Art Bohanan of the Knoxville Police Department was investigating the
abduction and murder of a girl from eastern Tennessee when the problem came to
light. Witnesses had seen the victim enter the suspect’s car, but none of her
fingerprints could be found.

Bohanan suspected that children’s prints may generally be difficult to
detect. Although in this case the child was the victim, Bohanan realised that in
a juvenile crime wave a similar lack of prints would give forensic scientists a
tough time.

Bohanan turned to Michelle Buchanan of Oak Ridge’s Chemical and Analytical
Sciences division for help. Buchanan asked volunteers between the ages of 4 and
17 and 19 and 46 to shake vials of alcohol between their thumb and forefinger.
The alcohol washed chemicals off the skin, which Buchanan then analysed using a
mass spectrometer.

The two groups showed a marked difference. “Children’s fingerprints contain
more volatile chemicals,” says Buchanan, “while adult prints display
longer-lasting compounds.” Buchanan reported her findings last week to delegates
at the American Chemical Society meeting in San Francisco.

Quasam is made up of flat planes of carbon atoms, like those found in
graphite, joined together in a three-dimensional lattice similar to that of
diamond by a network of silicon and oxygen atoms. “The combination of sp²
planes [carbon atoms with three bonds] and a three-dimensional sp³ network
[carbon atoms with four bonds, as in diamond] gives Quasam the strongest
features of both,” says Benjamin Dorfman, a materials chemist with Atomic Scale
Design in New York and the inventor of the new material. As a result, Quasam has
a density between 1.35 and 1.65 grams per cubic centimetre, less than half that
of diamond. Its hardness, up to 57 gigapascals, is around the lower end of the
hardness range for diamond. Dorfman presented his work at a meeting of the
Materials Research Society in Boston last month.

Quasam is made by fragmenting a simple organic compound containing carbon,
silicon and oxygen. The resulting charged ion-radicals are accelerated by an
electrical field onto a heated silicon-based material, where they split apart
and form new bonds. Because the planes in Quasam are bonded together by a
diamond-type lattice, Quasam is not a soft, lubricating material like graphite,
in which large planar sheets of carbon atoms slip past each other. Instead, it
contains only very small planes held rigidly in place, because the network of
silicon and oxygen atoms prevents larger graphite planes forming. Pure Quasam is
an electrical insulator, but it can incorporate within its lattice up to 40 per
cent by volume of other metals, such as iron and nickel, and can be made into a
good conductor.

The new material has a number of other useful properties. It is
highly resistant to chemical attack, and has the highest fracture toughness of
its family of materials. Most importantly, Quasam has virtually unchanging
mechanical properties and a constant thermal expansion coefficient—meaning
that it expands regularly with temperature—up to at least 400 °C. This
means that micro-mechanical sensors built from Quasam could guarantee an
accurate reading over a wide temperature range. Dorfman says he can produce the
material faster than the diamond-like carbon that is commonly used as a
coating.

Other researchers are excited by the discovery. “[Its] novelty
seems to be the incorporation of silica and metals,” says Paul May of the
University of Bristol, whose team is also working on diamond-like carbon
materials.

The device, called a Microlith, is fitted between the engine and a standard
catalytic converter. It consists of a series of squat metallic discs, or
monoliths, made from a coated metal alloy riddled with small pores or channels.
These channels are much shorter than those in the ceramic or metallic filters
used in standard converters: they have a ratio of channel length to diameter of
less than 5, compared with between 75 and 150 for ordinary converters.

When gas flows over a surface, a boundary layer of still gas builds up. The
longer the flow path, the thicker the boundary layer. In catalytic converters
the pollutant molecules must diffuse through this layer to get to the catalytic
surface of the monolith, which breaks them down. A thick boundary layer makes
this more difficult.

Because the channels through the Microlith’s disc-shaped monoliths are short,
the boundary layer is kept thin. This has the extra benefit of allowing heat
from the exhaust gas to spread into the catalyst more quickly, so it reaches its
operating temperature sooner. The short flow path “results in heat and mass
transfer coefficients an order of magnitude greater than for typical monoliths”,
says Bob Carter, one of the team’s development engineers.

As well as getting to work much faster than a conventional monolith, a
Microlith can convert the same amount of a test exhaust gas as a conventional
unit over 20 times as big, Carter and his colleagues have found. They say this
improved performance also depends on a specially developed coating, the details
of which are being kept secret.

The company has found that the performance of the Microlith “preconverter”
does not deteriorate with age and operation. “After 50 000 miles of engine
ageing this combination converter is [still] able to lightoff in less than 15
seconds,” says Subir Roychoudhury, leader of the development team. This means
that cars fitted with the Microlith and a standard converter meet the US’s
strictest emissions standard even after thousands of miles of motoring.

Rodriguez envisages the nanofibres packed into a cartridge containing enough
hydrogen to power an electric car for up to 8000 kilometres. Spent cartridges
could be exchanged for new ones and refilled.

The vehicles would be driven by fuel cells, in which the hydrogen combines
with oxygen to produce an electric current. A prototype vehicle based on
fuel-cell technology, the Necar II, was unveiled last May by Daimler-Benz. It
stores the hydrogen in pressurised gas cylinders (“A tank of the cold stuff”,
żěè¶ĚĘÓƵ, 23 November 1996, p 40). Several states in the US are
demanding that 2 per cent of cars on the market in 1998 have zero emissions, and
hydrogen cars, which only produce water vapour, would fit the bill.

Quite how the graphite nanofibres store so much hydrogen is not totally
clear. Even carbon nanotubes, which are being developed by a team led by Michael
Heben at the National Renewable Energy Laboratory in Denver, cannot store
anywhere near the levels being claimed by Rodriguez’s team.

Heben says: “The best figure we have been able to achieve using nanotubes for
hydrogen storage is 4 per cent by weight. 300 per cent by weight of hydrogen
would indeed, if true, be very interesting.” He remains doubtful about the new
figures, however. “The highest ratio of hydrogen to carbon in nature is found in
methane, which would correspond to 25 per cent by weight,” he says.

If Rodriguez’s figures are correct, hydrogen could account for as much as 75
per cent of the weight of a graphite nanofibre cartridge.

The key to this impressive storage capacity is the regular, closely packed
structure of the graphite nanofibres. The fibres are made from stacks of
graphite platelets and vary from 5 to 100 millimetres in length and from 5 to
100 nanometres in diameter.

Theoretical calculations of the hydrogen absorption capacity of
single-crystal graphite show that 6.2 litres of hydrogen per gram of graphite
could be achieved by covering the surface of the crystal in a single layer of
hydrogen molecules. The team at Northeastern University claims to have upped
this figure to 30 litres.

Rodriguez reckons the high capacity is due to several layers of hydrogen
molecules condensing inside the “slit pores” between the platelets by capillary
action. The spacing between the graphite layers is 0.34 nanometres, while
hydrogen molecules normally have an effective diameter of 0.26 nanometres. But
multiple layers of hydrogen could squeeze into the gap if the molecules were
interacting strongly with electrons in the graphite.

Terry Baker, a member of the team, says that when the hydrogen molecules are
absorbed, they lose a lot of their vibrational and rotational energy and
“shrink” to an effective radius of 0.064 nanometres. This leaves plenty of room
for more hydrogen molecules. “We probably produce about five layers,” says
Rodriguez.

The narrow slits stop oxygen and other larger molecules from squeezing in,
and this minimises the chance of an explosive reaction. Safety will still be a
major consideration, however. “I imagine some protection would be required for
the cartridge,” says Rodriguez.

Baker discovered graphite nanofibres as long ago as 1972 when he was working
for Britain’s Atomic Energy Authority at Harwell, but it is only recently that
Rodriguez’s team has developed a process for making large amounts of them. They
will not give too much away, but Baker will say that the process involves
reacting hydrocarbons with carbon monoxide on bi- or tri-metallic nickel or
iron-based catalytic particles. “The material itself will not be all that
expensive,” he says. “When the process is scaled up, it will cost less than
$1 per kilogram.”

To pump the nanofibres full of hydrogen, they must first be washed with acid
to remove metal impurities from the catalyst particles, and then heated to
over 900 °C and placed under a vacuum to remove any gases already clogging
up the slits. Hydrogen is then pumped in at an initial pressure of around 120
atmospheres. Rodriguez says it can take between 4 and 24 hours to fully charge
them up.

The pressure must then be maintained at 40 atmospheres to keep the
hydrogen in place, and the gas can be released by gradually reducing the
pressure. According to Rodriguez, the nanofibres can be refilled to the same
capacity at least 4 or 5 times.

Rodriguez presented the group’s findings at the annual Materials
Research Society meeting in Boston, Massachusetts, earlier this month.

The Sea of Galilee, also known as Lake Kinneret, is fed by the River Jordan,
which carries very little salt. “It comes into the lake carrying 20 milligrams
of chloride per litre,” says Michael Krom, a geochemist at the University of
Leeds. But water also enters the sea from springs, some of which are highly
saline.

Two decades ago, overground springs on the western shore were diverted away
from the lake, helping to reduce the level of chloride ions from 385 to 240
milligrams per litre. But this is still much too salty to drink. Water from the
lake provides 30 per cent of Israel’s needs, but must be diluted with purer
water before being added to the national supply. The water is also used to
irrigate crops in the Negev desert, where the salt collects in the soil.
Flushing away this salty crust costs Israel millions of gallons of precious
clean water each year.

Krom and his Leeds colleague Robert Mortimer, working with Ami Nisri of the
Lake Kinneret Research Laboratory and Mira Stiller of the Weizmann Institute of
Science in Rehovot, believe they have now discovered why the Sea of Galilee
remains so salty.

“All of the mud at the bottom of the lake has salt oozing out through it,”
says Krom. “In a number of places, springs punch through it. We’ve found three
so far, one of which is very strong.”

To detect the springs, the researchers dropped a probe containing
polyacrylamide gel into the mud on the lake bed, where it absorbed ions. Back at
the surface, the gel was sliced very thinly, and each slice was placed in fresh
water to release its ions. This gave an accurate measurement of the ion
concentration at different levels in the mud. “One sample went from 250
milligrams of chloride per litre on the bed of the lake to 10 000 milligrams per
litre just 10 centimetres down in the mud,” says Krom.

The researchers say that local fisherman could have served as good guides to
the location of the salty springs. “For some reason, fish like to gather around
them,” says Nisri. “It’s probably that they prefer the slightly higher
temperature of the water, rather than liking the more saline environment.”

Krom and his colleagues are now working out which springs to cap to achieve
the most rapid reduction in the sea’s salinity. “In practice we can’t stop all
the springs,” he says. But Israel’s Water Commission has set a target of
reducing the lake’s salinity to below 150 milligrams per litre.

Exactly how the springs might be capped has not yet been worked out, so the
researchers cannot say whether the commission’s target is attainable.