Magnetic and optical investigation of 40SiO2·30Na2O·1Al2O3·(29 − x)B2O3·xFe2O3 glass matrix

Samples of 40SiO₂·30Na₂O·1Al₂O₃·(29 − x)B₂O₃·xFe₂O₃ (mol%), with 0.0 ≤ x ≤ 17.5, were prepared by the fusion method and investigated by electron paramagnetic resonance (EPR), optical absorption (OA) and Mössbauer spectroscopy (MS). The EPR spectra of the as-synthesized samples exhibit two well-defined EPR signals around g = 4.27 and g = 2.01 and a visible EPR shoulder around g = 6.4, assigned to isolated Fe³⁺ ion complexes (g = 4.27 and g = 6.4) and Fe³⁺-based clusters (g = 2.01). Analyses of both EPR line intensity and line width support the model picture of Fe³⁺-based clusters built in from two sources of isolated ions, namely Fe²⁺ and Fe³⁺; the ferrous ion being used to build in iron-based clusters at lower x-content (below about x = 2.5%) whereas the ferric ion is used to build in iron-based clusters at higher x-content (above about x = 2.5%). The presence of Fe²⁺ ions incorporated within the glass template is supported by OA data with a strong band around 1100 nm due to the spin-allowed ⁵E_g–⁵T_2g transition in an octahedral coordination with oxygen. Additionally, Mössbauer data (isomer shift and quadrupole splitting) confirm incorporation of both Fe²⁺ and Fe³⁺ ions within the template, more likely in tetrahedral-like environments. We hypothesize that ferrous ions are incorporated within the glass template as FeO₄ complex resulting from replacing silicon in non-bridging oxygen (SiO₃O⁻) sites whereas ferric ions are incorporated as FeO₄ complex resulting from replacing silicon in bridging-like oxygen silicate groups (SiO₄).     

Synthesis,thermal behaviour and crystal structure of RbSrP3O9·3 H2O

Rubidium strontium cyclo-triphosphate trihydrate, RbSrP₃O₉·3 H₂O, was synthesized by reaction between cyclo-triphosphoric acid H₃P₃O₉ and rubidium and strontium carbonates. It crystallizes in the othorhombic system, space group Pnma, with a = 9.120(1) Å, b = 8.141(1) Å, c = 15.234(1) Å, V = 1 131.1(3) Å³, Z = 4. Crystal structure determination from single crystal data collected at 300 K shows that the P₃O₉ groups exhibit C_s symmetry and are not connected to each other. Rubidium (distorted octahedron) and strontium (distorted square antiprism) are coordinated by oxygen and water molecules yielding the formation of infinite chains interconnected to each other and to the P₃O₉ groups. The IR valence vibration bands of the P₃O₉ cycle have been identified in the domain 1 400–650 cm^–1 and related to the structural results. After water loss, the anhydrous phase crystallizes from an intermediate amorphous phase and further decomposes into Rb₂SrP₄O₁₂ and SrP₂O₆.     

Thermodynamics of formation of double salts M2SO4 · M′SO4 · 6H2O and M2SeO4 · M′SeO4 · 6H2O where M denotes Rb,or Cs and M′ denote Co,Ni, or Zn

This paper describes a chemical model that calculates (solid + liquid) equilibria in the (m₁Rb₂SO₄ + m₂CoSO₄)(aq), (m₁Rb₂SeO₄ + m₂CoSeO₄)(aq), (m₁Rb₂SO₄ + m₂NiSO₄)(aq), (m₁Rb₂SO₄ + m₂ZnSO₄)(aq), (m₁Rb₂SeO₄ + m₂ZnSeO₄)(aq), (m₁Cs₂SO₄ + m₂CoSO₄)(aq), (m₁Cs₂SeO₄ + m₂CoSeO₄)(aq), (m₁Cs₂SO₄ + m₂NiSO₄)(aq), (m₁Cs₂SeO₄ + m₂NiSeO₄)(aq), (m₁Cs₂SO₄ + m₂ZnSO₄)(aq), and (m₁Cs₂SeO₄ + m₂ZnSeO₄)(aq) systems, where m denotes molality at the temperature T=298.15 K. The Pitzer ion-interaction model has been used for thermodynamic analysis of the experimental osmotic and solubility data presented in the literature. The thermodynamic functions needed (binary and ternary parameters of ionic interaction, thermodynamic solubility products) have been calculated and the theoretical solubility isotherm has been plotted. The mixing parameters {θ(MN) and ψ(MNX)} have been chosen on the basis of the compositions of saturated ternary solutions and data on the binary solubility of the sulfate M₂SO₄. M^′SO₄ · 6H₂O double salts in water. To validate the mixing solutions model two different approaches have been used in evaluation of the ternary parameters: (I) preserving the same value of the binary mixing θ(MN) for the corresponding chloride, bromide, sulfate, and selenate systems with the same cations, and (II) with constant θ(MN) value (set equal to −0.05) for the all 11 sulfate and selenate systems. Very good agreement between experimentally determined and model predicted solubilities has been found. Important thermodynamic characteristics (thermodynamic solubility products, standard molar Gibbs free energy of formation) of the solid phases (simple salts, six sulfate – M₂SO₄ · M^′SO₄ · 6H₂O, and five selenate – M₂SeO₄ · M^′SeO₄ · 6H₂O – double salts) crystallizing in the systems under consideration are determined.     

