Tellurium thermal conductivity

A 99.5% Cu—0.5% Te alloy has been on the market for many years (78). The most widely used is alloy No. CA145 (number given by Copper Development Association, New York), nominally containing 0.5% tellurium and 0.008% phosphorous. The electrical conductivity of this alloy, in the aimealed state, is 90—98%, and the thermal conductivity 91.5—94.5% that of the tough-pitch grade of copper. The machinahility rating, 80—90, compares with 100 for free-cutting brass and 20 for pure copper. 

Silver is a white, ductile metal occurring naturally in its pure form and in ores (USEPA 1980). Silver has the highest electrical and thermal conductivity of all metals. Some silver compounds are extremely photosensitive and are stable in air and water, except for tarnishing readily when exposed to sulfur compounds (Heyl et al. 1973). Metallic silver is insoluble in water, but many silver salts, such as silver nitrate, are soluble in water to more than 1220 g/L (Table 7.3). In natural environments, silver occurs primarily in the form of the sulfide or is intimately associated with other metal sulfides, especially fhose of lead, copper, iron, and gold, which are all essentially insoluble (USEPA 1980 USPHS 1990). Silver readily forms compounds with antimony, arsenic, selenium, and tellurium (Smith and Carson 1977). Silver has two stable isotopes ( ° Ag and ° Ag) and 20 radioisotopes none of the radioisotopes of silver occurs naturally, and the radioisotope with the longest physical half-life (253 days) is "° Ag. Several compounds of silver are potential explosion hazards silver oxalate decomposes explosively when heated silver acetylide (Ag2C2) is sensitive to detonation on contact and silver azide (AgN3) detonates spontaneously under certain conditions (Smith and Carson 1977). 

B. Copper. Copper (mp 1,083°C), is a moderately soft metal which has a high electrical and thermal conductivity. Electrolytic copper, 99.9% pure, is used for electrical wire and free-cutting alloys, containing small amounts of sulfur or tellurium, are commonly used for sheet or bar stock. Copper may be machined, brazed, and soldered. However, because of its toughness, it is much less easy to machine than brass. It tends to work-harden but may be annealed by heating, followed by rapid quenching. 

The thermal conductivity of Siso.sPis.eTee.eSei shows additional features and deserves more discussion. It was shown [14] that the total thermal conductivity of this clathrate is much lower than for other Si-based compounds. At room temperature it reaches only 2.0 W m Moreover, the temperature dependence of the thermal conductivity is typical for glasses. It increases sharply from 2 to 50 K, then slowly reaches 2.0 W m at about 130 K and remains constant up to room temperature (Fig. 5.9). The glass-like behavior of this semimetallic compound is associated with the mass alteration of two types of the guest atoms, tellurium and selenium, coupled to a slight disorder in distribution of silicon and phosphorus atoms within the cationic framework. 

Bortnikov also gas chromatographed bis(triethyl germanyl) sulphide separating it from its silicon, selenium, sulphur, tellurium and tin analogues. Separation was achieved at 254°C on a stainless steel column (100 cm x 0.4 cm) packed with Chromasorb W supporting 20% Apiezon L with helium as carrier gas and thermal conductivity detection. 

Bortnikov et al separated bistriethylsilyl sulphide and related compounds containing silicon, selenium, sulphur, germanium, tellurium and/or tin as the central linking atom at 254°C in a stainless steel column (100cm x 0.4cm) packed with Chromosorb W, supporting 20% of Apiezon L, with helium as carrier gas and a thermal conductivity detector. Specific retention volume data are reported. 

Bortnikov et al have separated bis(triethylsilyl)sulphide and a series of related compounds containing sulphur, selenium, germanium, tellurium and/or tin as the central or linking atom. Separation was achieved on a 100cm x 0.4cm stainless steel column packed with 20% Apiezon L on Chromosorb W at 254 C using helium as carrier gas and thermal conductivity detection. Specific retention volume data are presented for this range of compounds. 

Sulphur, selenium and tellurium can be incorporated into Si in a variety of forms (Grimmeiss et al., 1981 Wagner et al., 1984). As isolated ions, they are all double donors, with levels around 260 and 550 meV from the conduction band. These impurities may also be introduced as pairs, which also act as a double donors (Pensl et al., 1986). Depending on the thermal history of the Si during diffusion of S, Se and Te, they may also be incorporated as higher-order impurity complexes (Grimmeiss et al., 1981 Wagner et al., 1984). 

The simplest recording medium is a bilayer structure. It is constructed by first evaporating a highly reflective aluminum layer onto a suitable disk substrate. Next, a thin film (15-50 nm thick) of a metal, such as tellurium, is vacuum deposited on top of the aluminum layer. The laser power required to form the mark is dependent on the thermal characteristics of the metal film. Tellurium, for example, has a low thermal diffusivity and a melting point of 452 °C which make it an attractive recording material. The thermal diffusivity of the substrate material should also be as low as possible, since a significant fraction of the heat generated in the metal layer can be conducted to the substrate. For this reason, low cost polymer substrates such as poly (methylmethacrylate) or poly (vinyl chloride) are ideal. 

The selenium and tellurium analogues of PPS have also been synthesized and investigated [50]. As prepared, polyphenylene selenide (PPSe) and polyphenylene telluride (PPTe) are insulators with conductivities of less than 10 S m Exposure of PPSe to AsFs results in an insulator-to-conductor transformation, with a maximum conductivity in the range 0.1-1 S m being achieved. The thermal stability of PPSe is similar to that of PPS, while PPTe is decomposed by relatively mild conditions. 

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