Supersaturation Ratio Research Articles

Role of Orthophosphate As a Corrosion Inhibitor in Chloraminated Solutions Containing Tetravalent Lead Corrosion Product PbO2

Addition of orthophosphate has been commonly employed to suppress lead levels in drinking water. Its detailed mechanism and time required for it to become effective, however, have not been fully elucidated. In this study, we investigated the mechanistic role of orthophosphate as a corrosion inhibitor in controlling lead release from tetravalent lead corrosion product PbO(2) in chloraminated solutions, a system representing distribution networks experiencing disinfectant changeover from free chlorine to monochloramine. In all experiments with orthophosphate addition of at least 1 mg/L as P, peaking of soluble Pb(II) concentration within the first 24 h was observed before lead concentrations decreased and stabilized at levels lower than 15 μg/L. The variation of soluble Pb(II) concentration could be attributed to the dynamics between the rate of PbO(2) reductive dissolution, primarily induced by monochloramine decomposition, and that of chloropyromorphite (Pb(5)(PO(4))(3)Cl) precipitation, which did not occur until a critical supersaturation ratio of about 2.36 was reached in the solution. Our findings provide insights to how orthophosphate reduces lead levels under drinking water conditions and highlight the potential risk of short-term elevated lead concentrations. Intensive monitoring following the disinfectant changeover may be required to determine the overall lead exposure when using orthophosphate as a corrosion inhibitor.

Hydrogen supersaturation in thermophilic mixed culture fermentation

Hydrogen concentration is important for the metabolic distribution in mixed culture fermentation (MCF) but hydrogen supersaturation is often ignored. In this study, hydrogen supersaturation in thermophilic MCF was investigated online by a membrane inlet mass spectrometry. The results showed that with the increase of glucose loading rate (from 13.5 to 137.5 mmol/L/d) and the decrease of Reynolds number (from 12,900 to 3500), the hydrogen partial pressure (PH2) remained almost unchanged, but the hydrogen concentration in liquid (H2aq) increased from 0.82 to 1.27 and from 0.68 to 1.21 mmol/L, respectively. It demonstrated that hydrogen supersaturation occurred and the supersaturation ratio was between 1.7 and 3.0. Meanwhile, higher H2aq resulted in lower hydrogen yield, lower glucose degradation rate and higher mole ratio of ethanol/(acetate + butyrate). Thus, H2aq is more appropriate than PH2 when discussing the H2 role in MCF. Furthermore, the calculated KLa clearly illustrated that the required KLa values for maintaining low H2aq were order of magnitudes higher than the experimental ones. Therefore, hydrogen supersaturation is inevitable in practice and should be considered in MCF.

Incipient calcium carbonate scaling of desalination membranes in narrow channels with spacers—experimental insights

Significant uncertainty exists regarding incipient membrane scaling (a criterion for determining water recovery and antiscalant use) with negative impact on optimization of RO plant design and operation. Experimental data are reported on the initial phase of RO-membrane scaling by weakly supersaturated brackish water (calcite supersaturation ratio S∼1.9 to 3.1) in a narrow spacer-filled channel, simulating local (constant flux) conditions in spiral-wound membrane (SWM) modules. Scanning electron microscopy image analyses of numerous membrane samples, combined with complete physico-chemical characterization of feedwater and retentate, provide new insights into early-phase membrane scaling. The unavoidable presence of small particles in feedwater (despite the use of tight cartridge filter) apparently promotes heterogeneous nucleation. Additionally, there is a clear evidence that, under these conditions, induction period for membrane scaling is practically non-existent. The initial deposit flux [mgCaCO3/(m2min)] on the membrane, obtained through measured crystal size distributions, exhibits strong dependence on supersaturation ratio; moreover, measured deposit fluxes are substantial and (if not mitigated) would be eventually detrimental to SWM performance. These data were obtained, while none of the frequently used parameters (bulk fluid turbidity, pH, Ca concentration, permeate flux) indicated particle/scale deposition on membranes. Implications of the new results, on practical and theoretical aspects of scaling, are discussed.

