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31/03/2006 5:43 PM
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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:
9.6E3 (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 SolidState Reactions
in the text.
Score:
0 / 1
(
Question not answered.
)
Question 2
(1 point)
True or False?
Increasing the amount of
cementite
in an ironcarbon 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 IronCarbon Alloys
in the text.
Score:
0 / 1
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 Winter '09
 OKON
 Polymer, Student response, NONFERROUS ALLOYS, Ferrous Alloys, Answer Choices a.

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