Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Potassium Vanadates of Mixed Valence as Sulfuric Acid Catalyst Precursors

The kinetics of hydrolytic precipitation of potassium vanadates K_xV₁₂O_31-δ ·nH₂O(0 < x ≤ 2.25; 0 <δ ≤ 1.15) from a KVO₃ solution at pH = 1.7 and 80°C in the presence of K₂SO₄ and VOSO₄ is controlled by second and third order reactions respectively occurring on the precipitate surface. This difference is due to the effect of VO²⁺ ions on the polymer anion [V₁₂ O_31-δ]ⁿ formation. Potassium vanadates K_xV₁₂O_31-δ ·nH₂O and K_xV₃O_8-δ·nH₂O (1.02 ≤ x ≤ 1.91; 0 ≤ δ ≤ 0.22) can be used as vanadium-containing precursors for sulfuric acid catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of oxygen nonstoichiometry on kinetics of oxygen exchange and diffusion in lanthanum-strontium cobaltites

The method of isotopic exchange was used to study the kinetics of oxygen exchange and diffusion in complex oxides of La_{1 − x} Sr _x Co_{1 − y} Fe _y O_{3 − δ} (x = 0.0, y = 0.0; x = 0.6, y = 0.2, 0.4). The rates of oxygen interfacial exchange and its diffusion coefficient were determined for LaCoO_{3 − δ} at the pressure of 5 torr in the temperature range of 600–850°C and at the temperature of 700°C in the pressure range of 1–70 torr. The contributions of the three exchange types were calculated. The order of the dependence of the interfacial exchange rate on the oxygen pressure was 0.51 ± 0.01. In the case of La_0.4Sr_0.6Co_{1 − y} Fe _y O_{3 − δ} (y = 0.2, 0.4) in the temperature range of 600–900°C at the oxygen pressure of 10 torr, the oxygen exchange rates and diffusion coefficients were determined in the material bulk and in the subsurface region; contributions of the three types of exchange were calculated. The paper considers the mechanism of oxygen exchange and diffusion as compared to nonstoichiometry in the oxygen sublattice of the La_{1 − x} Sr _x Co_{1 − y} Fe _y O_{3 − δ} oxides.     

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of Ln1 ? xSrxGa0.5 ? y/2Al0.5 ? y/2MgyO3 ? δ (Ln = La, Pr, Nd; x, y = 0.10, 0.15)

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of samples of Ln_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} (Ln = La, Pr, Nd; x, y = 0.10, 0.15) synthesized by a ceramic methods are studied. Methods of x-ray diffraction analysis and scanning electron microscopy reveal the La-containing samples to be homogeneous and have a perovskite structure. Magnesium does not dissolve in Pr-and Nd-containing systems but forms an individual phase based on magnesium oxide. Apart from magnesium oxide, in these systems there form extrinsic phases, specifically, LnSrGa₃O₇ and an unknown phase. The electroconductivity of La_{1 − x} Sr_xGa_{1 − y} Mg_yO_{3 − δ} decreases after substituting Al for Ga. Ceramic La_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_3−δ is a purely ionic conductor in the temperature interval 500 to 1000°C; Nd_xSr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} has predominantly ionic conduction; and the predominant type of conduction in Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} is electronic below 700–800°C, with the contribution of ionic conduction increasing at higher temperatures. Substituting Al for Ga raises the hardness of ceramics under study. Among the compositions studied, La_0.85Sr_0.15Ga_0.45Al_0.45Mg_0.10O_{3 − δ} and La_0.85Sr_0.15Ga_0.425Al_0.425Mg_0.15O_{3 − δ} exhibit a combination of electroconductivity and hardness that is optimal for application as electrolyte at reduced temperatures (600–800°C). The Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} system possesses mixed ionic-electronic conduction and high hardness, which makes it appealing for application as oxygen-penetrable membranes. Original Russian Text ? Yu.V. Danilov, A.D. Neuimin, L.A. Dunyushkina, L.A. Kuz’mina, N.S. Zybko, Z.S. Martem’yanova, A.A. Pankratov, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 1, pp. 57–65.     

Thermoelectric power and electrochemical studies on CdI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

A quaternary super-ion-conducting system, 20CdI₂ − 80[xAg₂O − y(0.7V₂O₅ − 0.3B₂O₃)] where 1 ≤ x/y ≤ 3, has been prepared by melt quenching technique. The electrical conductivity measured was the order of 10⁻⁴  S/cm at room temperature. The values of silver-ion transport number obtained by electromotive force technique are nearly unity. The thermoelectric power and electrochemical studies were done on the CdI₂–Ag₂O–V₂O₅–B₂O₃ system. The discharge and polarization characteristics were examined for different cathodes to evaluate the utility of these cells as power sources for low energy applications.     

