3D-Printed Thermite Brings The Heat, And The Safety

Thermites are a double-edged sword. Packing a tremendous energy density, and eager to produce tremendous heat when ignited, thermite is great for welding train tracks. But sometimes you might be looking for a little more finesse. A new approach to 3D printing thermites might just be able to tame the beast.

Most of us do our soldering while sitting safely indoors in a comfortable climate. The biggest dangers we’re likely to face are burnt fingertips, forgetting the heat shrink, or accidentally releasing the smoke monster. But outside of our homes and workshops, there’s a lot of extreme joining of metals going on. No matter where it’s done, welding and brazing in the field requires a lot of equipment, some of which is unwieldy and even more difficult to move around in harsh conditions.

Welding railroad tracks with thermite. Image via YouTube

The utility of brazing is limited by all the complex scaffolding of hardware required to support it. This limiting factor and the discovery of thermite led to exothermic welding, which uses an energetic material to provide enough heat to melt a filler metal and join the pieces. Energetic materials can store a lot of chemical energy and forcefully release it in a short period of time.

Thermites are made of metal oxide and metal powder, often iron oxide and aluminium. When ignited by a source of high heat, thermite compounds undergo an exothermic reduction-oxidation (redox) reaction as the aluminium reduces the number of electrons in the iron oxide atoms. More heat makes the reaction run faster, generating more heat, and so on. The result is molten iron and aluminium oxide slag.

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Retrotechtacular: Disposing Of Sodium, 1947-Style

A high school friend once related the story about how his father, a chemist for an environmental waste concern, disposed of a problematic quantity of metallic sodium by dumping it into one of the more polluted rivers in southern New England. Despite the fact that the local residents were used to seeing all manner of noxious hijinx in the river, the resulting explosion was supposedly enough to warrant a call to the police and an expeditious retreat back to the labs. It was a good story, but not especially believable back in the day.

After seeing this video of how the War Department dealt with surplus sodium in 1947, I’m not so sure. I had always known how reactive sodium is, ever since demonstrations in chemistry class where a flake of the soft gray metal would dance about in a petri dish full of water and eventually light up for a few exciting seconds. The way the US government decided to dispose of 20 tons of sodium was another thing altogether. The metal was surplus war production, probably used in incendiary bombs and in the production of aluminum for airplanes. No longer willing to stockpile it, the government tried to interest industry in the metal, but to no avail due to the hazard and expense of shipping the stuff. Sadly (and as was often the case in those days), they just decided to dump it.

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