Yorkshire Philosophical Society

Event Information

Explosives: The Past, Present and Future

Professor Jackie Akhavan, Head of the Centre for Defence Chemistry, Cranfield University.

This event will be preceded by a poster display and wine reception in the atrium, from 6.15 to 7pm, and an associated prize-giving at 7pm in Tempest Anderson Hall. See separate announcement. Please note that members arriving for the lecture between 7 and 7.30 pm will be invited to remain in the atrium until the presentation finishes. Folding seats will be available, and they will have the opportunity to view the posters, which will still be on display.

Explosives have been part of our lives for many years with the first recording of an explosive powder being used in China in 220 BC. In the 13^th Century Roger Bacon experimented with explosives by making black powder and by the end of the 13^th Century explosives were being used by many European countries.   Nowadays explosives are part of our everyday life; they are in airbags, ejector seats and fireworks as well as propulsion for space shuttles, demolition aids and under water cutting charges for off-shore gas lines.

Professor Jackie Akhavan introduces the various types of explosions and explains the conditions under which a chemical reaction becomes an explosive.  She explores the inputs to initiate the explosive and the subsequent outputs.  In looking at the past she covers explosive mixtures and then introduces the concept of molecular explosives which are used today.   Looking into the future she highlights current research activities.

Professor Jackie Akhavan is a Professor of explosives chemistry at Cranfield University and she is the Head of the Centre for Defence Chemistry.  She is a Fellow of the Royal Society of Chemistry and a Fellow of the Institute of Explosive Engineers.   Her expertise is in high explosives which includes polymer bonded explosives and pastes, synthesis of energetic polymers by flow nitration and synthesis of smart polymers for detection of explosives, and control of particle size by spray drying.  The unique facilities at Cranfield University allows Professor Akhavan and her team to manufacture up to ½kg of explosives, carry out safety and hazards tests as well as performance trials.

Member’s report

Explosions come in many forms – physical, chemical, nuclear. All involve rapid release of energy. Prof. Jackie Akhavan’s work at the Centre for Defence Chemistry focusses primarily on chemical explosions. In an enthralling talk, Jackie led us through the history of chemical explosives.

A chemical explosion is essentially an extremely rapid burning, or oxidising, process. A massive release of energy results in the rapid expansion of hot gas and a shock wave: an explosion. The power output of a candle may be around 50W; that of a much smaller amount of explosive ‘burning’ much more rapidly can be many hundreds of millions of times greater.

Early chemical explosives, such as the ‘black powder’ with which Roger Bacon experimented in the 13^th Century, consisted of a mixture of carbon and sulphur, with saltpetre (Potassium nitrate) as the oxidising agent. For centuries, the main improvements in this were devoted to increasing the speed of the reaction, mainly by reducing the grain size of the mixture. Dampening the mixture during production allowed the soluble saltpetre to penetrate the grains of carbon and sulphur, this more intimate mix resulting in a more rapid reaction.

In the 19^th and, particularly, 20^th centuries the intimacy of oxidant and substrate was further increased, with the two being made part of the same molecule: nitroglycerine, TNT (trinitrotoluene), guncotton, cordite, RDX.

As Jackie pointed out, not all explosives are military, or even destructive. Airbags, ejector seats and fireworks are just a few examples that depend on explosives. The talk was punctuated by film clips of a variety of explosives, of which perhaps the most spectacular was of a large aircraft deploying a pyrotechnic display of flares to distract heat-seeking missiles.

Peter Hogarth