Enthalpy of Interaction and Activation Energy for Thermal Degradation of Modified Forms of Lamellar Titanium Hydrogenphosphate

Abstract

Crystalline alpha titanium hydrogenphosphate (TPH), the derivatives of potassium (TPK), calcium (TPCa), barium (TPBa), lanthanum (TPLa), and the intercalated forms of n-butylamine (TPBA) and pyridine (TPPy) were prepared. Thermodynamics of ionic exchange and intercalation processes were performed through calorimetric titration. The enthalpic values for potassium, calcium, barium, and lanthanum gave: −0.54±0.04; 5.82±0.24; 1.11±0.09, and 5.85± 0.13 kJ mol-1, respectively. For the intercalation with butylamine and pyridine the values −42.5±0.15 and −66.76± 1.10 kJ mol-1 were obtained. The nonisolthermal Coats-Redfern method was used to calculate the kinetical parameters for thermal degradation of all matrices through thermogravimetric data. The matrices presented two or three mass loss steps. The activation energy (Ea) values for the condensation of the OH groups are 67, 155, 124, 147, 117, 318, and 477 kJ mol−1 for TPH, TPK, TPCa, TPBa, TPLa, TPBA, and TPPy, respectively. The plot of the enthalpic values as function of Ea gave a linear relationship, expressed by the equation: ΔintHθm=−0.212×Ea+31.070, which correlated the thermochemical and kinetical parameters.