Clarification of possible ordered distributions of trivalent cations in layered double hydroxides and an explanation for the observed variation in the lower solid-solution limit

Richardson, Ian

doi:10.1107/s2052519213027905

Cited by 27 publications

(32 citation statements)

References 35 publications

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“…This matches the magnesium/aluminium ratio of the LDH phase that is normally observed in long-term-cured alkali-activated slag samples, which is around 2•1. 20,53 This suggests that the addition of either CLDH or HT does not seem to have any significant impact on changing the layer cation compositions of the HT-like phases forming in silicate-activated AAS, consistent with the observations by XRD ( Figure 4) for these cements.…”

Section: Evolution Of Phase Assemblage At Later Agesupporting

confidence: 84%

Layered double hydroxides modify the reaction of sodium silicate-activated slag cements

Bernal

Provis

2019

Green Materials

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The impact of adding two types of layered double hydroxides (LDHs), commercial hydrotalcite (HT) and its thermally treated form (CLDH), on the reaction kinetics and phase assemblage development of a sodium silicate-activated slag cement was investigated. The reaction kinetics of LDH-modified cements was assessed by isothermal calorimetry, and the results were correlated with in situ attenuated total reflection Fourier transform infrared spectroscopy results collected over the first days of reaction, to identify the structural evolution of the main binding phase forming in these cements: a sodium-containing calcium aluminosilicate hydrate (C-(N)-AS -H)-type gel. The addition of either HT or CLDH into sodium silicate-activated slag paste accelerates the precipitation of reaction products and increases the formation of HT in these cements, without causing significant changes to the C-(N)-AS -H binding phase. This is extremely relevant in terms of the durability of alkali-activated slag cements, as a higher content of the HT-like phase has the potential to reduce their chloride permeability and enhance carbonation resistance. 52 Cite this article Ke X, Bernal SA and Provis JL (2019) Layered double hydroxides modify the reaction of sodium silicate-activated slag cements.

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Section: Evolution Of Phase Assemblage At Later Agesupporting

confidence: 84%

Layered double hydroxides modify the reaction of sodium silicate-activated slag cements

Bernal

Provis

2019

Green Materials

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“…This result provides further support for explaining Mg/Al ratios < 2 in terms of intimately intermixed low-Mg high-Al phases with Mg-Al LDH phases, e.g. TAH or N-A-S(-H) gel, because the low Mg/Al ratio of this solid solution phase is 2 (Richardson, 2013). However, the simulations predict that the fraction of Al in C-(N-)A-S-H gel (Al CNASH ) relative to the total amount of Al in the reaction products (Al CNASH /Al products ) is ~0.28 for slag reaction extents >50% ( Figure 5A), which is much less than the relative amount of four- Escalante-García, 2013; Wang and Scrivener, 1995), or in NS-AS/4 mass% PC blends cured for 3…”

Section: Simulated Reaction Of a Na2sio3-activated Slag Cementsupporting

confidence: 59%

“…Thermodynamic data for MA-OH-LDH were reformulated into an ideal solid solution thermodynamic model (MA-OH-LDH_ss) containing three end-members with Mg/Al ratios of 2, 3 and 4 (Table 1) to match the known chemical composition range of this solid solution (Mg (1-x) (Richardson, 2013)). …”

Section: Thermodynamic Model For Ma-oh-ldhmentioning

confidence: 99%

“…b The asterisks for the T2C*, T5C* and TobH* end-members indicate that these components have slightly modified thermodynamic properties but the same chemical composition relative to the T2C, T5C and TobH end-members of the downscaled CSH3T thermodynamic model (Kulik, 2011). c Thermodynamic properties based on the thermochemical data in (Allada et al, 2005) and solubility data in Gao and Li, 2012), section 2.2, with molar volumes calculated from (Richardson, 2013). d Not available e Molar volumes calculated from framework densities, lattice types and lattice cell parameters for each zeolite framework type (Baerlocher et al, 2007).…”

Section: Other Solid Phasesmentioning

confidence: 99%

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Thermodynamic modelling of alkali-activated slag cements

