The Dehydration And Dehydration Kinetics Of Cobalt (Ⅱ)-hexamethylenetetramine And Nickel (Ⅱ)-hexamethylenetetramine Compounds

Two cobalt(Ⅱ)-hexamethylenetetramine compounds and two nickel(Ⅱ)-hexamethylenetetramine compounds have been synthesized with CoCl₂·6H₂O (orNiCl₂·6H₂O) and hexamethylenetetramine, and characterized by means of elementaryanalysis and TG technique. The thermochromism, dehydrations and dehydrationkinetics of these compounds were studied.The composition of these compounds was defined by elementary analysis and TG.The compounds prepared by liquid phase reaction process are CoCl₂·2C₆H₁₂N₄·10H₂Oand NiCl₂·2C₆H₁₂N₄·10H₂O respectively, yet the compounds prepared by roomtemperature solid state process are CoCl₂·2C₆H₁₂N₄·7H₂O and NiCl₂·2C₆H₁₂N₄·2H₂Orespectively.Thermochromic experiments prove that CoCl₂·2C₆H₁₂N₄·10H₂O andCoCl₂·2C₆H₁₂N₄·7H₂O have good reversible thermochromism. Color's change owingto dehydration of CoCl₂·2C₆H₁₂N₄·10H₂O and hydration of CoCl₂·2C₆H₁₂N₄·7H₂O. ButNiCl₂·2C₆H₁₂N₄·10H₂O and NiCl₂·2C₆H₁₂N₄·2H₂O have no visible color's change atthe temperature when heating the crystals until 100℃.The dehydration kinetics of the four compounds were investigated using thenon-isothermal method by TG technique. The dehydration mechanism and associatedkinetics parameters were determined. The dehydration of CoCl₂·2C₆H₁₂N₄·10H₂O andCoCl₂·2C₆H₁₂N₄·7H₂O are all controlled by random nucleation and nuclei growthmechanism, the apparent activation energy are 104.40 kJ·mol^-1 and 104.62 kJ·mol^-1,and pre-exponential factor are 1013.20s^-1 and 1013.96s^-1, respectively.The dehydration mechanism of NiCl₂·2C₆H₁₂N₄·10H₂O is different from that ofNiCl₂·2C₆H₁₂N₄·2H₂O. The first stage of the dehydration of NiCl₂·2C₆H₁₂N₄·10H₂O is controlled by chemical reaction, with the apparent activation energy and preexponentialfactor are 233.32kJ·mol^-1 and 1033.00s^-1, respectively. The second stage ofthe dehydration is controlled by random nucleation and nuclei growth mechanism,with the apparent activation energy and pre-exponential factor are 188.51kJ·mol^-1 and1023.03s^-1, respectively. Yet the dehydration of NiCl₂·2C₆H₁₂N₄·2H₂O is controlled bycontracting sphere (spherical symmetry) mechanism, with the apparent activationenergy and pre-exponential factor are 100.35kJ·mol^-1 and 10^13.23s^-1, respectively.