不同钙硅比水化硅酸钙的太赫兹时域光谱研究

doi:10.16552/j.cnki.issn1001-1625.2026.0083

摘要/Abstract

摘要：

水化硅酸钙（C-S-H）是水泥基材料强度的主要来源，其结构具有无序非晶特征。揭示C-S-H的中程有序结构与宏观性能之间的关联，仍是水泥材料研究中的关键难题。本文利用太赫兹时域光谱技术（THz-TDS），系统研究了钙硅比（钙与硅的摩尔比，Ca/Si）为0.5~1.7时合成C-S-H的低能动力学特征。结合X射线衍射、傅里叶变换红外光谱及热重分析等表征手段，并引入有效介质理论去除微量结晶杂质的干扰，成功提取了C-S-H的本征太赫兹光学参数。并通过介电损耗归一化处理，在约1 THz处观测到C-S-H的玻色峰（boson peak）特征，并发现玻色峰强度随Ca/Si呈非单调演变，在Ca/Si为1.0处达到最大，并向两侧递减。基于太赫兹玻色峰频率，可计算得到中程序特征长度为1 nm量级。本研究表明，太赫兹玻色峰可作为探测C-S-H凝胶微观结构演变及刚度特性的有效指纹，为理解水泥水化产物的“结构-性能”关系提供了新的物理视角。

关键词: 水化硅酸钙, 太赫兹时域光谱, 钙硅比, 介电性质, 玻色峰, 中程序

Abstract:

Calcium silicate hydrate （C-S-H） is the main binding phase of hydrated Portland cement and largely determines strength and durability of concrete. It is nanocrystalline and mostly amorphous， with short-range order but no long-range periodicity. The medium-range order （MRO） that connects these two scales is thought to control the mechanical and transport behaviour of concrete， yet it is hard to measure， and the link between the nanostructure of C-S-H and its properties is still poorly understood. The boson peak， an excess of low-frequency vibrational states common to disordered solids， reflects both the MRO and the nanoscale fluctuation of elastic constants. For C-S-H it has been predicted by molecular-dynamics simulations but not yet measured. Terahertz （THz） radiation （0.1 THz to 10 THz） lies in the frequency range of these collective vibrations， so terahertz time-domain spectroscopy （THz-TDS） can be used to probe the boson peak directly.

C-S-H gels with nominal calcium-to-silicon molar ratios （Ca/Si） of 0.5， 0.8， 1.0， 1.4， and 1.7 （actual values 0.54 to 1.74 after impurity correction） were synthesized hydrothermally under nitrogen. They were characterized by X-ray diffraction （XRD）， Fourier-transform infrared spectroscopy （FTIR）， thermogravimetric analysis （TGA）， X-ray fluorescence， laser particle sizing and helium pycnometry， which revealed a poorly crystalline tobermorite-like gel with turbostratic stacking， and provided the contents of water and impurities （portlandite and calcite）. THz-TDS spectra were recorded in transmission on HDPE-diluted pellets over 0.4 THz to 3.0 THz， and the complex refractive index， absorption coefficient and dielectric function were obtained. To isolate the response of the gel itself， the dielectric contributions of the crystalline impurities were removed with an effective-medium （Bruggeman-Hanai-Sen） model， using volume fractions taken from XRD and TGA. For the measured particle sizes， the 1.0 THz to 1.5 THz range falls within the Rayleigh （weak-scattering） regime， so the spectral features come from intrinsic lattice dynamics rather than from particle scattering.

