Compositional study and properties characterisation of alkaline earth feldspar glasses and glass-ceramics

Fields in which metastable crystallisation of feldspars may occur as a result of heterogeneous nucleation were defined at 1000° C for the systems BaO-Al₂O₃-SiO₂, SrO-Al₂O₃-SiO₂, and CaO-Al₂O₃-SiO₂. The metastable fields of the above barium and calcium systems differ considerably from the respective primary liquidus fields of celsian and anorthite with the tendency for the stoichiometric compositions to be situated at the centre of the metastable region. Various physical and dielectric properties of the glasses and glass-ceramics of the three systems are presented and compared. High linear thermal expansion, high electrical resistivity, and low loss tangent and dielectric constant characterise these glass-ceramics. One of them (No. 2, table I) has, in addition, high heat resistance and translucency at high temperatures.