Silica gel and lithium chloride

Paula Dredge <paulad [at] ag__nsw__gov__au> writes

>We have recently been approached by a company marketing a new silica
>gel material as 'lithium chloride free'. They claim that the product
>we have been using, which does contain lithium chloride, is
>potentially destructive, particularly to metals. I wonder has anyone
>done the science? Is lithium chloride a risk when in close proximity
>to artifacts and artworks?

There may well be some cause for concern as lithium chloride is a
salt that physically absorbs moisture from the air and wets above
11% ambient RH. Assuming a museum environment at 45 - 55% RH or
lower for metals, the salt can expect to wet until it becomes a
saturated solution as the ambient environment provides a reservoir
of wetting moisture. An increase in local moisture content around
the silica gel would be expected to increase the RH in the immediate
area. However, the extent to which this impacts on an object in the
near vicinity would be dependent on the total amount of salt present
and the effect of air mixing.

Another potential problem is free lithium chloride that may become
liberated and airborne through handling the silica gel. It will
behave like any salt on a metal surface, and augment corrosion
mechanisms by increasing electrolytic potential. It is well
recognised that microscopic salt crystals deposited on a metal
surface are a major factor in increasing corrosion rates. But if the
silica gel is handled in a way so as to eliminate the likelihood of
contamination then the risk will be minimised.

In a museum environment where harm minimisation is a priority there
is justifiable concern but I see your point that it may just be an
over-inflated marketing strategy. If you can establish there is free
LiCl in your current silica gel with its current method of use then
it is clear it should be avoided.

Deborah Lau
Analytical and Conservation Scientist
CSIRO MIT
Corrosion Science and Surface Design
Gate 4, Normanby Road, Clayton, Victoria, 3169
Private Bag 33, Clayton South, Victoria, 3169
+61 3 9545 2830
Fax: +61 3 9544 1128


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                  Conservation DistList Instance 18:42
                  Distributed: Friday, March 11, 2005
                       Message Id: cdl-18-42-002
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