The precipitation of sparingly-soluble alkaline-earth metal phosphates in gelatine gels by diffusion of anion (i). the precipitation of calcium hydrogen phosphate dihydrate and basic calcium phosphates

The precipitation of different calcium phosphates in gelatine gels was studied by diffusion of disodium hydrogen phosphate solutions into ten percent gels containing calcium cation at liquid gel pHs from 6 to 11. At pHs 6.0 to 7.5, calcium hydrogen phosphate dihydrate (CaHPO₄ · 2 H₂O) was deposited as a continuous precipitate and then as rings of precipitate (the Liesegang phenomenon): their spacing coefficients varied with the reciprocal initial anion concentrations according to the Packter-Matalon relation. At liquid gel pHs 8.0, 8.5, tretacalcium phosphate (Ca₄H(PO₄)₃) was deposited as a continuous precipitate. At liquid gel pHs from 8.5 to 11, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, Ca/P ratios = 1.50 to 1.67) was deposited as a continuous precipitate. The mechanisms of precipitation of the different calcium phosphates (in gelatine gels) is briefly discussed.     

Effects of cadmium on crystallization of calcium phosphates

The precipitation of calcium phosphates in the presence of increasing cadmium amount was studied at 25 °C in dilute ammoniacal solutions ([Ca] = [P] = 0.005 M). An amorphous precipitate, an apatite‐like calcium phosphate and the compound Cd₅H₂(PO₄)₄·4H₂O are found according to pH and Cd concentration. The nucleation of hydroxyapatite is greatly delayed by cadmium, which influences also its crystallinity, but the effect tends to vanish with time. The role of cadmium is discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Ca on HoPO4·nH2O (n = 1 and 2) crystallization from phosphoric acid solution

Ca‐substituted holmium phosphate, isomorphic with tetragonal form of HoPO₄·H₂O was synthesized by crystallization from boiling phosphoric acid (2 M H₃PO₄) solution containing 0.02M of Ho and 0–0.2 M of Ca. Calcium concentration, higher than 0.2 M Ca in solution resulted in biphasic solid crystallization: tetragonal HoPO₄·H₂O and orthorhombic HoPO₄·2H₂O. Ca incorporation in the solid according to substitution mechanism: Ca²⁺ + H⁺ ↔ Ho³⁺ was limited to ∼3 wt.% and was coupled with simultaneous incorporation of HPO₄²⁻. Ca for Ho substitution caused an expansion of the tetragonal unit cell of HoPO₄·H₂O, resulted from differences in the ionic radii (r_Ca > r_Ho). Effects of thermal treatment at 900 °C were as follows: (i) the orthorhombic admixture of HoPO₄·2H₂O re‐crystallized into tetragonal anhydrous HoPO₄, (ii) Ca–at first dissolved in crystal structure of HoPO₄·H₂O was expelled from it during re‐crystallization to form Ca(PO₃)₂, and that was associated with a contraction of the unit cell; a ‐ and c‐ axes went down to the level of Ca‐free anhydrous tetragonal form of HoPO₄. (iii) HPO₄²⁻ present in the solids as prepared underwent condensation according to reaction 2HPO₄²⁻ → P₂O₇⁴⁻ + H₂O. Scanning electron micrographs revealed significant changes in size and morphology of the crystals ranging from spherical globules of HoPO₄·H₂O formed in Ca‐free H₃PO₄ with increasing diameter in the presence of lower Ca concentration to rod‐like crystals organized in bundles resembling the “scheaf of wheat”, while crystallized from phosphoric acid solution with higher than 0.2 M Ca.     

