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History
Of Helium
What
is helium?
Helium
is a colourless, odourless, tasteless inert gas lighter than air - at room
temperature and makes up about 0.0005% of the air we breathe
Source?
After
hydrogen, helium is the second most abundant element in the universe. It
has been detected spectroscopically in great abundance, especially in the
hotter stars. It is present in the Earth's atmosphere in about 1 part in
200,000. It is present in various radioactive minerals as a decay product,
but the major sources are from wells in Texas, Oklahoma and Kansas
Who
discovered Helium?
Helium
was first discovered by means of the spectroscope in the sun's stmosphere.
The discovery, made in 1868 by the strronomer Sir Norman Lockyer, was
followed in 1885 by Sir William Ramsay's proof that the element existed on
earth. He found it in the uranium ore, clevite. Later it was established
that helium is formed by the radioactive decay of many elements which emit
a-particles (nuclei of helium atoms) and is contained in all radioactive
minerals.
The
largest source of helium is natural gas, the richest in helium being the
gas from certain wells in Utah, USA. Next to hydrogen, helium is the
lightest gas known, has a lifting power equal 92% of hyrogen and the
advantage that it is inert and non-inflammable.
Helium
= Uses
Helium
is used for the inflation of airships, latex balloons and also for
cooling. Helium is widely used as an inert gas shield for arc welding; as
a protective gas in growing silicon and germanium crystals, and in
titanium and zirconium production. It is also used as a cooling medium for
nuclear reactors, and as a gas for supersonic wind tunnels. A mixture of
80% helium and 20% oxygen is used as an artificial atmosphere for divers
and others working under pressure. Helium is extensively used for filling
balloons as it is a much safer gas than hydrogen. One of the recent
largest uses for helium has been for pressurising liquid fuel rockets.
Ordinary
air contains 1 part in 200,000 of helium. It was the last gaseous element
to be liquefied, this being achieved by Omnes in 1908 in Leyden. Liquid
helium has many remarkable properties only imperfectly understood. As as
being scientifically fascinating it is indispensable in cryogenics (q.v)
as a medium for cooling other substances to temperatures near absolute
zero.
Hydrogen
fusion in the "H bomb" produces helium
HELIUM
[helium] , gaseous chemical element; symbol He; at. no. 2; at. wt. 4.0026;
m.p. below -272°C at 26 atmospheres pressure; b.p. -268.934°C at 1
atmosphere pressure; density 0.1785 grams per liter at STP ; valence
usually 0.
Helium
Flotation - Helium balloons
Helium
Balloons work by the law of buoyancy. As long as the helium plus the
balloon is lighter than the air it displaces, the balloon will float in
the air. Helium is a lot lighter than air. The difference is not as great
as it is between water and air (a litre of water weighs about 1,000 grams,
while a litre of air weighs about 1 gram), but it is significant. Helium
weighs 0.1785 grams per litre. Nitrogen weighs 1.2506 grams per litre, and
since nitrogen makes up about 80 percent of the air we breathe, 1.25 grams
is a good approximation for the weight of a litre of air.
Therefore,
if you were to fill a 1-litre soda bottle full of helium the bottle would
weigh about 1 gram less than the same bottle filled with air. That doesn't
sound like much -- the bottle itself weighs more than a gram, so it won't
float. However, in large volumes, the 1-gram-per-litre difference between
air and helium can really add up. This explains why blimps and balloons
are generally quite large -- they have to displace a lot of air to float.
Natural
Occurrence and Preparation
Helium
is rare and costly. Wells in Texas (where the Federal Helium Reserve was
established in 1925 near Amarillo), Oklahoma, and Kansas are the principal
world source. Crude helium is separated by liquefying the other gases
present in the natural gas; it is then either further purified or stored
for later purification and use
Some
helium is extracted directly from the atmosphere; the gas is also found in
certain uranium minerals and in some mineral waters, but not in economic
quantities. It has been estimated that helium makes up only about
0.000001% of the combined weight of the earth's atmosphere and crust; it
is most concentrated in the exosphere, which is the outermost region of
the atmosphere, 600-1500 mi (960-2400 km) above the earth's surface.
