Phase formation in the ScPO4-Na3PO4-Li3PO4 ternary system

The 950°C isothermal section of the ScPO₄-Na₃PO₄-Li₃PO₄ three-component system was plotted and studied; one-, two-, and three-phase fields were bounded. Three solid solution fields exist in the title system: one based on LiNa₅(PO₄)₂ complex phosphate (olympite structure), another on scandium-stabilized high-temperature Na₃PO₄ phase Na_{3(1 − x)}Sc _x/3□_2/3x PO₄ (space group Fm3m), and the third on Na₃Sc₂(PO₄)₃ (NASICON structure). All phases found in the title system are derivatives of phases that exist in its subsystems. Lithium-for-sodium isovalent substitutions in Na₃Sc₂(PO₄)₃ considerably increase the NASICON-type solid solution field but negatively influence the conductivity of the phase.     

NaBO<Subscript>2</Subscript>-Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-Na<Subscript>2</Subscript>WO<Subscript>4</Subscript> quaternary system

This is the first study of the NaBO₂-Na₂CO₃-Na₂MoO₄-Na₂WO₄ quaternary system by differential thermal analysis. Na₂[MoO_4(x)WO_{4(1 − x)}] solid solutions in the quaternary system are found to not decompose.     

Phase formation in the ZrO(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>-CsF-H<Subscript>2</Subscript>O system at low concentration of the phosphorus-containing component

The ZrO(NO₃)₂-H₃PO₄-CsF-H₂O system was studied at 20°C along the section at a molar ratio of PO₄³⁻/Zr = 0.5 (which is of the greatest interest in the context of phase formation) at ZrO₂ concentrations in the initial solutions of 2–14 wt % and molar ratios of CsF: Zr = 1−6. The following compounds were isolated for the first time: crystalline fluorophosphates CsZrF₂PO₄ · H₂O, amorphous oxofluorophosphate Cs₂Zr₃O₂F₄(PO₄)₂ · 3H₂O, and amorphous oxofluorophosphate nitrate CsZr₃O_1.25F₄(PO₄)₂(NO₃)_0.5 · 4.5H₂O. The compound Cs₃Zr₃O_1.5F₆(PO₄)₂ · 3H₂O was also isolated, which forms in a crystalline or glassy form, depending on conditions. The formation of the following new compounds was established: Cs₂Zr₃O_1.5F₅(PO₄)₂ · 2H₂O, Cs₂Zr₃F₂(PO₄)₄ · 4.5H₂O, and Zr₃O₄(PO₄)_1.33 · 6H₂O, which crystallize only in a mixture with known phases. All the compounds were studied by X-ray powder diffraction, crystal-optical, thermal, and IR spectroscopic analyses.     

Synthesis of hydroxyapatite by hydrolysis of α-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Conditions for hydroxyapatite (HAP) synthesis in aqueous solutions by hydrolysis of α-Ca₃(PO₄)₂ were studied. Temperature exerts a substantial effect on the rate of α-Ca₃(PO₄)₂ hydrolysis and also changes the morphology of the reaction products. At 40 °C, the plate-like intersecting (perpendicular to the surface of the initial particles) crystals of HAP grow. Their maximum size after the 24-h hydrolysis is 1–2 µm. Needle like HAP crystals are formed upon boiling of the suspension. The morphology observed for the HAP particles agrees well with the conclusions obtained by analysis of the kinetics of tricalcium phosphate hydrolysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 78–85, January, 2005.     

Interaction between two similar plane parallel double layers for Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> type asymmetric electrolytes at positive surface potential

The interaction between two similar plane double-layers for Mg₃(PO₄)₂ type asymmetric electrolytes was investigated with the aid of λ parameter method. The interaction energies for the system at positive surface potential were expanded in power series at low and high potential, respectively. The accurate numeral results and V′-ξ _d curves were given for y ₀ ≤ 20 and they can be used to check up the validity of approximate expressions obtained. When y ₀ ≥ 5, V′ hardly changes with y ₀. The interaction energies between two similar plane parallel double layers for symmetric and asymmetric electrolytes at y ₀ = 1 were compared; when ξ _d is small, the interaction energies for Mg₃(PO₄)₂ type electrolytes increase more drastically than for other type electrolytes. The present results are also fit for Al₂(SO₄)₃ type asymmetric electrolytes at negative surface potential. The article is published in the original.     

