High temperature brillouin scattering study of lanthanum and sodium aluminoborosilicate glasses
Introduction
Aluminoborosilicate glasses are becoming an important material in advanced materials; these glasses are incorporated in several technologies, including optical components, bioactive materials and flat panel display substrates. These glasses with a high rare earth content appear to be good candidates for the containment of minor actinides as they are an important part of the glass composition for nuclear waste storage [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]]. They are also matrices with interesting mechanical properties (Young's modulus E ~ 100 GPa, hardness H ~ 8 GPa), high glass transition temperatures (Tg ~ 900 °C) and high chemical durability [13,16]. Unfortunately, actinides are radioactive elements and are therefore difficult to handle. It is therefore easy to work with lanthanides because their chemical properties give them the same behavior when introduced into the glass matrix. This is why we use lanthanum, which is considered to simulate actinides. The structural effects of this composition have been studied, several experimental techniques have been used, such as TEM spectroscopy, infrared spectroscopy and NMR [1,2].To contain nuclear waste, the industrial solution adopted over the last thirty years has been vitrification. It consists of incorporating fission products and minor actinides into molten glass without distinction [6]. The fission products are thus definitively fixed in the core of the glass and the radioactivity of the activated elements is confined. The main advantage of glass is its amorphous nature. Unlike crystalline and well-structured materials, glass is the only material that can incorporate all the elements present in fission product solutions into its disordered structure through chemical bonds with its constituent elements. The radionuclides then participate in the very structure of the glass, it is not a simple coating but a true containment of all the elements down to the atomic scale [14]. In this study, we used Brillouin scattering spectroscopy to study the effect of aluminum/boron substitution on sodium lanthanum aluminoborosilicate glasses. To illustrate the interest of these glasses, a composition of five oxides was chosen: 55SiO2-(25-x) Al2O3-xB2O3–15Na2O–5La2O3 (with substitution; aluminum/boron). In order to study the effects of temperature and annealing on these glasses, in the composition range of x = 0–12.5% B2O3 between room temperature and melting temperature. This technique provides information on the macroscopic properties of the glasses and can also provide connections between acoustic properties and structure on a larger length scale [17]. In this work, we present the temperature dependence of the Brillouin displacement which allows the determination of the glass transition temperature. Indeed, as we mentioned at the beginning, this composition is a simplified composition of nuclear glasses but from a structural point of view, it is a very complex composition. We have therefore carried out this unique study in order to better understand the effect of boron on the acoustic properties to try to broaden the understanding of this structure which we have characterized and studied in our recently published papers [1,2], which showed that the study by infrared spectroscopy and NMR allowed a better understanding of the substitution of aluminum over boron. The results show an evolution of the matrix and that this substitution favors the appearance of phase separation in this system. To go further in the understanding, we will present in this paper the results obtained by Brillouin scattering spectroscopy.
Section snippets
Aluminoborosilicate glass: preparation and characterization
The composition was prepared using our method already published [1], (The analyzed glass compositions are presented in Table 1). 55SiO2– (25-x)Al2O3– xB2O3–15Na2O–5La2O3 (x = 0, 2.5, 5, 7.5, 10, 12.5) glasses composition were formulated with reagent grade SiO2 (purity 0.997), Na2O3(purity 0.998), Al2O3(purity 0.995), H3BO3 (purity 0.995), La2O3 (purity 0.996) (Alfa Aesar). The weight of each reagent has been calculated put up account their purity. The glasses were fabricating such that constant
Results and discussion
The evolution of the Brillouin frequency (νB) and the FWHM as a function of the temperature for the set of glasses (annealed glasses (red squares) and quenched glasses (black squares)) is presented in Fig. 3. (The size of the points on this graph reflects the experimental uncertainties).
3-1- Below Tg: The evolution of the Brillouin frequencyshiftνB and width as a function of temperature:we note that these frequencies show an abrupt change in regime for quenched glass (black dots) and annealed
Conclusion
In this study by Brillouin spectroscopy, we highlighted the sensitivity of this spectroscopy to the effects of annealing below the glass transition and the effect of aluminum/boron substitution. The Brillouin frequencies and widths show that acoustic phonon propagation is affected by annealing. The annealing of glass above Tg induces structural relaxation. This relaxation is manifested by a change in the configuration of the glasses on a long-distance scale.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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