Zn2+ Substitution by Pb2+ in Alkaline-boro-aluminosilicate Glass-ceramics: Microstructural Aspects

Abstract

This study exemplifies the effects of 5 wt.% Pb 2+ addition replacing the same Zn 2+ content on crystallization and microstructure of 10B2O3-16Al2O3-39SiO2-12MgO-12MgF2-4K2O-1Li2O-1AlPO4 (wt.%) glass-ceramic composite. Increase of linear thermalexpansion (6.93 to 7.18×10-6 /K at 50-600°C) in substituting Zn 2+ by Pb 2+ is attributed to the field-strength of cations. Opaque crystalline glass-ceramics are derived from the transparent glasses (synthesized by single-step melt-quenching at 1500 O C) by controlled heat-treatment at 1050°C and the predominant crystalline-phase was identified as fluorophlogopite mica, KMg3AlSi3O10F2. FFESEM of the ZnO containing glass-ceramics revealed that 100-200 µm sized plate-like crystals are in 'well-packed interlocked arrangement'; which changed to 'nanocrystalline microstructure' combined of 'spherical droplet like' nanocrystals (crystal size = 10-50 nm) in attendance of PbO. Decrease in linear thermal-expansion (11.03 to 7.93 × 10-6 /K at 50-700°C) due to the substitution of ZnO is ascribed to the crystallization inhibiting tendency of PbO towards boroaluminosilicate system. Thermal-expansion of ZnO containing glass-ceramic is large (> 11 × 10-6 /K at 50-700 and 50-800°C) which can exhibit their enough thermal shock resistivity to be suitable for high-temperature sealing application.