Silica gel is a kind of high-active absorbing material, which is generally obtained by reaction of sodium silicate and sulfuric acid together with aging, acidic soaking and other series of post-processing. Silica gel belongs to amorphous substance and its chemical formula is mSiO2 . H2O. With stable chemical property, it won't burn and won't dissolve in any solvent except for alkali and hydrofluoric acid. Silica gels of various models form different fined-pore structures owing to different manufacturing methods. Additionally, the chemical components and physical structure of silica gel determine that silica gel owns many characteristics which can't be substituted by other materials of same kind, such as high absorption performance, excellent thermal stability, stable chemistry, high mechanical strength and others.

According to the size of pore diameter, silica gel can be classified into m acro -pored silica gel, coarse-pored silica gel, B-type silica gel and fine-pored silica gel. Owing to different pore structures, their absorption performances are various and own different characteristics. Coarse-pored silica gel owns higher absorbing capacity under high relative humidity, fine-pored silica gel owns higher absorbing capacity than coarse-pored silica gel under lower relative humidity, and B-type silica gel owns absorbing capacity which is between coarse-pored and fine-pored silica gel owing to its pore structure is between coarse-pored and fine-pored silica gel. In addition, m acro -pored silica gel is generally used as catalytic agent carrier, delustering agent, toothpaste abrasive. Therefore, we should select different varieties according to different purposes.