Accelerated transformation of brushite to octacalcium phosphate in new biomineralization media between 36.5 °C and 80 °C

This study investigated the hydrothermal transformation of brushite (dicalcium phosphate dihydrate, DCPD, CaHPO₄·2H₂O) into octacalcium phosphate (OCP, Ca₈(HPO₄)₂(PO₄)₄·5H₂O) in seven different newly developed biomineralization media, all inspired from the commercial DMEM solutions, over the temperature range of 36.5 °C to 90 °C with aging times varying between 1 h and 6 days. DCPD powders used in this study were synthesized in our laboratory by using a wet-chemical technique. DCPD was found to transform into OCP in the Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^?, Cl^? and H₂PO₄^? containing aqueous biomineralization media in less than 72 h at 36.5 °C, without stirring. The same medium was able to convert DCPD into OCP in about 2 h at 75–80 °C, again without a need for stirring. Samples were characterized by using powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).     

Multicolor-emitting Ca3 -x-ySry(PO4)2:xEu2 + (0 ≤ x ≤ 0.075, 0 ≤ y ≤ 2.2) phosphors for light-emitting diodes

In this paper, a series of Ca_3 -x-ySr_y(PO₄)₂:xEu^2 +, (0 ≤ x ≤ 0.075, 0 ≤ y ≤ 2.2) phosphors were prepared by flux assisted solid-state reaction method, and their photoluminescence properties were investigated. The β- to β′-phase transition of Ca_3 -ySr_y(PO₄)₂ for high Sr^2 + content was observed from the XRD patterns, and the corresponding optical bandgaps were obtained experimentally. Various Eu^2 + emission centers were found, which generate tunable emission depending on the Sr^2 + concentration. Broad and intense excitation bands exist in Eu^2 + activated Ca₃(PO₄)₂, and the introduction of Sr^2 + further extends and enhances the excitation bands beyond 350 nm, which is beneficial to the applications on near ultraviolet LEDs. The morphology measurement reveals that the average size of particles with smooth surface is about 11.2 μm, which is suitable for the practical applications. These results indicate that the Ca_3 -x-ySr_y(PO₄)₂:xEu^2 + phosphors could be promising candidates for LEDs.     

Phase-matched UV generation at 0.1774 μm in KB(5)O(8) ·4H(2)O

Sixth-harmonic generation of the Nd:YAG laser frequency at 1.0642 μm has been achieved in KB(5) O(8) ˙ 4H(2) O by type-1 mixing the fundamental and fifth harmonic at room temperature. The phase-matching angles were measured to be (θ = 90°, φ = 68.5 ± 0.5°) and (θ = 80.0 ± 0.5 °, φ = 90°) in the x - y and y -z planes, respectively. Improved Sellmeier equations of this crystal are presented.     

Complexes with substituted 2,5-dihydroxy-p-benzoquinones: AE[C6(C2H5)2O4]·3H2O (AE=Ca,Sr, Ba)

Single crystals of AE[C₆(C₂H₅)₂O₄]·3H₂O belonging to space group P2₁2₁2₁ were grown in aqueous silicagel (AE=Ca, Sr) and in aqueous solution (AE=Ba), respectively. AE²⁺ is coordinated by four oxygen atoms of two bis-chelating [C₆(C₂H₅)₂O₄]²⁻ ions, thus forming infinite, corrugated chains extending along [010]. The coordination polyhedron is completed by additional water molecules. The coordination sphere is different for the three different AE²⁺ ions yielding CN increasing from Ca²⁺ to Ba²⁺. The principle features of the crystal structure, however, remain unchanged. Adjacent chains are interlinked by hydrogen bonds between water molecules of the coordination sphere and the oxygen atoms of the [C₆(C₂H₅)₂O₄]²⁻ ion.     

