The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the reme...The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting(TGZM)and Gibbs−Thomson(G−T)effects can take place on secondary dendrites.Besides,the intersection angle between the primary dendrite stem and secondary branch(θ)is found to increase fromπ/3 toπ/2 as the solidification proceeds.This is the morphological feature of the HO transformation,which can change the diffusion distance of the remelting/resolidification process.Thus,a diffusion-based analytical model is established to describe this process through the specific surface area(S_(V))of dendrites.The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification.In addition,the slope of the prediction curves is changed,indicating the variation of the local remelting/resolidification rates.展开更多
Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct...Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct clayey soil types, an Aridisol from Colorado （CO） in the U.S. Central Great Plains, and an Alfisol from Virginia （VA） in the southeastern USA following the application of switchgrass （Panicum virgatum） biochar. The switchgrass biochar was applied at four levels, 0%,0, 2.5%, 5%, and 10%, approximately equivalent to biochar additions of 0, 25, 50, and 100 t ha^-1, respectively, to the soils grown with wheat （Triticum aestivum） in an eight-week growth chamber experiment. We measured wheat shoot biomass and nitrogen （N） content and soil nutrient availability and N mineralization rates, and characterized the microbial fatty acid methyl ester （FAME） profiles of the soils. Net N mineralization rates decreased in both soils in proportion to an increase in biochar levels, but the effect was more marked in the VA soil, where net N mineralization decreased from -2.1 to -38.4 mg kg^-1. The 10% biochar addition increased soil pH, electrical conductivity, Mehlich- and bicarbonate-extractable phosphorus （P）, and extractable potassium （K） in both soil types. The wheat shoot biomass decreased from 17.7 to 9.1 g with incremental additions of biochar in the CO soil, but no difference was noted in plants grown in the VA soil. The FAME recovery assay indicated that the switchgrass biochar addition could introduce artifacts in analysis, so the results needed to be interpreted with caution. Non-corrected total FAME concentrations indicated a decline by 457o and 34% with 10% biochar addition in the CO and VA soils, respectively, though these differences became nonsignificant when the extraction efficiency correction factor was applied. A significant decline in the fungi：bacteria ratio was still evident upon correction in the CO soil with biochar. Switchgrass biochar had the potential to cause short-term negative impacts on plant biomass and alter soil microbial community structure unless measures were taken to add supplemental N and labile carbon （C）.展开更多
基金the support from the Natural Science Foundation of China(No.51871118)Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education,Lanzhou University,China(No.LZUMMM2021005)+1 种基金the Science and Technology Project of Lanzhou City,China(No.2019-1-30)State Key Laboratory of Special Rare Metal Materials,China(No.SKL2020K003)。
文摘The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting(TGZM)and Gibbs−Thomson(G−T)effects can take place on secondary dendrites.Besides,the intersection angle between the primary dendrite stem and secondary branch(θ)is found to increase fromπ/3 toπ/2 as the solidification proceeds.This is the morphological feature of the HO transformation,which can change the diffusion distance of the remelting/resolidification process.Thus,a diffusion-based analytical model is established to describe this process through the specific surface area(S_(V))of dendrites.The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification.In addition,the slope of the prediction curves is changed,indicating the variation of the local remelting/resolidification rates.
文摘Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct clayey soil types, an Aridisol from Colorado （CO） in the U.S. Central Great Plains, and an Alfisol from Virginia （VA） in the southeastern USA following the application of switchgrass （Panicum virgatum） biochar. The switchgrass biochar was applied at four levels, 0%,0, 2.5%, 5%, and 10%, approximately equivalent to biochar additions of 0, 25, 50, and 100 t ha^-1, respectively, to the soils grown with wheat （Triticum aestivum） in an eight-week growth chamber experiment. We measured wheat shoot biomass and nitrogen （N） content and soil nutrient availability and N mineralization rates, and characterized the microbial fatty acid methyl ester （FAME） profiles of the soils. Net N mineralization rates decreased in both soils in proportion to an increase in biochar levels, but the effect was more marked in the VA soil, where net N mineralization decreased from -2.1 to -38.4 mg kg^-1. The 10% biochar addition increased soil pH, electrical conductivity, Mehlich- and bicarbonate-extractable phosphorus （P）, and extractable potassium （K） in both soil types. The wheat shoot biomass decreased from 17.7 to 9.1 g with incremental additions of biochar in the CO soil, but no difference was noted in plants grown in the VA soil. The FAME recovery assay indicated that the switchgrass biochar addition could introduce artifacts in analysis, so the results needed to be interpreted with caution. Non-corrected total FAME concentrations indicated a decline by 457o and 34% with 10% biochar addition in the CO and VA soils, respectively, though these differences became nonsignificant when the extraction efficiency correction factor was applied. A significant decline in the fungi：bacteria ratio was still evident upon correction in the CO soil with biochar. Switchgrass biochar had the potential to cause short-term negative impacts on plant biomass and alter soil microbial community structure unless measures were taken to add supplemental N and labile carbon （C）.
