共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
Characterization of C-S-H from Highly Reactive β-Dicalcium Silicate Prepared from Hillebrandite 总被引:1,自引:1,他引:0
Yoshihiko Okada Hideki Ishida Kaori Sasaki J. Francis Young Takeshi Mitsuda 《Journal of the American Ceramic Society》1994,77(5):1313-1318
β-dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca2 (SiO3 )(OH)2 ) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, 29 Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C-S-H consisted mainly of a dimer and a single-chain polymer. Polymerization advances with increasing curing temperature and curing time. The C-S-H has an oriented fibrous structure and exhibits a 0.73-nm dreierketten in the longitudinal direction. On heating, the C-S-H dissociates to form β-C2 S. The temperature at which βC2 S begins to form decreases with increasing chain length of the C-S-H or as the Ca/Si ratio becomes higher. The high activity of β-C2 S is due to its large specific surface area and the fact that the hydration is chemical-reaction-rate-controlled until its completion. As a result, the hydration progresses in situ and C-S-H with a high Ca/Si ratio is formed. 相似文献
3.
Hideki Ishida Kaori Sasaki Yoshihiko Okada Takeshi Mitsuda 《Journal of the American Ceramic Society》1992,75(9):2541-2546
The effect of curing temperature (40°, 60°, 80°C) on the hydration behavior of β-dicalcium silicate (β-C2 S) was investigated. The β-C2 S was obtained by decomposition of hillebrandite, Ca2 (SiO3 )(OH)2 , at 600°C, has a specific surface area of about 7 m2 /g, and is in the form of fibrous crystals. The dependence of the hydration reaction on temperature continues until the reaction is completed. The hydration is completed in 1 day at 80°C and in 14 days at 14°C. The hydration mechanism is different above and below 60°C, but at a given temperature, the reaction mechanism and the silicate anion structures of C-S-H do not change significantly from the initial to the late stages of the reaction. High curing temperature and long curing times after completion of reaction promote silicate polymerization. The Ca/Si ratio of C-S-H shows high values, being almost 2.0 above 60°C and 1.95 below 40°C. 相似文献
4.
Sung-Woo Choi Seong-Hyeon Hong Young Jin Kim 《Journal of the American Ceramic Society》2009,92(9):2025-2028
The green emitting Ca2 SiO4 :Eu2+ (C2 S:Eu) phosphors were synthesized by the polymeric precursor process (Pechini-type), and the effects of calcination temperature and europium (Eu) doping concentration on the luminescent properties were investigated. The crystalline β-C2 S was obtained in the calcination temperature of 1100°–1400°C, and Eu was reduced into Eu2+ by annealing in 5% H2 /N2 atmosphere. The obtained C2 S:Eu2+ phosphors exhibited a strong emission at 504 nm under the excitation of λexc =350 nm. The highest photoluminescence (PL) intensity was observed in the C2 S:Eu2+ phosphors either calcined at 1300°C or doped with 3 mol% Eu. The obtained PL properties were discussed in terms of crystal structure, particle size and shape, surface roughness, and effect of concentration quenching. 相似文献
5.
Hideki Ishida Satoru Yamazaki Kaori Sasaki Yoshihiko Okada Takeshi Mitsuda 《Journal of the American Ceramic Society》1993,76(7):1707-1712
α-C2 SH can be synthesized by hydrothermal treatment of lime and silicic acid for 2 h at 200°C. When heated to 390–490°C, α-C2 SH dissociates through a two-step process to form an intermediate phase plus some γ-C2 S. This appears to be a new dicalcium silicate different from known dicalcium silicates—α, α'L , α'H , β, and γ phase—and is stable until around 900°C. At 920–960°C, all the phases are transformed to the α'L phase. The intermediate phase has high crystallinity and is stable at room temperature. 29 Si MAS NMR measurements indicate the possibility that it contains both protonated and unprotonated monosilicate anions. The intermediate phase that has passed through the α'phase at higher temperature yields β-C2 S on cooling. The intermediate phase is highly active, and completed its hydration in 1 day ( w/s = 1.0, 25°C). Among the crystalline calcium silicate hydrates with Ca/Si = 2.0, it is hillebrandite that yields β-C2 S at the lowest temperature. 相似文献
6.
