Composite ceramics of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 (BSTN) with coexistence of barium strontium titanate, Ba1-xSrxTiO3 (BST), and strontium barium niobate, SrxBa1-xNb2O6 (SBN) phases were successfully ...Composite ceramics of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 (BSTN) with coexistence of barium strontium titanate, Ba1-xSrxTiO3 (BST), and strontium barium niobate, SrxBa1-xNb2O6 (SBN) phases were successfully prepared in situ by controlling excess components according to a specially designed formula of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 and by using a traditional ceramic process. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersion spectrometer (EDS) were used to characterize the phase composition, morphology and the micro-area chemical composition of the composite ceramics. The results showed that the SBN tungsten bronze phase appeared and coexisted stably with the BST perovskite phase when the excess content of Nb2O5 was >6mol%, whereas the BST perovskite phase formed and coexisted stably with the SBN tungsten bronze phase when the excess content of TiO2 was >5.3mol%. In the case of the two phases being equivalent to each other in BSTN composite ceramics, Nb2O5 was hard to be resolved into the perovskite phase, however, a few of TiO2 was easy to be resolved in the tungsten bronze phase. The microstructure of the composite ceramics were consisted of two kinds of grains. The smaller polygonal grains were belonged to the BST phase, and the larger ones to the SBN phase. The coexistence of the two phases inhibited the growth of the BST crystal. The density of microstructure of the composite ceramic was higher than that of both the pure BST and SBN calcined at the same temperature for the same time.展开更多
The structure and catalytic properties of SrTiO3 perovskite-type oxide catalysts for oxidative coupling of methane (OCM) have been studied by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and m...The structure and catalytic properties of SrTiO3 perovskite-type oxide catalysts for oxidative coupling of methane (OCM) have been studied by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and microreactor tests. It has been shown that OCM catalytic properties of SrTiO3 catalysts are correlated to the Sr/Ti atomic ratio. Increasing Sr/Ti ratio in the perovskite?-type SrTiO3 catalysts results in the surface enrichment of Sr element, leading to the the higher content of adsorbed oxygen species on the surface of catalysts and thus higher C2 selectivity for OCM reaction.展开更多
文摘Composite ceramics of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 (BSTN) with coexistence of barium strontium titanate, Ba1-xSrxTiO3 (BST), and strontium barium niobate, SrxBa1-xNb2O6 (SBN) phases were successfully prepared in situ by controlling excess components according to a specially designed formula of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 and by using a traditional ceramic process. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersion spectrometer (EDS) were used to characterize the phase composition, morphology and the micro-area chemical composition of the composite ceramics. The results showed that the SBN tungsten bronze phase appeared and coexisted stably with the BST perovskite phase when the excess content of Nb2O5 was >6mol%, whereas the BST perovskite phase formed and coexisted stably with the SBN tungsten bronze phase when the excess content of TiO2 was >5.3mol%. In the case of the two phases being equivalent to each other in BSTN composite ceramics, Nb2O5 was hard to be resolved into the perovskite phase, however, a few of TiO2 was easy to be resolved in the tungsten bronze phase. The microstructure of the composite ceramics were consisted of two kinds of grains. The smaller polygonal grains were belonged to the BST phase, and the larger ones to the SBN phase. The coexistence of the two phases inhibited the growth of the BST crystal. The density of microstructure of the composite ceramic was higher than that of both the pure BST and SBN calcined at the same temperature for the same time.
文摘The structure and catalytic properties of SrTiO3 perovskite-type oxide catalysts for oxidative coupling of methane (OCM) have been studied by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and microreactor tests. It has been shown that OCM catalytic properties of SrTiO3 catalysts are correlated to the Sr/Ti atomic ratio. Increasing Sr/Ti ratio in the perovskite?-type SrTiO3 catalysts results in the surface enrichment of Sr element, leading to the the higher content of adsorbed oxygen species on the surface of catalysts and thus higher C2 selectivity for OCM reaction.
