A mechanism for the deflagration-to-detonation transition in ultrafine granular explosives

Research has been carried out into the mechanisms by which columns of ultrafine granular explosives undergo the deflagration-to-detonation transition (DDT). Unusual results have been obtained in columns of pentaerythritol tetranitrate (PETN) and cyclotrimethylene trinitramine (RDX) when the column density is below 50% of theoretical maximum density (TMD). Experimental evidence shows that these columns undergo a transition which does not include the compressive deflagrating stage that is a usual precursor to DDT. Instead a channel is created in the column by the gas given off during the initial burning. The eventual transition to detonation takes the form of a localized 'thermal' explosion occurring at some point on the column.