Oxygen nonstoichiometry and the thermodynamic properties of manganites Ca1 ? x ? ySrxLayMnO3 ? δ

The content of oxygen in Ca_{0.6 − y} Sr_0.4La _y MnO_{3 − δ}, where y = 0 and 0.05, was determined by coulometric titration over the temperature range 650–950°C at oxygen partial pressure in the gas phase varied from 10⁻⁴ to 1 atm. The results were used to calculate the partial molar enthalpy, Δ$ \bar H $ \bar H _O(δ), and entropy, Δ$ \bar S $ \bar S _O(δ), of oxygen in manganites. Changes in the Δ$ \bar H $ \bar H _O(δ) and Δ$ \bar S $ \bar S _O(δ) dependences caused by the introduction of lanthanum are evidence of the formation of local clusters of the double perovskite type in the Ca_0.6Sr_0.4MnO_{3 − δ} matrix.     

Solubility of neptunium oxide in the KURT (KAERI Underground Research Tunnel) groundwater

The solubilities of NpO₂(s) in the KURT (KAERI Underground Research Tunnel) granitic groundwater with low ionic strength were measured experimentally and calculated by a geochemical code. Then these results were compared with each other as well as with foreign results. The concentrations of neptunium were measured as 6·10⁻⁸−2·10⁻⁸ mol/L at a pH = 9.5–11.1 and Eh = −0.2 V, and less than 5·10⁻⁹ mol/L at a pH = 11.8–13.0 and Eh = −0.3–0.44 V. The dominant aqueous species were presumed as Np(OH)_x(CO₃)_y ^4−x−2y complexes and Np(OH)₄(aq) at pH = 9.5–13 under the Eh<−0.2 V reducing condition.     

Regions of stability of variable-composition perovskite phases La1?xSrxMn1?yMyO3 (M = Ti, Ni)

The formation of the orthorhombic solid solution series LaMn_1−y Ti _y O₃ with 0.0 ≤ y ≤ 0.15 and LaMn_1−y Ni _y O₃ with 0.0 ≤ y ≤ 0.4 was observed. The stability boundaries of the La_1−x Sr _x Mn_1−y M _y O₃ (M = Ti, Ni) perovskite phases were determined. Fragments of isobaric-isothermal sections of the phase diagrams of the La₂O₃-SrO-Mn₃O₄-TiO₂ and La₂O₃-SrO-Mn₃O₄-NiO systems in air at 1100°C were suggested. Original Russian Text ? E.A. Filonova, A.N. Demina, A.N. Petrov, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 10, pp. 1787–1790.     

Mixed conductivity and stability of A-site-deficient Sr(Fe,Ti)O<Subscript>3–δ</Subscript> perovskites

Deficiency in the A sublattice of perovskite-type Sr_{1– y} Fe_0.8Ti_0.2O_3–δ (y=0–0.06) leads to suppression of oxygen-vacancy ordering and to increasing oxygen ionic conductivity, unit cell volume, thermal expansion, and stability in CO₂-containing atmospheres. The total electrical conductivity, predominantly p-type electronic in air, decreases with increasing A-site deficiency at 300–700 K and is essentially independent of the cation vacancy concentration at higher temperatures. Oxygen ion transference numbers for Sr_{1– y} Fe_0.8Ti_0.2O_3–δ in air, estimated from the faradaic efficiency and oxygen permeation data, vary in the range from 0.002 to 0.015 at 1073–1223 K, increasing with temperature. The maximum ionic conductivity was observed for Sr_0.97Fe_0.8Ti_0.2O_3–δ ceramics. In the system Sr_0.97Fe_{1– x} Ti _x O_3–δ (x=0.1–0.6), thermal expansion and electron-hole conductivity both decrease with x. Moderate additions of titanium (up to 20%) in Sr_0.97(Fe,Ti)O_3–δ result in higher ionic conductivity and lower activation energy for ionic transport, owing to disordering in the oxygen sublattice; further doping decreases the ionic conduction. It was shown that time degradation of the oxygen permeability, characteristic of Sr(Fe,Ti)O_3–δ membranes and resulting from partial ordering processes, can be reduced by cycling of the oxygen pressure at the membrane permeate side. Thermal expansion coefficients of Sr_{1– y} Ti_{1– x} Fe _x O_3–δ (x=0.10–0.60, y=0–0.06) in air are in the range (11.7–16.5)×10^–6 K^–1 at 350–750 K and (16.6–31.1)×10^–6 K^–1 at 750–1050 K. Electronic Publication     

