The comparison of thermal stabilities of different organoclay intercalation complexes is presented in this work. Montmorillonite/monomer and montmorillonite/polymer intercalation complexes with similar basal spacings show a pronounced difference in changes of d001 values after 30 min heating. The hydrophilic and/or organophilic surface modification of the starting montmorillonite is an important factor affecting the intercalated amount of organic material and thus the expansion of the sheet silicate structure.
Authors:J. Kristóf, R. Frost, E. Horváth, L. Kocsis, and J. Inczédy
The thermal behaviour of ordered kaolinites from Hungary and Australia intercalated with potassium acetate, cesium acetate
and urea has been investigated by simultaneous TG-DTG-DTA, TG-MS, Raman microscopy and XRD. Remarkable changes in the thermal
decomposition pattern of the intercalates were obtained as a function of the nature of the intercalating re-agents. Replacing
the potassium cation to cesium leads to a change in the OH environments resulting in a more complicated dehydroxylation pattern.
The urea intercalates can be decomposed completely without dehydroxylating the mineral, although further treatments are necessary
to restore the original d-spacing.
Authors:S. Yariv, I. Lapides, K.H. Michaelian, and N. Lahav
Solid state intercalation of alkali halides into kaolinite takes place by heating pressed disks of dimethylsulfoxide (DMSO)-kaolinite
complex ground in different alkali halides. This reaction involves diffusion of the DMSO outside the interlayer space and
the alkali halide into the interlayer space. IR and Raman spectroscopy reveal two types of intercalation complexes: (i) almost
non-hydrous, obtained during thermal treatment of the DMSO complex; and (ii) hydrated, obtained by regrinding the disk in
air. The strength of the hydrogen bonds between intercalated water or halide anions and the inner surface hydroxyls decreases
in the order Cl−>Br−>I−. Chlorides penetrate the ditrigonal holes and form hydrogen bonds with the inner OH groups.
Authors:J. Kristóf, E. Horváth, R. Frost, and J. Kloprogge
The thermal behaviour of fully and partially expanded kaolinites intercalated with formamide has been investigated in nitrogen atmosphere under quasi-isothermal heating conditions at a constant, pre-set decomposition rate of 0.20 mg min–1 . With this technique it is possible to distinguish between loosely bonded (surface bonded) and strongly bonded (intercalated) formamide. Loosely bonded formamide is liberated in an equilibrium reaction under quasi-isothermal conditions at 118°C, while the strongly bonded (intercalated) portion is lost in an equilibrium, but non-isothermal process between 130 and 200°C. The presence of water in the intercalation solution can influence the amount of adsorbed formamide, but has no effect on the amount of the intercalated reagent. When the kaolinite is fully expanded, the amount of formamide hydrogen bonded to the inner surface of the mineral is 0.25 mol formamide/mol inner surface OH group. While the amount of surface bonded formamide is decreasing with time, no change can be observed in the amount of the intercalated reagent. With this technique the mass loss stages belonging to adsorbed and intercalated formamide can be resolved thereby providing a complex containing only one type of bonded (intercalated) formamide.
Authors:J. Kristóf, M. Tóth, M. Gábor, P. Szabó, and R. L. Frost
Intercalation complexes of three different Hungarian kaolinites with hydrazine and potassium acetate were investigated by FT-IR (DRIFT) spectrometry, X-ray diffraction, and thermogravimetry combined with mass spectrometry. Differences were found in the thermal behaviour of the complexes as well as in the rehydration — reexpansion patterns of the heated intercalates. An XRD method is proposed for the distinction of kaolinite and 7.2 Å halloysite present in the same mineral.
Authors:I. Lapides, N. Lahav, K. H. Michaelian, and S. Yariv
Intercalation complexes of kaolinite with a series of alkali halides (NaCl (trace amounts), KCl, RbCl, CsCl, NaBr, KBr, CsBr, Kl, Rbl and Csl) were obtained by a thermal solid state reaction between the kaolinite-dimethylsulfoxide intercalation complex and the appropriate alkali halide. The ground mixtures (1∶1 weight ratio) were pressed into disks that were gradually heated up to 250 °C for different times. X-ray diffractograms of the disks were recorded after each thermal treatment. At the end of the thermal treatment the disks were ground and basal spacings of the powders obtained. As a result of thermal treatment, alkali halide ions diffuse into the interlayers, replacing the intercalated dimethylsulfoxide molecules. Such a replacement may take place only if the thermal diffusion of the penetrating species is faster than the evolution of the intercalated organic molecule. With increasing temperature the intercalated salt diffused outside the interlayer space or underwent a thermal hydrolysis which resulted in the evolution of hydrogen halides from the interlayer space. Consequently, the amounts of intercalation complexes decreased at elevated temperatures.
