SABRINA GONCALVES DE MACEDO CARVALHO

SABRINA GONCALVES DE MACEDO CARVALHO

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Projeto e validação de arranjo experimental para avaliação de permeação gasosa em membranas cerâmicas
2023 - CARVALHO, S.G.M.; MUCCILLO, E.N.S.; MUCCILLO, R.
Atualmente diversas membranas cerâmicas têm sido desenvolvidas para permeação gasosa de espécies químicas como CO2, O2, H2, e outros, e uma importante medida de caracterização é a eficiência de permeação. Neste trabalho, um arranjo experimental para avaliação da permeação gasosa de membranas cerâmicas foi projetado e montado, com a possibilidade de medida simultânea de espectroscopia de impedância eletroquímica para estudo do comportamento elétrico. O arranjo consiste em dois tubos de alumina, entre os quais a amostra e fixada, com termopares e eletrodos de platina em ambos os lados da amostra. A permeação de gás através de uma membrana cerâmica pôde ser monitorizada com controladores de fluxo de massa, um espectrômetro de massa, e um analisador de impedância eletroquímica. Para testes e validação de dados, membranas cerâmicas porosas de oxido de cério dopado com óxido de gadolínio foram preparadas e infiltradas com uma composição eutética de carbonato de Li-Na.
W-doped Lanthanum Molybdenum Oxide/Lithium-Sodium-Potassium Carbonate Composite Membranes for Carbon Dioxide Permeation
2023 - MEDINA, MIDILANE S.; CARVALHO, SABRINA G.M.; TABUTI, FRANCISCO N.; MUCCILLO, ELIANA N.S.; FONSECA, FABIO C.; MUCCILLO, REGINALDO
Single-phase tungsten-doped lanthanum molybdenum oxide (La2MoWO9) ceramic powders were synthesized using the complex polymerization technique. Porous ceramic pellets were obtained by thermally removing graphite, which served as a pore former. The porous pellets were then impregnated with molten eutectic lithium-sodium-potassium carbonates. The energy dispersive X-ray analysis and scanning electron microscopy (FEG-SEM) images of the external and fracture surfaces of the La2MoWO9-(Li,Na,K)2CO3 composite dual-phase membrane revealed the percolation of the carbonate mixture through the pores. Electrochemical impedance spectroscopy measurements conducted at temperatures below and above the melting point of the eutectic carbonate composition demonstrated the contributions of oxygen and carbonate ions to the ionic conductivity of the dual membrane. The electrical conductivity of the carbonate ions within the membrane was continuously monitored for over 1300 h with negligible degradation, implying that the membrane could be used for long-term monitoring of CO2 without aging effects. A comparison of FEG-SEM images taken before and after this endurance test suggested minimal fouling, indicating that the membrane could potentially replace similar zirconia- and ceria-based composite membranes.
Design and validation of an experimental setup for evaluation of gas permeation in ceramic membranes
2023 - CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.; MUCCILLO, REGINALDO
An experimental setup for the evaluation of permeation of gaseous species with the possibility of simultaneously collecting electrochemical impedance spectroscopy data in disk-shaped ceramic membranes was designed and assembled. It consists of an alumina sample holder with thermocouple tips and platinum electrodes located close to both sides of the sample. Water-cooled inlet and outlet gas connections allowed for the insertion of the sample chamber into a programmable split tubular furnace. Gas permeation through a ceramic membrane can be monitored with mass flow controllers, a mass spectrometer, and an electrochemical impedance analyzer. For testing and data validation, ceramic composite membranes were prepared with the infiltration of molten eutectic compositions of alkali salts (lithium, sodium, and potassium carbonates) into porous gadolinia-doped ceria. Values of the alkali salt melting points and the permeation rates of carbon dioxide, in agreement with reported data, were successfully collected.
Development of stabilized zirconia–alkali salts dual membranes for carbon dioxide capture
2023 - MUCCILLO, REGINALDO; CARVALHO, SABRINA G.M.; DENALDI, RAFAEL L.; MUCCILLO, ELIANA N.S.
