Zn 2+ - Controlled Crystallization and Microstructure in K-Li-Mg-B-Si-Al-F Glass
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.526
Zn2+- Controlled Crystallization and Microstructure in K-Li-Mg-B-Si-Al-F Glass Mrinmoy Garai, Anoop K. Maurya, Shibayan Roy Materials Science Centre, Indian Institute of Technology, Kharagpur-721302, India
Abstract Text: The crystallization of (9-X) K2O-1Li2O-12MgO-10B2O3-40SiO2-16Al2O312MgF2-X PbO/BaO/ZnO (X =0/5) composition (wt.%) were studied by means of dilatometry, DSC, XRD, SEM and microhardness analysis. Density of base K-Li-Mg-B-Si-Al-F glass (2.59 g.cm–3) is found to be increased on addition of the network modifier oxides PbO, BaO and ZnO content. Addition of Pb2+, Ba2+ and Zn2+ furthermore increased the glass transition temperature (Tg.). A characteristic exothermic hump is found to be appeared in DSC thermograph at the temperature range 800-950°C; and that is ascribed to the formation of crystalline phase fluorophlogopite mica, KMg3(AlSi3O10)F2. Opaque glass-ceramics were prepared from K-Li-Mg-B-Si-Al-F glasses (with and without containing PbO, BaO and ZnO content) by controlled heat-treatment at 1000°C. Interlocked type microstructure combined of flake like fluorophlogopite mica crystals is obtained in ZnO-containing K-Li-Mg-B-Si-Al-F glass-ceramic; and such microstructural pattern is ascribed to cause large thermal-expansion (>11.5×10-6/K, 50-800°C).Vickers Microhardness of base glass-ceramic (5.12 GPa) is increased when contains ZnO (5.26 GPa). ZnO-containing boroaluminosilicate glass-ceramic is, hence, considered with potential interest as they can exhibit the microcrack resistivity in high temperature recycling operation (like SOFC).
INTRODUCTION Boro-alumino-silicate (BAS) based glass-ceramics are technologically important material because of their well-grained microstructure resulting in large thermal expansion value and enough mechanical strength [1-4]. K2O-Li2O-MgO-B2O3-SiO2-Al2O3-MgF2 is a kind of BAS system easily converts to mica glass-ceramic of fluorophlogopite (KMg3AlSi3O10F2) system by controlled heat-treatment [3, 4]. Alongside the uniform grained microstructure the mica glass-ceramics impart excellent machineability due to layered crystalline structure caused by a basal cleavage along the (001) planes of the plate-shaped crystals. Moreover, these typical sheet silicate structures (mica) provide unique microstructure containing excellent strength, uniformity, and enough thermal stress resistance capability [5]. When, the interlayer ion (i.e. alkali ion) of
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fluorophlogopite (KMg3AlSi3O10F2) crystal is substituted by a different monovalent or bivalent ion by means of similar size, mica phase appears as the solid solution having different chemical formula with a large variation in crystallization and microstructural properties [4, 6]. Bivalent ions like barium (Ba2+), zinc (Zn2+), lead
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