The equation for calculation of the activation energy of the diffusion of the evolved products through the matrix (E) from a single TG curve were proposed by solving Fick's laws. The solution is based on the similarly theory by utilizing
a Fourier number.
The proposed method was examined by using mass loss data for the dehydroxylation of some micas with and without FeO (muscovite
and its varieties and lepidolite) as determined from their TG curves. TheE values for the first stage of the dehydroxylation of these micas areE1,=85±10 kJ mol−1; for the final stageE2=380±40 kJ mol−1 and for the mass loss connected with fluorineEF=85±10 kJ mol−1.
Several isomorphic groups of micas: Muscovite-Phengite-Muscovite-Li-Muscovite; Biotite-Zinnwaldite-Lepidolite and Biotite-Phlogopite
were investigated by DTA, TG and DTG. Octehedral vacancies and the sites of octahedral cationic occupancy were determined
from IR-spectra of the hydroxyls. The influence of a composition and fine structure of the micas on the shape of the thermal
curves was discussed. A one to one correspondence between the isomorphic series members and individual thermal curves makes
it possible to determine the chemical composition of a mica sample. The combination of thermal and IR-spectra of hydroxyl
analyses permits to link the Order-Disorder data with thermal properties of mica.
Dimethylsulfoxide (DMSO) kaolinite complexes of low-and high-defect kaolinites were studied by thermo-IR-spectroscopy analysis.
Samples were gradually heated up to 170°C, three hours at each temperature. After cooling to room temperature, they were pressed
into KBr disks and their spectra were recorded. From the spectra two types of complexes were identified. In the spectrum of
type I complex two bands were attributed to asymmetric and symmetric H-O-H stretching vibrations of intercalated water, bridging
between DMSO and the clay-O-planes. As a result of H-bonds between intercalated water molecules and the O-planes, Si-O vibrations
of the clay framework were perturbed, in the low-defect kaolinite more than in the high-defect. Type II complex was obtained
by the thermal escape of the intercalated water. Consequently, the H-O-H bands were absent from the spectrum of type II complex
and the Si-O bands were not perturbed. Type I complex was present up to 120°C whereas type II between 130 and 150°C. The presence
of intercalated DMSO was proved from the appearance of methyl bands. These bands decreased with temperature due to the thermal
evolution of DMSO but disappeared only in spectra of samples heated at 160°C. Intercalated DMSO was H-bonded to the inner-surface
hydroxyls and vibrations associated with this group were perturbed. Due to the thermal evolution of DMSO the intensities of
the perturbed bands decreased with the temperature. They disappeared at 160°C together with the methyl bands.
DMSO-kaolinite complexes of low- and high-defect Georgia kaolinite (KGa-1 and KGa-2, respectively) were investigated by thermo-XRD-analysis.
X-ray patterns showed that DMSO was intercalated in both kaolinites with a d(001)-value of 1.11 nm (type I complex). The samples were gradually heated up to 170°C and diffracted by X-ray at room-temperature.
With the rise in temperature, due to the thermal evolution of the guest molecules, the relative intensity of the 1.11 nm peak
decreased and that of the 0.72 nm peak (neat kaolinite) increased indicating that the fraction of the non-intercalated tactoids
increased. The 1.11 peak disappeared at 130–140°C. During the thermal treatment of both complexes two additional peaks appeared
at 110 and 120°C, respectively, with d-values of 0.79–0.94 and 0.61–0.67 nm in DMSO-KGa-1 and 0.81–0.86 and 0.62–0.66 nm in DMSO-KGa-2, indicating the formation
of a new phase (type II complex). The new complex was obtained by the dehydration of type I complex and was composed of intercalated
DMSO molecules which did not escape. The new peaks disappeared at 150–160°C indicating the complete escape of DMSO.
Summary Thermo-XRD-analysis is applied to identify whether or not the adsorbed organic species penetrates into the interlayer space of the smectites mineral. In this technique an oriented smectite sample is gradually heated to temperatures above the irreversible dehydration of the clay, and after each thermal treatment is diffracted by X-ray at ambient conditions. In the thermal treatment of organo-clays, under air atmosphere at temperatures above 250°C, the organic matter is in part oxidized and charcoal is formed from the organic carbon. In inert atmosphere e.g. under vacuum above 250°C the organic matter is pyrolyzed and besides small molecules, charcoal is formed. If the adsorbed organic compound is located in the interlayer space, the charcoal is formed in that space, preventing the collapse of the clay. A basal spacing of above 1.12 nm suggests that during the adsorption the organic compound penetrated into the interlayer space. Thermo-XRD-analyses of montmorillonite complexes with anilines, fatty acids, alizarinate, protonated Congo red and of complexes of other smectites with acridine orange are described. To obtain information about spacings of the different tactoids that comprise the clay mixture, curve-fitting calculations on the X-ray diffractograms were adapted.