Authors:E. Horváth, J. Kristóf, R. Frost, Á. Rédey, V. Vágvölgyi, and T. Cseh
The thermal behaviour of halloysite fully expanded with hydrazine-hydrate has been investigated in nitrogen atmosphere under
dynamic heating and at a constant, pre-set decomposition rate of 0.15 mg min-1. Under controlled-rate thermal analysis (CRTA) conditions it was possible to resolve the closely overlapping decomposition
stages and to distinguish between adsorbed and bonded reagent. Three types of bonded reagent could be identified. The loosely
bonded reagent amounting to 0.20 mol hydrazine-hydrate per mol inner surface hydroxyl is connected to the internal and external
surfaces of the expanded mineral and is present as a space filler between the sheets of the delaminated mineral. The strongly
bonded (intercalated) hydrazine-hydrate is connected to the kaolinite inner surface OH groups by the formation of hydrogen
bonds. Based on the thermoanalytical results two different types of bonded reagent could be distinguished in the complex.
Type 1 reagent (approx. 0.06 mol hydrazine-hydrate/mol inner surface OH) is liberated between 77 and 103C. Type 2 reagent
is lost between 103 and 227C, corresponding to a quantity of 0.36 mol hydrazine/mol inner surface OH. When heating the complex
to 77C under CRTA conditions a new reflection appears in the XRD pattern with a d-value of 9.6 , in addition to the 10.2
Ĺ reflection. This new reflection disappears in contact with moist air and the complex re-expands to the original d-value
of 10.2 in a few h. The appearance of the 9.6 reflection is interpreted as the expansion of kaolinite with hydrazine alone,
while the 10.2 one is due to expansion with hydrazine-hydrate. FTIR (DRIFT) spectroscopic results showed that the treated
mineral after intercalation/deintercalation and heat treatment to 300C is slightly more ordered than the original (untreated)
Thermogravimetric data were used to calculate the kinetics of isothermal degradation of layered tetratitanate intercalated
with n-alkyldiamines H2N(CH2)nNH2 (n=2, 3, 4, 6 or 8). The hydrous matrix showed two mass loss steps from the thermogravimetric curve, corresponding to the release
of physisorbed and lattice water molecules. For the intercalated matrices a third mass loss was observed due to the release
of organic moiety. From these values, the amine intercalated matrices can be ordered in the following sequence of thermal
stability; C4>C2>C3≅C6>C8. Kinetic studies were carried out to the release of lattice water molecules. The kinetic model that
best adjusted the experimental isothermal TG data was the diffusion mechanism controlling process.
Supramolecular 2,3- and 2,5-pyridinedicarboxylate (PDC) intercalated
ZnAl-layered double hydroxides (2,3- and 2,5-PDC–ZnAl–LDHs) have
been prepared by ion exchange method. The structure and composition of the
intercalated materials have been studied by X-ray diffraction (XRD) and inductively
coupled plasma emission spectroscopy (ICP). The study indicates that the 2,3-PDC
and 2,5-PDC anions are accommodated as interdigitated bilayer and monolayer
arrangement respectively between the sheets of LDHs. Furthermore, their thermal
decomposition processes were studied by the use of in situ high temperature
X-ray diffraction (HT-XRD), and the combined technique of thermogravimetry-differential
thermal analysis-mass spectrometry (TG-DTA-MS) under N2 atmosphere. Based
on the comparison study on the temperatures of both decarboxylation and complete
decomposition of interlayer PDC, it can be concluded that 2,5-PDC–ZnAl–LDHs
has higher thermal stability than that of 2,3-PDC–ZnAl–LDHs.
Authors:J. Kristóf, R. Frost, J. Kloprogge, E. Horváth, and M. Gábor
The thermal behaviour of kaolinites intercalated with formamide, dimethyl sulphoxide and hydrazine has been studied by simultaneous
TG-DTG-DTA-EGA and TG-MS techniques. The complexes can be decomposed completely without dehydroxylating the mineral. It was
found that the amount of intercalated guest molecules per inner surface OH-group is close to unity for the formamide and dimethyl
sulphoxide intercalates. For the intercalation of hydrazine it was found that hydrazine is locked in the expanded mineral
as hydrazine hydrate and its amount is somewhat higher than that obtained for the other two reagents. The thermal evolution
patterns of the guest molecules revealed that all the three reagents are bonded at least in two different ways in the interlayer