[WWI] SPAD 13 Internal fitting

Mark Shannon shingend at ix.netcom.com
Thu Apr 19 19:59:35 EDT 2007

Salt water corrosion was a big factor in all of this.  Salt can disrupt the
oxide coating and start creating pits that spall the oxide off so the pit
grows.  A very effective demonstration is to dip aluminum foil in a
mercuric chloride solution (rinsing off the excess solution).  The sheet
will oxidize fast enough that it will become too hot to handle and flecks
of aluminum oxide will puff up into the air.  That is a case where the
mercury and chloride work together, and is extreme, but other salts will
cause the same mechanism at a slower pace.

A metallurgy reference such as the Chemical Rubber Company Handbook (CRC)
will list the compositions of many of the older alloys -- including the
specific maritime bronze and brass alloys.  (The original company is
defunct, but the reference book lives on)  Well primered and painted
aluminum is handy in aircraft, since you never know if it is going to end
up at an ocean side airstrip.

Mark Shannon
shingend at ix.netcom.com

> [Original Message]
> From: Ivan Carlos Ruchesi <ivruc at yahoo.com.ar>
> To: World War I Modeling Mailing List <wwi at wwi-models.org>
> Date: 4/18/2007 8:05:27 AM
> Subject: Re: [WWI] SPAD 13 Internal fitting
> >Yes, you are quite correct, the reference was to aluminium and not
>internal fittings in general. However, if it was the case that there was
>no benefit to coating aluminium then surely they changed their minds
>about this before the second great unpleasantness? Offhand, I can't >think
of any bare metal cockpits from WWII, or even the early >thirties. Japanese
aircraft for instance corroded very badly and >relatively quickly even
though they were constructed of >duraluminium. Even in the harsh
environment of the Pacific theatre >the material allied aircraft were
constructed from fared far better.
> >And I still maintain that the added weight of coating a few bits of
>metal in OT aircraft would be so small as to be completely >insignificant.
> >Andy
>   Like aluminium, several metals produce a thin oxide layer on their
surfaces to protect themselves from a more profound corrosion, e.g. copper,
brass, bronze, zinc, etc, this phenomen being called "pasivacion" in
Spanish. This is what allow brass ship propellers to last a long time
working in salt water. The problem arises, like in canned food,  when the
surface layer is punctuated, then the bare metal is quickly corroded by
oxigen. Perhaps the paint coatings are intended to protect that oxide
>   Ivan

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