Mechanism of solid-state conversion of non-stoichiometric hydroxyapatite to diphase calcium phosphate

Two non-stoichiometric hydroxyapatites (n-HA) with Ca/P molar ratios of 1.50 and 1.58 and one stoichiometric hydroxyapatite (s-HA) with Ca/P = 1.67 were prepared from chemically pure CaHPO₄·2H₂O and KOH. After sintering at 1050 °C for 4 h, n-HA with Ca/P = 1.50 was transformed into -Ca₃(PO₄)₂, n-HA with Ca/P = 1.58 was converted to diphase calcium phosphate (DCP), while s-HA underwent no chemical transformations. The sintered and unsintered samples of hydroxyapatite were studied by IR spectroscopy, chemical analysis, and X-ray diffraction analysis. The crystallite dimensions were calculated, and a model for the DCP structure was proposed. The mechanism of the solid-state n-HA to DCP conversion was proposed on the basis of this model and published values of the volume diffusion coefficients of the OH^–, Ca²⁺, and PO₄ ^3– ions at 1000 °C.     

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.     

Formation of titanium phosphate composites during phosphoric acid decomposition of natural sphene

Decomposition of mineral sphene, CaTiOSiO₄, by H₃PO₄ is investigated in detail. During the dissolution process, simultaneous calcium leaching and formation of titanium phosphate (TiP) take place. The main product of decomposition is a solid titanium phosphate-silica composite. The XRD, solid-sate NMR, IR, TGA, SEM and BET data were used to identify and characterize the composite as a mixture of crystalline Ti(HPO₄)₂·H₂O and silica. When 80% phosphoric acid is used the decomposition degree is higher than 98% and calcium is completely transferred into the liquid phase. Formation of Ti(HPO₄)₂·H₂O proceeds via formation of meta-stable titanium phosphate phases, Ti(H₂PO₄)(PO₄)·2H₂O and Ti(H₂PO₄)(PO₄).The sorption affinities of TiP composites were examined in relation to caesium and strontium ions. A decrease of H₃PO₄ concentration leads to formation of composites with greater sorption properties. The maximum sorption capacity of TiP is observed when 60% H₃PO₄ is used in sphene decomposition.The work demonstrates a valuable option within the Ti(HPO₄)₂·H₂O-SiO₂ composite synthesis scheme, to use phosphoric acid flows for isolation of CaHPO₄·2H₂O fertilizer.     

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.     

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.     

Crystal growth, structural, optical, dielectric and thermal studies of an amino acid based organic NLO material: L-phenylalanine L-phenylalaninium malonate

The mineral crandallite CaAl₃(PO₄)₂(OH)₅·(H₂O) has been identified in deposits found in the Jenolan Caves, New South Wales, Australia by using a combination of X-ray diffraction and Raman spectroscopic techniques. A comparison is made between the vibrational spectra of crandallite found in the Jenolan Caves and a standard crandallite. Raman and infrared bands are assigned to PO₄³⁻ and HPO₄²⁻ stretching and bending modes. The predominant features are the internal vibrations of the PO₄³⁻ and HPO₄²⁻ groups. A mechanism for the formation of crandallite is presented and the conditions for the formation are elucidated.     

Solid solutions between β-Ca3(PO4)2 and sodium-containing whitlockite

Mixtures of CaHPO₄, CaCO₃, and Na₂CO₃ were heated at 870°C under steam or under dry CO₂ until phase composition and weight were constant. According to chemical analysis and X-ray diffractometry the stability field of the β-Ca₃(PO₄)₂ phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β-Ca₃(PO₄)₂ and a new whitlockite with the composition Ca₁₀Na(PO₄)₇. The IR spectrum of these solid solutions shows that the point symmetry of the PO₄ groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β-Ca₃(PO₄)₂ and whitlockite. The composition of these solid solutions suggests that Na⁺ ions can replace H⁺ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites.     

