Thermophysical Properties of Propellants

Abstract

The determination of the thermophysical properties of some solid propellants have been made. The two thermal properties measured were specific heat and thermal diffusivity. The specific heat was measured by using a differential scanning calorimeter (DSC) and thermal diffusivity was measured by the flash diffusivity method. The samples used included both single crystal and pressed powders of ammonium perchlorate (AP), HMX and RDX.

The measurements of the propellants’ specific heat required the modification of both the DSC equipment and the technique to accommodate the decomposition products from the samples. A flow-through cover was installed for this purpose. The computerized control and analysis for the DSC was also changed. The specific heat of AP, HMX and RDX was measured using both small single crystals and small amounts of powder. The specific heat of the HMX in both its normal phase (beta) and the delta phase were obtained. There proved to be little difference in the specific heat between these two phases of the HMX.

The thermal diffusivity of HMX in pressed powder form was determined. It was necessary to develop a method of holding powdered samples so that propellants would not see the laser pulse directly in order to avoid excessive temperature rises or radiant energy transmission. A cup was designed to allow the powder to be pressed into it and to not allow an alternate heat path when the sample was under test.