In this paper, a novel nanocrystalline composite material of hydroxyapatite (HA)/polyvinyltrimethoxysilane (PVTMS)/iron(II)chloride tetrahydrate (Clsub.2FeHsub.8-Osub.4) 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, Nsub.2 and CO on the SiOsub.2/composite/Ag sensor device are investigated. The sensor with a 30 nm-thick layer of composite shows the highest response to vaporized ethanol, Nsub.2 and ambient CO. Overall, the composite and sensor exhibit a good selectivity to oxygen, vaporized ethanol, Nsub.2 and CO environments.
The production of MoO
3
from Sarcheshmeh molybdenite concentrate
via
a pyro-hydrometallurgical process was studied. The molybdenite concentrate and sodium carbonate were premixed and fused under air ...atmosphere. Then the fused products were leached in water and the dissolved molybdenum was recovered as ammonium molybdate. The ammonium molybdate was then calcined to produce molybdic oxide. At the fusion stage, the effect of the mass ratio of carbonate to sulfide on the reaction products and the solubility of the products was investigated. The results show that during the fusion, sodium molybdate and sodium sulfate are the final reaction products and sodium sulfide is detected as an intermediate reaction product. By melting at 850°C with 5wt% excess carbonate, the maximum solubility of the products is obtained. The molybdenum is recovered from the solutions as ammonium molybdate.
One-step mechanochemical process followed by thermal treatment has been used to produce calcium phosphate-based composite nanopowders. Effects of milling and subsequent heat treatment on the phase ...transition as well as structural features were investigated. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques. The results revealed that the dominant phases after mechanical activation were hydroxyapatite, anatase (TiO2), and periclase (MgO), while after thermal annealing process at 700°C hydroxyapatite along with geikielite (MgTiO3) and periclase (MgO) were the major phases. In addition, decomposition of hydroxyapatite to tricalcium phosphate (β-TCP) occurred after heat treatment in the range 900–1100°C which resulted in the formation of tricalcium phosphate-based composite nanopowders. Evaluation of structural features of the samples calculated by X-ray diffraction profiles analysis indicated that the average crystallite size of hydroxyapatite after 10h of milling and subsequent heat treatment at 700°C were about 21 and 34nm, respectively. TEM and SEM studies exhibited that the considerable morphological changes at temperatures ≥900°C had to be ascribed not only to grain growth, but also for the transformation of hydroxyapatite to β-TCP.
Corrosion is a harmful processes which by definition is a chemical or electrochemical reaction between a substance (usually a metal) and the environment which leads to a change in the properties of ...the substance and has destructive effects. In this study, new composites consisting of Al/WSsub.2/ZnTerp-2TH with 5 and 10 wt.% ZnTerp-2TH were prepared and the results were fully compared. Al/WSsub.2 played the role of matrix and ZnTerp-2TH played the role of reinforcement. In other words, as a novelty to prevent the corrosion of Al/WSsub.2, ZnTerp-2TH is designed and synthesized and showed good results when the corrosion ratio was reduced by the existence of ZnTerp-2TH. Furthermore, the NMR and mass analysis of ZnTerp-2TH were carried out, and the thermal properties, X-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy, morphology, energy-dispersive X-ray spectroscopy (EDX) analysis and corrosion behavior of the composites were also discussed in detail. The crystal size values of composites were calculated by the modified Scherrer method 34, 26 and 27 nm for Al/WSsub.2, Al/WSsub.2/5 wt.% ZnTerp-2TH and Al/WSsub.2/10 wt.% ZnTerp-2TH, respectively. The microstructural examination of the specimens showed that the reinforcing phase (ZnTerp-2TH) has a favorable distribution on the surface of Al/WSsub.2 when it covers the cracks and holes. In addition, the corrosion investigation results showed that the addition of ZnTerp-2TH to Al/WSsub.2 can improve the corrosion resistance when the Esub.corr and Isub.corr values of Al/WSsub.2/10 wt.% ZnTerp-2TH were recorded in tandem −724 mV/decade and 5 uA cmsup.−2.
The influence of milling parameters on the formation of titanium diboride nanopowders by mechanically induced self-sustaining reaction (MSR) was studied. A high-energy planetary ball mill was used to ...provide necessary conditions for the occurrence of MSR. Results showed that the formation and structural features of titanium diboride nanopowders were notably influenced by ball to powder weight ratio (BPR), total powder mass and weight fraction of diluent (NaCl). With BPRs of 10:1, 15:1 and 20:1, combustion reaction occurred after 73, 34 and 40min, respectively. The mechanosynthesized nanopowders were composed of TiB2 (major compound), MgO and Mg2TiO4 (unwanted phases). With a BPR of 15:1, the addition of 5wt% NaCl delayed the combustion reaction to 60min and led to the formation of TiB2, MgO and Mg2TiO4 with the crystallite size of around 24, 40 and 45nm, respectively. After leaching in 18% HCl aqueous solution at 60°C for 30min, the unwanted phases were completely removed and consequently a single-phase titanium diboride nanopowder with crystallite size of about 92nm was formed. According to the scanning electron microscope images, the leached powder was comprised of nanoparticles with an average size of about 140nm.
