共查询到20条相似文献,搜索用时 875 毫秒
1.
The concentration of ionic species in the solution in contact with hydrating tricalcium silicate (C3 S) has been studied as a function of time and in the presence of admixtures. The ionic product for calcium hydroxide (CH) was calculated as a function of time and correlated with calorimetric measurements and crystal growth data. The results support the hypothesis that nucleation of CH crystals controls the induction period and that their subsequent growth controls the second heat peak. The influence of admixtures can be predicted from their influence on CH crystal growth. However, solution data indicate that the system cannot properly be compared with the growth of pure CH; the combined role of C-S-H and CH must be considered. Some implications for C3 S hydration are discussed. 相似文献
2.
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
3.
R. L. BERGER ARNON BENTUR N. B. MILESTONE J. H. KUNG 《Journal of the American Ceramic Society》1979,62(7-8):358-362
The chemical and physical properties of C3 S, β-C2 S, a C3 S/C2 S blend, and portland cement pastes cured at 25°C were investigated. The H2 O specific surface areas of the calcium silicate samples follow a common linear relation when plotted against a CIS ratio. The β-C2 S had higher capillary porosity and N2 surface area, resulting from increased mesopore volume at the expense of micropores. All calcium silicate pastes had similar polysilicate content vs time curves, indicating an aging process which is not sensitive to the starting composition of the hydrating calcium silicate. The polysilicate content of portland cement was much lower than that of the corresponding calcium silicate pastes. Strength-capillary porosity relations for the various systems are discussed. 相似文献
4.
The adsorption of calcium lignosulfonate and salicylic acid was studied on the hydration products of the four principal components of portland cement. To investigate the adsorption as a function of development of hydration product, the determinations were made after varying hydration times. The times allowed were from 5 min to 24 hr for tricalcium aluminate (C3 A) and tetracalcium aluminoferrite (C4 AF) and from 1 hr to 28 days for β-dicalcium silicate (β-C2 S) and tricalcium silicate (C3 S). Samples were characterized with respect to surface area and poresize distribution. The effect of gypsum on the adsorption was also investigated. The results indicate that the amounts of salicylic acid and calcium lignosulfonate adsorbed on the hydration products of C3 A, and of calcium 相似文献
5.
Marie-Noëlle de Noirfontaine Sandrine Tusseau-Nenez Marcel Signes-Frehel Gilles Gasecki Caroline Girod-Labianca 《Journal of the American Ceramic Society》2009,92(10):2337-2344
Alite is the major compound of anhydrous Portland cement: it is composed of tricalcium silicate Ca3 SiO5 (C3 S) modified in composition and crystal structure by ionic substitutions. Alite is also the main hydraulic phase of cement and the most important for subsequent strength development. Using raw meals (rich in Ca3 P2 O8 ) as alternative fuels in cement plants raises the question about the effect of phosphorus on C3 S and its consequences on reactivity with water. This paper deals with a systematic study of C3 S triclinic T1 polymorph doped with P2 O5 in the range 0–0.9 wt%. All the samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electron-microprobe analysis. The appearance of a phase rich in phosphorus is shown. It displays a structure derivative of the α'H –Ca2 SiO4 polymorph, noted α'H –C2 S(P). As phosphorus content increases, C3 S is more and more decomposed into free lime and α'H –C2 S(P). The α'H phase was detected from 0.1 wt% P2 O5 and located at the interfaces of C3 S grains. Two identification keys are proposed in order to highlight the α'H –C2 S(P) phase: the XRD angular window at 2θCu =32.8°–33.2° and a smooth aspect on SEM micrographs. 相似文献
6.
Borate Distribution in Stabilized Stainless-Steel Slag 总被引:1,自引:0,他引:1
Dirk Durinck Sander Arnout Gilles Mertens Eddy Boydens Peter Tom Jones Jan Elsen Bart Blanpain Patrick Wollants 《Journal of the American Ceramic Society》2008,91(2):548-554
Disintegration of stainless-steel slag during cooling is caused by the β→γ transformation of dicalcium silicate (2CaO·SiO2 or C2 S). It is well established that disintegration can be avoided by borate additions, which are commonly believed to stabilize the high-temperature polymorphs by forming a solid solution with C2 S. In this study, the borate distributions in slowly cooled synthetic and industrial slag samples are determined. The slag microstructures are characterized using electron probe microanalysis (EPMA), quantitative X-ray diffraction (QXRD), and wavelength dispersive spectroscopy (WDS). The results show that only a limited fraction of the added borates forms a solid solution with the C2 S phase, while the main fraction is found in a calcium borosilicate phase. In combination with literature data, this suggests that slag stabilization involves more than the chemical stabilization of the high-temperature C2 S polymorphs. 相似文献
7.