Physicochemical properties and catalytic performance of Pr2 − x SrxCoO4 ± y mixed oxides for NO reduction by CO

Using the polyglycol gel method, a series of Pr_{2 − x} Sr_xCoO_{4 ± y} (0.2 ≤ x ≤ 1.0) mixed oxides were prepared, and their catalytic activities were studied in the test reaction of NO reduction by CO. The solid-state physicochemical properties, including crystal structure, defect structure, IR spectrum, valence state of B-site ions, nonstoichiometry oxygen (y), oxygen species, and redox properties, were characterized by means of XRD, IR, TPD, TPR, XPS, and chemical analysis. The results show that all mixed oxides display a K₂NiF₄ structure. When x = 0.2 and 1.0, the obtained samples still have little uncertain mixed oxides; however, the mixed oxides (x = 0.4, 0.6, 0.8) all represent a single A₂BO₄ phase. With the increase of x, lattice parameters, unit-cell volume, and average crystalline size decrease gradually, whereas microstrain density, the concentration of Co³⁺, the amounts of lattice oxygen released and the concentration of oxygen vacancy increase. The catalytic activities of Pr_{2 − x} Sr_xCoO_{4 ± y} catalysts for NO reduction by CO are closely correlated with oxygen vacancy and the concentration of Co³⁺. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 3, pp. 431–437. The text was submitted by the authors in English.     

Synthesis and photocatalytic activity of Ti[1 ? x]VxO[2 ? y]Cy whiskers in hydroquinone oxidation in aqueous solutions

Ti_1−x V _x O_2−y C _y (0 ≤ x ≤ 0.10 and x = 0.50) whiskers having the anatase structure were synthesized via thermolysis of vanadium-doped titanium glycolate of composition Ti_1−x V _x (OCH₂CH₂O)₂ (0 ≤ x ≤ 0.10 and x = 0.50). The starting reagents used to prepare Ti_1−x V _x (OCH₂CH₂O)₂ were mixtures of coprecipitated titanium and vanadyl hydroxides, which were heated in ethylene glycol at T ≤ 200°C: (1 − x)TiO(OH)₂ + xVO(OH)₂ + 2HOCH₂CH₂OH = Ti_1−x V _x (OCH₂CH₂O)₂ + 3H₂O↑. Thermolysis of vanadium-doped titanium glycolate in various gas media over a wide range of temperatures is useful to prepare titania samples doped with both vanadium and carbon to form a phase of the general composition Ti_{1 − x} V _x O_{2 − y} C _y whiskers prepared by thermolyzing Ti_{1 − x} V _x (OCH₂CH₂O)₂ in air at 450°C were found to have a high photocatalytic activity in hydroquinone oxidation in aqueous solutions irradiated in the UV spectral range; the photocatalyst’s activity increases with increasing vanadium concentration. When hydroquinone was irradiated in the blue, the maximal catalytic activity was discovered in a sample of composition Ti_0.50V_0.50O_2−y C _y . Quantum-chemical calculations support experimental data that the double doping of titania (Ti_1−x V _x O_2−y C _y ) enhances its photocatalytic activity compared to undoped anatase or anatase doped in one sublattice: Ti_1−x V _x O₂ and TiO_2−y C _y .     

Existence region, structure, and properties of YBa(Cu1? x Fe x )2O5+δ and (Y1? y Ba y )2 CuFeO5+δ solid solutions

We study the effect of Y³⁺ ↔ Ba²⁺ and Cu²⁺ ↔ Fe³⁺ substitutions on the structure, thermal expansion, electrical conductivity, and thermal e.m.f. of layered ferrocuprate YBaCuFeO_{5 + δ} · YBa(Cu_1−x Fe _x )₂O_{5 + δ} solid solutions with 0.45≤x≤0.55 are formed. The unit cell parameters, thermal expansivity, and oxygen nonstoichiometry index of the YBaCuFeO_{5 +δ} phase (δ) are almost independent of variations in the cationic composition of this phase. The electrical conductivity of layered yttrium barium ferrocuprate increases, whereas the activation energy of conductivity decreases in response to Ba²⁺ → Y³⁺ and Cu²⁺ → Fe³⁺ substitutions (with increasing copper(III) proportion in samples). The thermal e.m.f. of ceramics decreases when composition deviates from the cationic stoichiometry (YBaCuFeO_{5 +δ}). Original Russian Text ? A.I. Klyndyuk, E.A. Chizhova, V.M. Kononovich, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1672–1676.     

