Effect of C/S ratio on morphology and structure of hydrothermally
synthesized calcium silicate hydrate
HE Y ongjia 1,2，ZHAO Xiaogang1，LU Linnu＊2, 3, STRUBLE Leslie.J. 2, HU Shuguang1
(1. Key Laboratory for Silicate Materials Science and Engineering (Wuhan University of Technology),
Wuhan 430070, China
2. Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,
Urbana, IL61801,USA (He and Lu visiting scholars, Struble professor)
3. School of Science, Wuhan University of Technology，Wuhan 430070, China)
Abstract: The samples of the C-S-H ries were synthesized by hydrothermal reaction of fumed silica, CaO and deionized water at initial C/S ratios between 1.0-1.7. Pha composition and structural and morphology characteristics of C-S-H samples were analyzed by XRD, IR and SEM. Results showed that the d-spacing of (110) and (020) decread, the d-spacing of (200) incread, a
nd the d-spacing of (002) and (310) varied randomly, the polymerization of silica tetrahedra of C-S-H decread, and morphology of C-S-H samples varied from sheet shapes to long reticular fibers as C/S ratio incread.
Keywords: calcium silicate hydrate, C/S ratio, morphology, structure, hydrothermal synthesis
1. Introduction
The structure and properties of calcium silicate hydrate (C-S-H) have been the subject of considerable rearch for decades [1]. However C-S-H is very complicated, its composition, morphology, structure and properties vary with raw materials, W/C ratio, age, temperature, synthesi s method, etc. So C-S-H structure and properties remain important areas of rearch [2-5].
C-S-H can be prepared by different methods, including hydrothermal reaction of CaO and SiO2, aqueous reaction of CaO and SiO2, aqueous reaction of Ca(NO3)2.4H2O and Na2SiO3, and mechanochemical reaction of CaO and SiO2[6-8]. Different preparation methods lead to variation in structure of C-S-H. The atomic Ca/Si ratio (C/S ratio) of C-S-H is an important composition parameter that affects nonstructural characteristic of C-S-H. Then how does C/S ratio affect pha composition and structural and morphological characteristic of hydrothermal synthesized C-S-H?
In the prent study, the samples of the C-S-H ries were synthesized by hydrothermal reaction of fumed silica, CaO and deionized water at initial C/S ratios between 1.0-1.7, and we tried to answer the above question using XRD technique and IR and SEM investigation on synthesized C-S-H samples.
2. Experimental Procedures
(1) Raw materials
The fumed silica is amorphous silica with particle size of 0.014 um. The calcium oxide was freshly calcined from reagent grade CaCO3 at 1100 C for 2 hours. Deionized water was boiled and then top off with N2 gas.
(2) Sample preparation
The samples were prepared by the hydrothermal reaction of fumed silica (SIGMA-A LDRICH S5505), calcium oxide and deionized water at W/S=10 and initial C/S ratios of 1.0, 1.3, 1.5 and 1.7.
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Fumed silica andcalcium oxide were mixed with
deionized water in high - temperature resistant
plastic bottles, which were then aled and agitated
in a water bath at 95 C for 7 days.
The solid products were obtained by vacuum filtration using ashless filter paper (100 circles) and then washed with deionized water and filtered again three times. Finally, the solid products were dried overnight in a vacuum desiccator and stored under flowing N2gas at room temperature. Samples were named using their C/S ratios (samples with C/S ratios 1.0, 1.3, 1.5 and 1.7 were named CSH10, CSH13, CSH15, and CSH17, respectively).
3. Results and Discussion
(1) XRD
XRD results are given in Fig.1. Portlandite (CH), which is readily identified by its XRD peaks at 0.490 and 0.26 nm, and calcite were not obrved in any of the samples. In fact, characteristic peaks of CH were found in the XRD pattern of unwashed C-S-H sample with C/S ratio 1.7 although intensities of peaks were low. It indicated there were few unreacted CH in that C-S-H sample. However peaks o
f CH were not found in the XRD pattern of C-S-H sample with C/S ratio 1.7 in Fig.1, it was becau the C-S-H samples in Fig.1 were washed deionized water to get single C-S-H samples. CSH 10 of low C/S ratio 1.0 has unreacted fumed silica, as evidenced by the broad peak centered at about 21 degrees.
The XRD patterns were dominated by peaks of mi-crystalline C-S-H(1) at 0.307 nm, 0.280 nm, 0.183 nm, and 0.167 nm, which were prent for all samples. Semi-crystalline C-S-H(1) was the only pha detected by XRD in all the samples. Table 1 lists the XRD peaks of C-S-H obrved in the samples and how the peak positions varied with C/S. From Table 1 we can e the XRD spacings of the C-S-H samples vary systematically with C/S ratio, although the variation is small. And t he d-spacing of (110) and (020) decread, the d-spacing of (200) incread, and the d-spacing of (002) and (310) varied randomly as C/S incread. Cong’s XRD results of C-S-H synthesized at room temperature also indicated the d-spacing of (020) decread and the d-spacing of (200) incread as the C/S ratios incread, however, the d-spacing of （110）varied randomly, and the d-spacing of (002) decread as C/S incread [9].
