Composition Dependence Of Spontaneous Crystallisation Of Phosphosilicate Glass Melts During Cooling

The crystallisation behaviour of alumino-phosphosilicate melts during cooling is studied by means of differential scanning calorimetry, x-ray diffraction and viscometry. The results show that there is a pronounced impact of alkaline earth oxide, alkali oxide and fluoride on the crystal type and degree of crystallisation. It is found that adding NaF into the studied compositions slightly decreases melt fragility and improves both the glass forming ability and melt workability. This effect is associated with the unique structural role of NaF compared to the other modifier oxides. It is also found that the onset viscosity of crystallisation can be used as a parameter for describing both glass forming ability and melt workability.