Crystal Supersaturation Research Articles

Effect of Heat Transfer Driving Force and Ice Seed Loading on the Production of Ice and Salt from a Dilute Brine Treated Using Eutectic Freeze Crystallization

Eutectic Freeze Crystallization (EFC) is a separation technology that separates solute from solvent by cooling the brine to a temperature below its eutectic point, such that ice and salt simultaneously crystallize out of the solution. Achieving consistent production of ice and salt at high production rates has been a challenge for EFC. This is due to heat transfer limitations, which are more severe when EFC is applied to dilute brines. This work investigated the effect of the heat transfer driving force, ΔTLMTD, and ice seed loading (SL) on the production of ice and salt from a dilute brine. A 1.45 L stirred crystallizer was used for the experiments at varying coolant temperatures to investigate the effect of ΔTLMTD, and at varying seed masses to investigate the effect of seed loading. It was found that, as the ΔTLMTD increased, the yield of ice and salt increased. This was attributed to the increase in the heat transfer rate as ΔTLMTD and heat transfer rate are directly related. The ice yield was divided between ice in suspension and ice formed on the wall (scale layer), with a majority of the total ice yield being scale ice. Increasing the seed loading (SL) increased the yield of ice in suspension and decreased the yield of scale ice. The seeds allowed for increased surface area for crystallization in the bulk. This allowed for most of the supersaturation to be consumed in the bulk, leaving little supersaturation for crystallization at the wall. This reduced the propensity for scale formation. The reduction in the scale layer increased the heat transfer rate between the bulk and the coolant, allowing for more ice to be formed in suspension.

An experimental study of salt expansion in sodium saline soils under transient conditions

Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.

Solubility of N‐Guanylurea Dinitramide in Binary Solvent Mixtures

AbstractThe solubility of N‐guanylurea dinitramide (GUDN, Fox‐12) in binary solvent mixtures was measured. Binary solvents such as dimethyl sulfoxide (DMSO)/water and N,N‐dimethylacetamide (DMA)/water were investigated. The temperature was in the range of 0 °C to 70 °C for DMA‐water and 20 °C to 70 °C for DMSO‐water. The temperature dependence on the solubility was higher in DMA‐water than in DMSO‐water at the same fraction of water. On the other hand, the modeling data was obtained by using the Apelblat equation. The average relative errors are less than 3 %. Supersaturation for crystallization of GUDN in solution can be easily generated by adding water in DMSO (or DMA).

Polycrystalline growth in precipitation of an aromatic amine derivative and l-glutamic acid

The effect of initial supersaturation and temperature on the particle morphology of l-glutamic acid and an aromatic amine derivative has been compared in batch experiments by pH-shift precipitation in water at temperatures of 5–80 °C. At higher initial supersaturation ratios both systems give rise to polycrystalline particles, which have been identified to grow by a spherulitic growth mechanism. On the other hand, single crystals can be obtained at low values for the initial supersaturation. The aqueous aromatic amine system yields plate-like crystals, whereas the β-polymorph of l-glutamic acid crystallizes as needle-like particles at low initial supersaturation. While the monocrystalline plate-like particles are precipitated directly from solution in case of the aromatic amine, monocrystalline needles of β- l-glutamic acid could only be crystallized by transforming the initially precipitated metastable α-polymorph. The onset of polycrystalline growth can be observed at intermediate initial supersaturation in crystallization of both the aromatic amine and β- l-glutamic acid. The aromatic amine derivative shows switching from monocrystalline plate-like crystals at a constant initial supersaturation value, whereas β- l-glutamic acid displays a transition from needles to spherulites, at a supersaturation level that becomes lower as the temperature increases. This switch in growth mechanism could not be found for the α-polymorph of l-glutamic acid. The spherulite morphology becomes more compact at higher initial supersaturation ratios.

Multistep Crystal Nucleation: A Kinetic Study Based on Colloidal Crystallization

Crystallization via an amorphous precursor, the so-called multistep crystallization (MSC), plays a key role in biomineralization and protein crystallization. MSC has attracted much attention in the past decade, but a quantitative understanding of it has so far not been available. The major challenge is that the kinetics governing the nucleation of crystals occurring in the metastable amorphous precursor remains unclear. In this study, the kinetics of MSC is addressed experimentally. Most importantly, a mathematical method is developed to calculate the local nucleation rate of the crystals in the amorphous precursor, which is not accessible to conventional methods. This local nucleation rate is critical to the understanding of MSC, but it has never been dealt with experimentally because of the difficulties of in situ observation. With the local crystal nucleation rates, the supersaturation for crystallization and the crystal-liquid interfacial free energy in the amorphous precursor are evaluated.

