Les interactions organo-minérales contrôlent la stabilisation de la matière organique du sol. Les nanominéraux, résultant de l'altération continue des minéraux, précipitent à partir d'espèces ioniques à leur surface. Les derniers travaux de simulation en laboratoire se sont focalisés sur les nanophases de Fe et Al. Dans ce travail, des simulations en laboratoire ont été réalisées sur les processus d'altération de la biotite et les néoformations résultantes, après hydrolyse d’espèces dissoutes d'un système Si Fe Al Mg et K, en présence et en absence de C. La structure des phases a été caractérisée par TEM- EDX et Fe-EXAFS.En l'absence de C, des nanominéraux amorphes de 10-60nm sont formés, la composition étant contrôlée par le pH en fin d'hydrolyse. A pH4.2 et 7, leur composition est dominée par Fe, dont la polymérisation est perturbée par Al Si Mg et K. Inversement, à pH5, la polymérisation du Fe est limitée par la précipitation de grandes quantités de Si. En présence de C, les complexes organo-minéraux synthétisés sont des particules amorphes de 2-200nm. Leur taille augmente avec la teneur croissante en C jusqu'à un ratio métal/C de 1. La précipitation engendre 2 familles: (1) les petites particules chimiquement similaires à la solution de lixiviat; (2) les plus grosses fortement contrôlées par la teneur de C. La composition de ces dernières est dominée par Si lorsque C est faible, et par Fe lorsque C est élevé. Le changement de chimie entre les particules plus petites et plus grandes ainsi que le rôle de Si sont importants mais souvent négligés. Ainsi, ces résultats éclairent l'effet des variations de C sur l'affinité des espèces inorganiques dans les systèmes naturels / Organo-mineral interactions, due to the high reactivity of nanominerals, play a major role in soil organic matter stabilization. Nanominerals, which are the result of the continuous alteration of minerals, precipitate from ionic species at the mineral solution interface. In literature, only Fe and Al get emphasis with regard to batch-synthesized nanomineral studies. In this work, laboratory simulations were carried out on the post biotite alteration processes and the resulting neoformations after hydrolysis of the dissolved species from a Si Fe Al Mg and K system, in the presence and absence of C. New phases were characterized by TEM-EDX and EXAFS at the Fe K-edge.In C absence, 10-60nm sized amorphous nanominerals are formed whose composition is controlled by pH at the end of the hydrolysis. For pH4.2 and 7 phases, composition is dominated by Fe, whose polymerization is hindered by Al, Si, Mg and K. Conversely, at pH5, the overall presence of Fe is counteracted by precipitation of high amounts of Si. In C presence, precipitates are amorphous 2-200nm sized particles. This size increases with increasing C presence until a molar Metal:C=1. Precipitation resulted into two distinct size ranges. Smaller particles chemically resemble the leachate solution, while for larger particles it is influenced by C concentration. Composition of larger particles is dominated by Si at low C compositions while by Fe at higher ones. Interesting is the change in chemistry between smaller and larger particles as well as the role of Si often overlooked in other studies. Therefore, these results emphasize on effect of C variations on affinity of inorganic species in natural systems.

Submitted by Daniele Amaral (daniee_ni@hotmail.com) on 2016-10-18T18:18:09Z No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-21T14:03:42Z (GMT) No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-21T14:03:48Z (GMT) No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) / Made available in DSpace on 2016-10-21T14:03:54Z (GMT). No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) Previous issue date: 2016-08-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Magnesium hydride is a promisor candidate for H2 storage, manly due its high hydrogen gravimetric capacity (7.6% wt), low density, abundance and low cost. However, its H-absorption/desorption occurs only at temperatures around 673 K with slow kinetics. Moreover, Mg and MgH2 surfaces are highly reactive, easily forming MgO and/or Mg(OH)2 layers that lower the level the hydrogen storage properties. It described in the literature that the use the severe plastic deformation technique or the incorporation of additives such as LaNi5 improve the hydriding/dehydriding kinetics and lower the dehydrogenation temperature of Mg-based composites. In the present study, Mg-based hydrogen storage alloys has been developed in the following systems: MgH2 and MgH2 + LaNi5 using the cold rolling (CR) under inert atmosphere. The aspect analyzed in this study were the processing parameters (number of passes and roll rotation frequency) and the additive incorporation (LaNi5) during the processing and Habs / des behavior. The micro and nanoestrutural characterization for the obtained materials were made by means of X-ray diffraction (XRD), scanning a transmission electron microscopy (SEM and TEM), and the correlation of results obtained with the process route, showed that larger number of rolling passes and high frequency produces nanocomposites with great improvements in the hydrogen storage properties. Furthermore, was observed a catalytic effect with the addition of LaNi5 to MgH2, due the formation of new phases in hydriding/dehydriding process. The best result for hydrogen storage were obtained for the system MgH2+1,50 mol.% LaNi5 with low Habsorption / desorption temperatures, aspect interesting for MgH2. / O Mg é um material promissor para a armazenagem de hidrogênio, pela sua baixa densidade, abundância, custo relativamente baixo e capacidade de armazenagem de até 7,6 % p. No entanto, sua cinética de absorção/dessorção de H2 é lenta, e ocorre em temperaturas superiores a 300°C. Além disso, as superfícies do Mg e do MgH2 são susceptíveis à oxidação, gerando assim camadas de MgO ou ainda Mg(OH)2 que atuam como barreiras nos processos de absorção/dessorção do hidrogênio. É descrito na literatura que a rota de processamento utilizando a deformação plástica severa, assim como a incorporação de aditivos como o LaNi5 melhoram o desempenho dos nanocompósitos à base de Mg. Neste trabalho MgH2 e MgH2 + LaNi5 foram preparados utilizando a laminação a frio (CR, do inglês Cold Roll) em atmosfera controlada. Os aspectos analisados foram os parâmetros do processo de CR (número de passes e frequência dos cilindros). Os efeitos da adição do LaNi5 durante o processamento e no comportamento de absorção/dessorção de H2. A caracterização micro e nanoestrutural dos nanocompósitos obtidos, através da difração de raios-X, microscopia eletrônica de varredura e transmissão, e sua correlação com a rota de processamento; demonstrou que um elevado número de passes de CR a elevadas frequências produz nanocompósitos com propriedades atrativas para armazenagem de hidrogênio. Além disso, observou-se um efeito catalítico com a adição do LaNi5 ao MgH2, devido a formação de novas fases durante as etapas de absorção e dessorção de H2. As melhores características de armazenagem de hidrogênio foram obtidas para a mistura MgH2+1,50 mol.% LaNi5 na qual as medidas foram realizadas a baixas temperaturas, fato importante para o MgH2.