Solubility Curves Research Articles

Indirect assessment of the fusion properties of choline chloride from solid-liquid equilibria data

The temperature and enthalpy of fusion of choline chloride -[Ch]Cl- are not directly measurable since this compound decomposes upon melting. Yet, given the wide use of this compound in the preparation of deep eutectic solvents (DES), its thermophysical fusion properties are very important for a better understanding of these mixtures and the thermodynamic description of their solid-liquid phase diagrams. In this work, the fusion properties of choline chloride were estimated using the solubility curves of choline chloride in ten different ionic compounds, forming simple binary eutectic mixtures with quasi-ideal liquid phases. Experimental solid-liquid equilibria data for these systems -[Ch]Cl + ionic compounds- were measured, and the ideality of the systems assessed through the quantification of the activity coefficients and their comparison in each pair of binary solutions. The values estimated for the fusion properties of choline chloride are Tfus,[Ch]Cl = 597 ± 7 K and ΔfusH[Ch]Cl = 4300 ± 600 J mol−1. These were additionally checked by thermodynamic consistency tests and by the prediction of the solid-liquid curves with COSMO-RS model. The results obtained with both procedures allow us to guarantee the usefulness and robustness of the estimated data.

Thermodynamic properties of enantiotropic polymorphs of glycolide

In this work, two different polymorphs (form 1 and form 2) of glycolide were successfully prepared and characterized. The solubility of these two polymorphs in ethyl acetate, 1-propanol, ethanol, 2-propanol and 1-butanol at temperatures from 278.15K to 328.15K under atmospheric pressure (0.1MPa) was experimentally measured by using the isothermal gravimetrical method and correlated by the modified Apelblat model and the van’t Hoff equation. For all the selected solvents, the solubility curve of form 1 crossed the solubility curve of form 2 at a transition temperature in the above temperature range. Combining the results of DSC, solubility curves and dissolution data of these two polymorphs, it was confirmed that form 1 and form 2 were enantiotropic. The dissolution thermodynamic properties of glycolide form 1 and form 2 were also calculated.

LCST-Type Phase Behavior of Aqueous Biphasic Systems Composed of Phosphonium-Based Ionic Liquids and Potassium Phosphate

Although aqueous biphasic systems (ABS) composed of phosphonium-based ionic liquids (ILs) have demonstrated superior performance as viable media for biocompatible extraction processes, the formation of ABS with tetrabutylphosphonium trifluoroacetate ([P4444]CF3COO) and tributyloctylphosphonium bromide ([P4448]Br) were seldom investigated. To evaluate the hydrophilicity of [P4444]CF3COO and [P4448]Br, the solubility curves for the mixture of the ILs and water were determined. The influence of temperature on the phase behavior for the [P4448]Br + K3PO4 + H2O and [P4444] CF3COO + K3PO4 + H2O systems were also obtained. Results show that both [P4448]Br + H2O and [P4444]CF3COO + H2O binary systems undergo lower critical solution temperature-type phase transition, and the ABS composed of [P4444]CF3COO and [P4448]Br can be formed with K3PO4 at a wide range of temperatures. Moreover, the ABS are highly temperature dependent, and biphasic region expands with an increase in temperature. On the other hand, the capab...

Solubility of oxygen in Fe–Co melts containing titanium

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO2) =–7.194; logK(TiO2) =–6.125; logK(Ti3O5) =–16.793; logK(Ti2O3) =–10.224) to cobalt (logK(CoO · TiO2) =–8.580; logK(TiO5) =–7.625; logK(Ti3O5) =–20.073; logK(Ti2O3) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO2, TiO2, Ti3O5, and Ti2O3 are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO2 ↔ TiO2 decreases from 1.0 × 10–4% Ti in iron to 1.9 × 10–6% Ti in cobalt. The titanium content at the equilibrium point TiO2↔Ti3O5 increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti3O5 ↔ Ti2O3 decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.

