Crystallization features and physico-chemical properties of alkali and alkaline aluminoborate glass–ceramics

Abstract

Preparation and characterization of glass–ceramics based on CaO–Al2O3–B2O3 system, modified by replacing CaO by different alkali and alkaline earth oxides, and In2O3/Al2O3 substitustion were implemented. Different crystalline phases, including β-CaAl2B2O7, Na2Al2B2O7, LiAl5O8, Li4Al4B6O17, Li2AlBO4, SrAl2B2O7, BaAl2B2O7, α-(Ca1-x,Inx)Al2B2O7, and InBO3, were developed from the heat-treated glasses. The incorporation of In3+ in the position of Ca2+ in β-CaAl2B2O7 crystal lattice was responsible for phase transition of β-CaAl2B2O7 to α-CaAl2B2O7 phase. The coefficient of thermal expansion CTE of prepared glass–ceramics was between −65 × 10−7 and 72 × 10−7 K−1 in the temperature range from 25 to 600 °C. The glass–ceramic specimens containing XAl2B2O7 as the principal crystalline phase were characterized by negative CTE values. In contrast, the replacement of CaO in the base glass by alkali oxides like Na2O and Li2O led to a dramatic transformation of the negative CTE to postive values. The complete replacement of calcium oxide in the base glass by various alkali and alkaline earth oxides markedly decreased the chemical durability of the investigated glass–ceramic specimens, while substitution of Al2O3 by In2O3 resulted in improving the chemical stability of the crystalline samples. The density of the glass specimens were found to be within the range 2.35–3.38 g/cm3, while the density of the glass–ceramic samples was in the range of 2.37–3.13 g/cm3.