Sol-gel prepared β-TCP/FHA biphasic coatings

β-tricalcium phosphate/fluoridated hydroxyapatite (β-TCP/FHA) biphasic coatings were prepared on titanium alloy substrate by means of sol-gel method. The coatings combine the initial dissolution of β-TCP with the long-term stability of FHA to create a high quality bioactive coating. Ca(NO₃)₂, P₂O₅ and HPF₆ were dissolved in ethanol respectively and mixed in designed sequence and Ca : P : F ratios to form a sol. After the sol was refluxed for 24 h, the as-refluxed sol was used for FHA coating. β-TCP powders were dispersed into the sols to form colloidal sols for β-TCP/FHA biphasic coatings. The as-refluxed sols with different Ca : P : F ratios only resulted in apatite coatings with low F content. Biphasic coatings were prepared with the colloidal sols. The β-TCP contents of the coatings could be tailored by varying the amount of the powders in the colloidal sols. The surface morphology of the coatings becomes rougher with increasing amount of the powders, which favors cell attachment. However, excessive amount of powders results in powder agglomeration, leading to more cracks in the coatings. Fine powders and good dispersion are essential factors for good biphasic coatings.     

The CeO2–TiO2–ZrO2 sol–gel film: a counter-electrode for electrochromic devices

Thin films of CeO₂–TiO₂–ZrO₂ with 23 mol% of Ce, 45 mol% of Ti and 32 mol% of Zr were obtained by the sol–gel method. The precursor sol was prepared from a mixture of Ce(NH₄)₂ (NO₃)₆, Ti(OPrⁱ)₄ and Zr(OPrⁱ)₄ solubilized in isopropanol and then sonicated. Xerogels were characterized by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) and X-ray diffraction. The films were deposited by dip-coating technique on a glass plate coated with an indium tin oxide film (ITO) and thermally treated at 80 °C for 15 min. and heated at 450 °C for 15 min in an oxygen atmosphere. By means of the addition of a lithium salt (LiCF₃SO₃) to the precursor solution, films with different electrochemical performances were obtained. Their possible use as ion storage (counter-electrode) in electrochromic devices (ECD) was analyzed by spectroelectrochemical measurements using cyclic voltammetry and chronoamperometry coupled to spectrometric measurements.     

Preparation of Er2O3 thin films by sol-gel dipping process

Er₂O₃ thin films had been prepared by a sol-gel dipping process with Er(NO₃)₃ · 6H₂O as the precursor and collodion as the viscosity-increasing agent. The annealing temperature of gel films was 600 °C and the thickness of Er₂O₃ thin films increased linearly with the number of dippings at a rate of about 40 nm per dipping. This sol-gel dipping process provided a good reproducibility of the homogeneous Er₂O₃ thin films. The spectral and crystal properties of the thin films were studied in detail and the results indicated that the color of the thin films mainly resulted from an interference effect. Moreover, the optically transparent region of Er₂O₃ thin films was determined with photoacoustic spectroscopy.     

Solid-state reactions in V x O y (NH4VO3)-P2O5 and V x O y (NH4VO3)-(NH4)2HPO4 closed systems

Solid-state reactions in V _x O _y (NH₄VO₃)-P₂O₅ and V _x O _y (NH₄VO₃)-(NH₄)₂HPO₄ closed systems can be used to synthesize vanadyl hydrogen phosphate at 300°C and a variety of ammonium vanadium phosphates at lower and higher temperatures.     

EPR Study of Reactivity of Endohedral Metallofullerenes La@C82 and Y@C82

Abstract

Reactivity of La@C₈₂ in the mixture with C₆₀ and C₇₀ vs L₂pt^o, phosphoryl radical ?P(O)(OR)₂, and CF₃COOH has been studied using EPR spectroscopy. Whereas two former reagents did not change EPR spectrum, treatment with CF³COOH in toluene caused the disappearance of minor octet and a new signal was observed. Similar behaviour was found upon treatment of Y@C₈₂ with CF₃COOH. It is interpreted as selective protonation of one isomer of endohedral metallofullerene.     

Synthesis and characterization of biocompatible hydroxyapatite coated ferrite

Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical composition (CaO)_0.75(La₂0₃)_0.20(Fe₂O₃)₆ was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO₃)₂ and (NH₄)₂HPO₄ maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites could be useful for hyperthermia.     

