Pseudoboehmite

Pseudoboehmite is an aluminum compound having the chemical composition AlO (OH). It consists of finely crystalline boehmite. The water content is however higher than in boehmite.

History

Calvet et al. coined the term in 1952 Pseudeobömit when they synthesized a pure, synthetic aluminum hydroxide gel. The XRD spectrum is similar to that of boehmite but having a different relative intensity of the peaks.

Morphology

Pseudoboehmite consists essentially of microcrystalline boehmite which is composed of the same or similar octahedral layers in the XZ plane, but having no three-dimensional structure, because only a few elementary cells are present in the y- direction. It consists of a considerable number of crystallites with a single unit cell in the y direction, or single octahedral layers. It contains more water, which is usually located between the octahedral layers, usually arranged randomly, but sometimes regularly.

The water content consists of adsorbed and chemically bound water. The higher water content compared to boehmite can be explained by the smaller crystallites. While boehmite AlOOH consists of relatively long chains that end with H2O, these chains are significantly reduced under pseudo. The relative water content is significantly increased by the terminal water molecules:

There is a " slightly crystallized " Al3 compound of the composition Al2O3 * x H 2 O ( 1.0

At higher temperatures, pseudoboehmite converts to γ -alumina, wherein the size distribution of the pores is maintained up to 1000 ° C. At 1100 ° C, however, is already taking place, sintering and the specific surface area decreases, as a transition to α -Al2O3 will take place.

Production

Use

Pseudoboehmite is used as a binder in the production of FCC catalysts and adsorbents. It can also be used as a raw material for the production of activated alumina. A wide application is the production of γ -Al2O3 dar. This is due to the low cost, and high thermal stability and specific surface area for the preparation of sorbents, catalysts and catalyst supports used. Pseudoboehmite is also used for the production of α - Al2O3, which is used as refractory material, insulation and as Abrasionschutzmittel application.