Summary
The dehydration mass loss of samples of montmorillonite (a layered hydrated silicate) was measured in an environment at constant temperature and at constant undersatured water vapour content. The hydration curves were analysed by assuming the model of thermally activated, monoenergetic and first-order process compatible with the experimental results. Two dehydration kinetics with activation energies (0.21±0.02) eV and (0.34±0.02) eV were found that can be related to the existence of two kinds of water (structured and nonstructured) in the hydrated silicate interlayers. The possibility of an icelike structure of a fraction of the adsorbed molecules is briefly discussed. The experimental results show, furthermore, that in the investigated hydration range (up to about 10% in mass) the fraction of structured water has a maximum when the hydration is about 6%.
Riassunto
È stata misurata la perdita di massa per deidratazione di campioni di montmorillonite (un silicato idrato lamellare) in ambiente a temperatura e contenuto sottosaturo di vapore d'acqua costanti. Le curve di deidratazione sono state analizzate assumendo un modello di processo termicamente attivato, monoenergetico, del primo ordine, che è compatibile con i risultati sperimentali. Sono state individuate due cinetiche di deidratazione, con energie di attivazione di (0.21±0.02) eV e di (0.34±0.02) eV, che possono essere correlate all'esistenza di due tipi d'acqua, strutturata e non strutturata, negli spazi interlamellari del silicato idrato. La possibilità di una strutturazione tipo ghiaccio di una frazione delle molecole adsorbite è brevemente discussa. I risultati delle misure indicano inoltre che, nell'intervallo di idratazione indagato che va fino al 10% circa in massa, la frazione di acqua strutturata presenta un massimo quando l'idratazione è di circa il 6%.
Резюме
Измеряется гидратация образцов монтморилонита (слоистого гидратного силиката) при постоянной температуре и постоянном содержанин ненасыщенных водяных паров. Анализируются кривые гидратации. Обнаружено два процесса дегидратции с энергиями активации (0.21±0.02) эВ и (0.34±0.02) эВ, которые могут быть связаны с существованием двух типов воды (структурной и бесструктурной) в промежуточных слоях гидратного силиката. Обсуждается возможность существования доли поглощенных молекул со структурой, подобной структуре льда. Экспериментальные результаты показывают, что в исследованной области тидратации доля структурной воды имеет максимум, когда гидратация составляет порядка 6%.
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Andreotti, G., Loria, A., Mazzega, E. et al. Dehydration kinetics of a natural montmorillonite. Il Nuovo Cimento C 1, 123–135 (1978). https://doi.org/10.1007/BF02524834
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DOI: https://doi.org/10.1007/BF02524834