. 5 sec. Question 1 (1 point) Calculate the rate (in s^-1) of a reaction that obeys Avrami kinetics, knowing that the constants n and k have values of 1.1 and 4.2 x 10 -3 , respectively. Use scientific notation, significant figures in answer: 2 Student response: Not answered Correct answer: 9.6E-3 (9.6 * 10 -3 ) s^-1 General feedback: The Avrami equation is: where y is the fraction of the transformation that has occured at time t . The rate of transformation is given by: In order to solve for r , we need to determine how long it takes for half the transformation to occur. Making y = 0.5, we get: We solve for t , substituting our values for n and k , and then use that value in the rate equation above. For more information, see the section on The Kinetics of Solid-State Reactions in the text. Score: 0 / 1 ( Question not answered. ) Question 2 (1 point) True or False? Increasing the amount of cementite in an iron-carbon alloy will decrease the alloy's toughness and ductility. Student response: Correct Response Student Response Answer Choices a. True b. False General feedback: True . Cementite is harder, but more brittle than ferrite. Fe 3 C layers reinforce the ferrite layers in pearlite. However, because of its brittle nature, increased amounts of cementite also decrease the alloy's ductility and toughness (its ability to absorb impact energy). For more information, see the section on Mechanical Behaviour of Iron-Carbon Alloys in the text. Score: 0 / 1

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