Dehydration of synthetic and natural vivianite

Thermal analyses of synthetic and natural vivianite (Fe²⁺)₃(PO₄)₂·8H₂O) were determined using a high-resolution thermal analyser coupled to a mass spectrometer.Five dehydration weight loss steps were observed for the natural vivianite at 105, 138, 203, 272 and 437 °C. The first weight loss step involves the reaction (Fe²⁺)₃(PO₄)₂·8H₂O→(Fe²⁺)₃(PO₄)₂·3H₂O+5H₂O. The TGA/MS for the synthetic vivianite gave similar results to that of the natural sample. Mass spectrometry shows that water is lost up to 450 °C and after this temperature oxygen is lost. Changes in the structure of vivianite were followed using infrared emission spectroscopy. A model is proposed for the dehydration of vivianite.     

Zur Kenntnis der Kupferphosphate

Among the sparingly soluble copper(II)-phophates the existence of CuHPO₄·H₂O and of Cu₄H(PO₄)₃·3 H₂O was verified by X-ray powder-diagrams, other statements on preparations and X-ray diagrams were corrected. Cu₃(PO₄)₂·3 H₂O apparently does not exist. Structural analogies of Cu₄H(PO₄)₃·3 H₂O and CaHPO₄·2 H₂O may offer an explanation for the restraint hydrolysis of the calcium salt in presence of low copper concentrations. Pseudomalachite was synthesised hydrothermally.     

Comparison of one-, two-, and three-dimensional iron phosphates containing ethylenediamine

A new two-dimensional (2d) iron phosphate, (C₂N₂H₁₀)Fe₂O(PO₄)₂, has been synthesized under hydrothermal conditions in the system of FeCl₃-H₃PO₄-C₂N₂H₈-H₂O. The crystal data is: space group P2₁/c, a=10.670(1) Å, b=10.897(1) Å, c=9.918(1) Å, β=105.632(1)°, Z=4. The layered structure consists of double sheet layers, of composition Fe₂O(PO₄)₂, built from FeO₅ trigonal bipyramids and PO₄ tetrahedra. The amine holds the layers together via H-bonding. The study of the magnetic properties reveals two magnetic transitions at 160 and 30 K with spin-glass-like behavior below 160 K. By varying the hydrothermal conditions, three other iron phosphates were synthesized: the one-dimensional (1d) (C₂N₂H₁₀)Fe(HPO₄)₂(OH)·H₂O, the 2d (C₂N₂H₁₀)Fe₂(PO₄)₂(OH)₂, and the three-dimensional (3d) (C₂N₂H₁₀)₂Fe₄O(PO₄)₄·H₂O. The 1d compound can be used as the starting reagent in the synthesis of both the 2d compound and the 3d lipscombite Fe₃(PO₄)₂(OH)₂ due to the similar building blocks in their structures. In the 3d phosphate (C₂N₂H₁₀)₂Fe₄O(PO₄)₄·H₂O, manganese can substitute for half of the iron atoms. Magnetic study shows ordering transitions at about 30 K, however, manganese substitution depresses the magnetic ordering temperature.     

Solubility of some lanthanide sulfates in polycomponent systems containing H2SO4

Summary The paper presents data on the solubility of La, Ce, Pr, Nd sulfates in the polycomponent system La₂(SO₄)₃·8H₂O-Ce₂(SO₄)₃·8H₂O-Pr₂(SO₄)₃·8H₂O-Nd₂(SO₄)₃· 8H₂O-H₂SO₄-H₂O (at 25°C and 64°C) as well as in the same polycomponent system but in the presence of CaSO₄·2H₂O. The solubility of the sulfates — ocathydrates of Pr at 25°C and 64°C and of La and Ce at 64°C in tricomponent systemLn ₂(SO₄)₃·8H₂O-H₂SO₄-H₂O are also reported.

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Löslichkeit einiger Lanthanidsulfate in Mehrkomponenten-Systemen mit H₂SO₄

Zusammenfassung Die Arbeit präsentiert Daten für die Löslichkeit von La-, Ce-, Pr- und Nd-Sulfaten in den Vielkomponenten-Systemen La₂(SO₄)₃·8H₂O-Ce₂(SO₄)₃·8H₂O-Pr₂(SO₄)₃·8H₂O-Nd₂(SO₄)₃· 8H₂O-H₂SO₄-H₂O (bei 25°C und 64°C) sowie in den gleichen Systemen, jedoch in Anwesenheit von CaSO₄·2H₂O. Über die Löslichkeit von Sulfatoctahydraten von Pr bei 25°C und 64°C und von La und Ce bei 64°C in den Dreikomponenten-SystemenLn ₂(SO₄)₃·8H₂O-H₂SO₄-H₂O wird auch berichtet.

