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Scientists Solve the Molecular Puzzle of 'Flammable Ice'

Flame on! An unusual type of icy crystal has energy to burn.
(Image: © USGS)

Scientists have solved a molecular puzzle explaining the natural formation of gas hydrates, a type of flammable crystal also known as "the ice that burns."

Gas hydrates form when pockets of gas are locked in a cage of ice molecules. They form deep underground, mostly beneath the ocean floor but in some cases under permafrost, under high pressure and extreme cold according to the U.S. Geological Survey (USGS). If the hydrates decomposed, they would release the caged gas — a natural gas that would burn if exposed to a flame.

And though this flammable ice is widespread in clay-rich ocean sediments surrounding the continents, little was known about how it formed in minerals in these sediments. That's because the minerals' saltiness and pore size were thought to hinder gas hydrates from taking shape.

So, Taehyung Park and Tae-Hyuk Kwon, of the Korea Advanced Institute of Science and Technology, set out to investigate these conditions, according to a new study.

To do so, the researchers simulated this initial formation of gas hydrates, called gas hydrate nucleation, by applying an electric field to those clay-rich oceanic sediments.

Their research gave them new insights into this burning question, revealing the interactions in the clay that allow flammable ice crystals to emerge, the study authors wrote. [Greenhouse Gas Emissions: Causes & Sources]

"We found that gas hydrate nucleation is remarkably enhanced by surface charge on clay minerals," Park told Live Science in an email.

Since clay minerals are negatively charged, their electrochemical interaction with water is what sparks gas-hydrate formation, the study authors reported. 

Gas hydrates, which are mostly made up of methane hydrate, were discovered in the late 19th century, and for decades, they were merely seen as a pesky byproduct that accumulated in pipelines and obstructed the flow of oil and gas, according to the USGS. Since the 1980s, gas hydrates have generated keen interest worldwide as a potential energy source.

Gas-hydrate reservoirs are thought to hold energy stores surpassing the potential energy output of all the coal, oil and gas in the world, and plans by the U.S. government  to unlock these reserves have been lauded as capable of reducing the price of natural gas by as much as 30 percent, Live Science previously reported.

But the deposits, though widespread, are difficult to find; unlike gas and oil, gas hydrates are not concentrated in one area, making them a challenge to identify and extract.

In addition, extracting this combustible energy source could carry the risk of releasing stored greenhouse gases on an enormous scale, potentially accelerating the pace of human-induced climate change.

Understanding the link between clay minerals and gas hydrates will likely play a vital part in efforts to extract methane from hydrate deposits, and could even inform investigations into using ocean sediments for carbon dioxide storage, the scientists reported.

The findings were published online Feb. 8 in the journal Environmental Science and Technology.

Original article on Live Science.