Hydrous non-crystalline phosphates: structure, function and a new white pigment

Hydrated non-crystalline inorganic solids are often neglected due to the limited comprehension of their complex physico-chemical and structural properties. However, these non-crystalline materials exhibit a rich and varied chemistry, interesting for scientific and technological reasons. This work reviews general aspects of formation of hydrated non-crystalline solids, with special emphasis on aluminum (poly)phosphate materials. Precursors and concentration variations, temperature, ageing and reaction pH are trivial synthetic variables, but they promote the formation of a myriad of compounds adequate for many functions. Amorphous aluminum phosphates are widely employed in different industrial applications, providing good examples of the potential of hydrous amorphous solids.