Molten Na2CO3–K2CO3 (NKC, 56–44 mol%) eutectic compositions were vacuum-impregnated, at the eutectic temperature, into two porous ZrO2:8.6 mol% MgO (magnesium-partially stabilized zirconia, MgPSZ) and ZrO2:8 mol% Y2O2 (yttria-fully stabilized zirconia, 8YSZ) ceramics. Thermogravimetric analyses were performed in mixtures of that composition with MgPSZ and 8YSZ ceramic powders. Before impregnation, porosity was achieved in the two compounds by addition and thermal removal of 30 vol.% NKC. To ascertain the carbonates had filled up through the ceramic body, both sides of the parallel and fracture surfaces of the disk-shaped impregnated compositions were observed in a scanning electron microscope and analyzed by energy-dispersive X-ray spectroscopy. The electrical conductivity of the two ceramics, before and after impregnation, was evaluated by electrochemical impedance spectroscopy in the 5 Hz–13 MHz frequency range from approximately 530 to 740°C. The permeation of the carbonate ions through the membranes via the eutectic composition was assessed by the threshold temperatures of the onset of the carbonate ion percolation. The objectives were to prepare dual-phase membranes for the separation of carbon dioxide and for the development of carbon dioxide sensors.
Tape-casting and freeze-drying gadolinia-doped ceria composite membranes for carbon dioxide permeation
2022 - CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.; FONSECA, FABIO C.; MULLER, MICHAEL; SCHULZE-KUPPERS, FALK; BAUMANN, STEFAN; MEULENBERG, WILHELM A.; GUILLON, OLIVIER; MUCCILLO, REGINALDO
Porous ceria: 20 mol% gadolinia (20GDC) ceramic membranes were prepared by tape casting (TC) and freeze-drying (FD) techniques, obtaining ceramic matrices with randomly dispersed round pores and with an aligned pore structure, respectively. Samples were sintered at 1450 °C, followed by infiltration of molten eutectic sodium-lithium carbonates (NLC). The pore morphology of 20GDC-TC and 20GDC-FD composite membranes was evaluated by analysis of scanning electron microscopy images. The electrical resistivity was determined by electrochemical impedance spectroscopy in the 1 Hz - 10 MHz frequency range from 300 °C to 700 °C, covering the solid-to-molten NLC temperature range, showing that the aligned pore structure improved the conductivity of the ceramic matrix in addition to facilitating molten carbonate infiltration, improving the total (bulk + interfaces) electrical conductivity of the composite membrane. Permeation experiments showed high CO2 permeation rates reached 5.35 × 10−7 mol m−2 s−1 Pa−1 at 800 °C. The infiltration of molten sodium-lithium carbonate in gadolinium-doped ceria prepared by the freeze-drying technique is proposed as an optimized procedure for producing membranes for carbon dioxide separation.
Ionic conductivity of electric field-assisted sintered gadolinia-doped ceria/alkali salts membranes
2021 - CARVALHO, SABRINA G. de M.; MUCCILLO, ELIANA N. dos S.; MUCCILLO, REGINALDO
Ceramic-carbonate dual-phase membranes were prepared according to the usual procedure: by vacuum impregnation of molten sodium-lithium carbonates (NLC) into sintered porous ceria-20 mol% gadolinia (20GDC) solid electrolyte cylindrical pellets; and also by flash sintering samples with 75 wt.% (CeO2: 20 mol% Gd2O3) and 25 wt.% NLC. Sintering was accomplished by applying 200 V cm-1 to the membrane positioned in a sample holder of a dilatometer for monitoring thickness shrinkage, limiting the electrical current to 1 A. Electrochemical impedance spectroscopy measurements were performed in the 5 Hz-13 MHz frequency range from 300ºC to 600ºC in composite ceramic membranes, covering the solid-to-molten NLC temperature range. Analysis of the impedance diagrams allowed for the evaluation of the oxide ion and carbon dioxide ion conductivities. The Arrhenius plots showed the transition from oxide ion conduction (due to the solid electrolyte) to carbonate ion conduction (due to the molten NLC). The ionic conductivity values of membranes flash sintered at 420ºC in 2 min were higher than those of conventionally sintered membranes and similar to reported values of membranes sintered at 690ºC for 2 h.
Electric field-assisted sintering anode-supported single solid oxide fuel cell
2022 - MUCCILLO, REGINALDO; FLORIO, DANIEL Z. de; FONSECA, FABIO C.; CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.
Cosintering (La0.84Sr0.16MnO3 thin-film cathode/ZrO2: 8 mol% Y2O3 thin-film solid electrolyte/55 vol.% ZrO2:8 mol% Y2O3 + 45 vol.% NiO anode, ϕ = 12 × 1.5 mm thick pellet) was achieved by applying an electric field for 5 min at 1200°C. Impedance spectroscopy measurements of the anode-supported three-layer cell show an improvement of the electrical conductivity in comparison to that of a conventionally sintered cell. The scanning electron microscopy images of the cross-sections of electric field-assisted pressureless sintered cells show a fairly dense electrolyte and porous anode and cathode. Joule heating, resulting from the electric current due to the application of the AC electric field, is suggested as responsible for sintering. Dilatometric shrinkage curves, electric voltage and current profiles, impedance spectroscopy diagrams, and scanning electron microscopy micrographs show how anode-electrolyte-cathode ceramic cells can be cosintered at temperatures lower than the usually required.
