Saturday 7th July
The second lecture was about Materials in action given by Dr Diane Aston, training and education executive at the Institute of Materials, Minerals and Mining.
Dr Aston began by explaining that everything we use or make has its origins in the Earth’s crust. Geologists, geophysicists and geochemists locate the materials. Then mining experts extract the useful materials using surface or underground extraction (physical processes such as pumping water or chemical processes) and mineral and materials engineers help us to use these resources.
The Periodic Table of Elements is a valuable tool that tells us about the materials around us.
This is a picture Bingham Canyon Mine. It has been a source of copper ore and molybdenum for over a hundred years.
Once the materials have been removed materials engineers get to work. Processing includes heating and applying force. Looking at the structure involves identifying how atoms bond together in the microstructure. Looking at the properties involves identifying the strength and toughness etc. We want to improve the properties of the materials and identify the right material for the job.
Materials are usually classified as metals/alloys, polymers, ceramics and composites. They can be further categorised as structural or functional materials.
A lump of chromium
Metals have good mechanical properties. They are ductile, sonorous and lustrous. They are good electrical and thermal conductors. It is very hard to get metals 100% pure and this isn’t always desirable (gold is far too soft for jewellery on its own). Deliberately adding impurities produces alloys. The impurities help improve the properties of the metals. Iron becomes steel and if the balance of impurities is just right then the steel has high strengths.
Polymers can be natural or synthetic. They have relatively low melting points and densities. They are poor electrical and thermal conductors. They don’t tend to have the ordered structure of metals. Thermoplastics can be recycled providing they are sorted properly. Plastics can be moulded by compression.
4% of our oil becomes plastic. It would make great sense to have clean incinerators for plastics.
Ceramics are inorganic and non-metallic. They can be crystalline or amorphous. Have ionic or covalent bonding or a mixture of both. They can have a high melting point. They are strong and stiff in compression but brittle. They can be electrical and thermal insulators or conductors.
A piezoelectric actuator, costing 300 Euros, controlling the flow of fuels into a car engine is made out of ceramics.
Composites are made by mixing two materials from metals, polymers and ceramics.
It can be argued that this is the silicon age as it is an important material for making microchips (processing data). It is the second most common element.
Very pure silicon is processed in order to change its structure and properties.
It is possible to produce silicon as one grain, i.e. a single crystal. Structure is modifies on a microstructural level from polycrystalline to monocrystalline. Single crystals are sliced to produce very thin wafers.
The structure is modified at an atomic level by doping to make it easier for electrons to flow through the structure.
In 2005 a stamp sized silicon chip had 250 million electronic components on it.
The next part of the lecture involved at the materials involved in making jet engines. The materials need to be able to cope with extreme stress and temperature. Safety is critical. The blade design was the limiting factor. Blades need to be lightweight, strong and stiff. Titanium blades are made by superplastic forming and diffusion bonding. Blades have a hollow, corrugated cross-section.
Air entering is squeezed.
We took a look at the materials involved in making the turbine. The forced rotation of the turbine drives the rest of the engine and operates under extreme temperatures and pressures. They are made from nickel-based super alloy. Blades attach to the disc with a “fir tree root” and they have their own in-built cooling system. They are designed to resist temperatures of 16000 degrees at 30000ft. Their main problem is creep i.e. dislocations at grain (crystal) boundaries sliding.
Single crystal blade takes 8 to 9 hours to cool and solidify. It needs to withstand temperatures of 350 degrees above its melting point. This done by blowing cold air through holes in it. Smooth air flow over a smooth surface.
Dr Aston ended her lecture by showing us some silly putty. This is a non-newtonian fluid. It has a high shear rate which causes increased viscosity and it can shatter. If you get trapped in custard move about a lot as this will thicken it and you will find it easier to get out but if you get trapped in ketchup try and move as little as possible as too much force will make it very runny. Custard and silly putty are shear thickening non-newtonian fluids and ketchup is a shear thinning non-newtonian fluid.
References: http://www.iom3.org/ http://en.wikipedia.org/wiki/Bingham_Canyon,_Utah http://en.wikipedia.org/wiki/Bingham_Canyon_Mine http://en.wikipedia.org/wiki/Superplastic_forming http://www.msm.cam.ac.uk/phase-trans/2005/Amir/bond.html http://www.wenzel-group.com/scantec/en/case-studies/detail-industry.php?we_ID=2710 http://www.explainthatstuff.com/energy-absorbing-materials.html
