Tellurium

Description

Tellurium is one of the rarest elements on earth similar to selenium, and was discovered in Transylvania in 1782 by Franz-Joseph Muller von Reichenstein. The name derived from the Latin word for earth. Tellurium is occasionally found naturally, more often as telluride of gold, calaverite.

Chemical properties

Tellurium is a grayish or silvery white, lustrous, crystalline, semimetallic element. It may exist in a hexagonal crystalline form or an amorphous powder.Soluble in sulfuric acid, nitric acid, potassium hydroxide, and potassium cyanide solutions; insoluble in water. Imparts garlic-like odor to breath, can be depilatory. It is a ptype semiconductor and its conductivity is sensitive to light exposure. It is found in sulfide ores and is produced as a by-product of copper or bismuth refining.

Physical properties

Tellurium is a silver-white, brittle crystal with a metallic luster and has semiconductorcharacteristics. It is a metalloid that shares properties with both metals and nonmetals, andit has some properties similar to selenium and sulfur, located just above it in group 16 of theperiodic table.
There are two allotropic forms of tellurium: (1) the crystalline form that has a silvery metallicappearance and a density of 6.24 g/cm³, a melting point of 499.51°C, and a boiling point of988°C; and (2) the amorphous allotrope that is brown in color and has a density of 6.015g/cm³and ranges for the melting and boiling point temperatures similar to the crystalline form.

Isotopes

There are a total of 48 isotopes of tellurium. Eight of these are consideredstable. Three of the stable ones are actually radioactive but have such long half-livesthat they still contribute to the natural abundance of tellurium in the crust of the Earth.The isotope Te-123 (half-life of 6×10⁺¹⁴ years) contributes 0.89% of the total telluriumfound on Earth, Te-128 (half-life of 7.7×10⁺²⁴ years) contributes 31.74% to the naturalabundance, and Te-130 (half-life of 0.79×10⁺²¹ years) contributes 34.08% to the telluriumin the Earth’s crust. The other five stable isotopes and the percentage of theirnatural abundance are as follows: Te-120 = 0.09%, Te-122 = 2.55%, Te-124 = 4.74%,Te-125 = 7.07%, and Te-126 = 18.84%. The other 40 isotopes are all radioactive withshort half-lives.

Origin of Name

The name “tellurium” is derived from the Latin word for Earth, tellus.

Occurrence

Tellurium is the 71st most abundant element on Earth. It makes up a small portion ofigneous rocks and is sometimes found as a free element, but is more often recovered fromseveral ores. Its major ores are sylvanite (AgAuTe₄), also known as graphic tellurium, calaverite,sylvanite, and krennerite, all with the same general formula (AuTe₂). Other minor ores arenagyagite, black tellurium, hessite, altaite, and coloradoite. In addition, it is recovered fromgold telluride (AuTe₂). Significant quantities are also recovered from the anode “slime” of theelectrolytic refining process of copper production.

History

Discovered by Muller von Reichenstein in 1782; named by Klaproth, who isolated it in 1798. 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 the anode muds produced during the electrolytic refining of blister copper. The U.S., Canada, Peru, and Japan are the largest producers of the element. Crystalline tellurium has a silvery-white appearance, and when pure exhibits a metallic luster. It is brittle and easily pulverized. Amorphous tellurium is formed 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 flame, forming the dioxide. Molten tellurium corrodes iron, copper, and stainless steel. 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. Forty-two isotopes and isomers of tellurium are known, with atomic masses ranging from 106 to 138. Natural tellurium consists of eight isotopes, two of which are radioactive with very long half-lives. 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 catalysts are used in the oxidation of organic compounds and are used in hydrogenation and halogenation reactions. Tellurium is also used in electronic and semiconductor devices. It is also 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. Tellurium costs about 50￠/g, with a purity of about 99.5%. The metal with a purity of 99.9999% costs about $5/g.

Characteristics

The pure form of tellurium burns with a blue flame and forms tellurium dioxide (TeO₂).It is brittle and is a poor conductor of electricity. It reacts with the halogens of group 17, butnot with many metals. When it reacts with gold, it forms gold telluride. Tellurium is insolublein water but readily reacts with nitric acid to produce tellurous acid. If inhaled, it produces agarlic-like odor on one’s breath.

The Uses of Tellurium

Tellurium is a common constituent of ores that contain silver, gold, lead, antimony, and bismuth, and it is often present in small amounts in coal. Tellurium is widely used in metallurgy because it improves the properties of copper, tin, lead-based alloys, steel, and cast iron. It is used in rubber manufacturing to increase heat resistance and to retard the aging of rubber hoses and cable coatings. Small amounts are used in the electronics industry for lasers and photoreceptors. Tellurium is not an essential micronutrient; therefore, it is not found in nutritional supplements.
As coloring agent in chinaware, porcelains, enamels, glass; reagent in producing black finish on silverware; in manufacture of special alloys of marked electrical resistance; in semiconductor research.

