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On the thermal decomposition mechanism for dehydroxylation of alkaline-earth hydroxides (1976)

Criado, J. M. ; Morales, J.

Springer

Journal of thermal analysis and calorimetry 10 (1976), S. 103-110

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ISSN: 1572-8943

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Description / Table of Contents: Résumé L'énergie d'activation de la déshydroxylation sous vide des hydroxydes des métaux alcalins est calculée à partir des données thermogravimétriques. Les résultats expérimentaux obtenus avec Mg(OH)2, Ca(OH)2 et Sr(OH)2 sont en accord avec une loi de décomposition unimoléculaire et les énergies d'activation correspondantes sont du même ordre de grandeur que les enthalpies de décomposition. Par contre, du fait que la déshydroxylation de Ba(OH)2 a lieu en phase liquide et que BaO ne se dissout pas dans Ba(OH)2 fondu, la vitesse de la réaction est décrite par une cinétique d'ordre zéro et l'énergie d'activation est plus faible que l'enthalpie de décomposition.

Abstract: Zusammenfassung Die Aktivierungsenergie zur thermischen Dehydroxilierung von Erdalkali-Hydroxiden im Vakuum wurde aus thermogravimetrischen Daten errechnet. Die Versuchsergebnisse bezüglich Mg(OH)2, Ca(OH)2 und Sr(OH)2 sind mit einem unimolekularen Zersetzungsgesetz in Übereinstimmung und die entsprechenden Aktivierungsenergien sind den Werten der Zersetzungsenthalpien ähnlich. Im Gegensatz hierzu wird im Falle von Ba(OH)2, da der Dehydroxylierungsvorgang in der flüssigen Phase stattfindet und das BaO sich nicht im geschmolzenen Ba(OH)2 löst, die Reaktionsgeschwindigkeit durch eine Kinetik nullter Ordnung beschrieben und die Aktivierungsenergie liegt hierbei niedriger als die Zersetzungsenthalpie.

Notes: Abstract The activation energy for thermal dehydroxylation in vacuum of alkaline-earth hydroxides has been calculated from thermogravimetric data. The experimental results of Mg(OH)2 Ca(OH)2 and Sr(OH)2 are in agreement with an unimolecular decay law and their activation energies are similar to the values of enthalpies of decomposition. In contrast, as the dehydroxylation process of Ba(OH)2 takes place in liquid phase and the BaO does not dissolve into the molten Ba(OH)2, a kinetic of zero order describes the reaction rate and the activation energy is lower than the enthalpy of decomposition.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02179196

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Electronic Resource

Computer kinetic analysis of simultaneously obtained TG and DTG curves (1978)

Criado, J. M. ; Morales, J. ; Rives, V.

Springer

Journal of thermal analysis and calorimetry 14 (1978), S. 221-228

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ISSN: 1572-8943

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Description / Table of Contents: Résumé L'analyse cinétique des courbes TG et TGD obtenues simultanément lors de la décomposition de CaCO3 a été effectuée à l'aide d'un ordinateur. Dix équations cinétiques différentes ont été examinées pour établir le mécanisme moteur de la réaction. L'équation cinétique de type 2/3 (processus d'interface) ou l'équation de Jander (processus de diffusion) décrivent toutes deux de maniÊre satisfaisante les données cinétiques déduites des courbes TG et TGD. De ces résultats on conclut qu'il n'est pas possible de distinguer ces deux mécanismes en s'appuyant exclusivement sur l'analyse cinétique des courbes TG et TGD. Une meilleure approche du problÊme est possible si l'on effectue l'analyse cinétique des courbes TG et TGD simultanées en mÊme temps que celle d'une courbe isotherme. Ce procédé peut Être un bon moyen pour élucider le mécanisme des réactions de décomposition thermique à l'aide de méthodes cinétiques, sans informations supplémentaires.

Abstract: Zusammenfassung Es wurde die kinetische Analyse simultan erhaltener TG- und DTG-Kurven der Zersetzung von CaCO3 mittels Computer durchgeführt. Zehn verschiedene kinetische Gleichungen wurden zur Ermittlung des reaktionssteuernden Mechanismus erprobt. Die kinetischen Daten beider Zersetzungskurven können entweder durch eine “Zwei-Drittel“ kinetische Gleichung (Phasen-Grenzflächenprozess) oder eine Jander-Gleichung (Diffusionsprozess) befriedigend beschrieben werden. Aus diesen Ergebnissen wird gefolgert, dass keine Möglichkeit besteht diese beiden Mechanismen ausschliesslich durch die kinetische Analyse der TG- und DTG-Kurven von einander zu unterscheiden. Eine bessere Annäherung an das Problem ist durch die kinetische Analyse simultaner TG- und DTG-Kurven gemeinsam mit einer isothermen Kurve möglich. Dieser Vorgang erscheint als ein möglicher Weg zur Unterscheidung der Mechanismen thermischer Zetsetzungsreaktionen an Hand kinetischer Methoden ohne Zusatzliche Information.

Notes: Abstract The computer kinetic analysis of simultaneously obtained TG and DTG curves of CaCO3 decomposition has been carried out. Ten different kinetic equations have been tested to decide the mechanism which drives the reaction. Either a two-thirds kinetic equation (phase boundary process) or a Jander equation (diffusion process) satisfactorily describe the kinetic data of both decomposition curves. From these results we conclude there is no chance of differentiating between these two mechanisms by only the kinetic analysis of TG and DTG curves separately. A better approach to the problem is possible if the kinetic analysis is performed on simultaneous TG and DTG curves, together with an isothermal one. This procedure might be a valid way to establish the mechanisms of thermal decomposition reactions by means of kinetic methods without additional information.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01915159

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Observations of volcanic earthquakes and tremor at Deception Island - Antarctica (2006)

Alguacil, G. ; Almendros, J. C. ; Del Pezzo, E. ; [et al.]

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Publication Date: 2019-11-04

Description: Deception Island - South Shetlands, Antarctica is site of active volcanism. Since 1988 field surveys have been carried out with the aim of seismic monitoring, and in 1994 a seismic array was set up near the site of the Spanish summer base in order to better constrain the source location and spectral properties of the seismic events related to the volcanic activity. The array was maintained during the Antarctic summer of 1995 and the last field survey was carried out in 1996. Data show the existence of three different groups (or families) of seismic events: 1) long period events, with a quasi-monochromatic spectral content (1-3 Hz peak frequency) and a duration of more than 50 s, often occurring in small swarms lasting from several minutes to some day; 2) volcanic tremor, with a spectral shape similar to the long period events but with a duration of several minutes (2-10); 3) hybrid events, with a waveform characterised by the presence of a high frequency initial phase, followed by a low frequency phase with characteristics similar to those of the long period events. The high frequency phase of the hybrid events was analysed using polarisation techniques, showing the presence of P waves. This phase is presumably located at short epicentral distances and shallow source depth. All the analysed seismic events show back-azimuths between 120 and 330 degrees from north (corresponding to zones of volcanic activity) showing no seismic activity in the middle of the caldera. Particle motion, Fourier spectral and spectrogram analysis show that the low frequency part of the three groups of the seismic signals have similar patterns. Moreover careful observations show that the high frequency phase which characterises the hybrid events is present in the long period and in the tremor events, even with lower signal to noise ratios. This evidence suggests that long period events are events in which the high frequency part is simply difficult to observe, due to a very shallow source and/or hypocentral distance higher than that of hybrids, while the tremor is composed of rapidly occurring hybrid events. We propose a possible interpretation for the three groups of seismic events. These may be generated by multiple pressure-steps due to the rapid phase change from liquid to vapour in a shallow aquifer which comes in contact with hot materials. The pressure change can put a crack in resonance or excite the generation of multiple surface waves modes in the shallow layered structure.

Description: JCR Journal

Description: open

Keywords: volcanic earthquakes ; tremor ; antartica ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology

Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Type: article

Format: 5660911 bytes

Format: application/pdf

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Kinematics of the Iberia-Maghreb plate contact from seismic moment tensors and GPS (2007)

Stich, D. ; Serpelloni, E. ; Mancilla, F. ; [et al.]

