Reduction of metal oxides by carbon in graphite furnaces - Part 2. Temporal oscillations in atomic absorption during the process of slow evaporation of Al, Mn and Yb oxides in spatially isothermal and non-isothermal graphite atomizers

Temporal oscillations in the kinetics of carbothermal reduction of Al, Mn and Yb oxides in spatially isothermal side-heated tubes were investigated in the first part of this study. Microgram amounts of the elements, as their nitrates, were evaporated during slow heating (1-20 K s(-1)) of the graphite tube. Several features of this phenomenon were investigated, including the effects of sample mass and solution volume, the influence of Sr and the type (Ar and N-2) and flow rate (0-250 ml min(-1)) of sheath gas on the character of the atomic absorption spikes. Essentially, all effects were similar to those found with spatially non-isothermal tubes. Results of possible effects of condensation/re-evaporation processes on temporal oscillations of atomic absorption signals from Al and Yb oxides in spatially non-isothermal tubes are presented in the second part of this study. No influence of transport processes on the temporal oscillations during common conditions of sampling and heating was evident. The results suggest that the origin of the temporal oscillations lies with the primary sample residue. All the above support the gaseous carbide mechanism of formation of temporal oscillations in the atomic absorption signals.