Solubility Product Research Articles

Solubility of cinnarizine in natural deep eutectic solvent (camphor + menthol) and correlation with different solubility models

The objectives of the current investigation are (1) to determine the cinnarizine's equilibrium solubility values in four-different molar ratios of camphor and menthol-based natural deep eutectic solvents (NADES) (1:0.65, 1:0.97, 1:1.47 & 1:2.25) at 0.1 MPa atmospheric pressure and five-diverse temperature conditions [T = (298.15, 300.65, 303.15, 305.65 & 308.15) K], (2) to validate the experimentally obtained cinnarizine's solubility values with various empirical and local composition models and (3) to determine the thermodynamic properties of cinnarizine solubility in camphor and menthol-based NADES. In a preliminary pilot study, the solubility of cinnarizine was checked in different NADES-forming excipients such as camphor, capric acid, lauric acid, menthol and thymol at various molar ratios. At 1:0.97 molar ratio of camphor and menthol, the mole fraction solubility value of drug was augmented up to 4.6847 × 10−3 at 298.15 K in comparison to the other tested NADES-forming excipients. The highest cinnarizine's mole fraction solubility was obtained in 1:0.97 molar ratio of camphor and menthol NADES at 308.15 K with a value of 19.5207 × 10−3, while the lowest value (1.8 × 10−3) was obtained in 1:0.67 ratio of camphor and menthol NADES at 298.15 K. Solubility correlation results show that the modified Jouyban-Acree model was best-fitted as it was obtained with the lowest absolute average deviation percent and absolute relative deviation percent values. The findings of dissolution thermodynamic of cinnarizine in NADESs composed of camphor and menthol indicate that the cinnarizine dissolution in camphor and menthol-based NADESs is enthalpy-driven. Eutecticity could be of an effective strategy to overcome cinnarizine's obstacle during drug delivery system development.

A simple and rapid copper-assisted microprecipitation method for the on-site separation of inorganic arsenic species in water samples followed by hydride generation atomic fluorescence spectrometry determination

A simple and rapid microprecipitation procedure was developed using copper (Cu2+) as precipitating agent for the separation–preconcentration of inorganic arsenic species (As(III) and As(V)) in waters prior to their determination by hydride generation atomic fluorescence spectrometry (HG-AFS). This procedure is based on selective precipitation of anionic species of As(V) with Cu2+, leaving neutral As(III) in the filtrate. The complexation of As(V) with Cu(II) entails the precipitation as copper arsenate, Cu3(AsO4)2 due to its low solubility product. The copper arsenate precipitate was characterized by XRD and EDS measurements. Optimum conditions for efficient microprecipitation process are; pH: 5 to 6, Cu/As mass ratio: 100, equilibration time: 2–3 min and eluent volume: 2 mL of 0.03 mol L−1 HCl. A fast process time of 2 min is enough for the on-site separation of As(III) and As(V) with the detection limits (LOD) 0.012 and 0.034 μg L−1 respectively. The recoveries were found to be in the range of 98–102%. This simple and fast method was successfully utilized for the on-site separation of As(III) and As(V) in wide variety of water samples collected in and around Kiradalli Tanda village, Karnataka state, India, where severe arsenic-contamination exists in various water bodies.

Vapor-liquid-liquid equilibrium (VLLE), density, and viscosity of the ternary mixtures of normal hexane, water and bitumen at T=185–210°C and at P= 2.5 MPa

