Effect of Na+ Ions on the Mechanical Properties of Lithium Aluminosilicate Glass

A series of lithium aluminosilicate glasses with the composition of 70SiO₂–10Al₂O₃–5K₂O–15Li₂O–xNaCl (x = 0.5, 1.5, 2.5, 3.5 and 4.5 wt %) were prepared by the melt-quenching method. The effect of NaCl addition on mechanical properties was assessed. It was found that both the glass density and the hardness decreased with increasing content of NaCl from 0.5 to 3.5 wt %. Interestingly, Vickers hardness of the glass increased when NaCl content increased by 4.5 wt %. Raman test results show that NBO/T in the glass increases with NaCl, that is, the decrease of the degree of polymerization of the glass network due to the breaking of Si–O–Si bonds. Since the Si–O–Si covalent bond is the strongest bond in the silicate glass, the glass structure tends to be depolymerized, and the density and Vickers hardness decrease. Thus, we attribute the hardness increasing at 4.5 wt % NaCl addition to the fact that Na⁺ enters the network pores acting as network modifier.