Satoshi Uda Etsuro Asakura Masahisa Nagashima 《Journal of the American Ceramic Society》1998,81(3):725-729
The influence of the additive SO3 on the phase relationships in the quaternary system CaO-SiO2 -Al2 O3 -Fe2 O3 was investigated by observing the change of volume ratio of 3CaOSiO2 (C3 S) to 2CaOSiO2 (C2 S) + CaO (C) in the sintered material with the increase of SO3 content. The primary phase volume of C3 S in the quaternary phase diagram shrank with the increase of SO3 and disappeared when the SO3 content exceeded 2.6 wt% in the sintered material. Changes in the peritectic reaction relationship between CaO (C), 2CaOSiO2 (C2 S), 3CaOSiO2 (C3 S), 3CaOAl2 O3 (C3 A), 4CaOAl2 O3 Fe2 O3 (C4 AF), and liquid were also observed and discussed. 相似文献
8.
Reaction of Beta-Dicalcium Silicate and Tricalcium Silicate with Carbon Dioxide and Water Vapor 总被引:2,自引:0,他引:2
C. J. GOODBRAKE J. F. YOUNG R. L. BERGER 《Journal of the American Ceramic Society》1979,62(3-4):168-171
The carbonation-reaction kinetics of beta-dicalcium silicate (2CaO·SiO2 or β-C2 S) and tricalcium silicate (3CaO. SiO2 or C3 S) powders were determined as a function of material parameters and reaction conditions and an equation was developed which predicted the degree of reaction. The effect of relative humidity, partial pressure of CO2 , surface area, reaction temperature, and reaction time on the degree of reaction was determined. Carbonation followed a decreasing-volume, diffusion-controlled kinetic model. The activation energies for carbonation of β-C2 S and C3 S were 16.9 and 9.8 kcal/mol, respectively. Aragonite was the principal carbonate formed during the reaction and the rate of carbonate formation was coincident with depletion of the calcium silicates; C-S-H gel formation was minimal. 相似文献
9.
Beta C2 S was hydrated at room temperature with and without added CaCl2 or C2 H5 OH by methods previously studied for the hydration of C3 S, i.e. paste, bottle, and ball-mill hydration. The amount of reacted β-C2 S, the Ca(OH)2 concentration in the liquid phase, the CaO/SiO2 molar ratio, and the specific surface area of the hydrate were investigated. A topochemical reaction occurs between water and β-C2 S, resulting in the appearance of solid Ca(OH)2 and a hydrated silicate with a CaO/SiO2 molar ratio of ≃1. As the liquid phase becomes richer in Ca(OH)2 , the first hydrate transforms to one with a higher CaO/SiO2 ratio. Addition of CaCl2 increases the reaction rate and the surface area of the hydrate but to a much lesser extent than in the hydration of C3 S, whereas C2 H6 OH strongly depresses the hydration rate of β-C2 S, as observed for C3 S hydration. 相似文献
10.
Sang-Koo Kwon Seong-Hyeon Hong Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2000,83(5):1247-1252
Microstructural evolution during the heat treatment of cement clinker was investigated. Two model specimens, which consisted of faceted tricalcium silicate (C3 S) and spherical dicalcium silicate (C2 S) grains dispersed in a liquid matrix, were prepared with 5 wt% of large seed particles. The seed particles of faceted C3 S grains grew extensively, whereas those of the spherical C2 S grains grew rather slowly, relative to the matrix grains. As a consequence, C3 S grains exhibited a bimodal size distribution that was typical of exaggerated grain growth, whereas C2 S grains retained a uniform and normal size distribution. These results suggest that the growth of faceted C3 S grains was controlled by the interface atomic attachment, such as two-dimensional nucleation, and that of spherical C2 S grains was controlled by diffusion through the liquid matrix. The dependence of growth mechanisms on grain morphology has been explained in terms of the atomistic structure of the solid/liquid interface. 相似文献
11.
Donald E. Macphee Karen Luke Fred P. Glasser Eric E. Lachowski 《Journal of the American Ceramic Society》1989,72(4):646-654
Calcium silicate hydrate (C-S-H) gels are the principal bonding material in portland cement. Their solubility properties have been described, enabling pH and solubilities to be predicted. However, the gels also interact with other components of cements, notably alkalis. C-S-H has been prepared from lime and silicic acid in solutions of sodium hydroxide or potassium hydroxide and by the hydration of tricalcium silicate (C3 S) in sodium hydroxide solutions. Analyses of aqueous phases in equilibrium with 85 gels show that the aqueous calcium and silicon concentrations fit smooth curves over the range of increasing sodium concentrations. Where anomalous data occur, they correspond to solids with low lime contents: such gels are tentatively assumed to fall into a region where the presence of another gel phase influences the aqueous composition. Dimensional changes have been observed in the hydration products of C3 S as a function of alkali content and these may be relevant to the alkali-silica reaction. The significance of this and other data is discussed with reference to real cement systems. 相似文献
12.