This paper presents a study on the vapor-liquid-liquid equilibrium (VLLE) of a ternary system consisting of normal-hexane (n-C6) as a solvent, water (H2O), and Mackay River bitumen. The study was conducted at temperatures ranging from 185 to 210 °C and a pressure of 2.5 MPa. The solvent/steam and solvent/bitumen ratios were varied to understand the effect of solvent (n-C6) on the phase behavior and the thermophysical properties of the associated phases. The co-injected solvent with steam is often reported as the concentration of solvent in the solvent/steam mixture. Two concentrations of n-C6 in n-C6/water mixture, including mole fractions of 0.01 and 0.05 (i.e., 6.85 and 27.70 vol.%), were considered to examine the effect of the co-injected solvent with steam. Also, two different mole fractions of n-C6 in the mixture of bitumen/n-C6 at 0.7 and 0.4 (37.45 and 14.61 vol.%), respectively, were considered to examine the effect of solvent solubility in bitumen. In addition to the VLLE study, the viscosity and density of the two distinct liquid phases, hydrocarbon-rich oleic and water-rich aqueous phases, were measured and reported. The results from the experiment infer that the concentration of n-C6 co-injected with steam does not significantly affect the equilibrium phase concentrations and thermophysical properties. However, the mixture showed liquid-liquid equilibria (LLE) instead of the vapor-liquid-liquid equilibria (VLLE) when the concentration of n-C6 in bitumen/solvent mixture was less than the equilibrium solubility of n-C6 in the hydrocarbon-rich phase at that operating condition. Furthermore, the results suggest that the presence of bitumen in equilibrium with n-C6 and H2O has no significant effect on the concentration of n-C6 in the vapor phase when compared with the n-C6/H2O binary mixture. Thermodynamic modelling of the VLLE data was performed using the cubic plus association equation of state (CPA EoS). The matching parameters were obtained by tuning the two-phase data, and those parameters were used in predicting the VLLE data. The model was also used to construct the phase regions of the solvent/bitumen/water system on the ternary diagram at different temperatures and pressures. Different phase regions were determined by phase stability analysis. The findings provide insight into steam/solvent condensation behavior with applications to the solvent-aided thermal recovery of bitumen from oil sands.

Optimized thermodynamic properties of REE aqueous species (REE3+ and REEOH2+) and experimental database for modeling the solubility of REE phosphate minerals (monazite, xenotime, and rhabdophane) from 25 to 300 °C

Rare earth elements (REE) are critical elements found in monazite, xenotime, and hydrated REE phosphates which typically form in hydrothermal mineral deposits. Accurate predictions of the solubility of these REE phosphates and the speciation of REE in aqueous fluids are both key to understanding the controls on the transport, fractionation, and deposition of REE in natural systems. Previous monazite and xenotime solubility experiments indicate the presence of large discrepancies between experimentally derived solubility constants versus calculated solubilities by combining different data sources for the thermodynamic properties of minerals and aqueous species at hydrothermal conditions. In this study, these discrepancies were resolved by using the program GEMSFITS to optimize the standard partial molal Gibbs energy of formation (ΔfG°298) of REE aqueous species (REE3+ and REE hydroxyl complexes) at 298.15 K and 1 bar while keeping the thermodynamic properties fixed for the REE phosphates. A comprehensive experimental database was compiled using solubility data available between 25 and 300 °C. The latter permits conducting thermodynamic parameter optimization of ΔfG°298 for REE aqueous species. Optimal matching of the rhabdophane solubility data between 25 and 100 °C requires modifying the ΔfG°298 values of REE3+ by 1–6 kJ/mol, whereas matching of the monazite solubility data between 100 and 300 °C requires modifying the ΔfG°298 values of both REE3+ and REEOH2+ by ~15–31 kJ/mol and ~ 2–10 kJ/mol, respectively. For xenotime, adjustments of ΔfG°298 values by 1–26 kJ/mol are only necessary for the REE3+ species. The optimizations indicate that the solubility of monazite in acidic solutions is controlled by the light (L)REE3+ species at <150 °C and the LREEOH2+ species at >150 °C, whereas the solubility of xenotime is controlled by the heavy (H)REE3+ species between 25 and 300 °C. Based on the optimization results, we conclude that the revised Helgeson-Kirkham-Flowers equation of state does not reliably predict the thermodynamic properties of REE3+, REEOH2+, and likely other REE hydroxyl species at hydrothermal conditions. We therefore provide an experimental database (ThermoExp_REE) as a basic framework for future updates, extensions with other ligands, and optimizations as new experimental REE data become available. The optimized thermodynamic properties of aqueous species and minerals are available open access to accurately predict the solubility of REE phosphates in fluid-rock systems.