X-ray powder diffraction and IR study of NaMg(H2O)2[BP2O8]·H2O and NH4Mg(H2O)2[BP2O8]·H2O

NaMg(H₂O)₂[BP₂O₈]·H₂O was prepared by hydrothermal synthesis and was characterized by X-ray powder difraction and IR method. The title compound was synthesized from MgCl₂·6H₂O, NaBO₃·4H₂O, and (NH₄)₂HPO₄ with variable molar ratios using hydrothermal method by heating at 165 °C for 3 days. The X-ray powder diffraction data was indexed in hexagonal system, the unit cell parameters were found to be as a = 9.428, c = 15.82 Å, Z = 4 and the space group is P6₁22. It is isostructural with M^lM^ll(H₂O)[BP₂O₈] type compounds where M^l = Na, K; M^ll = Mg, Mn, Fe, Co, Ni and Zn. In addition NH₄Mg(H₂O)₂[BP₂O₈]·H₂O was also synthesized the first time in this research. Its unit cell parameters and hkl values were in good agreement with the sodium magnesium compound. The unit cell parameters are a = 9.529, c = 15.736 Å. The indexed X-ray powder diffraction data of both compounds which were not reported in the literature is presented in this work. The IR data of NaMg(H₂O)₂[BP₂O₈]·H₂O is also reported.     

Crystal Structure of Neptunium(V) Phthalate (NpO2)2(OOC)2C6H4·4H2O

The crystal structure of (NpO₂)₂(OOC)₂C₆H₄·4H₂O [rhombic cell: a = 15.937(3), b = 26.922(5), c = 8.020(2) Å, space group Pbcn, Z = 8, V = 3441.0(12) ų, d _calc = 2.988 g cm^{- 3}, CAD4, MoK , graphite monochromator, 2934 independent reflections; R ₁ = 0.0352, wR ₂ = 0.0951] was studied. The structure consists of NpO₂ ⁺ cations, H₄C₆(COO)₂ ^{2 -} anions, and molecules of coordinated and crystallization water. The crystal lattice involves neutral layers [(NpO₂)₂(OOC)₂C₆H₄(H₂O)₃] _n parallel to the {101} plane. The dioxocations in these layers are bonded to each other to form cationic networks [the Np···Np distance is 3.911(1)-4.202(1) Å]. The coordination polyhedra of Np(1) and Np(2) are pentagonal bipyramids (CN 7). The point group of the neptunyl(V) groups is close to D _h. These groups are bidentate ligands in the cation-cation interaction. The Np = O bond lengths are 1.852(6) [Np(1)-O(1)], 1.849(7) [Np(1)-O(2)], 1.845(7) [Np(2)-O(3)], and 1.841(7) Å [Np(2)-O(4)]; the O = Np = O bond angles are 178.6(3)° [O(2)-Np(1)-O(1)] and 177.4(3)° [O(3)-Np(2)-O(4)]. The equatorial plane of the Np(1) bipyramid consists of two oxygen atoms of adjacent Np(2)O₂ ⁺ dioxocations, two water molecules, and a single oxygen atom of the phthalate anion. The equatorial plane of the Np(2) bipyramid consists of two oxygen atoms of adjacent Np(1)O₂ ⁺ dioxocations, two oxygen atom of the phthalate anion, and a single water molecule. The bond lengths in the equatorial plane of the bipyramid lie in the following ranges: Np-Oyl 2.373(7)-2.437(7) Å (average 2.397 Å) , Np-Ophth 2.360(7)-2.474(7) Å (average 2.431 Å), and Np-Owater 2.534(8)-2.558(9) Å (average 2.544 Å). The phthalate anions are tridentate bridging ligands binding neptunium atoms only within a single cationic network.     

Complexes with substituted 2,5-dihydroxy-p-benzoquinones: The inclusion compounds [Y(H2O)3]2 (C6Cl2O4)3·6.6H2O and [Y(H2O)3]2 (C6Br2O4)3·6H2O

Single crystal of [Y(H₂O)₃]₂ (C₆Br₂O₄)₃·6H₂O and [Y(H₂O)₃]₂ (C₆Cl₂O₄)₃·6.6H₂O were grown in aqueous silicagel. The compounds are in principle isostructural. In Y chloranilate one additional water site is occupied as verified by X-ray single crystal structure analysis. Y³⁺ is nine-coordinated by three water molecules and six oxygen atoms of the bischelating (C₆X₂O₄)²⁻ ions (XCl, Br). The coordination polyhedron is an only slightly distorted tri-capped trigonal prism. The connection of Y³⁺ with the dianions leads to infinite, corrugated layers. The layer stacking yields cage-like cavities in which water molecules are accomodated. Hydrogen bonds interlink adjacent layers. Further hydrogen bonds involve the entrapped water molecules. DSC measurements indicated a complicated dehydration process which caused right at the start destruction of the single crystals.     

