Thermal and structural analysis of Li2OB2O3Al2O3 glasses with addition of CaF2 or LiF

https://doi.org/10.1016/j.radphyschem.2021.109619Get rights and content

Highlights

  • XRD measurements show that all samples are amorphous.

  • The thermal analysis shows the shift of the glass transition as a function of added fluoride.

  • ΔT is maximum for the samples LBA + 15LiF and LBA + 30CaF2.

  • KH is maximum for the samples LBA + 15LiF and LBA + 20CaF2.

Abstract

The thermal and structural properties of a Li2OB2O3Al2O3 glass matrix with the addition CaF2 or LiF were investigated by XRD and DTA. The results showed that the samples are glasses. The thermal analysis also showed a trend of the glass transition temperature shifting to lower temperatures, and the shift or new peaks of crystallization is observed as the LiF and CaF2 content goes up. The glass-forming tendency (GFT), thermal stability (TS) and the Reduced glass transition temperature (TgR) are discussed as a function of composition and results indicate that this parameters are highly sensitive to different compositions.

Introduction

Borate glasses are largely investigated in literature due to its large range of applications in various fields, such as medical research and treatment, engineering and industry (Srinivasa Reddy et al., 2007; Venkat Reddy et al., 2005; Koudelka et al., 2003; Donald et al., 1994; Mishra et al., 2007). The composition of borate glass (LBA) 50Li2O ⋅ 45B2O3 ⋅ 5Al2O3 (mol %), has been investigated due to characteristics as low cost and ease of production, as well as promising aspects when analyzed regarding ionizing radiation dosimetry (Venkat Reddy et al., 2005; Rojas et al., 2006a).

Potential advantages of using borate glasses in dosimetry includes the possibility to present an effective atomic number close to that of human tissue (desirable characteristic for personal dosimetry applications) and to use B-10 in its production, which could make it feasible to be used in thermal neutron dosimetry (Środa et al., 2019; Yahaba et al., 2017).

The Li2O present in the glass matrix is used to facilitate its crystallization process when transforming into a glass-ceramic and to increase the moisture resistance of the material, in comparison to pure borate glasses. The role of aluminum oxide (Al2O3) is to increase the chemical and thermal stability of the glass matrix (Demirkesen and Göller, 2003; Shimbo et al., 1986; Paul and Zaman, 1978; Sun et al., 2010; Silva et al., 2014). Glasses made from (B2O3) have a relatively low melting point, which reduces production time, and consequently, production cost.

Crystalline LiF and CaF2 are commonly studied and used in radiation dosimetry when doped/co-doped with different elements (Moscovitch et al., 2006; Pradhan, 2002; Massillon-JL et al., 2018). Investigations on the impact of adding these compounds as dopants in glassy matrix, with regards to structural, spectroscopic, and thermal characteristics, are found on literature (Riaz et al., 2017; ElBatal et al., 2019; Ayta et al., 2011), but to the best of our knowledge no studies have been published on the effects of this addition in structural and thermal characteristics of Li2OB2O3Al2O3 glasses. Understanding the effect of changing the glass composition in its formation and properties is a very important step that could help future research on other properties (e.g. dosimetric) of this glass system.

According to Biscoe and Warren (1938), borate glasses with the addition of alkali ions change the boron oxide units from B3 to B4. With different amounts of alkali ions added, the ratio of B3/B4 can change inside the glass, which can lead to phase-separated glasses. Zhu at al (Zhu et al., 2007) investigated phase-separation of lead borate (3.5PbO ⋅ 96.5B2O3) glasses under different gravity conditions, the authors related the phase separation for this composition, according the authors one phase is a borate-rich and the other phase is lead-rich phase. Phase separation is also reported by Arya et al. (2016) in glasses with composition: B2O3Li2O − ZnOV2O5. Ohkubo et al. (2021) using ab initio molecular dynamics (AIMD) simulations evaluated different compositions of Lithium Borosilicate glass. In this work, they analyzed the proportion of B3 and B4 as a function of the composition change and ion charge. The presence of B3 and B4 was identified by the authors.

Crystallization kinetics of LBA were investigated by Dantas et al. (2012). The authors used differential thermal analysis with a heating rate of 10 °C/min and obtained for the glass transition (Tg), onset peak of crystallization (Tx), and maximum crystallization peak (Tc) the following results: 385 °C, 466 °C and 498 °C, respectively. Moreover, the crystalline phases formed as a function of time and heating rate were investigated, from which was noticed the formation of two competing phases, as the heat treatment time increased: Li3AlB2O6 and LiBO2, with the latter occupying a bigger percentage of the glass-ceramic. Furthermore, several studies have been published analyzing the connection between different glass-ceramics and dosimetric properties, mainly based on TL and OSL analysis (Środa et al., 2019; Işik et al., 2020; Rojas et al., 2006b; Biró et al., 2015; Xu et al., 1016).