     

Influence of silicic acid and glauconite on thermal dehydration of Ca(H2PO4)2 · H2O

The thermal dehydration of mixtures of Ca(H₂PO₄)₂·H₂O with silicic acid and glauconite was studied by thermal (under dynamic and quasi-isothermal-quasi-isobaric conditions), X-ray and Chromatographic analyses.It was found that the dehydration of Ca(H₂PO₄)₂·H₂O is accelerated in the mixtures. SiO₂·nH₂O and glauconite react with the intermediates of dehydration of Ca(H₂PO₄)₂·H₂O, and silicophosphates and Al, K, Fe-phosphates are formed, respectively. The total degree of polymerization of calcium polyphosphates is lower in the mixtures than in Ca(PO₃)₂ itself.

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Zusammenfassung Mittels röntgenographischer, chromatographischer und thermischer (unter dynamischen und quasi-isothermen-quasi-isobaren Bedingungen) Analyse wurde die thermische Dehydratation eines Gemisches aus Ca(H₂PO₄)₂·H₂O, KieselsÄure und Glaukonit untersucht.Es wurde festgestellt, da\ die Dehydratation von Ca(H₂PO₄)₂·H₂O im Gemisch beschleunigt ablÄuft. SiO₂·nH₂O und Glaukonit reagieren mit den Zwischenprodukten der Dehydratation von Ca(H₂PO₄)₂·H₂O und formen Silikophosphate und Al,K,Fe-Phosphate. Der totale Polymerisationsgrad von Calciumpolyphosphat ist im Gemisch geringer als in Ca(PO₃)₂ selbst.

     

Untersuchungen zur Reaktion von konzentrierter Phosphors?ure mit reinen und korrodierten Stahloberfl?chen

Zusammenfassung Mittels Mößbauerspektroskopie wurde gefunden, daß sich aus Rostkomponenten neben den normalen Eisen (III)- und Eisen (II)-phosphaten auch ein saures Eisen (III)-phosphat bilden kann, wenn sie mit konzentrierter Phosphorsäure behandelt werden. Voraussetzung hierfür ist, daß die Ausgangsphase eine reine Fe³⁺-Verbindung ist. Das saure Eisen(III)-phosphat, wahrscheinlich FeH₃(PO₄)₂ · 2,5 H₂O, enthält Fe³⁺ in nahezu kubischer Umgebung, die Kristallstruktur hat jedoch niedrigere Symmetrie. Unterhalb von 28 K setzt eine magnetische Ordnung ein. Es sind zwei Fälle mit verschiedener Spinstruktur und Verkantungen zu unterscheiden.

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Studies of the reaction of concentrated phosphoric acid with clean and corroded steel surfaces

Summary It was found by Mössbauer spectroscopy that an acid ferric phosphate in addition to the normal phosphates is formed by treatment of rust components with concentrated phosphoric acid, provided the initial phase is a pure Fe³⁺ compound. The acid ferric phosphate, probably FeH₃(PO₄)₂ x 2.5 H₂O, contains Fe³⁺ at an approximately cubic lattice site, although the crystal structure is of lower symmetry. Below 28 K, the substance shows magnetic ordering. Two different cases with canted spin structures were found.

     

Über einen Isokonzentrationsschnitt in bezug auf Schwefelsäure im Dreistoffsystem Ammoniumsulfat-Eisen(III)sulfat-Wasser bei 25 °C

Zusammenfassung Untersucht wird ein Isokonzentrationsschnitt in bezug auf Schwefelsäure im Dreistoffsystem (NH₄)₂SO₄–Fe₂(SO₄)₃–H₂O bei 25 °C. Es wird ein Kristallisationsbereich von anomalen Mischkristallen auf der Basis (NH₄)₂SO₄ bei einem Eisen(III)-sulfatgehalt von 1,5% des Ammoniumsulfatgehalts ermittelt. Außerdem wird ein Kristallisationsbereich von Mischkristallen auf der Basis NH₄Fe(SO₄)₂·12 H₂O, ein Kristallisationsbereich von reinem NH₄Fe(SO₄)₂·12 H₂O und ein Kristallisationsbereich von Fe₂(SO₄)₃·9 H₂O festgestellt. Die Anwesenheit von Schwefelsäure in der Lösung vermindert die Löslichkeit aller Phasen im obigen System.Untersucht wird teilweise das Dreistoffsystem NH₄Fe(SO₄)₂–H₂SO₄–H₂O bei 25 °C. Es wird ein Kristallisationsbereich von NH₄Fe(SO₄)₂·12 H₂O, welches als feste Phase bis etwa 12% Schwefelsäure in der Lösung existiert, ermittelt. Es wird bewiesen, daß die anomalen Mischkristalle auf der Basis (NH₄)₂SO₄ metastabile, mit der Zeit langsamen Veränderungen unterliegende Systeme sind.