Physicochemical properties of non-stoichiometric oxides

One of the most important challenges with solid oxide fuel cells (SOFC) is to find cathode materials with high enough catalytic activity for the dissociation of the molecular oxygen. Oxide mixed conductors with the perovskite structure (ABO₃) and high Co content in the B site have been extensively studied to be used as cathode in SOFC. This is the second part of a review of high temperature properties of two mixed conductors systems. The first part was focused on the n = 2 Sr₃FeMO_6+δ (M = Fe, Co, Ni) Rudlesdden Popper phases, while in this paper we discuss the thermodynamic and transport properties of the perovskite solid solution Sr_1−x La _x Fe_0.2Co_0.8O_3−δ (0 ≤ x ≤ 0.4) in the temperature range 773 ≤ T ≤ 1173 K. In particular, the interest has been focused on the x = 0 sample, which exhibits large ionic conductivity values (σ_i ~1 S cm⁻¹), but suffers a structural transformation from cubic to orthorhombic symmetry because the ordering of the oxygen vacancies when the oxygen partial pressure decreases. Measurements of the oxygen chemical potential ( m_\textO2 \mu_{{{\text{O}}_{2} }} ) as function of oxygen content and temperature, coupled with high temperature X-ray diffraction data, permitted us to broaden the knowledge of the T–δ–p(O₂) phase diagram for the x = 0 sample. In addition, we have investigated the effects of the La incorporation on the stability range of the cubic phases of the Sr_1−x La _x Fe_0.2Co_0.8O_3−δ solid solution.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Crystal structures of La1 ? xSr2 + x(GeO4)(V1 ? xMoxO4) (x= 0?0.4) solid solutions

The phase compositions of theLaVO₄-SrMoO₄(1) and Sr₂GeO₄-SrMoO₄ (2) binary systems, which bound the Sr₂GeO₄-LaVO₄-SrMoO₄ (3) ternary system, and the LaSr₂(VO₄)(GeO₄)-Sr₂GeO₄+SrMoO₄ section (4) of system 3 are studied at subsolidus temperatures. Systems 1 and 2 consist of a mixture of the initial compounds, and the La_{1 − x} Sr_{2 + x} (GeO₄)(V_{1 − x} Mo _x O₄) (where 0 ≤ x ≤ 0.4) region of substitutional solid solutions with a palmierite structure is formed in system 3. The unit cell parameters of the solid solutions are determined. The distribution of the lanthanum and strontium cations over two positions of the cationic sublattice is described. Original Russian Text ? V.D. Zhuravlev, V.G. Zubkov, A.P. Tyutyunnik, Yu.A. Velikodnyi, N.D. Koryakin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 1, pp. 135–137.     

Differential pulse polarographic study of thiamine (vitamin B1) in neutral and acidic aqueous solutions

The differential pulse (dp) polarograms of thiamine in neutral aqueous solutions exhibited six peaks at low depolarizer concentration (⋦10⁻⁴ mol dm⁻³) and only three peaks at concentrations ≥10⁻³ mol dm⁻³. Only one of these was found to correspond to the diffusion-controlled reduction of this compound at the dme and this was shown to be an irreversible two-electron process. The kinetic parameters derived from the dp polarograms were found to be in good agreement with those calculated from classical polarograms and were:E _1/2=−1·261 Vvs SCE,an _a=0·54 andD≈3·5×10⁻⁶ cm² sec⁻¹ for 10⁻³ mol dm⁻³ thiamine in 0·1 mol dm⁻³ acetate buffer (pH 6·5). The reduction product has been identified as dihydrothiamine. The effect of pH on the dpp of thiamine was studied in the pH range 0–7. In the pH region 5·5 to 7·0 only one peak attributable to the B₁ ⁺ form of thiamine is present. In the pH region 3·5–5·5 another dpp peak attributable to the protonated form (B₁H²⁺) of thiamine was also observed. At pHs less than 3 only one peak was observed which could be attributed to the doubly protonated form (B₁ H₂ ³⁺) of thiamine. Surfactants like triton-X-100 and CTABr were found to inhibit the electroreduction of thiamine due to the strong adsorption of these compounds on the dme. Thiamine itself was found to have an inhibitory effect on its own electroreduction, although to a smaller extent.     

