Synthesis of NiMoO4 nanoparticles by sol–gel method and their structural,morphological, optical,magnetic and photocatlytic properties

Nickel molybdate (NiMoO₄) nanoparticles (NPs) were synthesized by sol–gel method. Utilizing water as solvent provides crystalline nanostructures. These nanocrystals were structurally characterized by X-ray diffraction, energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectra. Compositional stoichiometry was confirmed by EDX technique. The size and shape were observed by scanning electron microscopy (SEM) and transmission electron microscope (TEM). It was found that the obtained NPs were pure and single phase crystalline with monoclinic structure. The optical properties were studied by ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis–DRS) and photoluminescence (PL) measurements at room temperature. The magnetic properties were studied by vibrating sample magnetometer (VSM) and results showed superparamagnetic behavior of the obtained nanoparticles. Photocatalytic activity of NiMoO₄ was studied. The photocatalytic activity of NiMoO₄ was enhanced with the addition of TiO₂. The catalysts NiMoO₄, TiO₂ and NiMoO₄–TiO₂ nanocomposites (NC) were tested for photocatalytic degradation (PCD) of 4-chlorophenol (4-CP). It was found that PCD efficiency of NiMoO₄–TiO₂ NC was higher than that of pure NiMoO₄ and TiO₂.     

Effect of TiO2 on thermal,structural and third-order nonlinear optical properties of Ca–La–B–O glass system

A series of calcium lanthanum metaborate glasses in the composition (wt%) of 23.88CaO–28.33La₂O₃–47.79B₂O₃ modified with TiO₂ up to 20 wt% are prepared by a melt quenching technique to study the influence of TiO₂ on their thermal, structural, linear and nonlinear optical properties. The differential thermal analysis (DTA) studies have demonstrated significant effects due to the presence of TiO₂ on the glass forming ability and crystallization situations. The glass with 15 wt% TiO₂ has achieved a eutectic composition and also exhibited a better glass forming ability among the glasses studied. The FT-IR spectra of these glasses show mainly vibration modes corresponding to stretching of BO₃ trigonal, BO₄ tetrahedral units and of B–O–B bending bonds. At higher concentrations of TiO₂, development of vibration band around 400 cm^?1 has indicated the formation of TiO₆ structural units in the glass network. The red shift of optical absorption edge (UV cutoff) shows a monotonous decrease in direct and indirect optical band gap energies (E_opt) with an increase of TiO₂ content in the glasses based on their absorption spectra. The optical transparency of these glasses is found to be varied from 64 to 87% within the wavelength range 450–1100 nm depending on the TiO₂ content. Besides these studies, linear refractive indices, the nonlinear optical properties of these glasses have also been evaluated.     

Age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental Au–Ag–Cu–Pd–Zn alloy

The age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental casting gold alloy composed of 56Au–25Ag–11.8Cu–5Pd–1.7Zn–0.4Pt–0.1Ir (wt.%) were elucidated by characterizing the age-hardening behaviour, phase transformations, changes in microstructure and changes in element distribution. The fast and apparent increase in hardness at the initial stage of the aging process at 400°C was caused by the nucleation and growth of the metastable Ag–Au-rich phase and the Cu–Au-rich phase by the miscibility limit of Ag and Cu. The transformation of the metastable Ag–Au-rich phase into the stable Ag–Au-rich phase progressed concurrently with the ordering of the Cu–Au-rich phase into the AuCu I phase through the metastable state, which resulted in the subsequent increase in hardness. The further increase in hardness was restrained before complete decomposition of the parent α₀ phase due to the initiation of the lamellar-forming grain boundary reaction. The progress of the lamellar-forming grain boundary reaction was not directly connected with the phase transformation of the metastable phases into the final product phases. The heterogeneous expansion of the lamellar structure from the grain boundary caused greater softening than the subsequent further coarsening of the lamellar structure. The lamellar structure was composed of the Ag–Au-rich layer which was Cu-, Pd- and Zn-depleted and the AuCu I layer containing Pd and Zn.     