The Coprecipitation of Magnesium Iron (III) Hydroxide Powders from Aqueous Solution: Precipitate Compositions and Coprecipitation and Ageing Mechanisms

Series of magnesium iron(111) hydroxides were coprecipitated at ambient temperature from different mixed metal cation solutions, at C_{M tot} = 0.1 M and Mg/Fe₂ ratios from 4 to 1/4, with sodium hydroxide solution. The relevant single precipitations and the coprecipitations were monitored by potentiometric (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis. The coprecipitates onto aged α-FeOOH were simple mixtures of α-FeOOH and Mg(OH)₂. The main coprecipitates were either «molecular inclusion mixtures» of microcrystalline α-FeOOH with excess Mg(OH)₂ or similar mixtures of Mg(OH)₂ with excess α-FeOOH and some ten-twenty percent (relative to the Mg content) of magnesium hydroxo-ferrate(III) hydrate Mg[Fe(OH)₄]₂ · h H₂O. The coprecipitates aged in alkaline magnesium hydroxide suspension at 20 °C and 40 °C were mixtures of Mg(OH)₂, α-FeOOH and forty to ninety percent (relative to the Mg content) of Mg[Fe(OH)₄]₂ · h H₂O. The related α-FeOOH NaOH and α-FeOOH Mg(OH)₂ equilibria and the different coprecipitation mechanisms are discussed.     

Tribochemical synthesis of halogen-phosphate luminophores

The possibility of tribochemical synthesis of Ca₁₀(PO₄)₆ · (F, Cl)₂SbMn is shown. It was proved that the synthesis with the initial compounds CaHPO₄ · 2H₂O or β-Ca₃(PO₄)₂ is realized 1–2 hours faster than the synthesis when CaHPO₄ is used.     

Crystallization and Characterization of Calcium Phosphates: Brushite and Monetite

Spherulitic monetite (CaHPO₄) and brushite (CaHPO₄ · H₂O) of different morphologies which have close resemblance to those found in pathological joints, stones and dental calculi were crystallized in silica gel under acidic conditions. These crystals were characterized by x-ray powder diffraction, fourier transform infra-red, and thermogravimetric analyses. The molar ratios (Ca/P) were calculated from ICP analysis and found to be in agreement with the theoretical stoichiometric molar ratio. The microstructure of the spherulitic monetite crystals have been studied using scanning electron microscopy.     

Growth of single crystals of NaH2PO4 (NaDP), NaH2PO4 · H2O (NaDP · H2O), and NaH2PO4 · 2H2O (NaDP · 2H2O) sodium dihydrogenphosphate based on the analysis of the Na2O-P2O5-H2O phase diagram

The crystallization conditions for the NaH₂PO₄, NaH₂PO₄ · H₂O, and NaH₂PO₄ · 2H₂O solid phases have been established from the analysis of the phase diagram of solubility of the ternary Na₂O-P₂O₅-H₂O system in the temperature range from 0 to 100°C. Based on these data, the methods for growing sodium dihydrogenphosphate single crystals of the above compositions are developed. The initial components for preparing mother solutions were H₃PO₄ and NaOH solutions taken in certain weight ratios. For the first time, NaDP, NaDP · H₂O, and NaDP · 2H₂O single crystals were grown on a seed by the method of temperature decrease. The habits of the NaDP and NaDP · H₂O single crystals are determined. __________ Translated from Kristallografiya, Vol. 47, No. 5, 2002, pp. 937–944. Original Russian Text Copyright ? 2002 by Soboleva, Voloshin.     

Synthesis of magnesium oxysulfate whiskers in the presence of sodium dodecyl benzene sulfonate

Uniform magnesium oxysulfate (5Mg(OH)₂·MgSO₄·3H₂O) whiskers with a length of 10‐15 µm and a diameter of 0.4‐1.0 µm were synthesized in the presence of sodium dodecyl benzene sulfonate (Na‐SO₃‐C₆H₄‐C₁₂H₂₅) at 200°C for 1 h, using MgSO₄·7H₂O and NaOH as the reactants. Mg(OH)₂ precursor with poor crystallization and small crystal size was formed owing to the adsorption of sodium dodecyl benzene sulfonate on the Mg(OH)₂ surface. The quick dissolution of Mg(OH)₂ precursor in the subsequent hydrothermal reaction inhibited the occurrence of the sector‐like byproduct and promoted the formation of magnesium oxysulfate whiskers with uniform morphology. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Me2O-P2O5-H2O solubility phase diagrams and growth of MeH2PO4 single crystals (Me = Li, Na, K, Rb, Cs, NH4)