Complex Phosphates in the Li(Na)3]PO4-InPO4 Systems

Subsolidus sections in the systems Li₃PO₄-InPO₄ (950°C) and Na₃PO₄-InPO₄ (800, 900, and 1000°C) have been studied by X-ray powder diffraction. The compound Li₃In(PO₄)₂ has been synthesized, and the nasicon-type solid solution Li_{3(1 ? x)}In_{2 + x}(PO₄)₃ (0.67 ≤ x ≤ 0.80). has been found to exist. In the system Na₃PO₄-InPO₄, the solid solution Na_{3(1 ? x)}In_x/3PO₄ (0 ≤ x ≤ 0.2) and two complex phosphates exist: Na₃In(PO₄)₂ and Na₃In₂(PO₄)₃. These complex phosphates are dimorphic, with the irreversible-transition temperature equal to 675 and 820°C, respectively. Na₃In(PO₄)₂ degrades at 920°C. Ionic conductivity has been measured in some phases in the system.     

Whitlockite solid solutions in the Ca<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>-K<Subscript>3</Subscript>VO<Subscript>4</Subscript>-NdVO<Subscript>4</Subscript> system

Phase equilibria in the Ca₃(VO₄)₂-K₃VO₄-NdVO₄ system have been studied. An extensive calcium orthovanadate-based solid solution was found to form with the boundary compositions as follows: Ca₃(VO₄)₂-Ca₉Nd(VO₄)₇-Ca_9.33K_2.33(VO₄)₇-Ca_7.88K_2.63Nd_0.87(VO₄)₇. The unit cell parameters of the whit-lockite vanadates synthesized increase as the potassium and neodymium contents increase. Phase transitions from the low-temperature β phase to the β′ centrosymmetrical structure in Ca_{9.33 − 5z} K_{2.33 + z} Nd_3z (VO₄)₇ vanadates have been studied dilatometrically. The increase in the β ai β′ transition temperature caused by potassium is interpreted as arising from the filling in of vacant cation positions M(4) and M(6).     

A study of phase formation in the subsolidus region of the system Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MnMoO<Subscript>4</Subscript>-Cr<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phase relationships in the subsolidus region of the system Na₂MoO₄-MnMoO₄-Cr₂(MoO₄)₃ were studied by means of X-ray diffraction and differential-thermal analyses. The possibility of obtaining a variablecomposition phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ (0 ≤ x ≤ 0.5) and ternary molybdate NaMn₃Cr(MoO₄)₅ was examined. The temperature dependence of the conductivity of the phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ was analyzed.     

Effects of Cr doping on the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

A series of Cr-doped Li₃V_2???x Cr _x (PO₄)₃ (x?=?0, 0.1, 0.25, and 0.5) samples are prepared by a sol–gel method. The effects of Cr doping on the physical and chemical characteristics of Li₃V₂(PO₄)₃ are investigated. Compared with the XRD pattern of the undoped sample, the XRD patterns of the Cr-doped samples have no extra reflections, which indicates that Cr enters the structure of Li₃V₂(PO₄)₃. As indicated by the charge–discharge measurements, the Cr-doped Li₃V_2???x Cr _x (PO₄)₃ (x?=?0.1, 0.25, and 0.5) samples exhibit lower initial capacities than the undoped sample at the 0.2 C rate. However, both the discharge capacity and cycling performance at high rates (e.g., 1 and 2 C) are enhanced with proper amount of Cr doping (x?=?0.1). The highest discharge capacity and capacity retention at the rates of 1 and 2 C are obtained for Li₃V_1.9Cr_0.1(PO₄)₃. The improvement of the electrochemical performance can be attributed to the higher crystal stability and smaller particle size induced by Cr doping.     

Synthesis of ammonia from natural gas at atmospheric pressure with doped ceria–Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>–K<Subscript>3</Subscript>PO<Subscript>4</Subscript> composite electrolyte and its proton conductivity at intermediate temperature

A new type of oxide–salt composite electrolyte, yttrium doped ceria YDC–Ca₃(PO₄)₂–K₃PO₄, was developed and demonstrated for its promising use for ammonia synthesis. Using this composite electrolyte, ammonia was synthesized from nitrogen and natural gas at atmospheric pressure in the solid-state proton conducting cell reactor, and the optimal condition for ammonia production was determined . The evolved rate of ammonia is up to 6.95×10⁻⁹ mol s⁻¹ cm⁻².     