SAXS signature of the lamellar ordering of ionic domains of perfluorinated sulfonic-acid ionomers by electric and magnetic field-assisted casting
2020 - SILVA, JAQUELINE S. da; CARVALHO, SABRINA G.M.; SILVA, RODRIGO P. da; TAVARES, ANA C.; SCHADE, ULRICH; PUSKAR, LJILJANA; FONSECA, FABIO C.; MATOS, BRUNO R.
At present, small angle X-ray scattering (SAXS) studies of perfluorinated sulfonic-acid ionomers (PFSAs) are unable to fully determine the true shape of their building blocks, as recent SAXS modelling predicts disk- and rod-like nanoionic domains as being equally possible. This scenario requires evidence-based findings to unravel the real shape of PFSA building blocks. Herein, a SAXS pattern signature for a lamellar nanophase separation of the ionic domains of Nafion is presented, backed by mid and far infrared spectroscopy (MIR and FIR) and wide angle X-ray scattering (WAXS) data of Nafion in different ionic forms, a broad range of ionic phase contents (EW ~ 859–42 252 g eq-1) and temperatures. The study indicates that the lamellar arrangement of the ionic domains is the most representative morphology that accounts for the physical properties of this ionomer. The lamellar SAXS reflections of Nafion are enhanced in electric and magnetic field-aligned membranes, as confirmed by atomic force microscopy (AFM). Electric and magnetic field-assisted casting of Nafion allowed producing nanostructured and anisotropic films with the lamellas stacked perpendicularly to the field vector, which is the direction of interest for several applications. Such nanostructured Nafion membranes are bestowed with advanced optical and proton transport properties, making them promising materials for solar and fuel cells.
Electric field-assisted sintering (gadolinia-doped ceria/alkali salts) composite membranes
2020 - CARVALHO, S.G.M.; MUCCILLO, E.N.S.; MARQUES, F.M.B.; MUCCILLO, R.
Composite ceramic membranes were prepared according to two routes: (i) vacuum impregnation of molten eutec- tic sodium-lithium carbonates (NLC) into porous ceria-20 mol% gadolinia (20GDC) solid electrolytes; (ii) electric field-assisted sintering of a 25 wt% NLC/75 wt% 20GDC mixture. Porous 20GDC ceramics were obtained by controlled thermal removal of 40 vol% KCl added as pore former. Electric field-assisted (flash) sintering was car- ried out monitoring thickness during application of 200 V cm − 1 to the specimen positioned in a sample chamber inserted in a vertical dilatometer. The surfaces of the sintered membranes were observed in a scanning electron microscope. Electrochemical impedance spectroscopy measurements were performed in the 5 Hz to 13 MHz fre- quency range in the 280–580°C range. Arrhenius plots showed the transition from oxide ion conduction (due to the solid electrolyte) to carbonate ion conduction (due to the molten NLC). Membranes flash sintered at 420°C in 2 min showed electrical conductivity similar to membranes conventionally sintered at 690°C for 2 h.
Enhancement of the ionic conductivity in electric field-assisted pressureless sintered BITIVOX solid electrolytes
2019 - MEDINA, MIDILANE S.; CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.; MUCCILLO, REGINALDO
Bi4V1.8Ti0.2O11 (BITIVOX) ceramic pellets, prepared with powders obtained by a sol gel technique, were sintered either conventionally at 800 C/8 h or by applying an AC electric voltage, limiting the electric current through the pellets. Electric voltages were applied isothermally at 700 C and 800 C during 5 min in the green pellet positioned in the sample holder of a dilatometer for monitoring thickness variation. The BITIVOX pellets shrank 13.6% after applying 200 V cm􀀀1 at 800 C and 10.4% heating to 800 C for 8 h. Thermal analysis and X-ray di raction of the powders were performed to evaluate the crystallization temperature and the structural phase, respectively. The electrical behavior of the sintered BITIVOX pellets was analyzed by the impedance spectroscopy technique, showing that the sample flash sintered at 800 C/5 min had lower bulk resistivity than the sample conventionally sintered at 800 C/8 h. The surfaces of the sintered pellets were observed in a scanning electron microscope showing similar grain sizes and pore content in all sintered samples.