Nucleation kinetics of the formation of low dimensional calcium sulfate dihydrate crystals in isopropyl alcohol medium

AbstractCalcium sulfate dihydrate, constituted as uniform crystals of low dimensions, is a potential biomaterial for clinical applications like bone graft substitution and drug delivery. In this work, isopropyl alcohol has been used as a solvent to obtain low dimensional calcium sulfate dihydrate crystals from calcium nitrate ‐ sulfuric acid system. Reactants in 0.5 molar concentration at ambient conditions generated uniform rod‐shaped crystals of length 3–5 µm. Analysis using X‐ray Diffractometry and Fourier Transform Infrared Spectrometry showed the material to be well crystallized, phase‐pure calcium sulfate dihydrate.The nucleation kinetics has been studied by observing the induction time of phase formation in solutions of millimolar concentrations through turbidimetry at 300 K. The data have been analysed using classical nucleation theory to deduce parameters like interfacial tension (or surface free energy), nucleation rate and critical radius. The surface free energy obtained (5.6 mJ/m2) is comparatively lower than that reported for aqueous precipitation, which could be attributed to the presence of isopropyl alcohol. On escalating the supersaturation ratio, the nucleation rate drastically increased and the critical radius decreased exponentially. Particles formed at supersaturation 1.39 showed a monomodal distribution centered at 8.2 nm in Dynamic Light Scattering analysis. Comparable particle sizes were obtained in Transmission Electron Microscopy.

Biomimetic layer-by-layer templates for calcium phosphate biomineralization

Carboxylated, sulfated and/or phosphorylated surfaces are admitted as potential optimal templates for biomimetic deposition of calcium phosphate (CaP) coatings in view of improving implants’ osseointegration. Layer-by-layer films were built up consisting of anionic chondroitin sulfate (ChS), a biological carboxylated and sulfated polysaccharide and cationic poly(l-lysine) (PLL). The films were used as soft matrices to immobilize a model phosphoprotein, phosvitin (PhV). The respective roles of ChS, PLL and PhV terminal layers on the heterogeneous nucleation kinetics and the structure of CaP deposits obtained from supersaturated solutions were inspected. Critical supersaturation ratios and induction times preceding heterogeneous nucleation were precisely determined and interpreted within the framework of classical nucleation theory in order to derive the effective interfacial energies of CaP crystals. It was found that the potency of terminal layers toward CaP nucleation increased in the order: PLL<ChS<PhV. Beyond a supersaturation threshold, PhV-terminated films exerted unique influence on the nucleation kinetics, maintaining the induction time at a constant value owing to conformational change of the PhV molecules upon calcium bridging. Promisingly, all films templated the deposition of thin (a few micrometer thick) uniform coatings of octacalcium phosphate and possibly hydroxyapatite, the two most relevant biological phases of CaP.

Nucleation Kinetics of the γ‐Polymorph of DL‐Methionine

AbstractThe heterogeneous nucleation kinetics of γ‐DL‐methionine (γ‐DL‐met) in aqueous solution was measured using direct determination of the rate of nucleation based on measurements of particle (crystal) counts appearing in a microdroplet as a function of nucleation time. The nucleation rates increase with increasing temperature when the supersaturation ratio is used as a measure of the driving force, but the dependence is less clear when the nucleation rates are plotted against the absolute supersaturation. The nucleation rates were found to exponentially increase with respect to the supersaturation ratio of DL‐met. The measured nucleation kinetics follow trends expected from the classical nucleation theory (CNT), allowing approximate interfacial energies to be estimated by fitting the measured data to the CNT. The predicted interfacial energies and nucleation rates are consistent with results of similar species given in the literature.