The Me ₂O-P₂O₅-H₂O solubility phase diagrams are used to determine the optimum compositions and the temperatures for growing crystals of MeH₂PO₄ solid phases (Me = Li, Na, K, Rb, Cs, NH₄). The optimum conditions for dynamic growth of dihydrophosphates of the elements of the first group and ammonium are determined. LiH₂PO₄, NaH₂PO₄, NaH₂PO₄ · 2H₂O, NaH₂PO₄ · H₂O, KH₂PO₄, K(H,D)₂PO₄, RbH₂PO₄, CsH₂PO₄, and (NH₄)H₂PO₄ single crystals are grown on seed from aqueous solutions by the methods of temperature lowering and isothermal evaporation. __________ Translated from Kristallografiya, Vol. 49, No. 4, 2004, pp. 773–777. Original Russian Text Copyright ? 2004 by Soboleva, Voloshin.     

Ca for Er substitution in tetragonal ErPO4 · H2O crystallised from phosphoric acid solution

Erbium phosphate monohydrate with limited Ca for Er substitution, obtained through crystallisation from boiling phosphoric acid solution has been characterised by X‐ray diffraction, Ir‐spectroscopy and thermal analysis (TGA‐DTA) methods. The difference in the electric charge between di‐valent calcium and tri‐valent erbium in the solid crystallised was compensated by simultaneous substitution of HPO₄^2‐ for PO₄^3‐. Ca incorporation in erbium phosphate made expansion of tetragonal ErPO₄ · H₂O unit cell. After ignition at 900 °C the tetragonal crystal modification was maintained but the unit cell parameters of all the investigated phosphates, whether Ca‐substituted or Ca‐free, contracted to the same level. The unique contraction of the unit cell was resulted from recrystallisation of Ca‐substituted into Ca‐free erbium phosphate, while Ca was transferred into Ca(PO₃)₂ formed as a separate phase. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self-assembled dahlia-like cadmium hydrogen phosphate hydrate nanostructures as templates for cadmium hydroxyapatite hexagonal prisms

Cadmium hydroxyapatite (Cd-Hap, Cd₁₀(PO₄)₆(OH)₂) and cadmium hydrogen phosphate hydrate (Cd₅H₂(PO₄)₄·4H₂O) nanostructures with average crystallite sizes of about 38 and 44 nm, respectively, were prepared through a simple chemical process. The formation mechanism and characteristics of the Cd₅H₂(PO₄)₄·4H₂O precipitates prior to the hydrothermal process and Cd-Hap during the hydrothermal treatment were investigated with XRD, SEM, TEM and BET analyses. It was found that self-assembled dahlia-like Cd₅H₂(PO₄)₄·4H₂O nanostructure precipitates were formed due to interlace of preliminary nanosheets prior to the hydrothermal process, while nanostructure Cd-Hap hexagonal prisms were prepared after 15 h of hydrothermal treatment.     

Composition and morphology control of Fex(PO4)y(OH)z·nH2O microcrystals

A series of Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals were prepared by the hydrothermal reaction at 150 °C. The ratio of Fe²⁺/Fe³⁺ in Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals can be adjusted by using Na₂S₂O₃·5H₂O as a reducing agent. The morphology control of Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals was realized through regulating the molar ratio of LiAc·2H₂O/FeCl₃. Further, the morphology, structure and composition of Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals were also investigated by x‐ray diffraction (XRD), x‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) techniques. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of anhydrous dicalcium phosphate, DCPA, through sol-gel process, identification and phase transformation evaluation

Anhydrous dicalcium phosphate, CaHPO₄, DCPA, as a member of the series of calcium phosphates, has considerable biological importance to the biomineralization processes in bones and teeth, and has found practical applications in dental cements and restorative materials. This compound, can reconstruct hard tissues because of high solubility in vivo in comparison with many of the other calcium phosphate compounds. In this work, Ca-deficient DCPA was synthesized through sol-gel process as a new method. Ca(NO₃)₂ · 4H₂O and H₃PO₄ were employed as precursors and identified by XRD, FTIR and SEM spectroscopic techniques. The later technique makes the elemental analysis possible. The measured Ca/P molar ratio suggests, Ca_1−x(H₂PO₄)_2x(H₂PO₄)_1−2x (x = 0.02, 0.04 and 0.07) formula for the synthesized compounds. The effect of aging time and heat treatment (sintering stage) on phase purity and phase transformations of products were systematically studied. The minimum necessary aging time for Ca-deficient DCPA preparation was 24 h. From X-ray patterns of powders sintered at different temperatures, the sintering temperature of Ca-deficient DCPA was confirmed to be 300 °C. According to the experimental results, varying the temperature from 300 to 1000 °C gave different stable phases as products: Ca-deficient DCPA at 300 °C, hydorxyapatite (Ca₅(PO₄)₃OH, HA) at 600 °C and β-tri calcium phosphate (β-Ca₃(PO₄)₂, β-TCP) at 1000 °C.     

