Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular three-dimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other liquids, or may be filled by gas or vacuum. In the last case, the material is properly called silica xerogel.
A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. They are commonly encountered in foods to retain crispness. Industrially, desiccants are widely used to control the level of water in gas streams.
Aerogels are a class of synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid with extremely low density and extremely low thermal conductivity. Aerogels can be made from a variety of chemical compounds. Silica aerogels feel like fragile styrofoam to the touch, while some polymer-based aerogels feel like rigid foams.
Aerogels are produced by extracting the liquid component of a gel through supercritical drying or freeze-drying. This allows the liquid to be slowly dried off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. The first aerogels were produced from silica gels. Kistler's later work involved aerogels based on alumina, chromia, and tin dioxide. Carbon aerogels were first developed in the late 1980s.
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon composite, or just carbon, are extremely strong and light fiber-reinforced plastics that contain carbon fibers. CFRPs can be expensive to produce, but are commonly used wherever high strength-to-weight ratio and stiffness (rigidity) are required, such as aerospace, superstructures of ships, automotive, civil engineering, sports equipment, and an increasing number of consumer and technical applications.
The binding polymer is often a thermoset resin such as epoxy, but other thermoset or thermoplastic polymers, such as polyester, vinyl ester, or nylon, are sometimes used. The properties of the final CFRP product can be affected by the type of additives introduced to the binding matrix (resin). The most common additive is silica, but other additives such as rubber and carbon nanotubes can be used.
Sodium silicate is a generic name for chemical compounds with the formula Na
2xSi
yO
2y+x or (Na
2O)
x·(SiO
2)
y, such as sodium metasilicate (Na
2SiO
3), sodium orthosilicate (Na
4SiO
4), and sodium pyrosilicate (Na
6Si
2O
7). The anions are often polymeric. These compounds are generally colorless transparent solids or white powders, and soluble in water in various amounts.
Sodium silicate is also the technical and common name for a mixture of such compounds, chiefly the metasilicate, also called waterglass, water glass, or liquid glass. The product has a wide variety of uses, including the formulation of cements, coatings, passive fire protection, textile and lumber processing, manufacture of refractory ceramics, as adhesives, and in the production of silica gel. The commercial product, available in water solution or in solid form, is often greenish or blue owing to the presence of iron-containing impurities.