Thermal decomposition of heavy rare-earth butanoates, Ln(C3H7CO2)3 (Ln = Er, Tm, Yb and Lu) in argon

Abstract

The thermal behaviour of Ln(C3H7CO2)3 (Ln = Er, Tm, Yb or Lu) was studied in argon from room temperature by means of thermogravimetry and differential thermal analysis up to 1400 °C, by infrared spectroscopy, hot-stage optical microscopy and X-ray diffraction. Melting prior to decomposition was observed in all four compounds, but its course depends on the rare-earth element. Decomposition to sesquioxides proceeds via the formation of dioxymonocarbonates (Ln2O2CO3) and release of 4-heptanone (C3H7COC3H7) as well as carbon dioxide (CO2) without evidence for an intermediate oxobutanoate stage. During the decomposition of Ln2O2CO3 into the respective sesquioxides (Ln2O3), an intermediate plateau extending from approximately 550 to 850 °C appears in the TG traces. The overall composition during this stage corresponds approximately to Ln2O2.8(CO3)0.2, but the state is more probably a mixture of Ln2O2CO3 and Ln2O3. The stability of this intermediate state seems to decrease with the mass of the rare-earth elements. Complete conversion to Ln2O3 is reached at about 1100 °C. The overall thermal decomposition behaviour of the title compounds is different from previous reports for other rare-earth butanoates.