Electrochemical study on effect of Au,Ag, Pd and Pt on corrosion behaviour of Fe3Al in molten NaCl–KCl

The corrosion behaviour of Fe₃Al intermetallic alloyed with 1 at-%Ag, Au, Pt and Pd in NaCl–KCl (1∶1M) at 700°C, typical of waste gasification environments, has been evaluated using polarisation curves, linear polarisation resistance and electrochemical impedance spectroscopy measurements and compared with an Ni based alloy, namely Inconel 600. Results have shown that, for short testing times, the addition of noble elements increased the corrosion rate for base Fe₃Al intermetallic alloy, but it was decreased for long testing times by forming a protective corrosion product layer. Additionally, base Fe₃Al intermetallic alloy had higher corrosion rates than Inconel 600.     

Thermal expansion behavior,microhardness and electrochemical corrosion resistance properties of Au52Cu27Ag17–x(NiZn0.5)x alloys

The thermal expansion behavior, microhardness and electrochemical corrosion resistance of Au₅₂Cu₂₇Ag_17–x(NiZn_0.5)_x (x=0, 6 and 12) alloys were investigated by dilatometer (DIL), microhardness tester, electrochemical workstation, X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). With increasing x, the relative length expansion and DIL maximum temperature T_{l m} (i.e., thermal stability) of the alloys increase in thermal expansion measurements, which can be explained by the change of the atomic binding energy, mismatch entropy together with phase transformation. With the increase of x, the microhardness can be improved, but the corrosion resistance decreases; in addition, the anodic peak current densities of polarization curves decrease, which are related closely with the solid solution degree and dissolution of Ag, Ni and Zn alloying elements in Cl⁻-containing solution.     

Structure,phase composition and magnetic properties of Fe–Si–C system due to mechanical activation of Fe–Si alloy in organic liquids

Fineness, structure, phase composition, and magnetic properties of the powders produced by mechanical milling of Fe₈₀Si₂₀ in liquid hydrocarbon environment (heptane, heptane with oleic acid additive) in planetary ball mill have been studied. Under milling the alloys are saturated with the products of organic liquid decomposition – C, O, H, and then metastable amorphous and carbide phases form. The particle size decreases down to 0.1–0.2 μm. Isochronous (775 K, 1 h) annealing leads to the formation of the Fe₈Si₂C iron silicon carbide, as well as Fe₃Si and C – for milling in heptane, and Fe₃C and SiO₂ – for milling with oleic acid additive. The magnetic properties of the powders depend both on the milling time and milling environment, and on the annealing temperature. An increase in the coercivity from 13 up to 226 Oe correlates with the amount of the synthesized Fe₈Si₂C. It is ferromagnetic (T_c = 788 K) and temperature-resistant up to 870 K.     

Precipitation of Al3(Sc,Zr) particles in an Al–Zn–Mg–Cu–Sc–Zr alloy during conventional solution heat treatment and its effect on tensile properties

The effect of heat treatment on precipitation and growth of coherent nanometer-sized Al₃(Sc,Zr) particles and the effect of these particles on tensile properties of a direct chill (DC) cast Al–Zn–Mg–Cu–Sc–Zr alloy were studied. The size distribution, average size, number density and volume fraction of the Al₃(Sc,Zr) particles were determined as a function of the solution treatment temperature and time. An increase in the solution treatment temperature and time resulted in Al₃(Sc,Zr) particles with a larger mean diameter, higher volume fraction and lower number density. The particle size distributions were described well by normal (Gaussian) distributions. The kinetics of the phase transformation followed the Kolmogorov–Johnson–Mehl–Avrami law, with the Avrami exponent m = 0.404. Room temperature tensile properties were evaluated in the as-solution treated and artificially aged conditions. The coherent nanometer-sized Al₃(Sc,Zr) particles provided additional Orowan strengthening, which increased with increasing particle volume fraction and decreasing particle size, and varied from 75 to 118 MPa after different heat treatments.     

