Abstract:
Replacing the exchangeable interlayer ions in Palabora vermiculite with magnesium, aluminumor 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
ofwarped/buckled sheets that make up the expandedworm-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.
