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– within 16 h at 200 °C. These compounds were characterized by XRD, STA, FT-IR, SEM/EDS and BET analysis. It was found that gyrolite is a mesoporous material. Its specific surface area SBET = 143.15 m2/g, the radius of dominant plate pores rp = 80–90 Å, the calculated total pore volume ∑Vp = 0.661 cm3/g. Gyrolite texture changes upon introducing Na+ ions into its crystal structure: the specific surface area SBET diminishes to 27.24 m2/g, the radius of dominant cylindric pores rp = 60–70 Å, the calculated total pore volume #&8721Vp = 0.118 cm3/g.
that the cation exchange capacity of gyrolite depends on the concentration of copper ions in the Cu(NO3)2 solution, because a fivefold increase of the concentration (from 1.0 to 5.0 g/dm3) reduces the duration of the ion exchange reaction by a factor of three (from 15 min to 5 min). In solutions with higher initial concentrations of Cu2+ ions (10.0 and 20.0 g/dm3), the sorption proceeds more intensively and all the copper ions are adsorbed in 1 min. It should be noted that the cation exchange reactions are reversible in alkaline solution, because nearly 90% of the copper ions are adsorbed in a physical process, while the remaining part of the cation exchange process takes place in a chemical reaction. Furthermore, the crystal structure of gyrolite is stable in alkaline solution. The products of sorption were characterized by X-ray diffraction, thermogravimetry-differential scanning calorimetry and Fourier-transform infrared spectroscopy methods.
after 72 h, only partially recrystallizes into 1.13 nm tobermorite. Meanwhile, in the mixtures with less reactive CaO (96%), the stoichiometric composition (CaO/SiO2) of products of the synthesis varies from 0.66 to 0.83. When the CaO/SiO2 molar ratio in the initial mixture is equal to 1.0, the CaO reactivity has a significant effect on the composition of products forming in hydrothermal conditions. The products of the syntheses were characterized by X-ray diffraction analysis, simultaneous thermal analysis and Fourier transform infrared spectroscopy.
CaO/SiO2 = 0.83, 1.0 and SO3/(SiO2 + SO3) = 0, 0.0125, 0.025. The durations of isothermal curing at 200 °C were 4, 8, 16 and 72 h. It was established that sulfate ions improve the synthesis of 1.13 nm tobermorite in the CaO-SiO2onH2O-H2O system with CaO/SiO2 = 0.83 at 200 °C. However, a larger amount of gypsum (SO3/(SiO2 + SO3) = 0.025) stimulates the formation not only of 1.13 nm tobermorite but also of CaSO4 and xonotlite. In the CaO-SiO2onH2O-H2O system with CaO/SiO2 = 1.0, a small amount of sulfate ions prolong the persistence of intermediate compounds - 1.13 nm tobermorite and C-S-H (I). The products of synthesis were characterized by X-ray diffraction analysis, simultaneous thermal analysis and Fourier transform infrared spectroscopy.
from the mass of dry materials, added in the form of solution and additional water was used so that the water/solid ratio of the suspension was equal to 10.0. Hydrothermal synthesis of the unstirred suspension was carried out in saturated steam at 150, 175, 200 oC. The duration of isothermal curing was 4, 8, 16, 24, 32, 48, 72 and 168 h. The temperature of 150 oC is too low for the synthesis of gyrolite; the stoichiometric ratio C/S = 0.66 is not reached even after 168 h of synthesis neither in pure mixtures nor in mixtures with addition of Na2O. Na+ ions significantly influence the formation of gyrolite from the CaO-quartz mixtures in the temperature range from 175 oC to 200 oC. Gyrolite is formed at 175 oC after 168 h and at 200 oC after 16 h of isothermal curing. On the contrary, in pure mixtures it does not form even after 72 h at 200 oC. Na+ ions also change the compositions of intermediate and final products of the synthesis. In mixtures with 5% Na2O, intermediate compounds are C-S-H(I) and Z-phase, and the final products are gyrolite and pectolite. Meanwhile, in mixtures without this additive, the main intermediate compounds alfa-C2S hydrate and C-S-H(II), and the main products are 1.13 nm tobermorite and xonotlite.
desorption thermograms. It was determined that the thermal effect of desorption is close to the steam-heat of water vapour at temperatures up to 175 °C. This part of water vapour adsorption can be described by a physical adsorption model, only a small quantity of water vapour being chemisorbed. The crystal structure of gyrolite under a pressure of water vapour and at low temperatures (-197 °C) was stable.
primary mixtures was 1.0. Hydrothermal synthesis was carried out under the saturated steam pressure at temperatures of 90, 110, 130, 150 and 175 °C; the duration of isothermal curing was 2-72 h. It was determined that an increase of temperature significantly influences the stability, morphology and degree of crystallinity of C-S-H (I). It was found that C-S-H (I) is stable in the ranhe 90-130 °C. The overall morphology of C-S-H varies from the common fibrous type to irregular grains forming a reticular network. The compositions of intermediate products and of final products can be changed by adding calcium containing components (Ca(OH)2, CaO). In the mixtures with Ca(OH)2, an intermediate compound is C-S-H (I) and the final product is xonotlite. Meanwhile, in the mixtures with CaO, the main intermediate compounds are Z phase and C-S-H (I), and the main product is gyrolite.
mixtures were CaO/(SiO2 + Al2O3) = 0.66 and Al2O3/(SiO 2 + Al2O3) = 0 or 0.025. The amount of NaOH, corresponding to 5% of Na2O in the mass of dry material, was added in the form of solution. Due to the low solubility rate of quartz in the CaO-quartz-H2O system with C/S = 0.66 in the temperature range 150-200°C, low-base calcium silicate hydrates (Z-phase, gyrolite, pectolite, and others) do not form even after 72 hours of hydrothermal curing. It has been proved that gamma-Al2O3 and Na2O additives change the reaction mechanisms and composition of intermediate (final) products. In mixtures with Na2O, gyrolite starts to form already at 175°C. It should be noted that in the temperature range 175-200°C the final products are gyrolite and pectolite, and the intermediate compounds are C-S-H(l) and Z-phase. The formation of low-base calcium silicate hydrates in the CaO-quartz-Na2O-H2O system is slowed down when Al 2O3 is added because Al3+ ions stimulate the formation of tobermorite and prevent the formation of pectolite and Z-phas
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