Calcium hydroxyapatite solubilisation in the hydrochloric and perchloric acids

Summary Enthalpy of solution of calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (CaHap) in hydrochloric and perchloric acid solutions is measured by an isoperibol calorimeter and a C80 microcalorimeter. The former device is adapted to reactions occurring in concentrated acid solutions, whereas the microcalorimeter is suitable for slow processes happening in diluted acid solutions. Some solution mechanisms are suggested for different pH ranges. They are confirmed by complementary solution in the same solvent of the entities produced by the reaction between CaHap and the acid. These entities are CaCl₂; Ca(ClO₄)₂·nH₂O; Ca(H₂PO₄)₂ and H₃PO₄. Extrapolation of solution enthalpies to pH=7 leads to the solution enthalpy of (CaHap) in pure water, which is -406.2 kJ mol^-1 from HCl and -437.3 kJ mol^-1 from HClO₄.     

Two new open framework cobalt phosphates: NaCo3(OH)(PO4)2.1/4H2O and Na(NH4)Co2(PO4)2.H2O

Two new cobalt phosphates, NaCo₃(OH)(PO₄)₂.1/4H₂O (1) and Na(NH₄)Co₂(PO₄)₂.H₂O (2) have been synthesized hydrothermally and characterized by single crystal X-ray diffraction methods, vibrational (IR and Raman) spectroscopy, thermogravimetric analysis and magnetic measurements. The structure of 1 is a new framework type while 2 is an example of a chiral cobalt phosphate. Both phases contain channels in which the Na⁺, NH₄⁺ cations and H₂O molecules are located.     

Hydrothermal synthesis and morphology variation of cadmium hydroxyapatite

Cadmium hydroxyapatite (Cd-Hap) crystals were synthesized by hydrothermal method at 200 °C using the solutions of Cd(NO₃)₂·4H₂O and (NH₄)₂HPO₄. Influences of pH values and reaction time on the crystalline phases and morphology of the products were investigated. In low pH reaction media, Cd₅H₂(PO₄)₄·4H₂O was formed and a relatively high pH reaction media was necessary to obtain Cd-Hap. Morphology of the Cd-Hap crystals changed from stubby hexagonal prismatic to rod-like in shape with the increase in the pH value. This morphological change was explained by the difference in growth mechanism through intermediate phases, Cd₅H₂(PO₄)₄·4H₂O in the low pH reaction media and Cd₂P₂O₇·5H₂O in the high pH reaction media.     

Peroxo derivatives of hydroxyapatite and calcium hydrophosphate

Hydroxyapatite and calcium hydrophosphate peroxo solvates were synthesized and characterized by IR spectroscopy, powder X-ray diffraction, and TGA to be used as biocompatible and antibacterial medicaments in manufacturing calcium phosphate bioceramics for implantations in orthopedics and dentistry. A wide range of hydrogen peroxide percentages in stable mixtures of mCa₅(PO₄)₃(OH) + nCaHPO₄ · H₂O₂ · H₂O (ranging from 0.5 to 18%) allows composites to be prepared with a tailored active oxygen content.     

Decomposition thermique et etude vibrationnelle de NiNa4(P3O9)2·6H2O

We have studied the dehydration and the calcination under atmospheric pressure of cyclotriphosphate tetrahydrate of nickel and sodium, NiNa₄(P₃O₉)₂·6H₂O, between 25 and 700°C by thermal analyses (TG, DTA) infrared spectrometry and X-ray diffraction. This study allows us the identification and the crystallographic characterization of a new phase, NiNa₄(PO₃)6, obtained between 350 and 450°C. NiNa₄(PO₃)₆ crystallizes in the triclinic system, P_–1, with the following unit cell parameters a=6.157(3) Å, b=6.820(6) Å, c=10.918(6) Å, =80.21(5)°, =97.80(9)°, =113.49(3)°, V=409.8 ų, Z=1, M(19)=25 and F(19)=48 (0.0095; 42). The calcination of NiNa₄(PO₃)₆, between 500 and 600°C, leads to a mixture of long-chain polyphosphates NiNa(PO₃)₃ and NaPO₃. The kinetic characteristics of the dehydration of NiNa₄(P₃O₉)₂·6H₂O were determined and discussed. The vibrational spectrum of the title compound, NiNa₄(P₃O₉)2·6H₂O, was interpreted in the domain of the stretching vibrations of the P₃O₉ rings, on the basis of its crystalline structure and in the light of the calculation of the normal IR frequencies of the P₃O₉ ring with D_3h symmetry.

