scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 2: Quartz and amorphous silica

2019 ◽  
Vol 19 (9) ◽  
pp. 6035-6058 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Aqueous Solutions ◽  
Amorphous Silica ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Special Focus ◽  
Quartz Surface ◽  
Mineral Surface ◽  
Glass Vial ◽  
Immersion Freezing

Abstract. Divergent ice nucleation (IN) efficiencies of quartz, an important component of atmospheric mineral dust, have been reported in previous studies. We show here that quartz particles obtain their IN activity from milling and that quartz aged in water loses most of its IN efficiency relative to freshly milled quartz. Since most studies so far reported IN activities of commercial quartz dusts that were milled already by the manufacturer, IN active samples prevailed. Also, the quartz surface – much in contrast to that of feldspars – is not prone to ammonia-induced IN enhancement. In detail we investigate the influence of solutes on the IN efficiency of various silica (SiO2) particles (crystalline and amorphous) with special focus on quartz. We performed immersion freezing experiments and relate the observed variability in IN activity to the influence of milling, the aging time and to the exposure conditions since milling. Immersion freezing with silica particles suspended in pure water or aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, Na2SO4 and NaOH, with solute concentrations corresponding to water activities aw=0.9–1.0, were investigated in emulsified droplets by means of differential scanning calorimetry (DSC) and analyzed in terms of the onset temperature of the heterogeneous freezing signal Thet and the heterogeneously frozen water volume fraction Fhet. Quartz particles, which originate from milling coarse samples, show a strong heterogeneous freezing peak in pure water with Thet equal to 247–251 K. This IN activity disappears almost completely after aging for 7 months in pure water in a glass vial. During this time quartz slowly grew by incorporating silicic acid leached from the glass vial. Conversely, the synthesized amorphous silica samples show no discernable heterogeneous freezing signal unless they were milled. This implies that defects provide IN activity to silica surfaces, whereas the IN activity of a natural quartz surface is negligible, when it grew under near-equilibrium conditions. For suspensions containing milled quartz and the solutes (NH4)2SO4, NH4HSO4 or Na2SO4, Thet approximately follows ThetΔawhet(aw), the heterogeneous freezing onset temperatures that obey Δawhet criterion, i.e., ThetΔawhet(aw)=Tmelt(aw+Δawhet) with Δawhet being a constant offset with respect to the ice melting point curve, similar to homogeneous IN. This water-activity-based description is expected to hold when the mineral surface is not altered by the presence of the solutes. On the other hand, we observe a slight enhancement in Fhet in the presence of these solutes, implying that the compliance with the Δawhet criterion does not necessarily imply constant Fhet. In contrast to the sulfates, dilute solutions of NH3 or NaOH (molality ≥5×10-4 mol kg−1) reveal Thet by 3–8 K lower than ThetΔawhet(aw), indicating a significant impact on the mineral surface. The lowering of Thet of quartz suspended in dilute NH3 solutions is opposite to the distinct increase in Thet that we found in emulsion freezing experiments with aluminosilicates, namely feldspars, kaolinite, gibbsite and micas. We ascribe this decrease in IN activity to the increased dissolution of quartz under alkaline conditions. The defects that constitute the active sites appear to be more susceptible to dissolution and therefore disappear first on a dissolving surface.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 2 – Quartz and amorphous silica

2018 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Aqueous Solutions ◽  
Amorphous Silica ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Special Focus ◽  
Quartz Surface ◽  
Mineral Surface ◽  
Glass Vial ◽  
Immersion Freezing