Synthesis of nanocrystalline carbonated hydroxyapatite powder via nonalkoxide sol–gel method

Nanocrystalline hydroxyapatite powder was synthesized via nonalkoxide sol–gel method. Ca(NO₃)₂·4H₂O and P₂O₅ were mixed in ethanol, which led to a stable sol. STA, XRD and FTIR were used to characterize the calcined powders. The degrees of crystallinity and crystallite sizes were thereafter calculated from XRD patterns. The microscopic observations of the powder were performed using SEM and TEM. Results showed that a nanocrystalline hydroxyapatite powder was obtained after being heated at 450 °C for 6 h. Furthermore, increasing the calcining temperature caused both the formation of carbonate bonds and the increase in the crystallite sizes, and the degree of crystallinity.     

Structural characterization of zinc-substituted hydroxyapatite prepared by hydrothermal method

Zinc-substituted hydroxyapatite (Zn-HA) powders were prepared by hydrothermal method using Ca(NO₃)₂, (NH₄)₃PO₄ and Zn(NO₃)₂ as reagents. X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to characterize the crystalline phase, microstructure, chemical composition, morphology and thermal stability of Zn-HA. The results show that the substitution content of zinc (Zn) in Zn-HA powders prepared in NaOH solution is higher than that prepared in NH₃ solution, and is lower than that of the corresponding amount of starting materials. The substitution of the Zn ion for calcium ion causes a lower crystallinity of Zn-HA and changes the lattice parameters of Zn-HA, since the ionic radius is smaller in Zn²⁺ (0.074 nm) than in Ca²⁺ (0.099 nm). Furthermore, the substitution of the Zn ions restrains the growth of Zn-HA crystal and decreases the thermal stability of Zn-HA. Zn-HA powder prepared in NH₃ solution starts to decompose at 800 °C when the Zn fraction increases to 15 mol%, while that prepared in NaOH solution start to decompose at 5 mol% Zn. The substitution content of Zn significantly influences the thermal stability, microstructure and morphology of Zn-HA.     

Synthesis and properties of calcium hydroxyapatite/silk fibroin organomineral composites

The coprecipitation of calcium hydroxyapatite (HA) (Ca₁₀(PO₄)₆(OH)₃) and silk fibroin (SF) from an aqueous solution in the Ca(NO₃)₂–(NH₄)₂HPO₄–NH₃–H₂O–SF system has been used to synthesize HA/SF organomineral composites based on nanocrystalline HA, containing 2, 5, and 10 wt % SF. The synthesis products were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, scanning electron microscopy, and electron spectroscopy for chemical analysis.     

Evaluation of the physical and antimicrobial properties of silver doped hydroxyapatite depending on the preparation method

In the present study, the effect of the preparation method on the physical and antibacterial properties of silver doped hydroxyapatite (HAp/Ag) samples was investigated. HAp/Ag with 0.1–5 % of silver was prepared using two different modified wet chemical precipitation methods. A comparison of thermal stability and thermodynamical properties indicated that the thermal stability and sintering temperature of HAp/Ag were higher than those of pure hydroxyapatite if Ca(NO₃)₂·4H₂O, AgNO₃, NH₄OH and (NH₄)₂HPO₄ were used as raw materials. Phase composition and silver release were determined by XRD and ICP-MS. The study showed that, after 50 h in simulated body fluid 0.8–1.8 % of silver of the total silver amount was released from compact HAp/Ag scaffolds, and release kinetics strongly depended on the HAp/Ag preparation method. In vitro antibacterial activity of samples from each method against the bacterial strains Staphylococcus epidermidis and Pseudomonas aeruginosa was approved. Results showed that, in the case of using Ca(OH)₂, H₃PO₄ and AgNO₃ as raw materials for HAp/Ag synthesis, higher antibacterial activity towards both bacterial strains could be obtained.     

Direct nanocrystalline hydroxyapatite formation on titanium from ultrasonated electrochemical bath at physiological pH

An electrochemical method of producing nanocrystalline hydroxyapatite coatings on titanium surface is reported. The bath contained Ca(NO₃)₂ and NH₄H₂PO₄ in the molar ratio 1.67:1. The electrolyte was maintained at physiological pH and was ultrasonically agitated throughout the time of electrolysis. Coatings were deposited for 30 min at 10 and 15 mA/cm² and contained mono hydroxyapatite phase whose crystal sizes were lower than 30 nm. These sizes are comparable to the size of the bone hydroxyapatite crystals. Small globules of hydroxyapatite covered the coating surface completely. Fourier transformed infra-red spectroscopy (FT-IR) studies showed that the coatings contained large amounts of hydroxide and phosphate groups to enable the formation of hydroxyapatite. The coatings had a roughness (R_a) of about 0.3 μm and water contact angles of about 49°. Ultrasonic agitation promoted the formation of nanocrystalline structure which will help in better attachment of bone tissues to the implant surface.     