Myers

Lothenbach

Bernal

et al. 2015

Applied Geochemistry

184

132

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Please cite this article as: Myers, R.J., Lothenbach, B., Bernal, S.A., Provis, J.L., Thermodynamic modelling of alkali-activated slag cements, Applied Geochemistry (2015), doi: http://dx. AbstractThis paper presents a thermodynamic modelling analysis of alkali-activated slag-based cements, which are high performance and potentially low-CO 2 binders relative to Portland cement. The has been applied to AAS cements in the past (Lothenbach and Gruskovnjak, 2007), however the calcium silicate hydrate (C-S-H) thermodynamic model (Kulik and Kersten, 2001) used in that study does not explicitly define the uptake of Al and Na which is needed to fully describe C-(N-)A-S-H gel. Chemically complete definitions of Al chemistry in the thermodynamic models used to simulate the phases formed in AAS-based cements are important in enabling accurate prediction of the chemistry of these cements. The inclusion of alkalis as a key component in thermodynamic models for C-(N-)A-S-H gel is also important to enable correct description of the solubility relationships of this phase under the high pH conditions (>12) and alkali concentrations (tens to hundreds of mmol/L) relevant to the majority of cementitious materials (Myers et al., 2014). The CNASH_ss thermodynamic model used in the current paper was recently developed (Myers et al., 2014) to formally account for Na and tetrahedral Al incorporated in Ca/Si < 1.3 C-(N-)A-S-H gel. Here, this thermodynamic model is used to simulate the chemistry of AAS cements activated by aqueous solutions of NaOH ((NH) 0.5 ), Na 2 SiO 3 (NS), Na 2 Si 2 O 5 (NS 2 ) and Nc. This thermodynamic model can describe a large set of solubility data for the CaO-(Na 2 O,Al 2 O 3 )-SiO 2 -H 2 O and AAS cement systems, and closely matches the published chemical compositions of calcium aluminosilicate hydrate (C-A-S-H) gel, and the volumetric properties of C-(N-)A-S-H gel measured in a sodium silicate-activated slag cement (Myers et al., 2014). The CNASH_ss thermodynamic model is assessed here in terms of the prediction of solid phase assemblages and the Al content of C-(N-)A-S-H gel over the bulk slag chemical composition range which is most relevant to AAS cement-based materials. These simulations are performed using the Gibbs energy minimisation software GEM-Selektor v.3 an updated definition of Mg-Al LDH intercalated with OH -(MA-OH-LDH), and including some zeolites and alkali carbonates. The results are discussed in terms of implications for the design of high performance AAS-based cements.

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“…There is limited evidence that in certain mixed-metal LDHs with M 2+ : M 3+ concentrations of 2 : 1 the more highly charged cations avoid sharing hydroxide bridges. 35,37,52 This local rule leads to an ordered structure in which the M 3+ cations are surrounded only by M 2+ cations to give a periodic 'honeycomb' motif [ Fig. 4(a)].…”

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confidence: 99%

Structural characterisation of a layered double hydroxide nanosheet

et al. 2014

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We report the atomic-scale structure of a Zn₁₅₂Al-borate layered double hydroxide (LDH) nanosheet, as determined by reverse Monte Carlo (RMC) modelling of X-ray total scattering data. This study involves the extension of the RMC method to enable structural refinement of two-dimensional nanomaterials. The refined LDH models show the intra-layer geometry in this highly-exfoliated phase to be consistent with that observed in crystalline analogues, with the reciprocal-space scattering data suggesting a disordered arrangement of the Zn(2+) and Al(3+) cations within the nanosheet. The approach we develop is generalisable and so offers a method of characterising the structures of arbitrary nanosheet phases, including systems that support complex forms of disorder within the nanosheets themselves.

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Clarification of possible ordered distributions of trivalent cations in layered double hydroxides and an explanation for the observed variation in the lower solid-solution limit

Cited by 27 publications

References 35 publications

Layered double hydroxides modify the reaction of sodium silicate-activated slag cements

Layered double hydroxides modify the reaction of sodium silicate-activated slag cements

Thermodynamic modelling of alkali-activated slag cements

Structural characterisation of a layered double hydroxide nanosheet

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