The Uses of Tellurium

The metal is used in vulcanizing rubber, instorage batteries, and as a coloring agent inceramics. It is also used as an additive toiron, steel, and copper. Many tellurium saltsfind application on semiconductors.

The Uses of Tellurium

Tellurium’s major use is as an alloy with copper and stainless steel. It makes these metalseasier to machine and mill (cut on a lathe). It is also used as a vulcanizing agent in the productionof rubber, as a coloring agent for glass and ceramics, and for thermoelectrical devices.
Along with lithium, it is used to make special batteries for spacecraft and infrared lamps.Tellurium can be used as a p-type semiconductor, but more efficient elements can do a betterjob. It is also used as a depilatory, which removes hair from skin.
Although tellurium forms many compounds, most of them have little commercial value.

What are the applications of Application

Tellurium is a chemical which mediates the quantitative pinacolization of aromatic carbonyl compounds

Definition

A nonmetallic element with many properties similar to selenium and sulfur. Atomic number 52; group VIA of the period table; aw 127.60; valences of 2, 4, 6; eight stable isotopes.

Definition

tellurium: Symbol Te. A silvery metalloidelement belonging to group16 (formerly VIB) of the periodictable; a.n. 52; r.a.m. 127.60; r.d. 6.24(crystalline); m.p. 449.5°C; b.p.989.8°C. It occurs mainly as telluridesin ores of gold, silver, copper,and nickel and it is obtained as a byproductin copper refining. There areeight natural isotopes and nine radioactiveisotopes. The element is usedin semiconductors and smallamounts are added to certain steels.Tellurium is also added in smallquantities to lead. Its chemistry issimilar to that of sulphur. It was discoveredby Franz Müller (1740–1825)in 1782.

Production Methods

Elemental tellurium (Te) has some metallic properties, although it is classed as a nonmetal or metalloid. The name is derived from the Latin word for earth, tellus. Tellurium is occasionally found naturally, more often as telluride of gold, calaverite. The elemental form has a bright luster, is brittle, readily powders, and burns slowly in air. Tellurium exists in two allotropic forms, in the form of powder and hexagonal crystalline (isomorphous) with gray selenium. The concentration in the earth’s crust is about 0.002 ppm. It is recovered from anode muds during the refining of blister copper. It is also found in various sulfide ores along with selenium and is produced as a by-product of metal refineries. The United States, Canada, Peru, and Japan are the largest producers.
Tellurium’s industrial applications include its use as a metallurgical additive to improve the characteristics of alloys of copper, steel, lead, and bronze. Increased ductility results from its use in steel and copper alloys. Addition of tellurium to cast iron is used for chill control, and it is a basic part of blasting caps. It is used in some chemical processes as a catalyst for synthetic fiber production, and as a vulcanizing agent and accelerator in the processing of rubber.

General Description

Grayish-white, lustrous, brittle, crystalline solid; dark-gray to brown, amorphous powder with metallic characteristics. Used as a coloring agent in chinaware, porcelains, enamels, glass; producing black finish on silverware; semiconductor devices and research; manufacturing special alloys of marked electrical resistance. Improves mechanical properties of lead; powerful carbide stabilizer in cast iron, Tellurium vapor in "daylight" lamps, vulcanization of rubber. Blasting caps. Semiconductor research.

Reactivity Profile

Tellurium is attacked by chlorine fluoride with incandescence. When Tellurium and potassium are warmed in an atmosphere of hydrogen, combination occurs with incandescence [Mellor 11:40. 1946-47]. Burning Tellurium produces toxic Tellurium oxide gas. Avoid solid sodium, halogens, interhalogens, metals, hexalithium disilicide. Reacts with nitric acid; reacts with concentrated sulfuric acid forming a red solution. Dissolves in potassium hydroxide in the presence of air with formation of deep red solution; combines with halogens. Avoid antimony and chlorine trifluoride; chlorine trifluoride reacts vigorously with Tellurium producing flame. Fluorine and Tellurium react with incandescence. Lithium silicide attacks Tellurium with incandescence. Reaction with zinc is accompanied by incandescence (same potential with cadmium, only hazard is less). A vigorous reaction results when liquid Tellurium is poured over solid sodium [EPA, 1998].

Hazard

All forms of tellurium are toxic in gas form. The vapors of all the compounds of the dustand powder forms of the element should not be inhaled or ingested. When a person is poisonedwith tellurium, even in small amounts, the breath will smell like garlic.

Health Hazard

Although tellurium in elemental form haslow toxicity, ingestion can produce nausea,vomiting, tremors, convulsions, and centralnervous system depression. In addition,exposure to the metal or to its compoundscan generate garlic-like odor in breath, sweat,and urine. Such odor is imparted by dimethyltelluride that is formed in the body. Oralintake of large doses of the metal or itscompounds can be lethal. Clinical symptomsare similar for most tellurium salts,which include headache, drowsiness, lossof appetite, nausea, tremors, and convulsions.High exposure can produce metallictaste, dry throat, chill and other symptoms.Inhalation of dust or fume of the metalcan cause irritation of the respiratory tract.Chronic exposure can produce bronchitis andpneumonia.