Construction and utilization of rare earth complexes as efficient corrosion inhibitor in epoxy coating

Rare earth elements raised a lot of attention in many specialized applications. In this contribution, rare earth-containing corrosion inhibitors, 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP)-La, Ce and Pr are successfully synthesized and added as active fillers into epoxy coatings for the anti-corrosion of steel materials. In the immersion (NaCl aq. for 180 h) experiment, the EIS results show that low frequencies impedance (|Z|0.01 Hz) of the coatings follow the order of EP/H-Ce > EP/H-La > EP/H-Pr > EP blank. The |Z|0.01 Hz of EPH-Ce is found to be 106.60 Ω at 180 h with almost little change with immersion time. Similarly, the results of Tafel polarization experiments show that the HEDP-Ce-containing coating has the highest corrosion potential (−0.16 V) and the lowest corrosion current density (0.01 μA). The difference in anti-corrosion property is discussed and explained by the inherent properties of rare earth element, including electron configuration, solubility product and redox property.

The Effect of Isoniazid–Maltitol Solid Dispersions on Aqueous Solubility and Permeability

Maltitol (MAL) is a well-known polyol with potential pharmaceutical applications. Unlike other polyols, its utilization as a carrier for solid dispersions (SDs) has not been adequately investigated. This research studied the feasibility of MAL as an SD carrier to enhance the biopharmaceutical properties of a BCS class I/III drug, isoniazid (INH). SDs of INH–MAL were prepared by the fusion method, and physicochemical characteristics were investigated to determine the solid-state habit, solubility and permeation enhancement of INH. Fourier-transform infrared (FT-IR) spectroscopy demonstrated significant peak broadening for the SDs consisting of a higher MAL concentration. Powder X-ray diffraction indicated a decrease in degree of crystallinity with increasing MAL concentration. Hot-stage microscopy (HSM) and scanning electron microscopy (SEM) revealed that INH–MAL molar ratios affect the type of SD prepared via the fusion method. Results from the equilibrium solubility studies indicated significant INH solubility improvement (p &lt; 0.05) with SDs in comparison with the pure drug and physical mixtures. The artificial membrane permeation assay (PAMPA) of INH was positively affected by the presence of MAL. The results of the study indicated the potential for MAL as a carrier in the preparation of SDs for the solubility and/or permeability enhancement of drugs.

Improvement of solubility of epimedium flavonoid secondary glycoside components by traditional Chinese medicine polysaccharides and its mechanism

The poor solubility of insoluble components of traditional Chinese medicine(TCM) is an important factor restricting the development of its preparations. Natural polysaccharides of TCM can be used as functional components to increase the solubility of insoluble components. Epimedium flavonoid secondary glycoside components(EFSGC) have been shown to have positive effects on the prevention and treatment of osteoporosis, but they exhibit poor solubility. Therefore, the strategy of solubilizing EFSGC with TCM polysaccharides was adopted, and its effect on the permeability and stability of EFSGC was evaluated in this study. Based on the equilibrium solubility experiment of EFSGC, it was found that Panax notoginseng crude polysaccharide(PNCP) had the best solubilization effect on EFSGC among the ten kinds of TCM polysaccharides, which increased the solubility of EFSGC from 0.8 mg·mL~(-1) to 13.3 mg·mL~(-1). It should be noted that after the solubilization of EFSGC by preparation technology, the effects on permeability and stability should be considered. Therefore, this study also investigated these two properties. The results showed that PNCP increased the effective transmittance of EFSGC from 50.5% to 71.1%, which could increase the permeability of EFSGC significantly. At the same time, it could improve the stability of EFSGC in the simulated gastric juice environment. In order to explain the solubilization mechanism of PNCP on EGSGC, critical micelle concentration, particle size, potential, differential scanning calorimetry, and infrared spectroscopy were analyzed. It was preliminarily inferred that the mechanism was as follows: PNCP and EFSGC could self-assemble into aggregates for solubilization by intermolecular hydrogen bonding interaction in water. In summary, PNCP can not only improve the solubility of EFSGC but also improve its permeability and stability. This study lays the foundation for the application of TCM polysaccharides as a functional component to solubilize insoluble components.

