Pores are spaces in materials.
Pores are present in many materials, resulting in a material that is not fully dense. An example of pores are in sponges, where the gaps can hold water and help you wash dirty plates and dishes! However, pores are also found in other materials such as ceramics, metals and polymers.
Pores can change the behaviour of a material. Therefore, as a materials scientist we need to understand the following points:
The following resources and activities were displayed at the Big Bang Fair, National Exhibition Centre (NEC), Birmingham in Summer 2023.
Examples of materials include foams, aerated chocolate bars, sponges and rocks (e.g. pumice stones).
The boxes are a model for particle packing, and contain different sizes and geometries of particles. This is suitable for thinking of crystal structures or for powder processing in manufacturing ceramics.
Box 1: Big spheres, all the same size.
Box 2: Small spheres, all the same size.
Box 3: A combination of the spheres from Box 1 and Box 2.
Box 4: A combination of different geometries.
Further details on calculating packing fractions for particular crystal structures can be found here: PDF_Packing_Fraction_Calculations_20230617_DS.
Foam balls placed between Perspex discs show how pores affect the mechanical properties of ceramics. When there are less balls between the perspex discs, it is easier to squash the discs. This relates to the stiffness of materials as a function of porosity. Denser materials are stiffer.
Why do we want pores in these materials? How do we make the materials to get pores? Introduce gases in manufacture.
Pores in these materials make them better insulators. Why do pores make better insulators? (Hint: Think about conduction, convection and radiation mechanisms for heat transfer).
Metals containing pores can make them easier to break. Taking images of pores can be done using X-ray computed tomography. You may know about these if someone has broken a bone and has had an X-ray scan.
Metals have different crystal structures. The different crystal structures of metals affect the packing of metal ions. Some examples of different crystal structures include: Face-centered cubic (FCC) – Aluminium; Body-Centered Cubic (BCC) – Iron, and Hexagonal Close Packed (HCP) – Zinc. Further examples of materials with particular crystal structures and materials containing porosity can be found here: PDF_Crystal_Structure_Examples_20230617_DS.
The resources used at the Big Bang Fair 2023 stand are listed here: DM_Porosity_In_Materials_Resource_List_20230617_DS.
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