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Abstract  

Thermal analysis (DSC and HSM), and equilibrium solubility determinations were carried out to elucidate the mechanism of interaction at the solid state in the binary system triamterene-D-mannitol. Physical mixtures (5–90% w/w triamterene) and solid dispersions (5 up to 40% w/w triamterene) were prepared and studied. From DSC and HSM results, the thermal changes were associated with the variations in composition of the binary mixture, being more pronounced in the range 20–50% w/w. The binary phase diagram was proposed, although the exact position of the eutectic was uncertain. This is in accordance with a partial dissolution process detected by HSM. A linear increase in the solubility of triamterene with increasing aqueous mannitol concentration was obtained. The thermodynamic parameters of the solution properties were calculated, with an activation energy value of 96.081 kJ/mole. The solubilization increase was associated with complexation processes and hydrogen bonding formation.

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Abstract  

In the present investigation, DTA and TG techniques were used to study the thermal behaviour of montmorillonite treated with solutions of the pesticide aminotriazole (AMT), in nitrogen flow. These techniques have been complemented by mass spectrometry of the evolved gases (EGA-MS). AMT is adsorbed in the interlamellar space of montmorillonite as a cation. Results obtained in this study show that this provokes a shift of the dehydroxylation peak of montmorillonite to lower temperatures than those of the untreated clay. Montmorillonite protects the adsorbedAMT, delaying its first decomposition step, and catalysesAMT final decomposition at lower temperatures. The DTA curve of montmorillonite-AMT mechanical mixture differs from the sum of those of the clay mineral and the pesticide heated individually. Montmorillonite dehydroxylation occurs at lower temperature, indicating a complex formation betweenAMT and the mineral during the heating process. However the DTA of the mixture is different from that of the complex previously studied, indicating that in the complex obtained by heating the physical mixtureAMT is adsorbed as neutral molecule or as a product of its decomposition.

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Abstract  

Simultaneous DTA-TG has been carried out on a set of natural vermiculite samples. Based on their dehydration behaviour the samples can be divided in two groups: (a) those with DTA endothermic peak temperatures at 140°–150°C and 240°–270°C (pure vermiculties) and (b) those with peak temperatures at 95°–115°C (vermiculite with mica or mica-vermiculite interstratifications). The low temperature at which the endothermic effect in group (b) appears is discussed on the basis of dilution due to the inert layers of mica, differences in chemical composition, and lowering of interlamellar water bond energy.

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Abstract  

A microcomposite powder in the system TiO2—ZrO2 as a precursor of zirconium titanate (ZT) materials has been studied by thermal methods (DTA-TG) and X-ray diffraction (XRD). The microcomposite powder has been prepared by chemical processing of crystalline TiO2 (rutile, 10 mass% anatase),as inner core, coated with in situ precipitated amorphous hydrated zirconia gel, asouter core. The morphology and chemical composition of the resultant powders has been examined by SEM-EDX (Scanning electron microscopy-energy dispersive X-ray spectroscopy). Thermal behaviour of the microcomposite powder was reported, showing the dehydration and dehydroxylation of the zirconia gel, the crystallization into metastable cubic/tetragonal zirconia at temperatures 400—470°C, and the feasibility of preparing ZT powder materials by progressive reaction of TiO2 and ZrO2 at higher temperatures (1400°C).

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Abstract  

This paper examines binary polyethyleneglycol (molecular weight 6000)-Triamterene (PEG 6000-T) solid dispersions (5–40 w/w% of T) prepared by the fusion carrier method, and physical mixtures (5–90 w/w% of T) are studied using DSC and Hot Stage Microscopy (HSM). The use of these combined techniques allows to explain the thermal behaviour on the basis of dissolution of T in the liquid carrier according to the progressive disappearance of the original crystals over a wide range of temperatures (ca. 100°C). The above fact, and possibly the sublimation of T, also could explain that at low T content (<- 30 w/w%), DSC curves exhibited only a single endothermic peak and/or weak endothermic peaks. On the basis of DSC data, a tentative phase diagram of this system is proposed.

