Crystallographic defectA crystallographic defect is an interruption of the regular patterns of arrangement of atoms or molecules in crystalline solids. The positions and orientations of particles, which are repeating at fixed distances determined by the unit cell parameters in crystals, exhibit a periodic crystal structure, but this is usually imperfect. Several types of defects are often characterized: point defects, line defects, planar defects, bulk defects. Topological homotopy establishes a mathematical method of characterization.
CarbideIn chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. The carbides of the group 4, 5 and 6 transition metals (with the exception of chromium) are often described as interstitial compounds. These carbides have metallic properties and are refractory. Some exhibit a range of stoichiometries, being a non-stoichiometric mixture of various carbides arising due to crystal defects.
Sodium amalgamSodium amalgam, commonly denoted Na(Hg), is an alloy of mercury and sodium. The term amalgam is used for alloys, intermetallic compounds, and solutions (both solid solutions and liquid solutions) involving mercury as a major component. Sodium amalgams are often used in reactions as strong reducing agents with better handling properties compared to solid sodium. They are less dangerously reactive toward water and in fact are often used as an aqueous suspension. Sodium amalgam was used as a reagent as early as 1862.
PolyoxometalateIn chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are usually group 6 (Mo, W) or less commonly group 5 (V, Nb, Ta) transition metals and Tc in their high oxidation states. Polyoxometalates are often colorless, orange or red diamagnetic anions.
Pickling (metal)Pickling is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, and rust or scale from ferrous metals, copper, precious metals and aluminum alloys. A solution called pickle liquor, which usually contains acid, is used to remove the surface impurities. It is commonly used to descale or clean steel in various steelmaking processes. Metal surfaces can contain impurities that may affect usage of the product or further processing like plating with metal or painting.