Silica gel was patented by chemistry professor Walter A. Patrick at Johns Hopkins University, Baltimore, Maryland in 1919. The substance was known to exist as early as the 1640s.
In chemistry, silica gel is used in chromatography as a stationary phase. In column chromatography, the stationary phase is most often composed of silica gel particles of 40-63 micrometres. In this application, due to silica gel's polarity, non-polar components tend to elute before more polar ones, and this process is called normal phase chromatography. However, when hydrophobic groups are attached to the silica gel, then polar components elute first, and the method is referred to as reverse phase chromatography. Silica gel is also applied to aluminium or plastic sheets for thin layer chromatography.
In some cases, chelating groups have been covalently bound to silica gel. These materials have the ability to remove metal ions selectively from aqueous media. Chelating groups can be covalently bound to polyamines, which in turn have been grafted onto a silica gel surface, producing a material of greater mechanical integrity. Silica gel may also be combined with alkali metals to form a reducing agent.
Silica gel is most commonly encountered in everyday life as beads in a small paper packet. In this form, it is used as a desiccant to control local humidity to avoid spoilage or degradation of some goods. Since such packets may resemble sachets of sugar or salt and because silica gel may have added toxic chemical indicators, silica gel packets usually bear warnings for the user not to eat the contents.
Description of the chemical structure of silica and silica gel.
Silica gel is a granular, vitreous, porous form of silicon dioxide made synthetically from sodium silicate. Silica gel contains a nano-porous silica micro-structure, suspended inside a liquid. Most applications of silica gel require it to be dried, in which case it is called silica xerogel. For practical purposes, silica gel is often interchangeable with silica xerogel. Silica xerogel is tough and hard; it is more solid than common household gels like gelatine or agar. It is a naturally occurring mineral that is purified and processed into either granular or beaded form. As a desiccant, it has an average pore size of 2.4 nanometers and has a strong affinity for water molecules.
Silica gel is non-toxic, non-flammable, and non-reactive and stable with ordinary usage. It will react with hydrogen fluoride, fluorine, oxygen difluoride, chlorine trifluoride, strong acids, strong bases, and oxidizers. Silica gel is irritating to the respiratory tract and may cause irritation of the digestive tract, and dust from the beads may cause irritation to the skin and eyes, so precautions should be taken. Crystalline silica dust can cause silicosis, but synthetic amorphous silica gel is indurated, so does not cause silicosis. Additional hazards may occur when doped with a humid...