共查询到20条相似文献,搜索用时 0 毫秒
1.
Yoshihiko Okada Hideki Ishida Takeshi Mitsuda 《Journal of the American Ceramic Society》1994,77(3):765-768
Hydrothermal treatment of lime–silica mixtures under saturated steam pressures below 200°C usually gives C-S-H as an initial product, which reacts further to give crystalline calcium silicate hydrates. In this paper, C-S-H was hydro–thermally prepared using CaO and silicic acid at Ca/Si ratios of 0.3 to 2.0 and 120° to 180°C for 2 h. The C-S-H was examined mainly using 29 Si NMR by the magic angle spinning gate proton decoupling and cross polarization magic angle spinning methods. XRD for all of the C-S-H showed bands at 0.304, 0.280, 0.183, and 0.166 nm. NMR results showed that all of the C-S-H contained single chains of silicate anion, which became progressively longer as the Ca/Si ratio decreased, i.e., as the system became richer in silica. This was independent of the preparation temperature. The 0.8 ratio preparations at 180°C contained small amounts of double-chain structure of 1.1-nm tobermorite. The reaction processing in the lime- silicic acid mixtures is also discussed. 相似文献
2.
Wang-Hong Yang R. James Kirkpatrick Gary Turner 《Journal of the American Ceramic Society》1986,69(10):222-C
3.
Hideki Ishida Yoshihiko Okada Takeshi Mitsuda 《Journal of the American Ceramic Society》1992,75(2):359-363
The hydration behavior at 25°C of highly reactive β-dicalcium silicate synthesized from hillebrandite (Ca2 (SiO3 )(OH)2 ) was studied over a period of 7 to 224 d using 29 Si magic-angle spinning nuclear magnetic resonance (MAS NMR). The hydration product, C-S-H, contains Q2 and Q1 silicate tetrahedra, the chemical shifts of which are independent of the water/solid (w/s) ratio and curing time. Until the reaction is completed, the amounts of Q1 and Q2 formed are independent of the w/s ratio, being determined only by the degree of reaction. The ratio Q2 /Q1 increases as the reaction progresses and as the curing time becomes longer. From the values of Q2 /Q1 , it appears that the hydrate is a mixture of dimers and short single-chain polymers. The Ca/Si ratio of the hydrate is high, taking values close to 2.0, but the Ca/Si ratio does not influence the Q2 /Q1 ratio. It was also found that the NMR peak intensities allow quantitative assessment similar to XRD. 相似文献
4.
Ian G. Richardson Adrian R. Brough Rik Brydson Geoffrey W. Groves Christopher M. Dobson 《Journal of the American Ceramic Society》1993,76(9):2285-2288
Solid-state 27 Al and 29 Si magic angle spinning NMR spectroscopy has been combined with electron energy loss spectroscopy carried out in the transmission electron microscope to determine the location of Al substituting in a semicrystalline C-S-H gel present in a hydrated synthetic slag glass. The gel is found to contain mainly pentameric silicate chains in which the central silicon is substituted by aluminum. 相似文献
5.
Laurent Bonafous Catherine Bessada Dominique Massiot Jean-Pierre Coutures Bruno Le Holland Pierre Colombet 《Journal of the American Ceramic Society》1995,78(10):2603-2608
The effect on β-C2 S of two stabilizing agents, calcium sulfate and alumina, has been investigated using high-resolution 29 Si solid state NMR spectroscopy. Syntheses were achieved via the gel route, wet or dry processes. Room-temperature NMR spectra characteristics were analyzed as a function of the sintering temperature. The incorporation of Al3+ and S6+ ions, which finds expression in a noticeable line broadening, is shown to be effective above 1200°C. The 29 Si chemical shift is unchanged upon doping, suggesting a mean SiO4 tetrahedra geometry identical to that in pure β-C2 S. General trends on the structure adopted by C2 S upon Al3+ and S6+ doping are also discussed. 相似文献
6.
