Study of the crystallization in fast sintered Na-rich plagioclase glass-ceramic

Abstract

A dense, ∼94% of crystalline phase, glass-ceramic based on Na-rich plagioclase feldspar crystallizations has been obtained by a fast sintering process for the first time. By using Sr2+ and Ca2+ as nucleating agents, a unique hierarchical micro-nanostructure is developed in a fast sintering process at 1220 °C. In this work, a thorough study about crystallization processes of this novel material has been extensively carried out through thermal quenching experiments and supported by DTA/TG, Hot stage microscopy, XRD, FE-SEM, TEM/HRTEM and XPS measurements. The study reveals that crystallization takes place in two steps during the sintering process. Microcrystals nucleate on heating at temperatures >900 °C, while nanocrystals start nucleating at the dwelling temperature, 1220 °C. However, it is during holding and cooling time when nanostructures zones grow, and the unique highly crystalline micro-nanostructure is developed. Structural and compositional analysis supported by NMR, shows the main presence of Q4(nAl) albite-like sites and in lesser extent anorthite-like sites, corroborating the formation of a sodic plagioclase structure. The analysis of Si neighbours indicates that chemical environment presents a slight Si/Al disorder at short range.