Abstract. Divergent ice nucleation (IN) efficiencies of quartz, an important component of atmospheric mineral dust, have been reported in previous studies. We show here that quartz particles obtain their IN activity from milling and that quartz aged in water loses most of its IN efficiency relative to freshly milled quartz. Also, the quartz surface – much in contrast to that of feldspars – is not prone to ammonia-induced IN enhancement. In detail we investigate the influence of solutes on the IN efficiency of various silica (SiO2) particles (crystalline and amorphous) with special focus on quartz. We performed immersion freezing experiments and relate the reported contradictory behavior to the influence of milling, and to the aging time and conditions since milling. Immersion freezing with silica particles suspended in pure water or aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, Na2SO4 and NaOH, with solute concentrations corresponding to water activities aw = 0.9–1.0, were investigated in emulsified droplets by means of differential scanning calorimetry (DSC) and analyzed in terms of the onset temperature of the heterogeneous freezing signal Thet and the heterogeneously frozen water volume fraction Fhet. Quartz particles, which originate from milling coarse samples, show a strong heterogeneous freezing peak in pure water with Thet = 247–251 K. This IN activity disappears almost completely after aging for 7 months in pure water in a glass vial. During this time quartz slowly grew by incorporating silicic acid leached from the glass vial. Conversely, the synthesized amorphous silica samples show no discernable heterogeneous freezing signal unless they were milled. This implies that defects provide IN activity to silica surfaces, whereas the IN activity of a natural quartz surface is negligible, when it grew under near-equilibrium conditions. For suspensions containing milled quartz and the solutes (NH4)2SO4, NH4HSO4 or Na2SO4, Thet approximately follows Thet(Δawhet) (aw), the heterogeneous freezing onset temperatures that obey Δawhet-criterion, i.e. Thet(Δawhet) (aw) = Tmelt (aw + Δawhet) with Δawhet being a constant offset with respect to the ice melting point curve, similar to homogeneous IN. This water-activity-based description is expected to hold when the mineral surface is not altered by the presence of the solutes. On the other hand, we observe a slight enhancement in Fhet in the presence of these solutes, implying that the compliance with the Δawhet-criterion does not necessarily imply constant Fhet. In contrast to the sulfates, dilute solutions of NH3 or NaOH (molality ≥ 5 × 10−4 mol kg−1) reveal Thet by 3–8 K lower than Thet(Δawhet) (aw), indicating a significant impact on the mineral surface. The lowering of Thet of quartz suspended in dilute NH3 solutions is opposite to the distinct increase in Thet that we found in emulsion freezing experiments with aluminosilicates, namely feldspars, kaolinite, gibbsite and micas. We ascribe this decrease of IN activity to the increased dissolution of quartz under alkaline conditions. The defects that constitute the active sites appear to be more susceptible to dissolution and therefore disappear first on a dissolving surface.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 3 – Aluminosilicates

2018 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Ion Exchange ◽  
Aqueous Solutions ◽  
Water Activity ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Dilute Solutions ◽  
Scanning Calorimetry ◽  
Immersion Freezing ◽  
Alkali Salts