Stephen Kwan Judith LaRosa Michael W. Grutzeck 《Journal of the American Ceramic Society》1995,78(7):1921-1926
Strätlingite (2CaO·Al2 O3 ·SiO2 ·8H2 O) is a complex calcium aluminosilicate hydrate commonly associated with the hydration of slag-containing cements or other cements enriched in alumina. Strätlingite can coexist with the hydrogarnet solid solution [hydrogarnet (3CaO·Al2 O3 ·6H2 O)-katoite (3CaO·Al2 O3 ·SiO2 ·4H2 O)] and calcium silicate hydrate (C-S-H). Since Strätlingite is present in many blended cements, the knowledge of strätlingite's characteristic silicate anion structure and how aluminum is accommodated by the structure is important. Phase pure Strätlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate cement, CaO, NaOH, and water. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) and then further examined using 29 Si, with and without cross-polarization (CP), and 27 Al solid-state magic angle nuclear magnetic resonance spectroscopy (MASNMR). For the most part, NMR data for these strätlingites corroborate structural information available in the literature. The aluminum atoms are both tetrahedrally and octahedrally coordinated, and the silicon atoms exist predominantly as Q2 , Q2 (1Al), and Q2 (2Al) species. The presence of alkali affects the structure of strätlingite in subtle ways, significantly reducing the AlIV /A1VI ratio. 相似文献
7.
Sridhar Komarneni Rustum Roy Colin A. Fyee Gordon J. Kennedy Harold Strobl 《Journal of the American Ceramic Society》1986,69(3):42-C-
The environment of the Al and Si atoms of diphasic and single-phase aluminosilicate gels was determined by solid-state 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance (MASNMR) spectroscopy, The tetrahedral coordination of Al increased with decreasing Al/Si ratio in single-phase gels but not in diphasic gels. The results showed that ultrahomogeneous mixing on a next-nearest-neighbor level is achieved in single-phase aluminosilicate gels, while in diphasic gels this has successfully been avoided . 相似文献
8.
Dominique Massiot Pascal Dion Jean Fran¸ois Alcover Faiza Bergaya 《Journal of the American Ceramic Society》1995,78(11):2940-2944
The processing of kaolinite under controlled rate thermal analysis conditions (CRTA) provides homogeneously transformed samples at defined dehydroxylation rates. The kaolinite-to-metakaolinite transformation has been monitored by solid-state NMR and X-ray diffraction. The metakaolinite product is an amorphous material with no resolved XRD pattern and is based on a disordered polymerized silicon/aluminum network in which aluminum preferably occupies four- and five-fold structural positions in the ratio 60% AlVI , 30% AlV , and 10% AlVI . This complex dehydroxylation process has been viewed at different scales, with the aluminum NMR tracing a site-by-site destructon of the octahedral sheet and the silicon NMR and XRD following a more rapid destruction of the longrange order. 相似文献
9.
Sridhar Komarneni Colin A. Fyfe Gordon J. Kennedy Harold Strobl 《Journal of the American Ceramic Society》1986,69(3):45-C-
Magic-angle spinning nuclear magnetic resonance (MASNMR) spectroscopy (27 Al) detected the coordination of Al in clays containing as little as 0.26% Al2 O3 . The 29 Si MASNMR of fluorphlogopite showed three distinct Si chemical environments which suggested short-range ordering. Synthetic laponite and mica-montmorillonite showed broad 29 Si resonances indicative of short-range disorder. A saponite showed four 29 Si resonances. Considerable insight into the short-range ordering of clays can be gained by 27 Al and 29 Si MASNMR. 相似文献
10.
