The most abundant material on Earth exhibits some unusual chemical properties
when placed under extreme conditions.
Lawrence Livermore National
Laboratory scientists have shown that water, in hot dense environments,
plays an unexpected role in catalyzing complex explosive reactions. A catalyst
is a compound that speeds chemical reactions without being consumed. Platinum
and enzymes are common catalysts. But water rarely, if ever, acts as a catalyst
under ordinary conditions.
Detonations of high explosives made up of oxygen and hydrogen produce water
at thousands of degrees Kelvin and up to 100,000 atmospheres of pressure, similar
to conditions in the interiors of giant planets.
While the properties of pure water at high pressures and temperatures have
been studied for years, this extreme water in a reactive environment has never
been studied. Until now.
Using first-principle atomistic simulations of the detonation of the high explosive
PETN (pentaerythritol tetranitrate), the team discovered that in water, when
one hydrogen atom serves as a reducer and the hydroxide (OH) serves as an oxidizer,
the atoms act as a dynamic team that transports oxygen between reaction centers.
“This was news to us,” said lead researcher Christine Wu. “This
suggests that water also may catalyze reactions in other explosives and in planetary
This finding is contrary to the current view that water is simply a stable
“Under extreme conditions, water is chemically peculiar because of its
frequent dissociations,” Wu said. “As you compress it to the conditions
you'd find in the interior of a planet, the hydrogen of a water molecule starts
to move around very fast.”
In the molecular dynamic simulations using the Lab's BlueGene L supercomputer,
Wu and colleagues Larry Fried, Lin Yang, Nir Goldman and Sorin Bastea found
that the hydrogen (H) and hydroxide (OH) atoms in water transport oxygen from
nitrogen storage to carbon fuel under PETN detonation conditions (temperatures
between 3,000 Kelvin and 4,200 Kelvin). Under both temperature conditions, this
“extreme water” served both as an end product and as a key chemical
For a molecular high explosive that is made up of carbon, nitrogen, oxygen
and hydrogen, such as PETN, the three major gaseous products are water, carbon
dioxide and molecular nitrogen.
But to date, the chemical processes leading to these stable compounds are not
The team found that nitrogen loses its oxygen mostly to hydrogen, not to carbon,
even after the concentration of water reaches equilibrium. They also found that
carbon atoms capture oxygen mostly from hydroxide, rather than directly from
nitrogen monoxide (NO) or nitrogen dioxide (NO2). Meanwhile water disassociated
and recombines with hydrogen and hydroxide frequently.
“The water that comes out is part of the energy release mechanism,”
Wu said. “This catalytic mechanism is completely different from previously
proposed decomposition mechanisms for PETN or similar explosives, in which water
is just an end product. This new discovery could have implications for scientists
studying the interiors of Uranus and Neptune where water is in an extreme form.”
The research appears in the premier issue (April 2009) of the new journal Nature