Synthesis,characterization and thermochemistry of Cs(ASP) · nH2O (n = 0, 1)

New compounds of aspartic acid Cs(ASP) · nH₂O (n = 0, 1) have been synthesized and characterized by XRD, IR and Raman spectroscopy as well as TG. The structural formula of this new compound was Cs(ASP) · nH₂O (n = 0, 1). The enthalpy of solution of Cs(ASP) · nH₂O (n = 0, 1) in water were determined. With the incorporation of the standard molar enthalpies of formation of CsOH(aq) and ASP(s), the standard molar enthalpy of formation of −(1202.9 ± 0.2) kJ · mol⁻¹ of Cs(ASP) and −(1490.7 ± 0.2) kJ · mol⁻¹ of Cs(ASP) · H₂O were obtained.     

209Bi NQR in Mixed Oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3

It was earlier found from nuclear quadrupole resonance (NQR) measurements and computer modeling that -Bi₂O₃, Bi₃O₄Br and mixed oxides Bi₂O₃· 2Al₂O₃, Bi₂O₃· 2Ga₂O₃, Bi₂O₃· 3GeO₂, and 2Bi₂O₃· 3GeO₂exhibit local ordered magnetic fields from 30 to 200 G. It thus follows that these compounds are not diamagnets in a conventional sence of the word. With the aim of revealing previously unknown magnetic properties in bismuth(III) oxide-based Main Group element compounds, the mixed bismuth–boron oxides 2Bi₂O₃· B₂O₃, 3Bi₂O₃· 5B₂O₃, and Bi₂O₃· 3B₂O₃were prepared and studied using ²⁰⁹Bi NQR. The quadrupole interactions of the ²⁰⁹Bi nuclei and their electronic environment were studied, the crystallochemical features of the compounds were discussed, and the conformity of the ²⁰⁹Bi results to the X-ray structure data was verified. The preliminary tests in the field of a permanent magnet showed that the resonance intensities increase in external magnetic fields, indicating that a magnetism of unknown nature develops in the titled compounds. It was found reasonable to continue studies of the magnetic properties of these compounds using single-crystal ²⁰⁹Bi NQR in external magnetic fields.     

(Solid + liquid) equilibria for the ternary system (CsBr + LnBr3 + H2O) (Ln = Pr,Nd, Sm) at T = 298.2 K and atmospheric pressure,thermal and fluorescent properties of Cs2LnBr5·10H2O

The (solid + liquid) phase equilibria of the ternary systems (CsBr + LnBr₃ + H₂O) (Ln = Pr, Nd, Sm) at T = 298.2 K were studied by the isothermal solubility method. The solid phases formed in the systems were determined by the Schreinemakers wet residues technique, and the corresponding phase diagrams were constructed based on the measured data. Each of the phase diagrams, with two invariant points, three univariant curves, and three crystallization regions corresponding to CsBr, Cs₂LnBr₅·10H₂O and LnBr₃·nH₂O (n = 6, 7), respectively, belongs to the same category. The new solid phase compounds Cs₂LnBr₅·10H₂O are incongruently soluble in water, and they were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs₂PrBr₅·10H₂O, Cs₂NdBr₅·10H₂O and Cs₂SmBr₅·10H₂O in water were measured to be (52.49 ± 0.48) kJ · mol⁻¹, (49.64 ± 0.49) kJ · mol⁻¹ and (50.17 ± 0.48) kJ · mol⁻¹ by microcalorimetry under the condition of infinite dilution, respectively, and their standard molar enthalpies of formation were determined as being −(4739.7 ± 1.4) kJ · mol⁻¹, −(4728.4 ± 1.4) kJ · mol⁻¹ and −(4724.4 ± 1.4) kJ · mol⁻¹, respectively. The fluorescence excitation and emission spectra of Cs₂PrBr₅·10H₂O, Cs₂NdBr₅·10H₂O and Cs₂SmBr₅·10H₂O were measured. The results show that the upconversion spectra of the three new solid phase compounds all exhibit a peak at 524 nm when excited at 785 nm.     

