Mauricio Pereira Cantão

ESFOLIAÇÃO E HIDRATAÇÃO DA CAULINITA APÓS INTERCALAÇÃO COM URÉIA.

Well-ordered Georgia kaolinite (Kga-1b) obtained from the source Clay Repository of the Clay Minerals Society (USA) was intercalated with urea using grinding procedures. To achieve complete intercalation 20% of urea (in weight) was used, producing Al2Si2O5(OH)4 (N2H4CO)0,86 with an interplanar basal spacing of 1,08nm. After washing with water under ultrasound stirring at 363K, urea was completely removed and kaolinite was partially exfoliated. After drying under air, the material was converted to hydrated kaolinite with the composition Al2Si2O5(OH)4 (H2O)0,64 and an interplanar basal spacing of 0,84nm. In this compound, water molecules positioned between the layers of the silicate can be removed after calcination at 573K, regenerating structurally disordered kaolinite.

Mechanical properties of Ag-doped top-seeded melt-grown YBCO pellets

In the present work we report the mechanical properties of ca(b)-planes of Ag-doped top-seeded melt-grown YBaCuO (YBCO) pellets at different concentrations. Hardness and elastic modulus were obtained by instrumented indentation and fracture toughness by conventional Vickers indentation. Hardness profiles for both planes indicated values between 7-8 GPa at deep tip penetration. Significant differences in elastic modulus were observed as a function of Ag content for the ab-plane while no difference were seen for the ca(b)-plane. Doping with 5 wt. % Ag2O increases the hardness and elastic modulus for the ab-plane in relation to the undoped sample due to Ag solid-solution hardening. Indentation fracture toughness rises with Ag doping for the ab-plane. Intensive plastic deformation was observed in ca(b) plane for conventional Vickers indentation.

Avaliação da eficiência de uma célula a combustível estacionária de ácido fosfórico

Operation and performance of a commercial PAFC power plant were analyzed. Processes influencing energy conversion efficiency were studied in each module of the fuel cell power plant. The main processes were simulated using mass and energy balance equations, and the results were validated by means of experimental data. It was concluded that the electrical efficiency is higher in comparison with microturbines. The main result achieved is a better understanding of balance of plant processes, knowledge necessary for fuel cell power plant development.

Fluctuation conductivity of polycrystalline Y1-xPr xBa2Cu3O7-delta superconductors

We studied the effect of superconducting fluctuations on the electrical conductivity of granular samples of Y1 - xPrxBa2Cu3O7-d superconductors, with x = 0.01, 0.03, 0.05, 0.07 and 0.10. Samples were prepared by the standard solid-state reaction technique, with two different types of calcination process, in air at 900 oC ( x < 0.07 ) and in vacuum at 850 oC ( 0.05 < x < 0.10 ). For the samples prepared in air, our results revealed a splitting of the bulk transition, denoted by TC1 and TC2, besides the coherence transition. It was observed fluctuation regimes above the highest transition ( TC1 ) and the lowest transition ( TC2 ). For the samples calcinated in vacuum and high concentrations of Pr, changes were observed in the critical region with chemical substitution of the Pr ion for the Y ion. In the regime of approach to the zero resistance state it was observed an occurrence of a coherence transition for all concentrations of praseodymium.

Temperature Effect on Hydrogen Production from Reactions between Ethanol and Steam in the Presence of Pd-Ru/Nb2O5-TiO2 Catalyst

Temperature effect on the performance of Pd-Ru/Nb2O5-TiO2 (PRNT) catalyst on hydrogen production from reactions between ethanol and steam was evaluated. Parallel reactions occurred in all conditions studied according to what was observed by the presence of H2, CO2, CH4, CO, C2H4, C2H6, C2H4O and (C2H5)2O. While at 300 °C the process seems to be dominated by ethanol dehydrogenation and decomposition, at 375 °C dehydration it seems to compete for active sites with ethanol dehydrogenation and decomposition reactions. At 450 °C there is a dehydration reaction to ethane, basically competing at the same level with ethanol dehydrogenation decomposition reactions. Hydrogen production on PRNT catalyst is maximized at 300 °C.