Phase Change Materials (PCM) microcapsules with different shell compositions: Preparation, characterization and thermal stability

In this study, phase change materials (Rubitherm® RT 27) microcapsules were successfully obtained by two different methods. The main difference between them remains on the shell composition, as they are composed of different coacervates (Sterilized Gelatine/Arabic Gum for the SG/AG method and Agar-Agar/Arabic Gum for the AA/AG method). Microcapsules were thermally characterized by thermo-optical microscopy and differential scanning calorimetry. Using scanning electron microscopy, their spherical morphology (sphericity factor of 0.94-0.95) and their particle size distribution were determined, obtaining an average diameter of 12 μm for the SG/AG method and lower values for the AA/AG method, where nanocapsules were also observed (average diameter of 4.3 μm for the microcapsules and 104 nm for the nanocapsules). The thermal stability determination was carried out by Thermogravimetric analyses (TG) and the results show a high decomposition temperature, although the process takes places in four steps for the two mentioned methods. Moreover, the microcapsules obtained by the AA/AG method decompose in a more gradual way, as in the TG results a double step, instead of one, is appreciable. On the whole, the prepared microencapsulated PCM are totally capable of developing their role in thermal energy storage

The NaNO3–KNO3 phase diagram

Many papers have been published in relation to the NaNO3–KNO3 phase diagram determination in the last 160 years. These papers fall in two categories: (1) the solid–liquid equilibrium is assumed to be of the eutectic type, and (2) the solid–liquid equilibrium is considered as a loop with a minimum. The discordance between the two views is related to the slow transition kinetics that complicate the assessment of thermal ‘fluctuations’, and also to the appearance of a metastable form of potassium nitrate. The main result of this paper is the experimental phase diagram constructed with new experimental data so that we can assure that the second option is correct. This phase diagram is defined by a eutectoid invariant, an asymmetric immiscibility gap and a continuous solid solution with a minimum of melting point. Additionally, the ABθ model simulates correctly the experimental piece of evidence

The NaNO3–KNO3 phase diagram

Many papers have been published in relation to the NaNO3–KNO3 phase diagram determination in the last 160 years. These papers fall in two categories: (1) the solid–liquid equilibrium is assumed to be of the eutectic type, and (2) the solid–liquid equilibrium is considered as a loop with a minimum. The discordance between the two views is related to the slow transition kinetics that complicate the assessment of thermal ‘fluctuations’, and also to the appearance of a metastable form of potassium nitrate. The main result of this paper is the experimental phase diagram constructed with new experimental data so that we can assure that the second option is correct. This phase diagram is defined by a eutectoid invariant, an asymmetric immiscibility gap and a continuous solid solution with a minimum of melting point. Additionally, the ABθ model simulates correctly the experimental piece of evidence

A precise method to measure the specific heat of solar salt-based nanofluids

Publisher Copyright: © 2017, Akadémiai Kiadó, Budapest, Hungary.A novel material has been developed for thermal energy storage at high temperatures (>300 °C) with enhanced thermal transport and storage properties. It is considered more efficient than the current molten salts used in the concentrated solar power plants. It is composed of an inorganic salt doped with a small percentage of nanoparticles (NPs), which are claimed to increase the specific heat compared with that of the raw salt. Thus, a precise determination of this thermal property is essential to perceive this enhancement. The specific heat of solar salt (SS) and a mixture of SS with 1 mass% of alumina NPs have been measured by the differential scanning calorimetry (DSC) technique. An isothermal procedure based on modulated DSC has been established to perform the measurements. The influence of the type of crucible, the amount of sample inside the crucible and the presence of moisture on the scattering of the data has been studied. Reliable results with a low uncertainty (<10%) were achieved by the use of T-zero aluminium hermetic crucibles, the mass increment of analysed sample (30 mg) and the absence of moisture inside the crucibles.The authors would like to thank Izaskun Marañón and Gorka Imbuluzqueta for performing the DSC measurements and Tecnalia Research Corporation, where the experimental work has been carried out. This work was supported by the University of the Basque Country UPV/EHU (Zabalduz 2012 research program, Ph.D. thesis of Belén Muñoz-Sánchez); the Basque Government (Etortek 2014 project on thermal storage) and the MInisterio de Economía y Competitividad, MINECO (ENE2015-71083-R).Peer reviewe

Polyoxometalates (POMs): from electroactive clusters to energy materials

Polyoxometalates (POMs) represent a class of nanomaterials, which hold enormous promise for a range of energy-related applications. Their promise is owing to their "special"structure that gives POMs a truly unique ability to control redox reactions in energy conversion and storage. One such amazing capability is their large number of redox active sites that arises from the complex three-dimensional cluster of metal-oxide ions linked together by oxygen atoms. Here, a critical review on how POMs emerged from being molecular clusters for fundamental studies, to next-generation materials for energy applications is provided. We highlight how exploiting the versatility and activity of these molecules can lead to improved performance in energy devices such as supercapacitors and batteries, and in energy catalyst applications. The potential of POMs across numerous fields is systematically outlined by investigating structure-property-performance relationships and the determinant factors for energy systems. Finally, the challenges and opportunities for this class of materials with respect to addressing our pressing energy-related concerns are identified. This journal is </p

Polyoxometalates (POMs) : from electroactive clusters to energy materials

Altres ajuts: ICN2 is funded by the CERCA programme/Generalitat de Catalunya.Polyoxometalates (POMs) represent a class of nanomaterials, which hold enormous promise for a range of energy-related applications. Their promise is owing to their "special"structure that gives POMs a truly unique ability to control redox reactions in energy conversion and storage. One such amazing capability is their large number of redox active sites that arises from the complex three-dimensional cluster of metal-oxide ions linked together by oxygen atoms. Here, a critical review on how POMs emerged from being molecular clusters for fundamental studies, to next-generation materials for energy applications is provided. We highlight how exploiting the versatility and activity of these molecules can lead to improved performance in energy devices such as supercapacitors and batteries, and in energy catalyst applications. The potential of POMs across numerous fields is systematically outlined by investigating structure-property-performance relationships and the determinant factors for energy systems. Finally, the challenges and opportunities for this class of materials with respect to addressing our pressing energy-related concerns are identified