The influence of Cu(II) on the hydrothermal and thermal transformations of a synthetic hectorite was investigated by a combined approach using mainly X-ray diffraction, thermal analyses, and electron paramagnetic resonance spectroscopy. The presence of Cu(II) during hydrothermal treatment increased the crystallite size. Copper (II) was both structure-bound and associated with the inner surfaces of the particles. Upon heating, structural destabilization of the hectorite began at ∼400°C as indicated by the formation of free radicals. Between 600 and 700°C, the hectorite converted to enstatite, and in the presence of Cu(II), to enstatite and richterite. The formation of richterite as an additional conversion product is explained by the creation of structural weakness due to structure-bound Cu(II) in F-containing hectorite. Our results suggest that traces of Cu(II), typical of natural environments, may influence the conversion products in high-temperature geochemical systems.

The thermal stability of surfactant-modified clays plays a key role in the synthesis and processing of organoclay-based nanocomposites. Differential thermal analysis (DTA), thermogravimetric measurement and differential scanning calorimetry (DSC) were used in this study to characterize the thermal stability of hexadecyltrimethylammonium bromide-modified montmorillonites prepared at different surfactant concentrations. Analysis by DSC shows that the molecular environment of the surfactant within the montmorillonite galleries is different from that in the bulk state. The endothermic peak at 70–100°C in the DTA curves of the modified montmorillonites is attributed to both the surfactant phase transformation and the loss of free and interlayer water. With an increase of surfactant-packing density, the amount of water residing in the modified montmorillonite decreases gradually, reflecting the improvement of the hydrophobic property for the organoclay. However, the increase in the surfactant packing density within the galleries leads to a decrease in the thermal stability of the organoclays.

With an increase of initial surfactant concentration for the preparation of organoclays, the surfactant- packing density increases gradually to a ‘saturated’ state. It was found that the cationic surfactant was introduced into the montmorillonite interlayer not only by cation exchange but also by physical adsorption.

Intercalation of a wide variety of alkylammonium cations into the interlayer spaces of swelling clay minerals leads to many different applications, ranging from surface-charge measurements to rendering the clay compatible for the preparation of clay nanocomposites, but knowledge of the exact conformation of the intercalated organic species is still incomplete, thus preventing a full understanding of this process. The purpose of this study was to investigate the interlayer conformation of dodecyltrimethylammonium (DDTMA) bromide in rectorite as affected by the amounts of DDTMA intercalated, using a battery of physical and spectroscopic methods. The capacity of rectorite to intercalate DDTMA was equivalent to 1.67 times the cation exchange capacity (1.67 CEC) of the mineral even though the initial input was as much as 5.00 CEC. When the DDTMA intercalated was <0.50 CEC of the mineral, minimal counterion sorption was associated with DDTMA intercalation. Derivative thermogravimetric (DTG) analyses revealed a single-peak decomposition temperature (Tpeak) at 430°C. X-ray diffraction (XRD) analyses indicated a flat-lying monolayer of the intercalated molecules, while shifts in Fourier Transform infrared (FTIR) bands confirmed gauche conformation. These results suggested that cation exchange was the dominant mechanism. At the maximum intercalation, the DDTMA adopted a horizontal trilayer arrangement with mainly gauche conformation as determined by FTIR and XRD. Meanwhile a second Tpeak appeared at 255°C, similar to the Tpeak of solid DDTMA. Counterion bromide sorption accompanying DDTMA intercalation reached a capacity of 310 mmol/kg. The results indicated that van der Waals interaction was responsible for the DDTMA uptake at the amount beyond 0.50 CEC. When the amount of DDTMA intercalated was between 0.5 and 1.67 CEC, the XRD patterns showed non-integrality, i.e. the 002 reflection was split into two non-integral peaks with 2 × d002 < d001 and 3 × d003 > d001. They became integral at 1.67 CEC. The results suggest that the mineral might be composed of mixed layers of a monolayer intercalated rectorite and a trilayer intercalated rectorite, without a bilayer as intermediate, when the amount of DDTMA intercalated was between 0.5 and 1.67 CEC.

