Mechanical properties of zinc and calcium phosphates

Recent studies on a variety of metal phosphates (MP) have revealed that MPs tend to be soft at ambient pressure if the coordination on the metal cation is low and the degree of hydration or hydrogenation is high, while they are stiff otherwise. In addition, the softer MPs were found to stiffen dramatically more quickly with increasing pressure than the stiffer MPs. Here we review these findings and support their relevance with new results on the mechanical properties of tribofilms aged in air of relative humidity, which were produced from commercial, zinc phosphate-containing lubricant packages via heating and rubbing. We find that the films can soften quite substantially after having been exposed to humidity, as to be expected from the studies of bulk MPs. Moreover, when the hydrated films are exposed to high loads, the force-distance withdrawal curve becomes identical to that of unaged, non-hydrated films. A straightforward explanation of this observation is that large pressure reverses the hydration of the tribofilms.     

Cathodo- and thermally stimulated luminescence characterization of synthetic calcium phosphates

Cathodo- and thermoluminescence emission of calcium phosphates, synthetized by chemical precipitation and characterized by X-ray diffraction, environmental scanning electronic microscopy and energy dispersive spectroscopy have been studied. Thermal treatment at 1100°C increases the crystallinity, a phase transition (hydroxylapatite + β-tricalcium phosphate → β-tricalcium phosphate) and an enhancement of the luminescence emission. Cathodoluminescence and thermoluminescence display a very complex spectra in the UV–IR range where the wavebands would be associated with the presence of (i) hydroxyl groups, (ii) nonbridging oxygen hole centers, (iii) excited oxygens, (iv) peroxy groups, and (v) residual iron ions in the lattice.     

Dissolution and storage stability of nanostructured calcium carbonates and phosphates for nutrition

Rapid calcium (Ca) dissolution from nanostructured Ca phosphate and carbonate (CaCO₃) powders may allow them to be absorbed in much higher fraction in humans. Nanosized Ca phosphate and CaCO₃ made by flame-assisted spray pyrolysis were characterized by nitrogen adsorption, X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. As-prepared nanopowders contained both CaCO₃ and CaO, but storing them under ambient conditions over 130 days resulted in a complete transformation into CaCO₃, with an increase in both crystal and particle sizes. The small particle size could be stabilized against such aging by cation (Mg, Zn, Sr) and anion (P) doping, with P and Mg being most effective. Calcium phosphate nanopowders made at Ca:P ≤ 1.5 were XRD amorphous and contained γ-Ca₂P₂O₇ with increasing hydroxyapatite content at higher Ca:P. Aging of powders with Ca:P = 1.0 and 1.5 for over 500 days gradually increased particle size (but less than for CaCO₃) without a change in phase composition or crystallinity. In 0.01 M H₃PO₄ calcium phosphate nanopowders dissolved ≈4 times more Ca than micronsized compounds and about twice more Ca than CaCO₃ nanopowders, confirming that nanosizing and/or amorphous structuring sharply increases Ca powder dissolution. Because higher Ca solubility in vitro generally leads to greater absorption in vivo, these novel FASP-made Ca nanostructured compounds may prove useful for nutrition applications, including supplementation and/or food fortification.     

Synthesis,characterization, and thermo-mechanical properties of copper-loaded apatitic calcium phosphates

Copper is well known as a classical transition metal used in heterogeneous catalysis. In this study, copper-loaded apatitic calcium phosphates were prepared using incipient wetness impregnation (IWI) and ionic exchange (IE) methods. The interaction between copper precursor (copper nitrate trihydrate, Cu(NO₃)₂?3H₂O) and apatitic calcium phosphate (CaP) depended strongly on the preparation method and the content of copper-loaded. Using IE, copper(II) cations (Cu²⁺) were incorporated in the apatitic structure of CaP. The content of copper(II) cations seemed to be limited at about 2.2?wt.%. Calcination at 400?°C had no influence on the solids obtained by the IE method. Using IWI, the deposition of a theoretical copper content of 2?wt.% led to the incorporation of copper(II) cations in the apatitic structure of CaP by IE with Ca²⁺, despite the low quantity of aqueous solvent used. Therefore the resulting product was similar to that obtained by IE. When the theoretical copper content rose to 20?wt.%, the entire amount of copper precursor molecules were largely deposited, which resulted in the formation of copper oxide particles (CuO) after air calcination at 400?°C. Thermo-mechanical analysis study showed that the presence of copper oxide did not modify the thermal shrinkage of the initial calcium phosphate. On the other hand, thermal shrinkage was much more important in the case of CaP substituted with copper(II) cations.     

