A thermogravimetric study of thermal dehydration of copper hexacyanoferrate by means of model-free kinetic analysis

• Published in: Journal of thermal analysis and calorimetry 2017-08, Vol.129 (2), p.721-731
• Main Authors: Åkerblom, Ida E., Ojwang, Dickson O., Grins, Jekabs, Svensson, Gunnar
• Format: Article
• Language: English
• Subjects: Activation energy; Analysis; Analytical Chemistry; Chemical bonds; Chemistry; Chemistry and Materials Science; Copper; Copper hexacyanoferrate; Dehydration; Dehydration enthalpy; Enthalpy; Inorganic Chemistry; Kinetic analysis; Kinetics; Measurement Science and Instrumentation; Moisture content; oorganisk kemi; Physical Chemistry; Polymer Sciences; Reaction kinetics; Thermal dehydration; Thermogravimetry
• ISSN: 1388-6150; 1588-2926; 1588-2926
• DOI: 10.1007/s10973-017-6280-x

The kinetics of thermal dehydration of K 2x/3 Cu[Fe(CN) 6 ] 2/3 · n H 2 O was studied using thermogravimetry for x  = 0.0 and 1.0. Data from both non-isothermal and isothermal measurements were used for model-free kinetic analysis by the Friedman and KAS methods. The water content was determined to be n  = 2.9–3.9, plus an additional ~10% of water, likely surface adsorbed, that leaves very fast when samples are exposed to a dry atmosphere. The determined average activation energy for 0.2 ≤  α  ≤ 0.8 is 56 kJ mol −1 . The dehydration is adequately described as a diffusion-controlled single-step reaction following the D3 Jander model. The determined dehydration enthalpy is 11 kJ (mol H 2 O) −1 for x  = 0.0 and 27 kJ (mol H 2 O) −1 for x  = 1.0, relative to that of water. The increase with increasing x is evidence that the H 2 O molecules form bonds to the incorporated K + ions.