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In this study, superhydrophobic surfaces were fabricated on aluminium substrates by chemical etching method and surface modification with perfluorooctyl trichlorosilane (PFTS). The superhydrophobic surface of the aluminium substrate was synthesized by two-step process: first, the roughness on the aluminium surface was created by the chemical etching method. Then, the surface energy of the rough aluminium substrate was reduced by immersion in the PFTS solution. The surface wettability was measured by a droplet contact angle measurement. The morphology and chemical composition of the surface were detected by field emission scanning electron microscope and attenuated total reflection-Fourier transform infrared methods, respectively. The self-cleaning properties of the coated and bare aluminium substrates were investigated. Corrosion behaviour of the samples was evaluated using Tafel polarization and salt spray methods. The contact angle measurement results showed that the surface roughness due to chemical etching reduced the contact angle on the aluminium substrate to 24° and after surface modification, the contact angle increased to 157°. In the Tafel polarization test, after creating a superhydrophobic surface, the corrosion current density and corrosion potential of the aluminium substrate reached from 94.3 to 28.82 (µA cm−2) and −0.695 to −0.68 V, respectively. The superhydrophobic aluminium surface showed self-cleaning effect. [ABSTRACT FROM AUTHOR]

This research has investigated the optical properties of zinc sulfide commercial powder sintered via hot pressure (HP) and spark plasma sintering (SPS) methods. SEM images indicated that zinc sulfide commercial powder had spherical morphology, whereby nano rods smaller than 100 nm formed on spherical particles. Investigation of optical properties indicated that the zinc sulfide transparent ceramic prepared via HP (75%) had higher infrared transmission as compared to SPS (69%) within 8–12 micrometer. The stoichiometric ratio of S to Zn in the commercial powder was 1.5, which decreased to 1.1–1.3 after the sintering process. [ABSTRACT FROM AUTHOR]

In this study, Ta powder was produced from Ta scarp via chemical processes using Mg and Ca powders. Initially, tantalum scraps were converted to tantalum oxide (Ta2O5) at 1100 °C in an oxygen atmosphere. Tantalum oxide was then reduced to Tantalum powder with Mg in a vacuum environment at 950 to 1200 °C for 3 hours. The obtained Ta powders further were reacted with Ca at 950 °C for 5 hours in a vacuum atmosphere. The powders were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as conducting oxygen content measurement. The results showed that the average particle size of the produced Ta powders was around 58 nm with oxygen contents of 250 ppm. [ABSTRACT FROM AUTHOR]

In this work, the wear performance of nano- and ordinary MoSi2 plasma-sprayed coating on Ni substrate are compared. MoSi2 nanopowder is prepared by ball milling followed by heat treatment processes. Atmospheric plasma spraying with argon atmosphere protection has been used to deposit the powders onto the nickel substrate. Ni substrate, MoSi2 coating, and nano-MoSi2 coating were subjected to reciprocating wear test. Wear tests were done on a pin on plate machine by sliding MoSi2 coating and substrates without coating against 52100 steel as the pin, at a temperature of 27 °C in dry condition. A friction coefficient of 0.18 ± 0.1 is obtained for nanostructured MoSi2 coating, whereas a friction coefficient of 0.2 ± 0.1 is obtained for conventional MoSi2 coating under normal load of 20 N. Wear performance of nanostructured MoSi2 coating was better as compared to the conventional MoSi2 coating. The three observed dominant types of wear mechanisms were adhesive, oxidation and abrasive. Morphologies and phases of coating, wear tracks, wear debris and counterpart steel pins were evaluated by SEM with EDS and X-ray diffraction. The microhardness and adhesion strength of nanostructured MoSi2 coating are determined by 1000 HV and 27 MPa, respectively. [ABSTRACT FROM AUTHOR]

The mechanically activated annealing process was adopted to synthesize nanostructure MoSi2–SiC powders containing different SiC contents using Mo, Si, and SiC powders. Atmospheric plasma spraying technique was used to deposit the agglomerated powders of MoSi2–SiC nanocomposite under inert conditions on a nickel substrate. Phase identification and microstructural characteristics of the nanopowders and coatings were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and qualitative energy-dispersive spectroscopy (EDS). The microstructure of the plasma-sprayed coating consists of α and β-MoSi2, SiC, Mo5Si3, and a trace of SiO2 phases. It can be concluded that mechanically activated annealing synthesis with agglomeration is an effective method for the preparation of high-melting-point refractory compounds for using in plasma spraying process. The measured adhesion strength, microhardness, and roughness results of MoSi2–SiC coatings are also reported in the present work. [ABSTRACT FROM AUTHOR]

Among refractory metals, tantalum has long been the primary material of use in high strain rate applications. Hot pressing (HP) is a technique to produce specimens with high density and homogeneous microstructure. The individual effect of the HP or annealing heat treatment on high strain rate properties of tantalum powder compacts has been investigated, but little attention has been paid to the combined effect of subsequent annealing. In this study, the effect of annealing on the microstructure and mechanical properties of tantalum subjected to hardness and Split Pressure Hopkinson Bar (SHPB) test was investigated. After annealing at 1100°C, the grains are coarsened, thereby hardness and upper yield strength decreased to value 199 VHN and 1833 MPa, respectively. Moreover, an obvious increase in plasticity and toughness is detected at this temperature, indicating subsequent annealing is beneficial to improve the deformation properties of HPed powder compacts; the maximum plasticity of tantalum was 31.74% after annealing. [ABSTRACT FROM AUTHOR]

In this investigation, a two-step method for the preparation of magnesium silicide (Mg2Si) nanopowder was studied. This method is known as mechanical alloying followed by heat treatment. The results showed that the compositions of the combustion products depended on the milling time, heat treatment temperature, and starting mixtures. Pure Mg2Si nanopowder was formed after short milling time and heat treatment, from Mg and Si powders with the mole ratio of 2.1:1 (Mg:Si) at 500°C in Ar atmosphere. Using the Mg2Si nanopowder, Mg2Si ceramic was produced by spark plasma sintering at 800°C under 50 MPa for 15 min. Composition and structure of reactants and products were examined by X-ray diffraction ( XRD), field emission scanning electron microscopy ( FE- SEM) and high-resolution transmission electron microscopy ( HR- TEM). [ABSTRACT FROM AUTHOR]

In this research, diamond-like carbon (DLC) thin films were deposited on silicon substrates by radio-frequency plasma enhanced chemical vapor deposition method using gas mixture of CH4 and Ar. The effect of different CH4/Ar gas ratio on the structure, refractive index, transmission and hardness of the DLC thin films were investigated by means of Raman spectroscopy, ellipsometry, Fourier transform Infrared Spectroscopy and nano-indentation methods, respectively. Nuclear resonant reaction analysis was used to measure the amount of hydrogen and carbon in the thin films. Furthermore, wettability of the thin films was achieved by measuring of water contact angle (WCA). The results indicated that the structural properties of the diamond-like carbon thin films are strongly dependent on the composition of gas mixture. Based on ellipsometry results, refractive index of the thin films varied in the range of 1.89-2.06 at 550 nm. FTIR results determined that deposition of DLC thin films on silicon substrate led to an increase of the light transmission in IR region and these films have the potential to be used in silicon optics as the antireflective coatings in this region. Nano-indentation analysis showed that the thin films hardness changed in the range of 7.5-11 GPa. On the other hand hydrogen content and fraction of C‒H bonds in the samples increased by an increase in the gas ratio of CH4/Ar. Also, WCA measurements indicated that WCA for thin films with gas ratio of 3/7 is the most and equal to 79°. [ABSTRACT FROM AUTHOR]