Mechanical characteristics of composites of polylactide and nanosized calcium phosphates formed in supercritical carbon dioxide

Composite materials for biomedical applications based on polylactide, a bioresorbable polymer, and nanosized calcium phosphate (hydroxyapatite) were produced using supercritical (SC) carbon dioxide. For composites with different polymer-to-mineral ratios, the bending stress-strain diagrams were investigated. The elasticity moduli of composites obtained in SC-CO₂ from powdered bioresorbable polymer and bioactive nanoceramics ranged elastic modulus of natural bone. Experiments on adhesion of human embryonic fibroblasts demonstrated the suitability of generated samples for use in bone tissue scaffold engineering and regenerative medicine.     

Amorphous,nanocrystalline and crystalline calcium carbonates in biological materials

Raman spectroscopy is a powerful tool in identifying different calcium carbonate polymorphs. Here, the method is applied to cultured pearls from freshwater (genus Hyriopsis) and marine bivalve species (Pinctada maxima) as well as to shells of Diplodon chilensis patagonicus bivalves. Raman spectra for vaterite, detected for the first time in an adult shell, and amorphous calcium carbonate (ACC) are discussed. Results for ACC are compared with those of synthetically produced ACC and with the Raman spectroscopic features of stable biogenic ACC from the crustacean Porcellio scaber. Decomposition of the most intense signal of all calcium carbonate polymorphs—the ν₁ symmetric stretching mode of the carbonate ion—leads to the identification of two polymorphs within the ACC areas: a mixure of an amorphous and a crystalline fraction. The amorphous phase is characterised by a broad peak in the region of the lattice modes, which is composed of two distinct lattice modes with very high full‐widths at half‐maximum (FWHMs). The FWHMs of most of the crystalline fractions (in the range of 6.3–10.7 cm⁻¹) are too high for well‐crystallised materials and support reports of nanocrystalline calcium carbonate polymorph clusters in ACC. Crystallinity indices of different samples are calculated and found to be useful to describe roughly the state of crystallisation in the ACC areas. Copyright © 2010 John Wiley & Sons, Ltd.     

Metal-doped apatitic calcium phosphates: preparation,characterization, and reactivity in the removal of hydrogen sulfide from gas phase

With the expansion of human activities, there are more and more living areas adjacent to industrial and/or agricultural activities such as chemical processes, petroleum processes, paint finishing, food processing, livestock farming, composting plants etc. Bad odor is part of several nuisances caused by industrial and/or agricultural activities. Hydrogen sulfide (H₂S) is a typical odorous molecule which causes foul odor at very low concentration. This molecule is formed in different industrial installations, in particular in coal combustion, and petrochemical refinery. The separation and/or transformation of H₂S from gas phase to odorless products are important processes for sustainable development. In this paper, we communicate the preparation of new sorbents for the sorption of H₂S from a synthetic gas effluent. These sorbents consist in an inorganic phase (hydroxyapatite) as host particles, and well-dispersed particles of a metal oxide as guest particles which are the active phase for the removal of H₂S. At room conditions, iron, lead, and zinc doped calcium phosphates were found to be effective for the removal of H₂S. The performance of the sorbents depends on preparation method and the nature of active phases. This opens new prospects for the treatment of H₂S from gas phase.     

Radiation defect formation in strontium and calcium fluoride crystals doped by divalent cadmium and zinc ions

Ionization radiation is shown to reduce impurity ions to the univalent state in strontium and calcium fluoride crystals doped by divalent cadmium and zinc ions. In this case, a univalent ion is surrounded by eight equivalent fluorine ions and exhibits cubic symmetry O _h . At room temperature, the symmetry of the center is revealed to be sequentially lowered to C _3v and then to C _2v owing to the addition to the nearest environment of the impurity univalent ion of one or two anion vacancies, respectively, which are intrinsic defects not forming in undoped strontium and calcium fluoride crystals. Stable intrinsic defects are assumed to form through the separation of anion vacancy-interstitial fluorine ion pairs in the electric field induced by the reduced impurity ions. This electric field lowers the energy barrier to thermal separation of charged intrinsic defects.     

Élaboration et caractérisation d'un biomatériau à base de phosphates de calcium

The tricalcium phosphate–fluorapatite composite has a good aptitude to sintering at 1300 °C, so a densification rate of about 90% was reached with 33.16 wt% of fluorapatite. At 1300 °C, the increase of the content of fluorapatite in the composite favours the formation of the α tricalcium phosphate phase. The ³¹P MAS-NMR analysis reveals the presence of three tetrahedral P sites for the tricalcium phosphate, whereas the fluorapatite possesses only one. At temperatures higher than 1300 °C, the densification is hindered by grain growth and the formation of large pores. To cite this article: F. Ben Ayed, J. Bouaziz, C. R. Physique 8 (2007).     