Compositions of supersaturated solutions for enhanced growth of α-NiSO4 · 6H2O, Me 2Ni(SO4)2 · 6H2O, MeH2PO4 [Me = Li, Na, K, Rb, Cs, NH4], and K(H x D1−x )2PO4 single crystals

The possibility of determining the optimal compositions and temperatures of supersaturated solutions for enhanced growth of single crystals of congruently and incongruently dissolving solid phases from the solubility diagrams of ternary systems is shown, and this approach is justified. The NiSO₄-H₂SO₄-H₂O, Me ₂SO₄-NiSO₄-H₂O, and Me ₂O-P₂O₅-H₂O(D₂O) systems have been used to determine the optimal compositions and temperatures of supersaturated solutions for growth of α-NiSO₄ · 6H₂O, Me ₂Ni(SO₄)₂ · 6H₂O, MeH₂PO₄ [Me = Li, Na, K, Rb, Cs, NH₄], and K (H _x D_1?x )₂PO₄ (D is deuterium) single crystals.     

Structure Characterization of EDTA Transition Metal Complexes (II) Study on Ba[Co(HEDTA)H2O]2 · 4H2O

The d-d transition spectrum of Ba[Co(HEDTA)H₂O]₂ · 4H₂O crystal was measured at room temperature and experimental results are explained quantitativley by using the ligand field theory and the radial wave function of non-free Co(II) ion. The crystal structures and the electronic structures of M/Co-EDTA (M=Ba, Sr, Ca, Mg) complexes are also discussed.     

Influence of solvents on the hydrothermal formation of one‐dimensional magnesium hydroxide

The influence of solvents on the hydrothermal formation of one‐dimensional (1D) magnesium hydroxide (Mg(OH)₂) was investigated in this paper. Uniform 1D Mg(OH)₂ with a length of 10‐20 μm, a width of 100‐200 nm and a preferential growth along [110] direction have been synthesized by treating magnesium oxysulfate (5Mg(OH)₂·MgSO₄·3H₂O, abbreviated as 513MOS) nanowires in NaOH ethanol solution at 180 °C for 2.0 h. The experimental results indicated that the solvent of ethanol and NaOH concentration were essential for the conversion of 513MOS nanowires to 1D Mg(OH)₂. The slow release of MgSO₄ from 513MOS and the heterogenous precipitation of Mg(OH)₂ at the defects left by MgSO₄ dissolution promoted the formation of 1D Mg(OH)₂. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The coprecipitation of magnesium aluminium hydroxocarbonate powders from aqueous solution: Precipitate compositions and coprecipitation mechanisms

Magnesium aluminium hydroxocarbonate hydrates were coprecipitated from mixed metal nitrate solutions, at total C_M = 0.2 M and Mg/Al₂ = 1 ratio, with four sodium hydrogen carbonate-sodium carbonate solutions (of pH 8.1 to 11.5) at ambient temperature. The course of precipitation was monitored by potentiometric (pH) titration, and the compositions of the primary and final precipitates were determined by chemical analysis, infrared spectrophotometry and X-ray diffraction. Precipitation generally occurred through three stages, primary precipitation (of low CO₃ aluminium hydroxocarbonates) at low pH with evolution of carbon dioxide, their dissolution by complexing to form hydroxocarbonatoaluminate anions and then secondary precipitation of the final coprecipitate at higher pHs. The final product from coprecipitation by sodium hydrogen carbonate solution (pH 8.1) was mainly the magnesium hydroxocarbonatoaluminate ‘MAHC I’; the final products from coprecipitation by sodium hydrogen carbonate-sodium carbonate solutions (pH 9.4 and 10.3) were ‘MAHC I’/‘MAHC II’ mixture and ‘MAHC II’/‘MAHC I’ mixture whereas the final product from coprecipitation by sodium carbonate solution (pH 11.5) was a complex mixture if ‘MAHC II’ with ‘MAHC I’ and ‘MAHC III’;

