Combustion synthesis of lanthanum chromite starting from water solutions: Investigation of process mechanism by DTA–TGA–MS

The mechanism of combustion synthesis of lanthanum chromite was investigated by carrying out simultaneous differential thermal analysis (DTA), thermal-gravimetric analysis (TGA) and quadrupole mass spectrometry measurements (MS). The whole process was found to involve several phenomena: urea and nitrates thermal decomposition, exothermal reactions occurring directly between nitrates and urea as well as between their decomposition products, final reaction between solid oxides. In order to better understand the complex calorimetric, thermal-gravimetric and mass spectrometric curves, the behaviour on heating of each single reagent as well as that of binary mixtures, made by combining urea with each single nitrate, were also studied. Combustion synthesis was performed either under an oxidizing atmosphere or under an inert one. Chemical reactions possibly occurring during this combustion synthesis have been proposed on the basis of MS analysis of gaseous reaction products. The effect of using an excess of sacrificial fuel jointly with the addition of ammonium nitrate was also investigated.