Fire Hazard

A finely divided suspension of elemental Tellurium in air will explode. Insoluble in water. Burning Tellurium produces toxic Tellurium oxide gas. Avoid solid sodium, halogens, interhalogens, metals, hexalithium disilicide. Reacts with nitric acid; reacts with concentrated sulfuric acid forming a red solution. Dissolves in potassium hydroxide in the presence of air with formation of deep red solution; combines with halogens. Avoid antimony and chlorine trifluoride; chlorine trifluoride reacts vigorously with Tellurium producing flame. Fluorine and Tellurium react with incandescence. Lithium silicide attacks Tellurium with incandescence. Reaction with zinc is accompanied by incandescence (same potential with cadmium, only hazard is less). A vigorous reaction results when liquid Tellurium is poured over solid sodium.

Flammability and Explosibility

Non flammable

Safety Profile

Poison by ingestion and intratracheal routes. An experimental teratogen. Exposure causes nausea, vomiting, tremors, convulsions, respiratory arrest, central nervous system depression, and garlic odor to breath. Aerosols of tellurium, tellurium dioxide, and hydrogen telluride cause irritation of the respiratory system and may lead to the development of bronchitis and pneumonia. Experimental reproductive effects. Under the proper conditions it undergoes hazardous reactions with halogens (e.g., chlorine, fluorine), interhalogens (e.g., bromine pentafluoride, chlorine fluoride, chlorine trifluoride), metals (e.g., cadmium, potassium, sodium, platinum, tin, zinc), hexalithium disilicide, silver bromate, silver iodate. When heated to decomposition it emits toxic fumes of Te. See also TELLURIUM COMPOUNDS.

Potential Exposure

The primary use of tellurium is in the vulcanization of rubber and as an additive in ferritic steel production. It is also used as a carbide stabilizer in cast iron, a chemical catalyst; a coloring agent in glazes and glass; a thermocoupling material in refrigerating equipment; as an additive to selenium rectifiers; in alloys of lead, copper, steel, and tin for increased resistance to corrosion and stress, workability, machinability, and creep strength; and in certain culture media in bacteriology. Since tellurium is present in silver, copper, lead, and bismuth ores, exposure may occur during purification of these ores.

Environmental Fate

Metals are recalcitrant to degradation; therefore, no biodegradation studies have been performed on tellurium. No aquatic bioaccumulation data exist for tellurium; however, based on its density and low water solubility, it is unlikely to present a concern for bioaccumulation in the water column. No environmental monitoring data are available on the levels of tellurium in sediment or sediment-dwelling organisms. Therefore, it is unclear whether tellurium has the potential to bioaccumulate in this compartment. In humans, tellurium accumulates in the bones. Based on this, it may be assumed that tellurium has the potential to bioaccumulate in vertebrates.

Shipping

UN3288 Toxic solids, inorganic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required.

Purification Methods

Purify it by zone refining and repeated sublimation to an impurity of less than 1 part in 108 (except for surface contamination by TeO2). [Machol & Westrum J Am Chem Soc 80 2950 1958.] Tellurium is volatile at 500o/0.2mm. It has also been purified by electrode deposition [Mathers & Turner Trans Amer Electrochem Soc 54 293 1928].

Toxicity evaluation

Tellurium has a low toxicity in its elemental form, but dimethyltelluride is formed in the body. Tellurium caused a highly synchronous primary demyelination of peripheral nerves, related to the inhibition of squalene epoxidase, which blocks cholesterol synthesis. The sequence of metabolic events in sciatic nerve following tellurium treatment initially involves inhibition of the conversion of squalene to 2,3-epoxysqualene, and this block in the cholesterol biosynthesis pathway results, either directly or indirectly, in the inhibition of the synthesis of myelin components and the breakdown of myelin. The efficacy of garlic as a lipid-lowering agent has been recognized, but the biochemical mechanisms underlying this action are currently unknown. It is possible that organic tellurium compounds, which are found in high concentration in fresh garlic buds, may contribute to this action by inhibiting squalene epoxidase, the penultimate enzyme in the synthetic pathway of cholesterol. Weanling rats fed a diet rich in tellurium develop a demyelinating polyneuropathy because of inhibition of this enzyme in peripheral nerves. Chronic exposure to small amounts of tellurium found in garlic might reduce endogenous cholesterol production through inhibition of hepatic squalene epoxidase and so reduce cholesterol levels. Tellurium may also contribute to the characteristic odor of garlic.

Incompatibilities

Finely divided powder or dust may be flammable and explosive. Violent reaction with halogens, interhalogens, zinc and lithium silicide; with incandescence. Incompatible with oxidizers, cadmium; strong bases; chemically active metals; silver bromate; nitric acid.