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1.
The kinetics of solution of quartz and the crystallization of calcium silicate hydrate during hydro-thermal treatment of single crystals of quartz in saturated lime solutions were studied. Microscopic examination of sections of the product layer showed that the calcium silicate hydrate was of fibrous crystal habit and grew radially from nucleating centers in a general direction away from the quartz surface. X-ray diffraction established that the mineral was mainly xonotlite. The crystallization of the mineral did not follow the receding surface of the quartz; the product layer was extended only on the surface in contact with the lime solution. The silicate ions apparently diffused preferentially through the product layer although separate measurements proved that the membrane had no selective action against the diffusion of calcium ions. Plots of the weight of xonotlite versus square root of time gave straight lines indicating that the process was diffusion-controlled at 235° and 335°C. 相似文献
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Alla Popova Ghita Geoffroy Marie-France Renou-Gonnord Pascal Faucon Ellis Gartner 《Journal of the American Ceramic Society》2000,83(10):2556-2560
To better understand the mechanism of interaction between hydrating silicate-based cements and polymeric dispersants of the type used as superplasticizers in modern construction concretes, two different types of polymeric dispersant were added (at concentrations of 1 and 10 g/L) during the synthesis of calcium silicate hydrate (C-S-H) via the pozzolanic reaction in dilute slurries of lime and reactive silica, at Ca/Si ratios in the range of 0.66–1.50. Although both polymers gave degrees of adsorption of >79% in all cases studied, no significant structural modifications of the resulting C-S-H products were observed via X-ray diffraction or 29 Si magic angle spinning–nuclear magnetic resonance. These results differ from recent work in which it was shown that similar types of polymer could intercalate into the interlayers of C-S-H that was made using an alternative process. It is suggested that the process by which the C-S-H is formed may have a strong influence on whether C-S-H can intercalate polymers. This observation is relevant to understanding the fate of such polymers in concrete. 相似文献
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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
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Silicon Substitution for Aluminum in Calcium Silicate Hydrates 总被引:1,自引:0,他引:1
Pascal Faucon J. Claude Petit Thibault Charpentier J. François Jacquinot Fredéric Adenot 《Journal of the American Ceramic Society》1999,82(5):1307-1312
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Nicolas Lequeux Alain Morau Samuel Philippot Philippe Boch 《Journal of the American Ceramic Society》1999,82(5):1299-1306
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Calcium silicate hydrates, CaO–SiO2 -H2 O (C-S-H), were studied as a chloride fixation material. C-S-H of two different CaO/SiO2 ratios were synthesized and burned with calcium chloride in a temperature range from 600° to 1000°C. Minerals with a chemical composition of CaO·SiO2 ·CaCl2 and 9CaO·6SiO2 ·CaCl2 were identified by X-ray diffraction analysis. Comparing the diffraction intensity, it was found that the most efficient chloride fixation was attained when burned at 800°C. Changes in the morphology of silicate anion associated with burning and fixation of the chloride were studied in terms of chloride fixation capability using the trimethylsililation technique. It was confirmed that some silicate anions formed a glassy infinite chain where the chloride ions were fixed as a solid solution. 相似文献
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Relation Between the Compressive Strength and Porosity of Autoclaved Calcium Silicate Hydrates 总被引:1,自引:0,他引:1
SIDNEY MINDESS 《Journal of the American Ceramic Society》1970,53(11):621-624
Calcium silicate hydrates were produced by high-pressure steam curing of compacted mixtures of hydrated lime, ground quartz, and water using various lime/silica ratios, molding pressures, and times and temperatures of curing. Compressive strengths ranged from 825 to 32,000 psi and porosities from 0.25 to 0.45. The strengths depended chiefly on total porosity and pore size distribution; phase composition was of secondary importance with certain exceptions. In general, strength decreased as the proportion of larger pores increased. Compressive strengths were best fitted by the Bal'shin relation, S=S 0 (1-ɛ)m , or by the Ryshkewitch relation, S=S 0 e −be , where S =strength of porous material, S 0 =theoretical strength of similar nonporous material, ɛ=porosity, and b and m =empirical constants. 相似文献
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Alla Popova Ghita Geoffroy Ellis M. Gartner A. Lapp 《Journal of the American Ceramic Society》2002,85(5):1303-1305
