Surface strengthening of lithium disilicate glass-ceramic by ion-exchange using Rb,Cs nitrates

In order to further improve the flexural strength of lithium disilicate glass-ceramic, surface strengthening by ion exchange using Rb, Cs nitrates has been studied for the first time. The influences of ion exchange using rubidium and cesium salts on the flexural strength and corrosion resistance have been investigated. It was found that the mechanical properties of the lithium disilicate glass-ceramic could be increased greatly by the ion exchange in rubidium nitrate (RbNO₃) salt. After ion exchange for 4?h in RbNO₃ salt, the flexural strength and microhardness increased from 169?MPa and 587?kgf?mm^?2 (5.75?Gpa) of the original lithium disilicate glass-ceramic to 493?MPa and 654?kgf?mm^?2 (6.4?Gpa), respectively. Moreover, the corrosion resistance of the lithium disilicate glass-ceramic was further improved by ion exchange in rubidium and cesium nitrate salts. Furthermore, the maximum thickness of the ion exchange layer using RbNO₃ and CsNO₃ was only 4.3?µm and 0.45?µm respectively. Such a thin exchange layer, which will only require very low Rb⁺, Cs⁺ ions exchange amount, indicates that the molten salts of RbNO₃ and CsNO₃ can be reused for many times. So it is suggested that surface strengthening of lithium disilicate glass-ceramic by ion exchange using Rb, Cs nitrates is cost-efficient and very suitable for the actual production and applications.     

Effect of potassium and silver ion-exchange on the strengthening effect and properties of aluminosilicate glass

In this work, the aluminosilicate glass was subjected to ion-exchange using the KNO₃-AgCl mixed molten salt in order to strengthen the glass while imparting antimicrobial properties. The concentration distribution of K⁺ ions and Ag⁺ ions of the ion-exchanged glasses was characterized by EDS, the effects of ion-exchange temperature (460-500 °C), ion-exchange time (0.5-3 h) and AgCl concentration (0–2.5 wt%) in the mixed molten salt on the strengthening effect and properties of the glass were investigated. The results showed that Ag⁺-Na⁺ ion-exchange, K⁺-Na⁺ ion-exchange existed simultaneously, and Ag⁺-Na⁺ ion-exchange occurred preferentially. Due to the presence of metallic silver, the appearance of the Ag⁺ ion-exchanged glass was light yellow and its transmittance showed a decrease. The surface compressive stress trended up and then down with increasing temperature and time because of the stress relaxation effect. The Vickers hardness of ion-exchanged glass increased by 15%, and the densities and chemical stability were also increased. Ions leaching experiments showed that the Ag⁺ ions release concentration of silver-loaded glass in aqueous environment can reach the bactericidal level. It has been shown that ion-exchange of glass in KNO₃-AgCl mixed molten salts allowed the glass to be strengthened and incorporated with antimicrobial active ions, its chemical stability was improved, too.     

Strengthening of a lithium disilicate glass-ceramic by rapid cooling

In order to improve the mechanical properties, a traditional physical strengthening process was applied to a lithium disilicate (LD) glass-ceramic with a dual-phase microstructure consisting of a glassy matrix and LD crystals. The strengthening process was based on the transformation behavior of the glass-ceramic. The process was conducted by heating the glass-ceramic to a temperature below the dynamic softening point, and then rapid cooling in silicon oil (quenching). Residual stresses and mechanical properties of the glass-ceramic were investigated after the quenching. It was found that residual compressive macro-stresses could be induced in the surface layer of the LD glass-ceramic by the quenching. The residual stresses remarkably increased with increasing the quenching temperature to near the dynamic softening temperature. Compared with the corresponding annealing state, the LD glass-ceramic could be effectively strengthened and toughened by the quenching at a suitable temperature. The results displayed the strengthening possibility and potential of the LD glass-ceramic by the traditional physical process.     

