Sunday, June 3, 2007

48. Tunneling/Drilling materials


Mark said...

surely a non=flammable explosive is interesting here, regardless of its current uses mentioned below; it's production without the oxidizer requirement may be more sustainable and less polluting

Terrorist Explosive Blows Up Without Flames
By Jenny Hogan

An explosive sometimes used by terrorists does not burn when it detonates. Instead, its molecules simply fall apart. The chemist who has discovered this is so concerned by its implications that he has decided to abandon this line of research.

Triacetone triperoxide (TATP) has been used by suicide bombers in Israel and was chosen as a detonator in 2001 by the thwarted "shoe bomber" Richard Reid. Now calculations by Ehud Keinan from the Technion-Israel Institute of Technology in Haifa show that most of its explosive force comes from a rapid release of gas rather than a burst of energy.

In conventional high explosives such as TNT, each molecule contains both a fuel component and an oxidising component. When the explosive detonates, the fuel part is oxidised and as this combustion reaction spreads it releases large amounts of heat almost instantaneously.

TATP molecules are made up of fragments that could react in a similar way. But Keinan says that videos showing samples of TATP being detonated show that it can do so without producing any flame.

Oxygen and ozone

His team's calculations indicate why. Explosions are driven by the reaction that takes the least energy to start. In this case it is not oxidation but disintegration. The TATP molecule sheds acetone units, setting free the oxygen atoms that bound them together to form the gases oxygen and ozone. It also releases just enough energy to spread the reaction to the next molecule.

One molecule of TATP produces four of gas, giving TATP its explosive power. Just a few hundred grams of the material will produce hundreds of litres of gas in a fraction of a second.

"It's different to conventional explosives," agrees Jimmie Oxley, a chemist at the University of Rhode Island in Kingston, US, who has studied TATP and worked with Keinan on other projects. But it is not unique. The decomposition of azide, for example, which produces nitrogen gas but little heat, is used to fill airbags for cars.

TATP turns out to be the most extreme example so far, and it may be possible to design molecules that behave as an even more powerful explosive. But the idea does not appeal to Keinan. "I don't want to continue this kind of research," he says. Instead, he plans to work with security agencies to develop a device that can detect TATP.

- Journal reference: Journal of the American Chemical Society (DOI: 10.1021/ja0464903)

Mark said...

[gee, all we wanted: wars that are 'green' will make wars more prevalent...though good for construction forms of explosives.]

Environmentally Friendly Bombs Planned

By Charles Q. Choi, Special to LiveScience

posted: 27 May 2008 08:32 am ET

Biochemists report that a full detonation of a sample of a new type of nitrogen-rich explosive produces fewer toxic byproducts and is easier to handle than its carbon-rich counterparts.

Credit: Courtesy of Michael Goebel, Ludwig-Maximilians University

Biochemists report that a full detonation of a sample of a new type of nitrogen-rich explosive produces fewer toxic byproducts and is easier to handle than its carbon-rich counterparts.

Credit: Courtesy of Michael Goebel, Ludwig-Maximilians University

New explosives could be more powerful and safer to handle than TNT and other conventional explosives and would also be more environmentally friendly.

TNT, RDX and other explosives commonly used in military and industrial applications often generate toxic gases upon detonation that pollute the environment. Moreover, the explosives themselves are toxic and can find their way into the environment due to incomplete detonation and as unexploded ordnance. They are also extremely dangerous to handle, as they are highly sensitive to physical shock, such as hard impacts and electric sparks.

To make safer, more environmentally friendly explosives, scientists in Germany turned to a recently explored class of materials called tetrazoles. These derive most of their explosive energy from nitrogen instead of carbon as TNT and others do.

Tiny bombs were made from two promising tetrazoles with the alphabet-soup names of HBT and G2ZT. These materials proved less apt to explode accidentally than conventional explosives.

After the bombs were detonated in the laboratory, G2ZT also proved as powerful than TNT, and HBT more powerful than TNT and comparable to RDX, said researcher Thomas Klapötke, a chemist at the University of Munich in Germany.

In initial experiments, G2ZT and HBT produced fewer toxic byproducts than common explosives. Still, they did generate some dangerous hydrogen cyanide gas. But mixing these compounds with oxidizers not only avoids making hydrogen cyanide, but also improved performance, Klapötke said.

These compounds have great potential, "especially for large caliber naval and tank guns," Klapötke added.

Klapötke and his colleague Carles Miró Sabate are scheduled to detail their findings in the June 24 issue of the journal Chemistry of Materials.

The research was financially supported by the Ludwig-Maximilian University of Munich, the Fonds der Chemischen Industrie, the European Research Office of the U.S. Army Research Laboratory, the U.S. Army's Armament Research, Development and Engineering Center, and the Bundeswehr Research Institute for Materials, Explosives, Fuels and Lubricants.