Elsevier

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Publication Date: 2021-09-03

Description: The Iberian Peninsula and the Maghreb experience moderate earthquake activity and oblique, ∼ NW–SE convergence between Africa and Eurasia at a rate of ∼ 5 mm/yr. Coeval extension in the Alboran Basin and a N35°E trending band of active, left-lateral shear deformation in the Alboran–Betic region are not straightforward to understand in the context of regional shortening, and evidence complexity of deformation at the plate contact. We estimate 86 seismic moment tensors (MW 3.3 to 6.9) from time domain inversion of near-regional waveforms in an intermediate period band. Those and previous moment tensors are used to describe regional faulting style and calculate average stress tensors. The solutions associated to the Trans-Alboran shear zone show predominantly strike-slip faulting, and indicate a clockwise rotation of the largest principal stress orientation compared to the regional convergence direction (σ1 at N350°E). At the N-Algerian and SW-Iberian margins, reverse faulting solutions dominate, corresponding to N350°E and N310°E compression, respectively. Over most of the Betic range and intraplate Iberia, we observe predominately normal faulting, and WSW–ENE extension (σ3 at N240°E). From GPS observations we estimate that more than 3 mm/yr of African (Nubian)–Eurasian plate convergence are currently accommodated at the N-Algerian margin, ∼ 2 mm/yr in the Moroccan Atlas, and ∼ 2 mm/yr at the SW-Iberian margin. 2 mm/yr is a reasonable estimate for convergence within the Alboran region, while Alboran extension can be quantified as ∼ 2.5 mm/yr along the stretching direction (N240°E). Superposition of both motions explains the observed left-lateral transtensional regime in the Trans-Alboran shear zone. Two potential driving mechanisms of differential motion of the Alboran–Betic–Gibraltar domain may coexist in the region: a secondary stress source other than plate convergence, related to regional-scale dynamic processes in the upper mantle of the Alboran region, as well as drag from the continental-scale motion of the Nubian plate along the southern limit of the region. In the Atlantic Ocean, the ∼ 3.5 mm/ yr, westward motion of the Gibraltar Arc relative to intraplate Iberia can be accommodated at the transpressive SW-Iberian margin, while available GPS observations do not support an active subduction process in this area.

Description: Published

Description: 295-317

Description: JCR Journal

Description: reserved

Keywords: GPS ; Kinematics ; 04. Solid Earth::04.02. Exploration geophysics::04.02.06. Seismic methods

Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Type: article

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El sistema de yacimientos de mam\xc3\xadferos miocenos del Cerro de los Batallones, Cuenca de Madrid: estado actual y perspectivas (2008)

Morales, J. ; Pozo, M. ; Silva, P.G. ; [et al.]

Universidad de Zaragoza, Zaragoza

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Publication Date: 2024-01-12

Description: The Cerro de los Batallones (Los Batallones Butte) is located in the central-northern area of the Madrid Basin, central Spain. Nine vertebrates localities containing a large variety of mammals of Upper Vallesian Age (Late Miocene) have been found associated with the sediments forming the butte. From bottom to top, these sediments consist of magnesian lutite beds (Unit I), paleosols formed of sepiolite and opal (Unit II), and siliclastic, marlstone and carbonate beds (Unit III). The set of ERT profiles developed in Los Batallones Butte have demonstrate that electrical imaging techniques are an estimable tool for the characterization and prospecting of fossil sites developed in fine-grained siliciclastic sequences. These localities contain an exceptionally rich, varied and well-preserved vertebrate fauna together with invertebrate and plant fossils. Carnivore species are strikingly well represented at Batallones 1 and 3, and large herbivore species, such as mastodons, rhinoceros and giraffes, at Batallones 2, 4, 5 and 10. The taphonomical studies, together with the morphological features shown by the sedimentary fills of the mammal localities, permit an overall interpretation of these deposits as vertebrate traps. The study of these localities should offer a significant contribution to our understanding of the formation pattern of trap-like paleontological sites - which so far have been typically reported in karstic-type systems -, as well as an important source of paleobiological information about numerous vertebrate groups.

Keywords: Mammalia ; miocene ; Cerro de los Batallones

Repository Name: National Museum of Natural History, Netherlands

Type: info:eu-repo/semantics/bookPart

Format: application/pdf

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