Preparation of transparent water-repellent films by radio-frequency plasma-enhanced chemical vapour deposition

Preparation of transparent water-repellent films was carried out using three kinds of fluoroalkyl silanes (FASs) by radio-frequency plasma-enhanced chemical vapour deposition. The effects of the reaction conditions on the structures and properties of the films were studied. The films prepared showed high water repellency like poly(tetrafluoroethylene). The contact angles for water drops were about 107 °. The obtained contact angles depended on the length of perfluoroalkyl groups (C_nF_{2n + 1}-) in FASs. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to investigate the film properties. The existence of the fluorine-containing groups such as –CF₃, –CF₂– and > CF– was confirmed at the film surfaces. The contact angle decreased when oxygen was added to the plasma because of the decrease in the fluorine concentration in the deposited films by the decomposition of C–F bonds. The transmittance of the polycarbonate substrates coated using FASs was improved. The films also acted as an antireflective coating. This revised version was published online in November 2006 with corrections to the Cover Date.     

Nanostructured leaf like hydroxyapatite/TiO2 composite coatings by simple sol-gel method

We demonstrate an approach for the coating of nanostructured leaf like hydroxyapatite (HAp)/TiO₂ composite on glass substrate by sol-gel dip coating process. HAp/TiO₂ nanocomposite thin film was obtained by controlling the dipping rate and the dipping cycle. It was observed from Scanning Electron Microscope that leaf like nanostructured film was deposited on the glass substrate. However, the structure of the film was changed with the dipping cycle and dipping rate. Transmission Electron Microscopic analysis further confirms the morphology of the nanostructured coatings. The presence of Ti, O, Ca and P was detected by Energy Dispersive X-ray Analysis. We further confirmed the composite by X-ray diffraction analysis. Atomic Force Microscope analysis indicates that the films are composed of nanoparticles ranging from 100 to 200 nm and the films were observed to present well-defined grain boundaries. It has been shown that nanocomposite coatings are dependent on the sol concentration, dipping parameters, and the composition of HAp and TiO₂.     

N-Lauroyl sarcosine sodium salt mediated formation of hydroxyapatite microspheres via a hydrothermal route

Dandelion-like hydroxyapatite (HA) microspheres were successfully prepared using Ca(NO₃)₂·4H₂O and (NH₄)₃PO₄·3H₂O as raw materials and N-Lauroyl sarcosine sodium salt (Sar-Na) as template via a hydrothermal route. The chemical composition, structure, morphology and thermal properties of the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscope (FTIR), Scanning electron microscope (SEM) and Thermal gravimetric analysis (TG), respectively. The results demonstrate that, Sar-Na has great impact on the morphology of HA. With increasing the amount of Sar-Na, the morphology of HA varies from nanograins to nanorods, finally grows into dandelion-like microstructure. The obtained dandelion-like HA microspheres about 6 μm in diameter are composed of radially oriented nanorods. Furthermore, the possible formation mechanism of morphology change is also discussed.     

Solvent-free organic syntheses on mineral supports using microwave irradiation

 An expeditious and solvent-free approach for selective organic synthesis is described which involves simple exposure of neat reactants to microwave (MW) irradiation. The coupling of MW irradiation with the use of catalysts or mineral supported reagents, under solvent-free conditions, provides clean chemical processes with special attributes such as enhanced reaction rates, higher yields, greater selectivity and the ease of manipulation. Our recent results on this eco-friendly approach utilizing recyclable inorganic oxides or supported reagents such as Fe(NO₃)₃-clay (clayfen), Cu(NO₃)₂-clay (claycop), NH₄NO₃-clay (clayan), NH₂OH-clay, PhI(OAc)₂-alumina, NaIO₄-silica, CrO₃-alumina, MnO₂-silica, and NaBH₄-clay etc. are exemplified in MW-assisted deprotection, condensation, cyclization, oxidation and reduction reactions including the efficient one-pot assembly of heterocyclic molecules from in situ generated intermediates. Received: 20 October 1998 / Accepted: 27 December 1998     

Direct imaging by atomic force microscopy of surface-localized self-assembled monolayers on a cuprate superconductor and surface X-ray scattering analysis of analogous monolayers on the surface of water

A self-assembled monolayer of CF₃(CF₂)₃(CH₂)₁₁NH₂ atop the (001) surface of the high-temperature superconductor YBa₂Cu₃O_7-x was imaged by atomic force microscopy (AFM). The AFM images provide direct 2D-structural evidence for the epitaxial 5.5 Å square √2 × √2R45° unit cell previously predicted for alkyl amines by molecular modeling [J.E. Ritchie, C.A. Wells, J.-P. Zhou, J. Zhao, J.T. McDevitt, C.R. Ankrum, L. Jean, D.R. Kanis, J. Am. Chem. Soc. 120 (1998) 2733]. Additionally, the 3D structure of an analogous Langmuir monolayer of CF₃(CF₂)₉(CH₂)₁₁NH₂ on water was studied by grazing-incidence X-ray diffraction and specular X-ray reflectivity. Structural differences and similarities between the water-supported and superconductor-localized monolayers are discussed.     

