Structure and crystallization of glassy La2O3-CaO-SiO2-CaF2 system rare-earth slag with variable rare-earth content

Raman spectroscopy and differential scanning calorimetry were employed to investigate the structure, crystallization behavior and crystallization activation energy of the La2O3-CaO-SiO2-CaF2 (RE) slags with different RE contents. Raman spectroscopy analysis indicated that the RE oxide, La2O3, acted as a network modifier, with the increase in La2O3 content decreasing the degree of polymerization of the RE slag. As the La2O3 content increased, the number of highly polymerized Q(2) and Q(3) species gradually decreased, while the minimally polymerized Q(0) and Q(1) species increased, and depolymerizing the complex network structure in the slag. The slag mainly contained the following three crystal phases: (Ca, La)(5)(SiO4)(6)F, CaSiO3, and Ca4Si2O7F2. When the La2O3 content increased to 15%, an additional Ca2SiO2F2 crystalline phase appeared. Furthermore, an increase in the La2O3 content from 10 to 17% reduced the crystallization temperature of the RE phase in the slag from 1641 to 1599K. The crystallization behavior of the RE phase under different cooling rates revealed that the increase in La2O3 content reduced the effective crystallization activation energy of the RE phase, thus enhancing the crystallization of the RE phase. Thus, a correlation between the structure and crystallization of the RE slag was established.