Photoelectron spectroscopy of phosphites and phosphates

The ultraviolet photoelectron spectra (UPS) of trimethyl and triethyl phosphite, trimethyl and triethyl phosphate and four substituted phosphates are presented. Assignments are based on analogies to the UPS of phosphorus trichloride and phosphoryl trichloride and are substantiated by CNDO/2 computations. The mechanism of PO (axial) bond formation is discussed.     

Distribution of risk elements in the organism of sheep after industrial intoxication with zinc

Abstract

Diagnostics of experimental zinc intoxication by industrial emission from the zinc and copper factory on the basis of accumulation and distribution of Zn, Cu, Fe, Mo, Se, As, Cd and Pb in the liver, kidneys, spleen, musculature, uterus, ovaries, chorioidea of eye and bones in seven experimental and five control sheep is described. A daily intake of Zn from industrial emission was 6158.07 mg/an experimental animal. The first animals died of zinc intoxication on d 42 and the last one on d 58 of the experiment. The highest concentration of zinc in experimental animals died of zinc intoxication was in the liver dry matter (1167.3 ± 314.1 mg.kg^?1) and in the kidneys (1049.5 ± 283.7 mg.kg^?). Significantly higher Zn content compared with the control sheep was confirmed in the experimental ones in the liver, kidneys, ovaries and eye chorioidea (p < 0.01). The liver, kidneys, uterus were the organs with the highest Cu accumulation. The highest Fe accumulation was found in the spleen, kidneys and liver. Distribution of Mo and Se in the organs analyzed in experimental and control animals was similar. The industrial emission intake from the copper and zinc factory manifested in statistically higher accumulation of As, Cd and Pb in the organism of experimental sheep than in control ones (p < 0.05; methallothionein within the process of resorption, retention and metabolic activity (Kojima et al., 1991). The negative interaction between Zn and Pb is, above all, within the process of absorption (Elsenhans et al., 1978). Comparison of cumulation and distribution of As, Cd and Pb in the organs of experimental and control sheep revealed that in experimental animals the significant differences reflected the intake of these elements from industrial emission. Possibility for interaction relations with Zn, regarding the presence of the other toxic elements, appeared to be secondary.     

Effects of calcium and zinc on the adsorption of cobalt on γ-Fe2O3

The effects of calcium and zinc on the room-temperature coercivity of γ-Fe₂O₃ particles having cobalt ions adsorbed in 3M NaOH solution at 373K have been studied. When the Ca²⁺ ions are adsorbed on the γ-Fe₂O₃ prior to Co²⁺ ions adsorption, the coercivity of Co-modified γ-Fe₂O₃ significantly increases compared with that of γ-Fe₂O₃ modified only with Co²⁺ ions. In the case of Zn²⁺ ions, the coercivity of Co-modified γ-Fe₂O₃ is the same as that of γ-Fe₂O₃ modified only with Co²⁺ ions. The emission Mössbauer spectrum of⁵⁷Co²⁺ adsorbed on the surfaces of γ-Fe₂O₃ after pretreating with Ca²⁺ ions consists of a typical sextet of Fe³⁺ ions with hyperfine magnetic field, whereas those of γ-Fe₂O₃ modified only with Co²⁺ ions and with both Zn²⁺ and Co²⁺ ions show nonmagnetic components in addition to magnetic one. The effects of Ca²⁺ and Zn²⁺ ions on the adsorption of cobalt on the surface of γ-Fe₂O₃ are discussed from the viewpoint of site preference energy of cations in ferrite and distribution ratio of each cation.     

XPS analyses of lanthanides phosphates

XPS measurements were performed on lanthanide orthophosphates LnPO₄ (Ln: La, Ce, Nd, Gd), and correlated with XRD and some EDS analyses. Single lanthanide phosphates LnPO₄ and mixed lanthanide phosphates LnxLn^′1−xPO₄, all crystallized in a monoclinic structure similar to the monazite mineral. Results were examined qualitatively and quantitatively, by considering the Ln 3d lines, P 2p line and O 1s line.Ionic sputtering does not induce significant broadening nor an additional shift of the lanthanide peaks and does not have an effect on their chemical environments, except in the case of cerium. However, sputtering seems to significantly reduce the intensity of the O 1s and P 2p peaks, while Auger peaks of carbon and oxygen atoms interfere, respectively, with the 3d line of gadolinium and neodymium. Those phenomena are all the more important when the Nd and Gd content is weak and must be taken into account for a quantitative analysis of the spectra.The quantitative analyses reveal the expected results for single monazites. On mixed phosphates, the measured phosphorous and oxygen amounts are generally more valid for non-sputtered sample surfaces than for sputtered surfaces, while the calculated relative amount of lanthanides [Ln]/[Ln′] are correct in all the cases.One of the important goals of this work was to have a satisfactory value for the atomic ratio La/Gd, and particularly in the case of (La,Ce)PO₄ and (La,Gd)PO₄, to obtain good agreement between the calculated lanthanides ratio Nd/Gd and ratios estimated from XRD and EDS measurements.     

