分别针对包含 Cs、Sr、U 模拟核素的地质水泥固化体,以热处理温度为变量,通过考察固化体热处理前后质量、体积、抗压强度以及物相等参量的变化规律,以此评价地质水泥的热稳定性.实验结果表明,当T≤300 °C时,三类水泥固化体的外观无明显变化,体积收缩率控制在3%以下,抗压强度损失率低于25%,仅部分水化产物脱水引起较大失重,体现为显微结构中针状、网状特征组织减少,孔隙增加;当T>700 °C时,水泥外表面出现明显裂纹,水化产物已完全相变,但结构仍未见崩塌,显微组织变得更加致密并具有陶瓷结构特征,导致抗压强度随温度升高反向增大,展现出良好的高温热稳定性.新生成的硅灰石相 Ca3Si3O9发生同素异构转变是导致固化体表面开裂的主要原因.%[Background] The thermal stability of geological cement waste forms containing high pyrolysis products such as Sr and Cs, is an important index for performance evaluation of the nuclear waste solidified body. [Purpose] This paper aims to evaluate the thermal stability of geological cement waste forms. [Methods] Cement waste forms containing Sr, Cs and U were prepared. The changes of mass, volume, compressive strength and other parameters for cement waste forms were observed after heat treatment at different temperatures, and the phase and structure of the samples were analyzed by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). [Results] The experimental results showed that when T≤300 degree Celsius, the appearance of the three kinds of cement waste forms had no obvious change; volume shrinkage and the compressive strength loss rate were less than 3% and 25%, respectively. Only part of the hydration product dehydration caused a greater weight loss, corresponding to the decrease of the needle, reticular characteristic organization and the increase of porosity in microstructure. When T>700 degree Celsius,the cement surfaces had many significant cracks and hydration products had complete phase change, but the structure had not yet collapsed; the microstructure became more dense and had ceramic structural features, which resulted in a compressive strength increasing inversely with temperature, exhibiting good thermal stability at high temperature. The formation of the newly wollastonite phase Ca3Si3O9was the main reason for the surface cracking of the geological cement waste forms. [Conclusion] Compared with ordinary Portland cement (OPC) and alkali activated cement (AAC) cement waste forms, the geological cement waste forms have better thermal stability.
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