Synthesis of Calcium Aluminate Glasses

Calcium aluminate glasses can be made using a variety of techniques, depending on the composition required. The ease of devitification is a considerable concern if calcium aluminate glasses are to be used for optical purposes. Although a strong network former such as SiO2 can be added to improve glass-forming ability, this has detrimental effects on the optical properties.

Calcium aluminate glasses can be made quite easily by air quenching liquids of 61:39 composition, which is the composition most extensively used for glass fiber production [20, 44]. The glass-forming ability is considerably enhanced by adding components such as BaO, SrO, and NaO [21] without affecting the optical performance.

A further method of glass synthesis is container-less levitation techniques [39, 40, 49]. In this method, a ceramic precursor of appropriate composition is levitated by a gas jet and laser heated. Samples up to 4-mm diameter can be levitated in this way and because there is no container, heterogeneous nucleation is avoided. This means that liquids can be supercooled considerably and glasses formed from compositions are generally considered to be poor glass-formers, this includes calcium aluminate glasses. Fibers can be extracted from the levitated bead by using a tungsten “stinger” [13].