Modulation of Solid-state Thermal Reaction of Iron(III)Citrate by a Co-precursor Studied using Thermogravimetry: Evaluation of Kinetic and Thermodynamic Parameters and Nucleation Rate

Background: Solid state reaction of iron(III)citrate leads to a range of ironbased oxides by varying the reaction conditions, e.g., the presence of co-precursor. The influence of reaction conditions on the kinetics of the solid-state reaction of iron(III)citrate needs to be investigated. Objective: Kinetic analysis of the solid-state reaction of iron(III)citrate in the presence of a co-precursor has been explored to realize the influences of the co-precursor on the reaction process as well as decomposed material. Methods: Non-isothermal thermogravimetry profiles are deconvoluted to individual reaction steps. The model-free kinetic methodology is utilized to estimate step-wise activation energy and, hence, the reaction mechanism along with the reaction rate. Conversiondependent thermodynamic parameters and nucleation rate are estimated. XRD analysis has been used to characterize the decomposed material. Results: Thermogravimetry profiles obtained for an iron(III)citrate and malonic acid mixture are deconvoluted into six steps. The decomposed nanomaterial is identified as magnetite (size 10 nm). The observed reaction mechanisms associated with each step are different, where the activation/reaction rate is conversion-dependent. A good fit between the experimental and reverse-constructed conversion profiles is obtained. The nucleation rate at higher temperatures is affected by both the extent of conversion and the heating rate. A possible reaction pathway is proposed. The study elucidates the role of malonic acid as a co-precursor in modifying the thermal reaction of iron(III)citrate and product formation. Conclusion: This investigation proposes the applicability of suitable co-precursors as a potential controlling factor for preparing iron oxides from iron-based compounds.