Building Construction, Renovation, Maintenance & Advice

What Is Electricity?

What is Electricity?

What is electricity? Here we look at atoms, sub atomic particles electrons current in amps, electrical potential in volts, the elctrochemical series, why metals corrode and how we can prevent corrosion.


See the full Fixed Abode article "What Is This Electricity Stuff Anyway?" here


A Introduction to Electricity

Just to remind you of a boring fact - the word electricity takes it's name from the Latin ‘electrum’ which in turn comes from the Greek ‘elektron’ which of course means ‘amber’.

Amber?
Yes amber.
You see the ancient Greeks (this was a bit before the austerity crisis in the days when the Greeks could still afford to buy things) had a habit of rubbing things. They noticed that if you rubbed amber with something furry (such as a dead cat) it attracted small objects to say nothing of suspicious looks from the neighbours.

So what is going on here? Find yourself a comfortable chair, a nice cup of tea and a few panadol and we’ll start at the very beginning.

Atoms

As we all know everything is made up of ‘atoms’ and atoms are pretty small, they are even smaller than a mosquito’s belly button. You’ll need a very big magnifying glass to see one. Everything around us (including ourselves) is made up of atoms. There are only 118 known types of atoms that make up everything we know. These are the ‘elements’ which combine in different ways to form ‘molecules’. We all know that water molecules are formed by combining 2 atoms of hydrogen and 1 atom of oxygen.

Sub Atomic Particles

It was thought that atoms are the smallest particles in the universe but not so. The more the physicists looked into their magnifying glasses the more and smaller particles they found. Atoms are made up of even smaller particles, a large one, the ‘nucleus’, with smaller ones including ‘protons’ and ‘electrons’.

Electrons carry a negative electrical charge

Now we get to the interesting bit. The protons each have a positive electrical charge while the electrons have a negative electrical charge. The nucleus has no charge at all. Now if we add up the protons positive electricity and we take away the total of the electrons negative electricity we find that an atom has a ‘net electrical charge’. Different types of atoms have different numbers of protons and electrons and so they each have their own net electrical charge and, as atoms combine to make up molecules of different types of matter, the molecules of different materials also have their own net electrical charge.

If you are keeping up with this go and get another cup of tea and we’ll continue, if you are totally lost by now or perhaps bored out of your brain because you know all this already you might want to go and read the obituaries column.

We’ll carry on.

Electric Current

Protons tend to be very loyal and stick close to mum (the nucleus) but those recalcitrant little blighters the electrons are always a pain in the arteries and, like naughty little boys they are always on the move. They don’t stick close to mum and can even be ‘free electrons’ and move between atoms.

The flow of electrons can be quite useful at times, we know of it as 'electricity'. A flow of electrons (like water along a pipe) that we know of as an ‘electrical current’.

Electric Potential - volts

If we collect electrons in a single place we have ‘electrical potential’ and the more electrons we collect the greater the potential. We measure electrical potential in ‘volts’.

Everything around us contains electricity and the movement of electrons makes life possible. Without the ability to move electrons around our brains could not give instructions to our body parts (I suspect that would make life rather difficult).

There is one more thing we need to know which is that, unlike humans, in electricity ‘like’ does not attract ‘like’. If we take two things that both have a positive charge they will tend to repel each other, while things with opposite positive and negative charge will be attracted to each other.

Remember the old trick where you take a ballon and rub it on your chest and then ‘stick’ it on a wall. The balloon collects electrons from your jumper and becomes negatively charged, we call this ’static electricity’ of course, and it is attracted to the more positively charged wall. This is why when the Greeks rubbed amber with their dead cats the amber collected static electricity and attracted things.

The Electrochemical Series

As we have said different materials have their own electrical charge which can be either positive or negative, these we can list in order depending on their normal level of electrical charge. We call this an ‘electrochemical series’.