Thermodynamics and crystal chemistry of rhomboclase, (H5O2)Fe(SO4)2·2H2O, and the phase (H3O)Fe(SO4)2and implications for acid mine drainage

The system Fe 2 O 3 -SO 3 -H 2 O contains the most important minerals of acid mine drainage (AMD), iron oxides, and iron sulfates. For geochemical modeling of the AMD systems, reliable thermodynamic data for these phases are needed. In this work, we have determined thermodynamic data for the most acidic sulfates rhomboclase [(H 5 O 2 )Fe(SO 4 ) 2 ·2H 2 O or (H 3 O)Fe(SO 4 ) 2 ·3H 2 O] and the phase (H 3 O)Fe(SO 4 ) 2 . The actual compositions of the studied phases are (H 3 O) 1.34 Fe(SO 4 ) 2.17 (H 2 O) 3.06 (molecular mass of 344.919 g/mol) and (H 3 O) 1.34 Fe(SO 4 ) 2.17 (289.792 g/mol). Structural details for both phases were refined from synchrotron powder X-ray diffraction data. Enthalpies of formation were determined by acid-solution calorimetry. Low-temperature heat capacity was measured for rhomboclase by relaxation calorimetry but a critical analysis of entropies for several oxysalts showed that these data are too high. Entropies for both phases were estimated from a Kopp-rule algorithm. The enthalpies of formation and entropies were combined with previously published temperature-relative humidity brackets to generate an internally consistent thermodynamic data set for rhomboclase: Δ f H ° = –3202.03 kJ/mol, S ° = 378.7 J/(mol∙K); and for (H 3 O) 1.34 Fe(SO 4 ) 2.17 : Δ f H ° = –2276.25 kJ/mol, S ° = 253.2 J/(mol∙K). Solubility experiments at room temperature and at T = 4 °C agree well with previously reported data in the system Fe 2 O 3 -SO 3 -H 2 O. An inspection of the extended Pitzer model for Fe 3+ -SO 4 solutions shows that this model reproduces the general topology of the phase diagram, but the position of the calculated solubility curves deviates substantially from the experimental data. Solid-state 2 H MAS NMR spectra on deuterated rhomboclase show two isotropic chemical shifts δ iso ( 2 H) = of 8 ± 1 and 228 ± 1 ppm, assigned to D 5 O 2 + and Fe-OD 2 groups, respectively. Canonical ensemble (NVT) molecular dynamics simulations for (H 3 O)Fe(SO 4 ) 2 at T = 300 K showed that the H 3 O groups maintain their trigonal pyramidal geometry and perform different types of motion.

Effect of Seed Loading and Temperature of Seeding on Carbamazepine-Saccharin Co-Crystal

Objectives: In pharmaceutical industries, the properties of desired final crystal can be modified by seeding process. Seeding activities depend on seed loading, seed size, seed quality and the temperature of supersaturated solution at the time of seed addition. The effect of amount of seed and temperature of seeding on crystallisation and size distribution of carbamazepine-saccharin (CBZ-SAC) co-crystals have been investigated. Methods/Statistical Analysis: 0.5, 1.0 and 1.5 wt% seeds of constant size were added to the metastable zone width region during cooling crystallisation at seeding temperatures of 38.45, 40.35, 42.25, 44.15 and 46.05 oC. Findings: During the crystallisation process of CBZ-SAC co-crystal, nucleation occurred faster when seeding is close to the super solubility curve which is at the highest supersaturation. Crystal size distribution (CSD) results showed more fine particles formed at 38.45oC seed temperature. On the other hand, nucleation occurred slower when seeding is close to the solubility curve, which is at low supersaturation and therefore resulted in less number of fine particles formed. Application: Nucleation of CBZ-SAC co-crystals can be controlled easily by seeding, in which the addition of seed expedites the crystallisation process by providing the surface area for crystals to grow. The size and characteristic of the desired crystal can be adjusted via seeding application.

