Jensen Rune Wittendorff Mønster, Skibsted Jørgen
Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus C, Denmark.
Magn Reson Chem. 2025 Jul;63(7):476-494. doi: 10.1002/mrc.5528. Epub 2025 May 15.
Calcium silicates react readily with CO under aqueous conditions, forming CaCO and silica gel. This is utilized to produce new cement binders and to sequester CO, thereby contributing to a lowering of the CO footprint for the cement industry. The present work investigates aqueous carbonation of three hydraulic and three non-hydraulic calcium silicates with the aim of analyzing the impact of the Ca/Si ratio on the structure of the amorphous silica gel and on the extent and rate of carbonation. This information is obtained from Si NMR experiments, whereas C NMR and FT-IR are used to characterize the polymorphic forms of CaCO formed upon carbonation. The structure of the silica gel is not dependent on the type of carbonated calcium silicate or their Ca/Si ratio. In addition, the amounts of CaCO from TGA analysis match well the theoretical maximum values. Si and Si{H} CP/MAS spectra of a commercial silica gel are very similar to those observed for the carbonated calcium silicates, which strongly suggests that a hydroxylated silica gel without incorporated Ca ions constitutes the silica gel in carbonated calcium silicates. From C NMR and FT-IR, it is found that calcite is the principal CaCO polymorph for all samples carbonated for 6 h. However, aragonite and calcite do co-exist during the initial carbonation (20 min) of γ-CaSiO. Comparison of the carbonation evolution for the hydraulic and non-hydraulic calcium silicates strongly suggests that an early hydration and formation of C-S-H is not a required initial step in the aqueous carbonation process.
硅酸钙在水性条件下能与一氧化碳迅速反应，生成碳酸钙和硅胶。这一特性被用于生产新型水泥粘结剂并封存一氧化碳，从而有助于降低水泥行业的碳足迹。本研究调查了三种水硬性硅酸钙和三种非水硬性硅酸钙的水相碳酸化过程，旨在分析钙硅比（Ca/Si）对无定形硅胶结构以及碳酸化程度和速率的影响。这些信息通过硅核磁共振实验获得，而碳核磁共振和傅里叶变换红外光谱则用于表征碳酸化过程中形成的碳酸钙的多晶型形式。硅胶的结构并不取决于碳酸化硅酸钙的类型或其钙硅比。此外，热重分析得到的碳酸钙含量与理论最大值吻合良好。商业硅胶的硅-29和硅-29{H}交叉极化/魔角旋转光谱与碳酸化硅酸钙所观察到的光谱非常相似，这有力地表明，未掺入钙离子的羟基化硅胶构成了碳酸化硅酸钙中的硅胶。通过碳核磁共振和傅里叶变换红外光谱发现，对于所有碳酸化6小时的样品，方解石是主要的碳酸钙多晶型。然而，在γ-硅酸钙的初始碳酸化阶段（20分钟），文石和方解石确实共存。对水硬性和非水硬性硅酸钙的碳酸化过程进行比较，强烈表明早期水化和C-S-H的形成并非水相碳酸化过程中必需的初始步骤。
