Hirsty's wrote:
> I teach the principal, but have'nt a clue how to apply it in practice. The
> idea is to set up an electrical current so as to cause the Zinc used to
> corrode first (being more reactive than steel/ iron). I have never had the
> courage to use it as I am not sure if it would work and to what extent the
> surrounding area of the zinc block would be affected. The real problem is
> that Aluminium is a very reactive metal and is only used because it has
> been tamed due to the layer of oxygen on it's surface that is resistant to
> further attack. Once breached the aluminium underneath reacts very
> quickly. what is needed is some method of halting the reaction and then
> re-sealing the breach, but how ?
>
>
> "Steve Taylor" <[email protected]> wrote in message
> news:[email protected]...
>> Larry wrote:
>> > I guess it is the old electrolytic reaction of the steel frame and the
>> > aluminium, the door bottoms just rot.
>> >
>> > I was angry when I discovered the last owner of my pride and joys
> solution
>> > to this, but now I realise that to reconstruct the bottom with
> fibreglass is
>> > not a bad idea.
>> >
>> >
>>
>> What about a "sacrificial electrode" method ?
>>
>> Steve
The first requirement for the sacrificial electrode method is to have the
entire structure permanently immersed in an electrolyte. (It only works on
ships and marine structures below the water line.)
As I assume you have no plans for submarine operations, this counts it out
for protecting the whole structure. As far as local protection goes, you
already have a sacrificial anode - its the aluminium skin! To prevent it
corroding sacrificially relative to the steel door frame, there are two
solutions; ensure that there is no electrolyte (e.g.water) in contact with
both the steel and the alloy, or ensure there is no electrical contact
between the two metals. As both are difficult to achieve with complete
reliability except during design and manufacture (not even then, really),
you should probably do the best you can with both. And a good start here
is the Penetrol suggested, or a similar product, which has very low surface
tension on metal surfaces, and will penetrate the nooks and crannies that
hold water, and then dries. As it is an insulator, it helps to insulate the
metals, and the film will prevent the water from coming in contact with the
metals.
Hope this helps
JD