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Fig. 1. XRD powder patterns of C-S-H samples
Table 1 XRD peaks of C-S-H
d rang
e /nm★I %▲hkl◆V ariation
1.1840 - 1.582412002 d varied randomly
0.3030 - 0.3077100110
d decread as C/S
incread
0.2805 - 0.281914200
d incread as C/S
托福中文官网incread
0.1822 - 0.184135020
d decread as C/S
incread
0.1667 - 0.169913310 d varied randomly ★given on obrved values range; ▲mean intensity value;
◆bad on [1, 9]
(2) SEM
SEM micrographs of C-S-H samples are shown i n Fig.2. Prominent differences in morphology were
obrved between the different C-S-H samples. The C-S-H with C/S 1.0 exhibited a leafy or sheet shape in a den, laminar pattern. The C-S-H with C/S 1.3 was a mixture of small leaves and short fibers. The C-S-H
with C/S 1.5 exhibited longer fibers (laths) in a reticular pattern. The C-S-H with C/S 1.7 exhibited even longer fibers in a loo reticular pattern. Thus the C-S-H changed from den leafy shapes to long reticular fibers as C/S ratio incread from 1.0 to 1.7.
Fig. 2. SEM micrographs of C-S-H samplesdicks
(3) IR results
The IR spectra of all C-S-H samples are shown in
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Fig. 3. Table 2 shows the infrared absorption peaks
assigned to Si-O.
mas是哪个国家的缩写Fig.3 IR spectra of C-S-H samples
Table 2 Infrared absorption peaks assigned to Si-O
split
assignment★Wavenumber
Range/cm-1V ariation
δ(Si-O-Si) 455-463position of band shifted to low wavenumber as C/S incread
v s (Si-O-Si)652-667position of band shifted randomly as C/S incread
v (S i-O) Q1816-818position of band shifted rather subtle as C/S incread
v (S i-O) Q2970-984position of band shifted to low wavenumber as C/S incread
★bad on [10, 11]
All C-S-H samples had a characteristic band near 970 cm−1due to Si-O stretching vibrations in Q2 sites [10]. The intensity of this band decread as C/S incread, indicating that C-S-H with high C/S has less Q2 sites in its structure than C-S-H with low C/S. Fig.3 and Table.2 also show that the position of thi s Si-O Q2shifted to lower wavenumbers as C/S incread, indicating that the degree of polymerization decread as C/S incread in this range of C/S. Y u’s spectra also showed the similar behavior that the dominant Si-O Q2 stretch at about 970 cm-1shifted to lower wavenumber a
s C/S incread up to C/S 1.2, which they attributed to decreasing polymerization in this range of C/S.
All C-S-H samples had characteristic bands near 816 due to Si-O stretching vibrations in Q1 sites. As C/S incread, the positions of the characteristic bands shifted to lower wavenumbers, but rather subtle. The Si-O Q1stretch at about 816 cm-1is much sharper than Y u et al. obrved [10], which indicated order is higher than Y u et al. synthesized.It is mainly becau their C-S-H samples were synthesized at room temperatures, whereas our C-S-H samples were hydrothermal synthesized. High temperatures caud an increa in order. They showed a rather subtle increa in intensity of this peak as C/S incread, but no systematic change in wavenumber[10]. As C/S incread, it cannot be en an obvious systematic change in intensity from Fig3. The Si-O-Si band at about 670 cm-1was en by Y u et al. to decrea in intensity and increa in width at C/S >1.19, which they attributed to decread polymerization and decread order at the higher C/S values[10]. Fig.3 also shows a decrea in intensity of this peak, and increa in
width but the change in width is not obvious.
All C-S-H samples had characteristic bands near 460 cm-1due to Si-O-Si bending vibrations [11]. As
C/S incread, the position of the band shifted to lower wavenumber. The change indicated polymerization degree decread as C/S incread. In addition, all the C-S-H samples had characteristic bands near 1450, 1650, and 3440 cm-1. Their positions of band did not shift as C/S incread. The fact that all the C-S-H samples had the same characteristic IR band indicates that they all had the same chemical structure. The characteristic band near 1650 cm-1 is due to H-O-H bending vibration of molecular H2O in C-S-H, and the characteristic band near 3440 cm-1is due to the stretching vibration of the -OH bonds.
4 Conclusions
(1)Samples of C-S-H were synthesized by
hydrothermal reaction of fumed silica, CaO
and deionized water at initial C/S 1.0-1.7. (2)Semi-crystalline C-S-H(1) was the only pha
detected by XRD in all the samples. The
d-spacing of (110) and (020) decread, the
d-spacing of (200) incread, and the
d-spacing of (002) and (310) varied randomly
as C/S incread.
(3)Prominent differences in morphology were
obrved between the different C/S C-S-H
samples. Morphologies of C-S-H samples vary
from sheet to long reticular fibers C/S
incread.
(4)The infrared spectra had peaks attributed to
socks怎么读
δ(Si-O-Si), v s(Si-O-Si), v(Si-O) Q1, v (Si-O) Q2,sheer>英语免费翻译
-OH and H-O-H. The polymerization degree,
the content of (Si-O)Q2decread as C/S
incread.
5. Acknowledgments
This project was supported by the National Basic Rearch Program of China (973 Program)（No.2009CB23200）.References
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