PTFE has the lowest coefficient
of
friction of any known
solid material. It is used
as a non-stick coating for
pans and other cookware.
PTFE is very non-reactive,
and so is often used in
containers and pipework
for reactive chemicals.
Its melting point varies
between 260
C (FEP) and 327
C (PTFE), depending on which
specific Teflon polymer
is being discussed.
PTFE is sometimes said to be a spin-off from the US space
program with more down-to-earth applications; this is an urban legend, as
teflon cooking pans were commonplace before Yuri Gagarin's flight in 1961.
PTFE was discovered serendipitously by Roy Plunkett of DuPont in 1938, while
attempting to make a new CFC refrigerant, when the perfluorethylene
polymerized in its storage container. DuPont patented it in 1941, and
registered the Teflon trademark in 1944.
An early advanced use
was in the
Manhattan Project, as a material to coat valves and seals in the pipes holding
highly-reactive uranium hexafluoride
in the vast Uranium enrichment
plant at Oak Ridge, Tennessee,
when it was known as
K416.
It was first sold commercially
in 1946 and by
1950, DuPont was producing
over a million pounds (450
t) per year in
Virginia.
Teflon has been supplemented
with another DuPont product,
Silverstone, a three-coat fluoropolymer system that produces a more durable
finish than Teflon. Silverstone was released in 1976.
Amongst many other industrial applications, PTFE is used to coat certain
types of hardened, armour-piercing bullets, so as to reduce the amount of wear
on the firearm's rifling. These are often mistakenly referred to as "cop-killer"
bullets on account of PTFE's supposed ability to ease a bullet's passage through
body armour. Any armour-piercing effect is, however, purely a function of the
bullet's velocity and rigidity rather than a property of PTFE.
PTFE is an excellent electrical insulator with good dielectric properties.
This is especially true at high radio frequencies, making it eminently suitable
for use as an insulator in cables and connector assemblies and as a material for
printed circuit boards. Combined with its high melting temperature this makes it
the material of choice as a high performance substitute for the weaker and more
meltable polyethylene that is commonly used in low-cost applications.
Due to its low friction, it is used for applications where sliding action of
parts is needed: bearings, bushings, gears, slide plates, etc. In
these applications it performs
significantly better than
nylon and
acetal; it is comparable with UHMWPE, although UHMWPE is more resistant to wear
than Teflon. For these applications, versions of teflon with mineral oil or
molybdenum disulfide embedded as additional lubricants in its matrix are being
manufactured.
Gore-Tex
is a material incorporating
teflon membrane with micropores.
Toxicity
Non-stick coatings on household frying pans have been shown to release toxic
gases upon overheating. These gases are lethal to birds, and can cause flu-like
symptoms in humans. This polymer fume fever in humans may last for more than a
week in cases of moderate household exposure. This level of exposure can occur
when a Teflon pan is left unattended on a high-power gas burner in a small
unventilated apartment. In severe cases, decomposition chemicals can be lethal.
Reports of Teflon's apparent toxicity may be misleading, however, as sufficient
heat will thermally decompose most chemical substances. Teflon begins to
deteriorate after the temperature of cookware reaches about 500 F (260 C), and
begins to significantly decompose above 660 F (350 C). By comparison, cooking
fats, oils and butter will begin to scorch and smoke at about 392 F (200 C), and
meat is usually fried between 400-450 F (200-230 C), but hot spots in the pan
can easily exceed this temperature. In recent years, under the threat of
litigation, DuPont has
become more forthcoming about the risks of using Teflon on hot surfaces, but has
not stopped selling the product.
