Feature
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is solid carbon dioxide commonly known as ‘dry ice’ which,
under normal atmospheric pressure, changes phase at -78.5°C
from solid directly to gas by sublimation (or solidifies directly
from gas which is called ‘deposition’).
By all accounts, the French chemist, Thilorier was the first
to record the appearance of solidified CO 2 as dry ice when in
1835 he opened a cylinder containing liquid carbon dioxide to
observe it in liquid form. Almost immediately virtually all of the
liquid evaporated leaving a solid dry ice block at the bottom
of the cylinder. Over the following 80 to 90 years Thilorier’s
discovery was used in experiments at universities and privately-
owned research establishments, but no practical applications
were developed.
“One of the more recent
applications of dry ice blasting
is to remove smoke damage from
structures after fires.”
In 1923 a company in New York City, Prest Air Devices,
made solid dry ice for demonstration purposes, and in
1924 proposed dry ice to the railroad companies to use
for cooling in place of normal water ice currently used for
refrigerating food and perishables carriages on the grounds
that dry ice with double the cooling power of water would
be far more efficient. After initial successful trials, a dry ice
production plant was constructed in 1925 and the company
was incorporated as DryIce Corporation of America which
trademarked the name DryIce. By 1932 there were eight
major manufacturers of dry ice producing an estimated
amount of approximately 50 000 tons per year due to growth
of demand over only seven years which included the Great
Economic Depression starting in 1929.
USES OF DRY ICE
Today there are thousands of dry ice producers worldwide,
most of which sell dry ice as a commercial product although
some of them manufacture dry ice solely for their own use.
Dry ice is relatively easy to manufacture from either
carbon dioxide gas produced in fermentation plants or
carbon dioxide-rich gases occurring as by-products of other
processes such as production of ammonia from nitrogen and
natural gas fermentation. Carbon dioxide or carbon dioxide-
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rich gas is pressurised and refrigerated until it liquifies. Then,
just as Thilorier did in 1835, pressure is reduced. When this
occurs, some liquid carbon dioxide vaporises, causing a rapid
lowering of temperature of the remaining liquid. As a result,
the extreme cold causes the liquid to solidify into a snow-like
consistency. Finally, the snow-like solid carbon dioxide is
compressed into small pellets or larger blocks of dry ice.
Small pellets with a diameter of 16mm and smaller
cylindrical particles with a diameter of .2mm diameter)
have high surface-to-volume ratios so that they float on
oil or water and do not stick to skin because of their high
radii of curvature. The smaller cylindrical dry ice pellets are
used for ice blasting, quick freezing, flame extinguishers for
firefighting and containment of oil slicks by oil solidifying.
Mixtures of small and cylindrical particles are widely
used for blast cleaning. The pellets are shot from nozzles
in compressed air combining the power of the speed of the
pellets with the action of the sublimation which is highly
efficient in removing residues from industrial and other
equipment. Examples of materials removed include ink,
glue, oil, paint, mould and rubber. Dry ice blasting can
replace sandblasting, steam blasting, water blasting and
solvent blasting. There is also an environmental benefit of
dry ice blasting in that the residue is only sublimed CO 2 thus
making it a useful technique where residues from other
blasting techniques are undesirable. One of the more recent
applications of dry ice blasting is to remove smoke damage
from structures after fires.
Standard blocks of dry ice are manufactured in sizes of
between 20 and 30kg which are most commonly used in
shipping, because they sublime relatively slowly due to having
low ratios of surface area to volume. Blocks are also less costly
to use when large volumes of sublimated CO 2 are required for
example when cleaning out flammable vapours from oil and
fuel tanks. Other speciality applications of dry ice are to chill
steel and other metals during mechanical assemblies so that
strong interference fits result when temperatures rise back to
ambient and to create slugs of ice in valve less pipes needing
repairs or modifications.
In laboratories, making slurries of dry ice in organic
solvents provides mixtures of cold baths at temperatures
down to close to −100 °C. This practical application of dry ice
has been exceptionally useful in preventing what used to be a
common nuisance called ‘thermal runaway’ occurring in many
experimental research programmes.
Overall, however, the most common use of dry ice is still
to preserve food, perishables and items such as biological
samples that must remain cold or frozen without the use of
mechanical cooling. RACA
RACA Journal I January 2020
55