Influence of Process Parameters on the Characteristics of Struvite Pellets

With an ever-increasing demand for phosphate-based fertilizer, new sustainable sources of phosphorus are warranted. Recent technologies have successfully demonstrated the possibility of recovering phosphorus from wastewater-treatment plants as struvite, which is also a ready-made, slow-release fertilizer. However, process parameters that influence the operation of crystallizers and production of good-quality struvite pellets have yet to be fully understood. This paper discusses the influence of process parameters on the characteristics of struvite pellets. Among the various process parameters, upflow velocity and flow patterns in the crystallizer were found to influence the size and shape of the pellets. In the range (1.5–7.1) tested, supersaturation ratio did not appear to influence the crushing strength of the pellets formed. Midsized pellets, in the 2.0–2.5-mm range, exhibited the highest crushing strengths. Higher magnesium concentration in the crystallizer was able to increase the crushing strength of struvite pellets by as much as 15–27%.

Cubic SiC formation on the C-face of 6H–SiC (0 0 0 1) substrates

Nucleation and subsequent growth of cubic SiC (111) on Si- and C-faces of nominally on-axis 6H–SiC substrates was investigated. More uniform nuclei and twin boundary distribution was observed when 3C–SiC was grown on the C-face. This was attributed to a lower critical supersaturation ratio. A new type of defects which appear as pits in the C-face 3C–SiC layers related to homoepitaxial 6H–SiC spiral growth was found and described. The evaluation of the growth driving force for both polar faces showed that the homoepitaxial 6H–SiC spirals were not overgrown on the C-face due to low maximum supersaturation ratio. The XRD ω-rocking characterization shows a better structural quality of the 3C–SiC grown on the Si-face, however on the C-face the uniformity over the whole sample was higher. Unintentional doping by N (∼1016cm−3) was slightly higher on the C-face while Al doping was higher (∼1014cm−3) on the Si-face of the grown material, similarly to the doping of hexagonal SiC polytypes.

Impact of Curcumin Supersaturation in Antibacterial Photodynamic Therapy—Effect of Cyclodextrin Type and Amount: Studies on Curcumin and Curcuminoides XLV

Curcumin has been investigated as a potential photosensitizer (PS) in antimicrobial photodynamic therapy (aPDT). The phototoxic effect of curcumin is dependent on proper formulations of the compound because of the lipophilic nature of the molecule and the extremely low water solubility at physiological conditions. In the present study, the combination of curcumin with either a methylated β-cyclodextrin (CD) or polyethylene glycol-based β-CD or γ-CD polymers was investigated in aPDT using Escherichia coli (E. coli) and Enterococcus faecalis as model bacteria. Solutions with various supersaturation ratios of curcumin were prepared with the selected CD or CD polymers. The concept of supersaturation was then investigated as a mean to enhance the phototoxic effect of curcumin, especially toward the gram-negative bacteria E. coli. A high supersaturation ratio corresponded with high phototoxicity of E. coli. Depending on the curcumin preparation, the bacterial survival ranged from 0.01% to no significant effect after irradiation with blue light (29 J/cm(2) ). Temporal stabilization of the supersaturated state is necessary in order to retain high and predictable photoreactivity of the PS. Further studies will be needed in order to formulate curcumin preparations with acceptable hydrolytic and photolytic stability and a temporal stabilization of a supersaturated state.

Crystallization of Microparticulate Pure Polymorphs of Active Pharmaceutical Ingredients Using CO2-Expanded Solvents

The feasibility of the Depressurization of an Expanded Liquid Organic Solution (DELOS) method to process different active pharmaceutical ingredients (APIs) as finely divided powders with narrow particle size distribution, high crystallinity degree, high polymorphic purity, and free from residual solvent has been demonstrated. Cholesterol, acetylsalicylic acid (aspirin), naproxen, acetaminophen, and ibuprofen were chosen as model drugs. It has been demonstrated that the supersaturation ratio attained during crystallization from CO2-expanded solvents can be modulated through appropriate variations of process parameters — CO2 content and concentration of the initial solution. In view of the potential application that compressed fluids-based technologies have in the pharmaceutical industry, a preliminary scalability study of the process in compliance with the constraints imposed by the Good Manufacturing Practices (GMP) specifications is presented herein.

