Silica gel

== Description ==
An amorphous material of silica available as granules, powder, or beads. Silica gel is chemically inert, very porous, and hygroscopic. It has an internal network of interconnecting microscopic pores, yielding a typical surface area of 700-800 square meters per gram. First patented in 1919, for use in gas masks, silica gel adsorbs pollutants as well as water. It is used as a desiccant, pollutant sorbent, and as a humidity buffering agent. As a RH buffer, silica gel absorbs moisture in humid environments and releases water in dry air. Once equilibrated to set moisture level, silica gel will maintain that humidity level in a closed environment. Silica gel performs best at room temperature (70-80F) and high humidity (60-90%). The pore size in silica gel is related to its ability to adsorb water and other pollutants. Silica gel Type A with approximately pore size of 2.5 nm is most often used for vapor-phase moisture.
Examples of silica gel products preconditioned as humidity buffers are Art-Sorb®, Arten gel, Rhapid Gel, and PROsorb. Silica gel that is saturated with water can regenerated with heat (120 C for 2 hours) and used again. Some brands of commercial silica gel include a humidity indicator, such as cobalt chloride (blue when dry/pink when moist), iron salts (either orange or brown when dry/colorless when moist) or methyl violet (orange when dry/green when moist). Silica gel has also been used as a desiccant in Dri-die cockroach formulation.
* See product comparison information at Silica gel, commercial. 
== Synonyms and Related Terms ==
amorphous silica; gel de silice (Fr.); dessicant
Brand names: Britesorb [PQ Corp.]; Dri-die; Art Sorb [Creative Humidity]; GORE-TEX® silica tiles; Arten gel; Arten tiles; Aerosil; Prosorb, Rhapid Gel; Rhapid Pak; Scavengel
== Personal Risks ==
* Noncombustible 
* Hygroscopic 
* Contact may cause irritation
* Cobalt chloride is toxic
* ThermoFisher: SDS
== Resources and Citations ==
* AIC Conservation Wiki: Exhibit Technical Notes: Environmental Control
* Exhibit Guidelines Technical Note: Silica Gel Products and How to Use Them
* Exhibit Guidelines Technical Note: Conditioning Silica Gel
* Exhibit Guidelines Technical Note: Conditioning Silica Gel with a Saturated Salt Solution
* J.Tétreault, P.Bégin, Silica Gel: Passive Control of Relative Humidity, CCI Technical Bulletin no. 32. Canadian Conservation Institute. Ottawa (2017).
* Art Preservation Services: Silica Gel Technical Information
* S. Weintraub, "Demystifying silica gel", Objects Specialty Group Postprints, Vol.9, p. 169-194, 2002 Link
* R. Lafontaine, "Silica Gel", Technical Bulletin No. 10, Canadian Conservation Institute, October 1984
* G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 710
* Ralph Mayer, A Dictionary of Art Terms and Techniques, Harper and Row Publishers, New York, 1969 (also 1945 printing)
* Marjorie Shelley, The Care and Handling of Art Objects, The Metropolitan Museum, New York, 1987
* Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
* Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986
* Lynda A. Zycherman, J.Richard Schrock, A Guide to Museum Pest Control, FAIC and Association of Systematics Collections, Washington DC, 1988
* Matte Paint: Its history and technology, analysis, properties and conservation treatment, Eric Hansen, Sue Walston, Mitchell Bishop (ed.), J. Paul Getty Trust, Los Angeles, Vol. 30 of AATA, 1993
* Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
* Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002
* Marie Svoboda, Conservation Survey Index, unpublished, 1997
* A Glossary of Paper Conservation Terms, Margaret Ellis (ed.), Conservation Center of the Institute of Fine Arts, New York City, 1998
* AMOL reCollections Glossary -http://amol.org.au/recollections/7/c/htm
Category:Materials databaseCategory: MWGCategory: Climate/Environment