Thermal behavior in oxidative and pyrolysis conditions and characterization of some metal p-aminobenzoate compounds using TG–DTA, EGA and DSC-photovisual system

Abstract

Synthesis, thermal and spectroscopic study of solid bivalent transition metal compounds of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with p-aminobenzoate as ligand were performed. The thermal study was performed in oxidative and pyrolysis conditions, using the thermoanalytical techniques: Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), DSC-photovisual system and evolved gas analysis (EGA) by TG/DSC-FTIR. Infrared absorption spectroscopy (FTIR) and powder X-ray diffractometry (PXRD) were employing in the spectroscopic study. The general formula M(L)2.nH2O has been established by TG-DTA, elemental analysis and complexometry with EDTA, where M represents Mn, Co, Ni, Cu and Zn, L is p-aminobenzoate and n = 0 (Mn, Co), 1 (Ni), 1.5 (Zn), 2 (Cu). In oxidative condition (dry air atmosphere), the thermal decomposition occurred in one, two or three steps, with formation of the respective oxides (Mn3O4 CoO, NiO, CuO and ZnO). Under pyrolysis condition (N2 atmosphere), the thermal decomposition occurred in three or four steps, with mass loss still being observed up to 1000 °C. DSC-photovisual system curves provided information about of the dehydration and phase transformation processes, as well as their enthalpies. The EGA data allowed the identification of gaseous products evolved during pyrolysis and oxidative decomposition. The results of the FTIR and PXRD also provided information on the ligand's denticity and crystallinity of the compounds.