β-Cyclodextrin capped ZnS nanoparticles for CER-assisted colorimetric and spectrophotometric detection of Pb2⁺, Cu2⁺, and Hg2⁺ in an aqueous solution

Herein, simple, low-cost, and room-temperature synthesis of beta-cyclodextrin (β-CD) stabilized zinc sulfide nanoparticle (ZnS NP) through the chemical precipitation method has been reported for cation exchange reaction (CER) based colorimetric sensing of Pb2+, Cu2+, and Hg2+. Formation of β-CD stabilized ZnS NPs (ZnS@β-CD) was verified by physicochemical characterization techniques such as XRD, XPS, FE-SEM, and TEM. ZnS@β-CD NPs showed color change selectively for the metal ions Pb2⁺, Cu2⁺, and Hg2⁺ among the various metal ions including Sn2⁺, Cr³⁺, Mn2⁺, Fe³⁺, Co2⁺, Ni2⁺, and Cd2⁺. The solubility product of reactants and the transformed products are the reason for selective CER of ZnS@β-CD NPs towards Pb2⁺, Cu2⁺, and Hg2⁺ ions. ZnS@β-CD NPs dispersion revealed rapid color change from white to orange, black, and bright yellow on the addition of higher concentrations of Pb2⁺, Cu2⁺, and Hg2⁺ respectively. This color change is due to the formation of complete CER-transformed nanostructures such as PbS, CuS, and HgS in higher concentrations (10⁻1- 10⁻³ M) of corresponding metal ions. The partial CER altered products Zn1−x,PbxS, Zn1−xCuxS and Zn1−xHgxS were detected due to the appearance of pale color in the lower metal ions concentrations of 10⁻⁴ - 10⁻⁶ M. This CER assisted transformation was also monitored through spectrophotometric methods. Moreover, infrared spectroscopic analysis was used to testify the structure of CER transformed product. The synthesized ZnS@β-CD NPs act as an efficient CER-based sensor for distinguishing and determining Pb2⁺, Cu2⁺, and Hg2⁺ at different level concentrations in the aqueous solution.

Equilibrium solubility and thermodynamic study of daminozide in twelve neat solvents from (283.15 to 323.15) K

In the present study, solubility of daminozide was determined in twelve neat solvents (N,N-Dimethylformamide (DMF), 2-methoxyethanol, N-Methyl-2-pyrrolidone (NMP), 2-ethoxyethanol, Acetonitrile (MeCN), 2-propoxyethanol, methanol, ethanol, n-propanol, i-propanol, n-pentanol, 2-butoxyethanol) by using the gravimetrical method under the pressure of 0.1 MPa and temperature from 283.15 to 323.15 K. The maximum solubility value (102x1) of daminozide was found in NMP at 323.15 K (10.04), while the minimum solubility value (102x1) of daminozide was found in n-pentanol at 283.15 K (0.0149). At the temperature of 298.15 K, the order of the experimental solubility values (100x1) of daminozide in twelve neat solvents was: NMP (5.523) > DMF (3.294) > methanol (1.395) > 2-methoxyethanol (0.7839) > ethanol (0.5515) > 2-ethoxyethanol (0.3816) > n-propanol (0.2175) > i-propanol (0.1099) > 2-propoxyethanol (0.1083) > 2-butoxyethanol (0.0632) > MeCN (0.0386) > n-pentanol (0.0344). Five models including van't Hoff model, Buchowski-Ksiazczak λh model, NRTL model, UNIQUAC model and Jouyban model were employed to correlate and analyze the experimental solubility of daminozide. Based on the principle of similar compatibility, the miscibility of daminozide in the selected solvents was discussed with the help of Hansen solubility parameters (HSPs). Finally, the apparent thermodynamic properties were investigated and results indicated that the dissolution mechanism of daminozide in all selected solvents was an entropy-driven and endothermic process.

