The lack of thermodynamic information,such as primary phase fields and liquidus temperatures,in the CaO-SiO2-Nb2O5-La2O3 quaternary system phase diagram has restricted the comprehensive utilization of the niobium(Nb) ...The lack of thermodynamic information,such as primary phase fields and liquidus temperatures,in the CaO-SiO2-Nb2O5-La2O3 quaternary system phase diagram has restricted the comprehensive utilization of the niobium(Nb) and rare earth(RE) resources.In this work,the phase equilibria in low basicity region(w(CaO)/w(SiO2)<1) of CaO-SiO2-Nb2O5-(0-15 wt%)La2O3 system at 1373-1873 K were experimentally studied by thermodynamic equilibrium experiment,and then,the results were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometry(EDS).Additionally,an optimized method was proposed to process the compositions of equilibrium liquid phases at different temperatures.According to the experimental results,the univariate line between CaNb2O6,SiO2 and LaNbO4 primary phase fields,interface between CaNb2O6 and SiO2 primary phase fields and isothermal liquidus surfaces in SiO2 primary phase field were determined.Finally,the spatial phase diagram of CaO-SiO2-Nb2O5-La2O3 within specific region was constructed,and furthermore,the phase diagram was also presented in CaO-SiO2-Nb2O5 pseudo-ternary system with w(La2O3)=5 wt%,10 wt% and 15 wt%.The research results have guiding significance for the improvement of related phase diagram and the comprehensive utilization of Nb and RE resources.展开更多
Various environmental factors affect net primary productivity （NPP） of grassland ecosystem. Extensive reports on the effects of environmental variables on NPP can be found in literature. However, the agreement on th...Various environmental factors affect net primary productivity （NPP） of grassland ecosystem. Extensive reports on the effects of environmental variables on NPP can be found in literature. However, the agreement on the relative importance of various factors in shaping the spatial pattern of grassland NPP has not yet been reached. Here a grassland in situ NPP database comprising 602 samples in northern China for 1980-1999 was developed based on a literature review of published biomass and forage yield field measurements. Correlation analyses and dominance analysis were used to quantify the separate and combined effects of environmental variables （climate topography and soil） on spatial variation in NPP separately. Grassland NPP ranged from 4.76 g C m-2a-1 to 975.94gCm-2a-1, showing significant variations in space. NPP increased with annual precipitation and declined with annual mean temperature significantly. Specifically, precipitation had the greatest impact on deserts, followed by steppes and meadows. Grassland NPP decreased with increasing altitude because of water limitation, and positively correlated with slope, but weakly correlated with aspect. Soil quality showed positive effects on NPP. Annual precipitation was the dominant factor affecting the spatial variability of net primary productivity, followed by elevation.展开更多
基金Project supported by the National Key R&D Program of China(2017YFC0805100)the National Natural Science Foundation of China(51774087)the Fundamental Research Funds for the Central Universities China(N162506002)
文摘The lack of thermodynamic information,such as primary phase fields and liquidus temperatures,in the CaO-SiO2-Nb2O5-La2O3 quaternary system phase diagram has restricted the comprehensive utilization of the niobium(Nb) and rare earth(RE) resources.In this work,the phase equilibria in low basicity region(w(CaO)/w(SiO2)<1) of CaO-SiO2-Nb2O5-(0-15 wt%)La2O3 system at 1373-1873 K were experimentally studied by thermodynamic equilibrium experiment,and then,the results were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometry(EDS).Additionally,an optimized method was proposed to process the compositions of equilibrium liquid phases at different temperatures.According to the experimental results,the univariate line between CaNb2O6,SiO2 and LaNbO4 primary phase fields,interface between CaNb2O6 and SiO2 primary phase fields and isothermal liquidus surfaces in SiO2 primary phase field were determined.Finally,the spatial phase diagram of CaO-SiO2-Nb2O5-La2O3 within specific region was constructed,and furthermore,the phase diagram was also presented in CaO-SiO2-Nb2O5 pseudo-ternary system with w(La2O3)=5 wt%,10 wt% and 15 wt%.The research results have guiding significance for the improvement of related phase diagram and the comprehensive utilization of Nb and RE resources.
基金"Strategic Priority Research Program-Climate Change:Carbon Budget and Relevant Issues" of the Chinese Academy of Sciences(Project Number XDA05090305)
文摘Various environmental factors affect net primary productivity （NPP） of grassland ecosystem. Extensive reports on the effects of environmental variables on NPP can be found in literature. However, the agreement on the relative importance of various factors in shaping the spatial pattern of grassland NPP has not yet been reached. Here a grassland in situ NPP database comprising 602 samples in northern China for 1980-1999 was developed based on a literature review of published biomass and forage yield field measurements. Correlation analyses and dominance analysis were used to quantify the separate and combined effects of environmental variables （climate topography and soil） on spatial variation in NPP separately. Grassland NPP ranged from 4.76 g C m-2a-1 to 975.94gCm-2a-1, showing significant variations in space. NPP increased with annual precipitation and declined with annual mean temperature significantly. Specifically, precipitation had the greatest impact on deserts, followed by steppes and meadows. Grassland NPP decreased with increasing altitude because of water limitation, and positively correlated with slope, but weakly correlated with aspect. Soil quality showed positive effects on NPP. Annual precipitation was the dominant factor affecting the spatial variability of net primary productivity, followed by elevation.
