Mrinmoy Garai

Influence of Ce, Nd, Sm and Gd oxides on the properties of alkaline-earth borosilicate glass sealant

Abstract In this study, the influence of CeO2, Nd2O3, Sm2O3 and Gd2O3 on various properties of the melt-quench route derived SrO–CaO–ZnO–B2O3–SiO2 glass have been investigated. Both the precursor glasses and heat treated glasses are characterized by dilatometry, differential scanning calorimetry (DSC), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The density and coefficient of thermal expansion of the glasses varies in the range 3.557–3.804 g cm−3 and 10.5–11.2 × 10−6 K−1 (50–800 °C) respectively. Decrease in crystallization tendency with increase in cationic field strength of the ions is well supported by the increasing crystallization activation energy of the glasses calculated by Kissinger, Augis–Bennett and Ozawa models. XPS study revealed the presence of both Ce3+ and Ce4+ ions and an increase in characteristic binding energy of the respective rare earth elements from their core level studies. The Knoop hardness of the glasses varies in the range 6.03–6.28 GPa. The glass transition, glass softening and crystallization temperature; density and hardness of the glasses increased with increase in cationic field strength of the incorporated ions. The thermomechanical properties of the Gd2O3 containing glass advocate its applicability as the most promising sealant in solid oxide fuel cell.

Nucleating agent controlled crystallization and thermal properties of K–Mg–B–Al–Si–F glasses

In exploring the nucleating agent controlled crystallization of aluminosilicate glass, the K2O-MgO-B2O3-Al2O3-SiO2-MgF2 glass-system with excess TiO2 and ZrO2 content (5 wt%) were studied by means of a non-isothermal DSC technique, X-ray diffraction, FESEM and dilatometry. The aluminosilicate glasses were synthesized by single step melt quench technique at 1550°C (2 h). Addition of TiO2 and ZrO2 effectively increased the glass transition temperature (Tg) as well as softening point (Td). According to the DSC study, the crystallization exotherm exhibited the highest peak in the temperature range 800-950°C; and the crystallization temperature (Tc) considerably decreased in presence of ZrO2 content. The addition of 5 wt.% ZrO2 furthermore affects in increasing the glass phase stability due to formation of crystallization onset point at higher temperature. Opaque glass-ceramics were derived from the K2O-MgO-B2O3-Al2O3-SiO2-MgF2 glasses by the controlled heat treatment at 800°C, and the evolved crystalline phases were identified (XRD) as norbergite (Mg2SiO4.MgF2), clinohumite [Mg7F2(SiO4)3], chondrodite [Mg5F2(SiO4)2], mullite (3Al2O3.2SiO2) and enstatite (MgSiO3). After heat treatment at 950°C, the glasses were converted into fluorophlogopite mica (KMg3AlSi3O10F2) glass-ceramics; and such fluorophlogopite crystallization was enhanced in presence of ZrO2 content. Higher value of thermal expansion coefficient (CTE) is evaluated for these glassceramics; and it is ascribed due to the formation of mica crystals. The interlocked type mica containing glass-ceramic microstructure is achieved in such glass-ceramic when contains ZrO2. This directly suggests the usability of this ZrO2 containing K2O-MgO-B2O3-Al2O3-SiO2-MgF2 glass as solid oxide fuel cell (SOFC) sealant.

Nanoglass and Nanostructured Chalcogenide Glasses

In this chapter, a brief review of the emergent areas of metallic and chalcogenide glasses (ChGs) is presented. In the beginning, the basic concept, synthesis, properties, and applications of nanoglass are described. Nanoglasses of oxide glass systems are also documented here because the nanoglass formation is not limited to the metallic glass systems only, but nanoglasses of oxides are also reported. In the family of nanostructured ChGs, nanometal containing ChGs and nanocrystallinity in ChGs are most important. Hence synthesis, characterization techniques, properties, and applications of these two types of ChGs nanocomposites are elucidated with up-to-date literature evidence.

Effects of M2

In understanding the effect of K+ substitution by M2+ (M = Ca, Sr, and Ba) on crystallization and microstructural properties of boroaluminosilicate glass system, the SiO2-MgO-Al2O3-B2O3-MgF2-K2O-Li2O-AlPO4 glasses were prepared by single-step melt-quenching at 1500°C. Density of base glass (2.64 g·cm−3) is found to be decreased in presence of CaO and SrO. is increased by 5–10°C and decreased by 13–20°C on addition of M2+. The variation of , and decrease of thermal expansion (CTE) from 7.55 to 6.67–6.97 (×10−6/K, at 50–500°C) in substituting K+ by M2+ are attributed to the higher field-strength of Ca2+, Sr2+, and Ba2+. Opaque mica glass-ceramics were derived from the transparent boroaluminosilicate glasses by controlled heat treatment at 1050°C (duration = 4 h); and the predominant crystalline phase was identified as fluorophlogopite (KMg3AlSi3O10F2) by XRD and FTIR study. Glass-ceramic microstructure reveals that the platelike mica flake crystals predominate in presence of K2O and CaO but restructured to smaller droplet like spherical shaped mica on addition of SrO and BaO. Wide range of CTE values (9.54–13.38 × 10−6/K at 50–800°C) are obtained for such glass-ceramics. Having higher CTE value after crystallization, the CaO containing SiO2-MgO-Al2O3-B2O3-MgF2-K2O-Li2O-AlPO4 glass can be useful as SOFC sealing material.