Small-angle neutron scattering (SANS) was used to study calcium silicate hydrate (C-S-H) formed via pozzolanic reaction between calcium oxide and ultrafine silica in water or polymer solutions at a temperature of 20°C. The SANS profile of this product was consistent with a structure that consisted of platelets with maximum diameters of ∼20 nm (± 5 nm) in the x – y plane, which was similar to a structure that had been deduced in previous work via X-ray diffractometry. The presence of two different types of superplasticizer in solution (at a concentration of 10 g/L) had no significant effect on its formation kinetics or its SANS profile. 相似文献
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Nature of Interatomic Bonding in Controlling the Mechanical Properties of Calcium Silicate Hydrates 下载免费PDF全文
Chamila Dharmawardhana Morayo Bakare Anil Misra Wai‐Yim Ching 《Journal of the American Ceramic Society》2016,99(6):2120-2130
Calcium silicate hydrate (C–S–H) is the most important phase of hydrated cement gel which is the key material in construction industry. It is well accepted that hardened cement paste consists of either poorly crystalline or completely disordered phases. Although a myriad of speculative atomistic models of disordered C–S–H have been proposed, the fundamental basis of structure–property relationships remain elusive. This study focuses upon the correlations between mechanical properties and electronic structure based on well‐defined quantum mechanical parameters. We use 20 CSH minerals with known structure to gain fundamental understanding of structure–property relationship. The results indicate Si–O bond order density, which represents the cumulative bond strength of SiO bonds, has no direct correlation with bulk mechanical properties which is counterintuitive and against conventional wisdom. The variations are determined more precisely by the overall atomic and electronic structure dictated by bond order density of the Ca–O and hydrogen bonds (HB). Most importantly, there is a multifaceted balance between different types of interatomic bonds including the HBs in controlling mechanical properties. HBs categorized in relation to next nearest neighbor (NNN) enable us to identify specific types of HBs that are prevalent in CSH. In certain crystals such as suolunite, the HB network is organized in such a unique way that enhances its mechanical properties. The approach and findings presented in this paper points to a broad roadmap for the developing next‐generation cements. 相似文献
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Silicon-29 Magic Angle Spinning Nuclear Magnetic Resonance Study of Calcium Silicate Hydrates 总被引:4,自引:0,他引:4
Michael Grutzeck Alan Benesi Barry Fanning 《Journal of the American Ceramic Society》1989,72(4):665-668
The reaction products formed in a series of fully "equilibrated," roomtemperature-hydrated, fumed colloidal silica plus lime water mixtures were examined using 29 Si magic angle spinning nuclear magnetic resonance. The data suggest that two structurally distinct calcium silicate hydrate (C-S-H) phases exist in the system CaO–SiO2 –H2 O. The more silica-rich C-S-H (Ca/Si = 0.65 to 1.0) consists predominantly of long chains of silica tetrahedra (Q2 middle units) similar to those found in 1.4-nm tobermorite. The studied more lime-rich C-S-H (Ca / Si = 1.1 to 1.3) consists of a mixture of dimer (Q1 ) and shorter chains (Q1 end units and Q2 middle units) similar to that reported for synthetic jennite. No monomer units (Q0 ) were detected. 相似文献
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以四水硝酸钙(Ca(NO3)2·4H2O)和九水硅酸钠(Na2SiO3·9H2O)为原料,通过溶液法合成(20℃、60℃、80℃、100℃)的水化硅酸钙,采用XRD、SEM、IR、NMR测试方法研究了温度对水化硅酸钙微观结构的影响规律.结果表明:随着温度的升高(20~100℃),水化硅酸钙中(002)、(101)、(110)和(200)晶面间距逐渐减少;当温度由20℃升高到100℃时,水化硅酸钙中硅氧四面体的聚合度增加了55.6%,其微观形貌由无规则聚集体逐渐变成层状. 相似文献
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Structure of Calcium Silicate Hydrates Formed in Alkaline-Activated Slag: Influence of the Type of Alkaline Activator 总被引:1,自引:0,他引:1
Ana Fernández-Jiménez Francisca Puertas Isabel Sobrados Jesús Sanz 《Journal of the American Ceramic Society》2003,86(8):1389-1394
The influence of the alkaline activator (NaOH, waterglass, or Na2 CO3 ) on the structure of the hydrated calcium silicate formed in alkali-activated slag (AAS) cement pastes has been investigated by FTIR, 29 Si and 27 Al magic-angle scattering nuclear magnetic resonance, and TEM/EDX techniques. In all cases, the main product formed after 7 d of activation, with activators giving an Na2 O concentration of 4%, is a semicrystalline calcium silicate hydrate with a dreierkette-type anion. In these structures, linear finite chains of silicate tetrahedra ( Q 2 units) are linked to central Ca-O layers, and tetrahedral aluminum occupies bridging positions in the chains. The main chain length and the amount of aluminum incorporated in the tetrahedral chains depend on the activator used. The detection of Q 3 silicon entities in alkaline-activated slags is discussed in relation to the possible formation of cross-linked structures that may be responsible for increased flexural and compressive strengths in AAS mortars. 相似文献
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P. K. MEHTA 《Journal of the American Ceramic Society》1967,50(4):204-208
