Tellurium
|
 |
Atomic Number: |
52 |
|
Melting
Point: |
449.5 ºC |
| Atomic Symbol: |
Te |
|
Boiling
Point: |
988 ºC |
| Atomic Weight: |
127.60
amu |
|
Density: |
6240
kg/m 3
|
| Atomic
Radius: |
143.2 pm
|
|
Oxidation States: |
6, 4, -2 |
| Covalent Radius: |
135
pm |
|
Electron
Configuration: |
[Kr]5s24d105p4 |
| van der Waals
Radius: |
206 pm |
|
State of Matter: |
solid (nonmagnetic) |
History
(L. tellus: earth) Discovered by Muller von Reichenstein in 1782;
named by Klaproth, who isolated it in 1798.
Properties
Crystalline tellurium has a silvery-white appearance, and when pure it
exhibits a metallic luster. It is brittle and easily pulverized. Amorphous
tellurium is found by precipitating tellurium from a solution of telluric or
tellurous acid. Whether this form is truly amorphous, or made of minute
crystals, is open to question. Tellurium is a p-type semiconductor, and shows
greater conductivity in certain directions, depending on alignment of the atoms.
Its conductivity increases slightly with exposure to light. It can be doped
with silver,
copper,
gold,
tin, or other
elements. In air, tellurium burns with a greenish-blue flames, forming the
dioxide. Molten tellurium corrodes
iron, copper, and
stainless steel.
Sources
Tellurium is occasionally found native, but is more often found as the
telluride of gold (calaverite), and combined with other metals. It is recovered
commercially from anode muds produced during the electrolytic refining of
blister copper. The U.S., Canada, Peru, and Japan are the largest Free World
producers of the element.
Uses
It is mostly used in alloys with other metals. Tellurium improves the
machinability of copper and stainless steel, and its addition to lead decreases
the corrosive action of sulfuric acid on lead and improves its strength and
hardness. Tellurium is used as a basic ingredient in blasting caps, and is added
to cast iron for chill control. Tellurium is used in ceramics. Bismuth telluride
has been used in thermoelectric devices.
It has potential applications in cadmium telluride solar panels.
Some of the highest efficiencies for solar cell electric power
generation have been obtained by using this material, but this
application has not yet caused demand to increase significantly.
Isotopes
Thirty isotopes of tellurium are known, with atomic masses ranging from 108
to 137. Natural tellurium consists of eight isotopes.
Hazards
Tellurium and its compounds are probably toxic and should be handled with
care. Workmen exposed to as little as 0.01 mg/m3
of air, or less, develop "tellurium breath," which has a garlic-like odor.