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Abstract  

Thermoanalytical study of the pesticide 3-amino-1,2,4-triazole (ATA) has been carried out, using simultaneous DTA-TG in nitrogen flow, in order to know its thermal behaviour and stability. These techniques have been further complemented using evolved gas analysis and mass spectroscopy (EGA-MS). Two different stages of ATA decomposition were observed: after the first decomposition step, a mixture of compounds is obtained, according to MS data, being the principal component a compound of molecular weight 126. It is formed by a first order reaction mechanism, according to the kinetic study, withE a=124±8 kJ·mol−1. The second decomposition step takes place about 735°C, with evolution of HCN and NH3, being the final weight loss 96%.

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Abstract  

(Zr, Ti)O2 gels as precursors of zirconium titanate (ZT) powders were prepared by the sol-gel method, which involves hydrolysis of ZrClO2+TiCl4 in the presence or absence of hydrogen peroxide, in twopH ranges, 8–9 or 11–12. Thermal evolution of these precursors has been studied by DTA, BET surface area, XRD and SEM. Differences in DTA curves, surface area and morphology were observed. In particular, ZT prepared atpH=8–9 with hydrogen peroxide was purer, more homogeneous and presented a different morphology compared to ZT processed atpH=11–12; hydrated/hydroxylated Zr−Ti species were formed to a greater extent in the latter case. Addition of hydrogen peroxide during chemical processing of these gels plays a key role in controlling the crystallization temperature of ZT.

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Journal of Thermal Analysis and Calorimetry
Authors: P. Sánchez-Soto, M. Villacampa, J. Ginés, A. Ruiz-Conde, M. Avilés, and M. Arias

Abstract  

Several derivatives containing a new organic ring system, the tropane-6-spiro-5′-hydantoin structure (namely 8-alkyl-8-azabicyclo [3.2.1.] octane-6-spiro-5′-imidazoline-2′,4′-diones) have been characterized by thermal (DSC and simultaneous DTA-TG-DTG) and spectroscopic techniques (IR,1 H-NMR,13 C-NMR). X-ray powder diffraction and elemental analysis were applied for structural and molecular characterization. All the compounds melt in the range 160–250°C and undergo decomposition with progressive mass loss after the solid-liquid thermal transition with molecular degradation. It was found that tropane-6-spiro-5′-hydantoin derivatives with the hydantoin ring in β position are thermally less stable than those containing this ring in α position.

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Journal of Thermal Analysis and Calorimetry
Authors: E. Stepkowska, J. Bijen, J. Perez-Rodriguez, A. Justo, P. Sanchez-Soto, and M. Aviles

Abstract  

A simple water sorption/retention (WS/WR) test, followed by stepwise static heating, was applied to the study of cement quality and the reactivity of its grain surface. The physically bound water and hence the specific surface both in the unhydrated and in the hydrated state were estimated as a function of the hydration time. Rehydration after heating at 220°C and contact with air was different inWS from that inWR samples, which indicates a difference in microstructure. XRD proved the formation of portlandite during the sorption test and eventual heating at 200°C, and its transformation into carbonates on contact with air, especially on heating at 400°C. The contents of these compounds were estimated from the mass difference between 400 and 800°C, which was compatible with the mass change between 220 and 400°C and this indicates surface reactivity. The test may serve for the routine study of cement.

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Abstract  

The formation of crystalline inclusion complex of triamterene with β-cyclodextrin (β-CD) was studied, evaluating the thermal behaviour and dispersion state of this drug in different types of binary systems. Spray-drying and co-grinding (oscillating mill) mixtures of triameterene with β-CD were prepared in 1∶1 molar ratio. The changes of crystalline properties of original (untreated) triamterene, β-CD, and composites obtained by co-grinding and spray-drying were investigated in comparison with those produced in simple physical mixtures. The thermal behaviour of the different samples was investigated using DTA. X-ray diffraction was applied as a complementary technique. The results have been explained by formation of amorphous drug particles on spray-drying samples and co-grinding or alternatively by means of a solid dispersion formation or a combination of these two. A contamination effect by grinding media was also observed as increasing grinding time.

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