• ‘MAHC I’ was probably Mg₂[Al₄(OH)₁₀(CO₃)₃] · hH₂O,
• ‘MAHC II’ was probably Mg[Al₂(OH)₄(CO₃)₂] · h H₂O whereas
• ‘MAHC III’ was probably Mg[Al₂(OH)₆CO₃] · h H₂O.

     

Growth and characterization of calcium hydrogen phosphate dihydrate crystals from single diffusion gel technique

Calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O, CHPD) a dissolved mineral in urine is known to cause renal or bladder stones in both human and animals. Growth of CHPD or brushite using sodium metasilicate gel techniques followed by light and polarizing microscopic studies revealed its structural and morphological details. Crystal identity by powder x‐ray diffraction confirmed the FT‐IR and FT‐Raman spectroscopic techniques as alternate methods for fast analysis of brushite crystals which could form as one type of renal stones. P‐O‐P asymmetric stretchings in both FT‐IR (987.2, 874.1 and 792 cm^‐1) and FT‐Raman (986.3 cm^‐1, 1057.6 cm^‐1 and 875.2 cm^‐1) were found as characteristics of brushite crystals. Differential Scanning Calorimetry (DSC) analysis revealed brushite crystallization purity using gel method by studying their endothermic peaks. This study incorporated a multidisciplinary approach in characterizing CHPD crystals grown in vitro to help formulate prevention or dissolution strategy in controlling urinary stone growth. Initial studies with 0.2 M citric acid ions as controlling agent in the nucleation of brushite crystals further support the presented approach. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

DTA,DSC, and X-ray Powder Diffraction Studies on Some Zinc Selenate Hydrates

The thermal dehydration of ZnSeO₄ · 6 H₂O, ZnSeO₄ · 5 H₂O, and ZnSeO₄ · 3 H₂O has been studied by TG, DTA, and DSC-analyses. It has been established that the dehydration of ZnSeO₄ · 6 H₂O occurs stepwise and as intermidiate hydrates ZnSeO₄ · 5 H₂O, ZnSeO₄ · 3 H₂O and ZnSeO₄ · H₂O are produced. The enthalpy of dehydration of the observed phase transitions has been determined. The enthalpy of formation of ZnSeO₄ · 6 H₂O, ZnSeO₄ · 5 H₂O, ZnSeO₄ · 3 H₂O, and ZnSeO₄ · H₂O has been calculated on the basis of the DSC-data. ZnSeO₄ · 5 H₂O and ZnSeO₄ · 3 H₂O have been studied rentgenographically: ZnSeO₄ · 5 H₂O crystallizes in triclinic system with lattice parameters: a = 6.387(2) Å; b = 10.706(3) Å; c = 6.167(3) Å; α = 98.66(2)°; β = 109.32(3)° γ = 75.52(3)° V = 384.3(2) ų; SG P1 . ZnSeO₄ · 3 H₂O forms orthorhombic crystals with lattice constants: a = 8.165(4)Å; b = 11.314(5) Å; c = 12.465(7) Å; V = 1151.5(7) ų; SG Pbca.     

Formation of solution inclusions in bicrystals of potassium-cobalt/potassium-nickel and ammonium-cobalt/ammonium-nickel sulfates

The crystallization of epitaxial layers from aqueous solutions in the K₂Co(SO₄)₂ · 6H₂O-K₂Ni(SO₄)₂· 6H₂O and (NH₄)₂Co(SO₄)₂· 6H₂O-(NH₄)₂Ni(SO₄)₂ · 6H₂O systems has been studied. A mechanism is proposed to explain the experimentally observed phenomena, taking into account the effect that elastic stresses have on the crystallization kinetics.