In contrast to the general belief that formation of calcium trisulfoaluminate hydrate is accompanied by expansion even under conditions of restraint, Chatterji and Jeffery speculated that formation of calcium monosulfoaluminate hydrate is mainly responsible for the expansion phenomenon. Because of the importance of calcium sulfoaluminate hydrates in sulfate disruption of portland cement concretes and in expansive cements used for making crack-resistant concretes, the author, using data reported by Chatterji and Jeffery, attempted to reproduce their results. Some additional experiments were made to test the validity of their hypothesis. The results of the experiments showed that in every case, under conditions of restraint, it was formation of calcium trisulfoaluminate hydrate and not calcium monosulfate hydrate that caused significant expansions, which is contrary to the hypothesis of Chatterji and Jeffery. 相似文献
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Sodium lignosulfonate and naphthalene and melamine sulfonate formaldehyde condensates, dissolved in lime water, are adsorbed on C4 AH13 and C3 AH6 . When dissolved in dimethylsulfoxide the same admixtures are adsorbed on C4 AH13 but, apparently, not on C3 AH6 . The adsorption isotherms of the two polycondensates are very similar but different from those of lignosulfonate. This fact can be attributed to the considerable structural difference between the synthetic admixtures and the lignine derivative. The particle zeta potential is modified by the presence of the admixtures, minimum additions of which are enough to bring the zeta potential to negative constant values. Nevertheless, the values of the potential cannot be correlated with the viscosity of the aluminate hydrate pastes, since the viscosity first increases and then decreases as the admixture increases. This behavior can be explained by a bridging effect among the particles, which overcomes the repulsive effect due to zeta potential. 相似文献
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Calcium Silicate Carbonation Products 总被引:2,自引:0,他引:2
Seishi Goto Kenzo Suenaga Takeshi Kado Minoru Fukuhara 《Journal of the American Ceramic Society》1995,78(11):2867-2872
calcium silicates such as C3 S, βT-C2 S, and γgM-C2 S † were carbonated under saturated humidity at room temperature. Carbonation products were examined by DT-TGA, gasphase mass spectroscopy, and XRD. Two types of carbonate were produced: one type, which was rather poorly crystallized, was decarbonated at a very low temperature, below 600°C; the other type was a crystalline phase such as calcite, aragonite, and/or vaterite which was decarbonated above 600°C. The data were compared to existing data for calcium carbonates and basic calcium carbonates. The results suggest that an amorphous calcium silicate hydrocarbonate was one of the carbonation products which formed during the hydration/carbonation reaction. 相似文献
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MASAKI DAIMON SALAH A. ABO-EL-ENEIN GIRO ROSARA SEISHI GOTO RENICHI KONDO 《Journal of the American Ceramic Society》1977,60(3-4):110-114
Adsorption of N2 and water vapor was studied in completely hydrated tricalcium silicate and in fully hydrated tricalcium silicate from which Ca(OH)2 had been extracted. Compared with results obtained using N2 , water vapor adsorption led to increased values for small-pore volume, peak shifts to smaller sizes, and decreased values for large-pore volume. Marked hysteresis was observed in the case of water vapor adsorption; the resorption branch apparently represents the true pore structure. Extraction of Ca(OH)2 from the paste increased the calculated volume of small pores strikingly, suggesting that adsorption is hindered by Ca(OH)2 ; this tendency is more obvious in water vapor adsorption. The adsorption measurements indicate the existence of two kinds of pores, i.e. a wider intergel-particle pore and a smaller pore existing within the gel particle. The latter pore was further classified into intercrystallite and intracrystallite pores. 相似文献
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Soft X‐ray Ptychographic Imaging and Morphological Quantification of Calcium Silicate Hydrates (C–S–H) 下载免费PDF全文
Sungchul Bae Rae Taylor David Shapiro Peter Denes John Joseph Rich Celestre Stefano Marchesini Howard Padmore Tolek Tyliszczak Tony Warwick David Kilcoyne Pierre Levitz Paulo J. M Monteiro 《Journal of the American Ceramic Society》2015,98(12):4090-4095
Morphological details of calcium silicate hydrate (C–S–H) stemming from the hydration process of Portland cement (PC) phases are crucial for understanding the PC‐based systems but are still only partially known. Here we introduce the first soft X‐ray ptychographic imaging of tricalcium silicate (C3S) hydration products. The results are compared using both scanning transmission X‐ray and electron transmission microscopy data. The evidence shows that ptychography is a powerful method to visualize the details of outer and inner product C–S–H of fully hydrated C3S, which have fibrillar and an interglobular structure with average void sizes of 20 nm, respectively. The high‐resolution ptychrography image enables us to perform morphological quantification of C–S–H, and, for the first time, to possibly distinguish the contributions of inner and outer product C–S–H to the small angle scattering of cement paste. The results indicate that the outer product C–S–H is mainly responsible for the q?3 regime, whereas the inner product C–S–H transitions to a q?2 regime. Various hypotheses are discussed to explain these regimes. 相似文献