Radical and oxidative pathways in the pyrolysis of a barium propionate-acetate salt

Abstract

Film and powder samples from a BaAc2 solution in propionic acid/MeOH were decomposed in different atmospheres and their thermal decomposition was characterized by means of thermogravimetry coupled with evolved gas analysis techniques (TG-FTIR, EGA-MS) and chemical and structural methods (EA, XRD, FTIR). The thermal behavior of the films was found to be different than the corresponding powder, in terms of volatiles, kinetics, intermediate phases and purity of final product. The mixed Ba-Prop-Ac salt obtained from solution decomposes to BaCO3 before 400°C through oxidative degradation, and above 400°C in inert atmosphere through a radical path releasing symmetrical ketones. Its double melting behavior is also highlighted and its decomposition understood by comparison with BaProp2 and BaAc2 precursors, and put into context of YBa2Cu3O7-∂ (YBCO) film pyrolysis.

Effect of triethanolamine on the pyrolysis of metal-propionate-based solutions

“…The XRD of the dry film ( Fig. 1b) is in agreement with that of the mixed carboxylate salt Ba-Prop-Ac found in [26], suggesting that no new TEA-Ba complex is formed.…”

“…1b at 220°C shows new peaks toward lower angles, indicating a change in the barium carboxylate structure after solvent and water elimination taking place during TEA removal. As expected, also its carboxylic stretching bands have shifted from 1512 cm -1 to 1549 cm -1 during the 200°C-interval before oxidative degradation begins, due to dehydration and recrystallization [26]. The main TEA absorptions and the ester peak disappear after this stage, leaving a FTIR spectrum at the beginning of the third stage (280°C) that is identical to that of the barium carboxylate salt [26].…”

“…The FTIR spectra in Fig. 1a of the dry films show characteristic TEA vibration bands, and the partial replacement of acetate groups by propionates [37] with formation of a mixed Ba-Prop-Ac complex [18,26]. The XRD of the dry film ( Fig.…”

“…Since during decomposition of the barium carboxylate salt, propionic acid can evolve up to 150-200°C [26], it is reasonable to believe that the propionate units involved in the esterification come from the solvent. In fact, if they came from the salt, the last mass loss in Fig.…”

“…Finally, metal propionate salts have been shown to decompose following a radical path in inert atmosphere and high temperatures, releasing a symmetrical ketone (3-pentanone) and CO 2 [18][19][20][21][22][23] and forming the corresponding oxides (for YProp 3 ) or carbonates (for BaProp 2 ) by 500°C. In O 2 , oxidative degradation of the ligand is expected to occur at low temperature releasing propionic acid, acetaldehyde, CO 2 and water, but without changing the final phases [24][25][26]. Conversely, for CuProp 2 , propionic acid is expected to be the main volatile independently of the atmosphere [25], followed by acetaldehyde and CO 2 to give the corresponding oxide in film, and metallic copper as powder.…”