Gas-tight proton-conducting Nd2 − xCaxZr2O7 − δ (x = 0, 0.05) ceramics

Journal of Solid State Electrochemistry - Gas-tight Nd2 − xCaxZr2O7 − δ (x = 0, 0.05) pyrochlore materials have been prepared via...     

Thermodynamics of the O2/O2− redox couple in molten (LiCl + KCl + Li2O) systems

Activity coefficients of oxide ion were determined by the measurements of the standard formal potential of O₂/O^2? with a boron-doped diamond (BDD) electrode in molten (LiCl + KCl): LiCl:KCl = {58.5:41.5 (eutectic), 65:35, 70:30, 75:25} mol% at T = (673 to 803) K. The activity coefficient decreases with the increase of the LiCl content in the melt: (18.7 ± 1.5, 7.7 ± 1.0, 4.1 ± 0.4, and 1.6 ± 0.1), respectively, at T = 773 K in each melt. The result is explained by the attractive force between Li⁺ and O^2? which is stronger than that between K⁺ and O^2?.     

Relative permittivity increments for {xCH3OH + (1 − x)CH3OCH2(CH2OCH2)3CH2OCH3} fromT = 283.15 K toT = 323.15 K

Relative permittivities of { CH₃OH  +  CH₃OCH₂(CH₂OCH₂)₃CH₂OCH₃(2,5,8,11,14-pentaoxapentadecane, tegdme)} at temperatures from 283.15 K to 323.15 K and atmospheric pressure, were measured over the whole composition range. Experimental relative permittivities were fitted by a polynomial function in mole fraction. Values of relative permittivity were measured using a HP4284A precision LCR Meter together with the measuring cell HP16452A at 1 MHz. Relative permittivity increments were determined from experimental data and fitted to a variable-degree polynomial function. Different theoretical models were used to predict the permittivity of this mixture. The predictions are better when the volume change on mixing is considered.     

Measurements of the critical parameters for {xNH3 + (1 − x)H2O} with x = (0.9098, 0.7757, 0.6808)

Measurements of the critical parameters for {xNH₃ + (1 ? x)H₂O} with x = (0.9098, 0.7757, 0.6808) were carried out by using a metal-bellows variable volumometer with an optical cell. The expanded uncertainties (k = 2) in temperature, pressure, density, and composition measurements have been estimated to be less than 3.2 mK, 3.2 kPa, 0.3 kg · m^?3, and 8.8 · 10^?4, respectively. In each mole fraction, the critical temperature T_c was first determined on the basis of the intensity of the critical opalescence. The critical pressure p_c and critical density ρ_c were then determined as the point at which the meniscus disappears on the isotherm at T = T_c. The expanded uncertainties (k = 2) in the present critical parameters have also been estimated. Comparisons of the present values with the literature data as well as the calculated values afforded using the equation of state are also presented.     

Saturation molalities and standard molar enthalpies of solution of adenosine(cr), guanosine · 2H2O(cr), inosine(cr), and xanthosine · 2H2O(cr) in H2O(l)

Saturation molalities m(sat) in H₂O(l) have been measured for the substances adenosine(cr), guanosine · 2H₂O(cr), inosine(cr), and xanthosine · 2H₂O(cr) over the temperature range T=287.91 K to T=308.18 K by using h.p.l.c. The indicated states of hydration of these substances were established by performing Karl–Fischer analyses of samples of these substances which had been equilibrated over H₂O(l) and of samples obtained by passing air over the wet crystals (air dried samples). The crystalline phases of these substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Molar enthalpies of solution Δ_solH_m for adenosine(cr) and inosine(cr) were measured by using an isoperibol solution calorimeter. A “stacking” or “self-association” model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies L_φ for these substances. These γ and L_φ values were used to adjust the measured values of m(sat) and Δ_solH_m to the standard state and obtain values of the standard molar Gibbs free energy and enthalpy changes Δ_solG^∘_m and Δ_solH^∘_m, respectively, for the dissolution reactions of these substances. Values of Δ_solH^∘_m calculated from the temperature dependence of values of Δ_solG^∘_m were in good agreement with the values of Δ_solH^∘_m obtained by using calorimetry.     