Measurement of stress build-up of ion exchange strengthened lithium aluminosilicate glass

A recently developed nondestructive method was used to investigate the stress build-up in chemically strengthened lithium aluminosilicate glass. We utilized an updated version of the gradient scattered light method, which now enables more precise determination of the depth coordinates, recovering a more detailed stress profile around the knee. The main motivation of the work was to characterize and optimize the development of the knee-shaped breaking point in stress profile in lithium aluminosilicate glass prepared by the Saunders-Kubichan method of one-step strengthening in a mixture of KNO₃+NaNO₃ molten salt bath. In the industry, a two-step process is still commonly used to build such a stress profile; the one-step strengthening will simplify the process as well as save the cost. Compared to previous studies, which used a destructive method based on transmitted light photoelasticity, we found that in the samples ion exchanged for 24 hours, the knee-shaped breaking points were situated two times deeper whereas the case depths were 28% shallower. The measured stress profiles were validated by stress equilibrium and by comparison to Na⁺ ion concentration profiles.     

Effect of ZrO2 crystallization on ion exchange properties in aluminosilicate glass

Ion exchange has the potential to improve the mechanical properties of glass ceramics. In this work, ZrO₂ nanocrystals embedded transparent glass ceramics were prepared and effect of the crystallization on ion-exchange properties was investigated. The crystallization of ZrO₂ did not affect the transmittance and Vickers hardness due to the small nanocrystal size and the low crystallinity, but significantly enhanced the ion exchange depth of layer (DOL). X-ray diffraction, high resolution transmission electron microscope, Raman spectra and nuclear magnetic resonance analysis demonstrated that with the crystallization of ZrO₂, the charge compensator (Na⁺) was released, which promoted the transformation of highly coordinated Al into [AlO₄]⁻ tetrahedral units and the formation of Na⁺ balanced non-bridging oxygens. These changes in structure of glass made the Na⁺ more mobile and increased the DOL upon the crystallization. Results reported here may be useful for the development of glass-ceramic materials suitable for chemical strengthening.     

Sulfide Glass-Ceramic Electrolytes for All-Solid-State Lithium and Sodium Batteries

Sulfide glass-ceramic electrolytes with Li⁺ or Na⁺ ion conduction have been developed in last decade. High-temperature phases of Li₇P₃S₁₁ and cubic Na₃PS₄ are precipitated from mother glasses, and the obtained glass-ceramics show higher conductivity than the mother glasses. It is difficult to synthesize those high-temperature phases by conventional solid-state reaction, and glass electrolytes are thus important as a precursor for forming high-temperature phases. The highest conductivities at 25°C of 1.1 × 10⁻² S/cm for Li⁺ ion conductor (Li₇P₃S₁₁) and 7.4 × 10⁻⁴ S/cm for Na⁺ ion conductor (Na_3.06P_0.94Si_0.06S₄) are achieved in sulfide glass-ceramic electrolytes. All-solid-state batteries with sulfide glass-ceramic electrolytes were fabricated by cold press at room temperature. Sulfide electrolytes have favorable mechanical properties to form favorable solid–solid contacts in solid-state batteries by pressing without heat treatment. All-solid-state Li-In/S and Na-Sn/TiS₂ cells using sulfide glass-ceramic electrolytes operate as secondary batteries and exhibit good cycle performance at room temperature.     

Solid-liquid equilibria in concentrated aqueous salt solutions—systems with a common ion

A thermodynamic correlation is presented for solid-liquid equilibria in concentrated aqueous salt systems containing a common ion. It is assumed that no solid solutions are formed, although the solid phase can be a pure salt, a multiple salt or a hydrate. Predictions of solid-liquid equilibria in multicomponent systems are made using parameters calculated from solid-liquid equilibrium data for the constituent binary and ternary systems.Parameters are given for the prediction of solid-liquid equilibria in the aqueous system containing Na⁺, K⁺, Mg⁺⁺, NO^?₃, Cl^?, SO^--₄ from 0–50°C. These parameters correlate the available solid-liquid equilibrium data for ternary systems with an error in liquid-phase composition of less than 2 grams salt/100 grams H₂O. Errors are similar in the estimation of solid-liquid equilibria in four-component systems such as NaNO₃-NaC1-Na₂SO₄-H₂O.     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.     

