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Stability of hydrotalcite (Mg-Al layered double hydroxide) in presence of different anions
Abstract MgO contained in cementitious materials is experimentally observed to precipitate as poorly crystalline hydrotalcite (Mg-Al LDH). However, the geochemical modelling of hydrotalcite is challenging due to the lack of consistent thermodynamic dataset for this phase. Hydrotalcites with Mg/Al = 2 were synthesised in the presence of NaHCO3, NaCl, Na2SO4, NaNO3, and NaOH. Mass balance, XRD and FT-IR indicated the incorporation of the anions in the interlayer together with some carbonate. The crystallinity of the phase increased depending on the anion: SO4 2− < Cl− < NO3 − < OH− < CO3 2−. An in-situ increase of temperature monitored by XRD and TGA showed that the stability of the hydrotalcite structure with temperature also depended on the incorporated anion. The solubility products were calculated based on the solution analysis of samples re-equilibrated at different temperatures, while the entropy and heat capacity were obtained from the additivity method or the molar volume. A simple solid-solution model for hydrotalcite containing CO3, OH, SO4, Cl and NO3 is suggested.
Stability of hydrotalcite (Mg-Al layered double hydroxide) in presence of different anions
Abstract MgO contained in cementitious materials is experimentally observed to precipitate as poorly crystalline hydrotalcite (Mg-Al LDH). However, the geochemical modelling of hydrotalcite is challenging due to the lack of consistent thermodynamic dataset for this phase. Hydrotalcites with Mg/Al = 2 were synthesised in the presence of NaHCO3, NaCl, Na2SO4, NaNO3, and NaOH. Mass balance, XRD and FT-IR indicated the incorporation of the anions in the interlayer together with some carbonate. The crystallinity of the phase increased depending on the anion: SO4 2− < Cl− < NO3 − < OH− < CO3 2−. An in-situ increase of temperature monitored by XRD and TGA showed that the stability of the hydrotalcite structure with temperature also depended on the incorporated anion. The solubility products were calculated based on the solution analysis of samples re-equilibrated at different temperatures, while the entropy and heat capacity were obtained from the additivity method or the molar volume. A simple solid-solution model for hydrotalcite containing CO3, OH, SO4, Cl and NO3 is suggested.
Stability of hydrotalcite (Mg-Al layered double hydroxide) in presence of different anions
Bernard, Ellina (author) / Zucha, Wolfgang Jan (author) / Lothenbach, Barbara (author) / Mäder, Urs (author)
2021-11-14
Article (Journal)
Electronic Resource
English
ATR FT-IR , attenuated total reflectance Fourier-transform infrared , C-(A-)S-H , calcium (alumino-)silicate hydrate , C <inf>p</inf>° , heat capacity , FWHM , full width at half maximum , K<inf>s0</inf> , solubility product , LDH , layered double hydroxide , MAS NMR , magic-angle spinning nuclear magnetic resonance , M-(A-)S-H , magnesium (alumino-)silicate hydrate , Mg-Al-LDH , Mg and Al based layered double hydroxide = hydrotalcite , PC , Portland cement , S° , entropy , SCMs , supplementary cementitious materials , SSA<inf>BET</inf> , specific surface are obtained by using the Brunauer-Emmett-Teller equation , TGA-FT-IR , thermogravimetric analysis complemented with Fourier Transform Infrared detection of evolved gases , V<inf>cell</inf> , cell volume , V° , molar volume , XRD , X-ray powder diffraction , Hydrotalcite , Magnesium , Anions , Thermodynamic data
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