Characterization of urea-modified Palabora vermiculite: Fid-Bau Portal

Characterization of urea-modified Palabora vermiculite

Muiambo, Herminio F. / Focke, Walter W. / Atanasova, Maria / Benhamida, Aida

Abstract 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.

Highlights • 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.