The thermal stability of geopolymer pastes with different Si/Al ratios (1.5–3.0) and sodium activators (NaSiO and/or NaOH) were evaluated in this study. The inclusion of NaSiO induced an active geopolymer reaction, enhancing pre-heating compressive strength, but gradually reduced from 300 °C due to vapor pressure and microstructural deterioration caused by entrapped physically bound water. Conversely, the strength of geopolymers containing only NaOH remained stable or increased up to 600 °C, owing to additional geopolymerization from unreacted raw materials and compact matrix induced by thermal shrinkage. The aluminosilicate networks of all geopolymers remained relatively stable until crystalline nepheline formed above 800 °C; larger crystalline particles were formed in geopolymers with NaSiO owing to its denser geopolymer matrix, whereas smaller crystalline particles were formed in geopolymers with smaller Si/Al and only with NaOH, resulting in fewer voids and stable mechanical strength. Swelling of silica was notable in NaSiO-activated geopolymer, resulting in greater strength loss upon heating, indicating that NaSiO hinders the thermal stability of geopolymers at extreme temperatures.

中文翻译：

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根据硅铝比和钠活化剂评价偏高岭土基地质聚合物的热稳定性

本研究评估了具有不同 Si/Al 比 (1.5–3.0) 和钠活化剂（NaSiO 和/或 NaOH）的地质聚合物浆料的热稳定性。 NaSiO的加入引发了活跃的地质聚合物反应，增强了预热抗压强度，但由于蒸气压和截留的物理结合水引起的微观结构恶化，从300°C开始逐渐降低。相反，由于未反应的原材料和热收缩引起的致密基质发生了额外的地质聚合，仅含有 NaOH 的地质聚合物的强度在高达 600 °C 时保持稳定或增加。所有地质聚合物的硅铝酸盐网络都保持相对稳定，直到 800 °C 以上形成结晶霞石；由于地质聚合物基体较致密，NaSiO 地质聚合物中形成较大的结晶颗粒，而 Si/Al 较小且仅含 NaOH 的地质聚合物中形成较小的结晶颗粒，从而导致空隙较少和稳定的机械强度。在 NaSiO 活化的地质聚合物中，二氧化硅的溶胀现象很明显，导致加热时强度损失更大，表明 NaSiO 阻碍了地质聚合物在极端温度下的热稳定性。