Behavior of cesium cation in zeolite Y (FAU,Si/Al = 1.56) and their single-crystal structures, |Cs<Subscript>75−x</Subscript>Na<Subscript>x</Subscript>|[Si<Subscript>117</Subscript>Al<Subscript>75</Subscript>O<Subscript>384</Subscript>]-FAU (x = 35 and 54)

To study the tendency of Cs⁺ exchange into zeolite Y (Si/Al = 1.56) dependence on Cs⁺ and Na⁺ concentration of aqueous solution during exchange, two single-crystals of fully dehydrated, Cs⁺-and Na⁺-exchanged zeolites Y were prepared by the flow method using a mixed ion-exchange solution whose CsNO₃:NaNO₃ mol ratios were 1:1 (crystal 1) and 1:100 (crystal 2), respectively, with a total concentration of 0.1 M, followed by vacuum dehydration at 723 K. Their crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{ 3}\) m, respectively, and were refined to the final error indices R ₁/wR ₂ = 0.084/0.248 and 0.088/0.274 for crystals 1 and 2, respectively. In the structure of |Cs₄₀Na₃₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 1), 40 Cs⁺ ions per unit cell occupy five different equipoints; 3, 3, 14, 9, and 11 are at sites I, II′, II, IIIa and IIIb, respectively, whereas, the remaining 35 Na⁺ ions occupy three different sites: 9, 11, and 15 are at sites I, I′, and II, respectively. In the structure of |Cs₂₁Na₅₄|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 2), 21 Cs ⁺ ions per unit cell occupy three equipoints; 4, 6, and 11 are at sites II, IIIa, and IIIb, respectively. The residual 54 Na⁺ ions per unit cell are found at three different sites; 6, 20 and 28 are at sites I, I′, and II, respectively. The degrees of ion exchange are 53 and 28 % for crystals 1and 2, respectively. This result shows that the degree of Cs⁺ exchange decreased sharply by decreasing the initial Cs⁺ concentration and increasing the initial Na⁺ concentration in given ion-exchange solution.     

Synthesis and properties of polybenzoxazole-clay nanocomposites

A novel polybenzoxazole (PBO)/clay nanocomposite has been prepared from a PBO precursor, polyhydroxyamide (PHA) and an organoclay. The PBO precursor was made by the low temperature polycondensation reaction between isophthaloyl chloride (IC) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane with an inherent viscosity of 0.5 dl/g. The organoclay was formed by a cation exchange reaction between a Na⁺-montorillonite (Na⁺-Mont) clay and an ammonium salt of dodecylamine. The PHA/clay was subsequently thermal cured to PBO/clay. Both X-ray diffraction and transmission electron microscope analyzes showed that the organoclay was dispersed in the PBO matrix in a nanometer scale. The in-plane coefficient of thermal expansion (CTE) of PBO/clay film decreased with increasing amounts of organoclay. The CTE of PBO/clay film containing 7 wt% clay was decreased by 21% compared to the pure PBO film. Both of the glass transition temperature (T_g) and the thermal decomposition temperature of PBO/clay increased with increasing amounts of organoclay. The thermal decomposition temperature and the T_g of PBO/clay containing 7 wt% clay increased to 12 and 16 °C, respectively.     

Influence of inorganic salt on morphology,particle size,and luminescence properties of lanthanide ions doped Na0.5Gd0.5MoO4 microcrystals

A variety of tetragonal Na_0.5Gd_0.5MoO₄ microcrystals with different morphologies, dimensions, side lengths, and heights (microplates, tetragonal, and quasi-cubic structures) have been synthesized by a novel inorganic salt assisted hydrothermal approach. The influence of the addition of inorganic salt NaNO₃ on the phase structure, morphology, particle size, and luminescence performance of the samples has been systematically studied for the first time. A series of Na_0.5Gd_0.5MoO₄:Ln³⁺ (Ln = Eu, Tb, Dy, Sm, Yb/Er, Yb/Tm, Yb/Ho) phosphors with excellent down-conversion or up-conversion luminescence properties have been synthesized by doping proper rare earth activator ions into the host matrix. The addition of inorganic salt NaNO₃ and the calcination process can greatly improve the luminescence performances of the phosphors, which can be ascribed to the decrease of surface area and enhanced crystallinity of the Na_0.5Gd_0.5MoO₄ crystals. The as-obtained down-conversion and up-conversion multicolor luminescent materials show the intense characteristic emissions of Ln³⁺ and eminent thermal stability. Moreover, the corresponding LED devices fabricated by the phosphors display dazzling multicolor emissions, which directly verifies that the as-synthesized phosphors may have the prospect to be utilized in the field of optoelectronic devices and LEDs.     

