La3+存在形式对白云鄂博稀选尾矿微晶玻璃性能的影响

选取白云鄂博稀选尾矿和粉煤灰为主要原料, 采用熔铸法制备了0–4 wt%La₂O₃掺杂的CaO-MgO-Al₂O₃-SiO₂系微晶玻璃. 利用DTA, XRD, SEM, TEM+EDS和性能测试手段研究La³⁺在白云鄂博稀选尾矿微晶玻璃中的存在形式及其对该微晶玻璃显微结构、抗折强度和耐腐蚀性的影响. 结果表明, La³⁺以置换固溶方式进入辉石主晶相, 1 wt%的La₂O₃可促进辉石主晶相形成. 超过1 wt%的La₂O₃与基础玻璃组分反应生成Ca₃La₆(SiO₄)₆第二相, 并与辉石相争夺Ca²⁺和Si⁴⁺离子来阻碍辉石相形成. 添加1 wt% La₂O₃的微晶玻璃综合性能最优, 其抗折强度和密度分别为198 MPa和3.18 g/cm³.

Effect of existence form of La3+ on the properties of the Bayan Obo Mine tailing glass ceramics

Clarifying the effect of rare earth (RE) elements on the microstructure and properties of glass ceramics is technically and theoretically important for the further development. Thus the glass ceramics of the CaO-Al₂O₃-MgO-SiO₂ with 0–4 wt% La₂O₃ are fabricated from Bayan Obo Mine tailing and fly ash by means of the conventional melting method. Effect of the existence form and the concentration variation of La³⁺ ions on the crystallization behavior, microstructure and properties, such as bending strength, chemical resistance and density of the glass ceramics, are investigated by DTA, XRD, SEM, TEM and EDS. Results show that both the glass transition and crystallization peak temperature of the samples shift to high temperatures with increasing La₂O₃ content. Augite Ca(Mg, Al, Fe)(Si, Al)₂O₆] is the only crystalline phase in all the five samples. Augite crystals in the form of column are distributed uniformly within the residual glass, and their average size is below 100 nm. The crystallinity of augite has been effectively enhanced by the addition of 1 wt% of La₂O₃. Owing to the similar ion radius of La³⁺ and Ca²⁺, Ca²⁺ ions within augite have been partially substituted by La³⁺. Such a substitution can serve as one of the key factors to the enhancement of bending strength of the investigated material with 1 wt% of La₂O₃ because of the stronger bonding energy of La-O than Ca-O. With further increase of La₂O₃ from 1 to 4 wt%, the Ca₃La₆ (SiO₄)₆ secondary phase forms on the boundary between augite grains and residual glass phase in the form of irregular-shaped particles and this in turn hinders the growth of augite crystals. The crystallinity of augite will be decreased gradually since then. Meanwhile, the formation of this La-riched phase (Ca₃La₆(SiO₄)₆) may also prevent augite grains from growing through consuming Ca²⁺ and Si⁴⁺ ions which are two key constituent elements of augite grains. Therefore, there are two forms of La³⁺ ions in the glass ceramics developed from Bayan Obo Mine tailing: one is the substitution of Ca²⁺ ion by La³⁺ in augite crystalline phase, and the other is the forming of secondary crystalline phase La-riched Ca₃La₆ (SiO₄)₆. The glass ceramic sample with 1 wt% of La₂O₃ shows the optimum properties. Its density is 3.18 g/cm³, the bending strength is 198 MPa, and the weight loss in 20 wt% NaOH of this sample is lower than 1 wt%.