Reversible and irreversible dehydration of hydroxy-interlayered vermiculite from coastal plain soils

• Published in: Soil Science Society of America journal Vol. 52; no. 6
• Main Authors: Harris, W.G, Hollien, K.A
• Format: Journal Article
• Language: English
• Published: 01.11.1988
• Subjects: BALANCE HIDRICO DEL SUELO; BILAN DE L'EAU DANS LE SOL; FLORIDA; FLORIDE; HUMEDAD RELATIVA; HUMIDITE RELATIVE; PROPIEDADES TERMICAS; PROPRIETE THERMIQUE; REHIDRATACION; REHYDRATATION; SOL; SUELO; TIPOS FISIOGRAFICOS DE SUELOS; TYPE DE SOL GEOMORPHOLOGIQUE; VERMICULITA; VERMICULITE
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj1988.03615995005200060053x

Dehydration behavior of hydroxy-interlayered vermiculite (HIV) from three coastal plain soils was studied using x-ray diffraction (XRD) and thermal analysis. Relative humidity (RH) at 25 degrees C had little effect on HIV 001 XRD peaks, except for a 0.01 to 0.05 degrees 2-theta shift at RH approximately equals 0%. Heating to 50 degrees C shifted peak positions 0.10 to 0.20 degrees 2-theta for fine silts and 0.05 to 0.10 degrees 2-theta for coarse clays. Effects of 50 degrees C treatment were largely reversed by re-wetting, indicating that H2O re-entered interlayers. Heating to 115 degrees C broadened peaks and produced shifts of up 0.40 degrees 2-theta. Dehydration at greater than or equal to 115 degrees C was essentially irreversible, as indicated by lack of 001 expansion and failure to regain full sample weight at 100% RH. Peaks were markedly broadened and attenuated by heating to 165 and 225 degrees C, with full width at half maxima approaching 1.0 degrees 2-theta. No significant peak in the 1.0-nm region developed from interlayer collapse, even at 550 degrees C. Reversible dehydration may be attributable to free-H2O loss from interpolymer zones at temperatures below the onset of significant polymer dehydration. The data suggest that attraction between dehydrated polymers and 2:1-layer surfaces exceeds hydration forces, resulting in irreversible collapse and variable interlayer thickness. Re-entry of H2O into interlayers could be sterically impeded by the dehydrated polymers themselves or by their binding effect on layers. The 1.4-nm mineral in the soils studied exhibits thermal properties more consistent with HIV than an alternative vermiculite-kaolin intergradient structure