Silica gel is comprised of randomly linked spherical polymerized silicate particles, the primary particles. The properties of silica gels are a result of the size and state of aggregation of the primary particles and their surface chemistry. Modern silica gel technology enables the production of highly pure gels that are composed of nearly 100% SiO2 with tailor-made pore systems and surface properties. Silica gels can be produced from different raw materials. However, the synthesis from mineral acids, e.g. sulfuric acid, and aqueous sodium silicate is the only industrial relevant process today. Sulfuric acid and sodium silicate are mixed under controlled conditions to build the primary particles of the desired size, which polymerize and form the raw gel from which all types of silica gels are made. This glass-like gel is broken down into granules and then washed, aged, and dried to produce the highly porous materials. Silica gels are available in a wide range of particle sizes, each type having a well-defined particle size distribution.
Under optimum conditions Silica Gel “A “ when fully activated will dry air and other gases to the order of below 10 ppm corresponding to a dew point of less than -40* C. It is also recommended to be used for liquid phase operations.
Approximately 40 g (1.4 oz) of silica gel will absorb the moisture from three cubic feet of air. When drying objects it is important to keep the container size small in relation to the object being dried. This helps insure more rapid and thorough drying.
Granular Silica Gels are the materials of choice when it comes to static drying applications in which attrition resistance and particle irregularities are of minor importance. Granular silica gels exhibit the advantageous adsorption properties of silica gels combined with a high particle stability caused by the specific hardness of silica gel (4-5 on Moh scale). Silica gel granules are available in various particle sizes between 0.5 and 12 mm..
Beaded Silica Gels are characterized by the high purity and the specific adsorption/ regeneration properties of the silica gel and by superior particle integrity due to the combination of a beaded particle shape and the specific hardness of silica gel (4-5 on Moh scale). This heavy density Silica Gel is distinguished by its extremely fine pores which account for its high adsorption capacity over a wide range of humidity. Silica gel beads are available in various particle sizes between 0.5 and 8.0 mm..
Type A Silica Gel is broadly divided into two types – Indicating & Non Indicating.
Silica Gel White is known as Non-Indicating Silica Gel as it remains unchanged in appearance on adsorbing moisture. White Silica Gel is in the form of ivory-white semi-transparent round vitreous body or crystals with good absorption capacity but we cannot determine whether Silica gel has completely absorbed moisture or not. It has been confirmed that White Silica Gel causes no odor, toxin and pollution and is one of the most widely used damp proof agent in the world.
Blue Silica Gel is the Self Indicating Silica Gel as it is prepared by impregnating White Silica gel with Cobalt Chloride present in a concentration of 0.5 to 1% weight for weight, an indicator, which provides the Blue color appearance. Self – Indicating Blue Silica Gel will adsorb moisture in exactly the same way as standard non-indicating (white) silica gel but will actually indicate when they are becoming saturated by changing their colour from blue to pink thus indicating that it has adsorbed moisture and needs to be replaced.
Orange Silica Gel is also known as Self Indicating Silica Gel, it has been accepted as the perfect substitute for the indicating type blue silica gel as it is impregnated with an environment friendly indicator unlike Blue Silica Gel which has now been classified as carcinogenic in nature due to the presence of “Cobalt Chloride”.. With silicon dioxide as the main ingredient it has all the properties of blue silica gel but does not contains cobalt chloride. The composite dyeing agent without pollution to the environment has been successfully adopted during the manufacturing process of the orange silica gel.
There are two types of Orange Silica Gel – Orange to Green & Orange to Colorless, the latest & the better being Orange to Colorless as far as indication, adsorption capacity & environment is concerned.
When in dry state the particles are dark orange in appearance, as the particles take up moisture the color gradually changes from orange to dark green or almost colorless thereby indicating that Silica Gel has adsorbed moisture and requires immediate replacement or regeneration. The orange silica gel has won unprecedented acknowledgment and praise from the users since its commercial introduction into the markets.
Silica Gel is usually used in many products since moisture and condensation encourages the growth of mold and spoilage and may damage the goods. Silica Gel dries, avoids dampness, resists rust, fit for damp proof of instruments, meter, weapon, cartridge, electronic components, household apparatus, spare parts of machinery, leather, pharmacy, food, costume, textiles and other packed goods.
It is used as an air cleanser to restrain humidity in the air, as well as catalyzer carrier and dehydration for organic compounds as it has high density and high moisture absorption under low humidity. It has been used widely for ocean shipping with obvious effect to resist dampness in order to save goods because of high humidity in the process of ocean shipping.