Thermal behavior of layered double hydroxide Zn−Al− pyrovanadate : composition, structure transformations, and recovering ability

Abstract

Layered double hydroxides (LDHs) intercalated with vanadate anions have been recently discovered as promising active anticorrosive pigments. Estimation of true chemical composition and refinement of crystal structure of such LDHs are not straightforward because of a variety of the vanadate anion polytypes and their adsorption on the external surface of the hydroxide layers. By means of combination of methods of chemical analysis and application of X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis, the chemical composition of Zn–Al–vanadate, polytype of the intercalated anion, and relative content of adsorbed species were found. Two structural modifications of the Zn–Al–vanadate LDH corresponding to different arrangements of the pyrovanadate anions were detected in the range between room temperature and 100 °C. Transition between the modifications is reversible and dependent on the relative content of the crystal water in the interlayer. Calcination at 150 °C and above leads to the irreversible degradation of the LDH phase and formation of ZnAl2O4 (above 300 °C) and Zn3(VO4) (above 500 °C).