Widespread Solid Solutions of Hexahydrated Cobalt and Nickel Nitrates: Solid–Liquid Equilibria at 273.15 and 303.15 K and Characterization of Mixed Crystals of Homogeneous Composition

The isothermal solubility curves of the H2O–Co(NO3)2–Ni(NO3)2 ternary system were studied at 273.15 and 303.15 K, using a synthetic method based on conductivity measurements. The analysis of the equilibrium phases’ composition was conducted by UV–visible spectroscopy. The solid phases were first characterized by powder X-ray diffraction, which showed the formation of two substitutional solid solutions: Co(1−σ)Niσ(NO3)2·6H2O, which has a monoclinic structure, and Ni(1−ω)Coω(NO3)2·6H2O, which has a triclinic structure. Then the evolution of the lattice parameters of the crystals at 303.15 K, depending on the solid solution composition, was studied by single-crystal X-ray diffraction. The shrinkage of the monoclinic lattice increases with the increase of the nickel ions in the structure. The stability area of this solid solution is very wide as more than 7 cobalt ions in 10 could be replaced by nickel ions. However, the variation of the lattice parameters of the triclinic solid solutions remains limited, alt...

Effect of Seed Loading and Temperature of Seeding on Carbamazepine-Saccharin Co-Crystal

Objectives: In pharmaceutical industries, the properties of desired final crystal can be modified by seeding process. Seeding activities depend on seed loading, seed size, seed quality and the temperature of supersaturated solution at the time of seed addition. The effect of amount of seed and temperature of seeding on crystallisation and size distribution of carbamazepine-saccharin (CBZ-SAC) co-crystals have been investigated. Methods/Statistical Analysis: 0.5, 1.0 and 1.5 wt% seeds of constant size were added to the metastable zone width region during cooling crystallisation at seeding temperatures of 38.45, 40.35, 42.25, 44.15 and 46.05 oC. Findings: During the crystallisation process of CBZ-SAC co-crystal, nucleation occurred faster when seeding is close to the super solubility curve which is at the highest supersaturation. Crystal size distribution (CSD) results showed more fine particles formed at 38.45oC seed temperature. On the other hand, nucleation occurred slower when seeding is close to the solubility curve, which is at low supersaturation and therefore resulted in less number of fine particles formed. Application: Nucleation of CBZ-SAC co-crystals can be controlled easily by seeding, in which the addition of seed expedites the crystallisation process by providing the surface area for crystals to grow. The size and characteristic of the desired crystal can be adjusted via seeding application.

Solid–Liquid Phase Equilibria of Ternary Systems LiCl–LiBr–H2O and CaCl2–CaBr2–H2O at 288.15 K

The solubility data, composition of the solid solutions, and refractive indices of the LiCl–LiBr–H2O and CaCl2–CaBr2–H2O systems at 288.15 K were studied with the isothermal equilibrium dissolution method. The solubility diagrams and refractive index diagrams of the two systems were plotted at 288.15 K. There is no invariant point, one univariant solubility curve saturated with solid solution, and one crystallization field of the solid solution in the phase diagrams. The two systems belong to the solid solution type, and no double salts formed in the systems. The refractive indices calculated with an empirical equation agree well with the experimental data. By combining the composition equations and solubility equilibrium constant equations of the solid solutions, the solubilities of the two systems at 288.15 K were calculated on the basis of the Pitzer and Harvie–Weare models. The calculated solubilities agree well with the experimental results.

Partitioning of Co2+ and Mn2+ into meridianiite (MgSO4·11H2O): Ternary solubility diagrams at 270 K; cation site distribution determined by single-crystal time-of-flight neutron diffraction and density functional theory

We have grown single crystals of M2+SO4 hydrates at 270 K from aqueous solutions in the ternary systems CoSO4–MgSO4–H2O and MnSO4–MgSO4–H2O. These systems exhibit broad stability fields for a triclinic undecahydrate on the Mg-rich side (i.e., Co- or Mn-bearing meridianiite solid solutions) and stability fields for monoclinic heptahydrates on the Mg-poor side (i.e., Mg-bearing solid solutions of bieberite or mallardite). The solubility curves and distribution coefficients, describing the partitioning of M2+ ions between liquid and solid phases, have been determined by thermo-gravimetric and spectroscopic techniques. A subset of M2+SO4·11H2O specimens were selected for single-crystal time-of-flight neutron diffraction analysis in order to evaluate preferential occupancy of symmetry-inequivalent coordination polyhedra in the structure. Considering the nearly identical dimensions of the first coordination shells, there is a surprising difference in the distribution of Co and Mn over the two available sites.

