CaO含量对镧硼硅酸盐玻璃陶瓷晶相和化学稳定性的影响

采用熔融冷却法制备了Na₂O-CaO-La₂O₃-B₂O₃-SiO₂玻璃,经热处理获得了硅酸盐氧基磷灰石硼硅酸盐玻璃陶瓷,并采用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、差示扫描量热法(DSC)、产品一致性试验(PCT)法等方法探究了CaO取代SiO₂对该硼硅酸盐玻璃陶瓷物相、微观结构和化学稳定性的影响规律。结果显示:随着CaO含量增加,硅酸盐氧基磷灰石晶相衍射峰增强,其他晶相的衍射峰减弱直至消失,当CaO摩尔分数为15%时获得只含CaLa₄(SiO₄)₃O晶相的玻璃陶瓷样品;CaO含量会对玻璃陶瓷的晶相种类和晶体形状、大小、分布产生影响,CaO含量变化会造成陶瓷相晶体发生团簇和长大;采用PCT法浸泡28 d后,所有样品关于Si、Ca、La三种元素的归一化浸出率(g·m^-2·d^-1)均保持在10^-3数量级以下,表明其具有优异的化学稳定性,且CaO摩尔分数为15%的玻璃陶瓷样品化学稳定性最优异。研究结果表明,硅酸盐氧基磷灰石硼硅酸盐玻璃陶瓷是固化富La和某些锕系元素高放废物的潜在基材。

Effect of CaO Content on Crystalline Phases and Chemical Stability of Lanthanum Borosilicate Glass-Ceramics

The Na₂O-CaO-La₂O₃-B₂O₃-SiO₂ glass were prepared by melt-quenching method. Then, the silicate oxyapatite borosilicate glass-ceramics were obtained by heat treatment of the prepared glass. After that, the X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and the product consistency test (PCT) were used to explore the effect of CaO substitution for SiO₂ on phases, microstructure and chemical stability of borosilicate glass-ceramics. The results show that with the increase of CaO content, the diffraction peaks of silicate oxyapatite crystalline phase are enhanced, and the others are weakened until disappearing. When the mole fraction of CaO is 15%, only the CaLa₄(SiO₄)₃O crystalline phase is detected in the glass-ceramics samples. The crystalline phases types, shapes, sizes and distributions of glass-ceramics are affected by CaO content, and the cluster and growth of ceramics crystalline phases are caused by the change of CaO content. After immersing by the method of PCT for 28 d, the normalized leaching rates (g·m^-2·d^-1) of Si, Ca and La of all samples remain below the order of 10^-3, indicating that the glass-ceramics samples have excellent chemical stability. In addition, the glass-ceramics samples containing the CaO mole fraction of 15% exhibit the best chemical stability. The results show that the borosilicate glass-ceramics containing silicate oxyapatite are potential substrates for immobilization high-level radioactive wastes containing La-rich and some actinide rich.