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EMA 3010 Study Guide - Midterm Guide: Tungsten, Activation Energy, Covalent BondExam

Materials Engineering
Course Code
EMA 3010
Study Guide

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EMA 3010 – Section 2965
Spring 2009Dr. H. El-Shall
First Midterm Exam Date: 2/23/09
Due date 3/11/09
1. A) In order to plate a steel part having a surface area of 200 square inches
with a 0.002inch thick layer of nickel, how many atoms of nickel are required,
and how many moles?
B)How many grams of aluminium, with a dislocated density of 1010 cm/cm3
are required to give a total dislocation length that would stretch from New York
City to Los Angeles (3000 miles)?
C) What fraction of the bonding in SiO2 is covalent?
2. A) A force of 100,000 N is applied to a 10mm x 20mm iron bar having yield
strength of 400 MPa and a tensile strength of 480 MPa. Determine whether the
bar will plastically deform, and whether the bar will experience necking.
B) Calculate the minimum diameter of a cable (made from the same
material in part A) to support an elevator cab weighing 10,000 lbs.
3. Calculate the lattice parameters of Fe at room temperature and at 1000°C. Also,
calculate the packing factor and density in each case. Calculate the volume
change due to heating and comment on the answer.
4. A BCC alloy of tungsten containing substitutional atoms of vanadium has the
following properties.
Density: ρWV = 16.912gm/cm3. Lattice Parameter: a0.WV:=3.1378•10-8cm
Calculate the fraction of vanadium atoms in the alloy
5. Determine the number of vacancies, n, needed for a BCC ion lattice to have a
density of 7.87 gm/cm3
6. The diffusion coefficient for Cr in Cr2O3 is found to be 6x10-15 cm2/sec at 1000K,
and 1x10-9 cm2/sec at 1673 K. Calculate the activation energy and D0.
7. A BCC iron structure is to be manufactured that will allow no more than 50
grams of hydrogen to be lost per year through each cm2 of iron, at 673 K. If the
concentration at one surface is 0.05 H atoms per unit cell, and 0.001 H atoms per
unit cell at the second surface, determine the minimum thickness of the iron.

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