Chemical
Abbreviation
Element Electrical
Potential
volts
Chemical
Abbreviation
Element Electrical
Potential
volts
Li Lithium -3.04v H Hydrogen 0.00v
K Potassium -2.93v Ti Titanium +0.06v
Ca Calcium -2.87v Sb Antimony +0.10v
Na Sodium -2.71v Cu Copper +0.34v
Mg Magnesium -2.70v I Iodine +0.54v
Be Beryllium -1.85v Ag Silver +0.80v
Al Aluminium -1.66v C Carbon +0.81v
Mn Manganese -1.19v Hg Mercury 0.85v
Zn Zinc -0.76v Pt Platinum +1.19v
Cr Chromium -0.74v Au Gold +1.52v
Fe Iron -0.44v Fl Flourine +2.87v
Cd Cadmium -0.40v
Co Cobalt -0.28v
Ni Nickel -0.25v
Sn Tin -0.13v
Pb Lead -0.13v

If you look at our list all of these are elements which means they are fundamental building blocks in our world and they exist as atoms. Most are metals and the higher in the list they are then the more negative they are and the more active they are. Metals lower in the list are more positive, less active and more stable, these more stable metals we call ‘noble’ metals.

If two different metals are in electrical contact with each other, either directly touching or with some sort of conducting medium such as water connecting them, then electrons will flow from the one higher in this table towards the one that is lower. The metal the electrons flow from we call an ‘anode’ and the metal the electrons flow to is a ‘cathode’.

Electricity Causes Corrosion

What is important for us is that something else will occur - as electrons flow out of the metal it changes, it absorbs oxygen, it oxidises, that is it corrodes or, in the case of iron and steel, it rusts.

So as electricity flows from one metal to another the upper one in our list will corrode while the lower one will not. You will note that gold is right at the bottom of the scale - ever seen a rusty wedding ring? Even when we dig gold out of the ground it is not rusty.

This can give us all sorts of problems. If, in our plumbing system at home, we connect a piece of copper pipe to a piece of steel pipe the steel will rust far more quickly than if only steel is used. Hence that well known phrase “you might have gold taps but your pipes are rusty”. The advent of PVC pipes has removed many corrosion problems in plumbing systems.

Preventing Corrosion

Sacrifical Anode and Cathodic Protection

We can, however use it to our advantage. If we bolt a piece of aluminium or magnesium onto a piece of steel and put it in sea water the aluminium (higher in the list) will corrode and will stop the steel (lower in the list) from rusting. The piece of aluminium we call a ‘sacrificial anode’ - it makes the steel into a cathode, it stops the steel from rusting and provides what we call ’cathodic protection’.

This is important because inside our electric and solar water heaters there is a piece of aluminium fastened to the inside of the water tank to stop the steel tank rusting. Water heaters are notorious for suddenly rusting out once the sacrificial anode has corroded away. Studies in Australia many years ago revealed that solar water heater tanks could be expected to rust out after about 8 years (shortly after they paid for themselves). It is wise to install a new sacrificial anode.

painting

We can stop steel rusting by painting it, the paint acts as insulation to keep the steel and its electrons away from the oxygen and water in the air.

When painting steel we may add zinc (or formerly lead) to the paint, zinc in the paint corrodes first and so protects the steel.

Hot Dip Galvanising

If we want to seriously protect iron and steel we galvanise it by dipping it into a tank of molten zinc. Once again the layer of zinc on the steel corrodes in preference to the steel and so protects it.

Zinc Alume

Corrugated iron used for roofs was in the past usually galvanised, these days some aluminium is mixed with the zinc (this helps to stop the steel rusting if it gets scratched) and this is commonly known as ‘zinc alume’.

These days more and more people are using lightweight steel for roof frames. Roofs, may have to carry a lot of weight so it is very important that roof frames do not rust and so the steel must be of good quality and it must be very well galvanised or zinc alume coated.

Anodising

Some metals, such as aluminium, can be protected by ‘anodising’ them. We purposely corrode the surface of the aluminium to form a thick crust on the surface which then insulates the aluminium underneath protecting it from any further corrosion.

I've had enough of all this negativity for one day so I'll finish, you can take the panadol now.


Copyright © Phil Wilson September 2015
This article or any part of it cannot be copied or reproduced without permission from the copyright owner.

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