Flame retardants: inorganic oxide and hydroxide systems

Abstract

This category of flame retardants contains the two major additive flame retardants in use today — aluminium trihydroxide, A1(OH)3 and antimony trioxide, Sb2O3. The broad discussion is best separated into two parts. First we shall consider metal hydroxides, which in general decompose endothermically to liberate water. They are normally smoke suppressants and work predominantly in the condensed phase of combustion. Secondly, we shall deal with metal oxides, which are only smoke suppressants in specific circumstances and find greatest use as‘ synergists’ in conjunction with other flame retardant additives, notably those containing the halogens chlorine and bromine. As such they are often vapour phase flame retardants. Two noteworthy additives, or rather families of additives, the zinc borates and zinc stannates, fall into both categories. These are, for convenience, discussed under ‘Metal oxides’ below, although borates will be discussed more fully in a separate entry.