Sacrificial metals

[KingStromba]

Anyone ever thought of using a block of zinc on the inside of the rear arches to stop rust?

[Swervin_Mervin]

Waxoyl is cheaper.

[KingStromba]

How much is a zinc block?

[Swervin_Mervin]

Dunno but I bet you can't just squirt it on :P

[KingStromba]

So you dont actaully know what a zinc block does?

[Swervin_Mervin]

I assume you rub it on the bare metal?

[KingStromba]

No

[northy]

u ever heard of zinc primer mate ?

[KingStromba]

Yes, but you have to paint that on the metal.

Sacirificial zincs is used in the marine industry. When steel rusts it is because the iron in the steel reacts with oxygen (loss of electrons) as oxygen likes to gain eletrons to give itself a full outer shell.

Iron + oxygen = Iron oxide + water (iron has lost electrons to oxygen)


This rust (iron oxide) is what we see on our arches. If you place a block of zinc metal on the bare metal surface of the steel. The zinc loses electrons to the steel, which in tern passes them to the oxygen, The result is that the zinc block corrodes, and the steel doesnt.

Its a tried and tested way of preventing corrosion in the marine industry. All oil rigs have magnesium blockds attatched to their support legs to stop rust.

[big hp]

Its where you allow another more active metal to rust instead. This is called sacrificial protection. A zinc block is attached to the hull of a ship or i your wheel arch. Since zinc is more reactive than iron it will rust first. As it rusts it releases electrons making the ship slightly negatively charged, so the iron cannot rust.

Do I win a prize?

[KingStromba]

Been on the phone again hey? :D

[Tommo]

Zinc is low down in the Galvanic Series so is therefore more anodic than steel so if you coated the inside arch with zinc it would form a protective layer and a sacraficial anode. Good in theory but never seen it done on a car only on boats!!

[Swervin_Mervin]

Cool.

Does it weigh more than Waxoyl? :P

[big hp]

Been on the phone again hey? :D


I'm a design/production engineer so just looked in my folders :wink:

[KingStromba]

Youd only need a very small block. I too have seen it done alot in boats (salt water being very corossive and facilitating the spread of electrons).


I am deffinately going to do this before winter.

One block in each arch.

Two in the engine bay (one subframe and one higher up)

One in the tailgate.

One on the inside of each sill.

[big hp]

What size blocks you talking about Stromba?

I should imagine 1 sq inch would be enough. Might see if I can buy it through work.

[Swervin_Mervin]

Can I have some please? Cost dependant obviously.

[KingStromba]

Just phoned a marine shop in Yarmouth and a block is about 5-10 pounds depending on size. Magnesium is probably going to be better on a car the guy said and he said it will stop / greatly slow all rust for as long as the block is still not fully oxidise. :D

They come in all shapes and sizes and are available from all marine shops.

[big hp]

I'll price it up. It'll be a special order as we don't use it here. If we don't want things to rust we use S/S, Or send MS parts out for zinc and passivate plating.

[KingStromba]

What size blocks you talking about Stromba?

I should imagine 1 sq inch would be enough. Might see if I can buy it through work.


Yeah about 1 inch square. About £5 a block at that size. Im going for magnesium, due to its position in the periodic table.

[big hp]

Just phoned a marine shop in Yarmouth and a block is about 5-10 pounds depending on size. Magnesium is probably going to be better on a car the guy said and he said it will stop / greatly slow all rust for as long as the block is still not fully oxidise. :D

They come in all shapes and sizes and are available from all marine shops.


And the sizes recommended for cars were what Rob?

[KingStromba]

Hed never heard of it on cars. But a small block is enough to protect an outboard motor for 1 to 2 years in fresh water. Bearing in mind that will be submersed all that time, its going to last at least 2 years.


Zinc is generally used in salt water, magnisium in fresh water

[big hp]

Just make sure the magnesium doesn't get too hot in the engine bay :wink:

We had a Lathe burn to the ground when a magnesium wheel we were turning got too hot and caught fire. Its now standard practice to have 2 fire extinguishers beside your machine if your using this material.

[KingStromba]

haha, yeah good point, zinc may be safer. :P

[big hp]

haha, yeah good point, zinc may be safer. :P


:wink:

[Martin]

Better than neons! lol

[KingStromba]

Couple of magnesium blocks on the zorst when you sell the car. PMSL :P

[lagerlout1]

lol.... would light up the street, never mind the car.

I'd thought about this before for my TR. If you stand still long enough you can actually see it rust in front of your eyes...

[Swervin_Mervin]

What would you secure the blocks with?

[KingStromba]

Dont know.

[Swervin_Mervin]

:P

[Allan]

i might be wrong but im pritty sure they teach you this in school !
i know they taught it to us when i was doing my GCSE's

[Swervin_Mervin]

Am I correct in thinking that the block is iron and the head alloy?

[big hp]

You would secure the blocks with a bonding agent.

[KingStromba]

But needs to be a metal on metal contact

[Tommo]

How are they attached on ships??

[Lunner]

Yeah i learnt this in GCSE chemistry :roll:

[KingStromba]

They are attatched to ships by wires

[Lunner]

Only thign i can thing of is put a recess inot the face of the metal block to put bonding into, BUT you are goign to have to A) expose a bare section of metal insoide the wheel arch, rather you than me; and B)be able to remove it afterwards, which if it has been decently bonded on is not goign to be possible without damaging the car.

