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Resumen del trabajo presentado a la 1 & 2DM Conference and Exhibition, celebrada en Tokyo (Japón) del 28 al 29 de enero de 2020.

Trabajo presentado a la 1st International Conference on Nanofluids (ICNf) y 2nd European Symposium on Nanofluids (ESNf), celebrados en Castellón (España) del 26 al 28 de Junio de 2019., Recent work on graphene nanofluids in organic solvents and reduced graphene oxide in aqueous electrolytes are described. In addition to a thorough study of thermal properties of the former, the potential of RGO nanofluids for electrochemical energy storage (i.e. in novel flow cells) was studied.

Predicting the growth morphology of crystals, from the knowledge of their structure, can be done by applying: a) the Bravais-Friedel-Donnay-Harker (BFDH) rule stating that higher the spacing dhkl, higher the morphological importance (MI) of the {hkl} form b) the Hartman and Perdok (HP) rule grounded on the idea that higher the attachment energy value, higher the corresponding growth rate (Rhkl ) and, consequently, lower the morphological importance of the {hkl} form. According to the BFDH rule both ‘positive’ and ‘negative’ calcite forms must have the same morphological importance i. e. they appearance probability may be the same. However, their occurrence is very different and only the ’positive’ forms are commonly found both in nature laboratory. A PBC analysis is being performed in order to find the F-faces of the ‘negative’ forms and then its surface energy is calculate

This PhD thesis is focused in structural aspects of alkali nitrates. In the first chapter, we recollected the most important advancement in this field in alkali nitrates compounds published since 1970. Along this lines, crystal structure, polymorphism and phase transition is discussed first; second, crystal growth, and third, the morphology. And, finally a section concerning solid state miscibility and binary phase diagrams between these compounds is presented. The following chapters present a deeper study of growth morphology and how the impurities affect to the morphology and growth rate. These two topics are closely related because the growth morphology is a consequence of the growth rate ratio of different faces. Evidently, we chose only one compound of all the alkali nitrate family. It turned to be sodium nitrate, nitratine or NaNO3. First, in chapter 2, we calculate the morphology of nitratine by applying the two most common approaches to determine the theoretic morphology of crystals: the Bravais-Friedel-Donnay-Harker (BFDH) methodology and the periodic bond chains (PBCs) procedure proposed by Hartman and Perdok (HP). Then we compare the obtained morphology with the experimental growth shape. This compound is interesting from the morphological and structural point of view because it is isostructural with calcite, a calcium carbonate (CaCO3) polymorph. This fact will permit us to discuss how the charges affect the final crystal morphology; an introduction to this question is in chapter 2. In chapter 3 we sought to determination of the normal growth rates (R104) of {104} faces of sodium nitrate single crystals under isothermal conditions in the temperature interval 288 K  297.5 K and hence find the most probable growth mechanisms. Chapter 4 is devoted to the morphology change in NaNO3 crystals by the effect of impurities. It is followed by an atomic force microscopy (AFM) investigation of heterogeneous nucleation of nitratine on calcite in chapter 5. Finally, the NaNO3 – KNO3 phase diagram has been studied from both experimental and theoretical aspects in chapter 6.

In this paper, we focus on the measurement of the normal growth rates (R104) of {10.4} faces of nitratine (NaNO3) single crystals under isothermal conditions in the temperature interval 288-297.5 K in order to unravel the rate determining steps during crystal growth, depending on the hydrodynamic conditions. Owing to the elevated solubility of nitratine in water, the supersaturated system is very sensitive to temperature variation. In this sense, we have constructed a device to control the temperature (its accuracy is below 0.1 K) and the concentration throughout the experiments. We managed to measure the crystal growth of three symmetry equivalent {10.4} faces of NaNO3 under different hydrodynamic conditions. We found that growth of these faces depends on different rate determining steps (being either surface or volume diffusion limited) according to their position with respect to the solution flow. Finally, some thermodynamic crystallization parameters have been calculated to assess the rate determining steps.

L'aliatge Inconel® 600 esta dissenyada específicament per resistir ambients corrosius a altes temperatures. El sulfat de sodi fos es un possible candidat per actuat com a material per l’emmagatzemament d'energia per calor sensible i latent. Una possible aplicació d'aquest sistema consistiria en l'estalvi energètic per la producció d'electricitat a les central termosolars i fer-la independentment de la radiació solar. En aquest treball es pretén estudiar si l'Inconel® 600 es un metall adient per contenir el sulfat de sodi fos. La tècnica emprada en aquest estudi es el contacte per immersió a la sal fosa (sulfat de sodi) a 899ºC i a diferents temps d'exposició. S'estudiaran els productes de corrosió mitjançant diverses tècniques: difracció de raigs-X, fluorescència de raigs-X, microscòpia òptica i electrònica de escombrat i anàlisis elemental. Per saber si hi existeix una variació en la morfologia també s’exposa a la temperatura d’estudi una proveta d'Inconel® 600 un temps determinat, així es té una referència per poder comparar. Es discutiran les diferents morfologies trobades en funció de si l’aliatge està en contacte directe amb la sal fosa o amb els seus vapors, també es troba que la zona de separació presenta una morfologia diferent. Per últim es fan dos experiments variant altres factors: un amb la proveta polida per saber si l´acabat de la superfície té algun efecte; i l’altre per esbrinar si el tipus de contacte es decisiu en la velocitat de corrosió, en aquest cas es posa tota la proveta en contacte amb el sulfat de sodi fos.