The aim of the present study was to determine and elaborate on all changes in old-aged (OA) versus young-aged (YA) rat thyroids by using stereological, ultrastructural, hormonal, and gene expression analyses. We used 4- and 24-month-old male Wistar rats in our evaluation, presenting all changes in comparison with YA rats. Results showed that the thyroid parenchyma was characterized by higher absolute volumes of the gland, colloid, epithelium, and interstitium by 135, 135, 140, and 142% (p < 0.05) respectively, while the relative volumes of colloid and glands were unchanged. Ultrastructural analysis revealed less active glands, with smaller amounts of lysosomes, thyroglobulin (Tg) granules, and microvilli in the luminal colloid. Optical density values for thyroid peroxidase (TPO), Tg, and vascular-endothelial growth factor immunostaining remained unchanged; however, TPO and Tg exhibited visually stronger expression in small active follicles. Thyroxine (T4)-Tg, the relative intensity of fluorescence (RIF), serum T4, and the sodium-iodide symporter immunohistochemical and gene expressions decreased by 20, 40, 29, and 31% (p < 0.05), respectively, in OA thyroids. Pituitary thyroid-stimulating hormone (TSH) RIF increased by 44% (p < 0.05), but the TSH serum concentration remained unchanged. In conclusion, the obtained results indicate depression of the thyroid gland synthetic and secretory capacity with advanced age.

The thermal decomposition of hydrotalcite (HT), with chemical composition Mg1-xAlx(OH)2(CO3)x/2.(1-3x/2)H2O, (0.20 < x ≤ 0.33), is a complex sequence of dehydration, dehydroxylation and decarbonization and leads to the formation of a series of metaphases: HT-D (dehydrated HT), HT-B (partially dehydroxylated HT) and MO (mixed oxides with periclase-like structure). The evolution of water and CO2 in natural and synthetic hydrotalcites (a Mg/Al ratio between 2:1and 3.7:1), heated to 800°C, was investigated by differential thermal analysis, thermogravimetry and evolved gas analysis. At least six endothermic and two exothermic effects were established by computer-aided resolving of the curves. The formation of each HT metaphase was related to the release of a discrete number of water molecules depending on the Al content in the samples and each appeared as a corresponding endothermic peak in the DTA curves. The exothermic processes associated with the crystallization of HT-B and MO metaphases were specified by decomposition of DTA curves. The evolution of CO2 during the thermal decomposition of the carbonate groups was found to be different for the samples studied. The preservation of CO3 even at high temperatures was established for synthetic samples with a high Al content. The release of volatile H2O and CO2 (which comprise ~40% of the sample mass) provokes fine cracking both along and across the layers.

The thermal energy necessary for the removal of molecular water from Li+-, Na+-, Cs+-, Mg2+-, Ca2+-, Ba2+-, Alx(OH)yz+- and La3+-homoionic montmorillonite powders was determined by thermogravimetric analysis under atmospheric pressure. The weight loss curves and their derivatives exhibit one or several features related to the various populations of water molecules. The activation energy for water removal, which is the sum of the adsorption energy and the activation energy for diffusion, was calculated in each case using a simple first-order differentiation method. The results allow the physisorbed water and the water coordinated to the cations to be clearly separated. For the later population and with the exception of the Na-clay, a good correlation was found between the temperatures and activation energies for water removal and the polarizing power of the cations. Comparison with the results of mechanical tests performed on similar samples suggests that the creep of smectite clays is not controlled by mobility of the individual water molecules but by the mobility of the interlayer cations surrounded by their hydration shell.

Li8(Al6Si6O24)Cl2, a synthetic member of the sodalite family (Henderson and Taylor, 1977), was prepared by heating natural sodalite, Na8(Al- 6Si6O24)Cl2 (from Låven, Norway), in molten LiC1 at 800 °C for 2h, washing uncombined LiC1 from the product and drying at 110 °C Chemical analyses of the natural sodalite and the Li-sodalite are given in Table 1. The cell edge of the Lisodalite was 8.4476(9) Å (Si as internal standard: a = 5.43065/Å at 25 °C in good agreement with literature values (Henderson and Taylor, 1977).

Gypsum (CaSO4·2H2O) and brushite (CaHPO4·2H2O) are minerals with similar structures, despite not being isostructural. They both belong to the monoclinic system, but crystallize in different space groups. It is known that, to some extent, phosphate and sulphate groups can substitute for each other within the structure of these minerals. In the present work, the dehydration behaviour of experimentally produced Ca(SO4,HPO4)·2H2O solid solutions is assessed from thermogravimetrical (TG and DTG) and differential scanning calorimetry (DSC) analyses. For the applied experimental conditions it was not possible to obtain homogenous precipitates with compositions within 0.27 < XBr < 0.53, where XBr is the brushite mole fraction. The results reveal that the dehydration behaviour of solid solutions with compositions within the 0 < XBr < 0.27 interval tend to approach the dehydration process of pure gypsum. On the other hand, solid solutions with compositions within 0.53 < XBr < 1 involve higher dehydration temperatures than the brushite end-member, in a two-step process.