Obtenção da solução precursora, produção e caracterização de fibras cerâmicas de YBCO + Ag pela técnica de fiação por sopro de solução
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Data
2021-03-05
Autores
Pessoa, Alexsander Lourenço
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Um dos grandes desafios para a aplicação de nanofibras cerâmicas produzidas pela técnica de solution-blow spinning (SBS) está relacionado com a sua fragilidade. Mantas supercondutoras de YBCO compostas por essas nanofibras são tão frágeis que acabam se rompendo pela intensidade da força de Lorentz produzidas por supercorrentes de blindagem. Por outro lado, vários estudos com amostras bulk mostraram-se que ao inserir prata na matriz YBCO, que acaba reforçando a amostra supercondutora, evitando o aparecimento de rachaduras, deixando-a mais compacta e com maior elasticidade. A prata ainda atua como centro de ancoramento de fluxo magnético e na melhoria das conexões entre os grãos. Consequentemente, as propriedades mecânicas e supercondutoras (JC, por exemplo) são aprimoradas. Contudo, a dissolução da prata em uma solução contendo íons de Y, Ba e Cu que fosse adequada ao uso do SBS mostrou-se de extrema complexidade. Assim, este trabalho teve por objetivo desenvolver uma solução precursora de YBCO+Ag adequada para a produção de amostras cerâmicas fibrosas usando a técnica de SBS e sua consequente caracterização, principalmente com relação à morfologia e formação da fase YBa2Cu3O7−X. A solução consistiu da dissolução dos acetatos metálicos de ítrio, bário, cobre e prata e do polímero polivinilpirrolidona (PVP) (em uma proporção de 5:1 em peso [PVP:acetatos]) em 61,5wt% de metanol, 12wt% de ácido propiônico, e 26,5wt% de hidróxido de amônio, juntamente com 6wt% de PVP em solução. Sete quantidades diferentes de prata (0, 0.5, 2, 5, 10, 20 e 30% em peso da cerâmica final YBCO) foram usadas na produção de 2g de YBa2Cu3O7−X. As caracterizações de TG e DTA mostram que as temperaturas de cristalização e fusão parcial decrescem em cerca de 40°C nas amostras com Ag. Imagens de MEV mostram que, após a queima do polímero em 600°C, é produzida uma manta composta por nanofios de diâmetros médios de até 233 nm. No entanto, após o processo de sinterização a 925°C por 1 h, os nanofios das amostras com Ag encolhem seu diâmetro de tal forma a produzir exemplares tipicamente porosos com área superficial final muito menor, em torno de 56%, do que aquela apresentada por uma amostra sem Ag.
One of the great challenges for the application of ceramic nanofibers produced by the solution-blow spinning (SBS) technique is related to its fragility. YBCO superdonductive blankets composed of these nanofibers are so fragile that they break up due to the intensity of the Lorentz force produced by shielding supercurrents. On the other hand, several investigations with bulk samples doped with Ag show that the introduction of in YBCO matrix increase its stenght. Then, this dopant avoidcracks in the superconducting ceramics, improving them diversification and elasticity. Silver also acts as pinning centers which anchor magnetic flux and enhance the connection between grains. Consequently, the mechanical and superconducting properties (JC, for example) are improved. However, the dissolution of silver in a solution containing Y, Ba and Cu ions that was suitable for the use of SBS proved to be extremely complex. Thus, this work aimed to develop a precursor solution of YBCO + Ag suitable for the production of fibrous ceramic samples using the SBS technique and its consequent characterization, mainly with respect to the morphology and formation of theY Ba2Cu3O7−X phase. The solution consisted of dissolving the metallic yttrium, barium, copper and silver acetates and the polyvinylpyrrolidone polymer (PVP) (in a ratio of 5: 1 by weight [PVP: acetates]) in 61.5wt% methanol, 12wt% propionic acid, and 26.5wt% ammonium hydroxide, together with 6wt% PVP in solution. Seven different amounts of silver (0, 0.5, 2, 5, 10, 20 and 30wt% of the final YBCO ceramic) were used to produce 2g of Y Ba2Cu3O7−δ. The characterizations of TG and DTA show that the temperatures of crystallization and partial melting decrease by about 40°C in Ag-doped samples. SEM images show that, after burning the polymer by 600°C, a blanket is made up of nanowires with average diameters up to 233 nm. However, after the 925°C sintering process for 1 h, the nanowires of the samples with Ag shrink their diameter in such a way as to produce typically porous specimens with a much smaller final surface area, around 56%, than that presented by a now doped sample.
One of the great challenges for the application of ceramic nanofibers produced by the solution-blow spinning (SBS) technique is related to its fragility. YBCO superdonductive blankets composed of these nanofibers are so fragile that they break up due to the intensity of the Lorentz force produced by shielding supercurrents. On the other hand, several investigations with bulk samples doped with Ag show that the introduction of in YBCO matrix increase its stenght. Then, this dopant avoidcracks in the superconducting ceramics, improving them diversification and elasticity. Silver also acts as pinning centers which anchor magnetic flux and enhance the connection between grains. Consequently, the mechanical and superconducting properties (JC, for example) are improved. However, the dissolution of silver in a solution containing Y, Ba and Cu ions that was suitable for the use of SBS proved to be extremely complex. Thus, this work aimed to develop a precursor solution of YBCO + Ag suitable for the production of fibrous ceramic samples using the SBS technique and its consequent characterization, mainly with respect to the morphology and formation of theY Ba2Cu3O7−X phase. The solution consisted of dissolving the metallic yttrium, barium, copper and silver acetates and the polyvinylpyrrolidone polymer (PVP) (in a ratio of 5: 1 by weight [PVP: acetates]) in 61.5wt% methanol, 12wt% propionic acid, and 26.5wt% ammonium hydroxide, together with 6wt% PVP in solution. Seven different amounts of silver (0, 0.5, 2, 5, 10, 20 and 30wt% of the final YBCO ceramic) were used to produce 2g of Y Ba2Cu3O7−δ. The characterizations of TG and DTA show that the temperatures of crystallization and partial melting decrease by about 40°C in Ag-doped samples. SEM images show that, after burning the polymer by 600°C, a blanket is made up of nanowires with average diameters up to 233 nm. However, after the 925°C sintering process for 1 h, the nanowires of the samples with Ag shrink their diameter in such a way as to produce typically porous specimens with a much smaller final surface area, around 56%, than that presented by a now doped sample.
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Palavras-chave
Supercondutividade, Nanofio, Y123, Y123+Ag, SBS, Fiação por sopro de solução, Síntese, One-pot, Superconductivity, Nanowire, Solution Blow-Spinning