Received 1 April 2015; accepted 24 June 2015; published 1 July 2015

ABSTRACT

Information on the vaporization processes and thermodynamic properties of glass-forming oxide melts in the systems MgO-B₂O₃-SiO₂, CaO-B₂O₃-SiO₂, SrO-B₂O₃-SiO₂, BaO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, CdO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂, Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃-GeO₂-SiO₂ together with the earlier obtained data is discussed. These data were obtained by high-temperature mass spectrometric method. Various types of vapor species were found over oxide systems studied such as the associated, dissociated and polymerized products of vaporization. The regularities of the vaporization of the binary and multicomponent glass-forming oxide melts were illustrated and discussed from the point of view of the acid-base concept. Results on determination of thermodynamic functions in oxide systems were considered taking into account the main requirements for the confirmation of their reliability. The generalized lattice theory of associated solutions was used for the calculation of thermodynamic properties of the ternary silicate melts studied. Using this approach the different levels of deviations from the ideality in the melts under investigation were clarified. The relative numbers of bonds of various types formed in the melts considered were also calculated based on the generalized lattice theory of associated solutions.

Keywords:

Glass-Forming Oxide Melts, Thermodynamics, Vaporization, High Temperature Mass Spectrometry

1. Introduction

Development of the advanced glass materials requires the reliable information on vaporization processes and thermodynamic properties of glass-forming melts. This paper presents the review on the recent data obtained by Knudsen effusion mass spectrometric method on high temperature behavior of glass-forming oxide melts in the systems MgO-B₂O₃-SiO₂, CaO-B₂O₃-SiO₂, SrO-B₂O₃-SiO₂, BaO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, CdO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂, Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃-GeO₂-SiO₂. The systems under study have the wide range of practical applications in the production of glasses, enamels, glazers and ceramics as well as in the various high temperature technologies such as incorporation of nuclear wastes, obtaining of optical fibers and others. It was evidently shown [1] that Knudsen effusion mass spectrometric method is extremely powerful tool to study vaporization processes and thermodynamic properties of glass-forming oxide systems since this approach was suggested first [2] for the investigation of individual compounds. Recent advantages and improvements of this experimental technique may be found in [3]. Unfortunately one of the latest reviews on mass spectrometric study of inorganic compounds and materials at high temperatures [4] did not draw too much attention to glass-forming materials. This paper is an effort to meet this lack. In details the unique opportunities and features of high temperature mass spectrometric method for study of the vaporization processes and thermodynamic properties of oxide systems and materials are summarized in [1] [5]-[8]. It was illustrated that the main regularities of the vaporization of oxide systems were in agreement with the acid-based concept of interactions in the oxide melts. It was also repeatedly illustrated that the results on determination of thermodynamic functions in oxide systems were satisfied the main requirements for the confirmation of their reliability in comparison with data obtained by the electromotive force method and the high temperature solution calorimetric method.

2. Experimental

High-temperature Knudsen effusion mass spectrometry was used to study vaporization processes and to determine the partial pressures of vapor species as well as the component activities of the MgO-B₂O₃-SiO₂, CaO- B₂O₃-SiO₂, SrO-B₂O₃-SiO₂, BaO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, CdO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂, Bi₂O₃-B₂O₃- SiO₂ and Bi₂O₃-GeO₂-SiO₂ melts [9]-[18]. Measurements were performed with MS-1301 mass spectrometer developed by the Institute of Analytical Instrumentation of the Russian Academy of Sciences, Saint Petersburg, Russia. Vaporization was carried out using two effusion cells containing the sample under study and pure oxide (reference substance). The main part of experiments were done from molybdenum effusion cells except the PbO-B₂O₃-SiO₂ system when vaporization was carried out from quartz effusion cells [14]-[16] as well as except the Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃-GeO₂-SiO₂ systems when the iridium-plated molybdenum effusion cells were used [17] [18]. Ions were produced by electron ionization at an energy of 25 eV. To facilitate interpretation of mass spectra of vapor over glass-forming melts under consideration the appearance energies of ions were also measured. The installation was calibrated using the vapor pressure of gold, recommended by IUPAC as the standard.

