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Thermal Reactions of Synthetic Hectorite

Published online by Cambridge University Press:  01 July 2024

J. M. Green ,
K. J. D. Mackenzie  and
J. H. Sharp
J. M. Green
Affiliation:
Department of Ceramics with Refractories Technology, The University, Sheffield, England
K. J. D. Mackenzie
Affiliation:
Department of Ceramics with Refractories Technology, The University, Sheffield, England
J. H. Sharp
Affiliation:
Department of Ceramics with Refractories Technology, The University, Sheffield, England
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Abstract

The thermal reaction sequence of a synthetic hectorite (Laponite CP) was studied by X-ray diffraction, i.r. spectroscopy and thermal analysis. Although most of the interlayer water is removed at 200°C, a smally steady weight loss occurs until dehydroxylation is complete at about 700°C, indicating that an anhydrous intermediate phase is not formed prior to dehydroxylation. Immediately after dehydroxylation, enstatite and cristobalite can be identified, but lithium silicates are formed only from lithium-saturated hectorite. Around 1200°C a glass is formed by reaction of the alkalis with cristobalite, and removal of silica from the enstatite produces some forsterite. An inhomogeneous mechanism of dehydroxylation is postulated by analogy with that proposed for talc.

Résumé

Résumé

La séquence de réaction thermique d’un hectorite synthétique (Laponite CP) a été étudiée par diffraction des rayons X, spectroscopic à l’infra-rouge et analyse thermique. Bien que la plus grande partie de l’eau entre les couches intermédiaires disparaisse à 200°C, il se produit une petite perte régulière de poids jusqu’à ce que la déshydroxylation soit complète à environ 700°C, ce qui indique qu’une phase intermédiaire anhydre ne s’est pas formée avant la déshydroxylation. Immédiatement après la déshydroxylation, on peut identifier de l’enstatite et de la cristobalite, mais les les silicates de lithium sont formés seulement à partir d’hectorite saturé au lithium. A environ 1200°C, un verre se forme par réaction de l’alkali avec la cristobalite et la disparition de silice de l’enstatite produit de la forsterite. Un méchanisme non homogène de déshydroxylation est postulé par analogie avec celui proposé pour le talc.

Kurzreferat

Kurzreferat

Die thermische Reaktionsfolge eines synthetischen Hektorits (Laponit CP) wurde durch Röntgenbeugung, Ultrarot-Spektroskopie und thermische Analyse studiert. Obgleich der Grossteil des Zwischenschichtwassers bei 200°C bereits entfernt ist, so findet doch ein geringer, stetiger Gewichtsverlust statt bis die Dehydroxylierung bei ungefähr 700°C komplett ist, was darauf hindeutet, dass es vor der Dehydroxylierung nicht zur Bildung einer wasserfreien Zwischenphase kommt. Unmittelbar nach der Dehydroxylierung können Enstatit und Cristobalit identifiziert werden, während sich Lithiumsilikate nur aus mit Lithium gesättigtem Hektorit bilden. Um 1200°C finder durch die Reaktion von Alkalien mit Cristobalit Glasbildung statt, und die Entfernung von Silizium dioxyd as dem Enstatit liefert Forsterit. Für die Dehydroxylierung wird ein inhomogener Mechanism, analog dem für Talk, vorgeschlagen.

Резюме

Резюме

Поведение синтетического гекторита при нагревании изучено методами рентгенографии, ИК-спектроскопии и термического анализа. Хотя большая часть воды удаляется при 200, небольшая, но постоянная потеря веса все же имеет место вплоть до полной дегидроксилизации при температуре примерно 700; это указывает на то, что до завершения дегидроксилизации не происходит образования никакой промежуточной безводной фазы. Немедленно после дегидроксилизации в остаточном продукте обнаруживаются энстатит и кристобалит, литиевые силикаты образуются только из Li-насышенного гекторита. При температуре примерно 1200 в результате взаимодействия щелочных ионов с кристобалитом образуется стекло, а удаление кремнезема из энстатита приводит к образованию небольших количеств форстерита. Предполагается, что обнаруженный негомогенный механизм дегидроксилизации аналогичен подобному механизму для талька.

Type
Research Article
Information
Clays and Clay Minerals , Volume 18 , Issue 6 , December 1970 , pp. 339 - 346
Copyright
Copyright © 1970 The Clay Minerals Society

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