Orientador: Jose de Alencar Simoni / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-09T10:02:14Z (GMT). No. of bitstreams: 1 OliveiraJunior_NiltonGeraldode_M.pdf: 625277 bytes, checksum: e5c790f33e89db6dc410ed2f7eeef0d2 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho apresentam-se os aspectos do desenvolvimento de um sistema para dosagem de gás especialmente projetado para a investigação calorimétrica da adsorção de gases em sólidos. Descrevem-se a concepção e a adequação do sistema de dosagem de gás assim como a metodologia experimental adequada à utilização do referido sistema e os resultados que permitem avaliar seu desempenho. O sistema de dosagem construído consiste em uma linha de vácuo acoplada a um sensor de pressão e uma cela de adsorção dimensionada para ser inserida no calorímetro Thermométric modelo 2277. A adsorção do vapor de etanol em sílica-gel foi escolhida como "processo piloto" para os testes do desempenho do dispositivo devido à facilidade de preparação e condicionamento das substâncias e também ao grande número de dados disponíveis na literatura recente, referente às propriedades físico-químicas desse sistema. Os resultados das isotermas calorimétricas diferenciais, assim como a sistemática de condução dos experimentos nesse trabalho, é devidamente discutida comparativamente aos resultados recentes da literatura. Os resultados apontam para o fato de que o dispositivo funciona bem, dentro das expectativas químicas para o sistema piloto de adsorção utilizado / Abstract: This work presents the development aspects of a gas dosage system specially projected for calorimetric investigation of the gases adsorption onto solids. They describe it conception and the adequacy of the system of dosage of gas as well as the experimental methodology adjusted to the use of the related system and the results that allow to evaluate its performance. The constructed dosage system consists of a line of vacuum connected to a pressure sensor and a dimensioned adsorption cell to be inserted in the Thermométric calorimeter model 2277. The adsorption of the ethanol vapor on silica-gel was chosen as "pilot process" for the tests of the device performance due to easiness of preparation and conditioning of substances and also to great number of available data in recente literature, referring to physical-chemistry properties of this system. The differential calorimetric isothems results as well as the systematics of conduction of the experiments in this work, are duly argued comparativily to the recent results of literature. The results show that the device functions well in respect of the chemical expectations for the adsorption pilot process used / Mestrado / Físico-Química / Mestre em Química

Les processus élémentaires hétérogènes à l’interface gaz-solide présentent un intérêt fondamental dans de nombreux domaines tels que la catalyse hétérogène, la chimie atmosphérique et des milieux interstellaires, la rentrée atmosphérique de véhicules spatiaux ou encore la description des interactions plama-paroi. Cette thèse a pour objet l’étude de la dynamique des processus de collision non réactive de l’azote N2 sur une surface de tungstène W(100) et des processus de recombinaison moléculaire de l’hydrogène H2 sur des surfaces de tungstène W(100) et W(110). Leur dynamique quasi classique est simulée au moyen de surfaces d’énergie potentielle préalablement construites à partir de calculs de théorie de la fonctionnelle de la densité. Un potentiel multi-adsorbats est notamment développé pour tenir compte du taux de couverture de surface afin d’étudier la compétition entre la recombinaison directe, de type Eley-Rideal et la recombinaison par « atomes chauds » après diffusion hyperthermique d’un atome sur la surface. / Heterogeneous elementary processes at the gas-solid interface are ofgreat interest in many domains such as heterogeneous catalysis, atmospheric and interstellar media chemistry, spacecraft atmospheric re-entry and plasma-wall interactions description. This thesis focus on the dynamics of nitrogen, N2, non reactive scattering on a tungsten W(100) surface and hydrogen, H2, recombination processes on tungsten surfaces W(100) and W(110). The quasiclassical dynamics of these processes is simulated using potential energy surfaces based on density functional theory calculations. In particular, a multi-adsorbate potential is developed to include surface coverage in the dynamics simulation in order to scrutinize the interplay between both direct abstraction, the so-called Eley-Rideal recombination,and the Hot-Atom recombination process after hyperthermal diffusion on the surface

La rationalisation des processus chimiques élémentaires aux surfacesest d'intérêt primordial pour de nombreux phénomènes naturels ou d'intérêttechnologique. D'un point de vue fondamental, la façon dont l'énergie, concomitanteà toute réaction chimique, est distribuée parmi les degrés de liberté des moléculesformées et/ou transférée à la surface est loin d'être systématisée. Dans ce travail,des simulations, reposant sur la méthode des trajectoires quasi-classiques (QCT),sont réalisées pour examiner cette problématique lors de recombinaisons demolécules d'hydrogène (H2) et d'azote (N2) résultant de l'abstraction d'atomesadsorbés via collision par un atome provenant de la phase gazeuse sur des surfacesde Tungstène - W(100) et W(110) - à taux de couverture non nul. Ces processussont ici étudiés pour leur intérêt en physique des interactions plasma-paroi. Dessurfaces d'énergie potentielle, construites à partir de calculs de structure électroniquebasés sur la théorie de la fonctionnelle densité (DFT), sont utilisées pour simuler,dans le cadre de la mécanique classique - incluant les corrections semi-classiquespertinentes - les processus ultrarapides dit de "Eley-Rideal" et par "atomes-chauds"(sub-picoseconde). La mise en place de modèle effectifs, pour tenir compte de ladissipation de l'énergie aux phonons de la surface et aux excitations électroniques(paires électron-trou), permet de rationaliser la dynamique non-adiabatique del'abstraction atomique aux surfaces métalliques. / The rationalization of elementary processes at surfaces is of prime importance for numerous natural and technological areas. From a fundamental pointof view, the way the energy concomitant to any chemical reaction is distributed among the desorbing molecules degrees-of-freedom and the surface is far frombeing fully pictured. In this work, quasiclassical molecular dynamics (QCT)simulations have been carried out to investigate this issue for the recombination ofH2 and N2 resulting from atomic adsorbate abstraction by atom scattering off theW(100) and W(110) covered surfaces, these processes being of relevance inplasma-wall interactions. Potential energy surfaces, built from density functional(DFT) theory calculations, have been used to simulate, within the framework ofclassical dynamics (including semi-classical corrections), the subpicosecond Eley-Rideal and Hot-Atom processes. The implementation of effective models to accountfor energy dissipation to surface phonons and electron-hole pair excitations, have allowed to rationalize the non-adidabatic dynamics of atom abstraction at metalsurfaces.