3. Results and Discussion

Various types of vapor species were found over the glass-forming melts of the MgO-B₂O₃-SiO₂, CaO-B₂O₃-SiO₂, SrO-B₂O₃-SiO₂, BaO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, CdO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂, Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃-GeO₂-SiO₂ systems studied [9]-[18] such as the associated and dissociated products of vaporization, Table 1. It should be underlined that the composition of vapor found over these melts was in agreement with the

content of gaseous phase during vaporization of corresponding binary systems [1] and corresponding gaseous salts that were identified over them [19]. The main feature of thermodynamic description of glass-forming melts under study was the negative deviations from the ideal behavior. As examples Figure 1 and Figure 2 illustrate some of the recent experimental thermodynamic data obtained in the melts of the Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃- GeO₂-SiO₂ systems [17] [18]. The concentration dependences of the Bi₂O₃ isoactivity curves in Bi₂O₃-B₂O₃- SiO₂ melts at the temperature 1200 K [17] are presented on Figure 1. It is very important to mention that the level of the deviations of thermodynamic properties from the ideal behavior in the glass-forming melts considered was in agreement with the acid-base concept of interactions in oxide melts [1] and depended on the basicity of the melts (as in the case of the CaO-B₂O₃-SiO₂, SrO-B₂O₃-SiO₂, BaO-B₂O₃-SiO₂ systems [10]-[13]) or on the acidity of the melts (as in the case of Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃-GeO₂-SiO₂ systems [15]-[18], Figure 2). Modeling of thermodynamic properties of glass-forming melts in the MgO-B₂O₃-SiO₂, CaO-B₂O₃-SiO₂, SrO- B₂O₃-SiO₂, BaO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, CdO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂, Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃- GeO₂-SiO₂ systems was done using the generalized lattice theory of associated solutions (GLTAS) described in details for the application for glass-forming melts earlier in [1]. This approach is suggested by Barker [20] for modeling of organic mixtures and may be represented by the Guggenheim model of the strongly regular solutions in the systems where molecules differs on the sizes and their interaction energy depends on mutual orientation of the molecules. Peculiarities of description of this model to glass-forming melts under consideration may be found in [21]-[23] including the features of introduction of Bi₂O₃ in the structure of melt as in [24]. Thus the mutual agreement of thermodynamic properties of glass-forming oxide melts containing one oxide modifier and two glass-forming oxides (as in the present case) was repeatedly shown as the result of comparison of such modeling and experimental data obtained by high temperature mass spectrometric method. As an example of this fact Figure 1 shows the mutual correlation between experimental values of the Bi₂O₃ activities obtained in Bi₂O₃-B₂O₃-SiO₂ melts and results of modeling based on GLTAS at the temperature 1200 K [17]. One of the advantages of GLTAS model is the opportunity to find the correspondence between the changes of thermodynamic properties of glass-forming melt and its structure such as the relative number of bonds of different types formed in the melt when the second coordination sphere is taken into consideration. As it was mentioned above and shown on Figure 2 in Bi₂O₃-B₂O₃-SiO₂ melts the most negative deviations from the ideality was observed

compared with Bi₂O₃-GeO₂-SiO₂ melts. As the results of modeling using GLTAS information on the relative numbers of bonds in these melts may be also found [20]-[24]. The data obtained [17] [18] allows concluding that the Bi-O-Si bonds have the predominant role in the formation of the Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃-GeO₂-SiO₂ melts with the negative deviations from the ideality. As the molar ratio of B₂O₃(GeO₂):SiO₂ decreases the influence of Bi-O-Ge and Bi-O-Si bonds on the negative deviations from the ideality of these melts is more valid. The features of structural description of these glass-forming melts obtained as the result of modeling were successfully confirmed using X-ray scattering method [25]-[27].

4. Conclusion

Using high temperature Knudsen effusion mass spectrometric method it is shown that the composition of vapor over the MgO-B₂O₃-SiO₂, CaO-B₂O₃-SiO₂, SrO-B₂O₃-SiO₂, BaO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, CdO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂, Bi₂O₃-B₂O₃-SiO₂ and Bi₂O₃-GeO₂-SiO₂ melts are in agreement with the content of gaseous phase over corresponding binary systems. In the ternary glass-forming melts studied the negative deviations from the ideal behavior were found that were in agreement with the main statements of the acid-base concept. Reliability of application of the generalized lattice theory of associated solutions for modeling of thermodynamic properties and structural features of ternary glass-forming melts with one oxide modifier was illustrated.

Acknowledgements

Financial support for this work from the Russian Fund for Basic Research according to the Project N 13-03- 00718 and from Saint Petersburg State University according to the Project N 12.41.937.2015 is gratefully acknowledged.

Cite this paper

V. L. Stolyarova, (2015) Vaporization and Thermodynamics of Glass-Forming Oxide Melts: Mass Spectrometric Study and Modeling. Journal of Materials Science and Chemical Engineering,03,81-86. doi: 10.4236/msce.2015.37009

References