Esterification of Oleic Acid for Biodiesel Production Using a Semibatch Atomization Apparatus

Although biodiesel production is undoubtedly a mature technology, there are still ways to improve it, especially through process intensification. The present study investigated the esterification of oleic acid with ethanol for biodiesel production in a nonconventional atomization reactor. The effects of the oleic acid flow rate (1.3, 2.6, and 3.9 g/min), atomization pressure (50, 100, and 150 kPa), and temperature (323, 333, and 343 K) were evaluated by a complete factorial experimental design. The size of droplets was determined by computational image processing. A mathematical model was also developed to describe the conversion of oleic acid to ethyl ester as a function of molar concentration of components and operating conditions of the reactor. A hybrid estimation of parameters (pre-exponential factor, activation energy, and equilibrium and solubility constants) was performed using particle swarm optimization followed by the Broyden–Fletcher–Goldfarb–Shanno method. The Pareto analysis has shown that the increase in temperature in the reactor and the increase in atomization pressure have improved the conversion of oleic acid. Higher pressure values in the atomization nozzle led to the generation of small oleic acid droplets, which accelerated reagent consumption during the reaction. On the other hand, conversion values were reduced by increasing the oleic acid flow rate. The highest conversion of oleic acid (86.7%) was obtained under the following reaction conditions: temperature of 343 K, atomization pressure of 150 kPa, oleic acid flow rate equal to 1.3 g/min using 0.7% sulfuric acid (mol of sulfuric acid/mol of oleic acid), and 2 h of reaction time. The simulations showed that esterification is governed by temperature, but it is possible to observe that the atomization pressure affects more conversion of oleic acid under a low temperature (&lt;323 K).

Measurement of Henry's law constants of ethyl nitrate in deionized water, synthetic sea salt solutions, and n-octanol

Ethyl nitrate (EN; C2H5ONO2) is an important component of atmospheric “odd nitrogen” (NOy) whose main source is marine emissions. To correctly describe its air-water transfer and model its global distribution, accurate values for its temperature- and salinity-dependent Henry's law solubility constants are needed. Here, we report Henry's law (HScp) constants for EN in deionized (DI) water, synthetic sea salt solutions (SSS), and n-octanol at temperatures between 278.2 K and 303.2 K. For DI water, HScp constants of (2.03 ± 0.06) M atm−1 at 293.2 K and (4.88 ± 0.13) M atm−1 at 278.2 K were observed (all stated uncertainties are at the 1σ level). The data are best described by ln(HScp(aq)/[Matm−1]) = -(16.2 ± 0.4)+(4.94 ± 0.11) × 103/T and ln(HScp(octanol)/[Matm−1]) = -(11.1 ± 1.9)+(4.15 ± 0.33) × 103/T, from which the octanol-water partition coefficient (KOW) was calculated. A temperature-independent salting-out factor of 1.25 ± 0.03 and Setschenow constant of KS = (0.33 ± 0.04) mol kg−1 were determined for SSS. Liquid-phase losses of EN were negligible in all solvents (kl < 1 × 10−4 s−1). The HScp(aq) values agree with results by Kames (1993) but are between 2% (at 303.2 K) and 19% (at 278.2 K) lower than the widely used parameterization by Kames and Schurath (1992), indicating a systemic bias in the EN literature and modelling of the Earth's nitrogen cycle.

Determination of the solubility of MgSO4 in the Zinc hydrometallurgy system within the temperature range of 263.15 K–293.15 K

ABSTRACT Solid–liquid equilibrium solubility of magnesium sulphate (MgSO4) is essential for designing and optimising the removal and recovery of magnesium (Mg) from standard zinc (Zn) hydrometallurgy systems via freeze crystallization. In this study, the solubility data of MgSO4 in ternary system MgSO4-H2SO4-H2O and quaternary system MgSO4-ZnSO4-H2SO4-H2O were determined in different zinc sulphate (ZnSO4) concentrations and sulphuric acid (H2SO4) concentrations through the isothermal equilibrium method within the temperature range from 263.15–293.15 K. The results indicated that the solubility of MgSO4 decreased with decreasing temperature and increasing concentrations of H2SO4 and ZnSO4. Furthermore, the modified Apelblat equation was applied to correlate the experimental solubility data, yielding results consistent with the experimental findings. Furthermore, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy SEM-EDS analysis results indicated that the main phases of the equilibrium solid consist of mixed crystallization products of Zn sulphate heptahydrate (MgSO4·7H2O) and Mg sulphate heptahydrate (ZnSO4·7H2O). The microstructure of the equilibrium solid was affected by the sulphate concentration.

