Reactions with Tellurium
The phase diagram of the W-Te system as proposed by [1] and redrawn by [2] is shown in Fig. 119. The orthorhombic (space group Pmmn) ditelluride has been identified as the only intermediate phase [3 to 5], see the reviews [6 to 8]. The formation of WTe4 a
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Reactions with Tellurium
Reactions with Tellurium
The phase diagram of the W-Te system as proposed by [1] and redrawn by [2] is shown in Fig. 119. The orthorhombic (space group Pmmn) ditelluride has been identified as the only intermediate phase [3 to 5], see the reviews [6 to 8]. The formation of WTe4 as a thin coating on tungsten in Te melts at high temperatures (>700·C) is assumed in [9]. The solubility of W in Te is low « 0.3 at%) , as microscopic studies show [3]. wt"!. W
16000
10
1400 u oe:
1200
cu
~ 1000 cu
CI.
E ~
L/ I
20
30
40
50
60
70
90
80
100
I
I
I
-1--
1020t15·C
--:
I
800 ~ I
~ N
600 ';49.57°C
~
(W)-
451 t 2°C
400
-Te I 200 0 10 Te
I
20
Fig. 119.
30
I
40
I
50
at"!.
W
60
I
70
I
80
90
100 W
Phase diagram of the W-Te system according to [1, 2].
Metallic gray WTe 2 was obtained by heating stoichiometric mixtures of the elements in evacuated and sealed quartz ampules. The mixture was first tired tor 10 to 15 h at 600 to 700·C, then remixed by shaking, and again fired tor another 10 to 15 h at 1000 to 1200·C. Single crystals can be prepared by adding a few mg ot iodine (or bromine) and transporting the product in a thermal gradient trom 900 to 700·C [5]. The direct synthesis trom eLemental mixtures in heated, closed quartz tubes has aLso been used repeatedly as apreparation method [3, 4, 10, 11]. The thermal decomposition ot WTe 2 in a vacuum ot (1 to 2) x1 0- 2 Torr starts at 600 to 620·C and goes to completion at 800 to 850·C [10]. Alloying of tungsten with tellurium in vacuum starts at 640·C [10]. According to [9], the attack by Te vapor at elevated temperatures is minimal. A weight increase was noted between 700 and 800·C, but on further heating to 945°C the weight decreased, and, upon cooling the sample, a thin coating peeled off which was assumed to be WTe4 [9]. References: [1] Moffatt, W. G. (Handbook of Binary Phase Diagrams, Business Growth Services, Schenectady, New York, 1976). [2] Massalski, T. D. (Binary Alloy Phase Diagrams, Vol. 1f2, American Society tor Metals, Metals Park, Ohio, 1986, pp. 2118/9). [3] Morette, A. (C. R. Hebd. Seances Acad. Sci. 216 [1943] 566/8; Ann. Chim. [Paris] [11] 19 [1944] 130/43). Gmelin Handbook
VII Suppl. Vol. A Sb
H. Jehn et al., W Tungsten © Springer-Verlag Berlin Heidelberg 1993
Reactions with Boron
123
[4] Knop, 0.; HaraLdsen, H. (Can. J. Chem. 34 [1956] 1142/5). [5] Brixner, L. H. (J. Inorg. Nucl. Chem. 24 [1962] 257/63). [6] Hansen, M.; Anderko, K. (Constitution of Binary ALLoys, McGraw-HiLL, New York 1958, p. 1231). [7] Shunk, F. A. (Constitution of Binary ALLoys, 2nd Suppl., McGraw-HiLL, New York 1969, p. 700). [8] KorniLov, I. 1.; Matveeva; N. M.; Pryakhina, L. 1.; Polyakova, R. S. (MetaLLokhimicheskie Svoistva ELementov Periodicheskoi Systemy [MetaL-ChemicaL Properties of the ELements of the PeriodicaL System], Moscow 1966, pp. 179/82; C.A. 68 [1968] No. 16365). [9] Matson, L. K. (MLM-1720 (TID-4500) [1970] 1/14; N.S.A. 24 [1970] No. 29912). [10] OpaLovskii, A. A.; Fedorov, V. E.; Lobkov, E. Yu
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