What do we mean by interdependence and interrelation?
If you look at the molecular structure of a
material, you can get an idea of what kinds of properties
it will have. For example, a crystalline material has
a highly ordered molecular structure which makes it much harder
than a non-crystalline material. However, using special
processing techniques such as adding modifiers and fillers,
the hardness property of a non-crystalline material can be
improved. The key to understanding our material world
is that the structure, properties, processing and performance
of a material are all interdependent and interrelated.
Let's expand on this concept using rubber as
an example.
***Need questions to quiz on Properties, Structure,
Performance, and Processing***
Structure
The structure of a material is the arrangement of atoms,
ions, or molecules that make up the material. If the
atoms form an ordered, three-dimensional, geometric arrangement
like that seen here, then the material is known as a crystalline
solid. To some degree, the structure of a material
will dictate what kinds of properties it possesses.
For example, the highly ordered carbon atoms of a diamond
make it extremely hard.
The molecular structure of natural rubber is
composed of carbon atoms and smaller hydrogen atoms.
However, its amorphous mass of coiled and kinked chains readily
allows motion of its molecular chain making it extremely flexible.
In its natural form, rubber too soft to be used for any useful
purposes. Therefore, its properties were improved using
special processing techniques.
Can you identify the carbon and hydrogen atoms?
Properties
A material's properties are largely dependent
upon the internal arrangement of atoms (structure) and the
interaction with neighboring atoms. Some examples of
material properties include hardness, softness, elasticity,
and conductivity.
The long chain structure of natural rubber allows
it to spring back into shape when it is compressed or stretched.
Under a tensile load, the structure of rubber changes as the
bonds straighten and the chains become elongated. As
more and more stress is applied to the structure of rubber,
crystallinity is achieved. The increase in crystallinity
causes greater strength, increased hardness, and increased
rigidity in rubber.
insert pics of bond lengthening and straightening
The problem with natural rubber is it is too
soft and is prone to degrade as it ages. UV light, oxygen,
and heat all break down rubber's structure. In order
to make it more useful as a material, rubber can be processed
to yield better mechanical strength.
Processing
Processing is altering the internal structure
of a material by the addition of materials or the use of different
treatment methods to improve or change the properties of the
original material.
The problem with natural rubber is it is too
soft and broken down too quickly by UV light, oxygen, and
heat to be of much use. Therefore, in order to make
it a more useful material, there needs to be a way to improve
its mechanical properties.
In 1839, Charles Goodyear discovered a process
for converting soft natural rubber into a harder, less flexible
material which is known as the 'rubber' in our tires today.
Vulcanization is a process in which sulfur, when combined
with the natural compounds of rubber, cross links the molecular
chains at their double bonds to restrict molecular movement,
and increase hardness.
insert pic of processing natural and synthetic
rubber into tire
Today, tires are made by combining both natural
and synthetic rubbers. The rubbers are mixed with carbon
black, sulfur, and other chemical agents (modifiers) and then
extruded into sheets. Through a series of additional
processes, the natural rubber can be made into an automobile
tire with specific properties.
Performance:
Putting it all together
The resultant knowledge of the structure,
properties, and processing of materials is used by engineers
to ultimately obtain the desired performance of the material.
In our example starting from natural rubber, we know that
the molecular structure of the bonds allows flexibility and
resilience to spring back into shape.
However these properties alone were not enough
to make rubber a useful material. Natural rubber
is too soft and degrades quickly. As a result, adding
modifiers and fillers as well as other processing techniques,
the strength, rigidity, and hardness of rubber can be modified
to make an automobile tire.
