Hydroxyapatite (HAP) is one of the most attractive calcium phosphates which is used for different applications. While HAP has been mostly synthesized using wet methods, recently solid‐state synthesis ...methods have attracted more attention. Many efforts have been made to better understand the solid‐state synthesis mechanism. In this study, the kinetics of the solid‐state reaction between hydroxide calcium (Ca(OH)2) and phosphorus pentoxide (P2O5) was studied under nonisothermal conditions using isoconversional methods. The phase analysis revealed that HAP is the main product of this process with no impurity. Thermogravimetric (TG) curves were recorded at four heating rates (β = 5, 10, 12 and 15°C⋅min−1) and analyzed by several well‐known isoconversional methods. Activation energy values were determined for each extent of reaction, which varied from ∼139 to 100 kJ/mol at the reaction extent of 0.1–0.9. Comparison between activation energy values obtained by isoconversional methods revealed that Flynn–Ozawa–Wall and Vyazovkin's method are more accurate than other. The preexponential factor and the reaction model were determined through model‐free methods. The obtained results indicated that the reaction mechanism was chemically controlled or ordered‐based model. Furthermore, the results showed that formation of HAP does not depend on the heating rate; however, it proceeds with increasing temperature.
AZ31B Mg alloy specimens were coated by PEO technique in WC nano-powder containing phosphate based electrolyte under constant current densities. Wear rate and COF diagrams were plotted in order to ...investigation of WC nano-particles presence and it was found that nano-particle presence can decrease wear rate and COF significantly down to 77% and 55%, respectively. Cross sectional imaging showed that coating thickness increase with coating time and in case of nano-particle containing coatings become more compact but thickness decreases slightly. Investigation of surface morphology indicated that in presence of nano-powder, porosity as well as mean diameter of pores decreased, but prolonging coating time even in presence of nano-powder, led to mean diameter of pores reached up to 8.34µm. Presence of nano-powders, also increased hardness of coatings considerably.
•PEO-WC nanocomposite coating was synthesized on Mg Alloys by Plasma Electrolytic Oxidation.•We study the effect of WC nanoparticles and the time of coating on surface characterization and wear resistance of PEO-WC nanocomposite.
Al‐doped SnS thin films with different Al concentrations were deposited on fluorine doped tin oxide (FTO) substrate from aqueous solution containing 2 mM SnCl2 and 20 mM Na2S2O3 and various amounts ...of 5 mM AlCl3 solution. The pH, temperature, time, and deposition potential (E) of the solution were kept at 2.1, 60 °C, 30 min and −1 V, respectively. The deposited films were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), and UV‐Vis. XRD patterns obviously indicated that the synthesized Al‐doped SnS were polycrystalline with orthorhombic structure and by increasing the amount of Al concentration, the crystallinity was increased. The FESEM images showed that the morphology of the nanostructures was changed with increasing Al content. PL and UV‐Vis analysis were used to investigate the optical properties of materials. The PL spectra showed a red shift with increasing of Al concentration.
Al2O3‐C foam filters have been successfully used for steel and aluminum melts filtration. Improving the high‐temperature mechanical properties enhances the capability and application of these filters ...for the filtration of large steel casting parts along with ingot casting or continuous casting of steel for long periods of time. In this study, adding nano‐Al2O3 and/or nano‐TiO2 to the composition of Al2O3‐C filters was investigated. Uniaxially pressed Al2O3‐C samples containing additives in the range from 0 to 1.0 wt% of nano‐oxides were prepared. The physical and mechanical properties, as well as microstructural analysis, were measured after sintering at 1600°C for 5 hours under a petroleum coke bed. The results showed that the presence of nano‐Al2O3 particles in the composition led to an increase in the cold crushing strength (CCS) due to the formation of the Al3CON phase which acts as a chemical bonding between Al2O3 particles and the carbonaceous matrix. On the other hand, the addition of 1.0 wt% of nano‐TiO2 in the composition caused an increase of 50% in the hot modulus of rupture (HMOR), attributed to the formation of columnar Al2O3 grains in the microstructure.
