The most common substance on Earth exhibits a number of unusual chemical properties when it is found in extreme conditions.
Scientists from the Lawrence Livermore National Laboratory have shown that water, in compressed heat environments, serves an unexpected role as a catalyst for complex explosive reactions. A catalyst is a compound that accelerates chemical reactions without consuming it during the reactions. The metal platinum and enzymes are examples of common catalysts. But water, if at all, is only rarely used as a catalyst under normal conditions.
An explosion of TNT containing oxygen and hydrogen results in the creation of water at a temperature of thousands of degrees and a pressure of up to one hundred thousand atmospheres - conditions similar to those prevailing in the center of giant planets.
While the properties of pure water at high pressures and temperatures have been studied for many years, this extreme form of water in an active environment has never been studied - until now.
Using atomistic simulations of the detonation of the explosive PETN (pentaerythritol tetranitrate), the team discovered that in water, when a hydrogen atom serves as a reducer and the hydroxide serves as an oxidizer, the atoms act as a dynamic team that moves an oxygen atom between the reaction centers.
"This was news to us," said lead researcher Christine Wu. "These findings suggest that water may catalyze reactions in the activity of other explosives and in the cores of planets." These findings are in contrast to the popular view that water is only a stable explosion product.
"Under extreme conditions, water becomes a strange chemical form due to its frequent ability to decompose," said the researcher. "When you compress them into a situation similar to that in which they are found in the core of planets, the hydrogens of the water molecules start to move very quickly."
In the molecular dynamics simulations, the researchers found that the two forms, hydrogen and hydroxide, transfer oxygen from a nitrogen source to carbon fuel under the conditions of the PETN explosion (temperature of 4000-3000 Kelvin). At these temperatures this extreme form of water serves as both the final product and an important chemical catalyst.
For molecular explosives composed of carbon, nitrogen, oxygen and hydrogen, such as PETN, the three end products are the gases: water, carbon dioxide and molecular nitrogen. However, to date the chemical processes leading to these stable compounds are not clear enough.
The research team discovered that nitrogen transfers the oxygen on it mainly to hydrogen and not to carbon, even after the concentration of the water reaches equilibrium. They also noticed that carbon atoms capture the oxygen atoms mainly from the hydroxides, and not directly from the nitrogen forms present in the system: nitrogen monoxide or dioxide. Meanwhile, water breaks down and often combines into its components: hydrogen and hydroxide.
"The water coming out of the reaction is part of the energy release mechanism," says the lead researcher. "This accelerated mechanism is completely different from previous discharge mechanisms proposed by researchers for PETN or similar explosives, in which water is only a final product.
This new discovery has important implications for scientists studying the cores of the planets Uranus and Neptune, where water exists in its extreme form."
The research findings appear in the first issue (April 2009) of the new scientific journal Nature Chemistry.
