MECHANISMS CONTROLLING DIRECT SOLID SAMPLING OF SILICON FROM GOLD SAMPLES BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY .2. ATOMIZATION FROM AQUEOUS AND SOLID SAMPLES

The mechanisms that control atomization of silicon from aqueous solutions and from solid-gold samples were investigated, in vacuo and in real-time, by mass spectrometry to explain recently observed correlations of free Si evolution from aqueous and from solid-gold samples. The results from monitoring gaseous silicon species that evolved from these two types of samples indicate that atomization mechanisms differ substantially. Free Si and SiO vaporized from both sample types, but SiC2(g) and Si-2(g) were unique to the aqueous and to the solid-gold samples, respectively. These observations imply that atomization occurs via dissociative adsorption processes during heating of the aqueous samples. For the solid-gold samples, the Si impurities are carried by convection to the surface of the molten gold where they vaporize. It is speculated that the correlations in free Si formation at atmospheric pressure are because of gas-phase collisions. These collisions can enhance dissociation of the Si-2(g) that forms only during heating of the solid samples.