PIGMENTOS DE ÓXIDOS DE FERRO E ÓXIDOS MAGNÉTICOS: Método Inovador Sustentável

Abstract

Iron oxides are important components of various materials, they are closely connected to modern life which is either as protective or embellishing materials. For their chemical, physical or thermal stability; Both for its cost/benefit and recyclability. In this way, methods of preparation for size and shape control are of permanent technical feasibility study and with technological appeal. For its versatility, finding innovative and sustainable methods to synthesize iron oxides are incentives for further research. Sustainability exhibits low consumption of water and electricity, does not generate waste and minimize steps, for example filtration, purification and grinding, etc. In this sense, we explore the colloidal chemistry of citrus pectin, which, when gelling provides a control of the volume of water required, is a binder with excellent affinity with transition metals, which when burned provides an additional energy (42 MJ.kg-1) Acting as fuel, decreasing the calcination temperature and inducing magnetic properties or different colors. One surprising aspect was the combination of precursors (iron sulphates) with pectin having generated iron oxide pigments (IOPs) with different colors and shades. Iron (II) sulfate generated IOP-II300 (yellow), IOP-II600 (red) and IOP-II1000 (purple); While iron (III) sulfate produced IOP-III300 (yellow), IOP-III600 (red) and IOP-III1000 (violet). The IOPs were characterized with respect to the thermal behavior, structural and morphological properties, electronic and vibrational spectroscopies. The colloidal nature of IOPs was determined by electrophoretic mobility and dispersions optimized for optimum pH for dispersion in commercial (water-based) white paint, which pigmented coated surfaces of microscope slides for colorimetric measurements (CIEL*a*b*). On the other hand, magnetic iron oxides (MIO) were generated by gelation (80 °C, 4 h) and calcination (600 °C, 1 h). X-ray diffraction indicated the majority formation of the hematite (α-Fe2O3) and ferrite phases. Microscopy images show materials with a mean size below 50 nm. The texture properties indicated pore sizes of 7-30 nm whereas magnetic measurements indicated the formation of soft and hard oxides (coercivity between 90 and 400 Oe) and high magnetization saturation (50 emu.g-1).