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Caracterização elétrica e microestrutural de vitrocerâmicas condutoras por íon lítio com estrutura NASICON
(Universidade Federal de São Carlos, 2013-07-22) Semanate, José Luis Narváez; Rodrigues, Ana Candida Martins; https://lattes.cnpq.br/4499231813051400; https://lattes.cnpq.br/9824558997496023
This doctoral thesis presents results of the chemical, thermal, structural, microstructural and electrical characterization of glass and glass-ceramics with Li1,3Al0,3Ti1,7(PO4)3 (LATP), Li1,5Al0,5Ge1,5(PO4)3 (LAGP) and (LixNa1-x)1,5Al0,5Ge1,5(PO4)3 (LNAGP) compositions. All the compositions are shown to present homogeneous volume nucleation (Tgr ≤ 0.6), enabling their microstructures to be controlled through heat treatments, which in this study were single and double. The highly conductive NASICON-type phase was obtained in all the studied compositions. Secondary phases were also observed, albeit with no deleterious effect on the total electrical conductivity. Electrical characterization by impedance spectroscopy, performed at various temperatures below ambient temperature, enabled the contributions of the grain and grain boundary on the total electrical conductivity to be separated. An analysis of the two glass-ceramics, LATP and LAGP, leads to the conclusion that, in both cases, the total electrical resistance of the samples, and hence, their total electrical conductivity, is dominated by the grain boundary. The LATP composition presented higher electrical conductivity at room temperature, but also lower glass forming ability (very low Kgl). A Rietveld refinement of the LATP samples obtained by single heat treatment revealed that the concentration of lithium ions in the unit cell increases as a function of the heat treatment temperature. The electrical conductivity results indicate a relationship between this property and the thickness and volume fraction of grain boundaries, since the latter decrease with heat treatment temperature (in TTS case) and increase with nucleation time (in the case of TTD). The LATP samples obtained by TTD exhibited higher electrical conductivity than those obtained by TTS at the same temperature; however, this effect was not observed in the LAGP samples. The electrical conductivity of the LNAGP samples showed a mixed alkali effect in both the glasses and the corresponding glass-ceramics.
Desenvolvimento de sistema para monitoramento e controle de biorreator airlift de escala de bancada
(Universidade Federal de São Carlos, 2013-07-22) Torresam, Gabriel Deriggi; Badino Júnior, Alberto Colli; https://lattes.cnpq.br/3114111479745705
In the present work it was developed a system for monitoring and control of a bench scale concentric-tube airlift bioreactor of 5.0 L working volume. The software-based language G (Labview) provides the user monitor important process variables such as dissolved oxygen concentration, pH, volumetric flow rate of feed, pressure difference between two points along the axial direction and temperature in two regions of liquid phase flow phase, and it can act in the volumetric flow rate and gas stream composition at the input of bioreactor. Overall gas hold-up (eG) and gas hold-up in riser (eR) and downcomer (eD) regions were determined using volumetric expansion and gauge measurement methods. Mixing time (tm) and circulation time (tC) were determined by thermal and pH pulse methods. Dynamic pressure method was utilized for evaluating mass transfer measurement in airwater biphasic system. These methods were utilized in order to obtain significant hydrodynamic performance parameters as a function of superficial gas velocity in the riser (UGR). Analyses of the oxygen transfer dynamics were also used in the development of automatic control loop to control the dissolved oxygen concentration. As a concrete result, this study provided software for data acquisition and monitoring of all sensors in pneumatic bioreactor, providing a tool to explore the hydrodynamic performance and control of the dissolved oxygen concentration in concentric-tube airlift bioreactor during aerobic cultivations. The system validation was performed by comparing the results obtained in the hydrodynamics tests with those of literature and control loop was tested in simulations involving a cultivation of a strictly aerobic microorganism.