Transcript Slide 1

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Prepared by Dr Diane Aston, IOM3
Armourers and
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What is Materials Science and
Engineering?
Prepared by Dr Diane Aston, IOM3
The aim of this module is to introduce you to
the subject of materials science and
engineering and give you an appreciation of
why it is important to understand the
processing, structure and properties of
materials.
Prepared by Dr Diane Aston, IOM3
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Classes of materials
Prepared by Dr Diane Aston, IOM3
The session aims to introduce the subject of Materials Science
and Engineering and allow you to explore the different groups of
materials and their properties.
At the end of this session you should be able to:
• Explain what Materials Science and Engineering are and why they are
important;
• Appreciate the differences between the three types of primary bond
and the importance of weaker forces and explain the differences
between mixtures and compounds;
• Describe the difference between a crystalline and amorphous
material.
• Define metallic, polymeric, ceramic and composite materials and
identify the main type of chemical bonds associated with each group
of materials;
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Materials Science, Materials Technology and Materials
Engineering are all names given to the discipline concerned
with understanding everything there is to know about the
materials around us.
It is the study of the design, characterisation, manipulation,
production and application of materials.
‘Materials’ forms the bridge between fundamental science
and applied engineering as we need to understand materials
on a small scale in order to understand how and where we
can use them on a large scale.
There has been a materials expert of some kind involved in
designing and developing every single thing that you use
every single day of your life because everything is made out
of something. Materials experts are in demand!
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Armourers and
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WHAT ARE MATERIALS MADE OF?
If you start by understanding the building blocks of materials
everything else makes sense...
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• All materials are made from atoms.
• Atoms have a central nucleus
containing positively charged
protons and neutrons which have no
charge. These particles give the
atom its mass.
• The nucleus is surrounded by a cloud
of negatively charged electrons.
These particles are so small that they
are not considered to contribute to
the mass of the atom.
• The electrons in the cloud occupy
specific shells which correspond to
particular energy levels.
• Number of protons and electrons is
equal so atoms have no charge.
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• An element is comprised of atoms
that are all the same.
• Each element has a unique number
of protons, neutrons and electrons.
• Each element has an atomic number
equal to the number of protons and
an atomic mass.
• The atomic mass is not always a
whole number as many elements
have isotopes.
• The isotopes of a particular element
all have the same number of
electrons and protons but different
numbers of neutrons. For example
most carbon atoms have six neutrons
but some have seven or eight.
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Hydrogen
Helium
Sodium
Chlorine
Iron
1P, 1e2P, 2N, 2e11P, 12N, 11e17P, 18N, 17e26P, 30N, 26e-
I II
H
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
Fr Ra
Sc
Y
Lu
Lr
Ti
Zr
Hf
Rf
V Cr Mn Fe
Nb Mo Tc Ru
Ta W Re Os
Db Sg Bh Hs
Co
Rh
Ir
Mt
Ni
Pd
Pt
Ds
Cu
Ag
Au
Ry
Zn
Cd
Hg
Cn
III IV V VI VII VIII
He
B C N O F Ne
Al Si P S Cl Ar
Ga Ge As Se Br Kr
In Sn Sb Te I Xe
Tl Pb Bi Po At Rn
Uut Fl Uup Lv UUs UUo
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
Ac Th Ps U Pu Am Cm Bk Cf Es Fm Md No Lr
The Periodic Table as we know
it was conceived by Russian
scientist Dmitri Ivanovich
Mendeleev in 1869. He left
gaps in his original table which
were later filled as new
elements were discovered.
The columns are known as
groups and the rows as
periods.
• The Periodic Table is a very useful tool as it is a map of all the elements we have
from which we can build other materials.
• It gives us an indication of how heavy elements are, how reactive they are and
which ones might react together to give stable compounds.
• Some elements are very stable, others very reactive and some radioactive. Some
are very common, some very rare and some have only ever been produced by
synthesis in a lab.
• We tend to use mixtures and compounds of the elements rather than individual
ones.
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Armourers and
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Atoms are social creatures and like to be together!
The way in which atoms bond together to form molecules or
crystals affects some properties of materials.
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Compound
Mixture
• Made from two or more chemical
elements held together in a
particular spacial arrangement
by chemical bonds.
• Made from two or more chemical
substances by mechanical means
(e.g. stirring, shaking, melting).
• Properties are different to those
of the constituent elements.
• Elements are present in a
specific and constant ratio –
water is always two hydrogen
and one oxygen.
• Elements can only be joined or
separated by a chemical reaction.
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• Properties closely related and
dependent on ingredients.
• Ingredients can be added in any
ratio.
• Ingredients can be separated by
mechanical means (e.g. filtering,
evaporation, magnetism).
