Atomic and molecular spectra of vapours evolved in a graphite furnace.: Part 2:: Magnesium chloride

Electrothermal atomic and molecular absorption spectrometly was applied to investigate the vaporization of magnesium chloride. Using a CCD linear array detector, atomic and molecular absorption spectra were simultaneously measured in the range 200-400 nm. Vaporization was performed from pyrocoated and tantalum-lined graphite tubes; Ar and He were employed as furnace gas. A broad molecular band was first observed at 210 nm and attributed to MgCl(2)(g). The signal was followed by a partially resolved system at 266, 269, 273 nm and a three bands at 369, 376 and 382nm, which are characteristic of MgCl(g). The release of MgCl vapours was accompanied by Mg atomic absorption and by light scattering. MgCl(2) . 6H(2)O partially vaporizes as MgCl(2),(g) and partially reacts with the water of crystallization (hydrolysis reaction), leading to a mixture of magnesium hydroxychloride and hydroxide. By further heating of the condensed phase MgO(s) and MgCl vapours are formed. The hydrolysis process was favoured by long pyrolysis treatments or by stopping the gas flow during the pyrolysis step. In He atmosphere or when a tantalum-lined tube was used, the fraction of salt vaporized as MgCl(2), was increased, while scattering effects were not observed. (C) 1999 Elsevier Science B.V. All rights reserved.