Ultrasonic enhancing amorphization during synthesis of calcium phosphate

Amorphous calcium phosphate (ACP) has great application potential in biomaterials field due to its non-cytotoxicity, high bioactivity, good cytocompatibility, and so on. The results of this research demonstrated that ultrasonic obviously enhanced amorphization during synthesis of calcium phosphate. The ACP phase was relatively ideal when the solvent of Ca(NO₃)₂·4H₂O was ethanol and the solvent of (NH₄)₂HPO₄ was a mixture of water and ethanol, under ultrasonic. In-situ crystallization of ACP could be observed by HRTEM. The mechanism on the effects of ultrasonic on amorphization of the synthesized calcium phosphate was discussed. It was suggested that ultrasonic synthesis might be a facile method to prepare pure and safe ACP related biomaterials.     

Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing

Droplets of several micrometers in size can be formed in aqueous solution by atomization under ultrasonic irradiation at 2 MHz. This phenomenon, known as atomization, is capable of forming fine droplets for use as a reaction field. This synthetic method is called SARM (sono atomization for reactive mixing). This paper reports on the synthesis of a novel amorphous calcium carbonate formed by SARM. The amorphous calcium carbonate, obtained at a solution concentration of 0.8 mol/dm³, had a specific surface area of 65 m²/g and a composition of CaCO₃•0.5H₂O as determined using thermogravimetric/differential thermal analysis (TG-DTA). Because the ACC had a lower hydrate composition than conventional amorphous calcium carbonate (ACC), the ACC synthesized in this paper was very stable at room temperature.     

Studies on Calcium Release and H2O2 Level Produced by the Elicitor Induced Plant Cell by Fluorescence Probing

Using fluorescence probing technology, we studied the mechanism and interrelations of calcium release and H₂O₂ production in situ in living tissues of tobacco and cotton plants which were induced by pathogen elicitor, salicylic acid (SA) and pectinase respectively. Results showed that (1) pathogen elicitors could induced H₂O₂ response in epidermis cells regardless of environmental calcium, but in mesophyll protoplast, H₂O₂ response could only be induced at calcium condition. Similarly, SA and pectinase induced H₂O₂ response could only be observed at calcium condition; (2) pathogen elicitors could induce calcium response in both epidermis cells and protoplasts regardless of environmental calcium, while calcium response couldn’t be induced at non-calcium condition by SA and pectinase; (3) H₂O₂ response and calcium response in protoplast were faster than that in the whole cell. These results indicated that pathogen elicitors can induce the release of cell wall calcium and the cell wall calcium release is independent to pectinase. And it is concluded that free calcium influx is necessary for the oxidative burst and cell wall calcium has an irreplaceable role in defense signal transduction.     

Near-threshold electron-impact ionization of calcium atoms

The electron-impact ionization of calcium atoms is studied in the near-threshold energy range (from 6.11 to 16 eV). Experiments were performed by the method of intersecting electron and atomic beams with the recording of formed positive calcium ions. The electron beam (ΔE _1/2 = 0.15 eV) was formed using a hypocycloidal electron monochromator. An analysis of the specific features of ionization cross sections revealed a contribution from the excitation and decay of low-lying autoionization atomic states, which converge to the excitation thresholds of the 3d, 4p, and 5s ionic levels, and resonances (long-lived states of negative ions). The specific features of cross sections are identified using the experimental and theoretical data on photoionization (photoabsorption).     

Insight into the calcium carboxylate release behavior during Zhundong coal pyrolysis and combustion

In this paper, the dynamic behavior of calcium carboxylate release during Zhundong coal pyrolysis and combustion is studied via reactive molecular dynamics (ReaxFF MD) simulation. The molecular structure model of Zhundong coal is constructed based on the combination of the classic Hatcher coal model and experimental characterizations. Pyrolysis simulations on the coal model are performed at different temperatures ranging from 2000 K to 2800 K. The pyrolysis experiments are also carried out to validate the ReaxFF simulation. The results show that most of the calcium are released into the volatiles by the thermal decomposition of CM-Ca (coal/char matrix with calcium bonded) after releasing CO₂. The distributions of the calcium bonded to gas, tar and inorganics as well as the atomic calcium in the volatiles are quantitatively classified. The thermal cracking of tar fragments are significant at high temperatures leading to the conversion of calcium from tar into the organic gas. Furthermore, the nascent char model is constructed to study the release behavior of calcium in char combustion stage. The calcium is initially released in the form of oxidized calcium and atomic calcium. With increasing temperature, the oxidized calcium trends to convert to the organically bonded calcium. By using the Arrhenius expression, the kinetic parameters for the release of calcium into various species during pyrolysis and char combustion stages are quantitatively determined.     

