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Burning with a liquid flame.

Burning with a liquid flame

The word "burning' usually evokes an image of incandescent gases and flickering flames. Now Soviet scientists have discovered a material that burns with a liquid flame--a ball of light-red, glowing fluid that steadily grows as it skates across the material's surface while the material burns. Eventually, the ball reaches its maximum diameter and settles in the hollow created by its motion. Only traces of a white vapor that appear where the liquid ball touches the material's surface show that combustion continues. No gas flame is visible.

As reported in the Oct. 23 NATURE, the material is a compressed mixture of two substances: tetrazole and sodium tetrazolate. The experiments were done by a group of researchers at the Byelorussian State University in Minsk. Each sample consists of a solid cylinder, 20 millimeters in diameter and 30 mm in height. A red-hot wire is used to initiate combustion, which occurs both in air and in a nitrogen atmosphere.


At first, a molten layer forms on the material's surface, which gives off gaseous combustion products. Explosive sparking punctuates this layer. Then a 1-mm glowing liquid ball appears and, as it quickly skims the molten surface, gradually grows to 15 mm or more in diameter. The ball's internal temperature reaches 760| C, although tetrazole and sodium tetrazolate themselves are unstable at temperatures above 320| C.

The researchers found that they could stop the burning by turning the sample over or by blowing the ball off the surface. A cooled ball hardens into a light-gray, porous bead, indicating that the liquid ball contained gas bubbles. Analysis reveals the presence of sodium carbonate and complex nitrogen-carbon compounds. Nitrogen is the main gaseous product.

"The chemistry of the combustion process is unusual,' the researchers say. The glowing ball seems to dissolve the starting substances and absorb the tetrazole vapor. Conditions within the liquid ball allow the synthesis of heat-resistant sodium salts and polycylic nitrogen-carbon compounds.

"The liquid flame . . . allows substances to remain in the combustion zone for a long time,' say the scientists. "As a result, comparatively slow [chemical] processes, in particular polymerization, may take place in a liquid-flame reactor.'
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Title Annotation:compressed mixture of tetrazole and sodium tetrazolate
Publication:Science News
Date:Nov 8, 1986
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