Surface strengthening of building tiles by ion exchange with adding molten salt of KOH

The surface strengthening by ion exchange technology was used to improve the strength of thin building tiles. The effects of exchange time, exchange temperature, and content of KOH additive on strengthening of building tiles were investigated by analyzing the flexural strength and distribution of K⁺ in the samples. The results showed that the addition of .3 mol% KOH to the molten salt of industrial KNO₃ at 450°C for 5 h resulted in a maximum flexural strength of 86.53 MPa, which was 50.3% higher than that of the sample without ion exchange and 8.9% higher than without KOH addition. After ion exchange, the concentration of K⁺ ion in cross-section of the sample decreased with increasing distance from the sample surface, and the diffusion coefficient changed with the change of the content of KOH additive in the molten salt, increasing the diffusion coefficient of K⁺ ion from .93 × 10⁻¹⁵ to 1.8 × 10^–15 m²/s by adding .3 mol% KOH.     

Chemical Strengthening of Soda Lime Silicate Float Glass: Effect of Small Differences in the KNO3 Bath

Six slightly different KNO₃ baths were considered in this work, for the chemical strengthening of soda lime silicate glass. Five of these were commercially available pure KNO₃ salts for industrial or laboratory use and one was a salt from an unknown source that had been already used for at least 1000 h in Na–K ion exchange. Various amounts of sodium — the main impurity — calcium, and magnesium were measured in the six salts together with other more limited contaminants. Different strengthening effects associated with clearly dissimilar ion exchange efficiency were measured on glass treated in the different melts. The presence of Na — major impurity — in the salt was revealed to be not a critical aspect, at least up to concentration of about 0.5 wt%. Instead, the “blocking” effect caused by the presence of Ca and Mg in the KNO₃ bath (also in amounts of few tens of ppm) is shown to be a major issue.     

Clinoptilolites for nitrogen/methane separation

Clinoptilolites, naturally occurring zeolites, currently used by nuclear industry for ion exchange and drying, were evaluated for the nitrogen/methane separation. Ion exchange of purified clinoptilolite was carried out individually with the cations Na⁺, Mg²⁺, Ca²⁺, K⁺ and H⁺, and the adsorption isotherms and diffusion rates were measured. Purified and Mg-clinoptilolite show potential for nitrogen/methane separation and high-pressure adsorption isotherms were measured in a differential absorption bed. Pressure swing adsorption simulations were performed for purified clinoptilolite, Mg-clinoptilolite and the commercial sorbent ETS-4. Purified clinoptilolite shows slightly higher recovery and lower productivity than ETS-4 for similar product purity (∼95%). Mixed ion-exchanged clinoptilolites of Mg/Ca cations, K/Na cations and Mg/Na cations were also prepared and studied for the nitrogen/methane separation. Mg/Na (50/50) mixed ion-exchanged clinoptilolite exhibits very good equilibrium and kinetic selectivity in the low-pressure range, better than purified clinoptilolite. Mixed-exchange clinoptilolites were also found to show a wide range of adsorption characteristics with varying ratios of cation exchange, thereby making them suitable for further improvements in nitrogen/methane separation.     