This revised version was published online in November 2005 with corrections to the Cover Date.     

Preparation of Zr(IV)/Nb(V) Nasicon-like phosphates by a sol-gel method

The NbZr(PO₄)₃ and Na_0.5Nb_0.5Zr_1.5(PO₄)₃ Nasicon-like phases were prepared by the sol-gel method using (NH₄)₃ [NbO(C₂O₄)₃]·1.5H₂O, ZrOCl₂·8H₂O and NH₄H₂PO₄ in oxalic or tartaric acid mediums. The thermal evolution of the xerogels prepared was followed by XRD and IR techniques. Depending on reaction conditions, such as, pH and Zr⁴⁺/organic acid ratio, pure Nasicon-like phases can be prepared at different temperatures.     

Partial exchange of the Li, Na and K alkaline cations in the HNi(PO4)·H2O layered compound

The exchange of the Li⁺(1), Na⁺(2) and K⁺(3) alkaline cations in the layered HNi(PO₄)·H₂O was carried out starting from a methanolic solution containing the Li(OH)·H₂O hydroxide for (1) and the M(OH) (M=Na and K) hydroxides together with the (C₆H₁₃NH₂)_0.75HNiPO₄·H₂O phases for (2) and (3). The compounds are stable until, approximately, 280 °C for (1) and 400 °C for phases (2) and (3), respectively. The IR spectra show the bands belonging to the water molecule and the (PO₄)³⁻ oxoanion. The diffuse reflectance spectra indicate the existence of Ni(II), d⁸, cations in slightly distorted octahedral geometry. The calculated Dq and Racah (B and C) parameters have a mean value of Dq=765, B=905 and , respectively, in accordance with the values obtained habitually for this octahedral Ni(II) cation. The study of the exchange process performed by X-ray powder diffraction indicates that the exchange of the Li⁺ cation in the lamellar HNi(PO₄)·H₂O phase is the minor rapid reaction, whereas the exchange of the Na⁺ and K⁺ cations needs the presence of the intermediate (C₆H₁₃NH₂)_0.75HNiPO₄·H₂O intercalate in order to obtain the required product with the sodium and potassium ions. The Scanning electronic microscopy (SEM) images show a mean size of particle of 5 μm. The Li⁺ exchanged compound exhibits small ionic conductivity (Ω cm⁻¹ is in the 10⁻⁸-10⁻⁹ range) probably restrained by the methanol solvent. Magnetic measurements carried out from 5 K to room temperature indicate antiferromagnetic coupling as the major interaction in the three phases. Notwithstanding the Li and K phases show a weak ferromagnetism at low temperatures.     

Swelling of acrylate hydrogels filled with brushite and octacalcium phosphate

Hydrogels filled with CaHPO₄ · 2H₂O and Ca₈(HPO₄)₂(PO₄)4 · 5H₂O were synthesized from the acrylate derivatives of poly(ethylene glycol) by the photopolymerization method. The swelling behaviour of the filled and unfilled hydrogels in water was studied. The solubility of the photoinitiator in water and in the monomers was estimated.