Young-Min Kim Seong-Hyeon Hong Hwan Kim 《Journal of the American Ceramic Society》2002,85(8):1941-1946
A chlorine-bearing alinite cement was synthesized using reagent-grade chemicals, and the phase evolution and hydration behavior of the alinite clinker were examined. The effects of the MgO content on alinite formation and hydration also were investigated. Alinite began to appear at 1000°C from β-C2 S, C11 A7 CaCl2 , and unreacted raw materials, and an almost single-phase alinite was obtained at 1300°C. The alinite phase also was produced without MgO addition. However, CaO, β-C2 S, and C11 A7 CaCl2 phases were present. Alinite cements hydrated rapidly after a short incubation period, and the hydration products were C-S-H gels, Ca(OH)2 , and a Fridel's saltlike phase. The local environmental changes of silicon and aluminum during the formation and hydration of alinite were determined using magic-angle-spinning nuclear magnetic resonance spectroscopy. The Cl− -ion exsolution from the alinite paste during hydration was measured using ion chromatography. 相似文献
7.
Koichiro Fukuda Iwao Maki Suketoshi Ito Hideto Yoshida 《Journal of the American Ceramic Society》1995,78(12):3387-3389
A pseudobinary phase equilibrium diagram has been established for the P2 O5 -bearing Ca2 SiO4 -CaFe4 O7 system to confirm the occurrence of remelting reaction in α-Ca2 SiO4 solid solutions (C2 S(ss)). The reaction started at 1290°C immediately after the α-to-α'H transition and finished at 1145°C. The reaction products were made up of about 1 wt% of liquid and 99 wt% of solid α'H -C2 S(ss). The liquid exsolved at 1290°C was rich in Fe2 O3 , consisting of about 30 wt% of Ca2 SiO4 and 70 wt% of CaFe4 O7 . The liquid coexisting with α-C2 S(ss) precipitated new α'-phase crystals in association with the remelting reaction. 相似文献
8.
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
9.
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
10.
Koichiro Fukuda Iwao Maki Suketoshi Ito 《Journal of the American Ceramic Society》1996,79(11):2925-2928
Dicalcium silicate solid solutions (C2 S(ss)) doped with Na2 O, A12 O3 , and Fe2 O3 were examined by high-temperature optical microscopy. Surface deformation caused by a possible martensitic transformation between a'L and β phases was observed in situ under the microscope during temperature changes, indicating that the transformation was thermoelastic. Both the start and finish temperatures of the a'L -to-β and β-to-a'L transformations decreased with increased Na:(Na + Ca) ratio. Because of the athermal nature of the a'L -to-β transformation, the a'L phase, when cooled below the finish temperature, should have been completely converted to the β phase. 相似文献
11.
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
12.
Koichiro Fukuda Iwao Maki Kazuhiro Toyoda Suketoshi Ito 《Journal of the American Ceramic Society》1993,76(7):1821-1824
The α-to-α'H transition of Ca2 SiO4 solid solutions (C2 S(ss)) is a nucleation and growth process. This process was shown on time–temperature–transformation (TTT) diagrams for C2 S(ss) with different concentrations of foreign oxides (Na2 O, Al2 O3 , and Fe2 O3 ). The kinetic cutoff temperature and the activation energy for growth of the α'H phase increase steadily with increasing concentration of impurities. The activation energy for nucleation also increases above 950°C. The α'H phase, which exists in equilibrium with the α phase at 1280°C, is formed at a maximum rate at around 1100°C regardless of the chemical composition. The TTT diagrams enable us to predict, as a function of cooling rate, the phase constitution of C2 S(ss) at ambient temperature. 相似文献
13.
