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Author: search.filters.author.Subhashini, u.Subject: search.filters.subject.Fracture toughness

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    Investigation of mixed alkali effect on mechanical, structural and thermal properties of three-alkali borate glass system
    (Elsevier Ltd, 2016) Subhashini, u.; Shashikala, H.D.; Udayashankar, N.K.
    In the present communication, the results of investigation on mixed alkali effect (MAE) in mechanical, structural and thermal investigation of alkali zinc borate glasses with nominal composition 5Li2O-(25-x)K2O-xNa2O-60B2O3-10ZnO (x = 0, 5, 10, 15, 20 and 25 mol%) are reported. The samples were prepared using standard melt quenching technique. Fourier transform infrared (FTIR) spectroscopy, differential scanning calarometry (DSC) and Vickers indentation studies were performed to investigate the mixed alkali effect in the samples. From the DSC studies, it was observed that the thermal parameters viz., glass transition temperature (Tg), glass melting temperature (Tm), glass crystallization temperature (Tc), glass stability (S) and fragility (F) exhibit a non linear variation with respect to increase in compositional parameter (RNa). This behavior clearly indicated the presence of strong MAE in the samples. FTIR studies confirmed the presence of both [BO3] and [BO4] units, indicating the present glass networks to be made up of these two units placed in different structural groups. The non linear variation of peak positions of B-O-B bending and stretching of [BO3] and [BO4] units of each glass sample explain the role of modifier alkali elements and validates the existence of strong MAE. The microhardness and fracture toughness of the samples were measured using Vickers micro indentation technique and non linear variation of both the properties have been observed confirming the presence of MAE in these glass samples. © 2015 Elsevier B.V.
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    Influence of Fe3+ ions on optical, structural, thermal and mechanical properties of Li2O–Na2O–K2O–ZnO–B2O3 based glass system
    (Elsevier Ltd, 2020) Subhashini, u.; Shashikala, H.D.; Udayashankar, N.K.
    The effect of addition of Fe3+ ions in Li2O–Na2O–K2O–ZnO–B2O3 based glass system have been studied. The melt quenching technique is used to prepare the glass samples. The X-ray diffraction studies confirmed the amorphous nature of the samples. DSC thermographs indicate that the Tg is decreasing as the addition of Fe2O3 content. Increase in thermal stability is observed upon adding K2O to the F0 sample and increase in the Fe2O3 content further enhanced the thermal stability up to 187 °C. Optical band gap energy (Eg) of the studied glass system is found to reduce with increasing Fe2O3 content. A band observed around 450 nm in UV absorption spectra is due to the d-d transition of 6A1g(S) ? 4T2g(G) which indicates the presence of iron ion in trivalent state (Fe3+) with distorted octahedral symmetry. The oxide ion polarizability values determined using the refractive index and optical band gap energy are found to be increasing monotonically with partial incorporation of K2O content and with increasing Fe2O3 content. The FTIR and Raman spectroscopy studies confirmed the network modifier role of Fe2O3. The radial-median cracks produced due to Vickers indentation were studied and it confirmed the enhancement in brittleness of the samples as Fe2O3 content increased. Further efforts have been made to analyse and establish correlation between the physical and mechanical properties with the structural modification of the studied glass system. © 2019 Elsevier Ltd and Techna Group S.r.l.