SABRINA GONCALVES DE MACEDO CARVALHO

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  • Artigo IPEN-doc 29902
    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.
  • Artigo IPEN-doc 29597
    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.
  • Artigo IPEN-doc 29471
    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.
  • Artigo IPEN-doc 27167
    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.
  • Artigo IPEN-doc 26438
    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.
  • Artigo IPEN-doc 26437
    Electrical behavior of electric field-assisted pressureless sintered ceria-20 mol% samaria
    2019 - REIS, SHIRLEY L.; CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.; MUCCILLO, REGINALDO
    CeO2:20 mol% Sm2O3 green ceramic pellets were sintered conventionally at 1500 C/2 h and flash sintered by applying a 200 V cm􀀀1 electric field at 800 C, 1000 C and 1200 C. The thickness shrinkage of the pellets was followed bythe specimen being positioned inside a dilatometer adapted with platinum electrodes and terminal leads connected to a power supply for application of the electric voltage. The microstructure of the surfaces of the sintered samples were observed in a scanning electron microscope. The electrical properties were evaluated by the impedance spectroscopy technique in the 5 Hz–13 MHz frequency range from 210 C to 280 C. The main results show that (i) the final shrinkage level is nearly independent of the temperature when the electric field is applied and slightly better than that of the 1500 C sintered pellet, and (ii) the bulk conductivity of the sample flash sintered at 1200 C is similar to that of the sample sintered at 1500 C. The availability of a pathway for the electric current pulse derived from the applied electric field is proposed as the reason for the achieved shrinkages. Scavenging of the grain boundaries by Joule heating is proposed as the reason for the improved oxide ion bulk conductivity.
  • Artigo IPEN-doc 24719
    AC electric field assisted pressureless sintering zirconia
    2018 - CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.; MUCCILLO, REGINALDO
    3mol% yttria ionic conductors are sintered by applying AC electric fields with frequencies in the 0.5-1.0kHz range at 1100 degrees C. The sintering experiments are conducted in pressed pellets positioned between platinum electrodes inside a dilatometer furnace. The dilatometer is modified in order to allow for the simultaneous monitoring of thickness shrinkage, electric voltage, and current across the pellet. The results show that the higher the frequency of the electric field, the higher the attained shrinkage and the apparent density of the pellets. Increasing the frequency of the applied electric field leads to an increase in the Joule heating promoted by the electric current pulse through the polycrystalline ceramic sample. A higher frequency therefore leads to higher amount of thermal energy delivered to the sample, favoring enhanced densification. The ionic resistivity decreases in pellets sintered with increasing frequency of the applied electric field. We suggest that Joule heating favors pore elimination and the removal of chemical species at the space charge region, inhibiting the blocking of oxide ions at the interfaces.