Spontaneous ignition of wool. III. Calorimetry of slow oxidation reactions in materials of low thermal conductivity

Abstract

AbstractA method is described for calorimetry of oxidation reactions in porous materials of low thermal conductivity. The generated heat is allowed to flow through a thermal resistance composed of the sample itself, and measurement is made of the resulting temperature drop. If the thermal conductivity of the sample material is known, the reaction rate can be calculated. This method has advantages over conventional techniques of calorimetry since errors tend to be a proportional part of the quantity being measured, rather than a fixed error due to drift. This provides experimental simplicity at low rates of heat output, and the ability to operate over a range of temperatures. The reactant atmosphere can be replenished continuously. The method was used to measure the temperature coefficient of the reaction between dry pie wool and dry air, using calculated values of thermal conductivity. Measurements were made at reaction rates as low as 7 × 10−6 cal./sec./g. Even if the thermal conductivity of the material is not known, this method measures the ratio of reaction rate to thermal conductivity; and this ratio is of more fundamental importance in the spontaneous ignition of large piles of material than is the reaction rate itself.