In this work, an experimental practice is presented using low-cost materials, to obtain magnetic nanoparticles and also a didactic proposal was applied about the theme Nanoscience and Nanotechnology, based on a CTSA approach. The nanoparticles were characterized by light scattering and scanning electron microscopy. The proposal was composed of an experimental activity, discussions about the result of the characterization and introduced the themes Nanoscience and Nanotechnology and its applications. The results of the characterization suggest that the used methodology to obtain the nanoparticles was efficient for didactic purposes and the didactic proposal provided learning of scientific content and its applications.
Neste trabalho é apresentada uma prática experimental com materiais do cotidiano para obtenção de nanopartículas magnéticas e uma proposta didática com o tema Nanociências e Nanotecnologia, baseada na abordagem CTSA. As NPmag foram caracterizadas por espalhamento de luz e microscopia eletrônica de varredura. A proposta aliou a atividade experimental, discussões referentes à caracterização, introdução aos temas e suas aplicações. Os resultados da caracterização sugerem que a metodologia para obtenção das NPmag é eficiente para fins didáticos e a proposta didática proporcionou aprendizagem de conteúdos científicos e suas aplicações.
ABSTRACT Maghemite (γ-Fe2O3) and hematite (α-Fe2O3) are important iron oxides in Brazilian soils derived from basalt. Maghemite can transform into hematite when exposed to high temperatures. However, isomorphic substitution (e.g., Al3+) may largely influence this process. We analyzed the kinetics of thermal transformation of Al-maghemites into Al-hematites and some of its mineralogical aspects. Synthetic substituted maghemites with different degrees of Al-substitution (0.0, 1.0, 2.0, 2.9, 3.8, 5.6, 6.7, 10.0, 12.0, and 17.1 mol% Al) were subjected to a temperature of 500±10 °C for 0, 5, 10, 16, 64, 128, 192, 360, 720, 2160, 3600, 5040, and 6480 min. After thermal treatment, samples were characterized by X ray diffraction (XRD), differential thermal analysis (DTA), specific surface area (SSA) measurement, and total chemical analysis. XRD patterns were analyzed by Rietveld refinement, and maghemite and hematite contents were calculated using Rietveld refinement and the method proposed by Sidhu. Isomorphic substitution of Fe by Al increased the critical temperature of transformation and the time necessary for maghemite to hematite transformation. Rietveld refinement data showed a better fit than the data adjusted by the Sidhu method. Increasing isomorphic substitution also decreased lattice parameters and mean crystallite dimension (MCD) values in maghemite; but only c-dimension and MCD decreased with increasing Al-substitution in hematite. For maghemite, the SSA increased with isomorphic substitution, rising up to 5.9 mol% Al; for hematite, SSA increased linearly. SSA decreased with heating time, regardless of isomorphic substitution.