Thermodynamics of the volatilization of Tl[sub 2]O from Tl[sub 2]O, Tl[sub 4]O[sub 3], and Tl[sub 2]O[sub 3]

Journal Article · Thu Apr 22 00:00:00 EDT 1993 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100118a046· OSTI ID:5713368

Holstein, W L ^[1]

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1. Du Pont Central Research Development, Wilmington, DE (United States)

Volatile thallous oxide, Tl[sub 2]O, is used in the fabrication of thallium-containing high-temperature superconducting powders and films. The partial pressure of thallous oxide was measured as a function of temperature and oxygen partial pressure by the transportation method over liquid and solid Tl[sub 2]O, liquid and solid Tl[sub 4]O[sub 3], and solid Tl[sub 2]O[sub 3]. At low oxygen partial pressure, condensed Tl[sub 2]O is stable with respect to Tl[sub 4]O[sub 3] and Tl[sub 2]O[sub 3]. It melts at 852 [+-] 10 K and is very volatile, with a vapor pressure of about 1.0 [times] 10[sup [minus]2] atm at 900 K. At high oxygen partial pressure, Tl[sub 2]O[sub 3] is stable with respect to Tl[sub 2]O and Tl[sub 4]O[sub 3]. It does not melt congruently below 1,067 K. It volatilizes congruently through the reaction Tl[sub 2]O[sub 3](c) = Tl[sub 2]O(g) + O[sub 2](g), and the equilibrium vapor pressure of Tl[sub 2]O in oxygen at atmospheric pressure reaches 1.0 [times] 10[sup [minus]2] atm at about 1,050 K. Tl[sub 4]O[sub 3] exists as a thermodynamically stable phase at intermediate oxygen partial pressure. It melts at 990 [+-] 2 K, and it volatilizes congruently through the reaction Tl[sub 4]O[sub 3](c) = 2 Tl[sub 2]O(g) + 1/2O[sub 2](g). Thermodynamic properties for Tl[sub 4]O[sub 3](c) are estimated to be [Delta][sub f]H[degrees][sub 298] = [minus]520.7 kJ/mol and S[degrees][sub 298] = 259.0 J/(mol K). The experimental results of this study were combined with data in previous studies to estimate the high temperature thermodynamic properties of the thallium oxide phases. These properties were used to generate a phase diagram for the Tl-O system and to determine the equilibrium vapor pressure of thallous oxide over the condensed phases as a function of temperature and oxygen partial pressure. 30 refs., 10 figs., 3 tabs.

• OSTI ID: 5713368
• Journal Information: Journal of Physical Chemistry; (United States), Vol. 97:16; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
THALLIUM OXIDES
EVAPORATION
THERMODYNAMIC PROPERTIES
EQUILIBRIUM
HIGH-TC SUPERCONDUCTORS
PARTIAL PRESSURE
PHASE DIAGRAMS
RAW MATERIALS
TEMPERATURE DEPENDENCE
THEORETICAL DATA
CHALCOGENIDES
DATA
DIAGRAMS
INFORMATION
MATERIALS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SUPERCONDUCTORS
THALLIUM COMPOUNDS
400201* - Chemical & Physicochemical Properties
360600 - Other Materials
360607 - Other Materials- Superconducting Properties- (1992-)
661300 - Other Aspects of Physical Science- (1992-)