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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]

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]

The Si 3 N 4 -SiC micro-nano composites were fabricated via the spark plasma sintering method using MgSiN 2 as an additive. Response surface methodology and central composite design were applied to optimize the spark plasma sintering process for the fabrication of Si 3 N 4 -SiC/MgSiN 2 with improved density. The relation between the three parameters of sintering including temperature, pressure, and holding time was modeled and the optimized parameters were obtained. The best sintering results obtained for the sintering temperature, holding time, and pressure are 1700 °C, 487 s, and 49 MPa, respectively. The addition of MgSiN 2 as an additive and SiC as a secondary phase were also investigated in the present work. The Si 3 N 4 −5 vol% SiC composite exhibited high hardness (19 GPa) and fracture toughness values (6.5 MPa m 1/2 ) at room temperature. [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]

Abstract: Silicon nitride ultrafine powders were synthesized from a binary sol–gel route, in which tetraethoxysilane (TEOS) and saccharose were used to prepare a carbonaceous silica xerogel, and ferric nitrate was employed as an additive. The influence of reaction temperature and mass ratio of C to Si ( =0.1, 0.5, 1) on the synthesis of Si3N4 wires was studied. After purification, the Si3N4 sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectrum and Fourier transform infrared spectroscopy. The results show that the Si3N4 was fully formed with two kinds of morphologies including globular and wire with a diameter of 100–500nm and a length of several microns at reaction temperature of 1400°C for 10h in nitrogen flow (200ml/min) by employing the mass ratio of =0.5. [Copyright &y& Elsevier]