Obtenção de fitas de scheelita (CaWO4) via tape casting em base aquosa

• Ano de defesa: 2023
• Autor(a) principal: Siqueira, Nívia Luciana Costa de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Rio Grande do Norte; Brasil; UFRN; PROGRAMA DE PÓS-GRADUAÇÃO EM CIÊNCIA E ENGENHARIA DE MATERIAIS
• Palavras-chave em Português: Tungstênio; Scheelita; Tape casting; Fitas; CNPQ::ENGENHARIAS::ENGENHARIA DE MATERIAIS E METALURGICA
• Link de acesso: https://repositorio.ufrn.br/handle/123456789/55556

Scheelite, also known as calcium tungstate (CaWO4), is a mineral from the Wolframites group that holds significant economic importance due to its contribution to one of the largest quantities of tungsten production. In Brazil, the main extractiform scheelite deposits are located in the state of Rio Grande do Norte (RN), in the Seridó region, constituting the country's largest concentration of tungsten. However, the exploitation of this mineral has caused various negative environmental impacts in the mined areas, making it essential to develop technologies to mitigate the damages caused by the extraction and processing of this abundant resource in the state. Thin and solid films made with tungsten compounds exhibit great potential for dielectric, electronic, and optoelectronic applications, and can be produced through different methods. Tape casting is one of the simplest and well-established methods for film and tape manufacturing, being safe and non-toxic when carried out using an aqueous base. With this in mind, the objective of this study was to produce Scheelite tapes and analyze their properties. Five tapes were produced, gradually reducing the content of Scheelite residue (SR) from 100%, 75%, 50%, and 25% until complete substitution with concentrated Scheelite (SC). Physical-chemical characterization of the powders was conducted through fluorescence and X-ray diffraction tests, in addition to evaluating the rheology of the produced suspensions. The green tapes were characterized through Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Thermogravimetric Analysis (TGA), and dielectric measurements, aiming to assess the morphology, surface composition, thermal behavior, and dielectric properties of the tapes. X-ray diffraction identified the presence of scheelite, calcite, and quartz phases. The produced suspension exhibited pseudoplastic rheological behavior, ideal for tape casting. The produced tapes showed dielectric constants ranging from 7 to 3.4, average, in high-frequency ranges (0.1 to 1.5 GHz). Thus, a great potential is evidenced for tapes produced from the mixture of scheelite waste powder and concentrated scheelite in dielectric applications.