IMO you woudl be much better spent, srtripping all teh waxol out, and re primering and re-waxoling the arches

[KingStromba]

Doesnt matter if the metal is bare around the sacrificial metal (thats the whole point IT STOPS IT RUSTING) :roll:

[Jamie.]

the zinc works by being more reactive with "air" (oxygen and water) than the steel. so when "air" and water come into contact with the steel bodywork, the air and water mix which reacts with the steel to beome rusty are attracted to the zinc plate not the steel of the car bodywork. the process is called "displacement", that is two compounds/elements will always react with the most reactive substance, by-passing the lower "reactive" element/compound. it also does not matter where the zinc block is, so-long as it is on the car bodywork. however the zinc plate may need to be replaced from time-to-time depending on how corroded the plate becomes.
i dont think that zinc plates are very expensive but i could be wrong, i would give it a go though.

[KingStromba]

No doubt it will work, its been used in the marine industry for decades.

[Lunner]

I know how it works, i ahve an A level in chemistry :roll:

And Stromba i know it won't make a differnce if the metla is bare as it dwon't rust, but i still wouldn't want to do it

[FATBOY]

just to add my 2 peneths worth! in copper hot water cylinders(or in non plumbers talk"the tank in the airing cupboard") they have an internal sacrificial anode fitted!

[Lunner]

but copper is non-ferrious, or is that for the rest of the cenreal heating system, ie the metal radiators?

[FATBOY]

?????????? dunno mate! all i know is that on the side of cylinders are stickers that say sacrificial anode fitted! lol didnt think i was brainy did ya??? lol

[Lunner]

LOL, well annode is positivly charged, hence attracts negative ions in the liquid, this is how things are plated, iirc metal ions are generally negativly charged

[FATBOY]

hmmmmmmmmmmm im thinking that the anode is for the prevention of limescale build up in the bottom of the cylinder???? would that be right???

[BRUN]

you can buy kits like this for cars in America, it was on ClioSport i think about a month back

[summeh]

How about a magnesium plate in the boot, under the carpet??? WOuld be easy to place, and you could rig some bolts either side to keep it secure. ??? :)

sounds like a good idea to me !

[KingStromba]

There must be something on the market. This is old knowledge for boats.

[lagerlout1]

Yup. Probably closer to centuries than decades......

Copper is non ferrous, but it will be steadily dissolved by water i.e. molecules of copper will enter the water, and I would imagine the heat will help. (apologies to the chemists/scientists if that's bollocks!!)

That's why they banned copper saucepans etc because of the danger of copper poisoning.

We now use stainless steel for our brewing vessels (still called 'Coppers') and we add copper to the brew as the old copper lined vessels added taste to the beer.
It used to be done by chucking a bucket of copper finings into the wort, but it's now done at the blending stage by means of a sacrificial copper anode. Useless bit of info for you there. lol.

[Purple]

Found a small write-up on this subject.

http://www.abc.net.au/science/k2/homework/s95524.htm

[Swervin_Mervin]

Was quoted this elsewhere:

"The process is called "cathodic protection". You attach another metal which will corrode first, before the iron in your car, bridge or boat. The sacrificial metal that's usually used is zinc. As the iron turns into rust, it gives up electrons. If there's a lump of zinc nearby, the iron get the electrons back from the zinc and so stays protected, while the zinc begins to corrode away.

For this process to work, you need a complete electrical circuit to bring the electrons back. In the case of an outboard motor on a boat, the sea water completes the circuit. In the case of a bridge, the wet soil completes the circuit. But in your car, the only way to complete the circuit on all the metal in your car is to drive into sea water! "

[KingStromba]

Was quoted this elsewhere:

"The process is called "cathodic protection". You attach another metal which will corrode first, before the iron in your car, bridge or boat. The sacrificial metal that's usually used is zinc. As the iron turns into rust, it gives up electrons. If there's a lump of zinc nearby, the iron get the electrons back from the zinc and so stays protected, while the zinc begins to corrode away.

For this process to work, you need a complete electrical circuit to bring the electrons back. In the case of an outboard motor on a boat, the sea water completes the circuit. In the case of a bridge, the wet soil completes the circuit. But in your car, the only way to complete the circuit on all the metal in your car is to drive into sea water! "


As a scientist i can say that is bollocks. Electrons will travel from one metal to another as lond as there is contact.

Electrons flow out of the wires on your battery everytime you start your car. I dont see any sea water there. Trust me, metal on metal is enough

[lagerlout1]

Only if there is a potential difference. And the electrons will only 'flow' if there is a complete circuit. Hmmm. But any metal part of the car is part of the electrical circuit... so if you attach, via a load, the zinc block to the positive side of the circuit.... :lol: :lol: :lol:

[KingStromba]

The potential is caused by the iron reacting with oxygen. Iron loses electrons and this sets up a potential for electrons to flow from the zinc to the iron.

[lagerlout1]

Makes sense. It's such a simple idea though, you would have thought that back in the day (I mean when cars REALLy rusted) somebody would have already done it.... don't they galvanise the panels anyway??

You don't see many modern cars with rust theses days. Years ago, a 5 year old car would be a rot box. Nowadays if yu saw a 5 year old car with rust on you'd be horrified!!

[summeh]

look in the clio handbook, it has a nice sliced up diagram of a clio with the different layers of "rust protection", the first one being zinc galvanising.

i think thats right, im not at home so could check for sure :)

[KingStromba]

Yeah most modern cars have zinc protection hence the manufacturers can afford to give 12 year anti corrosion warrenties. The more modern the car the less likely it is to rust.

I was just going to do this on my Williams' problem spots such as the arches to ensure protection from rust.

[lagerlout1]

I say do it. Nothing to lose.