Paul J. Schilling Leslie G. Butler Amitava Roy Harvill C. Eaton 《Journal of the American Ceramic Society》1994,77(9):2363-2368
b29 Si and 27 Al MAS-NMR were performed on NaOH-activated blast-furnace slag to better characterize the amorphous and poorly crystalline phases which occur in this system. The unreacted glass has a mainly dimeric silicate structure represented by a broad 29 Si peak (FWHM = 15 ppm) centered at –74.5 ppm [ Q 1 ], with aluminum present exclusively in tetrahedral coordination. Upon reaction with 5M NaOH ( w/s = 0.4), three new 29 Si peaks with widths of ca. 2 ppm are formed at -78.5 Q 1 , –81.4 [ Q 2 (1Al)J, and -84.3 [ Q 2 ]. Relative peak areas indicate a mostly dimeric silicate structure for the tobermorite-like C─S─H layers, with roughly a third of the bridging sites occupied by aluminum, and less than 10% by silicon. In addition to the tetrahedrally coordinated aluminum substituted in the C─S─H structure, 27 Al MAS-NMR reveals the presence of aluminum in octahedral sites, which is attributed to the aluminate phase (C,M)4 AH13 . 29 Si results indicate rapid initial consumption of the glass, with roughly a third of the glass reacting within the first day and another third consumed over the following 27 days. 相似文献
11.
Synthesis of Glass-like Cordierite from Metal Alkoxides and Characterization by 27 Al and 29 Si MASNMR
Ulagaraj Selvaraj Sridhar Komarneni Rustum Roy 《Journal of the American Ceramic Society》1990,73(12):3663-3669
A sol-gel process for the preparation of glass-like cordierite and ceramic oxide powder is described. Metal alkoxide precursors were dissolved in 2-methoxyethanol and the metal cations were complexed using 2,4-pentanedione to overcome different hydrolysis rates of metal alkoxides which lead to microscopic inhomogeneities during gelation. Heating the gel in an aerated furnace resulted in ultrafine cordierite powder of stoichiometric composition at a relatively low temperature. Cordierite gel and glass were also prepared by other methods and compared with the above gel. The environments of aluminum and silicon in the glass and gels heated at various temperatures were studied using 27 Al and 29 Si magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Most of the heated gels and the glass showed resonances due to pentacoordinated aluminum along with 4- and 6-coordinated aluminum. The homogeneities of the resulting gels and glass are compared using the MASNMR data. 相似文献
12.
K. J. D. MacKENZIE I. W. M. BROWN R. H. MEINHOLD M. E. BOWDEN 《Journal of the American Ceramic Society》1985,68(5):266-272
Water is lost in two overlapping steps from well-crystallized pyrophyllite from Coromandel, New Zealand. The pyrophyllite structure survives the loss of the first 30% of the total water content, but the loss of a further 60% water in the second step results in the formation of pyrophyllite dehydroxylate, with corresponding changes in both the 29 Si and 27 Al solid-state NMR spectra. Detailed analysis of the 29 Si chemical shift of the dehydroxylate has allowed the silicate layer structure of this phase to be refined. A similarly detailed interpretation of the 27 A1 spectra is not possible because of electric field gradient effects which result in the loss of ∼90% of the A1 spectral intensity due to the formation of five-coordinate A1 on dehydroxylation. The loss of further water from the dehydroxylate on further heating results in the formation of mullite and cristobalite and is accompanied by changes in the 29 Si and 27 Al spectra which can be accounted for in terms of coordination changes in the structural regions which contained the residual hydroxyls. 相似文献
13.
R. F. Abreu J. Schneider M. A. Cincotto 《Journal of the American Ceramic Society》2005,88(6):1514-1520
The structure, surface fractal dimension, and global hydration kinetics of silica particles obtained from rice husk ashes (RHAs) were studied with 29 Si-NMR spectroscopy and spin–lattice relaxation techniques. Silica particles presented an amorphous fraction higher than 93%, with traces of silica-organic bonding and crystal-like domains. Fe-impurities are located preferentially on the surface of the particles. From the effect of these paramagnetic ions on the spin–lattice relaxation of Q3 and Q4 silicate groups, the surface of the particles was characterized as being effectively two-dimensional ( D =1.9±0.1). The hydration kinetics of the particles during the reaction with lime and water was monitored from 8 to 706 days. The process can be described by a power law, with the characteristic exponent higher than those measured for other cements. Also, Johnson–Mehl–Avrami expressions reproduce equally well the experimental data, with parameters compatible with growth habits and morphology known for C–S–H. Two types of Q2 tetrahedra were identified in C–S–H, which can be attributed to the bridging and nonbridging silicate groups predicted by the "dreier-kette" structural model of C–S–H. 相似文献
14.
