Characterization of urea-modified Palabora vermiculite

• Published in: Applied clay science 2015-03, Vol.105-106, p.14-20
• Main Authors: Muiambo, Herminio F., Focke, Walter W., Atanasova, Maria, Benhamida, Aida
• Format: Article
• Language: English
• Subjects: Aluminum; Distilled water; Exfoliation; Flakes; Ion exchange; Ion exchangers; Magnesium; Thermal mechanical analysis; Urea; Ureas; Vermiculite
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2014.12.019

Replacing the exchangeable interlayer ions in Palabora vermiculite with magnesium, aluminum or iron (III) ions does not affect the exfoliation onset temperature (456±11°C). However, co-intercalation of minor amounts of urea lowers the exfoliation onset temperature to 209±35°C. This significant decrease is attributed to the low thermal stability of urea which releases ammonia and water as blowing agents. Thermo-mechanical analysis indicates that the expanded vermiculite exhibits spring-like properties. Part of the original expansion is recovered when the applied force is removed. The observed hysteresis is attributed to the progressive flattening of warped/buckled sheets that make up the expanded worm-like structure. Provided the expanded flake has not been heated beyond 450°C, it can be reconstituted by applying a sufficiently high compressive force followed by equilibration with distilled water. Such flakes show the conventional exfoliation behavior when heated again. •Co-intercalation urea reduces the expansion onset temperature of Palabora “vermiculite”.•The expanded “vermiculite” exhibits spring-like behavior but there is some hysteresis.•Vermiculite exfoliation is reversible.