Thermal plasma synthesis of SiC from rice hull (husk)
Recently the synthesis of ultrafine powders has drawn considerable attention because these powders can have physical and chemical properties superior to those of bulk specimens. In particular, emphasis is on the preparation of ultrafine ceramic powders for their applications in the development of sintered products having higher density and lower sintering temperature. One such industrially important ceramic material is SiC. In many cases ultrafine SiC has been prepared by thermal plasma processes [1]. However, these processes require one or more reactive/corrosive gases. This letter describes a new method to overcome such problems. For this purpose thermally pretreated rice hull was used as the solid precursor. Rice hull, an agricultural waste product, was first used by Cutler [2] as a starting material for the production of silicon carbide. Since the rice hull route promises to be most economical, much attention has recently been paid to it [3-6]. Rice hull consists of silica in hydrated amorphous form, and cellulose which yields carbon when thermally decomposed. The relative abundance of silica with very high surface area in close proximity to active carbon in rice hull makes it amenable for SiC formation during the pyrolysis process. The possible reaction was given by Lee and Cutler [7] as
Silicon carbide and nitride from rice hulls. III: Formation of silicon nitride
Des coques de riz ont ete impregnees dans une solution de sulfate ferreux, trempees dans une solution d'amoniaque et traitees 30 mn a 700°C en l'absence d'air. On a ensuite forme SiN en cuisant les coques pretraitees, en atmosphere d'ammoniac, 30 mn a 2 h, a 1200-1500°C. On etudie les effets de la temperature de cuisson et du rapport fer/silice sur le rendement et le type de produit obtenu a l'aide de la spectrometrie RX et de l'analyse chimique
Design and assembly of ternary Pt/Re/SnO2 NPs by controlling the zeta potential of individual Pt, Re, and SnO2 NPs
AbstractIn this study Pt, Re, and SnO2 nanoparticles (NPs) were combined in a controlled manner into binary and ternary combinations for a possible application for ethanol oxidation. For this purpose, zeta potentials as a function of the pH of the individual NPs solutions were measured. In order to successfully combine the NPs into Pt/SnO2 and Re/SnO2 NPs, the solutions were mixed together at a pH guaranteeing opposite zeta potentials of the metal and oxide NPs. The individually synthesized NPs and their binary/ternary combinations were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) analysis. FTIR and XPS spectroscopy showed that the individually synthesized Pt and Re NPs are metallic and the Sn component was oxidized to SnO2. STEM showed that all NPs are well crystallized and the sizes of the Pt, Re, and SnO2 NPs were 2.2, 1.0, and 3.4 nm, respectively. Moreover, EDS analysis confirmed the successful formation of binary Pt/SnO2 and Re/SnO2 NP, as well as ternary Pt/Re/SnO2 NP combinations. This study shows that by controlling the zeta potential of individual metal and oxide NPs, it is possible to assemble them into binary and ternary combinations.
 Graphical abstractᅟ