Taigo Takaishi Masahide Takahashi Jisun Jin Takashi Uchino Toshinobu Yoko Masahide Takahashi 《Journal of the American Ceramic Society》2005,88(6):1591-1596
Structure of x PbO–(100− x )SiO2 ( x =25–89) glasses has been investigated by means of the X-ray and neutron diffraction and 29 Si MAS NMR measurements. In the radial distribution functions of all the glasses, the Pb–O correlation was observed at 0.23 nm, indicating that the PbO3 trigonal pyramids units do exist in the whole glass forming composition range. Furthermore the existence of the first Pb–Pb correlation at ∼0.385 nm in the whole composition range suggests that the basic structural unit is considered to be a Pb2 O4 unit, which consists of the edge-shared PbO3 trigonal pyramids. These results strongly imply that the Pb2 O4 units participate in the glass network constructed by SiO4 tetrahedra even at low PbO content. Differing from other lead-containing glass systems, these structural characteristics of Pb ions in the PbO–SiO2 glass system are responsible for the extremely wide glass-forming region. 相似文献
15.
The kinetics of paste, bottle, and ball-mill hydration of 3CaO SiO2 and the effects of additions of electrolytes and alcohols were studied. Paste and bottle hydrations proceed through periods of induction, acceleration, and decay. If 3CaO SiO2 is hydrated in an excess of H2 O, as in bottle hydration, the reaction rate is lower than that for paste hydration. The ball-mill hydration rate is much the highest and is controlled by the removal of the hydrate layer coating the 3CaO SiO2 particles. Electrolytes always accelerate and alcohols retard the reaction rate. Experimental results are discussed with reference to modern theories of the 3CaO SiO2 hydration mechanism. 相似文献
16.
Masamichi Tsuji Sridhar Komarneni Prakash Malla 《Journal of the American Ceramic Society》1991,74(2):274-279
17.
Steve W. Martin Debra Bain Karim Budhwani Steven Feller 《Journal of the American Ceramic Society》1992,75(5):1117-1122
18.
19.
Early Hydration of Tricalcium Silicate 总被引:1,自引:0,他引:1
M. E. TADROS JAN SKALNY R. S. KALYONCU 《Journal of the American Ceramic Society》1976,59(7-8):344-347
The hydration of tricalcium silicate (C3 S) in the preacceleration stages was studied. The C3 S particles carry a positive charge during the early stages of hydration. Following a rapid hydrolysis of C3 S, calcium ions adsorbed on the Si-rich surface of C3 S particles, greatly reducing their further dissolution, thus initiating the induction period. The [Ca2+ ] and [OH- ] continue to increase at lower rates and, because Ca(OH)2 crystal growth is inhibited by silicate ions, become supersaturated with respect to Ca(OH)2 . When the supersaturation reaches a value of ∼1.5 to 2.0 times the saturation concentration, nuclei are formed, and rapid growth of Ca(OH)2 and C-S-H is initiated. These products act as sinks for the ions in solution, thus enhancing the further dissolution of C3 S. 相似文献
20.
Adrian R. Brough Christopher M. Dobson Ian G. Richardson Geoffrey W. Groves 《Journal of the American Ceramic Society》1994,77(2):593-596
Selective isotopic enrichment of SiO2 with 29 Si in a mixture with tricalcium silicate (C3 S) has allowed the Si from this phase to be effectively labeled during the course of the hydration reaction, thus isolating its contribution to the reaction. A double Q2 signal has been observed in 29 SI solid-state MAS NMR spectroscopy of C-S-H gels of relatively low Ca/Si ratio, prepared by hydration or by carbonation of a C3 S paste. The origin of the weaker, downfield peak is discussed and tentatively attributed to bridging tetrahedra of a dreierkette silicate chain structure. 相似文献