Tellurium resistance

The mechanism of tellurium resistance has been investigated using genetic manipulation similar to that of Se (see above) and cellular oxidant capacity apparently plays an important role.144,206 A few tellurite determinants - both chromosomal and plasmid encoded - have been identified in bacte-ria.113,147 192 207 208 Recent studies have focused on the role of methyltransf-erases in Te resistance. Liu et a/.111 determined that the E. coli gene tehB uses S-adenosyl methionine and a methyltransferase in tellurite detoxification, but while no methylated tellurium compounds (see below) were observed, a loss of tellurite was observed in tellurite-amended cultures and Te complexation was inferred.191... 

As with selenium analysis, HGAAS also finds a place in Te determination. Basnayake et al. amended cultures of P. fluorescens K27 with 0.1 mM tellurite and, after 92-h growth, determined that approximately 34% of added Te was present as either precipitated, elemental Te in/or on centrifuged cells the balance of added Te remained in solution.190 In this same study, GC/MS was used for determination of DMTe in the same facultative anaerobe amended with tellurate.190 Earlier, GC/MS was used to analyze the headspace of a tellurium-resistant fungus amended with tellurite.215 This last is one of the few reports of the detection of dimethyl ditelluride in microbial headspace (see below). 

Tellurium is diamagnetic below its melting point. Its intrinsic electrical resistivity at room temperature is about 0.25 ohmcm, when the current is parallel to the i -axis, and decreases with increasing temperature and pressure. The element forms a continuous range of isomorphous solutions with selenium, consisting, in the soHd state, of chains of randomly alternating Se and Te atoms. 

The result is a hard, abrasion-resistant surface, important in many appHcations of cast kon. The depth of the chill may be controlled by regulating the amount of tellurium added. The casting shows a sharp demarcation line between the chilled and unchilled regions there is no intermediate or motded zone. Yet, the chilled portion shows excellent resistance to spalling from thermal or mechanical shock. Tellurium-treated kon is more resistant to sulfuric and hydrochloric acids than is untreated, unchilled gray kon. The amount added ranges from 0.005 to 0.1% ca 60% is lost by volatilization. Excessive addition causes porosity in the castings. 

Other Metals. Tellurium has been added to copper-base, lead-base, and tin-base bearing aUoys. In babbit-type aUoys, teUurium controls the stmcture and improves uniformity and fatigue resistance by restraining the tendency to segregation (see Bearing Materials). 

Tellurium has been recommended as an additive to magnesium to increase corrosion resistance (see Corrosion and corrosion control). The addition is highly exothermic but can be controUed by adding one teUurium tablet at a time to a sufficiently large bath of Uquid magnesium. The addition to teUurium and chromium improves the stress-corrosion resistance of aluminum—magnesium aUoys. 

Of the elements commonly found in lead alloys, zinc and bismuth aggravate corrosion in most circumstances, while additions of copper, tellurium, antimony, nickel, silver, tin, arsenic and calcium may reduce corrosion resistance only slightly, or even improve it depending on the service conditions. Alloying elements that are of increasing importance are calcium especially in maintenance-free battery alloys and selenium, or sulphur combined with copper as nucleants in low antimony battery alloys. Other elements of interest are indium in anodesaluminium in batteries and selenium in chemical lead as a grain refiner ". 

Basic physical properties of sulfur, selenium, and tellurium are indicated in Table 1.3. Downward the sulfur sub-group, the metallic character increases from sulfur to polonium, so that whereas there exist various non-metallic allotropic states of elementary sulfur, only one allotropic form of selenium is (semi)metallic, and the (semi)metallic form of tellurium is the most common for this element. Polonium is a typical metal. Physically, this trend is reflected in the electrical properties of the elements oxygen and sulfur are insulators, selenium and tellurium behave as semiconductors, and polonium is a typical metallic conductor. The temperature coefficient of resistivity for S, Se, and Te is negative, which is usually considered... 

Tellurium has been tested as a cathode material for use in conjunction with an anode made of alkali metal, primarily lithium, in power sources with a high specific energy and power [99], The theoretical specific energy for Li/Te pair is 612 Wh kg High-temperature (470 °C) cells with Li, Te, and eutectic (LiF-LiCl-Lil) electrolyte in the molten state, or with more convenient, albeit more resistive, paste-type electrolytes, have been tested in the laboratory. Similar layouts have been proposed for utilizing the Li/Se pair (theoretic cal specific energy 1,210 W h kg ) with the cell ingredients in the molten state (365 C) or with paste electrolyte at a lower temperature. 

Let us note finally, that tellurium has been considered as an appropriate component for the lead grid alloy in lead-acid batteries, as improving its durability, mechanical strength, and anti-corrosive ability. In investigating Pb-Te binary alloys with different contents of Te (0.01-1.0 wt%) in sulfuric acid solution it was shown recently [104] that the introduction of Te can inhibit the growth of Pb02 and increase corrosion resistance of the positive grid alloy of a lead-acid battery. By the... 

The silver white, shiny, metal-like semiconductor is considered a semimetal. The atomic weight is greater than that of the following neighbor (iodine), because tellurium isotopes are neutron-rich (compare Ar/K). Its main use is in alloys, as the addition of small amounts considerably improves properties such as hardness and corrosion resistance. New applications of tellurium include optoelectronics (lasers), electrical resistors, thermoelectric elements (a current gives rise to a temperature gradient), photocopier drums, infrared cameras, and solar cells. Tellurium accelerates the vulcanization of rubber. 

Unlike selenium there is no required biological role for tellurium in bacteria or plants that has been determined however, this may ultimately not be the whole story.111 Selenium was only viewed as a toxic metalloid with no necessary role for metabolism until at least the 1950s see above. While tellurite is less soluble than tellurate in aqueous solution, in general tellurite is probably more toxic to most organisms.190 The non Te-resistant wild type E. coli bacterium (Gramnegative) has MICs of 1 to 3 ppm for tellurite and tellurate.144,191,192 Tellurite is used to enrich and select for Staphylococcus aureus.169,193,194... 

In experiments parallel to those of Cowie and Cohen (see above), a Te-resistant fungi grown in high tellurite amendments with little available sulfur produced telluromethionine, tellurocysteine, and tellurocystine.140,203 So like selenium, tellurium can apparently substitute for sulfur under certain... 

Some of these exhibit very low resistivities and low activitation energies. Intermolecular interaction through tellurium atoms plays an important role in the conduction. ... 

Copper—lead—tellurium alloys have high wear resistance in sliding contacts. In copper—zinc alloys, the benefits of tellurium decrease with increasing zinc content and almost disappear when the zinc content exceeds 35%. 

Lead Alloys. A tellurium—lead alloy containing 0.02—0.1% tellurium, with or without antimony, was introduced in 1934 (81) as tellurium lead or Teledium. This alloy has higher recrystallization temperatures and corrosion resistance and takes a significandy longer time to soften at 25°C after cold work. 

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