Electrosomething or other

[doozer]

I am curious. What could you possible want to install for 150 to 200 years?

I would imagine given that amount of time dissimilar metals will corrode significantly. Probably to the point of failure. Is it vital that they are dissimilar metals and that they are irreplaceable for 150 years?

Aluminium is an interesting case because it is actually a highly reactive metal* but in the presence of oxygen it forms a tough oxide (rust) coating that stops further reaction. Perhaps as long as you don't continually damage that coating (e.g. they joint is completely immobile) it might last quite well.

*You would be amazed at the speed of the reaction. I have seen aluminium foil nearly catch alight after it has had the oxide coating removed by chemical treatment.

Graham

Anna Kettle wrote:

[bigcat]

NT

[doozer]

LOL. Yes maybe, but this isn't the whole house. It is a little (presumably) item in the loft made from iron and aluminium. I can't think of anything that fits the given description (and needs to last for 150+ years) in any house that I know.

Graham

[Anna Kettle]

Its not actually me that is using it but a fellow building conservator, working in the attic of an important building - the ceiling is trying to fall down and we are trying to stop it doing that. Standard practice is to do everything in stainless (threaded rod, screws, washers, wire etc) so I was surprised when they started using aluminium wire

It should be immobile so lets hope so

Anna ~~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repairs / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____|

01359 230642

[The Natural Philosopher]

Trouble is al oxide is fine to protect against pure water, but any acidity and ist gone. Salt likewise.

Its very interesting to visit old museums and see the occasioanl iron age sword, as a rotted sump, but almost perfect bronze swords...iron doesn't last AT ALL well.

Most of the early cast and wrought iron stuff is on the edge of destruction and needs painting everyt year.

[Anna Kettle]

OK so electrolytic rection occurs but does it matter?

A battery is set up which has the effect of moving aluminium atoms into the stainless steel and vv. Which is welding. Which is no problem in this situation

Have I got this right?

Anna

~~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repairs / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____|

01359 230642

[doozer]

Not really. What will probably happen is your aluminium will slowly turn to dust (aluminium oxide) while you iron stays relatively shiny an new looking. I wrote and article detailing how a battery works last year. Hopefully it's easy enough to follow and doesn't have to many glaring mistakes :o)

[Rob Morley]

Maybe something to do with thermal expansion? Can they not prevent the two metals from contacting by using some sort of barrier, like teflon tape?

[Anna Kettle]

part with difficulty [1]. Aluminium wire doesn't seem a good idea so I think I had better have a word with my friend

[1] The font doesn't show up at all well in my browser (Firefox). Its very blurry

Anna

~~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repairs / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____|

01359 230642

[Rod Hewitt]

[e-mail] (Anna Kettle) wrote in news: [e-mail]:

Looks fine to me - what version of Adobe (Acrobat) Reader have you got installed? I suggest upgrading to 7. If using a TFT screen, check out the Cooltype settings.

One reason that this occurs is colour management - the text might be set to

100% black but this is translated into some lower value for display. I think that earlier versions of the reader allow you to choose to diplay using the colour settings in the document or RGB - if so, choose RGB.

[doozer]

I wrote it in Latex and exported it as PDF this is a known problem with this set up, usually people say that it looks like the paper has got slightly wet and the ink has run. When I get the time I will export it again with the newer PDF libraries which I believe fix the problem. In the mean time the latest acrobat (if you are using windows) seems to display it correctly.

Graham

Rod Hewitt wrote: