Researchers from the United Kingdom, France and the DUBBLE beamline at the
European Synchrotron Radiation Facility (ESRF) have made a step forward in
research on glass. They have monitored the change in the structure of
zeolites, crystalline solids, into an almost perfect glass when heated.
They have done this by recording vibrations involving groups of atoms in
zeolites that subsequently characterise the glass. Their results are
published in the last issue of Science.

Zeolites are porous crystalline aluminosilicates, presenting a regular
arrangement of cages. In their natural state, they are components of soils
and can be barriers against the migration of radioactive elements. In
their synthetic form, zeolites are industrially applied as components of
washing powders and in the cracking of petroleum to make gasoline.
Due to their cage structure, zeolites have a low-density structure. They
melt at around 900°C, lower temperatures than most similar materials, such
as silica (sand), which melts at twice this temperature. If the heating is
carried out at a slow rate, low-frequency vibrational modes are
responsible for destabilizing the microporous crystalline structure. When
the cages collapse, zeolites contract, becoming 60% more denseheavier than
in their original form, and they adopt the structure of a glass. “We have
discovered the triggering mechanism”, says Neville Greaves, first author
of the paper.

The result is a mechanically and chemically stronger glass than the glass
used nowadays. “We believe this is the key to the synthesis of perfect
glasses”, asserts Neville Greaves. Would this mean no more broken wine
glasses? “This research could lead to that, but it is still far away. This
would also mean making glass invulnerable to water, for instance”, he
explains. The final aim is to find out the conditions in which the perfect
glass forms.

Scientists from the University of Wales, Aberystwyth, the DUBBLE beamline
at the ESRF, the Ecole Nationale Supérieure de Chimie of Paris (ENSCP) and
ISIS have characterized the low-frequency vibrations that appear in
zeolites during heating. The team has carried out their research in
neutron as well as X-ray facilities. ISIS is a neutron and muon source
located in the UK and a large part of the research presented was done
there. The researchers also used a unique X-ray diffraction technique on
the Dutch-Belgian beamline (DUBBLE) at the ESRF to determine the degree of
crystallinity from zeolites to glass, critical to evaluate the neutron
scattering results. “It is really great to combine synchrotron and neutron
techniques in the same observation”, explains Greaves.