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.

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).