Elsevier

Thermochimica Acta

Volume 630, 20 April 2016, Pages 90-96
Thermochimica Acta

Gibbs energy of formation of bismuth(III) oxide

https://doi.org/10.1016/j.tca.2016.02.006Get rights and content

Highlights

  • Electrochemical measurement of standard Gibbs energy of formation of Bi2O3.

  • A novel closed cell design with buffer electrode to avoid electrode polarization.

  • The results are discussed in comparison with earlier studies.

  • The results are in agreement with thermal data.

  • A complete thermodynamic data table for Bi2O3 is presented.

Abstract

The standard Gibbs energy of formation of Bi2O3 has been measured using a solid-state cell incorporating yttria-stabilized zirconia as the electrolyte and pure oxygen as the reference electrode. An innovative cell design, with a buffer electrode to absorb the electrochemical flux of oxygen through the electrolyte caused by trace electron/hole conduction, was used to measure the oxygen chemical potential over phase mixture Bi + Bi2O3 in the temperature range from 800 to 1473 K. A closed cell was used to avoid possible deviations from equilibrium caused by vaporization of bismuth and oxides of bismuth. The results for α-Bi2O3 in the temperature range from 800 to 1002 K can be summarized by,

ΔGfo(±230)/Jmol1=584235+289.28(T/K)

For δ-Bi2O3 in the temperature range from 1002 to 1078 K:

ΔGfo(±230)/Jmol1=553669+258.77(T/K)

The results are discussed in relation to thermodynamic information reported in the literature.

Introduction

The Gibbs energy of formation of bismuth(III) oxide has been measured at high temperatures by many investigators using electrochemical cells [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. However, these studies were carried out using open cells and conventional two-compartment cell designs. Because of the relatively high vapor pressures of bismuth and oxides of bismuth [11], [12], [13] in equilibrium with Bi + Bi2O3 at high temperature as shown in Fig. 1, possible deviation from equilibrium in open cells is a source of concern. Hence, a closed cell was used in this study to avoid problems caused by continuous vaporization. Polarization of electrodes caused by trace hole or electronic conduction in the solid electrolyte and consequent electrochemical permeability the solid electrolyte is a second source of concern. An innovative cell design is developed in this study to deflect this flux to a buffer electrode and avoid electrode polarization. In previous studies air [2], [5], [8], Cu + Cu2O [1], [7], Ni + NiO [6] and Fe + Fe1-xO [3] were used as secondary standards for oxygen chemical potential. The oxygen partial pressure in air is dependent on altitude and weather conditions such as humidity and wind velocity. In this study measurements are made using the primary reference standard for oxygen, O2 gas at 0.1013 MPa. The oxygen electrode is non-polarizable.

The heat capacity of α-Bi2O3 has been measured in the temperature range from 60 to 298 K by Anderson [14] and from 11 to 50 K by Gorbunov et al. [15]. The results from these two measurements are in reasonably good accord. The standard entropy of α-Bi2O3 at 298.15 K computed using the low temperature heat capacity data is 150.0 (±1.6) J/mol K. Although the early solution calorimetric measurements of the enthalpy of formation of α-Bi2O3 at 298.15 K by Ditte et al. [16] and Mixter [17] gave discordant results, Mah [18] later provided a reliable value using combustion calorimetry.

Section snippets

Materials

Bismuth metal and bismuth(III) oxide used in this study were 99.99 mass % pure and were supplied by Apache Chemicals. Spectrochemical analysis of Bi2O3 showed the major impurities which were Ca (43 mass ppm), Pb (32 mass ppm), Si (12 mass ppm), B (7 mass ppm) and Fe (5 mass ppm). High-purity (99.999 mole%) oxygen gas was dried by passage through columns containing silica gel and magnesium perchlorate. High-purity (99.999 mole%) Ar gas used in this study was also dried the same way. Residual

Results

The reversible emf values of the cell are recorded in Table 1 and plotted as a function of temperature in Fig. 4. There is change of slope at 1002 and 1078 K. The break in the slope at 1002(±2) K indicates α–δ transition of bismuth(III) oxide and the break at 1078(±2) K indicates the monotectic reaction. The liquid oxide in equilibrium with the metal at and above the monotectic temperature is nonstoichiometric and contains dissolved Bi as indicated in the phase diagram of the system Bi-O [5].

In

Conclusion

Measurements using a new design of the electrochemical cell, with an enclosed electrode to prevent volatilization and an auxiliary electrode to deflect the electrochemical oxygen flux through the electrolyte, has enabled more accurate measurements of the standard Gibbs energy of formation of Bi2O3 as a function of temperature. The results obtained in this study are fully consistent with calorimetric information available in the literature. A complete thermodynamic data Table for Bi2O3 has been

References (30)

  • D. Chatterji et al.

    Free energy of formation of Bi2O3, Sb2O3 and TeO2 from EMF measurements

    J. Electrochem. Soc.

    (1973)
  • G.M. Mehrotra et al.

    Standard free energy of formation of Bi2O3

    Z. Phys. Chem. Neue Folge

    (1976)
  • B. Isecke et al.

    Equilibria study in the bismuth-oxygen system

    Z. Phys. Chem. Neue Folge

    (1979)
  • S.C. Schaefer

    Electrochemical Determination of Thermodynamic Properties of Bismuth Sesquioxide and Stannic Oxide

    (1984)
  • S. Itoh et al.

    Activity measurements of liquid Bi–Sb alloys by the EMF method using solid electrolytes

    J. Jpn. Inst. Met.

    (1984)
  • Cited by (5)

    • Elastic and thermodynamic properties of α-Bi<inf>2</inf>O<inf>3</inf> at high pressures: Study of mechanical and dynamical stability

      2019, Journal of Physics and Chemistry of Solids
      Citation Excerpt :

      For each optimized structure, Hellmann-Feynman forces on atoms were smaller than 0.006 eV/Å, and the deviation of the stress tensor from the diagonal hydrostatic form was lower than 0.1 GPa. The simulations also provided the formation energy and cohesive energy of α-Bi2O3, -6.531 eV and 2.947 eV, respectively; in good agreement with experimental results [29]. The elastic constants were evaluated by computing the macroscopic stress for a small strain applying the stress theorem [30,31] as implemented in the VASP code.

    • Enthalpy of formation and lattice energy of bismuth perrhenate doped by neodymium and indium oxides

      2017, Thermochimica Acta
      Citation Excerpt :

      Compounds on the bismuth oxide basis are multifunctional materials which are perspective to be used as inorganic ecological pigments, ceramic oxygen generators, scintillators, etc. [1–10].

    View full text