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."
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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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