Phytoglobin Expression Alters the Na+/K+ Balance and Antioxidant Responses in Soybean Plants Exposed to Na2SO4

Soybean (Glycine max) is an economically important crop which is very susceptible to salt stress. Tolerance to Na₂SO₄ stress was evaluated in soybean plants overexpressing or suppressing the phytoglobin GmPgb1. Salt stress depressed several gas exchange parameters, including the photosynthetic rate, caused leaf damage, and reduced the water content and dry weights. Lower expression of respiratory burst oxidase homologs (RBOHB and D), as well as enhanced antioxidant activity, resulting from GmPgb1 overexpression, limited ROS-induced damage in salt-stressed leaf tissue. The leaves also exhibited higher activities of the H₂O₂-quenching enzymes, catalase (CAT) and ascorbate peroxidase (APX), as well as enhanced levels of ascorbic acid. Relative to WT and GmPgb1-suppressing plants, overexpression of GmPgb1 attenuated the accumulation of foliar Na⁺ and exhibited a lower Na⁺/K⁺ ratio. These changes were attributed to the induction of the Na⁺ efflux transporter SALT OVERLY SENSITIVE 1 (SOS1) limiting Na⁺ intake and transport and the inward rectifying K⁺ channel POTASSIUM TRANSPORTER 1 (AKT1) required for the maintenance of the Na⁺/K⁺ balance.     

Melt-compounded salt-containing poly(ethylene oxide)/clay nanocomposites for polymer electrolyte membranes

The present study demonstrates the use of a simple and versatile melt-compounding route to prepare NaClO₄-containing poly(ethylene oxide) PEO/clay nanocomposites combining excellent mechanical properties with a competitive level of the ionic conductivity. The nanostructure and the resulting thermal, mechanical and conductive properties of the salt-containing PEO/clay nanocomposites were found to be highly sensitive to the clay type, i.e. aspect ratio of the clay, to the presence of an organic modifier in the intergallery spacing, and to the salt concentration. The highest increase of the shear storage modulus is obtained in the presence of single silicate layers, thus an exfoliated nanostructure, having a high aspect ratio. These structures are only obtained with an (polar) organically modified clay (Cloisite 30B), regardless of the presence of salt. The use of non-organically modified clays (Cloisite Na⁺ and Laponite) resulted in intercalated nanocomposites, with only a minor improvement in stiffness. A strong interaction between the Na⁺ from NaClO₄ and the Cloisite 30B silicate layers might be responsible for an increased PEO crystallinity and resultant additional increase in stiffness. A mechanism is proposed whereby the Na⁺ ions are drawn away from the PEO phase, to be complexed by the silicate layers, or even ion-exchanged with modifier cations. The addition of clay did not greatly affect the ion conductivity below the melt temperature of PEO. At higher temperatures, the nanocomposites displayed only slightly lower conductivities compared to the PEO/NaClO₄ complex, due to the presence of the clay platelets.     

Cuprous delafossites,Cu3(MFeSb)O6 (M = Na,Li) with honeycomb arrays,realized by topochemical ion-exchange reactions

The current work describes the synthesis, structure, magnetic and optical properties of Cu¹⁺ based delafossite oxides, Cu₃(MFeSb)O₆ (M = Na, Li) synthesized by the topotactic ion-exchange reactions (around 400 °C) of CuCl with Na₄FeSbO₆ and Na₃LiFeSbO₆ in an inert argon atmosphere. The synthetic procedure is significant as the oxides could not be synthesized by the solid state methods. Chemical analysis coupled with energy dispersive spectral analysis confirmed the extent of replacement of Na⁺ ions by Cu⁺ ions. A complete exchange of alkali metal ion, Na⁺ by Cu¹⁺ in the interlayers of these honeycomb oxides has been achieved using a ratio of 1:3 between Na₄FeSbO₆ and CuCl. An additional exchange of approximately 70 % Na⁺ ions from the honeycomb arrays is possible by varying the ratio to 1:4. Rietveld refinements (space group C2/c) of the powder X-ray diffraction data have been carried out to ascertain the phase purity and to verify the structure formed by edge shared honeycomb arrays separated by Cu¹⁺ in dumbbell configuration (O–Cu¹⁺-O). X-ray photoelectron spectroscopy analysis confirmed the oxidation states of the constituent ions, specifically copper as Cu¹⁺. A similar method is adopted to synthesize Cu₃(LiFeSb)O₆ by reacting Na₃(LiFeSb)O₆ and CuCl in the ratio 1:3 at 400 °C. These new delafossite oxides, Cu₃(MFeSb)O₆ (M = Na, Li) and Cu₃((Cu_0.7Na_0.3)FeSb)O_6, exhibit interesting magnetic properties which are significantly different from the rock salt based parent sodium analogs. Dominant antiferromagnetic interactions with a specific ordering temperature have been observed for these samples containing Fe³⁺ (d⁵) ions in the honeycomb. UV–visible diffuse reflectance measurements indicated the decrease in the band gap of Cu¹⁺ based oxides. This study highlights the importance of low temperature ion-exchange reactions as an effective route to stabilize multifunctional materials of potential importance for various applications.     

