In situ quasi-elastic neutron scattering study on the water dynamics and reaction mechanisms in alkali-activated slags
In situ quasi-elastic neutron scattering study on the water dynamics and reaction mechanisms in alkali-activated slags
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DOI：
10.1039/c9cp00889f
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发表时间：
2019-05-28
影响因子：
3.3
通讯作者：
White, Claire E.
中科院分区：
文献类型：
--
作者：
Gong, Kai;Cheng, Yongqiang;White, Claire E.
在本研究中，采用原位准弹性中子散射 (QENS) 结合等温传导量热法 (ICC)、傅里叶变换红外光谱 (FTIR) 分析和 N-2 吸附测量，探讨 NaOH 和 Na2SiO3 活化矿渣（一类重要的低 CO2 水泥）形成过程中发生的水动力学和反应机制。我们表明，NaOH 活化炉渣中的单个 ICC 反应峰伴随着自由水向结合水的转变（来自 QENS 分析），这直接表明含钠铝取代硅酸钙水合物 (C-(N)-A-S-H) 凝胶的形成，如 FTIR 所证实。相比之下，Na2SiO3 活化的炉渣样品在 ICC 数据中表现出两个不同的反应峰，其中第一个反应峰与约束水向结合水和游离水的转化有关，第二个峰伴随着自由水向结合水和约束水的转化（来自 QENS 分析）。第二次转化归因于主要反应产物（即 C-(N)-A-S-H 凝胶）的形成，如 FTIR 和 N-2 吸附数据所证实。对 QENS、FTIR 和 N-2 吸附数据以及文献中的热力学信息的分析明确表明，第一个反应峰与初始凝胶（类似于 C-(N)-A-S-H 凝胶）的形成有关，该凝胶由 Na2SiO3 溶液中的 Na+ 离子和硅酸盐物质以及炉渣中溶解的 Ca/Al 物质控制。因此，这项研究证明了原位 QENS 与基于实验室的表征技术相结合，在阐明复杂材料中发生的水动力学和相关化学机制方面的力量，并为两种碱激活炉渣形成过程中发生的早期反应提供了重要的机制见解。
In this study, in situ quasi-elastic neutron scattering (QENS) has been employed to probe the water dynamics and reaction mechanisms occurring during the formation of NaOH- and Na2SiO3-activated slags, an important class of low-CO2 cements, in conjunction with isothermal conduction calorimetry (ICC), Fourier transform infrared spectroscopy (FTIR) analysis and N-2 sorption measurements. We show that the single ICC reaction peak in the NaOH-activated slag is accompanied with a transformation of free water to bound water (from QENS analysis), which directly signals formation of a sodium-containing aluminum-substituted calcium-silicate-hydrate (C-(N)-A-S-H) gel, as confirmed by FTIR. In contrast, the Na2SiO3-activated slag sample exhibits two distinct reaction peaks in the ICC data, where the first reaction peak is associated with conversion of constrained water to bound and free water, and the second peak is accompanied by conversion of free water to bound and constrained water (from QENS analysis). The second conversion is attributed to formation of the main reaction product (i.e., C-(N)-A-S-H gel) as confirmed by FTIR and N-2 sorption data. Analysis of the QENS, FTIR and N-2 sorption data together with thermodynamic information from the literature explicitly shows that the first reaction peak is associated with the formation of an initial gel (similar to C-(N)-A-S-H gel) that is governed by the Na+ ions and silicate species in Na2SiO3 solution and the dissolved Ca/Al species from slag. Hence, this study exemplifies the power of in situ QENS, when combined with laboratory-based characterization techniques, in elucidating the water dynamics and associated chemical mechanisms occurring in complex materials, and has provided important mechanistic insight on the early-age reactions occurring during formation of two alkali-activated slags.