Interaction between two double-layers for FeCl<Subscript>3</Subscript> and Na<Subscript>3</Subscript>PO<Subscript>4</Subscript> type electrolytes in case the signs of potentials on two plates are opposite

The interaction energies between two double layers for FeCl₃ or Na₃PO₄ type electrolytes at y ₀ > 0 >y _d>—y ₀ were calculated with the aid of 7n parameter methods and the accurate numeral results were given when the dimensionless surface potential of two double layers changes from -20 to +20. When ∣y _d∣ > 5, the absolute value of the interaction energies, ∣V’∣, for FeCl₃ type electrolytes at y ₀= 1 stops to increase. When y ₀> 8, the ∣V’∣ for FeCl₃ type electrolytes at y _d= -1 ceases to change. The influence of y _d on ∣V’∣ for FeCl₃ type electrolytes is more significant than the influence of y ₀. The variation of ∣V’∣ with y _d and y ₀ for Na₃PO₄ type electrolytes is opposite to that for FeCl₃ type electrolytes. The interaction energies between two dissimilar double layers for Na₂SO₄, CaCl₂, NaCl, Na₃PO₄ and FeCl₃ type electrolytes at y ₀= 1 and y _d = -10 are compared and the results indicate that the interaction energies close to each other for FeCl₃ and CaCl₂ type electrolytes and for Na₃PO₄ and Na₂SO₄ type electrolytes, respectively. ∣V’∣ increases with the raises of y ₀ or ∣y _d∣, but decreases with the raises of z ₊ or z _-.     

Crystallization and Phase Stability of CaSO<Subscript>4</Subscript> and CaSO<Subscript>4</Subscript> – Based Salts

Summary.  Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO₄·2H₂O), hemihydrate (CaSO₄·0.5H₂O) and anhydrite (CaSO₄). On the one hand the conversion of these phases into each other takes place in nature and on the other hand it represents the basis of gypsum-based building materials. The present paper reviews available phase diagram and crystallization kinetics information on the formation of calcium sulfate phases, including CaSO₄-based double salts and solid solutions. Uncertainties in the solubility diagram CaSO₄–H₂O due to slow crystallization kinetics particularly of anhydrite cause uncertainties in the stable branch of crystallization. Despite several attempts to fix the transition temperatures of gypsum–anhydrite and gypsum–hemihydrate by especially designed experiments or thermodynamic data analysis, they still vary within a range from 42–60°C and 80–110°C. Electrolyte solutions decrease the transition temperatures in dependence on water activity. Dry or wet dehydration of gypsum yields hemihydrates (α-, β-) with different thermal and re-hydration behaviour, the reason of which is still unclear. However, crystal morphology has a strong influence. Gypsum forms solid solutions by incorporating the ions HPO₄ ²⁻, HAsO₄ ²⁻, SeO₄ ²⁻, CrO₄ ²⁻, as well as ion combinations Na⁺(H₂PO₄)⁻ and Ln³⁺(PO₄)³⁻. The channel structure of calcium sulfate hemihydrate allows for more flexible ion substitutions. Its ion substituted phases and certain double salts of calcium sulfate seem to play an important role as intermediates in the conversion kinetics of gypsum into anhydrite or other anhydrous double salts in aqueous solutions. The same is true for the opposite process of anhydrite hydration to gypsum. Knowledge about stability ranges (temperature, composition) of double salts with alkaline and alkaline earth sulfates (esp. Na₂SO₄, K₂SO₄, MgSO₄, SrSO₄) under anhydrous and aqueous conditions is still very incomplete, despite some progress made for the systems Na₂SO₄–CaSO₄ and K₂SO₄–CaSO₄–H₂O. Corresponding author. E-mail: daniela.freyer@chemie.tu-freiberg.de Received December 17, 2002; accepted January 10, 2003 Published online April 3, 2003     

Synthesis and characterization of macroporous Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C composites as cathode materials for Li-ion batteries

The macroporous Li₃V₂(PO₄)₃/C composite was synthesized by oxalic acid-assisted carbon thermal reaction, and the common Li₃V₂(PO₄)₃/C composite was also prepared for comparison. These samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical performance tests. Based on XRD and SEM results, the sample has monoclinic structure and macroporous morphology when oxalic acid is introduced. Electrochemical tests show that the macroporous Li₃V₂(PO₄)₃/C sample has a high initial discharge capacity (130 mAh g⁻¹ at 0.1 C) and a reversible discharge capacity of 124.9 mAh g⁻¹ over 20 cycles. Moreover, the discharge capacity of the sample is still 91.5 mAh g⁻¹, even at a high rate of 2 C, which is better than that of the sample with common morphology. The improvement in electrochemical performance should be attributed to its improved lithium ion diffusion coefficient for the macroporous morphology, which was verfied by cyclic voltammetry and electrochemical impedance spectroscopy.     