The adsorption of the organic anionic dye Congo red (CR) by montmorillonite saturated with Na+, Cs+, Mg2+, Cu2+, Al3+ and Fe3+ was investigated by XRD of unwashed and washed samples after equilibration at 40% humidity and after heating at 360 and at 420°C. The clay was treated with different amounts of CR, most of which was adsorbed. Clay samples, untreated with CR, after heating showed collapsed interlayer space. Unwashed and washed samples, which contained CR, before heating were characterized by three peaks or shoulders, labeled A (at 0.96-0.99 nm, collapsed interlayers), B (at 1.24-1.36 nm) and C (at 2.10-2.50 nm). Peak B represents adsorbed monolayers of water and dye anions inside the interlayer spaces. Peak C represents interlayer spaces with different orientations of the adsorbed water and organic matter. Diffractograms of samples with small amounts of dye were similar to those without dye showing peak B whereas diffractograms of most samples with high amounts of dye showed an additional peak C. Heated unwashed and washed samples were also characterized by three peaks or shoulders, labeled A' (at 0.96 nm), B' (at 1.10-1.33 nm) and C' (at 1.61-2.10 nm), representing collapsed interlayers, and interlayers with charcoal composed of monolayers or multilayers of carbon. When the samples were heated from 360 to 420°C some of the charcoal monolayers underwent rearrangement to multilayers. In the case of Cu the charcoal decomposed and oxidized. The present results show that most of the adsorbed dye was located inside the interlayer space.
An intense blue organo-clay color pigment was obtained by adding naphthyl-1-ammonium chloride to a Na-montmorillonite aqueous
suspension followed by treatment with sodium nitrite. This treatment resulted in the synthesis of the azo dye 4-(1-naphthylazo)-1-naphthylamine
adsorbed onto the clay. The pigment was subjected to thermo-XRD-analysis and the diffractograms were curve-fitted. Heating
naphthylammonium-montmorillonite at 360°C resulted in the evolution of the amine at temperatures lower than those required
for the formation of charcoal and consequently the clay collapsed. On the other hand, heating the pigment at 360°C resulted
in the conversion of the adsorbed azo dye into charcoal. The clay did not collapse, thus proving that the azo dye was located
inside the interlayer space. Before the thermal treatment a short basal spacing in the pigment compared with that in the ammonium
clay (1.28 and 1.35 nm, respectively) indicated stronger surface π interactions between the clayey O-plane and the azo dye
than between this plane and naphthylammonium cation. The amount of dye after one aging-day of the synthesis-suspension increased
with [NaNO2]/[C10H7NH3] ratio but did not increase with naphthylammonium when the [NaNO2]/[C10H7NH3] ratio remained 1. After 7 and 56 aging days it decreased, indicating that some of the dye decomposed during aging.
Co- and Ni-montmorillonites adsorb in aqueous suspensions up to 13 mmol alizarinate per 100 g clay, onto the broken-bonds
whereas Cu-clay adsorbs up to 25 mmol dye per 100 g clay into the interlayer space. Unloaded Co-, Ni- and Cu-clays and samples
loaded with increasing amounts of alizarinate, were gradually heated in air to 360C and analyzed by X-ray diffraction. All
diffractograms were curve-fitted. Fitted diffractograms of non-heated samples, showed two peak components labeled C and D,
nm, characterizing tactoids with mono- and non-complete bilayers of water, respectively. After heating at 120C component
D decreased or disappeared and two new components A and B appeared at0.99 and1.08
nm, representing collapsed tactoids and tactoids with interlamellar oxy-cations, respectively. At 250C, C and D decreased
or disappeared but A and B appeared in all fitted diffractograms. Co- and Ni-clay after heating at 360C did not show C and
D. Components A and B proved that these clays collapsed indicating that initially there was no alizarinate in the interlayers.
At 360C, C and D persisted in the fitted-diffractograms of Cu-clay, representing tactoids with interlamellar charcoal formed
from the partial oxidation of adsorbed dye initially located in the interlayers.
Montmorillonite and Laponite loaded with
different amounts of tributylammonium cations (TBAH+),
up to 40 and 30 mmol, respectively, per 100 g clay, were studied by thermo-XRD-analysis.
TBAH-smectites heated at 300 and 420°C exhibited basal spacings of 1.30
and 1.24 nm, attributed to smectite tactoids with low- and high-temperature-stable
monolayer charcoals, respectively in the interlayers. DTA-EGA and TG of the
TBAH-smectites showed four stages of mass loss labeled A, B, C and D. Stage
A below 250°C, accompanied by an endothermic DTA peak, resulted from the
dehydration of the clay. Mass loss stages B, C and D, at 250–380, 380–605°C
and above 605°C, respectively, accompanied by exothermic DTA peaks, were
due to three oxidation steps of the organic matter. In mass loss stage B (first
oxidation step) mainly organic hydrogen was oxidized to H2O whereas carbon
and nitrogen formed low- and high-temperature-stable charcoals. In stages
C and D (second and third oxidation steps) low- and high-temperature- stable
charcoals were oxidized, respectively. Dehydroxylation of the smectites occurred
together with the second and third oxidation steps. Thermal mass loss at each
step was calculated from the TG curves showing that in montmorillonite the
percentage of high-temperature-stable charcoal from total charcoal decreased
with higher TBAH+ loadings of the clay whereas
in Laponite this percentage increased with higher loadings of the clay.