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Elemental sulfur coarsening kinetics.

Garcia AA, Druschel GK - Geochem. Trans. (2014)

Bottom Line: The addition of surfactants (utilizing ionic and nonionic surfactants as model compounds) results in a significant reduction of coarsening rates, in addition to known effects of these molecules on elemental sulfur solubility.DLS and cryo-SEM results suggest coarsening is largely a product of ripening processes rather than particle aggregation, especially at higher temperatures.Elemental sulfur sols coarsen rapidly at elevated temperatures and experience significant effects on both solubility and particle coarsening kinetics due to interaction with surfactants.

View Article: PubMed Central - PubMed

Affiliation: Department of Geology, University of Vermont, Delehanty Hall, Burlington, 05405 VT USA ; School of Earth and Space Exploration, Arizona State University, Tempe, 85287 AZ USA.

ABSTRACT

Background: Elemental sulfur exists is a variety of forms in natural systems, from dissolved forms (noted as S8(diss) or in water as S8(aq)) to bulk elemental sulfur (most stable as α-S8). Elemental sulfur can form via several biotic and abiotic processes, many beginning with small sulfur oxide or polysulfidic sulfur molecules that coarsen into S8 rings that then coalesce into larger forms: [Formula: see text] Formation of elemental sulfur can be possible via two primary techniques to create an emulsion of liquid sulfur in water called sulfur sols that approximate some mechanisms of possible elemental sulfur formation in natural systems. These techniques produce hydrophobic (S8(Weimarn)) and hydrophilic (S8(polysulfide)) sols that exist as nanoparticle and colloidal suspensions. These sols begin as small sulfur oxide or polysulfidic sulfur molecules, or dissolved S8(aq) forms, but quickly become nanoparticulate and coarsen into micron sized particles via a combination of classical nucleation, aggregation processes, and/or Ostwald ripening.

Results: We conducted a series of experiments to study the rate of elemental sulfur particle coarsening using dynamic light scattering (DLS) analysis under different physical and chemical conditions. Rates of nucleation and initial coarsening occur over seconds to minutes at rates too fast to measure by DLS, with subsequent coarsening of S8(nano) and S8(sol) being strongly temperature dependent, with rates up to 20 times faster at 75°C compared to 20°C. The addition of surfactants (utilizing ionic and nonionic surfactants as model compounds) results in a significant reduction of coarsening rates, in addition to known effects of these molecules on elemental sulfur solubility. DLS and cryo-SEM results suggest coarsening is largely a product of ripening processes rather than particle aggregation, especially at higher temperatures. Fitting of the coarsening rate data to established models for Ostwald ripening additionally support this as a primary mechanism of coarsening.

Conclusions: Elemental sulfur sols coarsen rapidly at elevated temperatures and experience significant effects on both solubility and particle coarsening kinetics due to interaction with surfactants. Growth of elemental sulfur nanoparticles and sols is largely governed by Ostwald ripening processes.

No MeSH data available.


Dynamic light scattering analysis of S8(Weimarn)(solid symbols) and S8(polysulfide)(open symbols) at different temperatures (20, 50, and 75°C).
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Fig1: Dynamic light scattering analysis of S8(Weimarn)(solid symbols) and S8(polysulfide)(open symbols) at different temperatures (20, 50, and 75°C).

Mentions: S8(Weimarn) and S8(polysulfide) coarsening rates were analyzed at different temperatures (Experiment set #2) (20, 50, and 75°C) (Figure 1). S8(Weimarn) coarsening rate at room temperature (20°C) is 1.65 nm/min (±0.304 nm); at 50°C the coarsening rate is 6.62 ± 0.506 nm/min, and at 75°C the coarsening rate is 19.1 ± 0.875 nm/min. The difference between room temperature (20°C) and 50°C is 4.97 nm/min faster at 50°C. The rate of coarsening at 75°C is 11.6 times faster than room temperature (20°C). S8(polysulfide) coarsening rate at room temperature (20°C) is 0.54 nm/min (±0.146 nm) for pH 3.1; at 75°C the coarsening rate is 5.51 ± 0.384 nm/min for pH 4.7. The differences in S8(Weimarn) and S8(polysulfide) coarsening rates likely reflect fundamental differences in the surface character of each particle, with the more hydrophobic S8(Weimarn) particles exhibiting a substantially different temperature effect on rates at 75°C.Figure 1


Elemental sulfur coarsening kinetics.

