Having been away for a few days I’ve had plenty of time to review my
earlier notes on this, and the responses from Iain. I really don’t
want to change anything that I wrote, and so Iain and I will have to
agree to disagree. That’s fine, makes for a more interesting life,
maybe. On other lists there would be a more, shall we say, robust
reply, but for here I’ll just leave it at that.
I will however make a couple or three points:
Aluminium piping in cryogenic service (LNG plant) has suffered
severe corrosion at an interface with steel, when bathed by
condensation. I was there.
Aluminium coated steel sheet isn’t at all exotic. In some parts of
the world it is cheaper than galvanised steel sheet, and in Australia
some thousands of square metres were used to cover cryogenic
insulation. I was there.
There is an important difference between the concepts of "hazard"
and “risk”. The first is an intrinsic property of a material, the
second also includes practical considerations such as containment and
quantity.
Using small quantities of room temperature phosphoric acid, where
the only contact route would be droplets on the skin of the hands,
would be assessed as having low risk. I assume adequate eye
protection. If you get some concentrated (sometimes called “syrupy”)
phosphoric acid on your hand you just put the workpiece down and walk
to the sink and rinse it off. Wash with soapy water and that’s the
end of it. Whole (or even half) body immersion would be an entirely
different matter, of course. Let’s not forget that millions of
people (but not me) drink Coca Cola every day, and that contains
phosphoric acid, and has been mentioned often enough here in
connection with cleaning metals. Most jewellers use sulphuric acid
or bisulphate pickle baths … phosphoric acid is in the same
league.
Sorry to have drifted away from the jewellery core of Orchid. If
anyone wants to pursue any of this with me I’ll be happy to discuss
it off-list.
Take care everyone, but don’t become so paranoid that you exclude
opportunities.
Kevin (NW England, UK)