Abstract
Effect of calcination temperature on the physico-morphological properties of CoC
2O
4·2H
2O–FeC
2O
4·2H
2O (1:2 mole ratio) mixture has been investigated using DTA–TG, XRD, Mössbauer effect (ME) spectroscopy, FT-IR and SEM measurements. DTA–TG results showed that the decomposition proceeds via four well-defined steps. The first is attributed to dehydration and formation of anhydrous mixture which decomposed in the second step to give CoC
2O
4–Fe
2O
3 mixture. In the third step, CoC
2O
4 decomposed and Co
3O
4–Fe
2O
3 mixture is formed. This mixture is thermally stable up to 920
°C, then Co
3O
4 reduced to CoO, which reacts directly with α-Fe
2O
3 to form CoFe
2O
4, in the fourth step. ME spectra demonstrated that part of α-Fe
2O
3 is formed in a superparamagnetic doublet state in the early stages of decomposition. As the temperature increased to 800
°C, the crystallites are grown and the superparamagnetism disappeared. At 1000
°C, a ferrimagnetic ordering ME spectrum fitted into two Zeeman sextets due to Fe
3+ at the two distinct sites of CoFe
2O
4 inverse spinel has been obtained. XRD patterns of samples calcined at 250 and 280
°C revealed none of XRD lines characteristic of α-Fe
2O
3, while the pattern of that fired at 1000
°C confirmed the presence of single-phase cubic spinel structure with no evidence of impurities. FT-IR and SEM studies are consistent with the previous results. Kinetic analysis of the dehydration and the oxalate decomposition reactions was performed under non-isothermal conditions using different integral methods of analysis. The dynamic TG curves showed a sigmoid shape and obeyed the Avrami–Erofeev equation characteristic of the solid state nucleation–growth mechanism. The activation parameters were calculated and discussed.