Ayta et al. (2010) investigated the LBA glass with addition of CaF2 and Mn in order to analyze the change in thermoluminescent (TL) properties of the glass. Additionally, the authors investigated the thermal properties of the LBA and its dependence with the amount of CaF2 and Mn added. The reported values for Tg, Tx and Tc were, respectively, 377 °C, 443 °C and 465 °C for the LBA glass. The authors also showed that these three parameters shifted to lower temperatures for the sample LBA+41CaF2+0.2Mn.

In other work from Ayta et al. (2011), the thermoluminescent, structural, and magnetic properties of undoped LBA were compared to LBA doped with Ti and LiF. It was identified a TL linear response of the LBA+50LiF+0.225TiO2 (wt%) for doses up to 100 Gy.

The characterization and definition of glasses are connected by thermal properties, in particular, what defined the samples as a glass is the presence of a glass transition temperature (Tg) (Zanotto and Mauro, 2017). The glass-forming tendency (GFT) and thermal stability (TS) are two examples of important parameters that are useful to better understand how the melt behaves. Dietzel (1968) proposed that the thermal stability of a glass is calculated by the difference between onset crystallization temperature Tx and glass transition Tg, ΔT = Tx-Tg. Saad and Poulain (1987) proposed the parameter S = (Tx − Tg)(Tc − Tx)/Tg, where Tc is temperature of the maximum of the first crystallization peak. Further, Hrúby (1972) proposed the parameter KH, obtained by the expression KH = (Tx − Tg)/(Tm − Tx), where Tm is the melting temperature. This parameter is related to the glass-forming tendency of the melt, and tries to quantitatively describe the behavior of the melt after cooling. The reduced glass transition temperature (TgR), (TgR = Tg/Tm) is calculated to obtain the information of whether the crystallization of the sample will be heterogeneous or homogeneous. According to Lu et al. (2000), if TgR > 0.58, the nucleation is heterogeneous, and if this value is less than 0.58, the crystallization is homogeneous.

In this context, the objective of this work was to analyze the undoped and LiF or CaF2 doped LBA glass matrix, regarding their thermal and structural properties. Characterization techniques such as X-Ray Diffraction (XRD) and Differential Thermal Analysis (DTA) were used in 14 distinct glass compositions and complemented by Thermogravimetric analysis (TGA) in selected samples.

Using the data obtained from DTA, ΔT, S, KH and TgR were calculated. The first three, in order to understand the stability and glass forming ability of the samples, and the fourth, to understand the nucleation process of each sample.

Section snippets

Experimental method

All the glass samples were prepared by using the melt-quenching technique, following the same experimental procedure: all the powders were prepared by mixing the correct proportion of high grade chemicals and then melted in a platinum crucible, in N2 atmosphere at 1100 °C for 30 min. The samples were then quenched between two metal plates at ambient atmosphere and temperature. The pure LBA glass sample, used as reference in terms of comparison with the other compositions, presented 50Li2O–45B2O3

Results and discussion

Fig. 1.a and 1.b show the X-ray diffraction of the glasses (LBA + xLiF) and (LBA + xCaF2) (wt %), respectively. The glass with x = 0 corresponds to the LBA matrix.

Analyzing Fig. 1.a and 1.b, it is clear the presence of wide halos, which is a characteristic of amorphous materials, indicating the formation of this type of material in all of the produced samples. We can see in Fig. 1.a the diffractograms of the LBA and the samples with 5, 10, 15 and 20% of LiF added to this glass matrix.

The LBA

Conclusion

The XRD results showed that the samples are all amorphous, and DTA thermograms indicated that all glass samples have the Tg. This results indicated that the rapid cooling process after melting was successful and glasses were formed.

The DTA results showed that the samples with addition of LiF have a tendency to shift all of its thermal events to lower temperatures, as well as the appearance of a new, subtle crystallization peak, as the fluoride content increases. Furthermore, the group of

CRediT authorship contribution statement

Matheus B. Tissot: Writing – original draft, Formal analysis, Writing – review & editing, Writing, original draft preparation, Performed the experiments, Formal analysis, discussion, Reviewing and Editing, Conceived of the present idea. João V.B. Valença: Writing – review & editing, Discussion, Reviewing, Conceived of the present idea. Anielle C.A. Silva: Writing – review & editing, Discussion, Reviewing, Performed the experiments, Conceived of the present idea. Noelio O. Dantas: Discussion,

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.

Acknowledgements

The authors would like to thank the financial support of: Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS) (projeto: 19/2551-0001978-5), Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes).

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