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• The number of electrons in the outer shell and
their distance from the nucleus affects the type of
bonding.
• The aim is always to have a full outer electron shell.
• Electrons can be shared in a number of different
ways to produce three types of strong chemical
bond.
• The type of bonding affects some of the materials
properties.
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• Characterised by atoms
sharing pairs of
electrons to achieve a
full outer shell.
• Tend to be poor
electrical and thermal
conductors and have
relatively low melting
points.
• Can form single
molecules or large
macromolecules.
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• Since electrons all have
the same negative
charge and like charges
repel the electrons try to
be as far away from each
other as possible.
• This leads to molecules
with specific fixed
shapes.
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• Characterised by
electrostatic attraction
between oppositely
charged ions in order to
get a full outer electron
shell.
• Tend to conduct
electricity in liquid state
and have relatively high
melting points.
• Can form large crystal
lattices.
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• Ionic crystal lattices can take on a number of
different geometries depending on the relative size of
the ions.
• There are 14 possible crystal structures.
Sodium chloride adopts a face
centred cubic structure
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Caesium chloride adopts a
body centred cubic structure
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• Characterised by sharing
of free electrons among
a lattice of positively
charged nuclei.
• Tend to be good
electrical and thermal
conductors.
• Form close packed
lattices due to nondirectional nature of the
bonding.
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• Different ways of laying up planes of close packed
atoms.
• Three main equilibrium crystal structures but
others are possible.
Hexagonal close
packed
Body-centred
cubic
Face-centred
cubic
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Van der Waals forces
Hydrogen bonding
• Intermolecular force.
• Sum of attractive and
repulsive forces between
molecules.
• Important in polymer
chemistry, nanotechnology
and surface science.
• Interaction of hydrogen atom
with an atom of oxygen,
nitrogen or fluorine from
another molecule or within
the same molecule.
• Reason that water expands
slightly as it freezes.
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Armourers and
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It is important to know how the individual molecules or crystals
in a material arrange themselves with regards to each other as
this can affect properties too.
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• In a crystalline material the atoms or molecules
arrange themselves in a regular way and this
pattern is constant throughout the material.
Crystalline materials are said to exhibit long range
order.
• A monocrystalline material contains just one
crystal and the structure is the same everywhere
you look within the material.
• In a polycrystalline material the atoms in each
individual crystallite or grain have the same
structure but the orientation varies between
adjacent grains.
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• Amorphous materials demonstrate no ordering at
all. This can either be because the molecules will
not fit together in a regular arrangement or
because the cooling rate has been too fast to allow
the atoms to become ordered.
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• In reality materials often have complex structures.
• They may consist of crystalline and non-crystalline regions
and may vary chemically throughout the structure as
segregation can occur on cooling and particles can form.
• The microstructure of an individual material could be
controlled by changing processing conditions but the type of
atomic bonding will remain the same. Materials in one
particular group tend to show a particular type of bonding.
• Understanding the relationship between processing,
structure and properties is key to materials selection.
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We can use the elements to make hundreds of thousands of
useful materials. We split these materials in to three primary
groups and one secondary group...
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Metals
Composites
Polymers
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Ceramics
• Most of the elements in the Periodic Table are
metallic and they are characterised by containing
metallic bonds. This is a non-directional type of
bonding so metals have roughly the same
properties in all directions.
• Metallic materials tend to:
• have good mechanical properties
• be ductile, malleable, sonorous and lustrous
• be good electrical and thermal conductors
• Wide range of densities, melting points and
corrosion resistance.
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• Don’t tend to make things out of pure metals.
• Making metal 100% pure can be difficult.
• Having some kind of ‘impurity’ can improve
properties.
• Alloys are made by mixing different metals and
non-metals together in different proportions.
• By combing different elements an infinite number
of alloys with exactly the right properties can be
made.
• Alloys are said to be solid solutions in which one
substance (the solute) is dissolved in another
(solvent).
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• Formed when the solvent and
solute have about the same
atomic radius.
• The solute atoms may be
slightly smaller or slightly
larger than the solvent.
• This introduces a slight strain
in the lattice making it more
difficult for the close packed
planes of atoms to slide
across each other, thus
strengthening the material.
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• Formed when the solvent
atoms are much larger then
the solute atoms.
• Solute sits in the gaps in the
lattice and make it more
difficult for the planes to slide
across each other.
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• Simple alloys are made by mixing just two metals
together.
• The metals may be mutually soluble at all
temperatures and compositions or they may only
exhibit limited solubility
• By changing relative proportions of the
constituents the properties can be controlled.
• For example:
• Brass is a mixture of copper and zinc
• Bronze is a mixture of copper and tin
• Solder is mixture of lead and tin
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• More complex alloys involve the addition of more
than one ingredient.
• Each ingredient contributes towards improving
properties in a particular way.