Solubility and the solution thermodynamics of l-proline in the aqueous binary mixture of NaCl and KCl solution

This paper presents a comprehensive investigation into the equilibrium solubility and thermodynamic behavior of l-proline, a biologically and pharmaceutically significant protogenic non-essential amino acid, in both aqueous and aqua-electrolytic solutions. The study explores the effects of concentration variations at specific temperatures and temperature variations at specific concentrations. The experimental analysis is conducted using analytical gravimetric techniques. The observed phenomena are explained based on various chemical interactions, including ion-dipole and dipole-dipole interactions, present in electrolytic and pure aqueous solutions of the amino acid. The salting in/out effect is also considered to support the solubility results. The experimental results demonstrate that l-proline exhibits increased solubility in the presence of electrolytes compared to pure aqueous solutions, considering the variations in both temperature and concentration. Furthermore, the solubility of l-proline is found to be higher in the presence of KCl than NaCl as an electrolyte in aqueous media. The physical properties and sizes of both the amino acid and electrolytes are identified as crucial factors influencing the observed solubility trends.

Synthesis and characterization of supramolecular assembly probenecid cocrystal

To improve the bioavailability and provide a lead compound for developing formulations of the highly water-insoluble prodrug probenecid (PRO), enhancing its solubility is a crucial challenge that needs to be addressed. Herein, we report the synthesis and solid-state characterization of a new pharmaceutical cocrystal, PRO-BPE, synthesized using trans-1,2-bis(4-pyridyl)ethylene (BPE) to improve the solubility of PRO. The PRO-BPE cocrystals were characterized using various analytical techniques, including differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, Fourier transform-infrared spectroscopy, and X-ray powder diffraction. Single-crystal X-ray diffraction was performed to determine the crystal structure of PRO-BPE. PRO-BPE crystallized in the triclinic crystal system P-1 space group and its asymmetric unit consists of half a BPE molecule and one PRO molecule. The N1 atoms located at both ends of the BPE molecule form stable hydrogen bonds with two PRO carboxyl hydrogens through N1···H4—O4 (1.777 Å, 166.78°) interactions, whereas the O3 atoms of the carboxylic groups form C1—H1···O3 (2.479 Å, 132.10°) hydrogen bonds with two pyridyl hydrogens, resulting in a stable seven-membered ring structure. Furthermore, these fragments are further assembled via C—H···O intermolecular interactions to form a two-dimensional layered structure. Interestingly, the two pyridyl rings of each BPE molecule engage in π···π interactions with the benzene rings of two other non-coplanar PRO molecules. Finally, a three-dimensional framework structure is formed through intramolecular non-covalent interactions. Comprehensive characterization analyses provided further information regarding PRO-BPE cocrystal formation. Based on the equilibrium solubility results, the water solubility of the PRO-BPE cocrystal was superior to that of pure PRO, with an increase of 2.43 times. In summary, this study provides the first evidence that cocrystals could enhance the solubility of PRO and offers valuable insights into the solid-state properties of PRO-BPE cocrystals.

Facile Preparation of the ZnSe/Ag2Se Binary Heterojunction for Photocatalytic Antibacterial Efficiency.

In a novel approach that capitalized on the differential solubility product (Ksp) of ZnSe and Ag2Se, a unique ZnSe/Ag2Se binary heterostructure was efficiently synthesized in situ. ZnSe/Ag2Se exhibited excellent antimicrobial efficiency under visible light. Incorporating Ag2Se into ZnSe significantly enhanced the photoelectric performance of the catalyst, greatly accelerating the separation of the photogenerated electrons in the system. Active species removal experiments determined that ·O2- and H2O2 played crucial roles in photocatalytic antibacterial efficiency. Further investigation into the levels of cellular membrane peroxidation, bacterial morphology, and intracellular contents concentration revealed that during the photocatalytic antimicrobial process, reactive oxygen species initially oxidize phospholipids in the cell membrane, leading to damage to the external structure of the cell and leakage of the intracellular contents, ultimately resulting in bacteria inactivation. The photocatalytic antimicrobial process of ZnSe/Ag2Se fundamentally deviates from conventional methods, offering new insights into efficient disinfection and photocatalytic antimicrobial mechanisms.

