Fast aging treatment for the synthesis of hydrocalumites using microwaves

Friedelʹs salt [Ca2Al(OH)6]Cl·2H2O, commonly known as hydrocalumite, was synthesized by co-precipitation following different aging treatments, using microwave irradiation or conventional heating and by refluxing or in autoclave, with the aim of decreasing the aging times (24 h) employed when aging by conventional heating or at room temperature. Hydrocalumites were characterized by XRPD, FT-IR, N2 physisorption, ICP-OES, TEM, TEM-electron diffraction and TGA techniques. The use of microwaves favors a faster crystalline growth in the stacking direction whereas the use of autoclave improves the lamellar crystallinity. The highest crystallinity was found for the sample aged with microwave irradiation by autoclaving at 453 K for 1 h. This sample presented the highest crystallite size in the stacking direction (76 nm), the largest lamellar crystals (4000 nm) with R3c symmetry, and the highest dehydration- and dehydroxylation temperatures.