The intrinsic refractive index （1.58 to 1.85） and the real part of the permittivity show little dispersion， indicating that the water in C-S-H is nano-confined or chemically bound； FTIR showed the Si—O band shifting to lower wavenumber and broadening as Ca/Si increased， consistent with depolymerization of the silicate chains. After the dielectric loss was normalized， every sample showed a broad boson peak near 1 THz （0.82 THz to 1.02 THz）， close to values reported for silicate glasses and to the molecular-dynamics prediction for C-S-H. Its intensity varied non-monotonically with composition， peaking at Ca/Si=1.0 and decreasing on both sides of this ratio. This same composition also corresponds to an inflection in the structural-water loss （200 ℃ to 350 ℃） and the narrowest XRD diffuse peak， marking a structural crossover at Ca/Si≈1.0 from a regime governed by silicate-chain connectivity to one governed by interlayer calcium. The boson-peak frequency corresponds to a medium-range dynamical correlation length of about 1.0 nm to 1.5 nm.

These measurements provide experimental evidence of a boson peak in C-S-H and link its strength to the Ca/Si-dependent medium-range order and elastic heterogeneity of the gel. The terahertz boson peak therefore offers a way to probe the low-frequency dynamics of C-S-H that complements the usual static structural methods.

Key words: calcium silicate hydrate, terahertz time-domain spectroscopy, calcium-to-silicon ratio, dielectric property, boson peak, medium-range order

中图分类号:

TQ172

李战国, 陈莹, 李悦, 李翔宇. 不同钙硅比水化硅酸钙的太赫兹时域光谱研究[J]. 硅酸盐通报, 2026, 45(8): 2637-2649.

LI Zhanguo, CHEN Ying, LI Yue, LI Xiangyu. Terahertz Time-Domain Spectroscopy of Calcium Silicate Hydrates with Varying Calcium-to-Silicon Ratios[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(8): 2637-2649.

图/表 12

图1 试验光路示意图

Fig.1 Schematic diagram of experimental optical path

图2 C-S-H样品的XRD谱

Fig.2 XRD patterns of C-S-H samples

图3 C-S-H样品的FTIR谱

Fig.3 FTIR spectra of C-S-H samples

图4 C-S-H样品的TG和DTG曲线

Fig.4 TG and DTG curves of C-S-H samples

表1 C-S-H的成分含量计算结果

Table 1 Calculation results of component content in C-S-H

Ca/Si	Mass fraction/%
Ca/Si	Free water	Interlayer water	Structural water	CH	CC
0.5	6.45	6.59	2.76	7.05	1.31
0.8	7.30	7.65	2.72	4.33	0.04
1.0	7.83	6.36	3.44	5.11	1.70
1.4	6.51	6.40	3.43	6.84	1.81
1.7	5.45	5.67	4.10	9.17	1.72

表2 C-S-H样品的XRF结果

Table 2 XRF results of C-S-H samples

Ca/Si	Mass fraction/%
Ca/Si	SiO₂	CaO	MgO	Al₂O₃	Cl	Fe₂O₃	Cr₂O₃	SrO	NiO	SO₃
0.5	64.695	34.430	0.502	0.308	0.035	0.030	—	—	—	—
0.8	52.392	46.065	0.264	0.042	1.208	—	0.029	—	—	—
1.0	48.249	51.501	0.204	—	0.040	—	—	0.006	—	—
1.4	42.698	56.821	0.232	0.091	—	0.095	0.050	—	0.013	—
1.7	37.863	61.367	0.331	—	0.076	0.151	0.064	—	—	0.076

图5 C-S-H样品的粒径分布

Fig.5 Particle size distribution of C-S-H samples

图6 C-S-H的时域信号和功率谱

Fig.6 Time-domain signal and power spectra of C-S-H

图7 CH和CC的介电性质

Fig.7 Dielectric properties of CHand CC

图8 C-S-H的本征折射率、介电常数、吸收系数和介电损耗

Fig.8 Intrinsic refractive index， permittivity， absorption coefficient， and dielectric loss of C-S-H

图9 不同Ca/Si的C-S-H的归一化介电损耗谱（太赫兹玻色峰）

Fig.9 Normalized dielectric loss spectra of C-S-H with different calcium-to-silicon ratios （Terahertz boson peaks）

图10 不同Ca/Si的C-S-H的太赫兹玻色峰误差

Fig.10 Errors of terahertz boson peak for C-S-H with different calcium-to-silicon ratios

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