Driving Force for Nucleation of Multi-Component Gas Hydrate

Based on driving force for crystallization of one-component gas hydrate, in this report an expression for the supersaturation for crystallization of multicomponen t gas hydrate is derived. Expressions for the supersaturation are obtained in isothermal and isobaric regimes. The results obtained are applied to the crystallization of hydrates of mixtures of methane plus ethane and can apply to other mixtures.

Anthracene Crystallization Induced by Single-Shot Femtosecond Laser Irradiation: Experimental Evidence for the Important Role of Bubbles

A mechanism of femtosecond laser-induced crystallization was investigated using a supersaturated solution of anthracene. When a single-shot femtosecond laser pulse with a pulse energy above 3.1 μJ/pulse was shot into a sufficiently supersaturated solution, crystallization of anthracene was induced immediately after irradiation at the vicinity of the laser focal point. The threshold energy of the crystallization (3.1 μJ/pulse) was in agreement with that of laser-induced bubble formation, which was a sequential process after shockwave emission, cavitation bubble formation, and collapse. Sufficient supersaturation for crystallization decreased with an increase in the pulse energy. These results suggest that crystallization is triggered in the processes resulting in bubble formation. Furthermore, crystallization was enhanced at the surface of the bubble. The crystallization mechanism was completely different from that reported previously based on photochemical reactions or molecular alignment due to a strong optical field.

A springtime cloud over the Beaufort Sea polynya: Three‐dimensional simulation with explicit spectral microphysics and comparison with observations

This paper addresses the formation of a cloud system associated with an arctic polynya in Beaufort Sea during springtime. Data were obtained as a part of the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) Arctic Clouds Experiment from the Canadian Convair 580 aircraft during 25 April 1998. These data include in situ observations of cloud microphysics and meteorological variables and remote measurements from satellite and airborne lidar. A three‐dimensional cloud‐resolving model with explicit bin‐resolving cloud microphysics is used to simulate the atmospheric boundary layer and cloud evolution associated with the polynya. After initialization with the aircraft sounding profiles, a quasi‐steady polynya‐induced atmospheric boundary layer (ABL) and a cloud system form. Strong turbulence in the ABL occurs above the polynya, the internal thermal boundary layer (ITBL) develops and grows upward in the downwind direction, and the ABL downwind of the polynya is separated into two decoupled layers. The cloud forms in the middle of the polynya, and its upper boundary lifts downwind while the lower boundary lowers and reaches the surface beyond the polynya southern boundary as a light fog. Farther to the south, the fog evaporates and transforms into an elevated cloud plume that extends for several tens of kilometers downwind. This cloud morphology is in good agreement with the lidar observations, which showed a cloud layer extending for more than 100 km downwind, and with the numerous previous observations. The simulated microphysical properties of a mixed cloud are similar to those observed. A new ice nucleation scheme resulted in cloud plume gradual crystallization along the wind and eventual transformation into diamond dust. Detailed evaluation of the water budget, supersaturation, and crystal size spectra showed that the ice crystal supersaturation relaxation times are 10–60 min; thus deposition on the crystals is rather slow, and only 1–5% of the available vapor is deposited on the crystals. The large ice crystal supersaturation relaxation time explains the relatively slow growth and gravitational fallout of the ice crystals, as well as the extensive propagation downwind of the plume.

Driving force for crystallization of gas hydrates

A general expression is derived for the supersaturation for crystallization of one-component gas hydrates in aqueous solutions. The supersaturation is the driving force of the process, since it represents the difference between the chemical potentials of a hydrate building unit in the solution and in the hydrate crystal. Expressions for the supersaturation are obtained for solutions supersaturated in isothermal or isobaric regime. The results obtained are applied to the crystallization of hydrates of methane, ethane and other one-component gases.

Basic processes accompanying solid-phase reactions on the silicon surface

A model of the basic processes accompanying solid-phase reactions (SPR) on the Si surface has been developed based on general physical considerations. The model considers these processes in various structures, including M–Si, Si–SiO2, and Si–Si3N4. Analytical expressions have been derived to estimate values of the elastic stresses, steady-state crystal supersaturation by point defects, and SPR activation energy. Data related to the type of point defect generated during SPR have been obtained. A rule to predict the sequence of phase formation in systems with a polyphase constitution diagram is proposed. In particular it is shown that the steady-state crystal supersaturation by self-interstitials during thermal oxidation of Si ranges from 2.4 to 4.4 at 1200 °C. However, the supersaturation by vacancies during the metal silicide formation varies in range from 102 to 107 depending on the reaction type and temperature. The analytical results have been compared with experimental data on the enhanced diffusion of impurities, growth of oxidation stacking faults, and growth parameters of metal silicide layers, and have shown good agreement.

Determination of the supersaturation in crystallization from solution of strong electrolytes

An expression for the exact determination of the driving force (the supersaturation) in the crystallization from solutions of strong electrolytes is submitted. The way for establishing the error involved in the calculation of the supersaturation from the concentration/solubility ratio is shown.