THERMAL-BEHAVIOR OF CHLORINE-ANTIMONY FIRE-RETARDANT SYSTEMS

The reactions which lead to SbCl3 on heating typical Sb2O3-organic chlorocompounds synergistic fire-retardant systems have been studied. It has been shown that the process takes place through antimony oxychlorides, either by their chlorination or thermal disproportionation. In particular, of the three existing oxychlorides (Sb8O11Cl2, Sb4O5Cl2, SbOCl), only Sb4O5Cl2 is readily detected in the range 400-700°C. Indeed, the oxychloride with least chlorine, Sb8O11Cl2, formed by chlorination of Sb2O3 or by thermal disproportionation of Sb4O5Cl2 together with SbCl3, seems to be rapidly chlorinated to Sb4O5Cl2. This last undergoes a relatively slower chlorination reaction to form volatile SbCl3, possibly through intermediate SbOCl which, however, cannot be detected because of its rapid disproportionation to Sb4O5Cl2 and SbCl3. Thus, Sb4O5Cl2 accumulates as a result of these reactions and it becomes the main direct supplier of antimony, as SbCl3, to the gas phase. This mechanism is also found to take place in a burning polypropylene matrix. © 1990.