Development of in-situ surface area analysis for detonators

Abstract

The surface area and compaction properties of explosive powders are of fundamental importance to the performance and ageing characteristics of detonators. Detonators contain limited quantities of compacted powder and removal of the powder for analysis destroys the compact and prevents performance testing. Thus, information on the effect of any physical or chemical changes in the compact through life on performance of the detonator is lost. At AWE a novel detonator test system has been designed which allows in-situ surface area analysis of powder compacts prior to performance testing. Compacts are generated using the centrifugal technique originally designed by Burt and Fewtrell [BURT, M.W.G., FEWTRELL, C.A., (1970), The Preparation of Powder Beds by Centrifugal Compaction Technique, In Proc: Particle Size Analysis 1970, pp. 321–338.] to remove operator dependency in the preparation of powder beds for air permeametry. Both air permeametry and gas adsorption methods are being developed to fully characterise porosity and surface area of the compacts prior to, and post, accelerated ageing. Initial studies have been carried out with pentaerythritol tetranitrate (PETN), a common crystalline high explosive known to be easily affected by the outgassing routines normally employed for gas adsorption methods. This paper will discuss the design of the detonator test system, the development of the analysis methods and the relationship between powder properties and performance results obtained to date.