Koichiro Fukuda Ken-ichi Matsunaga Takahiro Bessho Hideto Yoshida 《Journal of the American Ceramic Society》2005,88(4):954-962
The phase stability in part of the P2 O5 -bearing pseudoquaternary system CaO–SiO2 –Al2 O3 –Fe2 O3 has been studied by electron probe microanalysis, optical microscopy, and powder X-ray diffractometry. At 1973–1653 K, the α-Ca2 SiO4 solid solution [α-C2 S(ss)] and melt coexisted in equilibrium, both chemical variations of which were determined as a function of temperature. The three phases of melt, calcium aluminoferrite solid solution (ferrite), and C2 S(ss) coexisted at 1673–1598 K. On the basis of the chemical compositions of these phases, a melt-differentiation mechanism has been, for the first time, suggested to account for the crystallization behavior of Ca3 Al2 O6 solid solution [C3 A(ss)]. When the α-C2 S(ss) and melt were cooled from high temperatures, the melt would be induced to differentiate by the crystallization of ferrite. Because the local equilibrium would be continually attained between the rims of the precipitating ferrite and coexisting melt during further cooling, the melt would progressively become enriched in Al2 O3 with respect to Fe2 O3 . The resulting ferrite crystals would show the zonal structure, with the Al/(Al+Fe) value steadily increasing up to 0.7 from the cores toward the rims. The C3 A(ss) would eventually crystallize out of the differentiated melt between the zoned ferrite crystals in contact with their rims. 相似文献
13.
GERARDO CHIOCCHIO MARIO COLLEPARDI RENATO TURRIZIANI 《Journal of the American Ceramic Society》1975,58(5-6):185-188
Hydrated calcium silicates containing Al3+] or Fe3+] were prepared by autoclaving C3 S and β-C2 S in the presence of C3 A or C2 F at 190°C. Al3+] and Fe3+] diffuse into the crystal lattice of α-C2 SH and C3 SH1.5 . Solid solutions containing Al3+] and Fe3+] were placed in contact at 25°C with sources of sulfates, either in aqueous stirred suspensions or as pastes. Al3+] and Fe3+] remain stable in the solid solution, inhibiting the formation of ettringite. This absence of ettringite can explain the resistance of autoclaved cement pastes and concretes to sulfate attack. 相似文献
14.
The Pore Structure of Hydrated Cementitious Compounds of Different Chemical Composition 总被引:1,自引:0,他引:1
ARNON BENTUR 《Journal of the American Ceramic Society》1980,63(7-8):381-386
The pore structure ofβ-C2 S, C3 S, and portland cement pastes was investigated using mercury porosimetry and H2 O and N2 adsorption. The β-C2 S had more total macro- and mesoporosities than C3 S and portland cement pastes of a similar degree of hydration. C3 S and portland cement pastes had similar total porosities but differed in the porosity size distribution. In the mesopore range, the various test methods gave different results. These differences are discussed on the basis of the various models proposed for cement paste. It is shown that shrinkage could be correlated with the volume of pores <0.03 μm, but not with total porosity. 相似文献
15.
Member of oxides, including MgO, ZnO, La2 O3 , Al2 O3 , TiO2 , and F were reacted with C3 S, either individually or in combination, in order to stabilize a variety of polymorphic forms. The resultant phases were examined by both XRD and TEM. It was found that the results obtained by the conventional means of observing groups of reflections in powder X-ray diffraction patterns were not in agreement with the structure types identified by electron diffraction. In particular, the rhombohedral form of alite, synthesized by the addition of either ZnO or Al2 O3 + F to C3 S, was not observed by TEM although the corresponding X-ray patterns all displayed single peaks characteristic of the rhombohedral cell. Electron diffraction of C,S doped with 2.02 and 4.43% ZnO gave mono-clinic patterns, whereas C3 S doped with Al + F gave several forms, all of them different from the form produced by ZnO-doped C3 S. The addition of La2 03 produced a new hexagonal lattice with cell dimensions of a = 2.575 and c = 2.50 nm. When Al + F was incorporated in C3 S, the modifications found included the triclinic lattice characteristic of pure C3 S, the hexagonal lattice characteristic of La-doped C3 S, and a complex lattice distinguished by the presence of incommensurate doublet reflections and sometimes extra weak spots. A similar incommensurate superlattice was found in alites containing Mg, Al, and a large amount of Ti (0.13 mole). The Jeffery cell for the Mm modification of C3 S doped with 1.63% MgO was confirmed. 相似文献
16.
