Dehydroxylation of dioctahedral smectites in water vapor atmosphere

• Published in: Applied clay science Vol. 137; pp. 1 - 5
• Main Authors: Emmerich, Katja, Steudel, Annett, Merz, Daniela
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-03-2017
• Subjects: Cis-vacant; Smectite; Thermal analysis; Trans-vacant; Water vapor atmosphere; Water vapor atmosphere; Trans-vacant; Thermal analysis; Smectite; Cis-vacant
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2016.12.003

Due to dehydration and dehydroxylation, it has to be considered, that thermal treatment of large quantities of bentonites in industrial applications may result in a local water vapor atmosphere above the sample. This study investigates the consequences of a local water vapor atmosphere during thermal treatment of bentonites with emphasis on the influence of water vapor on the DHX of dioctahedral smectites with Na+-saturated interlayers.
The dehydroxylation behavior of Na+-exchanged montmorillonites in water vapor atmosphere was compared to dehydroxylation in dry synthetic air. Water vapor at atmospheric pressure delays dehydroxylation of montmorillonites by 50°C. The temperature boundary for dehydroxylation of trans-vacant and cis-vacant layers shifts by 50 to 75°C to higher temperatures. Interlayer Na+ acts as flux and partial melting results in hollow spheres and bubbles that delayed dehydroxylation and entrapped water after dehydroxylation, which is suddenly discharged at higher temperatures. The formation of high temperature phases after heating to 1000°C is controlled by the montmorillonite composition.
•Water vapor delayed dehydroxylation (DHX) of montmorillonites by 50°C.•DHX boundary of trans- and cis-vacant layers shifted 50 to 75°C under water vapor.•Partial melting of Na-saturated montmorillonite yielded hollow spheres and bubbles.•The heating atmosphere didn't influence the formation of high temperature phases.•High temperature phases are cristobalite, spinel, hematite, and amorphous material.