First-principles calculations of the structural and thermodynamic properties of bcc,fcc and hcp solid solutions in the Al–TM (TM = Ti,Zr and Hf) systems: A comparison of cluster expansion and supercell methods

The thermodynamic properties of solid solutions with body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp) structures in the Al–TM (TM = Ti, Zr and Hf) systems are calculated from first-principles using cluster expansion (CE), Monte-Carlo simulation and supercell methods. The 32-atom special quasirandom structure (SQS) supercells are employed to compute properties at 25, 50 and 75 at.% TM compositions, and 64-atom supercells have been employed to compute properties of alloys in the dilute concentration limit (one solute and 63 solvent atoms). In general, the energy of mixing (Δ_mE) calculated by CE and dilute supercells agree very well. In the concentrated region, the Δ_mE values calculated by CE and SQS methods also agree well in many cases; however, noteworthy discrepancies are found in some cases, which we argue originate from inherent elastic and dynamic instabilities of the relevant parent lattice structures. The importance of short-range order on the calculated values of Δ_mE for hcp Al–Ti alloys is demonstrated. We also present calculated results for the composition dependence of the atomic volumes in random solid solutions with bcc, fcc and hcp structures. The properties of solid solutions reported here may be integrated within the CALPHAD formalism to develop reliable thermodynamic databases in order to facilitate: (i) calculations of stable and metastable phase diagrams of binary and multicomponent systems, (ii) alloy design, and (iii) processing of Al–TM-based alloys.     

Sulfidation properties of TiAl–2 at.% X (X=V,Fe, Co,Cu, Nb,Mo, Ag and W) alloys at 1173 K and 1.3 Pa sulfur pressure in an H2S–H2 gas mixture

TiAl–2 at. % X (X=V, Fe, Co, Cu, Nb, Mo, Ag and W) alloys were sulfidized at 1173 K for 86.4 ks at a 1.3 Pa sulfur pressure in an H₂–H₂S gas mixture. The structure, phases, and compositions of the external sulfide scale and alloy surface layer were measured using EPMA and X-RD. The TiAl–2Ag and –2Cu alloys sulfidized faster than TiAl, and the alloy surface layer was thicker than that of TiAl. Sulfidation amounts of the TiAl–2X (X=V, Co, Fe, Mo, W and Nb) alloys were almost the same as that of TiAl, while the thickness of the alloy surface layer decreased in the order: V>Co>Fe>Mo>[Cr (by Narita T, Izumu T, Yatagai M, Yoshioka T. Intermetallics, 2000;8:371)]>W>Nb. The sulfide scale was composed of multi-layer structures: an outermost (rich in Ti-sulfides), an outer (rich in Al₂S₃), an inner (a mixture of Ti-sulfides and Al₂S₃), and an innermost (rich in Ti-sulfides) layer. The alloy surface layer also had a multi-layer structure, and was classified into four groups: group 1 for TiAl–2V and –2Co alloys as well as TiAl binary alloy where the surface layer consists of alloy substrate/TiAl₂/TiAl₃/sulfide scale, group 2 for TiAl–2Nb, –2Mo, and –2W (and also– 2Cr) alloys with alloy substrate/TiAl₂/TiAl₃/(Nb, Mo, W or Cr)–Al alloy/sulfide scale, group 3 for TiAl–2Cu and –2Ag alloys with alloy substrate/TiAl₂/Ti (Al, Ag or Cu)₃ with an L1₂ structure/TiAl₃/sulfide scale, and group 4 for TiAl–2Fe alloy with alloy substrate/TiAl₂/Ti(Al,Fe)₃ with an L1₂ structure/TiAl₃/FeAl₃/sulfide scale. Diffusion paths for these four groups were shown in a tentative Ti–Al–X ternary phase diagram.