Sacrificial anode

Post by **Alasdair** » Thu Jan 01, 1970 1:00 am

I wonder if anyone could help, I am wanting to purchase some Zinc a bloke of about 4" by 3" by 2" deep to be used as a sacrificial anode for my moggie, (i.e. I want it to stop the rusting of the vehicle) does anyone know where I can get hold of any from.

Post by **tuning72** » Thu Jan 01, 1970 1:00 am

Hi
I would try a ship builder or oil rig manf.
They use a "sacrificial" zinc plate on metal hulled or rigs. The last time I done this I got it from Newcastle on Tyne......Ivor......

Post by **stephen** » Thu Jan 01, 1970 1:00 am

I have heard of these before, could one of you please explain the theory behind the use of a sacrificial anode.. will it help my sacrificial bank account on Jemima?

Post by **Alasdair** » Thu Jan 01, 1970 1:00 am

thanx for your help.

Stephen, the theory behind it is that in the reactivity table zinc is more reactive than mild steel (ie the chassis) so the zinc reacts with the air rather than the steel. That is the theory of a scrificial anode.
So if you are expeansing some broblembs with rusting chassis's or body parts then get a block of zinc a bolt it on to an area of the car, but is must be attached to a clean bit of steal otherwise it wont work. hope this enlightens you.
Alasdair

Post by **Kevin** » Thu Jan 01, 1970 1:00 am

Hi
You don`t state whereabouts you are, but if you are anywhere near one of the canals Grand Union ect, the Chandlers that serve them ( for instance there is one at Uxbridge Middlesex ) should have what you want as there are plenty of steel hulled barges & narrowboats, if not try this site
www.uk-narrowboatdirectory.co.uk
let us know how you get on and if the theory works ( why has no one tried this before )

Post by **tuning72** » Thu Jan 01, 1970 1:00 am

Hi
The Earth lead should be directly connected to the Plate as also if possible any other Earth (G/box?) I beleive there is still some argument about "Electron Flow".
Neg to Pos. or Pos to neg.? For some reason the modern thinking is Pos to Neg reduces the Electro-Chemical action of corrosion.
Corrosion has become more pronounced since the advent of "Monocoque" chassis/body units.
(It would take pages to give history?)
I welded my plate with low temp. rod for dissimilar metals. Not sure whether it was this or the "Waxoyl" that slowed the corrosion.?
I would like to hear a more experienced point of veiw......Ivor........
[ This Message was edited by: tuning72 on 30-04-2002 22:50 ]

Post by **lowedb** » Tue Jul 22, 2003 7:26 pm

Second time today I've tried to remember school lessons. That was a long time ago. Anyway, I've been thinking about this sacrificial anode. If it was so easy, why do car manufacturers go to the bother of plating all over every panel, instead of fixing on a plate?

I think the answer is it only works when whatever you are trying to protect is immersed in a conductive liquid. The zinc and iron make a primitive cell, where the zinc is the anode, the steel the cathode. Since the current flow will be electrons from the cathode to the anode, positive zinc ions from the anode to the cathode, you end up electroplating the zinc onto the steel (hence the anode is sacrificed as it gets eaten away). This prevents the steel being plated onto something else.

Some domestic hot water tanks (the round ones with the red jacket!) employ a similar technique. There is a small strip of some sort of metal (maybe zinc again) in the bottom, with one end welded to the base.

Post by **brixtonmorris** » Fri Oct 31, 2003 9:59 pm

there is a theory to do with weather you car is pos or neg earth. ive heard that positive earth is better.

Post by **rayofleamington** » Tue Nov 04, 2003 2:18 am

Had a look on their site and it looks good, until you look closely.

The system may actually work quite well!! Unfortunately the technical proof on the site is as watertight as a collander. There's no good reason for that if it does really work.

I think a lot of the scientific arguements are flawed and the majority of recommendations are anecdotal.
There is comment on 'independent verification of test results' and even a banner and comment from a university... But the university results are NOT shown and the coment does NOT specify which of the products was actually endorsed by the university- (there are other products such as rust converter paint.)
The independant test results mentioned do NOT state what kind of testing was done - it is possible to show good results for any corrosion prevention system if you make the test in a way that it will work - This doesn't mean you get any improvement when you use it under real world conditions. The most fundamental part of corrosion testing is to correleate the test method to the real world in some way but this just insn't mentioned.
Therefore the advertising is deliberately misleading. These things do NOT happen by accident, it is done to make more sales.

