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A study on the thermal decomposition of iron-cobalt mixed hydroxides

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Abstract

Thermal decomposition of pure Fe(OH)3 and mixed with Co(OH)2 were studied using TG, DTA, kinetics of isothermal decomposition and electrical conductivity measurements. The thermal products were characterized by X-ray diffraction and IR spectroscopy. The TG and DTA analysis revealed the presence of Co2+ retards the decomposition of ferric hydroxide and the formation of α-Fe2O3. The kinetics of decomposition showed that the mixed samples need higher energy to achieve thermolysis. The investigation of thermal products of mixed samples indicated the formation of cobalt ferrite on addition ofx=1 or 1.5 cobalt hydroxide. The electrical conductivity accompanying the thermal decomposition decreases in presence of low ratio of Co2+ (x=0.2) via the consumption of holes created during thermal analysis. The continuous increase in σ values on increasing of Co2+ concentration corresponded to the electron hopping between Fe2+ and Co3+.

Zusammenfassung

Mittels TG, DTA und der Kinetik von Messungen der isothermen Zersetzung und der elektrischen Leitfähigkeit wurde die Zersetzung von Fe(OH)3 in reinem Zustand und vermengt mit Co(OH)2 untersucht. Die thermischen Produkte wurden mittels Röntgendiffraktion und IR-Spektroskopie charakterisiert. TG und DTA zeigen, daß die Zersetzung von Eisen(III)-hydroxid und die Bildung von -Fe2O3 durch Gegenwart von Co2+ verzögert wird. Die Zersetzungskinetik zeigt, daß die Mischproben mehr Energie für die Thermolyse benötigen. Die Untersuchung der thermischen Produkte zeigt die Bildung von Cobaltferrit bei Zusatz vonx=1 oder 1,5 Cobalthydroxid. Die elektrische Leitfähigkeit nimmt bei der thermischen Zersetzung in Gegenwart von niedrigen Co2+-Konzentrationen (x=0.2) durch Verbrauch der bei der Thermoanalyse geschaffenen Löcher ab. Das monotone Ansteigen der -Werte bei steigender Co2+-Konzentration stimmt mit dem Überspringen von Elektronen zwischen Fe2+ und Co3+ überein.

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Authors and Affiliations

  1. Department of Chemistry, Faculty of Science, Assiut University, Assiut, Egypt

    A. A. Said, K. M. Abd El-Salaam, E. A. Hassan, A. M. El-Awad & M. M. Mohamed

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  1. A. A. Said
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  2. K. M. Abd El-Salaam
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  3. E. A. Hassan
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  4. A. M. El-Awad
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  5. M. M. Mohamed
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Said, A.A., Abd El-Salaam, K.M., Hassan, E.A. et al. A study on the thermal decomposition of iron-cobalt mixed hydroxides. Journal of Thermal Analysis 39, 309–321 (1993). https://doi.org/10.1007/BF01983530

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