10.1 structure of the main types of engineering

10.1 Knowing the structure and classification of
engineering materials

 

The aim of this report is to produce a report that
summarises the structure of the main types of engineering materials, this
includes metals, polymers, ceramics, composite materials and smart materials I
will also explain the structure of my chosen metal. Depending on my research I
will produce a ‘Family Tree’ that groups engineering materials into categories
according to their properties.  

Periodic Table

In the periodic table there are 7 groups and elements
in the same group are similar to each other. The elements are arranged in order
of increasing atomic number. The elements in the first group are alkali metals,
these types of metals are usually so reactive that they are usually found in
nature combined with other elements. Elements in the second group are alkaline
earth metals, they are 6 chemicals that are very reactive and are at standard
temperature and pressure. In the third group, rare earth metals are found, the
elements all occur naturally. In the fourth group there are also rare earth
metals alongside two non-metals; carbon and silicon. This is the same for the 5th
and 6th group, non-metals and rare earth metals are found in these
groups. In the 7th group, halogens are found, halogens have low
melting and boiling points, this is typical for non-metals. There is also a
trend in state from gas to liquid as you go down group 7. Finally, Noble gases,
these are found in group 0. Noble gases are all chemically unreactive gases. An
example of a use of a noble gas is Helium, which is used for balloons and air
ships, since helium is much less dense than oxygen, so balloons and airships
filled with it float upwards. There are more groups but all of the elements in
those groups are transition metals. Transition metals are good conductors of
heat and electricity. Transition metals are also malleable, they have high
melting points, except for mercury which is liquid at room temperature.

The structure of an atom, an atom consists of
electrons which surrounds the nucleus, which contains protons and neutrons. The
neutrons but protons and electrons are electrically charged. Protons have a
relative charge of +1 and electrons have a relative charge of -1. The number of
protons in an atom is called the atomic number, in the periodic table the
elements are arranged in atomic number order. The electrons are arranged in
energy levels/shells; different energy level can hold different numbers of
electrons. The electronic structure of an atom is a description of how the
electrons are arranged. There is a link between the positions of elements in
the periodic table and the electronic structure.

 

 

 

 

 

 

 

 

A valence electron is an outer shell electron that is
associated with an atom, and that can also participate in the formation of a
chemical bond if the outer shell is not closed. But in a covalent bond, both
atoms in the bond contribute one valence electron in order to form a shared
pair. A covalent bond is formed between non-metal atoms; they combine together
by sharing electrons. Covalent compounds have no free electrons and no ions so
they don’t conduct electricity. The shared pair of electrons holds the two
atoms together; it is called a covalent bond. The group of atoms bonded
together this way is a called a molecule.

Bonding between atoms

In Ionic bonding both positive and negative ions
attract one another and bind together to form a new substance; this is what
ionic bonding is. Atoms turn into ions when they lose or gain electrons. There
are several ways in which atoms chemically combine to make a compound. In metal
ions, a metal atom may lose electrons, the atom is then left with more protons
than electrons and therefore it is a positive ion. On the other hand, non-metal
ions may gay electrons and become negatively charged atoms. Ionic compounds
usually have high melting point and do not conduct electricity when solid but
do conduct electricity when molten.

In metallic bonding, the particles in a metal are all
held together by metallic bonds. Metallic bonding is a strong attraction
between closely packed positive metal ions and a ‘sea’ of delocalized
electrons. The attraction between these two must be overcome for the metal to
be melted or boiled. The forces of attraction are strong, so metals have high
melting and boiling points. Metals also have electrons, which are free to move,
carrying a charge from place to place, which allows metals to conduct
electricity.

A compound is formed when atoms from different
elements join by chemical bonds. This pretty much means that compounds will
always exist as molecules and no as separate atoms. However, some atoms do not
join up at all, therefore they stay single atoms.

Finally, a molecule is a group of atoms that are
bonded together. A molecule represents the smallest fundamental component of a
chemical compound that is able to take part in a chemical reaction.

 

Structure of metals

The structure of a metal consists of particles in a
metal that are held together by strong metallic bonds. It would take a lot of
energy to separate these particles. Solid metals are crystalline; this means
particles are held closely together and in regular arrangement. Metals have
loose electrons in the outer shells, which form a sea of delocalized negative
charges around the tightly packed positive ions. Strong electrostatic forces
hold the particles together. The properties of metal are changed by adding
other elements to it. A combination of two or more elements, where at least one
element is a metal, this is called an alloy. An alloy contains atoms of
different sizes, which changes the regular arrangement of atoms. Therefore
making it more difficult for the layers to slide over each other and causing
the metal to snap or break. Alloys are harder/stronger than the pure metal.

Furthermore, there are Ferrous and non-ferrous metals.
A Ferrous metal will contain iron and a non-ferrous metal will not. Non-ferrous
metals are also more resistant to corrosion and are not magnetic. Some examples
of non-ferrous metals are aluminium and aluminium alloys.

Common crystal lattice structure; they have structures
that can be described as Body Centric Cubic (BCC) packing of spheres. The other
two common ones are Face Centred Cubic (FCC), which are spheres packed together
diagonally and Hexagonal Closest Packaging (HCP), which have a hexagonally
closely packed crystal structure. Metals have a crystalline structure, which is
not usually visible but can be seen using a galvanized lamp for example. When a
metal starts to solidify from its molten state, millions of tiny crystals begin
to grow. The longer the cooling process the larger the crystals grow. Each
grain is a distinct crystal and they form inside the solid metal.