Applications
1. Silica gel breathers are used in power transformers for the breathing process.
2. Silica gel is the most commonly used desiccant means hygroscopic drying agent.
3. We usually find Silica Gel small packets inside packaged items such as electronic items, food-items, medical equipment, etc. These packets are used to keep that particular item dry.
Properties
1. Silica gel absorbs water. This is the main property due to which silica gel is used as a drying agent.
2. It can absorb water up to 40% of its weight.
3. Generally it is used in beads and granular form.
4. Commonly blue-colored silica gel is used. Bright orange and colorless silica gel are also used. Please note that the colors used are for moisture level indication purposes. For example, blue silica gel turns light pink and then colorless after moisture/water absorption. Cobalt chloride is used in blue colored silica gel.
Composition
Let’s look at the chemical reaction of silica gel with water. So that we can understand how silica gel absorbs water.
Silica gel chemical formula is Si-OR
Where
Si = Silica, and
R = Alkyl group such as methyl.
Now when silica gel comes in contact with water. Chemical reaction is
Si-OR + H2O = Si-OH + R-OH
Then water gets separated by water condensation as follows.
Si-OH + Si-OH = Si-O-Si + H2O
Here we can see H2O gets separated.
Then alcohol condensation occurs as follows.
Si-OH + Si-OR = Si-O-Si + R-OH
Here we can see R-OH gets separated.
So this is how silica gel absorbs water.
Can we Reuse Silica Gel?
Yes. These silica gel crystals can be regenerated by heating them at a temperature of 150 degrees Celsius. Nowadays new advanced Silica Gel breathers for transformers are available in the market. These breathers are equipped with a heating coil at their bottom to regenerate silica gel crystals by heating them. This avoids frequent replacement of silica gel in the breathers.