Abstract. Aluminosilicates (such as feldspars, clay minerals and micas) and quartz (a crystalline form of silica), constitute the majority of airborne mineral dust. Despite similarities in structures and surfaces they differ greatly in terms of their ice nucleation (IN) efficiency. Here, we show that determining factors for their IN activity include surface ion exchange, NH3 or NH4+ adsorption, as well as surface degradation due to the slow dissolution of the minerals. We performed immersion freezing experiments with the (Na-Ca)-feldspar andesine, the K-feldspar sanidine, the clay mineral kaolinite, the micas muscovite and biotite, and gibbsite (Al(OH)3, a mineral form of aluminum hydroxide) and compare their IN efficiencies with those of the previously characterized K-feldspar microcline and quartz. Samples were suspended in pure water as well as in aqueous solutions of NH3, (NH4)2SO4, NH4Cl and Na2SO4, with solute concentrations corresponding to water activities aw = 0.88–1.0. Using differential scanning calorimetry (DSC) on emulsified micron-sized droplets, we derived onset temperatures of heterogeneous (Thet) and homogeneous (Thom) freezing as well as heterogeneously frozen water volume fractions (Fhet). Suspensions in pure water of andesine, sanidine and kaolinite yield Thet = 242.8 K, 241.2 K and 240.3 K, respectively, while no discernable heterogeneous freezing signal is present in case of the micas or gibbsite (i.e. Thet ≈ Thom ≈ 237.0 K). The presence of NH3 and/or NH4+-salts as solutes has distinct effects on the IN efficiency of most of the investigated minerals. When feldspars and kaolinite are suspended in very dilute solutions of NH3 or NH4+-salts ( ~ 0.99), Thet shifts to higher temperatures (by 2.6–7.0 K compared to the pure water suspension). Even micas and gibbsite develop weak heterogeneous freezing activities in ammonia solutions. Conversely, suspensions containing Na2SO4 cause Thet of feldspars to clearly fall below the water-activity-based immersion freezing description (Δaw = const) even in very dilute Na2SO4 solutions, while Thet of kaolinite follows the Δaw = const curve. The water activity determines how the freezing temperature is affected by solute concentration alone, i.e. if the surface properties of the ice nucleating particles are not affected by the solute. Therefore, the complex behavior of the IN activities can only be explained in terms of solute-surface-specific processes. We suggest that the immediate exchange of the native cations (K+/Na+/Ca2+) with protons, when feldspars are immersed in water, is a prerequisite for their high IN efficiency. On the other hand, excess cations from dissolved alkali salts prevent surface protonation, thus explaining the decreased IN activity in such solutions. In kaolinite, the lack of exchangeable cations in the crystal lattice explains why the IN activity is insensitive to the presence of alkali salts (Δaw = const). We hypothesize that adsorption of NH3 and NH4+ on the feldspar surface rather than ion exchange is the main reason for the anomalous increased Thet in dilute solutions of NH3 or NH4+-salts. This is supported by the response of kaolinite to NH3 or NH4+, despite lacking exchangeable ions. Finally, on longer timescales (hours to days) the dissolution of the feldspars in water or solutions becomes an important process leading to depletion of Al and formation of an amorphous layer enriched in Si within less than an hour. This hampers the IN activity of andesine the most, followed by sanidine, then eventually microcline, the least soluble feldspar.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 3: Aluminosilicates

2019 ◽  
Vol 19 (9) ◽  
pp. 6059-6084 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Ion Exchange ◽  
Aqueous Solutions ◽  
Water Activity ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Dilute Solutions ◽  
Scanning Calorimetry ◽  
Immersion Freezing ◽  
Alkali Salts

Abstract. Aluminosilicates and quartz constitute the majority of airborne mineral dust. Despite similarities in structures and surfaces they differ greatly in terms of their ice nucleation (IN) efficiency. Here, we show that determining factors for their IN activity include surface ion exchange, NH3 or NH4+ adsorption, and surface degradation due to the slow dissolution of the minerals. We performed immersion freezing experiments with the (Na-Ca)-feldspar andesine, the K-feldspar sanidine, the clay mineral kaolinite, the micas muscovite and biotite, and gibbsite and compare their IN efficiencies with those of the previously characterized K-feldspar microcline and quartz. Samples were suspended in pure water as well as in aqueous solutions of NH3, (NH4)2SO4, NH4Cl and Na2SO4, with solute concentrations corresponding to water activities aw equal to 0.88–1.0. Using differential scanning calorimetry (DSC) on emulsified micron-sized droplets, we derived onset temperatures of heterogeneous (Thet) and homogeneous (Thom) freezing as well as heterogeneously frozen water volume fractions (Fhet). Suspensions in pure water of andesine, sanidine and kaolinite yield Thet equal to 242.8, 241.2 and 240.3 K, respectively, while no discernable heterogeneous freezing signal is present in the case of the micas or gibbsite (i.e., Thet≈Thom≈237.0 K). The presence of NH3 and/or NH4+ salts as solutes has distinct effects on the IN efficiency of most of the investigated minerals. When feldspars and kaolinite are suspended in very dilute solutions of NH3 or NH4+ salts, Thet shifts to higher temperatures (by 2.6–7.0 K compared to the pure water suspension). Even micas and gibbsite develop weak heterogeneous freezing activities in ammonia solutions. Conversely, suspensions containing Na2SO4 cause the Thet of feldspars to clearly fall below the water-activity-based immersion freezing description (Δaw= const.) even in very dilute Na2SO4 solutions, while Thet of kaolinite follows the Δaw= constant curve. The water activity determines how the freezing temperature is affected by solute concentration alone, i.e., if the surface properties of the ice nucleating particles are not affected by the solute. Therefore, the complex behavior of the IN activities can only be explained in terms of solute-surface-specific processes. We suggest that the immediate exchange of the native cations (K+, Na+, Ca2+) with protons, when feldspars are immersed in water, is a prerequisite for their high IN efficiency. On the other hand, excess cations from dissolved alkali salts prevent surface protonation, thus explaining the decreased IN activity in such solutions. In kaolinite, the lack of exchangeable cations in the crystal lattice explains why the IN activity is insensitive to the presence of alkali salts (Δaw= const.). We hypothesize that adsorption of NH3 and NH4+ on the feldspar surface rather than ion exchange is the main reason for the anomalous increased Thet in dilute solutions of NH3 or NH4+ salts. This is supported by the response of kaolinite to NH3 or NH4+, despite lacking exchangeable ions. Finally, the dissolution of feldspars in water or solutions leads to depletion of Al and formation of an amorphous layer enriched in Si. This hampers the IN activity of andesine the most, followed by sanidine, then eventually microcline, the least soluble feldspar.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline

