Synthetic Allophane and Imogolite

Summary In order to prepare allophane and imogolite in the laboratory, solutions containing l–2× 10 –3 M orthosilicic acid and 4–0.5 × 10 –3 M A1C1 3 (SiO 2 /Al 2 O 3 molar ratio; 0.5, 1.0, 2.0, 4.0 and 8.0) were heated at 95–100°C for 113 hours after addition of NaOH (NaOH/Al molar ratio; 1.0, 2.0, 2.8 and 3.0). Boehmite was found in the precipitates from all solutions with initial SiO 2 /Al 2 O 3 ratios of 0.5. Imogolite was found with allophane II in the products from solutions with SiO 2 /Al 2 O 3 ratios of 1.0 or greater and with NaOH/Al ratios of 2.8 or less (final pH 5.0), whereas allophane I was found in the precipitates from solutions with the same SiO 2 /Al 2 O 3 ratios but with the NaOH/Al ratio of 3.0 (final pH = 5.0–6.3). The mode of formation, chemical composition, infrared spectra, electron micrographs, electron diffraction patterns and differential thermal analysis curves of synthetic imogolite and allophanes (I and II) were compared with those of their natural counterparts.