Influence of Temperature on Strain Induced Precipitation Kinetics in Microalloyed Steels

Starting from the expression of Dutta and Sellars for the beginning of strain induced precipitation in microalloyed steels, the influence of temperature on t0.05 parameter has been studied. Although the equation given by these authors reproduces well the typical “C” shape of the curve of precipitation start time Ps, the expression is not reliable for all cases. The precipitation-time-temperature (PTT) diagrams have been plotted thanks to a new experimental study carried out by means of hot torsion tests on approximately twenty microalloyed steels having different contents of Nb, V and Ti. Mathematical analysis of results recommends the modification of some parameters such as supersaturation ratio (Ks) and constant B, which is no longer a constant but a function of Ks when the latter is calculated at the nose temperature (TN) of curve Ps. The value of parameter B is deduced from the minimum point or nose of the Ps curve, where ∂t0.05/∂T is equal to zero, and it can be demonstrated that B cannot be a constant. The new expressions for these parameters derive from the latest studies developed by the authors and this work supposes an attempt to improve the model. The expressions are now more consistent and predict with remarkable accuracy the PTT curves.

A Multiphysics Model of In Vitro Transcription Coupling Enzymatic Reaction and Precipitation Formation

Multiphysics modeling, which integrates the models studied in different disciplines so far, is an indispensable approach toward a comprehensive understanding of biological systems composed of diverse phenomena. However, the variety of the models is narrower than the actual diverse phenomena because of the difficulty in coupling independent models separately studied in different disciplines for the actual coupled phenomena. In this study, we develop a mathematical model coupling an enzymatic reaction and mineralization formation. As a test case, we selected an in vitro transcription system where a transcription reaction occurs along with the precipitation formation of magnesium pyrophosphate (Mg2PPi). To begin, we experimentally elucidated how the transcription reaction and the precipitation formation are coupled. In the analysis, we applied a Michaelis-Menten-type equation to the transcription reaction and a semiempirical equation describing the correlation between the induction period and the supersaturation ratio to the precipitation formation, respectively. Based on the experimental results, we then integrated these two models. These models were connected by supersaturation that increases as the transcription reaction proceeds and becomes the driving force of the precipitation. We believe that our modeling approach could significantly contribute to the development of newer multiphysics models in systems biology such as bone metabolic networks.

Biomimetic type morphologies of calcium carbonate grown in absence of additives

This report demonstrates how typical particle morphologies documented in biomimetic mineralization studies of calcium carbonate will precipitate also from solutions without adding modulating additives, at supersaturation levels below the solubility level of amorphous calcium carbonate (ACC). In the literature, hexagonal plates and flower structures of vaterite, as well as dumbbell structures of aragonite are explained by non-classical aggregation mechanisms from precursor crystals, assisted and stabilized by biomolecules, ions and templates, or by transformation from ACC. By performing experiments at both depleting and constant low supersaturation ratios for a range of temperatures, we show that the vaterite morphology changes from hexagonal monocrystalline plates expressing the basal (001) faces, to dendritic flower shapes and finally to spherulites, as a function of increasing supersaturation. Aragonite goes through a similar transition from monocrystalline elongated structures to polycrystalline dumbbells and spherical structures. We conclude that the key to understand the shape development is quantification of the activity based supersaturation and the realization that calcium carbonate forms along classical crystallization pathways. The higher number of crystals required for aggregation based growth is not favoured at these low supersaturation values. Dislocation and surface nucleation driven crystal growth is responsible for faceted morphologies at moderate supersaturation, whereas dendritic and spherulitic growth patterns appear due to interface instability at higher driving forces.

