Authors:A. Justo, J. Pérez-Rodríguez and P. Sánchez-Soto
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.
Authors:J. Ginés, M. Arias, A. Rabasco and P. Sánchez-Soto
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.
Authors:G. Colón, M. Avilés, J. Navío and P. Sánchez-Soto
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).
Authors:P. Sánchez-Soto, E. Morillo, J. Pérez-Rodríguez and C. Real
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, withEa=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%.
Authors:J. Ginés, M. Arias, A. Rabasco and P. Sánchez-Soto
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
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.
Authors:E. Morillo, J. Pérez-Rodríguez, C. Real and P. Sánchez-Soto
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.
Authors:J. Navío, F. Marchena, M. Macías, P. Sánchez-Soto and P. Pichat
(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.
Authors:P. Sánchez-Soto, M. Villacampa, J. Ginés, A. Ruiz-Conde, M. Avilés and M. Arias
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.
Authors:P. Sánchez-Soto, A. Ruiz-Conde, R. Bono, M. Raigón and E. Garzón
The thermal evolution of a slate rock sample (Berja, Almería, Spain) has been studied. The phase minerals identified in this
sample were mica (illite), chlorite (clinochlore) and quartz as major components, with minor microcline, iron oxide and a
mixed-layer or interstratified phase (montmorillonite-chlorite). This slate is highly silico-aluminous (48.33 mass% silica,
22.04 mass% alumina), and ca. 20 mass% of other elements, mainly Fe2O3 (8.35 mass%), alkaline-earths and alkaline oxides.
Two main endothermic DTA effects, centered at 640 and 730°C, were observed. The more important contribution of total mass
loss (7.15 mass%) was found between 500–900°C, with two DTG peaks detected at 630 and 725°C. All these effects were associated
to the dehydroxylation of structural OH groups of 2:1 layered silicates mixed in the slate. The dehydroxylation of the layered
silicates evidenced by dilatometry, produced a rapid increase of expansion between 600–800°C. The thermal evolution of the
slate upper 800°C indicated the first sintering effects associated to shrinkage, which is also favoured by its low particle
size (average 23 μm) and the presence of a liquid or vitreous phase as increasing the heating temperature. The application
of thermal diffractometry to the slate sample allowed to study the formation of dehydroxylated crystalline phases from the
layered silicates after heating. At 1000°C, β-quartz, dehydroxylated illite, iron oxide, relicts of microcline and the vitreous
phase were present in the sample. All these results are interesting to know the thermal behaviour of a complex mineral mixture
as identified in the slate.
Authors:M. Avilés, J. Ginés, J. del Rio, J. Pascual, J. Pérez-Rodríguez and P. Sánchez-Soto
This paper examines the polymerization of acrylonitrile to poly(acrylonitrile)(PAN), and its cyclization, in bulk form and using N,N-dimethylformamide (DMF) as solvent in which both monomer and polymer are soluble. Thermal analysis of the resultant products after polymerization has been performed by DSC and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Scanning electron microscopy has been used to study the morphology of the resultant products and after thermal treatments. The DSC thermal curve of PAN-DMF sample is quite different from the PAN bulk sample, showing a single sharp exothermic peak associated with nitrile group polymerization (cyclization) of PAN at lower temperature (240°C) than that of bulk PAN sample (314°C). Cyclization of PAN was confirmed by IR spectroscopy. It was found that the amide molecules are difficult to eliminate completely in the product obtained after the polymerization reaction, even after prolonged heating at 110°C, and remain occluded. The formation of a complex by dipolar bonding is also possible and it is discussed. It is concluded that the amount of heat evolved as well as the temperature interval over which it is released are influenced by the chemical processing of PAN when using DMF as solvent of both monomer and polymer. Pyrolysis of these PAN samples revealed the release of occluded molecules of DMF, and several compounds containing nitrogen produced from the thermal degradation processes. All these results are interesting to know the chemical processing of carbon fibres and activated carbon fibres from PAN modified precursors.