For me, one of the most irritating things about woo-mongering is the implication that we need magic and fairy stories to make something awesome. But as this blog as a whole and this series of posts in particular aims to prove, reality is plenty awesome enough on its own.
Today’s example of awesomeness is… Little Science!
During this series of posts, I’ve mentioned Big Science twice. Big Science is great, but I don’t want to give the impression that it’s the be all and end all of awesome! So it’s time to turn the spotlight on little science – the stuff that influences our daily lives without us really noticing.
Here is a picture of 5 random objects I chose from around my flat. They are: a non-stick frying pan, a mirror, a fork, a battery, and an LED reading light. I’m going to try and tell you about the little (and not-so-little) science behind all of these things.
1. Non-stick frying pan. This one’s easy. The non-stick coating on the pan is something called Teflon, a polymer made of carbon and fluorine. It’s otherwise known as PTFE – polytetrafluoroethylene. The reason it is so fabulously non-sticky is a property called hydrophobicity: PTFE repels water. This can be easily demonstrated by putting a drop of water on a PTFE surface. The droplet will be much “rounder” than a similar droplet on a non-PTFE surface. This is really easier to see with a picture:
In research, the angle which a droplet of water makes with a surface is used to characterise the hydrophobicity of a surface. Cool, huh?
PTFE is also very inert, that is to say, non-reactive. For this reason it’s used to protect pipes and containers from corrosive chemicals, and I use it every day in the lab as a liner for my steel reaction vessels. It’s also an excellent lubricant because it generates very little friction when rubbed against other surfaces.
2. A mirror. Used to examine ones reflection to aid in the beautification process, mirrors are packed with science. They are generally made of a sheet of glass with a thin metallic film applied to the back, but this isn’t as simple as it sounds. In order to make a mirror in this way, you have to have a metal which is highly reflective, stable, non-toxic, and capable of sticking to glass. Mercury is great at sticking to glass (and was used in some of the first glass mirrors), but is inconveniently poisonous. Gallium and its alloys also stick to glass (I found this out the hard way in the lad by accidently turning a microscope slide into a mirror) but are rather expensive…
Silver is a classic choice for mirror making, but it won’t stick to glass on its own, so the production of silver backed mirror has several steps. Here’s a video which explains it in detail, which is worth watching with the sound up for the first few seconds alone.
Clean glass is sprayed with tin chloride, which provides something for the silver to stick to. Then a silver solution is applied, followed by a layer of copper to protect the silver from tarnishing, and finally layers of paint to protect the thin metallic films. Making silver mirrors is a chemical process.
Some mirrors are made by applying a thin layer of aluminium in a vacuum chamber. This is a physical process, and it’s particularly useful for making mirrors that need to have the reflective surface on the front (e.g telescopes) because the product of aluminium “tarnishing” is transparent, and protects the surface from further corrosion.
If we were to get into the subject of mirrors that reflect things other than visible light, I could go on all night. Let me just briefly mention that there are acoustic mirrors, X-ray mirrors, neutron mirrors (which are used to direct and focus neutron beams at ISIS!) and many more…
3. A fork. This is made of stainless steel, which in turn is made by adding chromium to ordinary steel. Similarly to the aluminium coating on a mirror, the chromium forms a thin layer of oxide on contact with air which protects the steel from corrosion.
4. A battery. Specifically a 9-volt PP3 non-rechargeable zinc carbon battery! The battery provides a voltage for use in an electric circuit due to chemical reactions which occur inside it. In this type of battery, the zinc is oxidised at the negative terminal, and manganese oxide is reduced at the positive terminal. As I was taught in school, when you’re talking electrons, Oxidation is Loss, Reduction is Gain (OILRIG!)so there are excess electrons at the negative terminal, and too few electrons at the positive, so the electrons will “flow” through your circuit from the negative to the positive terminal… simple!
The field of electrochemistry is one of the most active in today’s physical and materials chemistry research departments. Battery related subjects include new materials for rechargeable batteries which can power big things like cars, making environmentally friendly batteries and tiny batteries for our ever-shrinking electronic gadgetry. Research into chemical reactions involving oxidation and reduction, and the use of electrodes and electrolytes, is truly epic in scale.
5. An LED light. Now, LEDs are really cool. LED stands for “light-emitting diode”, and there’s some really cool physics behind the technology. Let me try and explain without you all falling asleep. In a material called a semiconductor, the electrons are arranged in two distinct “bands”, one of which is tightly bound to the atomic nuclei, and one of which is loosely bound. Electrons in this loosely bound band can ‘flow’ easily from atom to atom, and it’s for this reason it is called the “conduction band”. If electrons are present in the conduction band, the material will conduct electricity. Semiconductors have a band gap between these bands, so some kind of external input, such as heat, is required for electrons to hop up into the conduction band.
If you take a semiconductor and add another material to it, it’s possible to alter the positions of the electrons, either by adding more to the conduction band, or taking some away from the tightly-bound band, also called the “valence band”. In an LED, both of these types of semiconductor are used. When a current is applied to the LED, electrons flow from the material with excess electrons towards the material with too few. Along the way the electrons drop from the conduction band to the valence band which represents a reduction in energy. Because this energy has to go somewhere, it is emitted as light.
The colour of an LED is determined by the size of the gap between the valence and conduction bands. A larger band gap will lead to light on the blue end of the spectrum, a smaller band gap will lead to red light. And the colours can be further altered by combining different materials, coatings on the LED’s glass housing, lenses and mirrors.
I probably failed in my attempt to keep you awake, but I could talk about these things all evening!
Little science is just as awesome as its bigger, flashier brother! And if anyone out there wants to send me their pictures or lists of five random objects, I’ll do more instalments of “little science” in the future!