|
|Section2= |Section5= |Section6= |Section7= |Section8= }} Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide (or alumina), Al2O3. These compounds together are the major components of the aluminium ore bauxite. Freshly precipitated aluminium hydroxide forms gels, which are the basis for the application of aluminium salts as flocculants in water purification. This gel crystallizes with time. Aluminium hydroxide gels can be dehydrated (e.g. using water-miscible non-aqueous solvents like ethanol) to form an amorphous aluminium hydroxide powder, which is readily soluble in acids. Aluminium hydroxide powder which has been heated to an elevated temperature under carefully controlled conditions is known as activated alumina and is used as a desiccant, as an adsorbent in gas purification, as a Claus catalyst support for water purification, and as an adsorbent for the catalyst during the manufacture of polyethylene by the Sclairtech process. ==Nomenclature== The naming for the different forms of aluminium hydroxide is ambiguous and there is no universal standard. All four polymorphisms have a chemical composition of aluminium trihydroxide (an aluminium atom attached to three hydroxide groups).〔 Gibbsite is also known as hydrargillite, named after the Greek words for water (hydra) and clay (argylles). The first compound named hydrargillite was thought to be aluminium hydroxide, but was later found to be aluminium phosphate; despite this, both gibbsite and hydrargillite are used to refer to the same polymorphism of aluminium hydroxide, with gibbsite used most commonly in the United States and hydrargillite used more often in Europe. In 1930 it was referred to as α-alumina trihydrate to contrast it with bayerite which was called β-alumina trihydrate (the alpha and beta designations were used to differentiate the more- and less-common forms respectively). In 1957 a symposium on alumina nomenclature attempted to develop a universal standard, resulting in gibbsite being designated γ-Al(OH)3 and bayerite becoming α-Al(OH)3 and nordstrandite being designated Al(OH)3. Based on their crystallographic properties, a suggested nomenclature and designation is for gibbsite to be α-Al(OH)3, bayerite to be designated β-Al(OH)3 and both nordstrandite and doyleite are designated Al(OH)3. Under this designation, the α and β prefixes refer to hexagonal, close-packed structures and altered or dehydrated polymorphisms respectively, with no differentiation between nordstrandiate and doyleite.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「aluminium hydroxide」の詳細全文を読む スポンサード リンク
|