Crystal structure of a double Np(V) ammonium propionate, NH4[(NpO2)3(C2H5COO)4(H2O)]·3H2O

The structure of NH₄[(NpO₂)₃(C₂H₅COO)₄(H₂O)]·3H₂O was studied by single crystal X-ray diffraction. The single crystals were prepared by hydrothermal synthesis. In the structure, there are three crystallographically independent Np atoms with different equatorial surrounding. All of them have CN 7; the coordination polyhedron is a distorted pentagonal bipyramid. Each NpO ₂ ⁺ cation is bonded to four other cations, acting simultaneously as a bidentate ligand and a coordination center for two other dioxocations. The cation-cation interactions result in formation of trigonal-hexagonal cationic networks.     

Ca2+ ⇌ Pb2+ exchange reaction of calcium silicate hydrate: Ca5Si6O18H2 · 4H2O

Recently it has been demonstrated that synthetic calcium silicate hydrate Ca₅Si₆O₁₈H₂ · 4H₂O shows cation exchange properties. In this paper we give the mass balance and thermodynamic data of the Ca²⁺ Pb²⁺ exchange which occurs in 1.1 nm tobermorite when placed in dilute Pb²⁺ solutions. The solid and solution phases have been analysed. The free energy of the exchange reaction at room temperature has been calculated. The X-ray powder diffraction data of the exchanged product have been reported. The crystallinity of the exchanger remains intact after ion exchange.     

In vitro biocompatibility and antimicrobial activity of wet chemically prepared Ca10−xAgx(PO4)6(OH)2 (0.0 ≤ x ≤ 0.5) hydroxyapatites

Herein, we report the effect of silver ions on the physical, antimicrobial and cytocompatibility properties of wet chemically synthesized silver doped Ca_10?xAg_x(PO₄)₆(OH)₂ (0.0 ≤ x ≤ 0.5) hydroxyapatites (HAp). Silver ions containing HAp exhibit the comparable density, hardness and enhanced antimicrobial properties, in comparison to parent HAp. The optical absorption measurements confirm the presence of silver ions in the doped compositions, which are responsible for as increased antimicrobial property of doped HAp materials for x > 0.3. The cytotoxicity behavior of the doped HAp was evaluated using mouse fibroblast (L929) cell line. The important result has been that doped HAp (x > 0.3) exhibit statistically (significant) lower cell viability in comparison to undoped HAp. However, no difference in cellular functionality on doped HAp surfaces, in terms of cell adhesion and proliferation could be qualitatively observed in reference to undoped HAp. In order to explain the observed antimicrobial and cell viability properties, the in vitro release of Ag⁺ ions has been quantified using Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) and solubility was measured by weight loss in acetate buffer solution.     

Oxidation of FeCrAl foils at 500–900°C in dry O2 and O2 with 40% H2O

Abstract

High temperature resistant FeCrAl alloys are frequently used in high temperature applications such as heating elements and metal based catalytic converter bodies. When exposed to high temperatures an adherent, slowly growing, dense aluminium oxide layer forms on the surface, which protects the underlying alloy from severe degradation. The composition, structure and properties of the formed oxide layer are strongly dependent on the alloy composition, temperature and oxidation environment. In this study, the Sandvik 0C404 FeCrAl alloy, in the form of 50 μm thick foils, was exposed isothermally in the temperature range 500–900°C for 168 hours in dry O₂ and in O₂ with 40 vol.% H₂O. The surface morphology, composition and microstructure of the grown oxide scales were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), grazing incidence X-ray diffraction (GIXRD), Auger electron spectroscopy (AES), and time of flight secondary ion mass spectrometry (TOF-SIMS). The oxidation process was faster at 900°C than at 500 and 700°C. At 500°C a thin (10–20 nm) mixed oxide of Fe, Cr and Al was formed. Exposure at 700°C resulted in a similar (40–50 nm) duplex oxide, in both dry O₂ and in O₂ with 40 vol.% H₂O. These oxide scales consisted of an inner and an outer relatively pure alumina separated by a Cr-rich band. This type of duplex oxide scale also formed at 900°C with a thin inward growing α–Al₂O₃ at the oxide/metal interface and an outward growing layer outside a Cr-rich band. However, at 900°C the outward growing layer showed two types of oxide morphologies; a thin smooth base oxide and a much thicker nodular oxide grown on top of substrate ridges. In dry O₂ atmosphere, the main part of this outward growing layer had transformed to α–Al₂O₃. Only in the outer part of the thick oxide nodules, metastable alumina was found. When exposed in the presence of water vapour the main part of the metastable alumina remained untransformed.     

