Videos
https://www.youtube.com/watch?v=zd9HJV8kTTM
Calcite is a mineral made of carbon (chemical symbol C), calcium (Ca) and oxygen (O). For every carbon atom there is one calcium atom and three oxygen atoms. Calcite is a crystal and therefore is made up of the same building block repeated over and over again.
The consequences of this regular repeating structure can be seen macroscopically; first in the shape of the overall crystal, and secondly when the crystal breaks. Calcite always breaks along certain direction, which correspond to specific layers of atoms. This process is called cleavage, and is the same mechanism that enables thin slate roofing tiles to be produced. Imagine you have a tower of Lego bricks, if bent, it will always break at the joins between the bricks. The same idea applies to the calcite crystal. When it was hit with the hammer in the video, it broke along its weakest directions, producing smaller regular shapes, which reflect the underlying crystal structure.
For us, as materials scientists, it is incredibly important to understand how materials deform when they are put under different types stress (simply hit roughly with a hammer, or carefully pushed with a knife blade). If we can understand how they deform, we can then start to work out how to prevent this deformation and so create new materials with more desirable properties!
https://www.youtube.com/watch?v=2a9eI5gGxQA
In the video we can see a thin stainless steel foil being heated by a candle. You should notice that as the steel is heated, the colour changes.
Steel is a classical example of a type of material called an alloy, made by dissolving elements in one another. Steels are made by mixing a small amount of carbon into iron. This process, known as alloying, can radically change the properties of the material, making them harder or stronger or environmentally resistant.
As the steel is heated, oxygen in the air reacts with the steel surface forming compounds called oxides. Stainless steels, like this one, also contain the element Chromium. It is the Chromium oxide that forms during the heating that gives rise to the colours we see. Depending on the thickness of the oxide layer, we see a different colour. This thickness then depends on the temperature reached by the material at that point. We can therefore use this colour to suggest how the temperature varied across the surface during the heating process (shown on the diagram). The colours and their related temperatures are as follows: Golden (200-240°C), Red (240-270°C), Violet (280°C), Blue (290°C), Grey (over 360°C).
Blacksmiths use these colours to indicate the temperature to which the alloy has been heated to, and therefore the physical properties it may have. The picture below shows a sword that has been heated in this way – a process called tempering. The golden colour on the edge of the blade shows that the metal was much cooler here compared to the middle. This makes the edge of the blade very hard, but the centre of the blade remains softer. This is essential for swords and knives as it provides the toughness needed for the edge of the blade but prevents the blade from becoming very brittle – which would lead to the sword shattering when you tried to use it!
https://www.youtube.com/watch?v=cWJyH1Il9XA
Cornflakes are magnetic because they contain a significant amount of iron, a magnetic material. Standard cornflakes contain around 8 milligrams of iron per 100 grams (so 0.008% of the weight of a cornflake is iron). This is enough to cause a floating cornflake to move when it is near a magnet.
We know that materials like iron (and materials that contain iron, like steel) are magnetic. However, they don't always act like permanent magnets - we can't use a random piece of steel to pick up other bits of steel. So, what makes a magnetic material act like a permanent magnet?
In any magnetic material, the atoms act like small magnets. In permanent magnets, all these small magnets line up. This makes the material act like one big magnet.
In magnetic materials that don't act like magnets, like steel, all these small magnets are misaligned, so they cancel each other out. However, when a permanent magnet is placed next to the material, all the small magnets in the magnetic material are attracted to the big magnet and become aligned. This means they start acting like a big magnet too so the materials now attract each other.
Usually, if the permanent magnet is removed, then the material will go back to being misaligned again. However, we can permanently magnetise a material by holding it in a strong magnet field. This is what happens to knives and forks if we store them on a magnetic rack in the kitchen, or if we hold a paperclip next to a permanent magnet for a long time.
https://www.youtube.com/embed/Zi5jI3L6QAE
A fantastic example of an amazing property of some alloys that is caused and controlled by the arrangement of the atoms - the ability of a solid piece of metal to ‘remember’ a previous shape! These Shape Memory alloys, made from titanium and nickel, can be used to control and optimise airflow in jet engines where conventional hydraulic or electrical control systems would be unable to operate. But how do they work?
The Shape memory effect is controlled by a structural rearrangement on the atomic scale. You can find out more about this process on our Engineering Atoms page.