Role of sensitivity of zinc oxide nanorods (ZnO-NRs) based photosensitizers in hepatocellular site of biological tissue

Laser Physics - Zinc oxide nanorods (ZnO-NRs) with high surface to volume ratio and bio compatibility are used as an efficient photosensitizer carrier system for achievement of Hepatocellular...     

Luminescence spectroscopy of Ln-doped Bi-containing phosphates and molybdates

The photoluminescence (PL) emission and excitation spectra of undoped and doped with rare-earth (RE = Eu, Tb) ions K₃Bi₅(PO₄)₆ and K₂Bi(PO₄)(MoO₄) crystals are studied in 3.7–14 eV region of the excitation photon energies at T = 8 and 300 K. The mechanisms of the host-related and RE-related luminescence in 3.7–7 eV region of the excitation photon energies are revealed in comparative analysis of the PL spectra of studied compounds. It is assumed that the excitation mechanisms of host luminescence of K₃Bi₅(PO₄)₆ and K₂Bi(PO₄) (MoO₄) crystals below 4.8 eV are related to Bi³⁺ ions in oxygen surrounding. An efficient energy transfer from the Bi³⁺-related luminescence centers to the emitting RE centers exists in crystals with low concentration of the RE dopants (1%). The PL excitation spectra of K₃Bi₅(PO₄)₆ crystals with high concentration of Eu dopants are formed by O – Eu CT transitions.     

Theoretical calculations of electron densities in zinc chalcogenides and in zinc fluoride

Self-consistent, non-relativistic Hartree-Fock calculations on a finite cluster of atoms with zinc at the center have been performed on the zinc blende compounds ZnTe, ZnSe, ZnS, on ZnO (wurtzite structure), ZnO (NaCl structure), and on ZnF₂ (rutile-type structure) to obtain changes in s electron density (0) at the⁶⁷Zn nucleus. We solved the eigenvalue problem of the dynamic matrix to calculate the second-order Doppler shiftS _SOD using appropriate force constant models and determined the isomer shiftS from the measured center shift for each compound. Our calculations clearly show the importance of the covalency of the Zn-ligand bond for the origin ofS and fully corroborate the experimental linear correlations between decreasingS values and increasing electronegativity of the ligands. The most important contribution to (0) comes from the Zn(4s) electrons, with a smaller but significant contribution from the Zn(3s) electrons. For the change of the mean-square nuclear charge radius for the Mössbauer transition in⁶⁷Zn, we obtain r ²=+(13.9±1.4) × 10^–3 fm².     

Chemical treatment of TiO2-based coatings formed by plasma electrolytic oxidation in electrolyte containing nano-HA, calcium salts and phosphates for biomedical applications

TiO₂-based coatings were formed on titanium alloy by plasma electrolytic oxidation (PEO) in an electrolyte containing nano-HA, calcium salts and phosphates. Bioactive surface was formed after chemical treatment (NaOH aqueous solution) of the PEO coating. The surface of the PEO coating was mainly composed of Ti, O, Ca and P showing anatase and rutile; while that of the chemically treated PEO (CT-PEO) coating mainly contains Ti, O, Ca and Na showing anatase, rutile and amorphous phase. And the chemically treated surface exhibits dissolution of P and introduction of Na during the chemical treatment process. The chemical treatment has no effect on the chemical states of Ca and Ti of the PEO coating. In addition, the surface constituents of the CT-PEO coating show a uniform distribution near its surface with increasing depth. When incubated in a simulated body fluid for 7 and 14 days, the PEO coating does not exhibit apatite-forming ability; however, apatite was successfully deposited on the CT-PEO coating after 7 days probably due to the formation of hydroxyl functionalized surface, enhancing the heterogeneous nucleation of apatite. The addition of nano-HA in the electrolyte has effects on the surface character and apatite-forming ability of the PEO coating; however, it has no obvious influence on those of the CT-PEO coatings.