Electrical conductivity and glass transition temperature (T g ) measurements on some selected glasses used for nuclear waste immobilization Binoy Kumar Maji, Hrudananda Jena ⁎, R. Asuvathraman Materials Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam- 603102, India abstract article info Article history: Received 7 September 2015 Received in revised form 11 December 2015 Accepted 19 December 2015 Available online xxxx Borosilicate glass, alumino-borosilicate glass, barium borosilicate glass and lead borosilicate glasses were pre- pared by melting the glass forming reagents of the respective glass compositions in air ambience. The glasses were characterised by powder X-ray diffractometry. The electrical conductivity of these four glasses was mea- sured by impedance measurements. The conductivities were attributed mainly due to conduction of Na + ion in the glass network and were in the range of 9.92 × 10 -9 –1.74 × 10 -3 Ω -1 cm -1 at 400–900 K. The activation energies of conduction for these glasses were found to be 0.96 ± 0.01 eV for borosilicate glass, 1.19 ± 0.01 eV for alumino-borosilicate glass, 1.19 ± 0.01 eV for barium borosilicate glass and 1.24 ± 0.01 eV for lead borosilicate glass. Diffusion coefficient of the conducting species (Na + -ion) was calculated from the conductivity values using Nernst Einstein equation, and the values were in the range of 5.28 ± 0.03 × 10 -13 –1.78 ± 0.01 × 10 -8 cm 2 s -1 . Glass transition temperatures of these glasses were measured by differential scanning calorimetry as well as by dilatometric methods. T g measured by differential scanning calorimetry were found to be 813 ± 4, 820 ± 4, 785 ± 4 and 749 ± 4 K for borosilicate glass, alumino-borosilicate glass, barium borosilicate glass and lead boro- silicate glass respectively, and T g measured by dilatometric method was 799 ± 5, 818 ± 5, 781 ± 5 and 742 ± 5 K for borosilicate glass, alumina-borosilicate glass, barium borosilicate glass and lead borosilicate glass respectively. © 2015 Elsevier B.V. All rights reserved. Keywords: Oxide glasses Electrical conductivity Diffusion coefficient Glass transition temperature Dilatometric method 1. Introduction Borosilicate glass (BSG) is a world wide accepted matrix for the vit- rification of radioactive waste for safe storage and disposal [1,2]. Vitrifi- cation of waste is carried out by using various melting techniques at and above 1273–1473 K. Joule heated ceramic melting (JHCM) is one of them. Pure borosilicate glass (SiO 2 –B 2 O 3 ) exhibits negligibly low con- ductivity, addition of alkali oxides (Na 2 O, Li 2 O etc.) as modifiers to the borosilicate glass enhances the electrical conductivity of borosilicate glass [3]. By further increasing the concentration of the modifier oxides, electrical conductivity of the glass increases; conductivity reaches a value of ~3 × 10 -3 S/cm by adding 50 mol% of alkali oxides to it [4]. The addition of waste elements (Cs,Sr,Mo,Zr etc.) would influence the structural changes along with the formation of various point defects in the glass matrix. The structural changes will affect the mobility of the cations and anions thereby affecting the electrical conductivity of the glass. A comprehensive understanding on transport properties of the glasses with varying composition and waste loading is essential for the smooth operation of waste vitrification process in the nuclear indus- try. Various compositions of borosilicate glasses have been explored by researchers by changing the modifier concentrations to see efficacy of the resulting glass in terms of glass formation, durability towards vari- ous waste elements, stability at higher temperatures, mobility of ionic species etc. towards nuclear applications. Data on electrical conductivity of the glass compositions at elevated temperatures is essential and is one of the important parameters for the vitrification of the glasses by JHCM process. Electrical conductivity data on some borosilicate glasses containing mainly SiO 2 ,B 2 O 3 ,Na 2 O as the constituents of the glass are available in the literature [5–9]. However, electrical properties of the modified compositions of BSG such as alumino borosilicate glass (AlBSG), barium borosilicate glass (BaBSG) and lead borosilicate glass (PbBSG) are poorly studied at elevated temperatures. Therefore, electri- cal conductivity measurements on these modified compositions have been carried out at elevated temperatures. These glasses are not only used as waste matrix for nuclear waste vitrification in the glassy state (pure glass phase) but also used as an encapsulating phase to the ce- ramic waste forms as glass bonded composites. Glass bonded apatites [10,11] and glass bonded sodalites are the examples of such matrices. Alumino borosilicate glass was used for the preparation of glass bonded sodalite [12,13]. Similarly, barium borosilicate glass and lead borosili- cate glasses were studied to immobilize sulphate bearing liquid waste and high level radioactive waste containing 90 Sr, 99 Tc, 99 Mo, 137 Cs, 192 Ir, 226 Ra etc. generated from reprocessing of spent nuclear fuel [14, Journal of Non-Crystalline Solids 434 (2016) 102–107 ⁎ Corresponding author. E-mail address: hruda66@yahoo.co.in (H. Jena). http://dx.doi.org/10.1016/j.jnoncrysol.2015.12.008 0022-3093/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol