Effects of doping route on microstructure and mechanical properties of W−1.0wt.%La2O3 alloys

A comparative study was conducted by using solution combustion synthesis with three different doping routes(liquid-liquid(WL10), liquid-solid(WLNO) and solid-solid(WLO)) to produce nanoscale powders and further fabricate the ultrafine-grained W-1.0 wt.%La2O3 alloys by pressureless sintering. Compared with pure tungsten, W-1.0 wt.%La2O3 alloys exhibit ultrafine grains and excellent mechanical properties. After sintering, the average grain size of the WLO sample is larger than that of WL10 and WLNO samples;the microhardness values of WL10 and WLNO samples are similar but larger than the value of WLO sample. The optimized La2O3 particles are obtained in the WL10 sample after sintering at 1500 ℃ with the minimum mean size by comparing with WLNO and WLO samples, which are uniformly distributed either at grain boundaries or in the grain interior with the sizes of(57±29.7) and(27±13.1) nm, respectively. This study exhibits ultrafine microstructure and outperforming mechanical properties of the W-1.0 wt.%La2O3 alloy via the liquid-liquid doping route, as compared with conventionally-manufactured tungsten materials.

Carbothermal synthesis of Si_3N_4 powders using a combustion synthesis precursor

Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 ＋ C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid （Si source）, polyacrylamide （additive）, nitric acid （oxidizer）, urea （fuel）, and glucose （C source）. Scanning electron microscopy （SEM） micrographs showed that the obtained precursor exhibited a uniform mixture of SiO2 ＋ C composed of porous blocky particles up to -20 μm. The precursor was subsequently calcined under nitrogen at 1200-1550℃ for 2 h. X-ray diffraction （XRD） analysis revealed that the initial reduction reaction started at about 1300℃, and the complete transition of SiQ into Si3N4 was found at 1550℃. The Si3N4 powders, synthesized at 1550℃, exhibit a mixture phase of α- and -Si3N4 and consist of mainly agglomerates of fine particles of 100-300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.

Effect of stearic acid on the morphological and structural evolution of mechanically milled Nb-based powder

Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The slructural evolution and morphological evolution of the milled powder were characterized by X-ray diffraction （XRD）, scanning electron mi- croscopy （SEM）, and energy dispersive spectroscopy （EDS） analysis. It is indicated that an appropriate amount of stearic acid accelerates the particle refinement process and favors the production of superfine Nb-based particles with good dispersivity and high activity. However, an inappropriate amount of stearic acid has an adverse effect on the refinement process.

Facile synthesis of transition metal carbide nanoparticles embedded in mesoporous carbon nanosheets for hydrogen evolution reaction

Transition metal carbides(TMC)modified by mesoporous carbon nanosheets(MCNSs)with high activity,fast elec-tron/ion transfer and long durability are considered as promising electrocatalysts for hydrogen evolution reaction(HER).