Synthesis and crystal structure of phosphate Ba<Subscript>1.5</Subscript>Fe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Double phosphate Ba_1.5Fe₂(PO₄)₃ was synthesized and structurally studied. Single crystals were synthesized by the fusion method. Cubic crystals, Z = 4, space group P2₁3, a = 9.866(1) Å. This structure is built of polyhedrons of four types: PO₄ tetrahedrons, two virtually regular FeO₆ octahedrons, BaO₁₂ twelve-vertex polyhedrons, and BaO₉ nine-vertex polyhedrons. These polyhedrons share common oxygen vertices to form three-dimensional [Fe₂(PO₄)₃]_3∞ framework containing barium atoms in cavities.     

Structural relaxation of scintillating Ce-doped NaGd(PO<Subscript>3</Subscript>)<Subscript>4</Subscript> glass

Structural relaxation of scintillating Ce-doped Na–Gd phosphate glass with a nominal composition of Ce:NaGd(PO₃)₄ was experimentally studied using non-isothermal thermo-mechanical analysis, and the relaxation process was described by the Tool–Narayanaswamy–Mazurin model. The distribution of relaxation times was expressed by the empirical Kohlrausch–Williams–Watts relaxation function with relaxation time directly proportional to dynamic viscosity. The model parameters and material constants were obtained by the nonlinear regression analysis of thermo-mechanical data. It has been concluded that the model used of structural relaxation correctly describes relaxation processes in studied Ce-doped NaGd(PO₃)₄ glass.     

Synthesis and structure of phosphates M<Subscript>0.5</Subscript>Ti<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phosphates M_0.5Ti₂(PO₄)₃ (M = Ni, Zn) were synthesized by the sol-gel method and characterized by the methods of X-ray diffraction, IR spectroscopy, and electronic microprobe analysis. Structures of Ni_0.5Ti₂(PO₄)₃ and Zn_0.5Ti₂(PO₄)₃ were studied by Rietveld method using the X-ray powder diffraction data.     

Impact of carbon coating thickness on the electrochemical properties of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C composites

A series of Li₃V₂(PO₄)₃/C composites with different amounts of carbon are synthesized by a combustion method. The physical and electrochemical properties of the Li₃V₂(PO₄)₃/C composites are investigated by X-ray diffraction, element analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and electrochemical measurements. The effects of carbon content of Li₃V₂(PO₄)₃/C composites on its electrochemical properties are conducted with cyclic voltammetry and electrochemical impedance. The experiment results clearly show that the optimal carbon content is 4.3 wt %, and more or less amount of carbon would be unfavorable to electrochemical properties of the Li₃V₂(PO₄)₃/C electrode materials. The results would provide some basis for further improvement on the Li₃V₂(PO₄)₃ electrode materials.     

PuPO<Subscript>4</Subscript>(cr,hyd.) Solubility Product and Pu<Superscript>3+</Superscript> Complexes with Phosphate and Ethylenediaminetetraacetic Acid