An electonic system with electrodes and sacrificial material is going to work if fully immersed, but much harder to explain what the real improvement will be on a car under damp conditions.

One major factor they completely forget to mention is the influence of 'oxygen differential' in the corrosion equation or the catalytic effect of existing or migrated oxided. They only mention the impurity/free radical action in solution causing the reaction - that is a very biassed view of how corrosion works on a vehicle structure.

If you ever wonder why a vehicle rusts away more at the ovlelapping joints / seams? They certainly don't explain it.

What does 'prevents approximately 76% of rust' actually mean?
Is this relating to base material loss by weight, or surface area or to rust in terms of locations on a vehicle. Is this by using the electronic system alone, or more than likely in combination with the additional rust conversion / prevention paints.
If someone uses statistics without an explanation, just remember how the saying goes...

OK whinge over ;-) - it just annoys me when allegedly 'proven' stuff turns out to be anything but what it says. This means you just can't trust any marketing material unless it is bullet proof.

Post by **Kevin** » Tue Nov 04, 2003 2:04 pm

there is an Australian device which offers money back guarantees and quotes references from various user's,

Ah but as you say you dont have much rain and salty roads, I bet you could get good references for the product in other places like Cyprus and Sri Lanka as well

Post by **alainmoran** » Tue Nov 04, 2003 6:10 pm

I'm inclined to agree with Ray here, the whole sacrificial anode approach is unlikely to work in air ... the air itself just cant conduct enough charge to setup the desired effect, and thereby protect the car.

The way that the Zinc works in both the sacrificial plate AND galvanized versions is that it generates a potential (voltage) between itself and the metal it is protecting. This provides protection, because the zinc becomes positivley charged, and the negativley charged (or rather electron-rich) oxidants are attracted more to the zinc than the protected metal.

In the case of the boat, the water acts as a good dielectric which allows the electric field to cover a very large area of the boat (most large boats have several anodes), in air however that area of protection is very much reduced due to the dielectric properties of air (which are closer to that of an insulator than a dielectric!).

That's why we have galvanised steel on land ... the zinc thing still works, however over a MUCH shorter range than in water. ie: It can only protect areas in the range of millimeters, that's why why when you scratch a galvanised sheet it doesnt rust, but if you file/scrape/rub away a section of the zinc coating it rusts just like normal steel.

I myself have never heard of these products which claim to protect your car from rust, I personally* cant see any way in which they could ever work effectivley, or at least never work as effectivly as a few open bags of multi-sorb and a dry garage, or a few tins of mastic applied after a long dry summer.

Alain.

*: I only have a BSc in Physics, so I'm no Dr or Prof or anything, so maybe dont take my word for anything ;)

Post by **rayofleamington** » Tue Nov 04, 2003 9:11 pm

I wasn't trying to discount it.. (though I'm still not convinced ;-) )
the thing was that the site promised a lot for the product but just failed to back up a single promise in a technical way.

As there is a standard for it then it would pay to choose a product that is certiufied to the standard and has PUBLISHED test results that show what the benefit was.
The second site you mentioned gave very good and stringent procedures for manually rust proofing the car. If they were followed including the re-checking re-application of special paint every 2 months then the car will last a whole lot longer (with or without the electronic gizmo)

I'm certainly on the cautious side. I've seen too many adverts for 'fools gold' petrol modifying systems (inline magnetising on the fuel line.. tin pellets in the tank). These are selling stuff that makes all kind of promises for which the vehicle manufacturers and petrol companies alike can find no basis.
Millions of people are being conned with that kind of rubbish, so some of us with a technical knowledge nolonger buy into something unless it's properly proven.

Post by **Willie** » Tue Nov 04, 2003 9:49 pm

An interesting discussion gents....but when you've all finished
just Waxoyl it thoroughly and you will have no rust problems.

Post by **Kevin** » Wed Nov 05, 2003 1:21 am

Millions of people are being conned with that kind of rubbish

Hence why when the unleaded additives were tested over hear the so called market leaders (those that had advertised the most) did either not submit their product for testing or failed the tests, marketing as Ray says is a powerful tool at times

Post by **alainmoran** » Wed Nov 05, 2003 2:57 pm

when the unleaded additives were tested over hear the so called market leaders (those that had advertised the most) did either not submit their product for testing or failed the tests

Yarg ... so youre saying that some unleaded additives are better than others .. scary thought!

So, which ones are good and which ones are pants?