Helium is abundant in outer space; it makes up about 23% of the mass of
the visible universe. It is the end product of energy-releasing fusion
processes in stars (see interstellar matter ). Uses Helium's
noncombustibility and buoyancy (second only to hydrogen) make it the most
suitable gas for balloons and other lighter-than-air craft. A mixture of
helium and oxygen is often supplied as a breathing mixture for deep-sea
divers and caisson workers and is used in decompression chambers; because
helium is less soluble in human blood than nitrogen, its use reduces the
risk of caisson disease, or the "bends."
Helium
is used wherever an unreactive atmosphere is needed,
e.g.,
in electric arc welding, in growing crystals of silicon and germanium for
semiconductors, and in refining titanium and zirconium metals. It is also
used to pressurize the fuel tanks of liquid-fueled rockets. Liquid helium
is essential for many low temperature applications printed balloons
balloons balloon shop
Helium
in a Balloon
If
you put helium in a balloon and let go of the balloon, the balloon rises
until it pops. When it pops, the helium that escapes has no reason to stop
-- it just keeps going and leaks out into space. Therefore, in the
atmosphere there is very little helium at any given time. The helium that
is there comes from alpha particles emitted by radioactive decay. In
places that have a lot of uranium ore, natural gas tends to contain high
concentrations of helium (up to 7 percent). This makes sense, since the
decay of uranium emits lots of alpha particles and a natural gas pocket
tends to be a sealed container underground. Helium is cryogenically
distilled out of natural gas to produce the helium we put in balloons.
What
causes helium balloons to lose their lift after a day or two?
In
brief, because the helium leaks out, they shrink, and become heavier than
the volume of air they displace. This causes them to lose buoyancy and
"sink" in the air. The weight balance that keeps a balloon
afloat does not leave a lot of room for leakage, so once a little leaks
out the balloon falls.
Sometimes
you can catch a balloon right around the time it is neutrally buoyant, and
applying heat (your hand, for instance) or cold (rub with ice cube) will
change its volume just enough to make it rise or sink in the air.
Lowest
Melting Point
Helium
has the lowest melting point of any element and has found wide use in
cryogenic research, as its boiling point is close to absolute zero. Its
use in the study of superconductivity is vital.
Liquid
helium (4He) exists in two forms, 4He I and 4He II, above and below 2.174K
respectively
The
latter is unlike any other known substance. It expands on cooling, its
conductivity for heat is enormous and neither its heat conduction nor
viscocity obeys normal rules. It remains liquid down to absolute zero at
ordinary pressures, but can readily be solidified by increasing the
pressure.
Biological
Role
Helium
has no known biological function, but it is non-toxic.
Helium
in the Sun
Helium
in the sun is generally believed to be formed by nuclear fusion. This is
where nuclei of hydrogen, the lightest element, combine to form helium
with huge amounts of energy released. Spectroscopic evidence for the
presence of helium in the sun was first obtained during a solar eclipse in
1868. A bright yellow emission line was observed and was later shown to
correspond to no known element; the new element was named by J. N. Lockyer
and E. Frankland from helios [Gr.,=sun].
Helium
was isolated (1895) from a sample of the uranium mineral cleveite by Sir
William Ramsay. Properties and Isotopes Helium is less dense than any
other known gas except hydrogen and is about one seventh as dense as air.
Helium
is Extremely unreactive, it is an inert gas in Group 18 of the periodic
table . Natural helium is a mixture of two stable isotopes, helium-3 and
helium-4. In helium obtained from natural gas about one atom in 10 million
is helium-3. The unstable isotopes helium-5, helium-6, and helium-8 have
been synthesized. The alpha particles that are emitted from certain
radioactive substances are identical to helium-4 nuclei (two protons and
two neutrons). Helium-4 is unusual in that it forms two different kinds of
liquids. When it is cooled below 4.22°K (its boiling point at atmospheric
pressure) it condenses to liquid helium-I, which behaves as an ordinary
liquid. When liquid helium-I is cooled below about 2.18°K (at atmospheric
pressure), liquid helium-II is formed. Liquid helium-II has a number of
unusual properties. It is sometimes called a superfluid because it has
extremely low viscosity. It also has extremely high heat conductivity and
expands on cooling. It cannot be contained in an open beaker since a thin
film of it creeps up the side, over the lip, and flows down the outside.
The study of these phenomena is a part of low-temperature physics. When
helium-3 is liquefied and cooled it does not exhibit the properties of
liquid helium-II; this difference in properties between helium-3 and
helium-4 can be explained in terms of quantum mechanics.
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