To determine the solubility product of PuPO₄(cr, hyd.) and the complexation constants of Pu(III) with phosphate and EDTA, the solubility of PuPO₄(cr, hyd.) was investigated as a function of: (1) time and pH (varied from 1.0 to 12.0), and at a fixed 0.00032 mol⋅L⁻¹ phosphate concentration; (2) NaH₂PO₄ concentrations varying from 0.0001 mol⋅L⁻¹ to 1.0 mol⋅L⁻¹ and at a fixed pH of 2.5; (3) time and pH (varied from 1.3 to 13.0) at fixed concentrations of 0.00032 mol⋅L⁻¹ phosphate and 0.0004 mol⋅L⁻¹ or 0.002 mol⋅L⁻¹ Na₂H₂EDTA; and (4) Na₂H₂EDTA concentrations varying from 0.00005 mol⋅L⁻¹ to 0.0256 mol⋅L⁻¹ at a fixed 0.00032 mol⋅L⁻¹ phosphate concentration and at pH values of approximately 3.5, 10.6, and 12.6. A combination of solvent extraction and spectrophotometric techniques confirmed that the use of hydroquinone and Na₂S₂O₄ helped maintain the Pu as Pu(III). The solubility data were interpreted using the Pitzer and SIT models, and both provided similar values for the solubility product of PuPO₄(cr, hyd.) and for the formation constant of PuEDTA⁻. The log ₁₀ of the solubility product of PuPO₄(cr, hyd.) [PuPO₄(cr, hyd.) \rightleftarrows\rightleftarrows Pu³⁺+PO₄^3-\mathrm{Pu}^{3+}+\mathrm{PO}_{4}^{3-}] was determined to be −(24.42±0.38). Pitzer modeling showed that phosphate interactions with Pu³⁺ were extremely weak and did not require any phosphate complexes [e.g., PuPO₄(aq), PuH₂PO₄²⁺\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+}, Pu(H₂PO₄)₂⁺\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{2}^{+}, Pu(H₂PO₄)₃(aq), and Pu(H₂PO₄)₄^-\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{4}^{-}] as proposed in existing literature, to explain the experimental solubility data. SIT modeling, however, required the inclusion of PuH₂PO₄²⁺\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+} to explain the data in high NaH₂PO₄ concentrations; this illustrates the differences one can expect when using these two different chemical models to interpret the data. Of the Pu(III)-EDTA species, only PuEDTA⁻ was needed to interpret the experimental data over a large range of pH values (1.3–12.9) and EDTA concentrations (0.00005–0.256 mol⋅L⁻¹). Calculations based on density functional theory support the existence of PuEDTA⁻ (with prospective stoichiometry as Pu(OH₂)₃EDTA⁻) as the chemically and structurally stable species. The log ₁₀ value of the complexation constant for the formation of PuEDTA⁻ [ Pu³⁺+EDTA^4-\rightleftarrows PuEDTA^-\mathrm{Pu}^{3+}+\mathrm{EDTA}^{4-}\rightleftarrows \mathrm{PuEDTA}^{-}] determined in this study is −20.15±0.59. The data also showed that PuHEDTA(aq), Pu(EDTA)₄^5-\mathrm{Pu(EDTA)}_{4}^{5-}, Pu(EDTA)(HEDTA)⁴⁻, Pu(EDTA)(H₂EDTA)³⁻, and Pu(EDTA)(H₃EDTA)²⁻, although reported in the literature, have no region of dominance in the experimental range of variables investigated in this study.     

Synthesis,phase formation,and thermal expansion of sulfate phosphates with the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> structure

The NaFeZr(PO₄)₂SO₄ and Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 sulfate phosphates with the NaZr₂(PO₄)₃ (NZP) structure were synthesized and studied using X-ray diffraction, electron microprobe analysis, IR spectroscopy, and simultaneous differential thermal and thermogravimetric analysis. The phase formation and thermal stability of the compounds were studied by powder X-ray diffraction and DTA–TG. The Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 structure was refined by full-profile analysis. The structure framework is composed of randomly occupied (Fe,Zr)O₆ octahedra and (P,S)O₄ tetrahedra; the Pb²⁺ ions occupy extra-framework sites. The thermal expansion of Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 in the temperature range from–120 to 200°C was studied by temperature X-ray diffraction. In terms of the average linear coefficient of thermal expansion (α_av = 1.7 × 10^–6°C^–1), this compound can be classified as having low expansion. The combination of different tetrahedral anions (a phosphorus and a smaller sulfur one) in the NZP resulted in a decrease in the framework size and cavities and enabled the preparation of low-expansion sulfate phosphate with a smaller extra-framework cation (cheap Pb) instead of larger cations (Cs, Ba, Sr) used most often in the monoanionic phosphates.     

Interactions between two similar plane parallel double layers for Na<Subscript>3</Subscript>PO<Subscript>4</Subscript> type asymmetric electrolytes at positive surface potential

The interactions between two similar plane double-layers for Na₃PO₄ type asymmetric electrolytes are described using hyperelliptic integrals. The mathematical treatments of hyperelliptic integrals are much more difficult than those of elliptic integrals. The system was successfully treated with the aid of the λ parameter method. The interaction energies for the system at positive surface potential are expanded in power series at low, moderate, and high potentials, respectively. The accurate numeral results and V′-ξ _d curves are given for y ₀ ≤ 20 and can be used to check the validity of approximate expressions obtained. When y ₀ ≥ 5, V′ hardly changes with y ₀. The interaction energies between two similar plane parallel double layers for symmetric and asymmetric electrolytes at y ₀ = 1 were compared; when ξ _d → 0, the interaction energies for Na₃PO₄ type electrolytes are much larger than for electrolytes of other types. The present results are also fit for FeCl₃-type asymmetric electrolytes at negative surface potential. The text was submitted by the author in English.