Excipient Impact on Fenofibrate Equilibrium Solubility in Fasted and Fed Simulated Intestinal Fluids Assessed Using a Design of Experiment Protocol.

Solubility is a critical parameter controlling drug absorption after oral administration. For poorly soluble drugs, solubility is influenced by the complex composition of intestinal media and the influence of dosage form excipients, which can cause bioavailability and bioequivalence issues. This study has applied a small scale design of experiment (DoE) equilibrium solubility approach in order to investigate the impact of excipients on fenofibrate solubility in simulated fasted and fed intestinal media. Seven media parameters (bile salt (BS), phospholipid (PL), fatty acid, monoglyceride, cholesterol, pH and BS/PL ratio) were assessed in the DoE and in excipient-free media, and only pH and sodium oleate in the fasted state had a significant impact on fenofibrate solubility. The impact of excipients were studied at two concentrations, and for polyvinylpyrrolidone (PVP, K12 and K29/32) and hydroxypropylmethylcellulose (HPMC, E3 and E50), two grades were studied. Mannitol had no solubility impact in any of the DoE media. PVP significantly increased solubility in a media-, grade- and concentration-dependent manner, with the biggest change in fasted media. HPMC and chitosan significantly reduced solubility in both fasted and fed states in a media-, grade- and concentration-dependent manner. The results indicate that the impact of excipients on fenofibrate solubility is a complex interplay of media composition in combination with their physicochemical properties and concentration. The results indicate that in vitro solubility studies combining the drug of interest, proposed excipients along with suitable simulated intestinal media recipes will provide interesting information with the potential to guide formulation development.

Non-variant phenomena in heterogeneous systems. New type of solubility diagrams points

The article gives a general classification of non-invariant points in phase equilibrium diagrams of all possible types. The complete topological isomorphism of the diagrams of fusibility, solubility, and liquid-vapor equilibria in various sets of variables is demonstrated. The stability of mono-variant equilibria near the non-variant points is investigated. Recurrent formulas for calculating the number of topological elements of phase diagrams are given. A previously undescribed type of non-invariant points and phase processes in the solubility diagrams is described and characterized. The last ones have no topological analogs in other types of diagrams. Thus, we have carried out, as far as is available to the authors, a complete classification of invariant points and invariant processes in phase equilibrium diagrams of an arbitrary type and with an arbitrary number of components.

Solubility product of chromate analogue of hydrogarnet (Ca3Al2[CrO4]0.12[O4H4]2.88(s)) at 25 °C

Chromium (Cr)-hydrogarnet (Ca3Al2 [CrO4]0.12[O4H4]2.88(s)) is a critical host of hexavalent chromium [Cr(VI)] in cementitious and alkaline solids such as chromium ore processing residue (COPR). Leaching from COPR often results in Cr(VI) contamination of soil and groundwater. Although Cr-hydrogarnet has been synthesized and characterized previously, its solubility product (Ksp) is poorly constrained. Accurate determination of this thermodynamic parameter is critical to quantify the extent of Cr(VI) dissolution from COPR in water. In this contribution, the Ksp of Cr-hydrogarnet was determined by (i) hydrothermal synthesis of the solid at 150 °C in alkaline conditions in two batches; and (ii) batch equilibration experiments over 745 d from undersaturation and over 60 d from supersaturation. For each synthesized batch of solids, Cr-hydrogarnet solubility in ultrapure water at 25 °C in triplicate reactors was measured. Time-dependent aqueous samples were collected, and concentrations of Cr(VI) and co-solutes and pH were measured until a steady state was attained from undersaturation, after which the state was perturbed by the addition of 7× Cr(VI) to trigger the supersaturation experiment. X-ray diffraction and SEM-EDS analyses on the reacted solids confirmed the presence of Cr-hydrogarnet and its constituent elements, respectively. In addition, calcite and aluminum oxyhydroxides were formed as minor secondary phases. The log ion activity products at steady states attained from undersaturation and supersaturation were 72.36 ± 0.86 and 72.75 ± 0.14, respectively. A mean log Ksp of 72.55 ± 0.87 at 25 °C for the reaction Ca3Al2 [CrO4]0.12[O4H4]2.88(s) + 11.52H+ ↔ 3Ca2+ + 2Al3+ + 0.12CrO42− + 11.52H2O was proposed. Furthermore, the new thermodynamic constant was used to analyze data from two previous COPR equilibration studies in water and identify the governing mechanisms of Cr(VI) release.

