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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Síntese, caracterização e estudo da estabilidade de ferrofluídos preparados a partir de nanopartículas de ferrita de cobalto / Synthesis, characterization and stability study of ironfluids using cobalt ferrite nanoparticles

Lemes, Maykon Alves 14 November 2012 (has links)
Submitted by Marlene Santos (marlene.bc.ufg@gmail.com) on 2014-10-03T17:39:54Z No. of bitstreams: 2 Dissertação - Maykon Alves Lemes - 2012.pdf: 2492320 bytes, checksum: 3e1d392d822413232c98d491ac722c8b (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2014-10-03T20:44:00Z (GMT) No. of bitstreams: 2 Dissertação - Maykon Alves Lemes - 2012.pdf: 2492320 bytes, checksum: 3e1d392d822413232c98d491ac722c8b (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-10-03T20:44:00Z (GMT). No. of bitstreams: 2 Dissertação - Maykon Alves Lemes - 2012.pdf: 2492320 bytes, checksum: 3e1d392d822413232c98d491ac722c8b (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2012-11-14 / Cobalt ferrite nanoparticles were synthesized in the present work by the coprecipitation method from copper (II) and iron (III) chlorides in an alkaline solution under stirring at a speed of 20,000 rpm and heating at 70 oC. Oleic and stearic acids were used as surfactants, and the resulting magnetic gels were then dispersed in mineral oil. XRD, FTIR, TGA, Mössbauer spectroscopy, and VSM were used for characterizing the cobalt ferrite nanoparticles, and DLS and digital images for the resulting colloidal dispersion. The nanoparticle dispersion was also investigated by a 23-1 fractional factorial design. Digital images acquired by a CCD camera in RGB format were used to estimate the stability of the nanofluids. Multivariate image analysis in conjunction with PCA was employed to evaluate sedimentation times of the synthesized nanofluids. PLS, PCR, and MLR combined with genetic and successive projection algorithms were also used to estimate both the sedimentation time and the concentration of the nanoparticles in the mineral-oil based nanofluids. The square of the productmoment correlation coefficient through the digital image data for the multivariate calibration methods were higher than 0.93. The best prediction performance for estimating the sedimentation time of the nanoparticles was achieved by GA-PLS (RMSEP = 0.77 min and r2 = 0.9997). On the other hand, PCR presented the best results for estimating the concentration of the nanoparticles in the nanofluids (RMSEP = 0.029% min and r2 = 0.9991). / Nanopartículas de ferrita de cobalto foram sintetizados pelo método de coprecipitação a partir dos cloretos de cobalto (II) e ferro (III) em uma solução alcalina sob agitação de 20.000 rpm e aquecimento a 70 0C. Essas nanopartículas foram surfactadas com ácido oleico e ácido esteárico, formando géis magnéticos usados na dispersão em óleo mineral. As nanopartículas de ferrita de cobalto foram caracterizadas por DRX, FTIR, TG, mössbauer e curvas de magnetização. Já as dispersões coloidais foram caracterizadas por espalhamento dinâmico de luz e imagens digitais. Um planejamento fatorial fracionário 23-1 foi realizado a fim de verificar a melhor rota para dispersar as nanopartículas. Imagens digitais obtidas através de uma câmera digital CCD foram utilizadas para estudar a estabilidade dos nanofluidos. O tempo de sedimentação desses nanofluidos foi avaliado usando análise multivariada de imagens em conjunto com PCA, através dos gráficos de escores com variância total acima de 80%. PLS, PCR e MLR, combinados com os algoritmos genético e das projeções sucessivas, foram empregados para avaliar o tempo de sedimentação e a concentração de nanopartículas nos nanofluidos. Os métodos quimiométricos aplicados aos dados de imagens digitais demonstraram que há grande correlação (r2 > 0,93) entre os dados de imagem e as propriedades tempo de sedimentação e concentração de nanopartículas. Para a determinação do tempo de sedimentação das nanopartículas de ferrita de cobalto o modelo GA-PLS apresentou melhores resultados, com RMSEP de 0,77 min e r2 de 0,9997. Já para a determinação da concentração das nanopartículas PCR obteve melhor desempenho, com RMSEP de 0,029% e correlação de 0,9991.

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