Titanium oxide (TiO2) nanoparticle coatings were deposited on the 316L stainless steel substrates by sol‐gel method. The morphology, structure, and corrosion resistance of the coating were analyzed ...using SEM, AFM, X‐ray diffraction, and electrochemical techniques. The deposition parameters employed to realize the anticorrosion performance including calcinations temperature, polyethylene glycol (PEG) content, pH value, and number of dipping cycles were investigated. Taguchi statistical experiments were carried out to determine the influence of the deposition variables on anticorrosion properties and optimal conditions. The results indicated that a higher anticorrosion performance of TiO2 films could be achieved using 1 g of PEG in a sol with pH in range of 7–9, six cycles of dipping, and calcination temperature at 400°C. The Tafel polarization measurements indicate that icorr value decreases about 200 times and the Rcorr value increases around 57 times compared with uncoated 316L stainless steel.
Silver-doped hydroxyapatite (Ag-doped HA) nanopowders were synthesized using calcium hydroxide (Ca(OH)2), phosphorus pentoxide (P2O5) and silver nitrate (AgNO3) precursors, through a one-pot ...mechanochemical process. The influence of dopant content on the phase formation, structural properties and morphological features was examined. The results showed that the as-prepared powders were single-phase hexagonal HA in the absence of the dopant. With the addition of the dopant, a similar phase structure was achieved, however some changes were observed with regards to the peak position and broadening. With the increase of Ag substitution, some alterations in the structural features of the milled powders were observed, where the crystallite size, lattice strain and crystallinity degree were between 25 ± 18 and 33 ± 14nm, between 0.486 ± 0.0.161 and 0.824 ± 0.477, and between ~ 83 and 93%, respectively. From the Fourier transformed infrared (FTIR) spectroscopy spectra, the location of the CO3-derived bands revealed that the replacement of PO43− by CO32− (B-type) was dominant in the Ag-doped HA nanopowders. This facile solid-state method is an alternative process for the preparation of bioceramic nanopowders.
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•Ag-doped HA nanopowders were synthesized by a one-pot mechanochemical treatment.•Morphological and structural features were examined as a function of dopant content.•Spheroidal particles showed an average size of 32 ± 1nm in the case of Ag-doped HA.•Unit cell volume unpredictably decreased due to the vacancy induced lattice relaxation.
Dissimilar transient liquid phase (TLP) bonding of GTD-111 and IN-718 nickel-based superalloys was investigated using BNi-9 (AWS A5.8/A5.8M) as an interlayer. The effect of the bonding time on the ...microstructure and mechanical properties of the TLP-bonded specimens was studied at 1100 °C using optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy-dispersive spectrometry (EDS), and micro-hardness and shear strength analyses. Joint microstructural studies revealed that at the bonding times shorter than 75 min, nickel- and chromium-rich borides were formed with the joint centerline. The volume fraction of intermetallic compounds decreased with the increase of the bonding time and the diffusion of boron element whereby the isothermal solidification eventually completed after 75 min. Micro-hardness investigations along the bonding joint showed that the hardness of an isothermal solidification zone (ISZ) decreased with the completion of isothermal solidification. The hardest zone in the joint structure belonged to the athermal solidification zone (ASZ). The shear strength test results showed that incrementing the bonding time increased the shear strength where the shear strength value at 1 min/1100 °C (320 MPa) raised to 590 MPa after the completion of isothermal solidification.
In this paper, a novel nanocrystalline composite material of hydroxyapatite (HA)/polyvinyltrimethoxysilane (PVTMS)/iron(II)chloride tetrahydrate (Cl2FeH8-O4) with hexagonal structure is proposed for ...the fabrication of a gas/temperature sensor. Taking into account the sensitivity of HA to high temperatures, to prevent the collapse and breakdown of bonds and the leakage of volatiles without damaging the composite structure, a freeze-drying machine is designed and fabricated. X-ray diffraction, FTIR, SEM, EDAX, TEM, absorption and photoluminescence analyses of composite are studied. XRD is used to confirm the material structure and the crystallite size of the composite is calculated by the Monshi–Scherrer method, and a value of 81.60 ± 0.06 nm is obtained. The influence of the oxygen environment on the absorption and photoluminescence measurements of the composite and the influence of vaporized ethanol, N2 and CO on the SiO2/composite/Ag sensor device are investigated. The sensor with a 30 nm-thick layer of composite shows the highest response to vaporized ethanol, N2 and ambient CO. Overall, the composite and sensor exhibit a good selectivity to oxygen, vaporized ethanol, N2 and CO environments.
