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Abstract  

The aim of this paper is to evaluate and explain the fitting of dynamic TG curves by a mixture of logistic functions. This model assumes that more than one physical process may be involved in each mass loss step and that each physical process may extend along all the experiment. One of the main sources of difficulties in TG is that, very often, different stages of decomposition substantially overlap each other. Several real and simulated TG curves were analysed in this paper. An optimal fitting of the TG curves was obtained by a mixture of logistics. In many cases the optimal fitting reproduces accurately the TG curve. Accordingly, the TG curve can be understood as a sum of parallel reactions, where each single reaction is represented by one or a small number of logistic components. Additionally, making use of the analytical derivative of the fitting, a mixture of Arrhenius reaction order equations was applied to the same curves. In all the cases, the fitting obtained with the mixture of Arrhenius was worse than the obtained with the mixture of logistics. A software was developed to automatically perform these tasks. The physical meaning of the fitting was explained.

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Journal of Thermal Analysis and Calorimetry
Authors:
J. Pascual
,
F. Corpas
,
J. López-Beceiro
,
M. Benítez-Guerrero
, and
R. Artiaga

Abstract  

A Spanish red mud was thermally characterized. Chemical and mineralogical composition were determined by XRF and XRD.The thermal events observed in the range from room temperature to 1300°C were related to the sample composition. The first mass loss step was related to free water content, while many of the other processes were related to dehydration processes. It was found that most of the decomposition reactions of hydrohematite, ferrihydrite, aluminogoethite, boehmite, silicates and carbonates were strongly overlapping. It was also explained the formation of silicates and calcium titanate, which presence was confirmed at 1000°C by XRD.

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Journal of Thermal Analysis and Calorimetry
Authors:
L. Núñez-Regueira
,
J. A. Rodríguez-Añón
,
J. Proupín
,
B. Mouriño
, and
R. Artiaga-Diaz

Summary The European policy on energy focus on the search for alternative and renewable sources of energy where forest biomass plays a significant role. In this article, calorific values of different kinds of forest residues (leaves, thin branches, barks, etc.) are reported. These values were measured by combustion bomb calorimetry with the objective of understanding, through different risk indices, the behaviour of forest waste in the case of wildfires, and also to study the use of forest residues as raw materials to be used as energy sources. The study was complemented with determination of elemental analysis, flammability using a standard epiradiator, thermodegradation analysis, and different mechanical tests trying to get relationships between thermal behaviour and some physical properties. The study was carried out on Eucalyptus globulus Labill and Pinus pinaster Aiton, because these forest formations have both high economical and ecological interest in Galicia (NW Spain).

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Journal of Thermal Analysis and Calorimetry
Authors:
R. Artiaga
,
A. Garcia
,
L. Garcia
,
A. Varela
,
J. Mier
,
S. Naya
, and
M. Grana

Abstract  

The nickel-titanium alloys are usually known as Shape Memory alloys because of their ability to return to some previously defined shape or size when subjected to the appropriate thermal procedure. Mechanical properties of a nickel titanium wire were investigated by DMTA using cylindrical tension mode. The Young"s modulus, the maximum strain and residual deformation have been calculated. Recovery of previously deformed samples was observed in constant stress temperature ramp tests. Relaxation stress behaviour at temperatures above the austenitic transformation has been studied. The strain and frequency ranges of linear response have been determined by dynamic experiments. Strain amplitude of 0.1% and frequency of 1 Hz have been chosen for the temperature ramp dynamic experiments. A big change between 65 and 95C is observed in the storage modulus. The values of E' at temperatures below and above the transition are essentially constant. Finally, the effects of the frequency at different temperatures have been examined.

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Journal of Thermal Analysis and Calorimetry
Authors:
C. Gracia-Fernández
,
J. Tarrío-Saavedra
,
J. López-Beceiro
,
S. Gómez-Barreiro
,
S. Naya
, and
R. Artiaga

Abstract

The use of pressure cell attached to a temperature modulated differential scanning calorimeter (TMDSC) is investigated to perform modulated DSC experiments at high pressures (TMPDSC). No previous reports were found on the use of TMPDSC. In this study, the proposed method is applied to the study of the pressure effect on the curing reaction of an epoxy system. Curing quasi-isothermal modulated experiments were performed at different pressures to evaluate the vitrification time. Linear heating modulated tests were also successfully performed at different pressures to separate the reversing glass transition effect from the residual exothermic cure reaction. The curing enthalpy, conversion versus temperature, and glass transition of the fully cured thermoset were also evaluated. All the studied parameters resulted to be affected by the pressure in the range from atmospheric pressure to 35 bar. It was observed that the curing enthalpy, the reaction rate and the conversion at any given time increase with any pressure increment. The usefulness of TMDSC to characterize the curing of thermosets is extended by PTMDSC to situations, i.e., aeronautics industry, where pressure curing is needed.

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Journal of Thermal Analysis and Calorimetry
Authors:
J. González-Irún Rodríguez
,
P. Carreira
,
A. García-Diez
,
D. Hui
,
R. Artiaga
, and
L. Liz-Marzán

Abstract  

The effect of silica nanofiller on the glass transition of a polyurethane was studied by DSC. The pristine polymer exhibits a single glass transition at about –10C. Uniform SiO2 spheres with different average sizes and narrow size distributions were synthesized in solution by the Stber method [1]. Both the effects of silica content within the polymer and particle size were investigated, as well as two different surface treatments. Scanning electron microscopy (SEM) clearly confirms the presence of the particles within the polymer matrix, showing uniform distribution and no agglomeration. While shifting of the glass transition has been reported by many authors, we have not seen any noticeable shift in this polymer. Surprisingly, we found no relevant effects when either increasing the filler content or changing the particle size. Different amounts of particles with average diameters of 175, 395 and 730 nm did not affect the glass transition temperature of the pristine polymer.

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Journal of Thermal Analysis and Calorimetry
Authors:
C. A. Gracia-Fernández
,
P. Davies
,
S. Gómez-Barreiro
,
Beceiro J. López
,
J. Tarrío-Saavedra
, and
R. Artiaga

Abstract

The development of photopolymers was helped by the development of photocalorimetry, which is now a basic technique for the study of these materials. This work shows how to obtain vitrification times in single isothermal curing experiments by monitoring the reversing heat capacity along time in modulated temperature DSC–photocuring systems, overcoming the time-consuming problem of standard DSC. The effects of the light intensity and the isothermal curing temperature on the vitrification time of a photocurable system were evaluated. The results obtained at a given curing temperature with different light intensities indicate that the UV-light affects the molecular mobility hindering the vitrification process. The effects of the curing temperature on the vitrification time, the conversion at the vitrification time and the maximum conversion were also evaluated.

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