Koichiro Fukuda Iwao Maki Keisuke Adachi 《Journal of the American Ceramic Society》1992,75(4):884-888
A series of Ba-bearing Ca2 SiO4 solid solutions (C2 S( ss )), (Ba x Ca1− x )2 SiO4 with 0.075 x 0.30, were prepared and examined by X-ray and electron beam diffraction. They are all made up of orthorhombic domains 120° different in orientation around the common c axis of the former α phase. The C2 S solid solution with x = 0.075 shows a superstructure incommensurate along the a axis with λ (modulation wavelength) = 3.5 and commensurate along the c axis with Δ= 3. With x = 0.15, modulation is observed only along the a axis and Δ= 3.4. No evidence of superstructure is found with x = 0.24; the space group and cell dimensions are comparable with those of pure α 'H -C2 S. The C2 S( ss ) with x = 0.30 gives a superlattice with the cell-edge length of 3 b . All the C2 S( ss ), when reheated at 1000°C for 24 h, produced lamellae of the trigonal phase T nearly in parallel with (001) of the host α 'L phase. The crystallographic orientation between the two phases is
This indicates that the above Ba-bearing C2 S( ss ) phases occur as precursors to the thermodynamically more stable two-phase mixtures. 相似文献
This indicates that the above Ba-bearing C
17.
The chemical and physical compositions of C-S-H formed in paste hydration of C3 S cured at 4°, 25°, and 65°C and of C2 S and a C3 S/C2 S blend cured at 25°C were studied using quantitative X-ray diffraction analysis (QXDA), extraction, and thermal effluent gas analysis (TEGA) to determine the free CH content. The amount of CH determined by extraction is greater than or equal to that determined by QXDA. The difference between the two results increased with the H2 O surface area of the paste, indicating the existence of adsorbed CH in the form of Ca2+ and (OH)− ions which cannot be measured by QXDA and suggesting that the extraction method is better for estimating the composition of C-S-H. 相似文献
18.
Linghong Zhang Lionel J. J. Catalan Raymond J. Balec rew C. Larsen Hassan Haji Esmaeili Stephen D. Kinrade 《Journal of the American Ceramic Society》2010,93(1):279-287
The effects of aliphatic sugar alcohols (e.g., threitol, xylitol, sorbitol) on the hydration of tricalcium silicate (C3 S) and ordinary portland cement (OPC) were investigated and compared with those of sucrose, a well-established cement set retarder. Only sugar alcohols which contain threo diol functionality retarded the setting of C3 S and OPC, their efficacy increasing with the number of threo hydroxy pairs and, to a smaller extent, with the overall population of hydroxy groups. None, however, were as effective as sucrose. The initial and final setting times increased exponentially with the concentration of saccharide, although the hydration of OPC was less inhibited than that of C3 S. Saccharides function as "delayed accelerators," that is, cement hydration is first inhibited and then proceeds faster than in saccharide-free cement. This behavior is consistent with the theory that the induction period is controlled by slow formation and/or poisoning of the stable calcium silicate hydrate (CSH) nuclei. The early inhibiting influence of saccharides on CSH precipitation is apparently stronger than on the growth of crystalline calcium hydroxide. Saccharides did not negatively affect the degree of hydration and compressive strength of fully set OPC paste; on the contrary, sorbitol yielded modest increases. 相似文献
19.
The rate of paste hydration of 3Ca O·SiO2 (C3 S) and the effects of additions of CaCl2 , CdI2 , and CrCl3 , were studied by differential thermal analysis and thermogravimetry. X-ray analyses were used to identify the synthesized C3 S. The salts CaCl2 , CdI2 , and CrCl3 , accelerated the hydration of C3 S. The degree of hydration was estimated by the amount of Ca(OH)2 , formed, as determined by TG. 相似文献
20.
Calcium aluminosulfate (Ca4 Al6 O16 S or C4 A3 ̄) was prepared by direct synthesis from calcium and aluminum nitrates, and aluminum sulfate. CaAl4 O7 (CA2 ) formed as an intermediate at 900°C, and C4 A3 ̄ was the main phase after calcination at 1100°C. The specific surface areas after calcination at 1100° and 1300°C were ∼2.5 and 1 m2 /g, respectively. Hydration was investigated using XRD, DSC, SEM, conduction calorimetry, and solid-state 27 Al MAS-NMR spectroscopy. Calorimetry showed that the induction period was longer than that of a sample prepared using conventional solid-state sintering, and this was attributed to the formation of amorphous coatings. Crystalline hydration products, principally calcium monoaluminosulfate hydrate and aluminum hydroxide, appeared subsequently. Although the induction period was very long, complete hydration occurred as early as 3 d in the sample calcined at 1100°C and was 91% complete in the sample calcined at 1300°C. 相似文献