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An isoconcentration section with respect to sulphuric acid of the ternary system ammonium sulphate-ferric sulphate-water at 25 °C

The system (NH₄)₂SO₄–Fe₂(SO₄)₃–H₂O was investigated at 25 °C with an excess of H₂SO₄. The crystallization ranges of the anomalous mixed crystals based on ammonium sulphate, the mixed crystals on the basis of the double-salt NH₄Fe(SO₄)₂· ·12 H₂O, the crystallization ranges of Iron(III)-ammonium sulphate and Fe₂(SO₄)₃·9 H₂O were determined. The presence of H₂SO₄ in the solution lowers the solubilities of the different phases occurring in the said system. The system NH₄Fe(SO₄)₂–H₂SO₄–H₂O was partially studied at 25 °C. The crystallization range of iron-ammonium alum existing as a solid phase at equilibrium at sulphuric acid concentrations up to ca. 12% in the solution is described. It was shown that the anomalous mixed-crystals based on ammonium sulphate undergoe slow changes with time.

     

Quantum chemical and spectroscopic analysis of calcium hydroxyapatite and related materials

Amorphous calcium hydroxyapatite was examined by vibrational spectroscopy (Raman and infra-red (IR)) and quantum chemical simulation techniques. The structures and vibrational (IR, Raman and inelastic neutron scattering) spectra of PO₄³⁻ ion, Ca₃(PO₄)₂, [Ca₃(PO₄)₂]₃, Ca₅(PO₄)₃OH, CaHPO₄, [CaHPO₄]₂, Ca₃(PO₄)₂·H₂O, Ca₃(PO₄)₂·2H₂O and Ca₃(PO₄)₂·3H₂O clusters were quantum chemically simulated at ab initio and semiempirical levels of approximation. A complete coordinate analysis of the vibrational spectra was performed. The comparison of the theoretically simulated spectra with the experimental ones allows to identify correctly the phase composition of the amorphous calcium hydroxyapatite and related materials. The shape of the bands in the IR spectra of the hydroxoapatite can be used in order to characterize the structural properties of the material, e.g., the PO₄³⁻ ion status, the degree of hydrolysis of the material and the presence of hydrolysis products.     

Synthesis and characterization of new strontium 4-carboxyphenylphosphonates

Several new strontium 4-carboxyphenylphosphonates, i.e., two modifications of Sr(HOOCC₆H₄PO₃H)₂, SrH(OOCC₆H₄PO₃)·H₂O, Sr₃(OOCC₆H₄PO₃)₂·4H₂O and Sr₃(OOCC₆H₄PO₃)₂·5.7H₂O were prepared and characterized by elemental analysis, thermogravimetry, X-ray powder diffraction and infrared spectroscopy. It was found that the compositions of these compounds depend on the acidity of the reaction medium. In addition, the presented compounds are interconvertible in dependence on pH. The position of the acid hydrogen atom in SrH(OOCC₆H₄PO₃)·H₂O was determined from the IR spectra of the studied compounds.The structure of the β modification of Sr(HOOCC₆H₄PO₃H)₂ was solved from its X-ray powder diffraction pattern using an ab initio method (the FOX program) with subsequent Rietveld refinement in the FULLPROF program. The compound is monoclinic, with the space group P2₁/c (No. 14), a=49.88(2), b=7.867(2), c=5.602(3) Å, β=128.68(2)°, and Z=4. It has a one-dimensional structure with an inorganic part built of SrO₈ distorted tetragonal antiprisms.     

Polynuclear iron(III) pivalates

The formation of magnetically active polynuclear Fe^III pivalates in the FeSO₄·7H₂O-KOOCCMe₃ system was studied. The reaction of FeSO₄·7H₂O (1) with KOOCCMe₃ in EtOH in air afforded the antiferromagnetic trinuclear complex [Fe₃O(OOCCMe₃)₆(H₂O)₃]⁺[OOCCMe₃]^–·3EtOH. A change of the solvent (EtOH) in this system to a 40:1 benzene—THF mixture resulted in the formation of the antiferromagnetic hexanuclear cluster [Fe₆(O)₂(OH)₂(OOCCMe₃)₁₂(HOOCCMe₃)(THF)]·1.5C₆H₆. The addition of trimethylacetic acid to EtOH and recrystallization from hexane gave rise to the antiferromagnetic coordination polymer [K₂Fe₄(O)₂(OOCCMe₃)₁₀(HOOCCMe₃)₂(H₂O)₂]_n (7). Recrystallization of the latter from acetonitrile afforded the antiferromagnetic tetranuclear complex K₂Fe₄(O)₂(OOCCMe₃)₁₀(HOOCCMe₃)₂(MeCN)₂. The structures of these compounds were established by X-ray diffraction analysis, and their magnetic susceptibilities and thermal decomposition were investigated.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2403–2413, November, 2004.