Ion Exchange in Molten Salts. II: The Occlusion of Lithium,Sodium, Potassium and Silver Nitrates in the Respective Forms of Zeolite A.

The occlusion of lithium, sodium, potassium and silver nitrates from the anhydrous melts in the respective zeolites has been studied by measuring the gain in weight and by direct analysis. The results in moles of occluded nitrate per formula weight of zeolite M₁₂^I[(AlO₂)₁₂(SiO₂)₁₂] are 11.7 for LiNO₃, 10 for NaNO₃ and 10 for AgNO₃ and essentially zero for KNO₃. A model is proposed for the structure of the occlusion compound Na₂₂[(AlO₂)₁₂(SiO₂)₁₂(NO₃)₁₀], in terms of four Na_I⁺ ions and four [Na_I - NO₃ - Na]⁺ groups at the apexes of the cubic unit cell and four [Na_II - NO₃ - Na]^+1/3 groups coordinated with two [NaNO₃]^?2/3 groups at the faces, to explain the properties of the occluded zeolites.     

Rapid and phase pure synthesis of microporous copper silicate (CuSH–1Na) with 12-ring channel system

Phase pure sample of the microporous copper silicate CuSH–1Na has been obtained by simplified hydrothermal method without using additives (H₂O₂ and Na₂HPO₄). Ion exchange of Na⁺ by Cs⁺, Ca²⁺ and Sr²⁺ ions showed that the structure can suffer partial replacement of the charge compensating cations. Ion exchange with Cs⁺ resulted in distinct dehydration while the ion exchange with Sr²⁺ increased the total amount of water. Water content in the Ca-exchanged sample is comparable to the as-synthesized sodium phase. Raman spectroscopy revealed that the divalent cations as Ca²⁺ and Sr²⁺ induce stronger local structural deformations than the monovalent Cs⁺. These structural changes have been also followed by the refined lattice distortions. Magnetic analyses showed that CuSH–1Na presents a very weak ferromagnetic interaction along the Cu²⁺ chains with a nearly vanishing Curie–Weiss temperature. This magnetic coupling is associated with super-super-exchange interactions through Cu–Na–O–Na–Cu paths. Antiferromagnetic coupling, attributed to inter-chains super-super-exchange interactions, competes with the ferromagnetic one and prevails at the lowest temperature.     

Solubility of Na2SO4, Na2CO3 and their mixture in supercritical water

The solubility of many salts in water decreases dramatically with temperature in the vicinity of the critical point of pure water. Examples of these salts are sulfates of sodium, potassium, lithium and sodium carbonate. These salts are usually produced during supercritical water oxidation (SCWO) and contribute to fouling. The solubility of Na₂CO₃ and Na₂SO₄ has been determined in pure form and in the presence of each other, for the temperature range relevant to SCWO. The experimental procedure was to pass the salt solution through a tube at constant temperature. After a brief initiation period during which no salt sticks to the tube, the salt above the solubility limit deposited on the tube surface. The solution leaving the section was thus at the solubility limit. A rapid decrease in the salt solubility was observed just above the pseudo-critical temperature. For supercritical conditions, the solubility of each salt in the form of a mixture was quite close to the solubility of pure salt. At the highest fluid density considered (480 kg/m³) the presence of Na₂CO₃ reduces the solubility of Na₂SO₄, as might be expected from the “common-ion effect”.