Synthesis and stability of α-tricalcium phosphate doped with dicalcium silicate in the system Ca3(PO4)2–Ca2SiO4

The aim of this study was to synthesize materials of α-tricalcium phosphate doped with small amounts of dicalcium silicate, by solid state reaction, at high temperature and slow cooling to room temperature. The obtained materials were characterized by X-ray diffraction, Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy, showing that there is a region between 0.5 and 4.0 wt.% of dicalcium silicate where solid solution α-tricalcium phosphate (α-TCPss) is stable to room temperature.     

Effect of fluoride on apatite formation from Ca4(PO4)2O in 0.1 mol L−1 KH2PO4

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) was investigated in 0.1 mol l–1KH2PO4 containing 0–83 mol l–1 KF. Characterization of the final apatite phase formed by the hydrolysis was made with X-ray diffraction and SEM. The initial pH was between 4.5 and 5.4, depending on the solutions, and the pH rapidly increased and was kept constant between 7.3 and 6.5. An increase in KF concentration tended to lower the pH in the final stage of hydrolysis. The calcium concentration was considerably lower than the phosphorus concentration throughout the reaction. The fluoride concentration decreased shortly after the start of hydrolysis. The hydrolysis of TTCP in 0.1 mol l–1 KH2PO4 proceeded to form hydroxyapatite via DCPD when the KF concentration was low. The hydrolysis product was a calcium-deficient non-stoichiometric hydroxyapatite with a Ca/P ratio of about 1.5. With an increase in the KF concentration in the 0.1 mol l–1 KH2PO4 solution, TTCP directly transformed into hydroxyapatite containing F- ions or fluorapatite and with improved crystallinity. The addition of fluoride in the solution initially accelerated the formation of apatite. However, the layer of newly formed apatite adhering to the TTCP particles retarded TTCP dissolution; as a result, hydrolysis was delayed. IR analysis showed that the apatite phase contained HPO2–4 ions in the structure. The formula for the hydrolysis product of TTCP in the presence of fluoride can be expressed as follows: Ca10–x(HPO4)x(PO4)10–x(OH)2–x–yFy. © 1998 Chapman & Hall.     

Transformations of neat and heated struvite (MgNH4PO4⋅6H2O)

Struvite (MgNH₄PO₄?6H₂O) is the mineral phase of one of the urinary tract stones of humans and animals, besides being an important phase seen in waste water treatment and purification plants. Single-phase and highly crystalline struvite powders were synthesized in this study at room temperature in aqueous solutions containing dissolved salts of MgCl₂?6H₂O and (NH₄)₂HPO₄ at the Mg/P molar ratio of 1.00. As-synthesized, crystalline struvite powders (neat powders) completely transformed into cryptocrystalline apatitic calcium phosphate (Ap-CaP), in less than 72 h, when soaked in Ca-containing saline solutions at 37 °C. Moreover, crystalline struvite powders heated at temperatures from 90° to 200 °C became x-ray amorphous. Amorphous powders stirred for 4 h at room temperature in water containing dissolved diammonium hydrogen phosphate recrystallized back into struvite.     

