Name of Element: Tellurium
Element Classification: Semimetallic
Atomic Number: 52
Atomic Mass: 127.6 amu
Melting Point (°K): 722.7
Boiling Point (°K): 1263
Crystal Structure: Hexagonal
Density (g/cm3): 6.24
Specific Heat (@20°C J/g mol): 0.201
Fusion Heat (kJ/mol): 17.91
Evaporation Heat (kJ/mol): 49.8
Pauling Negativity Number: 2.1
First Ionizing Energy (kJ/mol): 869
Oxidation States: 6, 4, 2
Lattice Structure: Hexagonal
Lattice Constant (Å): 4.450
Description: Crystalline Tellurium has a silvery-white appearance, and exhibits a metallic lustre when pure. It is brittle and easily pulverised. Tellurium is a p-type semiconductor, and shows varying conductivity with crystal alignment. Its conductivity increases slightly with exposure to light. Tellurium can be doped with silver, copper, gold, tin, or other elements.
Separation: Most Tellurium is made as a byproduct of copper refining. The extraction technology is highly complex and the specific method selected depends upon the other trace compounds and elements present along with Tellurium. Typically, the first step involves an oxidation in the presence of sodium carbonate (soda ash).
Cu2Te + Na2CO3 + 2O2 → 2CuO + Na2TeO3 + CO2
The tellurite Na2TeO3 is acidified with sulphuric acid and the tellurium precipitates out as the dioxide (leaving and selenous acid, H2SeO3, in solution). Tellurium is liberated from the dioxide by dissolving in sodium hydroxide, NaOH, and electroytic reduction.
TeO2 + 2NaOH → Na2TeO3 + H2O → Te + 2NaOH + O2
"Tellurium", Los Alamos National Laboratory, 2003-12-15, http://periodic.lanl.gov/elements/52.html.
Tellurium Basic Atomic Spectroscopic Data, National Institute of Standards and Technology, http://physics.nist.gov/PhysRefData/Handbook/Tables/telluriumtable1.htm
Hudgens, S.; Johnson, B. (2004). "Overview of Phase-Change Chalcogenide Nonvolatile Memory Technology". Material Research Society Bulletin 29 (11): 1–4. http://www.engr.sjsu.edu/sgleixner/mate270/LectureNotes/Hudgens_MRS.pdf.
"Mineral Yearbook 2007: Selenium and Tellurium". United States geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/selenium/myb1-2007-selen.pdf.
"Ultra-pure organotellurium precursors for the low temperature MOVPE growth of II/VI compound semiconductors". Journal of Crystal Growth 93: 744–749. 1988. doi:10.1016/0022-0248(88)90613-6
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- Photovoltaics, Electronics and Semiconductors:
- Thin-film CdTe photovoltaic panels are the fastest growing segment of the solar industry.
- Bismuth Telluride (Bi2Te3) is used in thermoelectric cooling (TEC) devices.
- Tellurium dioxide is used in the media layer of several types of rewritable optical discs, including rewritable Compact Discs (CD-RW) and Digital Video Discs (DVD-RW).
- Cadmium zinc telluride (CdZnTe) is used in solid-state X-ray detectors.
- Mercury cadmium telluride (HgCdTe) is used as an infrared sensitive semiconductor material.
- The next generation of computer chips, named phase change memory (PCM) are based on Tellurium.
- Metallurgical Applications: Tellurium is added to lead to improve its strength and durability, and to decrease the corrosiveness of acids. When added to stainless steel and copper, it improves the workability of these metals.
- Chalcogenide Glasses: Tellurium based materials are used in optics applications as lenses or fibers.
- Rubber Industry: Tellurium dioxide is used as an accelerator in rubber vulcanization.
- Polymer/Plastics Industry: Organic tellurides are used as initiators for living radical polymerization and electron-rich mono- and di-tellurides are used as antioxidants.
- Microbiology: Tellurium based chemicals are used in the identification of pathogens.