Studying effect of MoO3 on elastic and crystallization behavior of lithium diborate glasses

The effect of MoO3 addition on the crystallization characteristics of 2Al2O3–23Li2O–(75 − x) B2O3 glass (where x MoO3 = 0, 10, 20, and 40 mol %) has been investigated. The compositional dependence of the glass transition (Tg), and crystallization (Tc) temperatures was determined by the differential thermal analysis (DTA). It was found that both the Tg and Tc decrease with increasing MoO3 content. The amorphous nature of the as-quenched glass and crystallinity of the produced glass–ceramics were confirmed by X-ray powder diffraction (XRD) analysis. Glass–ceramics embedded with diomignite (lithium diborate, Li2B4O7) were produced from all investigated glasses by heat-treating the as-quenched glasses at the appropriate temperatures obtained from the DTA traces. Addition of MoO3 to the glass composition at 10% MoO3, causes the formation of lithium molybdenum oxide (Li4MoO5) crystalline phase in addition to the diomignite phase. Increasing MoO3 content to 20% causes a phase transformation of lithium molybdenum oxide from the (Li4MoO5) to the (Li2MoO4) phase and the formation of another lithium borate (Li4B2O5) phase in addition to the diomignite. Further increase of MoO3 content to 40% results in another phase transformation to the lithium aluminum molybdenum oxide [LiAl(MoO4)2], and, in this case, the molybdenum content was excess enough to crystallize the molybdate (MoO3) itself. Scanning electron microscopy (SEM) was used to characterize the morphology and microstructure of the formed solid solution phases. The values of the Tg decrease with increasing the MoO3 content. The ultrasonic wave velocities and elastic moduli were determined using the pulse-echo method. Both velocities (vL and vT) were increased as the MoO3 content, this increase can be attributed to the higher bond strength of Mo–O (607 kJ mol−1) than that of B–O (392 kJ mol−1).