Boehmite

Boehmite is a commonly occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition of AlO (OH ) and γ - AlOOH and developed predominantly granular to massive aggregates of white, light yellow, yellow-green or red-brown color with white stroke color. Only rarely forms boehmite small, tabular to prismatic crystals of a few millimeters in size.

Etymology and history

It is unclear if the boehmite after the German geologist and paleontologist Johannes Böhm (1857-1938) or after the German - Czech chemist and Corr was named a member of the Czechoslovak Academy of Sciences, Johann (Hans Jan ) Böhm ( 1895-1952 ).

It was first found and described in 1925 by the chemist Johann Böhm ( 1895-1952 ) and the geologist J. de Lapparent 1927, who called it boehmite.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the boehmite belonged to the mineral class of " oxides and hydroxides " and then to the Department of " hydroxides and oxide hydrates ," where he, along with akaganeite, diaspore, Feitknechtit, Feroxyhyt goethite, Groutit, lepidocrocite, manganite, schwertmannite and Tsumgallit formed a distinct group.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the boehmite also in the class of " oxides and hydroxides ," there but in the department of the " Hydroxide (without V or U) " a. This division is also further divided by the possible presence of hydroxide ions (OH) and crystal water (H2O) as well as the crystal structure, so that the mineral according to its composition and structure in the sub-department " hydroxides with OH, excluding H2O; Layers of edge-sharing octahedra " is to find where it forms the unnamed group 4.FE.15 only together with lepidocrocite.

The classification of minerals according to Dana assigns the boehmite in the class of " oxides and hydroxides " and there in the department of " hydroxides and hydroxy- oxides ". Here he is named the " Böhmitgruppe " with the system no. 06:01:02 and the other members lepidocrocite and Guyanait within the subdivision " hydroxides and hydroxy- oxides having the formula: X3 O OH " to find.

Modifications and varieties

Boehmite is a modification of aluminum hydroxide and closely related diaspore ( α - AlO (OH) ).

Education and Locations

Boehmite along with diaspore, gibbsite, and iron minerals hematite and goethite a component of bauxite.

Worldwide, boehmite so far (as of 2011) are detected at around 130 localities. In Germany the mineral previously could only be found at the Bear Stone in the Erzgebirge. In Austria, boehmite found inter alia in Dreistetten in Lower Austria, in the bauxite deposits of the lower mountain in Salzburg and at White Water in Reichraminger Hintergebirge in Upper Austria. In Switzerland, the mineral previously occurred only in the community Collombey on in the canton of Valais.

Other localities include Australia, Brazil, China, Dominican Republic, France, Ghana, Greece, Greenland, Guyana, Iraq, Israel, Italy, Jamaica, Japan, Cambodia, Canada, Colombia, Madagascar, Mexico, New Zealand, Nigeria, Norway, Russia, Sweden, Slovakia, Sudan, Turkey, Hungary, the United States of America ( USA) and Vietnam.

Crystal structure

Boehmite crystallizes in the orthorhombic space group ( Raumgruppen-Nr. 63) with the lattice parameters a = 2.86 Å; b = 12.22 Å and c = 3.69 Å and four formula units per unit cell.

Use

As part of boehmite bauxite is an important raw material for the production of aluminum.

By careful dehydration (dehydration ) of boehmite can be chemically aluminum oxide ( Al2O3) are generated, which is used mainly for the production of ceramics, as a refractory material or in modern armor for vehicles.

One uses " boehmite " for corrosion protection. Layers Properly generated ( by boiling deionized water or water vapor) are colorless to milky, substantially pore- free, tasteless and completely harmless. The pH range is between 3.5 and 9 boehmite layers protect against attacks by boiling tap water, fruit acids, lactic acids and slightly aggressive food and beverages. Further they are used for protecting inner walls of vessels, heat exchangers and piping systems because it can be applied after assembly.