Investigation of the Selective Growth of ZnO and Zn(OH)2 Films Deposited by Chemical Bath Near Room Temperature

Zinc oxide (ZnO) and zinc hydroxide (Zn(OH)2) thin films were deposited by the chemical bath deposition onto glass substrates at temperatures of 25°C, 35°C and 45°C. The experimental conditions for the selective deposition of the films such as the concentration of the reagents, temperature, and pH of the chemical bath were determined from the predictions of the species distribution diagrams (SDDs) and solubility curves (SCs). SDDs and SCs were elaborated by considering the chemical reagents, temperature, and pH, and give information about the probability of formation of specific compounds. The reagents used were ZnSO4, KOH, and NH4NO3. The physicochemical of the synthesis of both ZnO and Zn(OH)2 films are proposed. X-ray photoelectron spectroscopy and X-ray diffraction indicate the presence of ZnO and/or Zn(OH)2 compounds, where the selective deposition of each material (or coexistence) is dependent on the bath temperature and pH. The crystalline structure was hexagonal (zincite) for ZnO and orthorhombic (wulfingite) for Zn(OH)2. The bandgap energy of the deposited films ranged from 3.32 to 3.51 eV. A better understanding of the selective deposition of specific compounds by controlling the experimental parameters represents an important step toward the fabrication of nanomaterials with tailored properties for a wide range of applications.

Synthesis of ZnS Thin Films by Chemical Bath: From Room Temperature to 90°C

A physicochemical analysis was performed on the solution used for synthetizing zinc sulfide (ZnS) films by chemical bath; such solution contained zinc chloride, potassium hydroxide, ammonium nitrate and thiourea as chemical reagents. Solubility curves and species distribution diagrams were used to obtain the best conditions for ZnS deposition in a wide range of bath temperatures between 25 and 90°C. Solubility curves evidenced the necessity to adjust the thiourea concentration for each bath temperature in order to obtain enough amounts of sulfur ions needed for ZnS formation. The thiourea concentrations were fixed at 0.2 M (90°C), 0.6 M (60°C), 1.25 M (40°C), and 2.25 M (25°C) to get higher quality films. Characterization results of films deposited at the conditions described above showed the films to have a bandgap energy value between 3.65 and 3.72 eV, stoichiometry of [Zn]/[S] ≈1, and homogeneous and agglomerate-free surfaces, which make them proper for solar cells applications.

Solubility curves and nucleation rates from molecular dynamics for polymorph prediction - moving beyond lattice energy minimization.

Current polymorph prediction methods, known as lattice energy minimization, seek to determine the crystal lattice with the lowest potential energy, rendering it unable to predict solvent dependent metastable form crystallization. Facilitated by embarrassingly parallel, multiple replica, large-scale molecular dynamics simulations, we report on a new method concerned with predicting crystal structures using the kinetics and solubility of the low energy polymorphs predicted by lattice energy minimization. The proposed molecular dynamics simulation methodology provides several new predictions to the field of crystallization. (1) The methodology is shown to correctly predict the kinetic preference for β-glycine nucleation in water relative to α- and γ-glycine. (2) Analysis of nanocrystal melting temperatures show γ- nanocrystals have melting temperatures up to 20 K lower than either α- or β-glycine. This provides a striking explanation of how an energetically unstable classical nucleation theory (CNT) transition state complex leads to kinetic inaccessibility of γ-glycine in water, despite being the thermodynamically preferred polymorph predicted by lattice energy minimization. (3) The methodology also predicts polymorph-specific solubility curves, where the α-glycine solubility curve is reproduced to within 19% error, over a 45 K temperature range, using nothing but atomistic-level information provided from nucleation simulations. (4) Finally, the methodology produces the correct solubility ranking of β- > α-glycine. In this work, we demonstrate how the methodology supplements lattice energy minimization with molecular dynamics nucleation simulations to give the correct polymorph prediction, at different length scales, when lattice energy minimization alone would incorrectly predict the formation of γ-glycine in water from the ranking of lattice energies. Thus, lattice energy minimization optimization algorithms are supplemented with the necessary solvent/solute dependent solubility and nucleation kinetics of polymorphs to predict which structure will come out of solution, and not merely which structure has the most stable lattice energy.