Luminescence of calcium orthoborate doped by Ce3+ ions

The luminescence properties of calcium orthoborate Ca₃(BO₃)₂ doped with cerium are studied upon x-ray (～30 keV) and VUV (3.5–15 eV) synchrotron excitation. The emission bands peaked at 392 and 420 nm are attributed to interconfigurational transitions of Ce³⁺ ions. The short-wavelength emission band at 340 nm is caused by radiative decay of exciton-like states. The fundamental absorption edge of Ca₃(BO₃)₂ is found to be near 7.1 eV. Based on thermoluminescence data and other information, the behavior of defects in Ca₃(BO₃)₂:Ce³⁺ is studied.     

Electronic structure of gadolinium calcium oxoborate

Gadolinium calcium oxoborate (GdCOB) is a nonlinear optical material that belongs to the calcium-rare-earth (R) oxoborate family, with general composition Ca₄RO(BO₃)₃ (R³⁺ = La, Sm, Gd, Lu, Y). X-ray photoemission was applied to study the valence band electronic structure and surface chemistry of this material. High resolution photoemission measurements on the valence band electronic structure and Gd 3d and 4d, Ca 2p, B 1s and O 1s core lines were used to evaluate the surface and near surface chemistry. These results provide measurements of the valence band electronic structure and surface chemistry of this rare-earth oxoborate.     

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.     

Superradiance at a wavelength of 535 nm in a mixture of calcium and thallium vapors

The results of the first experiments in which the superradiance in Tl vapors on the transition with green wavelength 5350 Å (a resonance transition 3D ₂?4F ₃ in calcium) are presented. The dependence of pulse peak intensity on thallium vapor density is investigated. A computer simulation is performed showing the possibility of a substansial decrease in duration of superradiance pulses in a mixture of thallium and calcium vapors.     

Raman spectroscopic characterization of the magnesium content in amorphous calcium carbonates

A series of Mg‐bearing synthetic amorphous calcium carbonates (ACC) were characterized by Raman spectroscopy. The spectra showed a systematic increase in the carbonate ν₁ peak position from the control samples that contained 0.0 mol % MgCO₃ to samples that contained up to 43 mol % MgCO₃. The relationship is best described by the function: mol % MgCO₃ = (ν₁ – 1079.66) / 0.2017. The Mg content is equally well‐predicted by a correlation with the instrumentally corrected ν₁ full width at half maximum that is quantified by: mol % MgCO₃ = (ν₁ – 23.26) / 0.1969. An analysis of the Raman data collected for ACC combined with insights from crystalline materials suggests that compositional dependencies arise from changes in the local metal–oxygen bonds as Mg substitutes for Ca. The calibrations described here provide a rapid and nondestructive means of determining the Mg content of ACC, with additional advantages of minimal sample preparation and a high degree of lateral spatial resolution (approximately 1 µm). This method may be appropriate for investigations of heterogeneous samples such as biominerals. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermal depolarization in crystals of calcium fluoride doped with oxygen

The study of thermally induced depolarization (TD) in crystals of calcium fluoride doped with oxygen reveals the existence of nearest-neighbour (nn) dipolar complexes comprising substitutional oxide ions (O_s^2?) and fluoride ion vacancies (F_v^?) on nn sites. Evidence for this relaxation is seen in TD experiments both on pure calcium fluoride doped with oxygen and on Na⁺ doped CaF₂ crystals that had been heated in air. Similar measurements on CaF₂: Y³⁺, O^2? reveal six separate relaxations, two of which are due to Y_s^3??F_i^? complexes that do not involve oxygen, one is due to O_s^2??F_v^? dipoles, and one is t the T₁ complex, Y_s³⁺ (O^2?)₄(F_v^?)₃. The remaining two relaxations were not identified but are probably d larger defect clusters.     

Silicene-terminated surface of calcium and strontium disilicides: properties and comparison with bulk structures by computational methods

The bulk and surface structures of calcium and strontium disilicides are investigated by computational methods using density functional theory. The investigated structures are R6, R3 and P1-CaSi₂ and P1-SrSi₂. The investigated properties are the cleavage energy at the silicene sheet, buckling of the bulk and surface silicene layers, charge transfer from calcium to silicon, band structure of bulk and surface-terminated structures and adsorption energies on H atoms and H₂ molecules on the silicene-terminated surface of the R3 phase. The cleavage energy at the silicene surface is low in all cases. Structures P1-CaSi₂ and R3-CaSi₂ contain silicene sheets with different coordination to Ca, while R6-CaSi₂ contains both types of the sheets. It is shown that the properties of the two types of silicene-like sheets in R6-CaSi₂ are similar to those of the corresponding sheets in P1-CaSi₂ and R3-CaSi₂, and the thermodynamically stable R6 phase is a good candidate for experimental investigation of silicene-terminated surface in calcium disilicide.     