2018 ◽  
Vol 18 (10) ◽  
pp. 7057-7079 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Beiping Luo ◽  
Thomas Peter
Keyword(s):  
Aqueous Solutions ◽  
Water Activity ◽  
Volume Fraction ◽  
Pure Water ◽  
Freezing Temperature ◽  
Solute Concentration ◽  
Ice Nucleation ◽  
Specific Chemical ◽  
Airborne Dust ◽  
Immersion Freezing

Abstract. Potassium-containing feldspars (K-feldspars) have been considered as key mineral dusts for ice nucleation (IN) in mixed-phase clouds. To investigate the effect of solutes on their IN efficiency, we performed immersion freezing experiments with the K-feldspar microcline, which is highly IN active. Freezing of emulsified droplets with microcline suspended in aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, NH4NO3, NH4Cl, Na2SO4, H2SO4, K2SO4 and KCl, with solute concentrations corresponding to water activities aw = 0.9–1.0, were investigated by means of a differential scanning calorimeter (DSC). The measured heterogeneous IN onset temperatures, Thet(aw), deviate strongly from ThetΔawhet(aw), the values calculated from the water-activity-based approach (where ThetΔawhet(aw)=Tmelt(aw+Δawhet) with a constant offset Δawhet with respect to the ice melting point curve). Surprisingly, for very dilute solutions of NH3 and NH4+ salts (molalities ≲1 mol kg−1 corresponding to aw ≳ 0.96), we find IN temperatures raised by up to 4.5 K above the onset freezing temperature of microcline in pure water (Thet(aw=1)) and 5.5 K above ThetΔawhet(aw), revealing NH3 and NH4+ to significantly enhance the IN of the microcline surface. Conversely, more concentrated NH3 and NH4+ solutions show a depression of the onset temperature below ThetΔawhet(aw) by as much as 13.5 K caused by a decline in IN ability accompanied with a reduction in the volume fraction of water frozen heterogeneously. All salt solutions not containing NH4+ as cation exhibit nucleation temperatures Thet(aw)<ThetΔawhet(aw) even at very small solute concentrations. In all these cases, the heterogeneous freezing peak displays a decrease as solute concentration increases. This deviation from Δawhet = const. indicates specific chemical interactions between particular solutes and the microcline surface not captured by the water-activity-based approach. One such interaction is the exchange of K+ available on the microcline surface with externally added cations (e.g., NH4+). However, the presence of a similar increase in IN efficiency in dilute ammonia solutions indicates that the cation exchange cannot explain the increase in IN temperatures. Instead, we hypothesize that NH3 molecules hydrogen bonded on the microcline surface form an ice-like overlayer, which provides hydrogen bonding favorable for ice to nucleate on, thus enhancing both the freezing temperatures and the heterogeneously frozen fraction in dilute NH3 and NH4+ solutions. Moreover, we show that aging of microcline in concentrated solutions over several days does not impair IN efficiency permanently in case of near-neutral solutions since most of it recovers when aged particles are resuspended in pure water. In contrast, exposure to severe acidity (pH ≲1.2) or alkalinity (pH ≳11.7) damages the microcline surface, hampering or even destroying the IN efficiency irreversibly. Implications for IN in airborne dust containing microcline might be multifold, ranging from a reduction of immersion freezing when exposed to dry, cold and acidic conditions to a 5 K enhancement during condensation freezing when microcline particles experience high humidity (aw≳0.96) at warm (252–257 K) and NH3/NH4+-rich conditions.

