Alkali ions play a crucial role in cement hydration as they are the first species to dissolve, resulting in a pH increase, which promotes the hydration reactions. The location of the alkalis after hydration is less understood; however, it is known that significant amounts are associated with the principal binding component, the calcium-silicate-hydrate (C–S–H) phase. The present work investigates the potential of ²³Na NMR to study adsorption, incorporation, and hydration states of sodium in pure C–S–H phases with Ca/Si ratios of 0.8 and 1.4, synthesized from Ca(OH)₂ and silica in 0.5 M NaOH solutions. The ²³Na NMR spectra (14.1 T) of the synthesized samples are dominated by a featureless resonance from sodium coordinated to water in [Na(H₂O)₆]⁺ complex ions. Dehydration of the samples in an oven, by long-term MAS spinning, or by storage at different humidities results in a systematic shift of the main resonance toward lower frequency, reflecting sequential removal of H₂O from the sodium hydration shell. Lineshape analyses reveal that the low-frequency shifts result from increasing quadrupole couplings for constant isotropic chemical shifts. Rehydration of the samples shows that water can be incorporated into the hydration shell again. ²³Na MAS and MQMAS NMR spectra at different magnetic fields (14.1 and 22.3 T) allow identification of three distinct sodium environments in the C–S–H samples, for which ²³Na isotropic chemical shifts and quadrupolar product parameters have been determined with good accuracy. The three resonances are assigned to a surface Na site and two interlayer Na sites in the C–S–H structure.

中文翻译：

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1H 和 23Na NMR 实验在碱性条件下合成的 C-S-H 相中的钠位点和水合状态


碱离子在水泥水化中起着至关重要的作用，因为它们是最先溶解的物质，导致 pH 值升高，从而促进水化反应。水合后碱的位置知之甚少。然而，众所周知，大量与主要结合成分、硅酸钙水合物 (C-S-H) 相相关。目前的工作研究了 ²³ Na NMR 在研究 Ca(OH) 合成的 Ca/Si 比为 0.8 和 1.4 的纯 C-S-H 相中钠的吸附、掺入和水合状态的潜力。 ) ₂ 和二氧化硅在 0.5 M NaOH 溶液中。合成样品的 ²³ Na NMR 谱 (14.1 T) 主要是[Na(H ₂ O) ₆ ] ⁺ 络离子。通过长期 MAS 旋转或在不同湿度下储存，在烘箱中对样品进行脱水，导致主共振系统地向较低频率移动，反映了从钠中顺序去除 H ₂ O水合壳。线形分析表明，低频位移是由于恒定各向同性化学位移增加四极耦合所致。样品的再水化表明水可以再次并入水化壳中。 ²³ 不同磁场（14.1 和 22.3 T）下的 Na MAS 和 MQMAS NMR 谱可以识别 C-S-H 样品中三种不同的钠环境，其中 ²³ Na 各向同性化学位移和四极产物参数的测定具有良好的准确性。三个共振分配给 C-S-H 结构中的一个表面 Na 位点和两个层间 Na 位点。