Vaporization of zinc during thermal treatment of ZnO with tetrabromobisphenol A (TBBPA)

In the present work we investigate the vaporization of zinc or its compounds during thermal treatment of ZnO with tetrabromobisphenol A. Samples of 2g of ZnO:TBBPA (3.34:1) were isothermally heated in a laboratory-scale furnace at temperatures from 490°C to 950°C, and the solid, condensed and gaseous products formed were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. The results obtained indicate that the vaporization of ZnBr₂ formed strongly depends on heating time and temperature, yet is restrained by char, if formed with sufficient yield (above 15wt%). Starting from 850°C, this char commences carbothermic reduction of any remaining ZnO, which from then begins to evaporate as zinc metal vapor. Volatilization of zinc is completed at 950°C. The presence of 5vol.% of oxygen has no significant effect on the vaporization of formed ZnBr₂, the carbothermic reduction or the volatilization of metallic zinc. Strongly oxidizing conditions (20vol.% of oxygen), however, boost the oxidation of char and thus the vaporization of ZnBr₂, but prevent carbothermic reduction of any un-reacted ZnO by depleting this char.