Tellurium
is a
chemical element
. It has the chemical symbol
Te
and the
atomic number
52. It has 52
protons
and 52
electrons
. Its
mass number
is 127.6. It has 8 natural
isotopes
. 4 are stable and 4 are
radioactive
. One of the radioactive ones lasts longer than any other isotope. It has a
half life
of 2.2 x 10
24
years (2.2 septillion years).
It is a
brittle
silver-white
semimetal
. When it is pure it has a metallic shine. It is ground easily. It can be made in an amorphous form. It is a
semiconductor
. It changes conductivity a little when light shines on it, similar to
selenium
. It is corrosive to many metals when molten.
Tellurium is an unreactive element. It can react with reactive metals to make tellurides. It can burn in air to make
tellurium dioxide
. It can be
oxidized
even more to
tellurium trioxide
. It does not
corrode
. The chemistry of tellurium is similar to some chemistry of
selenium
and
sulfur
, although its compounds are more reactive and the element is less reactive. It does not dissolve in most acids, although it dissolves in concentrated
sulfuric acid
to make a special red tellurium cation.
Tellurium makes
chemical compounds
in several
oxidation states
: -2, +2, +4, and +6. -2 compounds are normally found in
tellurides
. They are strong
reducing agents
. Tellurides are normally the main ore of tellurium. Most natural tellurides are not pure, so they are much less reactive. +2 compounds are found in some tellurium halides, like
tellurium(II) chloride
and
tellurium(II) bromide
. They are the rarest oxidation state. +4 compounds are found in
tellurites
and
tellurous acid
. They are weak oxidizing agents, that can be
reduced
to tellurium. Tellurites are made by reacting tellurium dioxide with a metal oxide. +6 compounds are found in
tellurates
and
telluric acid
. They are powerful oxidizing agents. Tellurates are made by reacting telluric acid with metal oxides.
-
Tellurium dioxide mineral
-
Lead telluride mineral
-
Cadmium telluride crystal
-
Calaverite, a telluride mineral
Tellurium is a very rare mineral. There is 14 times more
silver
in the earth than there is tellurium. Tellurium is sometimes found as an element, but most of the times is found as tellurides. Gold tellurides (
Calaverite
) are found in the earth. They are valuable ores of both tellurium and gold. This gold ore was not recognized as gold during one
gold rush
and was used as a filler. It was then discovered that it was gold telluride, making another gold rush. Telluride cannot replace sulfide in elements like selenide does.
Tellurium can be taken from gold telluride by dissolving the gold telluride in concentrated sulfuric acid. The tellurium dissolves to make a red solution, while the gold sinks to the bottom.
A more common way of extracting tellurium from tellurides is to heat the tellurides. The tellurides are heated with
sodium carbonate
and air. This makes
sodium tellurite
.
Selenites
are normally found as an impurity. They are separated by reacting them with sulfuric acid. The selenites stay in solution. The tellurites turn into tellurium dioxide. Then the tellurium dioxide is reacted with
sulfur dioxide
dissolved in sulfuric acid to make tellurium metal. The tellurium can be melted and reformed to make bars of tellurium metal.
The main use of tellurium is in
alloys
. It is used in
iron
,
copper
, and
lead
alloys. It makes the metals more easily machinable (able to be shaped by a machine). It improves strength and durability of lead and makes it more resistant to
corrosion
by sulfuric acid.
Tellurium is also used in
cadmium telluride
solar cells
. These are very efficient. It can be alloyed with both
cadmium
and
mercury
to make mercury cadmium telluride, an
infrared
sensitive
semiconductor
. It is used in some rewritable (able to be erased and written again)
optical discs
.
Lead telluride
is used in another type of infrared sensor.
It is also used to color ceramics. It is used to make
fiberglass
that is used in
telecommunications
(telephones, internet, etc.). It helps increase the
refraction
. It is also used in delay
blasting caps
. Rubber can be
hardened
.
Tellurium is not really used in any living things. Some fungi, though, can use tellurium instead of selenium or sulfur. Most organisms can
metabolize
tellurium to make dimethyl telluride, which is a garlic-smelling chemical. If someone eats a tellurium compound, it gives them garlic breath.
Tellurium is very toxic.
[1]
- ↑
Sigma-Aldrich Materials Safety Data Sheet for Tellurium