Disproportionation of Q m (0 ≤ m ≤ 4) species in partially devitrified Li2Si2O5 glasses with small amounts of P2O5

The effect of addition of small amounts of P₂O₅ in the lithium disilicate glasses results in the scavenging of lithium metal ions by a phosphate group, Li₃PO₄. As a consequence of the scavenging, the silicate network partially repolymerises. The phosphate group remains intact during heat treatment of the optically clear, X-ray amorphous and slightly nucleated base glasses. However, the relative amounts of the silicate species, Q_m (0 ≤ m ≤ 4), are dependent on the state of the glasses. These amounts, in the optically clear and X-ray amorphous, do not change with heat treatment but they do change, i.e. disproportionation occurs in the slightly nucleated and milky coloured glasses. The disproportionation follows the relation 2Q₃ → Q₂ + Q₄ which is evident from the relative intensity of the different peaks.