     

Effect of microwave exposure on the morphology of calcium hydroxyapatite nanocrystals synthesized from aqueous solutions

The results of physicochemical examination (chemical analysis, XRD, IR spectroscopy) of the products synthesized in the Ca(OH)₂–H₃PO₄–H₂O system under microwave exposure are used to analyze the composition–synthesis conditions–structure–dispersion–properties relationships and to determine the effect of microwave irradiation on the size and morphology of the synthesized calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) nanocrystals.     

Syntheses, crystal structures and optical spectroscopy of Ln2(SO4)3·8H2O (Ln=Ho, Tm) and Pr2(SO4)3·4H2O

The lanthanide sulphate octahydrates Ln₂(SO₄)₃·8H₂O (Ln=Ho, Tm) and the respective tetrahydrate Pr₂(SO₄)₃·4H₂O were obtained by evaporation of aqueous reaction mixtures of trivalent rare earth oxides and sulphuric acid at 300 K. Ln₂(SO₄)₃·8H₂O (Ln=Ho, Tm) crystallise in space group C2/c (Z=4, a_Ho=13.4421(4) Å, b_Ho=6.6745(2) Å, c_Ho=18.1642(5) Å, β_Ho=102.006(1) Å³ and a_Tm=13.4118(14) Å, b_Tm=6.6402(6) Å, c_Tm=18.1040(16) Å, β_Tm=101.980(8) Å³), Pr₂(SO₄)₃·4H₂O adopts space group P2₁/n (a=13.051(3) Å, b=7.2047(14) Å, c=13.316(3) Å, β=92.55(3) Å³). The vibrational and optical spectra of Ho₂(SO₄)₃·8H₂O and Pr₂(SO₄)₃·4H₂O are also reported.     

Crystal structure and vibrational spectra of tetrasodium dimagnesium dihydrogen diphosphate octahydrate Na4Mg2(H2P2O7)4·8H2O

A tetrasodium dimagnesium dihydrogen diphosphate octahydrate Na₄Mg₂(H₂P₂O₇)₄·8H₂O was synthesized. It crystallizes in the monoclinic system, space group P2₁/m (no. 11), Z=4, and its unit-cell parameters are: a=8.0445(3) Å, b=11.5244(5) Å, c=9.0825(4) Å, β=113.1401(2)°, V=774.28(6) Å³. The structure was determined by single-crystal X-ray diffractometry and refined to a R index of 0.0294 (wR=0.0727) for 1878 independent reflections with I>2σ(I). The framework is made by the alternance of layers of MgO₆/NaO₆ octahedra and double tetrahedra PO₄ along b-axis. Such layers are characterized by the presence of strong hydrogen bonds. (H₂P₂O₇)²⁻ anions exhibit bent eclipsed conformation. Besides, the crystal was analyzed by FT-IR and micro-Raman vibrational spectroscopy. No coincidences of the majority of the Raman and infrared spectra bands of Na₄Mg₂(H₂P₂O₇)₄·8H₂O confirms a centrosymmetric structure of this material. The vibrational spectra confirm the bent POP configuration in this compound.     

IR and Raman spectra of two layered aluminium phosphates Co(en)3Al3P4O16 · 3H2O and [NH4]3[Co(NH3)6]3[Al2(PO4)4]2 · 2H2O

The FT IR and FT Raman spectra of Co(en)₃Al₃P₄O₁₆ · 3H₂O (compound I) and [NH₄]₃[Co(NH₃)₆]₃[Al₂(PO₄)₄]₂ · 2H₂O (compound II) are recorded and analysed based on the vibrations of Co(en)₃³⁺, Co(NH₃)₆³⁺, NH₄⁺, Al---O---P, PO₃, PO₂ and H₂O. The observed splitting of bands indicate that the site symmetry and correlation field effects are appreciable in both the compounds. In compound I, the overtone of CH₂ deformation Fermi resonates with its symmetric stretching vibration. The NH₄ ion in compound II is not free to rotate in the crystalline lattice. Hydrogen bonding of different groups is also discussed.     

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.