• They may be a mixture of substitutional and
interstitial ingredients and particles may also be
present.
• For example:
• Steel is Fe and C with other elements such as Nb,
Ti, N, Ni, Cr, Mn, B, Si
• Ni-based superalloys contain Cr, Mo, Mn, Al, Fe, B,
Re, Ru
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• Tend to be organic compounds consisting of large
covalently bonded molecules of repeated structural
units held together by weaker Van der Waals
forces.
• Poly many, mer parts
• Includes many natural and synthetic materials.
• Tend to have relatively low melting points and
densities, and be electrical and thermal insulators.
Polymer are not as strong as metals
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• Molecules tend to have long backbone with side
groups coming off.
• Geometry of molecules dictates whether polymer
will be crystalline or amorphous.
• Can be split into three subgroups:
• Thermosoftening materials
• Thermosetting materials
• Elastomers
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• Often called thermoplastics, they can be melted
and shaped by the application of heat.
• Consist of long, covalently bonded molecules held
together by weaker Van der Waals forces.
• Can be elastic and flexible or glassy and brittle.
This depends on whether they are crystalline,
semi-crystalline or amorphous materials and this
is influenced by the shape of the polymer
molecules.
• Include PE, PP, PS, PC, PVC, PMMA.
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• Non-renewable materials originating from oil.
• Can be recycled provided they are sorted.
• Very durable materials, lasting for many hundreds
of years without degradation.
• Many used in low-tech, high volume applications
such as packaging, textiles and seating.
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• Individual covalently bonded molecules are held
together by cross links to create a continuous three
dimensional lattice of strong bonds.
• Once a thermoset has solidified in a particular
shape and the cross-link covalent bonds have
formed, it cannot be re-melted.
• Thermosets tend to be stronger but more brittle
than thermoplastics.
• Include melamine, epoxy resin, bakelite, vulcanized
rubber.
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• Elastomers can be thermosoftening or
thermosetting polymers.
• They generally consist of cross-linked 3D
networks.
• Characterised by ability to extend considerably
without plastic deformation as rather than
breaking bonds, the molecules are simply being
straightened out.
• Include natural rubber and synthetic rubbers such
as nitrile, butyl, polybutadiene, silicone rubber.
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• Inorganic, non-metallic solid prepared by the
action of heat and subsequent cooling.
• Can be crystalline or amorphous.
• Bonding can be ionic, covalent or a mixture, but
ceramics only ever contain strong bonds.
• As a consequence of the strong bonds they can
have very high melting points.
• Strong and stiff in compression but brittle.
• Can be electrical and thermal insulators or
conductors depending on their structure and
bonding.
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• Structural ceramics
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• Clay-based materials
• Bricks, pipes, tiles
• Engineering ceramics
• Used for their thermal, electrical or impact properties
• Oxides, nitrides, carbides
• Refractories
• Kiln linings, fire retardants, crucibles
• Whitewares
• Earthenware, stoneware, porcelain for tableware, sanitaryware,
pottery and tiles.
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• Composites are made by mixing materials from the
other groups together.
• The new composite material has superior
properties to its constituent materials.
• Composites can be defined by the matrix or
background material: metal matrix, polymer
matrix, ceramic matrix composite or by the type of
reinforcement: carbon fibre, glass fibre composites.
• By changing the type, size, shape and amount of
reinforcement the properties can be changed.
• Composites include many natural materials.
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• Materials are all around us and Materials Scientists
and Engineers play a vital role in designing,
characterising, selecting and using the materials
we take for granted everyday.
• Materials generally fall into one of three primary
classes, namely metals, polymers and ceramics or
they are composites made by mixing materials
together.
• Each class of materials is characterised by a
particular type of bonding and has key features to
its structure.
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Armourers and
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Prepared by Dr Diane Aston, IOM3
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Crystal structures practical
Microstructure research
Materials selection exercise
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• Working in small groups use a readily available system for the
construction of structural models (molymod or Cochranes of
Oxford) to build unit cells of common structures such as HCP,
FCC and BCC, graphite, diamond, etc..
• If a commercial kit is not available you could use plasticene
balls and straws or polystyrene balls.
• Look at the structures from difference angles and see if you
can determine which structures are strongest and why.
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• Working in small groups or individually look at common
objects and try and determine whether they are crystalline or
non-crystalline and the reasons why.
• Use cooked spaghetti to simulate the structure of crystalline,
semi-crystalline and amorphous materials.
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• Look at common objects made from different metals,
polymers, ceramics and glasses and identify the key
properties of that material which make it fit for purpose.
• For example pans are made from metals as they are good
thermal conductors but pan handles are made from polymers
as these are good insulators.
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Armourers and
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Prepared by Dr Diane Aston, IOM3