Influence of hydrothermal treatment on the microstructure and oxidation resistance of a Zn4B2O7·H2O (4ZnO·B2O3·H2O) coating for C/C composites

Antioxidant modification for C/C composites by in situ hydrothermal synthesise at 140 °C of a 4ZnO·B₂O₃·H₂O crystallite coating has been successfully achieved. The influence of hydrothermal time on the phase composition, microstructure of the as-prepared Zn₄B₂O₇·H₂O (4ZnO·B₂O₃·H₂O), and its antioxidant modification for C/C composites were investigated. Samples were characterised by XRD, SEM, isothermal oxidation test and TG-DSC. Results show that, 4ZnO·B₂O₃·H₂O crystalline coating is achieved on the surface of C/C composites after the hydrothermal treatment at 140 °C for time in the range of 2–12 h. A smooth and crack-free 4ZnO·B₂O₃·H₂O layer can be obtained when the hydrothermal time reaches 8 h. Isothermal oxidation test demonstrates that the oxidation resistance of C/C composites is improved. The as-modified composites exhibit only 1.52 g·cm^?2 weight loss after oxidation at 600 °C for 15 h, while the non-modified one shows a 6.57 g·cm^?2 weight loss after only 10 h oxidation. For the uncoated C/C composite the oxidation rate is approximately linear with time (non-protective oxidation), thus at 15 h exposure one can estimate the mass loss to be 6.57 g·cm^?2 after 10 h for direct comparison with the coated samples.     

The oxidation of Fe3Al–(0, 2, 4, 6%)Cr alloys at 1000 °C

Thermomechanically treated Fe₃Al–(0, 2, 4, 6at.%)Cr alloys were isothermally oxidized at 1000 °C in air, and their oxidation characteristics were studied using thermogravimetric analyzer, X-ray diffractometer, scanning electron microscope, electron probe microanalyzer, and TEM/EDS. It was found that Cr decreased the oxidation resistance of Fe₃Al alloys to a certain extent. The oxide scales that formed on the unalloyed Fe₃Al alloys consisted primarily of α-Al₂O₃ containing a small percentage of dissolved iron ions. Less than 1% of dissolved chromium ions was additionally present in the oxide scale formed on the Fe₃Al–Cr alloys. An Al-free, Fe-enriched zone was formed beneath the oxide scale, owing to Al consumption to form the oxide scale. The oxide scale on all alloys had poor adherence.     

Synthesis and crystal structure of a new Np(V) oxalate, Na4(NpO2)2(C2O4)3·6H2O

A new oxalate complex, Na₄(NpO₂)₂(C₂O₄)₃·6H₂O, with the Np:C₂O₄ ratio of 2:3 was synthesized and studied by single crystal X-ray diffraction. In the crystal, the NpO ₂ ⁺ cations and oxalate anions are bound in open networks [(NpO₂)₂(C₂O₄)₃] _n ^4n- parallel to the bc plane. The Na(1) cations are accommodated in large voids of the neptunyl oxalate networks with the formation of crimped mixed-cation layers of the composition [Na₂(NpO₂)₂(C₂O₄)₃] _n ^2n- . The negative charge of the layers is compensated by the Na(2) cations arranged between the layers. The Np atoms have a pentagonal bipyramidal coordination surrounding with the equatorial plane formed by the oxygen atoms of three oxalate anions. The structure contains tridentate-bridging and tetradentate-bridging oxalate anions.     

Synthesis of Double Uranyl Phthalates of the M4[(UO2)4(μ3-O)2(C6H4C2O4)4] ⋅ nH2O Type with M = NH4, K, and Cs. Crystal Structure of K4[(UO2)4O2(C6H4C2O4)4] ⋅ 3H2O

Double U(VI) phthalates with NH ₄ ⁺ , K⁺, and Cs⁺ ions in the outer sphere were synthesized. The X-ray phase analysis shows that their structures are similar. Single crystals were prepared and the structure of K₄[(UO₂)₄(μ₃-O)₂(C₆H₄C₂O₄)₄] ? 3H₂O was solved. In the [(UO₂)₄O₂(C₆H₄C₂O₄)₄]^4? anions forming the main structural motif, each bridging oxygen atom μ₃-O combines one pentagonal and two hexagonal bipyramids, which, in turn, are combined in centrosymmetrical tetramers. The phthalate ions have coordination capacity equal to 3; each ligand coordinates U(1) in the bidentate fashion via one carboxy group and U(2) in the bidentate fashion to form a planar seven-membered chelate ring.