Pseudoboehmite is an

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

compound with the chemical composition AlO(OH). It consists of finely crystalline

boehmite Boehmite or böhmite is an aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium ore bauxite. It is dimorphous with diaspore. It crystallizes in the orthorhombic dipyramidal system and is typically massive in habit. It is ...

. However, the

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

content is higher than in boehmite.

History

Calvet et al. coined the name ''pseudoboehmite'' in 1952 when they synthesized pure aluminium hydroxyde gel. Its XRD pattern is similar to that of boehmite but the relative intensities of the peaks differ.

Morphology

Pseudoboehmite is essentially finely crystalline boehmite which consists of the same or similar octahedral layers in the xz plane but lacks three-dimensional order because of a restricted number of unit cells in y direction. It consists of a significant number of crystallites which contain a single unit cell along y or single octahedral layers. It contains more water which is commonly intercalated between octahedral layers, normally randomly arranged, but sometimes regularly. The water content consists of adsorbed and chemically bound water. The higher water content compared to boehmite can be explained by a smaller crystallite size. While boehmite consists of relatively long AlOOH chains that have terminal H₂O groups, the chains in pseudoboehmite are significantly shorter. This translates into a significantly higher specific water content due to the terminal water groups: Pseudoboehmite_structure

It is a "poorly crystallized" Al³⁺ compound with the composition Al₂O₃ · x H₂O (1.0 < x < 2.0) with interplanar spacings increased in the 20direction to 0.67 nm in comparison with 0.617 nm for

. At higher temperatures pseudoboehmite is transformed to γ-

alumina Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly ...

but the pore size distribution remains unchanged up to 1000 °C.{{cite book, author=Nogi, K., author2=Naito, M., author3=Yokoyama, T., title=Nanoparticle Technology Handbook, S., page= 204 At around 1100 °C however, specific area significantly decreases because of

sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plas ...

related to a transformation to α-Al₂O₃.

Synthesis

Pseudoboehmite can be synthesized by aging non-crystalline

aluminium hydroxide Aluminium hydroxide, , is found as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic and acidic propert ...

gels at pH values between 5.0 and 7.4.

Uses

Pseudoboehmite is used as binder for FCC catalysts and adsorbents. It is also a raw material for activated alumina.

References

Aluminium compounds