C. J. GOODBRAKE J. F. YOUNG R. L. BERGER 《Journal of the American Ceramic Society》1979,62(9-10):488-491
The carbonation of wetted powders of beta-dicalcium silicate (β·2CaO·SiO2 =β-C2 S) and tricalcium silicate (3CaO·SiO2 = C3 S) was studied as a function of reaction conditions. The water/solids ratio is an important parameter and there is an optimum value for each silicate. Relative humidity and the partial pressure of CO2 also strongly affect the reaction. The rate of carbonation can be conveniently represented by plotting the degree of carbonation against the logarithm of time. C-S-H and calcite are the initial reaction products. Subsequently, carbonation of the C-S-H produces silica gel, whereas aragonite may form if the system is allowed to dry out. 相似文献
14.
An intimate Ba-Al-Al2 O3 -SiO2 powder mixture, produced by high-energy milling, was pressed to 3 mm thick cylinders (10 mm diameter) and hexagonal plates (6 mm edge-to-edge width). Heat treatments conducted from 300° to 1650°C in pure oxygen or air were used to transform these solid-metal/oxide precursors into BaAl2 Si2 O8 . Barium oxidation was completed, and a binary silicate compound, Ba2 SiO4 , had formed within 24 h at 300°C. After 72 h at 650°C, aluminum oxidation was completed, and an appreciable amount of BaAl2 O4 had formed. Diffraction peaks consistent with hexagonal BaAl2 Si2 O8 , BaAl2 O4 , β-BaSiO3 , and possibly β-BaSi2 O5 were detected after 24 h at 900°C. Diffraction peaks for BaAl2 O4 and BaAl2 Si2 O8 were observed after 35 h at 1200°C, although SEM analyses also revealed fine silicate particles. Further reaction of this silicate with BaAl2 O4 at 1350° to 1650°C yielded a mixture of hexagonal and monoclinic BaAl2 Si2 O8 . The observed reaction path was compared to prior work with other inorganic precursors to BaAl2 Si2 O8 . 相似文献
15.
David H. Chmielewski Kenneth H. Sandhage 《Journal of the American Ceramic Society》1995,78(9):2504-2512
Bi2 Sr2 Ca2 Cu2 O8±δ -type compound thick films were exposed to oxygen-argon-gas mixtures (1% to 20% oxygen gas) at elevated pressures (up to 207 MPa) and temperatures (500° to 940°C) for times ranging from 5 to 96 h. At a sufficiently high oxygen fugacity and temperature, Bi2 Sr2 Ca1 Cu2 O8±δ decomposed via a solid-state reaction. Room-temperature X-ray diffractometry and electron probe microanalysis of decomposed films revealed the presence of Bi2 (Sr,Ca)2 -Cu1 O6±θ ro-type compound, Bi2 Sr2 ,Ca1 O8±δ -type compound, and CuO. Bi2 Sr2 Ca1 Cu2 O8±δ decomposition was accompanied by a modest weight gain, which was consistent with an oxidation reaction. The solid-state decomposition reaction could be reversed by heat treatment of decomposed films at 860°C in pure, flowing oxygen at ambient pressure. 相似文献
16.
Doreen D. Edwards Pollyanna E. Folkins Thomas O. Mason 《Journal of the American Ceramic Society》1997,80(1):253-257
Subsolidus phase relationships in the Ga2 O3 –In2 O3 system were studied by X-ray diffraction and electron probe microanalysis (EPMA) for the temperature range of 800°–1400°C. The solubility limit of In2 O3 in the β-gallia structure decreases with increasing temperature from 44.1 ± 0.5 mol% at 1000°C to 41.4 ± 0.5 mol% at 1400°C. The solubility limit of Ga2 O3 in cubic In2 O3 increases with temperature from 4.X ± 0.5 mol% at 1000°C to 10.0 ± 0.5 mol% at 1400°C. The previously reported transparent conducting oxide phase in the Ga-In-O system cannot be GaInO3 , which is not stable, but is likely the In-doped β-Ga2 O3 solid solution. 相似文献
17.
