Abstract
Imogolite is a unique tubular aluminum silicate having Si/Al molar ratio of 0.5. The external and internal tube diameters of imogolite are approximately 2.0 nm and 0.5 to 1.0 nm, respectively. The length of the tube ranges from a few dozen nm to a few 4 m. Because imogolite has not only large specific surface area but also high adsorption capacity and high affinity for water, it is expected to be used as heat exchange material and desiccant. Imogolite, however, doesn't exist in abundance in nature, so it must be artificially synthesized much before it is used as industrial materials.
We prepared concentrated instantaneously mixed solutions from sodium orthosilicate and aluminum chloride solutions. Al concentration of these solutions was 100 mmol L-1. Instantaneously mixed solutions were dialyzed for some dozen hours and heated in glass centrifuge tube with reflux condensers at around 100°C for 120 h. We obtained appreciable amount of imogolite from dialyzed solutions. Al concentration of the starting inorganic solution is the highest to yield imogolite.
We also heated instantaneously mixed solution without dialysis at 100°C for 144 h in erlenmeyer flasks with reflux condensers heterogeneously and homogeneously. The former heating condition gave near-translucent gel and the latter gave white dense precipitate. We found that more than 90% Si and 80% Al in the initial mixed solutions were incorporated into the both precipitates and the Si/Al ratios of the products were from 0.54 to 0.56. The XRD patterns and FTIR spectra were similar. These precipitates gave broad XRD peaks at 3.4 and 2.2 Å, slight peak at around 22 and 12 Å. The FTIR spectra showed broad and strong bands at 965, 570 and 430 cm-1. TEM observation showed that these products consisted of very fine solid particles and they formed spherical and semispherical aggregates.
