Download Crystals and Triboluminescence

Vikram Singh, 8R
Crystals and Triboluminescence
In our Chemistry lessons on saturated solutions and solubility
curves we learnt that a saturated solution is a solution in which no
more solute can dissolve in the solvent at that temperature. In general,
the hotter the solvent, the more solute (solid) it can dissolve i.e.
solubility increases with temperature. So if a saturated solution at high
temperature is allowed to cool down its solubility decreases i.e. less
solute can dissolve in the solvent and so some of the solute should
come out of solution and crystallise.
To demonstrate this we had grown some sugar crystals. For
this we had prepared a saturated solution of sugar (the solute) with
boiling water (the solvent) and let the solution cool. We suspended a
star made of pipe cleaner in the hot saturated sugar solution and set it
aside to cool. After a few days, we removed the star and it was
covered with sugar crystals.
Since the star was added to a saturated sugar solution at
nearly the boiling temperature of water, as it cooled, the solubility of
the water decreased. So the water could not hold as much sugar in
solution and so some sugar came out of solution and crystallised
onto the star.
While waiting for the crystals to form, I did some research on
how crystals are formed and what interesting properties they have.
One very intriguing phenomenon I came across was
Triboluminescence (described below). I wanted to observe it myself
so I grew more crystals and added food colours to have different
colour crystals.
Triboluminescence is when a flash of light is produced when a material is crushed, ripped, scratched,
or rubbed. The term triboluminescence comes from the Greek word tribein (to rub) and the Latin word
lumen (light). Triboluminescence can be observed as flashes of light when sugar crystals are crushed in
a dark room. Triboluminescence is also called fractoluminescence meaning light emitted when crystals
are fractured.
How to observe triboluminescence?
Apparatus: Sugar Crystals, pliers, and a dark room preferably at night, a large clear plastic
container(optional) to contain the flying pieces of crushed sugar
Method:
• Go to a dark room and let your eyes adjust to the darkness.
• Place a sugar crystal between the prongs of the pliers and place it inside the clear plastic
container.
• Crush the crystal.
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Vikram Singh, 8R
Observation: You should be able to observe some flashes of light as the crystal smashes.
Although I observed the flashes of light (triboluminescence) with all the different crystals, the
flash was so quick that I could not take any pictures of it. The picture above is from the BBC - Bang
goes the theory website (http://www.bbc.co.uk/bang/handson/sugar_glow.shtml).
Why does triboluminescence happen?
The phenomenon of triboluminescence is not fully understood. Scientists believe that when you apply
enough mechanical pressure to break a crystal, some of the atoms along the fracture lines are ripped
apart, separating some of the electrons from their nuclei. When enough charge has accumulated, the
electrons jump back across the fractures. They collide with molecules in the air, ionising nitrogen gas
molecules and making them glow with a blue luminescence.
Scientists have compared the spectrum of
light emitted during the triboluminescence of sugar
Triboluminescence
and found it to be the same as the spectrum produced
spectrum of sugar.
by lightning which is caused by electrical charge
passing through the air, exciting the nitrogen gas
molecules in the air. So triboluminescence can be
thought of as lightning on a very small scale. The light
produced by triboluminescence is very faint because
most of the light emitted is in the ultraviolet spectrum
(wavelengths < 380nm), and only a small fraction is in
the visible spectrum.
Triboluminescence has been observed in
many minerals like quartz, fluorite, calcite, many
feldspar minerals and many other materials.
The first known use of triboluminescence was
by the Uncompahgre Ute Indians form central Colorado. They built ceremonial rattles from buffalo hide
and filled them with clear quartz crystals from the mountains of Colorado. When the rattles were shaken
at night, the quartz crystals rubbed against each other and produced flashes of light, visible through the
translucent buffalo hide.
References:
1. Wikipedia: Triboluminescence. http://en.wikipedia.org/wiki/Triboluminescence
2. http://geology.com/minerals/triboluminescence/
3. Wintergreen Candy and Other Triboluminescent Materials: Linda M. Sweeting, Department of Chemistry,
Towson University, Scientific Experiments at Home website series, September, 1998. http://
pages.towson.edu/ladon/wg/candywww.htm
4. Cape Cod's "Magic" Quartz Pebbles: Robert N. Oldale, United States Geological Survey, Coastal and
Marine Geology Program, website article, May 2007. http://woodshole.er.usgs.gov/staffpages/boldale/
pebbles/
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