• Stony Brook University

• ESG 332 Materials Science I

Prof Clive Clayton Instructor EGS 332 exam #1 October 13th 2016
Answer all questions.
(Please note that cheating will lead to a grade of F)
1.) Define the following terms as completely as possible giving diagrams where
appropriate:-
Electronegativity (5pts)
Solid solubility and what factors affect its limit (10pts)
Burgers vector of an edge dislocation (5pts)
Give the electronic configuration Kr Atomic Number 36 (5pts)
2.) Briefly describe the following:-
the essential differences between surface, bulk and grain boundary diffusion (10pts)
the Ficks first and second laws of diffusion and illustrate for each a practical use of these
laws.(15pts)
3) Briefly describe four ways to strengthen a metal. Give diagrams to illustrate your
answer.(25pts)
4) Describe fully the atomic processes which give rise to Plastic deformation (5pts)
5)- Sketch and label the Energy-distance curve for the following metals exhibiting:
a) high elastic modulus
b) low hardness
c) high self-diffusivity
d) low melting point.
Explain your answers briefly (20pts)
1.) Define the following terms as completely as possible:-
Electronegativity-
-Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is
assigned a value of 4.0, and values range down to caesium and francium which are the
least electronegative at 0.7.
Hydrogen Bonding (5pts)
 Hydrogen Bonding arises from Secondary Bonding or Van Der Waals bonding. It
is a special type of secondary bonding found to exist between molecules that
have hydrogen as one of its parts. The bonding results from coulombic attraction
between the positive end of a dipole and the negative region. Hydrogen bonding
occurs in compounds NH3, H2O, and HF. The noticed trend is that Hydrogen has
bonded to some of the most electronegative elements causing Hydrogen to
acquire a significant amount of positive charge. Also, each of the elements the
hydrogen has bonded to has had 1 active lone pair. If we take H2O as the lead
example one can see that a water molecule can form four hydrogen bonds
potentially with other water molecules. This means that there is the exact amount
of lone pairs so that every hydrogen + atom can be involved with hydrogen
bonding. This is one of the main reasons that water is a permanent dipole. The
magnitude of hydrogen bonds can be seen as high as 51kj/mol. This is one of the
main reasons why water boils at a much greater temperature that other
compounds.
Solid solubility and what factors affect its limit (10pts)
 A solid solution forms when a solute is added to a host material, and it maintains
its crystal structure with no new structures forming. A solid solution is
homogenous in composition with its impurity atoms occurring uniformly within the
solid. There are two types of impurity defects which are interstitial and
substitution. Substitution: has solute or impurity atoms replace or substitute host
atoms. There are four features that affect a solids ability to dissolve with another
material
o Atomic Size Factor: If the atomic radii between two atoms is less than
15% of each other solutes may be accommodated for. If they’re greater
than 15% then there will be many distortions within the lattice.
o Crystal Structure: For metals both crystal structures must be the same
o Electronegativity: The more electropositive one element is and the more
electronegative the other is increases the likelihood that they will form an
intermetallic compound instead of a substitutional solid solution
o Valences: A metal will have more of a tendency to dissolve another metal
of higher valency than one of lower valency.
Burgers vector of an edge dislocation (5pts)
 A vector that denotes the magnitude and direction of lattice distortion associated
with a dislocation. Fig 4.3(pg75) The atom positions around an edge dislocation.
Edge, screw, or mixed dislocation is defined by the relative orientations of
dislocation line and burgers vector. For an edge they are perpendicular (fig 4.3).
 An edge dislocation: a linear defect that centers on the line that is defined along
the end of the extra half-plane of atoms. Dislocation lines or edge dislocations,
result in atoms being squeezed together and atoms being pulled apart. The
dislocation is seen as atoms bending around the extra half-plane.