Why to synthesize vaterite polymorph of calcium carbonate on the cellulose matrix via sonochemistry process?

Vaterite is an important biomedical material due to its features such as high specific surface area, high solubility, high dispersion, and small specific gravity. The purposes of this article were to explore the growth mechanism of vaterite on the cellulose matrix via sonochmistry process. In the work reported herein, the influences of experimental parameters on the polymorph of calcium carbonate were investigated in detail. The calcium carbonate crystals on the cellulose matrix were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Experimental results revealed that all the reactants, solvent, and synthesis method played an important role in the polymorph of calcium carbonate. The pure phase of vaterite polymorph was obtained using Na₂CO₃ as reactant in ethylene glycol on the cellulose matrix via sonochmistry process. Based on the experimental results, one can conclude that the synthesis of vaterite polymorph is a system process.     

Defect structure of lanthanum-doped calcium titanate

The defect structure of lanthanum-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure (10⁰–10^?18 atm.) dependence of the electrical conductivity at 1000° C and 1050°C. Two types of charge compensation were observed, namely electronic and ionic. For P₀₂ < 10^?15 atm. the carrier concentration was fixed by the amount of lanthanum (donor) added and the conductivity was found to be independent of oxygen partial pressure (electronic compensation). For higher oxygen partial pressure conditions (P₂₂ > 10^?13 atm.) the extra charge of the lanthanum was compensated by doubly ionized calcium vacancies (ionic compensation). In the ionic compensation region, a model involving a shear structure is discussed.     

Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes

The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl₂) and sodium carbonate (Na₂CO₃) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals.     

Radiation-induced radical ions in calcium sulfite

We have used EPR to study the effect of γ radiation on calcium sulfite. We have observed and identified the radiation-induced radical ions SO ₂ ⁻ (iso) with g = 2.0055 and SO ₂ ⁻ (orth-1) with g₁ = 2.0093, g₂ = 2.0051, g₃ = 2.0020, identical to the initial and thermally induced SO ₂ ⁻ respectively, SO ₃ ⁻ (iso) with g = 2.0031 and SO ₃ ⁻ (axial) with g_⊥ = 2.0040, g_∥ = 2.0023, identical to mechanically induced SO ₃ ⁻ . We have established the participation of radiation-induced radical ions SO ₃ ⁻ in formation of post-radiation SO ₂ ⁻ . __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 467–472, July–August, 2006.     

EPR of Cu2+-doped tris-sarcosine calcium chloride

The EPR study of the Cu²⁺-doped tris-sarcosine calcium chloride (TSCC) at room temperature is reported. Two magnetically inequivalent sites for Cu²⁺ were observed. The rhombic spin Hamiltonian parameters are determined by fitting the EPR spectra for two centres: Cu²⁺(I) g₁ = 2.0276, g₂ = 2.0517, g₃ = 2.4019, A₁ = 82, A₂ = 128, A₃ = 152 [G] and Cu²⁺(II) g₁ = 2.0231, g₂ = 2.0368, g₃ = 2.5294, A₁ = 76, A₂ = 92, A₃ = 156 [G]. The ground state wave function is also determined. The g-anisotropy is evaluated and compared with the experimental value. Further, the optical study of the crystal at room temperature is carried out and the nature of bonding in the complex is discussed.     

Radiation effects in samarium-doped calcium fluoride

A study was conducted of the effects of gamma radiation on samarium (Sm)-doped calcium flouride (CaF₂) crystals. Optical absorption measurements indicate that many of the Sm³⁺ ions are converted to Sm²⁺ during irradiation. Heavy doses of 10⁶ rad also modify the trapping structures and enhance certain defects within the crystals. A comparison is provided between unirradiated and heavily irradiated CaF₂ crystals with three Sm concentrations: 0.01, 0.1, and 1.0 molar-percent. Thermoluminescence measurements indicate that the crystals with high Sm content provide less luminescence and that the activation energy is less than seen in the 0.01 molar-percent Sm crystals.     

Coherent calcium puff signals driven by intracellular noises

In many cell types, intracellular calcium is released from internal stores through calcium release channels which are distributed in clusters with a few tens of channels. Localized calcium release events, i.e. Ca^{2 +} puffs, are subjected to stochastic channel dynamics and fluctuations of environmental calcium. Driven by the internal channel noise or external calcium noise, the localized calcium puffs show a coherence resonance phenomenon at weak stimulus. Our study indicates that coherent calcium puffs with an enhanced periodicity can be achieved with external calcium noise more easily than with internal channel noise.     

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.