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Formation of calcium sulfate through the aggregation of sub-3 nanometre primary species.

Stawski TM, van Driessche AE, Ossorio M, Diego Rodriguez-Blanco J, Besselink R, Benning LG - Nat Commun (2016)

Bottom Line: The reaction starts through the fast formation of well-defined, primary species of <3 nm in length (stage I), followed in stage II by their arrangement into domains.The variations in volume fractions and electron densities suggest that these fast forming primary species contain Ca-SO4-cores that self-assemble in stage III into large aggregates.Within the aggregates these well-defined primary species start to grow (stage IV), and fully crystalize into gypsum through a structural rearrangement.

View Article: PubMed Central - PubMed

Affiliation: School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.

ABSTRACT
The formation pathways of gypsum remain uncertain. Here, using truly in situ and fast time-resolved small-angle X-ray scattering, we quantify the four-stage solution-based nucleation and growth of gypsum (CaSO4·2H2O), an important mineral phase on Earth and Mars. The reaction starts through the fast formation of well-defined, primary species of <3 nm in length (stage I), followed in stage II by their arrangement into domains. The variations in volume fractions and electron densities suggest that these fast forming primary species contain Ca-SO4-cores that self-assemble in stage III into large aggregates. Within the aggregates these well-defined primary species start to grow (stage IV), and fully crystalize into gypsum through a structural rearrangement. Our results allow for a quantitative understanding of how natural calcium sulfate deposits may form on Earth and how a terrestrially unstable phase-like bassanite can persist at low-water activities currently dominating the surface of Mars.

No MeSH data available.


Related in: MedlinePlus

Evolution of the fitting parameters as a function of time.(a) Elongated scatterers with lengths, L, and cross-sectional radii, R, up to ∼1,500 s; (b) pre-factors φVpart(Δρ)2 and φ(Δρ)2 up to ∼1,500 s; the average of the φ(Δρ)2 product is marked with a horizontal solid line; (c) mean effective hard-sphere radii <ReHS> and their s.d.'s, σ characterizing <SHS(q)>; (d) local volume fractions, v, characterizing <SHS(q)>; (e) surface area contribution, A′, and surface fractal dimension, Ds, characterizing <SSF(q)>. Note that up to 600 s the A′ and Ds values exhibited very large uncertainty, due to the limited contribution of large scatterers in the low-q range of the scattering patterns. For Ds (<600 s) any value between 2 and<3 would produce reasonable fits, but the yielded A′ values for all Ds>2 were significantly out of trend and are thus not shown; (f) pre-factor φVpart(Δρ)2 evolution up to 5,400 s; (g) Degree of crystallization α versus time from the corresponding WAXS measurements derived from the change in the area of the (020) WAXS reflection of gypsum measured simultaneously with the corresponding SAXS patterns. The background colours in a–f indicate stages I–IV, according to the legend. Time scales are in seconds (horizontal axes) except for g where they are in thousands of seconds.
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f3: Evolution of the fitting parameters as a function of time.(a) Elongated scatterers with lengths, L, and cross-sectional radii, R, up to ∼1,500 s; (b) pre-factors φVpart(Δρ)2 and φ(Δρ)2 up to ∼1,500 s; the average of the φ(Δρ)2 product is marked with a horizontal solid line; (c) mean effective hard-sphere radii <ReHS> and their s.d.'s, σ characterizing <SHS(q)>; (d) local volume fractions, v, characterizing <SHS(q)>; (e) surface area contribution, A′, and surface fractal dimension, Ds, characterizing <SSF(q)>. Note that up to 600 s the A′ and Ds values exhibited very large uncertainty, due to the limited contribution of large scatterers in the low-q range of the scattering patterns. For Ds (<600 s) any value between 2 and<3 would produce reasonable fits, but the yielded A′ values for all Ds>2 were significantly out of trend and are thus not shown; (f) pre-factor φVpart(Δρ)2 evolution up to 5,400 s; (g) Degree of crystallization α versus time from the corresponding WAXS measurements derived from the change in the area of the (020) WAXS reflection of gypsum measured simultaneously with the corresponding SAXS patterns. The background colours in a–f indicate stages I–IV, according to the legend. Time scales are in seconds (horizontal axes) except for g where they are in thousands of seconds.

Mentions: where L is the length, R the radius, φ the volume fraction of primary scatterers, Δρ is the scattering length density difference between the scatterers and the matrix (solvent) and Vpart is the volume of a single particle (scatterer). Seff(q) represents the general expression for the effective interparticle structure factor19: in stage I primary species were non-interacting, hence Seff(q)=1, but for stages II–IV Seff(q)≠1 as it is indicated by the changes at q<1 nm−1 (Fig. 2a,b). The expression for the cylindrical form factor is used here as the best approximation, and we do not imply that species are rigid. In Fig. 3a, the evolution of the radius and length (R and L) of the formed primary species, that are characterized by a cylindrical form factor, is shown up to ∼1,500 s (stages I–III). Between 30 and ∼800 s, the length of the formed entities, L, remained constant with a value of ∼2.8 nm. Subsequently, these primary species gradually grew in length reaching ∼4 nm at ∼1,500 s (∼30% increase). Their average radius was <0.3 nm and remained constant up to ∼1,500 s. The fitting of the scattering curves in all other experiments yielded R=0.2±10% nm and L=2.7±12% nm, confirming that independent of reaction conditions, these individual primary species constituted the building blocks for the larger aggregates (Supplementary Fig. 1 and Supplementary Note 1).