Diffusion Welding of Surface Treated Alloy 800H

Diffusion welding of heat-resistant alloys has attracted interest in the manufacturing of components with complex configurations. Controlling secondary precipitates along the interface is necessary to enhance the quality of the diffusion welding. Surface treatment to increase the solubility product (Ksp) of Ti-rich carbide is proposed to accomplish such an enhancement. The reduction of secondary precipitates along the interface induced grain boundary migration across the interface. The chemical compositions at/near the interface satisfied the material specifications. The mechanical properties of the diffusion weldment were similar to those of Alloy 800H that underwent the same thermo-mechanical processes in the range of 25–700 °C. At 25 °C, the tensile strength was 553 MPa, which satisfied the minimum specified tensile strength described in ASTM B: 409-22. The location of failure was random in the gauge section, and dimples, the evidence of the macroscopic plastic deformation, were observed on the fracture surface.

Discovery of supergene REE-fluorocarbonate minerals in weathered spheres of Xiajialing regolith-hosted rare earth element deposit in Xiangshan, Jiangxi Province, South China

The Xiangshan ore field is developing not only a volcanic-related hydrothermal U deposit, but also a regolith-hosted rare earth elements (REE) deposit in the middle of the volcanic rock basin, where the spheroidal weathering layer has the highest REE content. Weathered spheres may play an important role in REE mineralization. To explore the enrichment and migration processes of REE in weathered spheres at different weathering stages, the mineralogy and geochemistry of the bedrock and weathered spheres with different weathering degrees of Xiajialing REE deposits were investigated. Results showed that the REE+Y concentration was 270–310 ppm in bedrock and 372–2377 ppm in weathered spheres, respectively. With an increase in weathering, the REE+Y content increased and then decreased, and the maximum value was observed in the core of the moderately weathered sphere sample. A large number of supergene REE-fluorocarbonate minerals were discovered in the weathered spheres (particularly in samples with a high REE content), and were mainly distributed in biotite and plagioclase. The REE2O3 (including Y2O3) content of the supergene REE minerals was 69.04–80.89 wt%. The supergene REE minerals were enriched in La2O3 (21.69–25.95 wt%), Nd2O3 (12.13–23.58 wt%), and Y2O3 (2.74–14.27 wt%), but lacked Ce2O3 (<1 wt%), and contained a certain amount of F (2.66–6.23 wt%). The Raman spectra of the supergene REE-fluorocarbonate showed several bands at 272, 741, 1103, and 3100–3700 cm−1. These results indicate that REE are adsorbed on clay minerals that were formed by weathering of biotite and plagioclase; thus, the concentrations of REE around the clays were extremely high and may have exceeded the solubility product (Ksp) of the REE-fluorocarbonate, which contributed to the supergene REE-fluorocarbonate deposits. The formation of supergene REE-fluorocarbonate minerals may be one of the most important causes of the extreme enrichment of REE in some weathered sphere samples. However, the supergene mineral is easily weathered and would dissolved with weathering proceeding, leading to a decrease in the REE content in the sphere samples that have experienced relatively strong weathering. The supergene REE-fluorocarbonate may be an important intermediate product in the formation of the Xijialing regolith-hosted REE deposit.