Introducing and classifying materials

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Introducing and classifying materials
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Atom

• Definition
• The smallest part of an element that can exist
  chemically

This image shows the smallest portion into which
an element can be divided (atom) and still retain
its properties, made up of a dense, positively
charged nucleus surrounded by a system of
electrons.
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Molecule

• Definition
• Two or more atoms that are normally bonded
  together covalently.

This image shows a number of atoms bonded
together with a chemical bond in which the
attractive force between atoms is created by the
sharing of electrons (covalently).
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Alloy

• Definition
• A mixture that contains at least one metal.
  This can be a mixture of metals or a mixture of
  metals and non-metals.

These Motocross goggles are made of an alloy mix
of metal and plastic.
Alloy rims are a mixture of metal and other
materials
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Composite

• Definition
• A mixture composed of two or more substances
  (materials) with one substance acting as the
  matrix or glue.

Many tennis rackets, racing bicycles, and skis
are now fabricated from a carbon fibre-epoxy
composite that is strong, light, and only
moderately expensive.
A cross section view of a carbon-epoxy composite
showing the strong and stiff graphite fibres
embedded in the tough epoxy matrix.
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Bonds

• Bonds are a force of attraction between atoms.
• There are three main types of bond
• Ionic
• Covalent
• Metallic

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Bonds

• Ionic
• An ionic bond (or electrovalent bond) is a type
  of chemical bond based on electrostatic forces
  between two oppositely-charged ions. In ionic
  bond formation, a metal donates an electron, due
  to a low electro negativity to form a positive
  ion or cation (a cation is an ion with a positive
  charge. It is the inverse anion). In ordinary
  table salt (NaCl), the bonds between the sodium
  and chloride ions are ionic bonds.

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Bonds

• Covalent
• Covalent bonding is a form of chemical bonding
  that is characterized by the sharing of pairs of
  electrons between atoms. In short,
  attraction-to-repulsion stability that forms
  between atoms when they share electrons is known
  as covalent bonding.

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Bonds

• Metallic
• Metallic bonding is the bonding between atoms
  within metals. It involves the delocalised
  sharing of free electrons among a lattice of
  metal atoms. Thus, metallic bonds may be compared
  to molten salts.
• Metallic bonding is the electrostatic attraction
  between the metal atoms or ions and the
  delocalized electrons, also called conduction
  electrons. This is why atoms or layers are
  allowed to slide past each other, resulting in
  the characteristic properties of malleability and
  ductility.

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Introducing and classifying materials
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• Materials can be classified into groups according
  to similarities in their microstructures and
  properties.
• Several classifications are recognised, but no
  single classification is perfect. It is
  convenient to be able to classify materials into
  groups which have characteristic combinations of
  properties.

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• For this course materials are classified into the
  following groups
• Timber
• Metals
• Ceramics
• Plastic
• Textile Fibres
• Food
• Composites
• Some of these groups have subdivisions

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• Subdivisions
• Timber Natural Wood or Composite. Hardwood or
  softwood.
• Metals Ferrous or Nonferrous.
• Ceramics Stoneware, Earthenware or Porcelain.
• Plastics Thermosets and Thermoplastics.
• Textile Fibres Natural or synthetic.
• Food Animal or Vegetable origin.
• Composites are difficult to classify due to
  variability and the development of new ones.