Formation of supported lipid bilayers of charged E. coli lipids on modified gold by vesicle fusion

We describe a simple way of fusing E. coli lipid vesicles onto a gold surface. Supported lipid bilayers on metal surfaces are interesting for several reasons: transducing a biological signal to an electric readout, using surface analytical tools such as Surface Plasmon Resonance (SPR), Infrared Reflection Absorption Spectroscopy, Neutron Reflectivity or Electrochemistry. The most widely used method to prepare supported lipid membranes is fusion of preexisting liposomes. It is quite efficient on hydrophilic surfaces such as glass, mica or SiO2, but vesicle fusion on metals and metal oxide surfaces (as gold, titanium oxide or indium tin oxide), remains a challenge, particularly for vesicles containing charged lipids, as is the case of bacterial lipids. We describe a simple method based on modifying the gold surface with a charged mercaptopropionic acid self-assembled monolayer and liposomes partially solubilized with detergent. The formed bilayers were characterized using a Quartz Crystal Microbalance with dissipation (QCM-D) and Atomic Force Microscopy (AFM). Some advantages of this protocol are that the stability of the self-assembled monolayer allows for repeated use of the substrate after detergent removal of the bilayer and that the amount of detergent required for optimal fusion can be determined previously using the lipid-detergent solubility curve.

Direct adjustment of wax thermodynamic model parameter to micro Differential Scanning Calorimetry thermograms

Among the flow assurance subjects, wax deposition plays a major role. As exploration an oil production moves towards deeper water frontiers, longer tiebacks increase the risk of wax deposition, which is assessed through modeling. In modeling schemes, the phase behavior of solid wax is essential and it is available through either a measured solubility curve or through thermodynamic models. These thermodynamic models normally need tuning and, due to the experimental difficulties of measuring solubility curves for real fluids, are tuned to the wax appearance temperature (WAT). To reduce the uncertainties of adjusting a model to just one point, a procedure to directly simulate DSC curves from a liquid-solid thermodynamic model is proposed. This new strategy allows a full thermogram adjustment without going through the empirical integration of the experimental DSC. Experimental DSC thermograms and simulated curves are presented for five standard single wax mixtures. Then, the solubility curves obtained from the model are compared to the experimental literature data and the difference between simulated wax disappearance temperature (WDT), experimental WDT and experimental wax appearance temperature (WAT) are discussed.

Phase separation analysis of Extem/solvent/non-solvent systems and relation with membrane morphology

The phase separation behavior of Extem/water/solvent systems for various solvents and Extem/NMP/non-solvent systems for different types of coagulants was investigated. Ternary phase diagrams of studied systems were constructed based on cloud point data obtained by titration at room temperature. In the first part, N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were employed as solvent and water was used as coagulant. The cloud point curves from these systems showed that Extem/NMP/water and Extem/DMSO/water has the smallest and largest demixing gap, respectively. Subsequently, water, methanol, and glycerol were employed as coagulants and NMP was selected as solvent. The obtained results indicated that water and methanol had the strongest and weakest coagulant power, respectively. The linearized cloud point and precipitation value were applied to identify the strength of the non-solvent for casting solution (Extem/NMP) with a certain concentration. The solubility curve of Extem was obtained using the Hansen solubility parameter, calculated by a group contribution method. In order to evaluate the influence of different solvents and non-solvents on the final structure of the resulting membranes, scanning electron microscopy (SEM) was used. The morphology of the membranes prepared from Extem/solvent/water systems (except Extem/DMSO/water) showed a finger like sub-layer, while a sponge-like structure was observed for the Extem/DMSO/water system. Using methanol as coagulation medium resulted in a thick dense layer over a macroporous sub layer, while a fully sponge like structure with microporous skin layer was obtained for the Extem/NMP/glycerol system. In order to find the source of these unexpected observations, thermodynamic and kinematic aspects such as binary interaction parameters, heat of mixing, viscosity and diffusion rate were discussed thoroughly.

