Structure, microstructure, optical and magnetic properties of cobalt aluminate nanopowders obtained by sol-gel process

Abstract

The aim of this study was to detennine the effect of different complexing agents and of the annealing tem perature on the structural, morphological and optical properties of the synthesized precursors. Thus, cobalt aluminate nanoparticles were prepared by the sol-gel method using polyacrylic acid, glycine or citric acid as complexing agents. The synthesis performed at 500 °C for 5 hours led to dark green powders composed of solid solutions denoted Co 2+ [ Agci-x) Co�;i]O4 and of amorphous alumina (39.8wt%). Calcination at temperatures above 900 °C caused the powder colour to change from dark green to blue. A direct spinel structure Co 2+ [ Al� + ] 04 is all the more achieved as the annealing temperature is high. The powder obtained using polyacrylic acid as the complexing agent at 900 °C for 5 hours revealed the best morphology; it consisted of agglomerates of primary particles with a quasi-spherical shape and a size in the range 20-40 nm.

Preparation and characterisation of green nano-sized ceramic pigments with the spinel structure AB2O4 (A = Co, Ni and B = Cr, Al)

“…After 900°C, no discernible mass loss was observed on the TGA curves. DTA curves showed slight endothermic inflections at around 925 °C, which can be attributed to the reduction of Co 3+ to Co 2 + [24].…”

Correlation between degree of crystallinity and bluing of Zn1–Co Al2O4 (0≤x≤1) nanopowders prepared by soft chemistry route

“…The phase percentage values thus obtained were corrected with those of the prepared mixture; this makes it possible to deduce the degree of the crystalline and amount of amorphous phases in the sample (Table 2). The sample obtained at 700 ° C has been a degree of crystallinity of about 88%; this value increases as the annealing temperature increases, and this phenomenon can be explained by the introduction of amorphous alumina, under the effect of temperature, into the spinel structure [32].…”

Synthesis of cobalt aluminate spinel by sol-gel process: Investigation of starting reagents and precursors obtained after pyrolysis

“…The normal spinel structure of CoAl2O4 is known for its blue colour. The inverse or mixed structure can exhibit different colours, and it changes from dark green and turquoise to blue depending on the replacement amount of Co 2+ , Al 3+ and Co 3+ in the tetrahedral and octahedral sites [1][2][3]. The blue spinel of cobalt has attracted significant attention as a colouring agent in glaze and bulk tile compositions due to its superior properties, such as chemical and thermal stability as well as colour stability [4][5][6][7][8].…”

“…In previously reported studies, our group has reported the effect of the variation in pH for the synthesis and type of complexing agent on the texture of the powders obtained after heat treatment. These studies have reported that synthesis conducted in a neutral medium and using polyacrylic acid as the complexing agent leads to nanocrystalline CoAl2O4 spinel powder [3,23]. In this study, particular attention was focused on the starting reagents and effect of chelating agents on the pyrolysis step during sol-gel synthesis.…”

“…The pure cobalt aluminate phase is characterized by the appearance of the (331) reflection [17,[34][35][36]. The synthesis conditions (including type of complexing agent, calcination temperature, synthesis pH) were examined and applied in our recent study [3,23]. Results revealed that the cobalt aluminate oxide is obtained at 900 °C whatever the pH and the nature of the complexing agent used.…”