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1.
D. Shakhvorostov M. A. Nicholls P. R. Norton M. H. Müser 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(3):347-352
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. 相似文献
2.
A. Barrera-Villatoro T. Rivera-Montalvo V. Correcher J. Garcia-Guinea J. Zarate-Medina 《光谱学快报》2018,51(1):22-26
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. 相似文献
3.
Lidija Posavec Jesper T. N. Knijnenburg Florentine M. Hilty Frank Krumeich Sotiris E. Pratsinis Michael B. Zimmermann 《Journal of nanoparticle research》2016,18(10):310
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. 相似文献
4.
《Composite Interfaces》2013,20(8):647-660
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. 相似文献
5.
E. N. Antonov A. V. Popova I. I. Selezneva V. V. Trofimov A. Yu. Fedotov A. S. Fomin 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(8):1189-1194
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. 相似文献
6.
U. Wehrmeister D. E. Jacob A. L. Soldati N. Loges T. Hger W. Hofmeister 《Journal of Raman spectroscopy : JRS》2011,42(5):926-935
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. 相似文献
7.
Sonia Stita Marta Galera Martínez Huynh Pham Xuan Ange Nzihou Patrick Sharrock 《Composite Interfaces》2013,20(6):503-515
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. 相似文献
8.
A. V. Egranov E. A. Radzhabov A. I. Nepomnyashchikh V. F. Ivashechkin I. E. Vasil’eva 《Physics of the Solid State》2008,50(9):1740-1746
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. 相似文献
9.
《Comptes Rendus Physique》2007,8(1):101-108
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). 相似文献
10.
S. Chattopadhyay G.L. Findley S.P. McGlynn 《Journal of Electron Spectroscopy and Related Phenomena》1981,24(1):27-36
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 PO (axial) bond formation is discussed. 相似文献
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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. 相似文献
14.
Toshihide Tsuji Yoshikazu Mochida Keiji Naito Koji Shibuya 《Hyperfine Interactions》1992,68(1-4):287-290
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. 相似文献
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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. 相似文献
17.
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... 相似文献
18.
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. 相似文献
19.
D. W. Mitchell T. P. Das W. Potzel M. Köfferlein H. Karzel W. Schiessl M. Steiner G. M. Kalvius 《Hyperfine Interactions》1994,90(1):411-415
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. 相似文献
20.
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. 相似文献