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Name: Lisa
Status: educator
Grade: 9-12
Location: Outside U.S.
Country: USA
Date: Fall 2011

Can you tell me how silica gel is correctly categorized (I see it called narrow or large pore as well as Type A, B and C)? What is the difference? Are they all used the same way, as a desiccant?

Hi Lisa,

The "A", "B" and "C" designations of silica gel refer to the pore size. The "A" type has large numbers of very small pores, and is generally used as a desiccant. Water vapor is adsorbed into these pores, or water vapor already adsorbed, is released upon heating. This is the type normally found in small bags packed in electronic and optical products.

The "C" type has somewhat fewer (but still very large numbers) large pores. This type is used for large volumes of liquid water absorption, commonly as cat litter.

The "B" type has pore sizes that are smaller than the "C" type, but still larger than the "A" type. It is also used a liquid absorber.

Each of the three types is chemically identical, but pore size is optimized for the use to which they are put.

Regards, Bob Wilson

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