Garcia AA, Druschel GK - Geochem. Trans. (2014)

Dynamic light scattering analysis of S8(Weimarn)(solid symbols) and S8(polysulfide)(open symbols) at different temperatures (20, 50, and 75°C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4631715&req=5

Fig1: Dynamic light scattering analysis of S8(Weimarn)(solid symbols) and S8(polysulfide)(open symbols) at different temperatures (20, 50, and 75°C).
Mentions: S8(Weimarn) and S8(polysulfide) coarsening rates were analyzed at different temperatures (Experiment set #2) (20, 50, and 75°C) (Figure 1). S8(Weimarn) coarsening rate at room temperature (20°C) is 1.65 nm/min (±0.304 nm); at 50°C the coarsening rate is 6.62 ± 0.506 nm/min, and at 75°C the coarsening rate is 19.1 ± 0.875 nm/min. The difference between room temperature (20°C) and 50°C is 4.97 nm/min faster at 50°C. The rate of coarsening at 75°C is 11.6 times faster than room temperature (20°C). S8(polysulfide) coarsening rate at room temperature (20°C) is 0.54 nm/min (±0.146 nm) for pH 3.1; at 75°C the coarsening rate is 5.51 ± 0.384 nm/min for pH 4.7. The differences in S8(Weimarn) and S8(polysulfide) coarsening rates likely reflect fundamental differences in the surface character of each particle, with the more hydrophobic S8(Weimarn) particles exhibiting a substantially different temperature effect on rates at 75°C.Figure 1

Bottom Line: The addition of surfactants (utilizing ionic and nonionic surfactants as model compounds) results in a significant reduction of coarsening rates, in addition to known effects of these molecules on elemental sulfur solubility.DLS and cryo-SEM results suggest coarsening is largely a product of ripening processes rather than particle aggregation, especially at higher temperatures.Elemental sulfur sols coarsen rapidly at elevated temperatures and experience significant effects on both solubility and particle coarsening kinetics due to interaction with surfactants.

View Article: PubMed Central - PubMed

Affiliation: Department of Geology, University of Vermont, Delehanty Hall, Burlington, 05405 VT USA ; School of Earth and Space Exploration, Arizona State University, Tempe, 85287 AZ USA.

ABSTRACT

Background: Elemental sulfur exists is a variety of forms in natural systems, from dissolved forms (noted as S8(diss) or in water as S8(aq)) to bulk elemental sulfur (most stable as α-S8). Elemental sulfur can form via several biotic and abiotic processes, many beginning with small sulfur oxide or polysulfidic sulfur molecules that coarsen into S8 rings that then coalesce into larger forms: [Formula: see text] Formation of elemental sulfur can be possible via two primary techniques to create an emulsion of liquid sulfur in water called sulfur sols that approximate some mechanisms of possible elemental sulfur formation in natural systems. These techniques produce hydrophobic (S8(Weimarn)) and hydrophilic (S8(polysulfide)) sols that exist as nanoparticle and colloidal suspensions. These sols begin as small sulfur oxide or polysulfidic sulfur molecules, or dissolved S8(aq) forms, but quickly become nanoparticulate and coarsen into micron sized particles via a combination of classical nucleation, aggregation processes, and/or Ostwald ripening.

Results: We conducted a series of experiments to study the rate of elemental sulfur particle coarsening using dynamic light scattering (DLS) analysis under different physical and chemical conditions. Rates of nucleation and initial coarsening occur over seconds to minutes at rates too fast to measure by DLS, with subsequent coarsening of S8(nano) and S8(sol) being strongly temperature dependent, with rates up to 20 times faster at 75°C compared to 20°C. The addition of surfactants (utilizing ionic and nonionic surfactants as model compounds) results in a significant reduction of coarsening rates, in addition to known effects of these molecules on elemental sulfur solubility. DLS and cryo-SEM results suggest coarsening is largely a product of ripening processes rather than particle aggregation, especially at higher temperatures. Fitting of the coarsening rate data to established models for Ostwald ripening additionally support this as a primary mechanism of coarsening.

Conclusions: Elemental sulfur sols coarsen rapidly at elevated temperatures and experience significant effects on both solubility and particle coarsening kinetics due to interaction with surfactants. Growth of elemental sulfur nanoparticles and sols is largely governed by Ostwald ripening processes.

No MeSH data available.