Surface compositional changes upon heating cobalt oxalate dihydrate in vacuum

X-ray photoelectron spectroscopy (XPS) was chosen to explore changes occurring in the surface composition, structural and chemical state of atoms during the course of thermal decomposition of CoC2O4?2H2O under ultrahigh vacuum conditions. Accordingly, a large set of high-resolution core-level and Auger spectra was recorded as a function of temperature and time. Some Co-related XPS characteristics, including Auger parameter, were found to be sensitive to the local chemical and structural environment of Co atoms, demonstrating non-monotonic variation in the temperature range of intense dehydration. Isothermal decomposition was shown to proceed via formation of a two-phase system composed of metallic Co and oxygen-deficient oxalate and could be described by Avrami?Erofeev or Prout-Tompkins kinetic models. The long-term isothermal decomposition of the oxalate at 380 ?C produced nearly oxygen-free Co covered by a substantial amount of carbon in carbidic form (-19 at%) and as graphitic overlayer (-26 at%). On the contrary, heating of the oxalate to 500 ?C produced Co particles covered by surface CoO (-29 mol%) with traces of carbidic and graphitic carbon. XRD, TG and DTA coupled with mass spectrometry were employed as complementary techniques.