Synthesis and characterization of pigments of the LaAl1−xFexO3 system – Application in ceramic and polymer

Abstract

Pigments from the LaAl1−xFexO3 (x = 0.00 to 1.00) system were synthesized through the citrate method and thermally treated at 910 °C for 4 h. The samples obtained were characterized through X-ray diffraction (XRD), Mössbauer spectroscopy (MS), field effect scanning electronic microscopy (FE-SEM), energy dispersive spectroscopy (EDS) and diffuse reflectance spectroscopy in the UV–Visible (DRS UV–Vis). The XRD analysis revealed the formation of perovskite as a single phase, crystallizing in the rhombohedral crystalline system with values 0.00 ≤ x ≤ 0.80, and in the orthorhombic system with x > 0.80 value. Through the Mössbauer spectroscopy, it was possible to follow the phase transformation and determine at which iron concentrations the coexistence of the perovskite rhombohedral and orthorhombic phases occurred. The electronic microscopy enabled to identify that the pigments presented particles of ideal size to be applied as ceramic pigments. Regarding coloration, the increase in Fe3+ concentration in the LaAl1−xFexO3 system provoked lattice distortions, altering the pigment band gap values and consequently their color. The pigments obtained presented coloration varying from white (LA), greenish-yellow (LAF1 to LAF5) and orange (LAF6 to LF). The pigments were applied to the enameling of ceramic pieces at 850 °C, decorative burning temperature and presented good color and opacity. Thus, the system under study presented suitable properties to be used as pigment to ceramic and polymer, in addition to presenting low toxicity, a fundamental characteristic in the current scenery of environmental and human health concerns.