Thermodynamic properties of two zinc borates: 3ZnO·3B2O3·3.5H2O and 6ZnO·5B2O3·3H2O

Two pure zinc borates with microporous structure 3ZnO·3B₂O₃·3.5H₂O and 6ZnO·5B₂O₃·3H₂O have been synthesized and characterized by XRD, FT-IR, TG techniques and chemical analysis. The molar enthalpies of solution of 3ZnO·3B₂O₃·3.5H₂O(s) and 6ZnO·5B₂O₃·3H₂O(s) in 1 mol · dm⁻³ HCl(aq) were measured by microcalorimeter at T = 298.15 K, respectively. The molar enthalpies of solution of ZnO(s) in the mixture solvent of 2.00 cm³ of 1 mol · dm⁻³ HCl(aq) in which 5.30 mg of H₃BO₃ were added were also measured. With the incorporation of the previously determined enthalpy of solution of H₃BO₃(s) in 1 mol · dm⁻³ HCl(aq), together with the use of the standard molar enthalpies of formation for ZnO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(6115.3 ± 5.0) kJ · mol⁻¹ for 3ZnO·3B₂O₃·3.5H₂O and −(9606.6 ± 8.5) kJ · mol⁻¹ for 6ZnO·5B₂O₃·3H₂O at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles.     

LOCAL STRUCTURE OF PROTONATED MORDENITES WITH SiO2/Al2O3 ≈ 15 PROBED BY MULTINUCLEAR NMR

Journal of Structural Chemistry - Two samples of protonated mordenite with close nominal molar ratios (MRs) SiO2/Al2O3 equal to 15.0 and 15.2 are studied by various physicochemical methods. Both...     

Protonation thermodynamics of some aminophenol derivatives in NaCl(aq) (0 ⩽ I ⩽3 mol · kg−1) at T = 298.15 K

The acid–base properties of four aminophenol derivatives, namely m-aminophenol (L1), 4-amino-2-hydroxytoluene (L2), 2-amino-5-ethylphenol (L3) and 5-amino-4-chloro-o-cresol (L4), are studied by potentiometric and titration calorimetric measurements in NaCl_(aq) (0 ? I ? 3 mol · kg^?1) at T = 298.15 K. The dependence of the protonation constants on ionic strength is modelled by the Debye–Hückel, SIT (Specific ion Interaction Theory) and Pitzer equations. Therefore, the values of protonation constants at infinite dilution and the relative interaction coefficients are calculated. The dependence of protonation enthalpies on ionic strength is also determined. Distribution (2-methyl-1-propanol/aqueous solution) measurements allowed us to determine the Setschenow coefficients and the activity coefficients of neutral species. Experimental results show that these compounds behave in a very similar way, and common class parameters are reported, in particular for the dependence on ionic strength of both protonation constants and protonation enthalpies.     

Al2O3·3H2O阻燃环氧树脂机理探讨

采用氧指数测定法与热重法研究了Al2O3·3H2O对环氧树脂固化物的阻燃效果与机理.结果表明,Al2O3·3H2O在热分解方面与树脂固化物有阻燃匹配性,并能以零级反应快速失去2个结晶水分子,失水后形成的活性氧化铝促进了树脂固化物热解时转化成难燃物的能力,具有较高的阻燃效果.     

Synthesis and thermochemical characteristics of Na2O · Al2O3 · 2.5H2O

A pure phase of monosodium aluminate hydrate Na₂O · Al₂O₃ · 2.5H₂O (MAH) is synthesized and characterized by means of XRD, IR, SEM, TGA, and DSC. The heat capacity of the compound is measured in the temperature range of ?100 to 100°C, and the thermal contributions to enthalpy and entropy are calculated. The standard entropy, enthalpy, and Gibbs energy of formation of MAH at 298 K are estimated.