Thermal decomposition of silicon diimide, Si(NH)2 , in vacuum resulted in very-high-purity, fine-particle-size, amorphous Si3 N4 powders. The amorphous powder was isothermally aged at 50° to 100° intervals from 1000° to 1500°C for phase identification. Examination of ir spectra and X-ray diffraction patterns indicated a slow and gradual transition from an amorphous material to a crystalline α-phase occurring at 1200°C for >4 h and/or 1300° to 1400°C for 2 h. As the temperature was increased to ≥1450°C for 2 h, the crystalline β-phase was observed. Phase nucleation and crystallite morphology in this system were studied by electron microscopy and electron diffraction combined with TG as functions of temperature for the inorganic polymer starting materials. Powders prepared in this manner with 4 wt% Mg3 N2 added as a sintering aid were hot-pressed to high-density fine-grained bodies with uniform microstructures. The optimum hot-pressing condition was 1650°C for 1 h. Silicon concentration steadily increased as the hot-pressing temperature or time was increased. A method for chemical etching for high-density fine-grained Si3 N4 is described. Electrical measurements between room temperature and ∼500°C indicated dielectric constant and tan δ values of 8.3±0.03 and 0.65±0.05×10−2 , respectively. 相似文献
18.
The stability of the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound has been evaluated under conditions of elevated temperature (500°-860°C) and elevated oxygen fugacity (i.e., in O2 /Ar gas mixtures containing ≤120% O2 , at total pressures of 5207 MPa). At sufficiently high oxygen fugacities and temperatures, the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound transformed into a mixture of a strontium-rich (Bi,Pb)1 -(Sr,Ca,Cu)2 Oy -type compound, a calcium-rich (Bi,Pb)2 -(Sr,Ca,Cu)2 Oy -type compound, CuO, and a small amount of (Sr,Ca)O. The decomposition of the (Bi,Pb)2 Sr2 Ca2 -Cu3 O10±δ -type compound was accompanied by a 2%-3% weight gain, which was consistent with an oxidation reaction. The conditions of oxygen fugacity and temperature leading to decomposition, and the resulting decomposition products, are compared for the (Bi,Pb)2 Sr2 Ca2 Cu2 O10±δ -type and Bi2 Sr2 Ca1 Cu2 O8±Ψ -type compounds. 相似文献
19.
The reciprocal salt pair Sr2 SiO4 -Sr2 GeO4 -Ba2 GeO4 -Ba2 SiO4 was investigated using X-ray powder diffraction and DTA. Unlimited solubility in the low-K2 SO4 structure type (α') occurs throughout the system above 85°C. The nonlinear changes of some lattice constants of the solid solutions are discussed. A stable monoclinic low-temperature (β) form of Sr2 SiO4 was found which converts reversibly to the high-temperature α'-modification at 85°C. The enthalpy of the β-α' transition is 51 cal/mol. In the reciprocal salt pair the β-form solid solutions occur in a very narrow region below 85°C. 相似文献
20.
Hideki Ishida Katsumi Mabuchi Kaori Sasaki Takeshi Mitsuda 《Journal of the American Ceramic Society》1992,75(9):2427-2432
Experiments on hydrothermal synthesis were conducted using quartz or silicic acid and lime as starting materials at Ca/Si = 2.0. It is possible to synthesize pure hillebrandite (Ca2 (SiO3 )(OH)2 ) having the theoretical composition by heating at 200°C for 10 h or at 250°C for 5 h. The synthesized product is fibrous, open at each end, and has a length of 20 to 30 μm. Calcium silicate hydrate gels are produced at the initial stage of the reaction. These react further with the unreacted lime to give hillebrandite. However, when silicic acid is used as silica, hillebrandite with tricalcium silicate hydrate is observed at 250°C because of the high reaction rate of silica. On heating, hillebrandite starts to decompose at about 500°C and produces low-crystalline β-Ca2 SiO4 , which is stable at room temperature and has a remarkably large specific surface area of about 7 m2 /g. The decomposition reaction rate in a single crystal is rapid, and the reaction is considered to proceed topotactically. 相似文献