Dynamic simulation of periodic attenuation in seeded precipitation of sodium aluminate solution

Periodic attenuation in seeded precipitation of sodium aluminate solution has been known to adversely influence the production of alumina in the Bayer process. In this paper, a mathematical model is established to simulate the dynamics of the periodic attenuation. A Population Balance Method is used in the model to define the particle size distribution (PSD) of aluminum hydroxide precipitates. Factors considered in the model include the particle characteristics, growth, and agglomeration of seed crystals, and the nucleation in sodium aluminate solution. This model is calculated by using the discretized population balance method and the simulation results are validated with experimental data. The dynamic evolution of the PSD during seeded precipitation is believed to involve the following key process. The ratio of the liquor supersaturation to the specific surface area of finer seeds (L<45μm) first reaches its maximum. It is then followed by a rapid grain refinement. Understanding this process is very useful in determining the optimal moment when the operational parameters should be adjusted in order to eliminate the periodic attenuation in industrial production.

Salt transport and crystallization in non-isothermal, partially saturated porous materials considering ions interaction model

Crystallizing salt changes the inner pore structure of materials. MIP tests of cement mortar and brick saturated with NaCl, CaCl 2, Na 2SO 4 solutions were performed. The changes of porosity, pore size distribution and pore shape (ink-bottle type pores) were investigated by performing two intrusion–extrusion cycles. The crystallization pressure bursts the mezopores. During salt crystallization the additional heat is released, which must be considered in energy conservation equation of multiphase domain. The model of coupled heat, moisture and salt transport considering the salt crystallization is presented. The key factor while modeling the salt crystallization is the kinetics of salt phase change, which is approximated in the presented research by means of Freundlich non-equilibrium isotherms. In order to calculate the solution supersaturation ratio the short and long range ions interaction was taken into account applying the Pitzer model. The mathematical model was solved using FEM and FDM and some practical examples were calculated and discussed. It was proved that the higher rate order appears in the kinetic law the higher crystallization pressure might be generated. The approximation procedures were tested numerically.

The inhibitory effects of carboxymethyl inulin on the seeded growth of calcium carbonate

Kinetics of precipitation of calcite (CaCO 3) from aqueous solution in the presence of carboxymethyl inulin (CMI) was investigated under strictly controlled temperature, pH, supersaturation ratio ( S = 4.8) and ionic strength ( I = 0.1 M). The highly reproducible constant composition technique was used to study the influence of biopolymers of crystal growth of CaCO 3, on CaCO 3 seed crystals at pH 8.5 and 25 °C. The crystal growth of calcium carbonate (CaCO 3) was inhibited in the presence of CMI at low concentration (2.5 × 10 −9 to 25 × 10 −9 mol/L). The larger number of negatively charged functional groups exhibited a 95% growth rate inhibition at a concentration of 15 × 10 −9 mol/L. The higher inhibition efficiency is related to the maximum surface charge density due to adsorbed polymer.

Initial Stages of Barium Sulfate Formation at Surfaces in the Presence of Inhibitors

The formation of barium sulfate (BaSO4) in the oilfield is known to occur as a precipitation process from the aqueous phase within oil production facilities. This barite deposition causes many problems related to flow assurance. In this paper, the initial stages of barium sulfate deposition on a metallic surface are investigated. The mass rate of deposition of barite on the surface was measured using a quartz crystal microbalance (QCM). The morphology of the deposited BaSO4 was then observed directly with an atomic force microscope (AFM) and the main crystal faces of barite were identified. Both the formation kinetics and the crystallography of the deposited barium sulfate were studied at three supersaturation ratios and in the presence and absence of 2 chemical scale inhibitors, namely, polyphosphino carboxylic acid (PPCA) and diethylene triamine penta acetic acid (DETPMP). In addition, the precipitation of the barite in the bulk phase was also monitored (by turbidity measurements) thus giving a more complete description of the overall bulk/surface barium sulfate kinetics. PPCA proved to be an effective barite inhibitor both at the surface and in the bulk phase in these measurements. DETPMP did not perform so well but there are several reasons why this may be so in such early time experiments and these are discussed in the paper. Thus, such experiments must be interpreted with some caution when we are relating the results to the oilfield scale system. In the industrial application addressed here, the brine system is very specific in that it is at relatively high ionic strength, the divalent cations (Ca2+/Mg2+/Sr2+) play an important role and the supersatuaration ratios of barite are very high. However, barite deposition is currently a very significant problem in the oil and gas industry, and this paper presents findings that will contribute to better ways of managing barite scale in the future.