Chlorapatite nanopowders (n-CAp) were produced by a novel facile mechanochemical process. Results showed that the formation of n-CAp proceeded in several steps. At the beginning of milling, the main ...products were stoichiometrically deficient chlorapatite and calcium oxide. Eventually, high crystalline CAp nanopowder was obtained after 300min of milling. By increasing the milling time to 300min, the lattice strain increased significantly to around 0.0108±0.0005, while the crystalline size declined sharply to about 28±2nm. Similarly, the crystallinity degree of the samples was influenced by the milling time and reached about 77±4% after 300min of milling. SEM observations indicated that the milled sample had cluster-like structure which was consisted of fine particles with a mean size of about 95nm.
Display omitted
•Chlorapatite nanopowders were produced by a novel facile mechanochemical process.•After 300min of milling, crystalline size reached about 28±2nm.•The crystallinity degree of the samples was influenced by the milling time.•Chlorapatite nanopowders had cluster-like structure with a mean particle size of about 95nm.•The formation of n-CAp proceeded in several steps.
TiC–MgO composite was synthesized using mixtures of TiO2, Mg, and wood dust via a mechanochemical process. The influence of various Mg values (0–2.4mol) on the titanium carbide formation and the ...mechanism of reactions during the milling of TiO2–Mg–C mixture were investigated. Phase transformations, grain size, strain, lattice parameters, and morphology of the powders during the milling process were examined using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Thermodynamic calculations revealed that the Mg value played a main role. Consequently, the overall reaction enthalpy and adiabatic temperature (Tad) changed with variation of the magnesium content. Experimentally, after 10h of milling, TiC was synthesized in the mixture powder with stoichiometric ratio (Mg=2mol). The type of reactions was mechanically induced self-sustaining reaction (MSR). In addition, at lower Mg content (Mg=1.5), the heat resulted from magnesiothermic reaction also activated the carbothermal reduction. Further decrease in the Mg value (Mg=0.5 and 1mol) resulted in formation of MgTiO3 as a major phase. Using the excess Mg value (Mg=2.2 and 2.4molMg) as a diluent agent led to formation of Mg2TiO4 besides the MgO and TiC phases.
•Mg content plays a key role in the mechanochemical behavior of Mg–TiO2–C.•By increasing milling time, an exothermic reaction occurs before magnesium melting.•Magnesiothermic reaction provided enough heat for activating carbothermic reaction.•Mg, within a range of 1.5–2.2mol promoted a self-sustaining reaction.
In this research, nanocomposite coating was deposited on magnesium matrix AZ31B alloy using the micro arc oxidation (MAO) method. MAO was carried out in SiC-nanoparticles containing suspension using ...the sodium silicate and sodium aluminate bases at constant current density. The effect of nanopowder addition and MAO periods were also investigated in the present work. Using the Scanning electron microscopy (SEM), the thickness and surface morphology of the coatings were studied. The coefficient of friction and abrasion rate curves were used to analyze nanopowder addition on resistance to abrasion, while the potentiodynamic curves were used for assessing the resistance to corrosion in the ceramic nanocomposite coating deposited on surface of alloy AZ31B. The morphological studies on surface of coatings revealed that the cavitation level and size increases with the increasing coating duration. Besides, Energy Dispersive X-Ray Diffraction (EDS) analyses from cross section and surface of the prepared coatings revealed that nanopowder distribution on interface of coating with matrix and boundaries of the cavities is almost uniform. The cross section studies of the coatings revealed that their thickness increases, as coating duration prolongs. Furthermore, the corrosion behavior of the samples indicated that presence of nanopowder does not significantly affect the resistance to corrosion of the coatings; however, coefficient of friction and abrasion rate of coatings indicates a respective rise and drop in presence of these nanopowders.
An investigation was carried out to assess the applicability of transient liquid phase bonding of two dissimilar super-alloys with different interlayers. The effect of using three types of interlayer ...such as BNi-2, BNi-3, and BNi-9 on microstructure and mechanical properties was studied in the GTD-111/IN-718 system at 1100 °C for different bonding time. To determine the compositional changes and microstructure in the joint region, field emission scanning electron microscopy equipped with energy dispersive spectroscopy was utilized. The formation of Ni3B in the athermally solidified zone (ASZ) is controlled by the B content and, accordingly, the morphology of Ni3Si is governed by the Si content. The Cr content might impede the relocation of B from the interlayer into the base metal and the formation of CrB inside the ASZ is dominated by the Cr content. The high micro-hardness of the eutectic compounds is originated from the formation of boride matrixes such as Ni or Cr boride. The shear strength of the joint using BNi-9 after the completion of isothermal solidification is lower compared that that using BNi-3 and BNi-2, which could be related to the absence of Si in the filler metals constituent and the significant presence of Cr in BNi-9.
Spex mills are among the most important tools for synthesizing nanocomposite powders. However, review of the literature reveals that due to their complex geometry, an accurate simulation of these ...tools has not been accomplished yet. The SPEX mills are considered to be of higher energy than the other mills; hence they have an obvious potential to produce combustion reactions and consequently rapid synthesis of nanocomposites. In the present work, a novel modeling is performed on the Spex mills and the self-ignited reactions are simulated. The proposed modelling correlates the milling parameters with the ignition time using a mathematical formula. The mathematical formula ensures that if the milling parameters are known, the ignition time in combustion reactions is predictable. An optimization process is then conducted to optimize the milling and reaction parameters in order to minimize the ignition time predicted by the mathematical formula. The results show that the combination of modeling and optimization processes leads to the prediction and minimization of ignition time, which in turn brings about significant benefits including saving the energy and time consumed as well as reducing the costs of producing nanocomposite powders. At the end, a few case studies were performed for evaluating the results obtained by the modeling and optimizing algorithms. The result showed a good agreement between the experimental data and the simulated ones.
