Nonisothermal crystallization kinetics and microstructure evolution of calcium lanthanum metaborate glass

This paper reports results on the crystallization kinetics of 35.5CaO–7.25La₂O₃–57.25B₂O₃ glass under nonisothermal conditions based on the studies carried out from the differential thermal analysis upon using various well-established models. The crystalline phases formed during the optimized ceramization process have been confirmed from the X-ray diffraction. The activation energies of the first (formation of CaLaB₇O₁₃) and second (formation of LaBO₃) crystallization events have been estimated using the conventional methods of Kissinger, Augis–Bennett, Ozawa, and Matusita, and the results are found to be in good agreement with each other. The Avrami exponents that are determined by these models for the crystallization of CaLaB₇O₁₃ and LaBO₃ are found to be in the range of (1.81–2.35) and (4.03–4.65), respectively. This indicates that the formation of CaLaB₇O₁₃ is dominated by a surface crystallization, whereas LaBO₃ is formed by three-dimensional bulk crystallization with an increased rate of nucleation. This observation is further validated by microstructural investigation, which shows the formation of CaLaB₇O₁₃ phase as a surface layer and a bulk crystallization of LaBO₃ in optimally ceramized samples.