scholarly journals Enhanced ice nucleation efficiency of microcline immersed in dilute NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup>-containing solutions

2018 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Beiping Luo ◽  
Thomas Peter
Keyword(s):  
Volume Fraction ◽  
Pure Water ◽  
Freezing Temperature ◽  
Ice Nucleation ◽  
Ice Melting ◽  
Salt Solutions ◽  
Point Curve ◽  
Mineral Dusts ◽  
Immersion Freezing ◽  
Mixed Phase Clouds

Abstract. Potassium containing feldspars (K-feldspars) have been considered key mineral dusts for ice nucleation (IN) in mixed-phase clouds. To investigate the effect of solutes on their IN efficiency, we performed immersion freezing experiments with the K-feldspar microcline, which is highly IN active. Freezing of emulsified droplets with microcline suspended in aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, NH4NO3, NH4Cl, Na2SO4, H2SO4, K2SO4 and KCl, with solute concentrations corresponding to water activities aw = 0.9–1.0, were investigated by means of a differential scanning calorimeter (DSC). The measured heterogeneous ice nucleation onset temperatures, Thet (aw) deviate strongly from Thet∆awhet (aw), the values calculated from the water-activity-based approach (where Thet∆awhet (aw) = Tmelt (aw + ∆awhet) with a constant offset ∆awhet with respect to the ice melting point curve). Surprisingly, for very dilute solutions of NH3 and NH4+-salts (molalities  ~ 0.96), we find IN temperatures raised by up to 4.5 K above the onset freezing temperature of microcline in pure water (Thet (aw = 1)) and 5.5 K above Thet∆awhet (aw), revealing NH3 and NH4+ to significantly enhance the IN of the microcline surface. Conversely, more concentrated NH3 and NH4+ solutions show a depression of the onset temperature below Thet∆awhet (aw) by as much as 13.5 K caused by a decline in IN ability accompanied with a reduction in the volume fraction of water frozen heterogeneously. All salt solutions not containing NH4+ as cation exhibit nucleation temperatures Thet (aw)  ~ 0.96) at warm (252–257 K) and NH3/NH4+-rich conditions.

Der Verteilungsraum von physikalisch gelöstem Sauerstoff in wäßrigen Lösungen organischer Substanzen / The Distribution Space of Physically Dissolved Oxygen in Aqueous Solutions of Organic Substances

1976 ◽  
Vol 31 (7-8) ◽  
pp. 339-352 ◽  
Author(s):  
Rolf Zander
Keyword(s):  
Aqueous Solutions ◽  
Pure Water ◽  
Free Water ◽  
Water Volume ◽  
Protein Solutions ◽  
Oxygen Solubility ◽  
Organic Substances ◽  
Distribution Space ◽  
Specific Partial Volume ◽  
Heterogenous System

Abstract In order to evaluate the distribution of molecular oxygen in biological systems, the oxygen solubility (ml/ml atm) at 37 °C in aqueous solutions of thirty organic substances with different concentrations was measured by the classical Van Slyke principle. The oxygen solubility always (with the exception of hemoglobin) decreases exponentially with increasing concentration of the respective substance. In all cases this behavior is described highly significant by a simple empiric exponential function, when the substance concentration as well as the oxygen solubility of pure water is given. The influence of one substance on oxygen solubility contributes additively to the over-all solubility value of a solution of several dissolved substances. Changes in oxygen solubility and, therefore, oxygen distribution in aqueous solutions may be related to three main phenomena: 1. restriction of the free water volume by the specific partial volume of a dissolved substance (e. g. urea solutions), 2. existence of non-solvent water for oxygen (especially in solutions of amino acids), 3. adsorption of oxygen at the interphase in a heterogenous system (e. g. protein solutions).

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