Hydrolytic precipitation of calcium polyvanadates from vanadium(IV) and vanadium(V) solutions

The effect of VO²⁺ ions on the composition and kinetics of calcium polyvanadate precipitation from solutions with 1.5 ≤ pH ≤ 9 at 80–90°C has been studied. For 1,5 ≤ pH < 3 and V⁴⁺/V⁵⁺ = 0.11–9, the precipitated compounds have the general formula Ca _x V _y ⁴⁺ V _12?y ⁵⁺ O_31?δ · nH₂O (0.8 ≤ x ≤ 1.06, 2 ≤ y ≤ 3, 0.94 ≤ δ ≤ 1.5). The maximum vanadium(IV) proportion (y = 3) in the precipitates is achieved when V⁴⁺/V⁵⁺ = 0.5?1.0 in the solution and pH is 3. Polyvanadate precipitation at pH 1.7 has a long induction period (up to 30 min), which is not observed for V⁴⁺/V⁵⁺ > 0.1. Precipitation in solutions with pH 3 occurs only when VO²⁺ ions are added, with a maximum rate near V⁴⁺/V⁵⁺ = 0.2 and in presence of chloride ions. The processes are controlled by a secondorder reaction on the polyvanadate surface.     

Synthesis and thermolysis of substitutional solid solutions (Cu1?yMy)2(OH)PO4·xH2O (x = 0.1?0.2; M = Zn, Co, Ni)

Substitutional solid solutions (Cu_1−y Zn _y )₂(OH)PO₄·xH₂O (0 ≤ y ⩽ 0.26, x = 0.1−0.2), (Cu_1−y Co _y )₂(OH)PO₄·xH₂O (0 ≤ y ≤ 0.10, x = 0.1−0.2), and (Cu_1−y Ni _y )₂(OH)PO₄·xH₂O (0 ≤ y ≤ 0.08, x = 0.1−0.2) were synthesized. The unit cell parameters of the resulting phosphates were determined, and their IR absorption spectra were measured. The reactants were H3PO4 and mixtures of hydrous carbonates of the appropriate metals. Thermolysis of the solid solutions was examined with (Cu_1−y Co _y )₂(OH)PO₄·xH₂O (0 ≤ y ≤ 0.10, x = 0.1−0.2) as an example.     

Synthesis, characterization, and electrical conductivity of new Aurivillius-type oxide-ion conductor

A new oxide-ion conductor of Aurivillius family with a general formula Bi₂Al _x V_{1 − x} O_{5.5 − x − δ}; 0 ≤ x ≤ 0.20 (BIALVOX) was synthesized by the sol-gel citrate route. Powder X-ray diffraction and simultaneous thermogravimetric and differential thermal analyses confirmed that the calcination of BIALVOX xerogels is fully completed at around 500°C after three hours of thermal treatment. It has been found that the β-orthorhombic phase is stabilized with compositions x ≤ 0.07, whereas the stabilization of the γ′-phase takes place for x ≥ 0.10. AC impedance spectroscopic investigation suggested that the charge accumulation at grain boundaries is thermally activated process. However, the maximum electrical conductivity (7.73 × 10⁻⁵ S cm⁻¹) noticed for BIALVOX.13 at 300°C was attributed to the maximum vacancy concentration in the equatorial planes, responsible for the ion diffusion through the structure. This has been further evidenced by the temperature dependence of dielectric permittivity.     

Volume and compressibility effects in the formation of metal-EDTA complexes

We used precise measurements of ultrasonic velocity and density to study the complexation of ethylendiaminetetraacetic acid (EDTA) with Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ at 25‡C and pH 12. From these measurements we obtained the changes in the molar concentration increment of the ultrasonic velocity δA, the apparent molar adiabatic compressibility δK_sΦ, and the apparent molar volume δV_Φ of complex formation. The hydration contributions δ(AV_h) to the volume effect of binding range from 39.6 to 46.6 cm³-mol^-1 while the hydration contribution to the adiabatic compressibility change in the binding, δ(δK_h), ranges from 103.9X 10^-4 to 131.1 X 10^-4 cm³-mol^-1-bar^-1. These data are interpreted in terms of dehydration of interacting molecules,i.e., transfer of water molecules from the hydration shells of cations and EDTA into the bulk water. The ratio δ(δV_h)/ δ(δV_h) is in the range 0.35 to 0.38 bar, indicating a dominant contribution from the dehydration of charged atomic groups in the volume and the compressibility effects of complex formation.