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Vapour pressure and standard enthalpy of sublimation of KBF4 by a TG based transpiration technique by R. Pankajavalli; K. Ananthasivan; S. Anthonysamy; P.R. Vasudeva Rao is a Materials Science article available to read on EtoBox.

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A horizontal thermobalance was adapted as a transpiration apparatus for the measurement of the vapour pressure of KBF 4 (s). Attainment of equilibrium was ascertained by the invariance of the measured values of the vapour pressures over a range of flows under isothermal conditions. Measured values of the vapour pressures could be represented by the least-squares expressions: log (p/Pa) = 8.16(±0.01) -4892(±248)/T(K) (538-560 K), log (p/Pa) = 6.85(±0.06) -4158(±240)/T(K) (576-660 K), which correspond to the equilibria of orthorhombic and cubic KBF 4 vapours, respectively. From these expressions the temperature of transformation of the orthorhombic to the cubic phase was identified to be 561 K. From the slopes of the above equations, the enthalpies of sublimation of the orthorhombic and cubic phases were found to be (93.7 ± 4.7) and (79.6 ± 4.6) kJ mol À1 , respectively. These values differ by 14.1 kJ mol À1 which could be ascribed to the enthalpy of the orthorhombic to cubic phase transition of KBF 4 . Third-law analysis of the vapour pressure data yielded a value of (104.6 ± 1.0) kJ mol À1 for DH o sub of KBF 4 (s) at 298.15 K.

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Author

R. Pankajavalli; K. Ananthasivan; S. Anthonysamy; P.R. Vasudeva Rao

Publisher

Elsevier Science; Elsevier ; Elsevier BV (ISSN 0022-3115)

Published

2005

Language

EN

Field

Materials Science (Physical Sciences)