Effect of struvite seed crystal on MAP crystallization

AbstractBACKGROUND: There has been considerable controversy over the effect of seed crystal additions on crystallization of magnesium ammonium phosphate hexahydrates (MAP). In this study, batch experiments were carried out to verify this effect using synthetic solutions.RESULTS: Addition of seed crystals could increase the rate of MAP crystallization and significantly shorten the reaction crystallization time, especially for solutions with a lower supersaturation ratio (Ω). Crystallization time of MAP with and without seed addition can be expressed by two different formulas, in which the crystallization with feed addition followed an exponential function, and the secondary formula fitted a two‐order power function. When 0.422 g L−1 of seed crystals was added the equilibration time for crystallization calculated by the formula was reduced by 75 min for low supersaturation ratio solution and 26 min for medium supersaturation ratio solution.CONCLUSION: To increase the MAP reaction rate and to shorten induction and equilibration times, seed crystal addition should be practiced Copyright © 2011 Society of Chemical Industry

Effect of electrodeposition conditions on the electrochemical capacitive behavior of synthesized manganese oxide electrodes

Galvanostatic electrodeposition techniques were applied for the preparation of novel electroactive manganese oxide electrodes. The effects of supersaturation ratio on the morphology and crystal structure of electrodeposited manganese oxide were studied. Manganese oxide electrodes were synthesized by anodic deposition from acetate-containing aqueous solutions on Au coated Si substrates through the control of nucleation and growth processes. By changing deposition parameters, a series of nanocrystalline manganese oxide electrodes with various morphologies (continuous coatings, rod-like structures, aggregated rods and thin sheets) and an antifluorite-type crystal structure was obtained. Detailed chemical and microstructural characterization of as-deposited electrodes was conducted using SEM, TEM and AAS. Manganese oxide thin sheets show instantaneous nucleation and single crystalline growth, rods have a mix of instantaneous/progressive nucleation and polycrystalline growth and continuous coatings form by progressive nucleation and polycrystalline growth. In addition, the electrochemical behavior was investigated by cyclic voltammetry. The experimental results show that manganese oxide electrodes, with rod-like and thin sheet morphology, exhibited enhanced electrochemical performance. The highest specific capacitance (∼230 F g −1) and capacitance retention rates (∼88%) were obtained for manganese oxide thin sheets after 250 cycles in 0.5 M Na 2SO 4 at 20 mV s −1.

Nanoparticle Growth Analysis by Molecular Dynamics: Spherical Seed

Three-dimensional condensation on a spherical nanoscale seed was simulated by classical molecular dynamics. In order to observe the effects of the dimension of seeds and thermodynamic conditions on the condensation characteristics, initial seed size and system supersaturation ratio were the factors that were examined. At supersaturation ratios above the critical value, two stages of nucleation were found to exist within the system, where the first stage is from the seed growth and the second from homogeneous nucleation. Therefore, the growth and homogeneous nucleation characteristics were each decomposed and analyzed separately. The Yasuoka-Matsumoto method was used to calculate the nucleation and growth rate. The homogeneous nucleation characteristics coincided with the classical nucleation theory. The condensation characteristics, however, showed a discrepancy with the modified classical nucleation theory for completely wetted heterogeneous nucleation, where no supersaturation ratio influence could be observed. The seed size was found to have a reciprocal effect on the growth rate, but showed to be insignificant on the homogeneous nucleation characteristics for this system. The critical nucleus size from kinetic analysis showed a greater difference compared to the first nucleation theorem, classical nucleation theory, or free energy analysis. All in all, the classical nucleation theory showed relatively good agreement compared to previous homogeneous nucleation studies by molecular dynamics, but a modification was found to be necessary when applying to heterogeneous growth of nanoparticles.