Muiambo, Herminio FranciscoFocke, Walter WilhelmAtanasova, Maria TodorovaBenhamida, Aida2015-01-302015-01-302015-03Muiambo, HF, Focke, WW, Atanasova, M & Benhamida, A 2015, 'Characterization of urea-modified Palabora vermiculite', Applied Clay Science, vol. 105-106, pp. 14-20.0169-1317 (print)1872-9053 (online)10.1016/j.clay.2014.12.019http://hdl.handle.net/2263/43509Replacing 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.en© 2014 Elsevier B.V. All rights reserved. Notice : this is the author’s version of a work that was accepted for publication in Applied Clay Science. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Applied Clay Science, vol. 105-106, pp.14-20, 2015. doi : 10.1016/j.clay.2014.12.019.VermiculiteUreaIon exchangeExfoliationThermal mechanical analysisPostprint Article