12 November, 2013

"We'll start by making some gunpowder"

A quote from the lecture on Thursday evening, entitled "The Science of Fireworks and Explosives", which I attended with a few people from work. Prof. Chris Bishop was the master of ceremonies, and he did indeed make some gunpowder, firing a Brown Bess gun at the end of the lecture (loaded only with wadding)!

The lecture was advertised as a "family lecture", with "loud bangs, bright flashes, and some smoke". The fumehood used during the lecture just about dealt with the smoke, but did start giving out (beeping) towards the end of the lecture, when the accumulated smoke from the displays started to get too much. Even though it was aimed mostly at young people, I was engrossed by the displays, explanations and Bishop's red lab coat! The chemistry was explained in broad terms (sulphur=fuel, charcoal=fuel, saltpetre=oxygen), but there was interesting tidbits of information for those with a more in depth chemistry knowledge : Did you know a good ratio for gunpowder is 75:15:10 Saltpetre:Charcoal:Sulphur? It was explained that gunpowder produces quite a "soft" explosion (more of a "push", hence its use in fireworks, for example). But what if you want a proper bang/crack? The talk then moved on to metals, both in flash powder (metal fuel) and fireworks (colours). The predictable metal-salts-in-a-Bunsen-burner section was spiced up a bit by the use of methanol solutions of salts like SrCl (red), NaCl (orange), CaCl (orange) and CuCl (aquamarine). The MeOH spilled on to the floor at one stage, starting a small fire! Some of the parents looked a bit worried, but Chris's able assistant walked to the side of the stage to receive a fire blanket. (Waving it over the fire, rather than placing it carefully!)
Another picture from the lecture. This is of lycopodium powder being blown through a Bunsen flame.
 Then the main topic : fireworks. Types (four classes : 1. Indoor 2. Garden 3. Display 4. Professional), effects (white glitter, strobes, orange popping, screechers)

Finally nitrocellulose, dynamite, HMX tubing, nitrogen triiodide (very loud!)

This child exploded into just CO2 and water shortly after this photo

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