(78a) Lifetime Expectancy of (slowly) Autocatalytic Decomposing Materials

A large number of materials and substances show decomposition reactions during handling, production and transport. The amount of heat and pressure generated during this decomposition will determine if a substance can be considered thermally stable in a specific packaging size and temperature. Often the so called Self Accelerating Decomposition Temperature (SADT) is calculated for materials showing decomposition. This temperature is defined as the temperature at which the amount of heat produced by the decomposition reaction is equal to the heat loss of its packaging. For materials decomposing according to a pseudo zero order reaction (Arrhenius like reactions) this method can be considered correct. For materials showing autocatalytic decompositions the amount of heat generated is dependent on product lifetime and the conditions it was exposed to, which we will call history. This is in sharp contrast to the constant heat production that is shown in case of a pseudo zero order reaction.

In order to calculate a conservative value for the SADT of autocatalytic decomposing materials the heat generated at the maximum speed of the reaction should be used. The speed of decomposition varies a lot among different autocatalytic decomposing materials the under storage conditions. The time it takes to reach critical levels of heat production can vary between hours to years depending on the type of material. For these type of materials it is not relevant to determine the temperature at which self-heating occurs, but the time it takes to reach a critical level of heat production at a certain temperature and package size.

This paper will first discuss the flaws of the different methods to determine the SADT in case of autocatalytic decomposing materials. Secondly a method is proposed to determine the life time expectancy of autocatalytic decomposing materials, taken into account for the history of the material.