Banca de QUALIFICAÇÃO: LUCAS FRANKLIN DE LIMA

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : LUCAS FRANKLIN DE LIMA
DATE: 01/10/2025
TIME: 10:00
LOCAL: Remoto
TITLE:

NICKEL TUNGSTATE FROM SCHEELITE LEACHING PRECURSORS: SYNTHESIS AND CHARACTERIZATION

KEY WORDS:

Nickel tungstate; scheelite; leaching; supercapacitors

PAGES: 77
BIG AREA: Engenharias
AREA: Engenharia Química
SUBÁREA: Processos Industriais de Engenharia Química
SPECIALTY: Processos Inorgânicos
SUMMARY:

The global energy scenario faces the progressive depletion of fossil resources and the increasing impacts of global warming, driving the development of technologies that combine high energy efficiency with reduced environmental impact, notably storage devices such as supercapacitors, fuel cells, and batteries, as well as the production of hydrogen and synthesis gas from methane. Scheelite (CaWO₄) constitutes a significant source of tungsten, especially in the Seridó region, RN, being widely used in the form of carbide (WC) in metallurgy tools, civil construction, mining, and oil and gas drilling, in addition to tungstates applicable in supercapacitors, electrocatalysts, and sensors. In this study, NiWO₄ membranes were synthesized using the EDTA-Citrate complexation method, employing tungsten oxide obtained by acidic leaching of scheelite concentrate as a precursor, a procedure that increased the WO₃ content from 71.8% to approximately 93% and significantly reduced impurities, as evidenced by XRF, XRD, and FE-SEM analyses. The pellets were characterized in terms of morphology and dielectric properties, showing that the precursor purity and nickel stoichiometric adjustment directly influence the dielectric constant and dielectric loss: the pellet sintered with WO₃ obtained by leaching exhibited ε = 6.45 and tan δ ≈ 6.824×10⁻²; the pellet with the same WO₃ content but with excess nickel showed ε = 7.16 and tan δ ≈ 6.562×10⁻²; while the pellet produced with high-purity WO₃ displayed ε = 17.59 and tan δ ≈ 4.809×10⁻², indicating that higher purity maximizes dipolar polarization and reduces electrical losses. XRD analysis and Scherrer method calculations allowed estimating average crystallite sizes of 96.78 nm (5 h) and 95.14 nm (10 h), demonstrating that calcination time did not significantly affect the crystalline dimension. These results demonstrate that controlling the precursor purity and NiWO₄ stoichiometry is crucial to optimize its dielectric performance, highlighting the potential of the synthesized membranes for applications in supercapacitors and other high-performance electrochemical devices.

COMMITTEE MEMBERS:
Presidente - 349801 - CARLSON PEREIRA DE SOUZA
Interna - 1271737 - CAMILA PACELLY BRANDÃO DE ARAÚJO
Externa ao Programa - 1218001 - LIANA FRANCO PADILHA - UFRNExterno à Instituição - GILSON GARCIA DA SILVA - IFRN