Influence of temperature, [Ca2+], Ca/P ratio and ultrasonic power on the crystallinity and morphology of hydroxyapatite nanoparticles prepared with a novel ultrasonic precipitation method

Nanocrystalline hydroxyapatite was prepared by a precipitation method with the aid of ultrasonic irradiation using Ca(NO₃)₂ and NH₄H₂PO₄ as source material and carbamide (NH₂CONH₂) as precipitator. The influence of Ca/P molar ratio, precipitation temperature, concentration of Ca²⁺ ([Ca²⁺]) and ultrasonic power on the crystallinity of the nanopowder were systematically investigated by XRD analysis. The size of the as-prepared particles was analyzed using TEM and XRD methods. The results revealed that the monophase hydroxyapatite could be obtained at the following technological conditions: [Ca²⁺] = 0.01–0.1 mol/L, ultrasonic power = 300 W, Ca/P (mol) = 1.2–2.5 and T = 313–353 K. In addition, the acicular and spherical particles could be prepared at different ultrasonic powers of 300 and 200 W, respectively.     

Intercalation of pyrographite by NO2+ and NO+ salts

BF₄^?, PF₆^? and SbF₆^? ions have been intercalated into pyrographite HOPG by chemical oxidation. The graphite is oxidized by NO₂⁺ (or NO⁺ in certain experiments) coming from NO₂BF₄, NO₂PF₆ and NO₂SbF₆ (or NOSbF₆) salts dissolved in dry nitromethane. X-ray diffraction allows us to determine the identity period along the $\text{c}$ axis leading to the stage n and the interpianar distance d_I. Relative weight change leads us to believe that the MF_x^? anions are solvated by the solvent. Chemical analyses confirm this hypothesis allowing us to give to these compounds the ideal formula C⁺_23nMF^?_x (CH₃NO₂)_y.     

Effect of etching on dielectric constant and surface composition of SiCOH low-k films in inductively coupled fluorocarbon plasmas

SiCOH low-k (k = 2.8) film etched in fluorocarbon (CF₄ and CHF₃) inductively coupled plasmas was characterized in this work. The surface composition and molecular structures of the low-k films after etching in the CF₄, CHF₃, CF₄/Ar, and CHF₃/Ar plasmas were characterized. A higher etch rate was observed with the CF₄ plasmas than with the CHF₃ plasmas. The etch rate of the low-k film in the CF₄ plasmas was decreased and the etch rate in the CHF₃ plasmas was increased by the Ar addition. After etching the low-k films, a decrease in the dielectric constant of up to 0.19 was observed. The thickness of the fluorocarbon (CF_x) layer and CF_x (x = 1, 2, 3)-to-carbon ratio obtained from the XPS C 1s peak increased with decreasing etch rate. The k-value was correlated with amount of Si-CH₃ and Si-O related groups determined from the Fourier transform infrared (FT-IR) spectrum. The Si-O related peaks were markedly decreased after etching in the CF₄ and CF₄/Ar plasmas. The lower k-value was attributed to the increase of the Si-CH₃/Si-O ratio after etching low-k film.     

Reactively sputtered MoO3 films for ammonia sensing

We report the gas-sensing properties of ion-beam sputter deposited MoO₃ thin-films. The change in the DC conductivity was measured in dry N₂ with 10% O₂ in the presence of up to 490 ppm of NH₃, NO, NO₂, C₃H₆, CO and H₂. At ∼440 °C the film was found to be very sensitive to NH₃, with 490 ppm increasing the conductivity by approximately a factor of 70. This was approximately 17 times greater than the response to the other gases. The NH₃ response was strongly affected by the accompanying levels of O₂, NO₂ and H₂O. For example, changing the accompanying O₂ levels from 1% to 20% decreased the NH₃ response by approximately a factor of 20. Similarly, the presence of 100 ppm NO₂ (in 10% O₂) decreased the NH₃ response by approximately a factor of three, and 1% water vapor decreased it by more than a factor of two. The NH₃ response, however, was relatively unaffected by 100 ppm of accompanying NO, C₃H₆, CO or H₂. XPS measurements show that the increased conductivity in the presence of NH₃ was also accompanied by a partial reduction of the surface MoO₃. We observed an increase in the resistance of the films after extended time at elevated temperatures.