Reagent grade chemicals were used to explore glass formation ability and allocate the glass forming area for the glass system SiO2-P2O5-Al2O3-MgO-Na2O. FT-IR, DTA, DSC and TMA techniques were employed to characterize the obtained glasses. The multicomponent, mixed network glasses, in which AlPO4 tetrahedral units are being incorporated into the network structure through substitution for pairs of SiO4 tetrahedra, exhibit high durability, low thermal expansivity (at Al2O3/P2O5 ˃1), relatively high softening temperatures (at low P2O5 contents) and an increased thermal stability (poor tendency for crystallization). When heated at high temperatures and / or for long periods of time, and depending on their AlPO4 content, together with the Al2O3/P2O5 ratio, the glasses crystallize through a multistage process involving reconstruction and depolymerization of the glasses network structure. The crystallization behavior of many different glasses was investigated, phases identified and characterized, through XRD, and SEM coupled with EDX and X-ray mapping together with optical microscopy. The powder ceramization route had to be used to achieve the devitrification of the glasses with high thermal stability. Berlinite, corundum, spinel, indialite and cordierite among others were the crystallizing phases when different glasses were heated for various times. Microporous materials made of some of these technically favorable minerals, and characterized by an interesting morphologies were obtained, through acid leaching of some of the glass-ceramics produced. It is believed that the glass system under investigation is a fertile one, the crystallization of some glasses within it, represents another fabrication route for obtaining glass-ceramics with specific crystalline phases, as well as microporous materials made of such phase. In both cases, packages of the most suitable properties are obtainable.
Combining high hardness and crack resistance in mixed network glasses through high-temperature densification