Formation of calcium sulfate through the aggregation of sub-3 nanometre primary species.

Stawski TM, van Driessche AE, Ossorio M, Diego Rodriguez-Blanco J, Besselink R, Benning LG - Nat Commun (2016)

Evolution of the fitting parameters as a function of time.(a) Elongated scatterers with lengths, L, and cross-sectional radii, R, up to ∼1,500 s; (b) pre-factors φVpart(Δρ)2 and φ(Δρ)2 up to ∼1,500 s; the average of the φ(Δρ)2 product is marked with a horizontal solid line; (c) mean effective hard-sphere radii <ReHS> and their s.d.'s, σ characterizing <SHS(q)>; (d) local volume fractions, v, characterizing <SHS(q)>; (e) surface area contribution, A′, and surface fractal dimension, Ds, characterizing <SSF(q)>. Note that up to 600 s the A′ and Ds values exhibited very large uncertainty, due to the limited contribution of large scatterers in the low-q range of the scattering patterns. For Ds (<600 s) any value between 2 and<3 would produce reasonable fits, but the yielded A′ values for all Ds>2 were significantly out of trend and are thus not shown; (f) pre-factor φVpart(Δρ)2 evolution up to 5,400 s; (g) Degree of crystallization α versus time from the corresponding WAXS measurements derived from the change in the area of the (020) WAXS reflection of gypsum measured simultaneously with the corresponding SAXS patterns. The background colours in a–f indicate stages I–IV, according to the legend. Time scales are in seconds (horizontal axes) except for g where they are in thousands of seconds.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4821993&req=5

f3: Evolution of the fitting parameters as a function of time.(a) Elongated scatterers with lengths, L, and cross-sectional radii, R, up to ∼1,500 s; (b) pre-factors φVpart(Δρ)2 and φ(Δρ)2 up to ∼1,500 s; the average of the φ(Δρ)2 product is marked with a horizontal solid line; (c) mean effective hard-sphere radii <ReHS> and their s.d.'s, σ characterizing <SHS(q)>; (d) local volume fractions, v, characterizing <SHS(q)>; (e) surface area contribution, A′, and surface fractal dimension, Ds, characterizing <SSF(q)>. Note that up to 600 s the A′ and Ds values exhibited very large uncertainty, due to the limited contribution of large scatterers in the low-q range of the scattering patterns. For Ds (<600 s) any value between 2 and<3 would produce reasonable fits, but the yielded A′ values for all Ds>2 were significantly out of trend and are thus not shown; (f) pre-factor φVpart(Δρ)2 evolution up to 5,400 s; (g) Degree of crystallization α versus time from the corresponding WAXS measurements derived from the change in the area of the (020) WAXS reflection of gypsum measured simultaneously with the corresponding SAXS patterns. The background colours in a–f indicate stages I–IV, according to the legend. Time scales are in seconds (horizontal axes) except for g where they are in thousands of seconds.
Mentions: where L is the length, R the radius, φ the volume fraction of primary scatterers, Δρ is the scattering length density difference between the scatterers and the matrix (solvent) and Vpart is the volume of a single particle (scatterer). Seff(q) represents the general expression for the effective interparticle structure factor19: in stage I primary species were non-interacting, hence Seff(q)=1, but for stages II–IV Seff(q)≠1 as it is indicated by the changes at q<1 nm−1 (Fig. 2a,b). The expression for the cylindrical form factor is used here as the best approximation, and we do not imply that species are rigid. In Fig. 3a, the evolution of the radius and length (R and L) of the formed primary species, that are characterized by a cylindrical form factor, is shown up to ∼1,500 s (stages I–III). Between 30 and ∼800 s, the length of the formed entities, L, remained constant with a value of ∼2.8 nm. Subsequently, these primary species gradually grew in length reaching ∼4 nm at ∼1,500 s (∼30% increase). Their average radius was <0.3 nm and remained constant up to ∼1,500 s. The fitting of the scattering curves in all other experiments yielded R=0.2±10% nm and L=2.7±12% nm, confirming that independent of reaction conditions, these individual primary species constituted the building blocks for the larger aggregates (Supplementary Fig. 1 and Supplementary Note 1).

Bottom Line: The reaction starts through the fast formation of well-defined, primary species of <3 nm in length (stage I), followed in stage II by their arrangement into domains.The variations in volume fractions and electron densities suggest that these fast forming primary species contain Ca-SO4-cores that self-assemble in stage III into large aggregates.Within the aggregates these well-defined primary species start to grow (stage IV), and fully crystalize into gypsum through a structural rearrangement.

View Article: PubMed Central - PubMed

Affiliation: School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.

ABSTRACT
The formation pathways of gypsum remain uncertain. Here, using truly in situ and fast time-resolved small-angle X-ray scattering, we quantify the four-stage solution-based nucleation and growth of gypsum (CaSO4·2H2O), an important mineral phase on Earth and Mars. The reaction starts through the fast formation of well-defined, primary species of <3 nm in length (stage I), followed in stage II by their arrangement into domains. The variations in volume fractions and electron densities suggest that these fast forming primary species contain Ca-SO4-cores that self-assemble in stage III into large aggregates. Within the aggregates these well-defined primary species start to grow (stage IV), and fully crystalize into gypsum through a structural rearrangement. Our results allow for a quantitative understanding of how natural calcium sulfate deposits may form on Earth and how a terrestrially unstable phase-like bassanite can persist at low-water activities currently dominating the surface of Mars.

No MeSH data available.


Related in: MedlinePlus