Heat capacity and thermodynamic functions of brookite TiO2. (February 2016)

• Record Type: Journal Article
• Authors: Che, Xiangli; Li, Liping; Zheng, Jing; Li, Guangshe; Shi, Quan
• Is Part Of: Journal of chemical thermodynamics. Volume 93(2016:Feb.)
• Page Start: 45
• Page End: 51
• Publication Date: 2016-02
• Subjects: Brookite -- Heat capacity -- Thermodynamic properties -- Thermal stability; Thermodynamics -- Periodicals; Thermochemistry -- Periodicals; Thermodynamique -- Périodiques; Thermochimie -- Périodiques; Thermochemistry; Thermodynamics; Periodicals; 541.369
• DOI: 10.1016/j.jct.2015.09.018
• Languages: English
• ISSNs: 0021-9614

Abstract

Graphical abstract: Highlights: Heat capacity data and thermodynamic properties for brookite TiO2 are presented. Thermodynamic data for brookite are different from those for rutile and anatase TiO2 . Thermal stability for brookite, anatase, and rutile TiO2 are discussed. Abstract: This work represents the first report on the heat capacity of brookite TiO2, which was measured using a Quantum Design physical property measurement system (PPMS) in the temperature range of 2 K to 300 K. The experimental data were fitted using a series of theoretical functions for low temperatures ( T < 15 K), orthogonal polynomials for mid temperatures (15 < T < 75 K), and a combination of Debye and Einstein functions for high temperatures ( T > 75 K), from which the thermodynamic functions of brookite TiO2 were calculated. The standard molar entropy and molar enthalpy for brookite TiO2 at T = 298.15 K were determined to be 52.61 ± 0.53 J · K −1 · mol −1 and 9.03 ± 0.09 kJ · mol −1, respectively, leading to a Gibbs free energy of −6.65 ± 0.18 kJ · mol −1 . Strikingly, this Gibbs free energy was found to be slightly less than those reported for rutile TiO2 (−6.377 kJ · mol −1 ) and anatase TiO2 (−6.198 kJ · mol −1 ) (Smith et al., 2009). Further data analyses demonstrated that the thermal stability of TiO2 polymorphs follows a sequence of anatase < rutile < brookite at T = 298.15 K.