Silica gel is an amorphous form of silicon dioxide, which is synthetically produced in the form of hard irregular granules (having the appearance of crystals) or hard regular beads. A micro porous structure of interlocking cavities gives a very high surface area (800 square meters per gram). It is this structure that makes silica gel a high capacity desiccant. Water molecules adhere to the Silica Gels surface because it exhibits a lower vapor pressure than the surrounding air. When equilibrium of equal pressure is reached, no more adsorption occurs. Thus the higher the humidity of the surrounding air, the greater the amount of water that is adsorbed before equilibrium is reached. It is in these higher humidity conditions (above 50% Relative Humidity) that stored or in-transit items are susceptible to damage. The beauty of silica gel is the physical adsorption of water vapour into its internal pores. There is no chemical reaction, no by products or side effects. Even when saturated with water vapour, silica gel still has the appearance of a dry product, its shape unchanged. Silica Gel is one of the oldest and most popular desiccant and adsorbent used for a wide number of industrial and consumer applications.
Silica Gel is a highly activated adsorbent, furnished in a wide range of mesh sizes to suit various industrial applications. It is non-corrosive, odorless, tasteless, non-toxic, and chemically inert. It is a highly porous form of silica, with an extremely large internal surface area. The silica gel does not undergo any chemical reaction during adsorption and does not form any by products. It is non-deliquescent and will not change its size or shape. Even when the silica gel is water saturated, it remains dry and free-flowing.
Silica gel has a very high porosity, around 800 m²/g, allows it to adsorb water readily, making it useful as a desiccant (drying agent). It can reduce the relative humidity in a closed space to around 40%. Once saturated with water, the gel can be regenerated (dried) by heating it to 150°C (300°F) for 1.5 hours per liter (about 1 dry quart measure or about 30oz weight) in a thick-walled Pyrex dish. Silica gel is non-toxic, non-flammable and chemically unreactive.
Regeneration of Silica Gel is done by heating the crystals in an oven at a temperature of not more than 300° F (149° C) for approximately three hours or until the crystals turn blue or transparent white. Dehydrating the desiccant may also be accomplished by heating in a microwave oven. Using a 900 watt oven heat the crystals for three minute intervals until the color change occurs. The exact amount of time necessary will depend upon the oven wattage. Spreading the desiccant in a broad pan in a shallow layer will speed the process. Heating to 325Â° F (149Â° C) or more, or using a microwave oven over 900 watts can damage the gel and render it unable to adsorb moisture.
Silica Gel has a very strong affinity for water and will adsorb it in preference to most other substances. It is also a good adsorbent for HC1, gasoline-range hydrocarbons, CO2, C12, sulphur and nitrogen compounds, aromatics, and many others. Silica Gel is in wide use in many industries for a myriad number of applications where a high capacity desiccant or selective adsorbent is required.