More than 500 million people live in the shadow of a volcano, but predicting an eruption can be tricky. Forecasts based on periodic gas sampling could be improved with the volcanic equivalent of a breath tester that picks up changes in the composition of gases spewing from its vent.
Most instruments would melt if placed inside the mouth of a volcano, but Alton Horsfall and Nick Wright at the Centre for Extreme Environment Technology at Newcastle University, UK, have been using silicon carbide to create electronic components that can venture where no instruments have ever gone before. "Silicon's a wonderful material to about 175 °C and then it goes horribly wrong, whereas silicon carbide runs to around 600 °C on a practical level," explains Horsfall.
Silicon carbide's ability to withstand high-temperature and high-radiation environments comes from the exceedingly strong bonds between the silicon and carbon atoms, but these tough properties also make it difficult to work with and expensive to manufacture.
Now Horsfall and Wright have managed to manipulate silicon carbide into viable electronic components. "The sensors are sensitive to oxygen, hydrogen, hydrogen sulphide and sulphur dioxide, that we've tested so far, and can achieve a sensitivity of the order of 10 parts per million," says Horsfall. Although there are still issues with cross-sensitivity, Horsfall hopes to have sensor arrays that can identify unique gases in a mixture within a year.
The next challenge is to integrate them into a device about the size of a smartphone. "Ultimately we hope the devices will be self-powered, using energy-harvesting technologies such as solar cells," says Horsfall.
Such devices could be used in a multitude of dangerous locations; monitoring radioactivity in nuclear waste storage sites, for example, or tracking the pollution inside a jet engine or car exhaust.
In the case of volcanoes, Horsfall and Wright envisage leaving an instrument at the lip of a gas vent to continuously monitor the emerging gases. A radio-frequency transmitter will send the results back to volcanologists in a lab.
Changes in the composition of volcano breath can be a clear sign of imminent eruption; for example, emissions of sulphur increased by an order of magnitude prior to the eruption of mount Pinatubo in the Philippines in 1991. And although we can't stop volcanoes from erupting, a forewarning can provide vital time to prepare.
Horsfall presented the research at the Extreme III Technology Showcase Event at Newcastle University last week.
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