On Fri, 12 Mar 2010 11:03:15 GMT, (Doug Miller) wrote:

In article , " wrote:
On Fri, 12 Mar 2010 03:34:44 GMT, (Doug Miller) wrote:

In article ,
" wrote:
On Thu, 11 Mar 2010 23:27:52 GMT, (Doug Miller) wrote:

In article , "chaniarts"
wrote:
Doug Miller wrote:
In article
,
harry wrote:

The only benifit of cast iron is it doesn't rust much.

As compared to copper or aluminum, which ... don't rust at all,
actually.

huh? rust is the metal changing into an oxide. both copper and aluminium
rust, forming copper oxide (green) and aluminim oxide (white). they just
don't rust orange like iron does.

Wrong. Rust is, by definition, hydrated iron oxide. Copper and aluminum
*oxidize*, but only iron can rust.

Oxides of copper and aluminum are not porous, either (oxidation stops
quickly). Rust is.

Oxidation of iron stops pretty quickly, too, as long as it stays dry.

We are talking about hydronic and steam heat systems.

Yes, and there -- in closed systems, at least -- oxidation stops pretty
quickly, too, as soon as the oxygen is used up.

Except that the systems aren't sealed. The oxygen is never "used up".