Kuai-She Wang

Spheroidization of molybdenum powder by radio frequency thermal plasma

To control the morphology and particle size of dense spherical molybdenum powder prepared by radio frequency (RF) plasma from irregular molybdenum powder as a precursor, plasma process parameters were optimized in this paper. The effects of the carrier gas flow rate and molybdenum powder feeding rate on the shape and size of the final products were studied. The molybdenum powder morphology was examined using high-resolution scanning electron microscopy. The powder phases were analyzed by X-ray diffraction. The tap density and apparent density of the molybdenum powder were investigated using a Hall flow meter and a Scott volumeter. The optimal process parameters for the spherical molybdenum powder preparation are 50 g/min powder feeding rate and 0.6 m3/h carrier gas rate. In addition, pure spherical molybdenum powder can be obtained from irregular powder, and the tap density is enhanced after plasma processing. The average size is reduced from 72 to 62 µm, and the tap density is increased from 2.7 to 6.2 g/cm3. Therefore, RF plasma is a promising method for the preparation of high-density and high-purity spherical powders.

Oxidation layering mechanism of graphene-like MoS2 prepared by the intercalation-detonation method

Graphene-like MoS2 has attracted significant interest because of its unique electronic, optical, and catalytic properties with two-dimensional lamellar structure. Three kinds of intercalated MoS2 samples were prepared using different oxidation layering methods, which are the first steps of intercalation-detonation. The oxidation layering mechanism of graphene-like MoS2 was systematically characterized using Fourier transform infrared, X-ray photoelectron, and Raman spectroscopy techniques. The bulk MoS2 sample was gradually oxidized from the edge to the interlayer in the presence of concentrated H2SO4 and KMnO4. A large number of hydroxyl groups were bonded to the sulfur atom layer, forming S–OH bonds in the basal planes of the MoS2 structure. The addition of deionized water to concentrated H2SO4 generated a large amount of heat, promoting the generation of more S–OH bonds, destroying residual Van der Waals forces between the layers, and finally stripping off parts of the flakes. The continuous addition of deionized water in the high temperature stage resulted in the largest oxidative intercalation effect. Additionally, the η factor was determined to compare the intensities of B1u and A1g peaks in the Raman spectra and quantify the effect of oxidative intercalation. The highest value of η was obtained when deionized water was added continuously during the preparation of intercalated MoS2.