Parr Instruments

Ordinary oxygen bomb combustion calorimetry is used to measure the heat of combustion or reaction of materials in oxygen or inert atmospheres. Even for high strength vessels, such as the Parr 1104 Oxygen Combustion Bomb, the conditions necessary to detonate small amounts of highly reactive materials are often difficult to achieve and can result in unpredictable consequences. For example, the conventional heat of combustion of pentaerythritol tetranitrate (PETN) [C5H8N4O12] in oxygen is 1957 cal/g while the heat of detonation in vacuum is 1490 cal/g (a 24% difference). Additionally, it is well known that the degree of confinement of explosive materials significantly influences the released energy. For unconfined or lightly confined charges, the released energy is largely retained in the products. When the charge is heavily confined, the detonation energy, for the most part, is converted to kinetic and internal energy of the confining case. For example, the conventional heat of combustion of 2,4,6-trinitrotoluene (TNT) in oxygen is 3590 cal/g. The heat of detonation for TNT at a charge density of 1.53 g/cc is 1093 cal/g and at a charge density of 0.998 g/cc is 870 cal/g. In contrast, an unconfined reaction yields approximately 600 cal/g.