The effect of pH and the process of direct or inverse synthesis of silicon-Substituted hydroxyapatite prepared by hydrolysis in aqueous medium

Nanosized hydroxyapatite with silicon substitution Ca10(PO4)6−x(SiO4)x(OH)2−xâ–¡x (0 ≤ x ≤ 2)  of same silicon concentrations, variation of pH and the method of inverse and direct synthesis were successfully prepared first time by the theoretical maximum  of incorporation of Si into the hexagonal apatite structure   by   precipitation method aqueous. The effects        of the Si substitution on crystallite size, particle size and morphology of the powders were investigated. The crystalline phase, microstructure, morphology and particle size of hydroxyapatite and silicon substituted hydroxyapatites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), EDX coupled with SEM and transmission electron microscopy (TEM).The samples were successfully synthesized as a single-phase apatite, and crystallization of apatite was enhanced during heating. The results obtained in this study show that the kinetics between different direct and inverse process showed different reactivities, in the presence of varying pH. Compared with the two methods, the inverse method have higher kinetic in the formation of hydroxyapatite silicate because of the difference in lattice parameters. The grain size of Si-HA samples is clearly finer than that of pure HA sample and this decreases with increasing Si content. The growth of HA nanorods with temperature can be described by “oriented attachmentâ€. According to this theory the adjacent HA crystallites would coalesce in one particular direction on the (1 1 0) high energy planes, creating templates                        to form elongated rod-like structure.  Fourier Transform Infrared Spectroscopy analysis reveals,  the silicon incorporation to hydroxyapatite lattice occurs via substitution of silicate groups for phosphate groups. Substitution of phosphate group    by silicate in the apatite structure results in a increase in the lattice parameters in both a-axis and c-axis of the unit cell

Elaboration of Novel NanoparticulateTiO2-P25@n-TiO2 Composite for Photocatalysis

A new mechanically stable TiO2-P25@n-TiO2 nanocoating was prepared after grafting of size-selected titanium-oxo-alkoxy particles on P25-TiO2 nanoparticles surface and their immobilization on a glass substrate followed by a thermal treatment. The 5-nm oxo-TiO2 particles were prepared in a sol-gel reactor with rapid reagents micromixing. The photocatalyst with 65% TiO2-P25 loading shows the highest activity towards ethylene degradation in a continuous-flow fixed-bed reactor. This material has a higher activity compared to that prepared by a conventional sol-gel method with strongly polydispersed titanium-oxo-alkoxy nanoparticles and clusters. The reaction conditions were explicitly analyzed along the reactor as a function of the ethylene concentration in framework of a kinetic model, which shows interplay between zero and first order processe

Optimisation of a diamond nitrogen vacancy centre magnetometer for sensing of biological signals

Sensing of signals from biological processes, such as action potential propagation in nerves, are essential for clinical diagnosis and basic understanding of physiology. Sensing can be performed electrically by placing sensor probes near or inside a living specimen or dissected tissue using well established electrophysiology techniques. However, these electrical probe techniques have poor spatial resolution and cannot easily access tissue deep within a living subject, in particular within the brain. An alternative approach is to detect the magnetic field induced by the passage of the electrical signal, giving the equivalent readout without direct electrical contact. Such measurements are performed today using bulky and expensive superconducting sensors with poor spatial resolution. An alternative is to use nitrogen vacancy (NV) centres in diamond that promise biocompatibilty and high sensitivity without cryogenic cooling. In this work we present advances in biomagnetometry using NV centres, demonstrating magnetic field sensitivity of approximately 100 pT/$\sqrt{Hz}$ in the DC/low frequency range using a setup designed for biological measurements. Biocompatibility of the setup with a living sample (mouse brain slice) is studied and optimized, and we show work toward sensitivity improvements using a pulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic artifacts in NV-ensemble widefield fluorescence imaging are investigated

Vickers microhardness and indentation fracture toughness of tantalum sesquinitride, η-Ta2N3

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