Effects of solution degassing on solubility, crystal growth and dissolution—Case study: Salicylic acid in methanol

The influence of dissolved gases on the crystallization parameter solubility, MZW, growth and dissolution rates was investigated experimentally using degassed and non-degassed (air-saturated) solutions. The results of this study show that degassing has no effect on the solubility curve of the used model substance salicylic acid (SA) in methanol (MeOH). This reveals in the assumption that a thermodynamic effect of dissolved gases can be excluded. Growth rates were measured by means of a desupersaturation method and the results indicate that the growth rates of SA are not affected by degassing. The results of the dissolution rate measurements reveal a distinct decrease in dissolution rates for non-degassed solutions compared to degassed solutions, especially, at low temperature (10°C).To explain this phenomenon the gas solubility, represented by oxygen, in MeOH in dependence on the SA concentration was estimated by means of Hansen Solubility Parameters (HSP) [1]. It was found that the oxygen solubility decreases with increasing SA content which explains the inhibition of crystal dissolution in non-degassed solution compared to degassed solution. Moreover, this kind of ‘drowing-out’ mechanism would not appear in growth rate measurements, where indeed no effect of degassing could be observed.

Measurement and Correlation of Solubility on Reactive Crystallization of Methyl D-(−)-4-Hydroxy-phenylglycinate

In this paper, the solubility of methyl D-(−)-4-hydroxy-phenylglycinate was measured under the different pH levels, pure solvents, mixed solvents, ionic strength, and impurities in the temperature range from 283 to 323 about 5 K intervals by using laser method at atmospheric pressure. The results reveal that the solubility of methyl D-(−)-4-hydroxy-phenylglycinate increases with increasing temperature in all selected solvents, which decreases with increasing mole fraction composition of water in the mixed solvents. The solubility curve of methyl D-(−)-4-hydroxy-phenylglycinate in the aqueous solution at different pH is “U” shape and the solubility of methyl D-(−)-4-hydroxy-phenylglycinate increases with concentrations of ammonium chloride and has no obvious changes when its concentration increases up to 1.25 mol/kg. It is beneficial to maximize the reaction conversion rate of D-4-hydroxyphenylglycine methyl ester hydrochloride and reduce the residual D-4-hydroxyphenylglycine methyl ester hydrochloride on ...

Measurements and calculations of solid-liquid equilibria in the quaternary system NaBr–KBr–Na2SO4–K2SO4–H2O at T = 348 K

Using an isothermal dissolution equilibrium method, solid-liquid equilibria in the quaternary system NaBr–KBr–Na2SO4–K2SO4–H2O were studied at T = 348 K. The phase diagram, water diagram and the density-composition diagram were plotted according to the experiment results. One double salt Na2SO4·3K2SO4 was found in the quaternary system at T = 348 K. There are five areas of crystallization, seven univariant solubility curves, and three invariant points. Respectively, the five crystallization regions are Na2SO4·3K2SO4, NaBr, KBr, Na2SO4 and K2SO4. Based on the chemical model of Pitzer's electrolyte solution theory, the solubilities of the quaternary systems NaCl–KCl–Na2SO4–K2SO4–H2O, NaBr–KBr–Na2SO4–K2SO4–H2O have been calculated at T = 348 K. The calculation diagrams were plotted. Comparing experimental measurement with calculation, the results showed that the calculated results are in accordance with experiments.

Thermodynamics of oxygen solutions in titanium-containing Fe–Co melts

Performed for the first time, the thermodynamic analysis of oxygen solutions in titanium-containing Fe–Co melts showed that the deoxidizing power of titanium with increasing cobalt content of the melt first decreases, reaches a minimum at a cobalt content of 20%, and then increases. The titanium contents [%Ti]* at equilibrium points between the oxide phases TiO2, Ti3O5, and Ti2O3 were determined. The curves of the oxygen solubility in titanium-containing iron–cobalt melts pass through a minimum, which shifts toward lower titanium contents with increasing cobalt content of the melt. Further alloying with titanium leads to an increase in the oxygen concentration of the melt so that the higher cobalt content of the melt, the steeper the increase in the oxygen content after the minimum as titanium is added to the melt.