Sub- and supercritical hydrothermal route for the synthesis of xonotlite nanofibers for application to green concrete materials

Musumeci, Valentina; Camacho, Paula Sanz; Xu, Ke; Monteiro, Paulo J.M.; Dolado, Jorge S.; Aymonier, Cyril

doi:10.1016/j.supflu.2022.105583

Cited by 7 publications

(2 citation statements)

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“…That could be due to the fact that the increase in temperature is conducive to accelerating the reaction rate and shortening the reaction time. Notably, the recent work by Aymonier et al [27] illustrated that xonotlite can be synthesized within seconds in supercritical conditions (400 °C, 23.5 MPa), but trace impurities (calcite, wollastonite and vaterite) present in the reaction product. This is consistent with the results of thermodynamic calculations, showing that performing the xonotlite synthesis reaction under higher temperatures is not always preferable.…”

Section: Reaction (1)mentioning

confidence: 99%

“…This results in an ambiguous lowest formation temperature for xonotlite. Aymonier [27] was able to synthesize xonotlite in the supercritical water (400 °C and 23.5 MPa), effectively reducing the reaction time of days and hours to several seconds, thereby suggesting that high temperature has the potential to significantly decrease reaction time. Kawaguchi and Tashiro [24] studied the effect of the Ca/Si molar ratio of raw materials on the synthesis of xonotlite, and they reported that the most suitable Ca/Si molar ratio was 0.6-1.2.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamics of the hydrothermal synthesis of xonotlite

Liu

Huang

et al. 2023

Mater. Res. Express

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Xonotlite, as a new type of inorganic material, has been widely used in the fields of building insulation, friction braking, and bionic composite materials. However, the main method of producing xonotlite, the dynamic hydrothermal method, is regarded as a black box process. While the synthesis mechanism is still unclear, the synthesis conditions could be only optimized through trial-and-error experimentations. In this work, we established a thermodynamic model of the Ca(OH)2-SiO2-H2O system under hydrothermal conditions, and investigated influencing factors of the xonotlite synthesis. The results show that the synthesis reaction of xonotlite is exothermic, and that the standard free energy change comes mainly from the enthalpy change. We also reveal that, for the temperature range of 20 to 220℃, the standard free energy change of xonotlite synthesis reaction is negative, indicating the spontaneous forward reaction. However, due to side reactions, the predicted lowest temperature of xonotlite synthesis is around 170℃. In addition, our studies propose the optimum conditions to synthesis xonotlite with a purity of 99%: reaction temperature, 200℃; Ca/Si ratio, 0.9-1.0; water-solid ratio, no more than 20; pH, 7-8. For xonotlite synthesis with other raw materials, such as Ca(OH)2-SiO2, Ca(OH)2-K2SiO3, Ca(NO3)2·4H2O-Na2SiO3·9H2O and CaCl2·2H2O-Na2SiO3·9H2O, optimum synthesis conditions are also suggested. Those results provide thermodynamics fundamentals to synthesis reaction optimization, which is also an essential guideline to large-scale industrial xonotlite production.

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Section: Reaction (1)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%