Iron isotopes,represented byδ^(56)Fe,serve as valuable tools for constraining the surface iron processes and as potent tracers for studying the biogeochemical cycle of iron.Nevertheless,our comprehension of iron isot...Iron isotopes,represented byδ^(56)Fe,serve as valuable tools for constraining the surface iron processes and as potent tracers for studying the biogeochemical cycle of iron.Nevertheless,our comprehension of iron isotopes in the land surface processes of the Tibetan Plateau(TP)remains limited.In this study,we present the results of iron isotopic composition(δ^(56)Fe)in the surface soils of the TP,encompassing both glacial and non-glacial regions characterized by rugged and flat topographies.Our findings reveal that soilδ^(56)Fe values ranged from-0.01‰±0.05‰to 0.14‰±0.01‰,with the highest values observed in eastern locations(0.14‰)and the lowest appeared in the northeast(-0.1‰).On a global scale,theδ^(56)Fe values observed in Tibetan soils exhibited relatively small variability compared to reservoirs marked by significant iron isotope fractionation.By contrast,the range of TP soils measured here was slightly larger than that of the Chinese Loess.Furthermore,we discerned noticeable spatial variations inδ^(56)Fe across the large-scale region of TP,indicating a gradual increase trend from the northeast to the south and from the west to the east.These regional disparities inδ^(56)Fe likely arise from a combination of constraining factors,including differences in mineralogy,lithological variations,organic matter content,and variations in chemical weathering intensity.This study is pivotal in advancing our understanding of land surface iron isotope dynamics and its role in the biogeochemical cycle within the TP region.展开更多
Twenty kinds of adsorptions of HCN on the Fe（100）, Fe（111） and Fe（110） surfaces at the 1/4 monolayer coverage are found using the density functional theory. For Fe（100）, the adsorption energy of the most stabl...Twenty kinds of adsorptions of HCN on the Fe（100）, Fe（111） and Fe（110） surfaces at the 1/4 monolayer coverage are found using the density functional theory. For Fe（100）, the adsorption energy of the most stable configuration where the HCN locates at the fourfold site with the C-N bonded to four Fe atoms is 1.928 eV. The most favored adsorption structure for HCN on Fe（111） is f-η3（N）-h-η3（C）, in which the C-N bond is almost parallel to the surface, and the adsorption energy is 1.347 eV. On Fe（110）, the adsorption energy in the most stable configuration in which HCN locates at the two long-bridge sites is 1.777 eV. The adsorption energy of the parallel orientation for HCN is larger than that of the perpendicular configuration. The binding mechanism of HCN on the Fe（100）, Fe（111） and Fe（110） surfaces is also analyzed by Mulliken charge population and the density of states in HCN. The result indicates that the configurations in which the adsorbed HCN becomes the non-linear are beneficial to the formation of the addition reaction for hydrogen. The nature that the introduction of Fe into the catalyst could increase the catalytic activity of the bimetallic catalyst in the addition reaction of hydrogen for nitriles is revealed.展开更多
First-principles calculations based on density functional theory （DFT） and the generalized gradient approximation （GGA） have been used to study the adsorption of CO molecule on the perfect and defective FeS 2 （10...First-principles calculations based on density functional theory （DFT） and the generalized gradient approximation （GGA） have been used to study the adsorption of CO molecule on the perfect and defective FeS 2 （100） surfaces. The defective Fe 2 S（100） surfaces are caused by sulfur deficiencies. Slab geometry and periodic boundary conditions are employed with partial relaxations of atom positions in calculations. Two molecular orientations, Cand O-down, at various distinct sites have been considered. Total energy calculations indicated that no matter on perfect or deficient surfaces, the Fe position is relatively more favored than the S site with the predicted binding energies of 120.8 kJ/mol and 140.8 kJ/mol, respectively. Moreover, CO was found to be bound to Fe atom in vertical configuration. The analysis of density of states and vibrational frequencies before and after adsorption showed clear changes of the C–O bond.展开更多
Grinding operation is a finishing process often employed when high precision and narrow geometric tolerances are required.These requirements can be achieved only if cutting conditions are properly selected,especially ...Grinding operation is a finishing process often employed when high precision and narrow geometric tolerances are required.These requirements can be achieved only if cutting conditions are properly selected,especially the cooling-lubrication technique.In general,grinding is performed in presence of cutting fluid,however,due to the environmental impacts and costs of the conventional coolant delivery technique(flow rates from 4 L/min to 300 L/min),alternative cooling-lubrication techniques have been developed on restriction of the coolants use.Among the several techniques,MQL(minimum quantity of lubricant)technique has received special attention from machining users because of its advantages in terms of surface quality of workpiece and drastic reduction in use of coolant.In this context,this paper evaluated the performance of the MQL technique as compared to the flood coolant in peripheral surface grinding of AISI P100(VP100)steel with conventional aluminum oxide grinding wheel in relation to the surface roughness(Ra and Rz).Input parameters tested were equivalent chip thickness(0.09μm,0.18μm and 0.27μm)and flow rate of the cutting fluid(60 mL/h,150 mL/h and 240 mL/h)of the MQL system.Results showed that the grinding with MQL technique provided lower surface roughness values compared to conventional flood cooling,especially when machining under the intermediary cutting conditions.Also,with exception of heq of 0.09 m,the MQL technique resulted in lower values of Rz parameter as compared to the conventional coolant technique,regardless of the flow rate tested.展开更多
基金supported by the National Natural Science Foundation of China(Nos.42201152,42371139)the Gansu Province Natural Science Foundation Key Project(No.23JRRA858)+2 种基金the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(No.CUG240629)the“CUG Scholar”Scientific Research Funds at China University of Geosciences(Wuhan)(No.2023092)EJRP is supported by the German Research Foundation(DFG)through the Heisenberg Programme“Multiscale Simulation of Earth Surface Processes”。
文摘Iron isotopes,represented byδ^(56)Fe,serve as valuable tools for constraining the surface iron processes and as potent tracers for studying the biogeochemical cycle of iron.Nevertheless,our comprehension of iron isotopes in the land surface processes of the Tibetan Plateau(TP)remains limited.In this study,we present the results of iron isotopic composition(δ^(56)Fe)in the surface soils of the TP,encompassing both glacial and non-glacial regions characterized by rugged and flat topographies.Our findings reveal that soilδ^(56)Fe values ranged from-0.01‰±0.05‰to 0.14‰±0.01‰,with the highest values observed in eastern locations(0.14‰)and the lowest appeared in the northeast(-0.1‰).On a global scale,theδ^(56)Fe values observed in Tibetan soils exhibited relatively small variability compared to reservoirs marked by significant iron isotope fractionation.By contrast,the range of TP soils measured here was slightly larger than that of the Chinese Loess.Furthermore,we discerned noticeable spatial variations inδ^(56)Fe across the large-scale region of TP,indicating a gradual increase trend from the northeast to the south and from the west to the east.These regional disparities inδ^(56)Fe likely arise from a combination of constraining factors,including differences in mineralogy,lithological variations,organic matter content,and variations in chemical weathering intensity.This study is pivotal in advancing our understanding of land surface iron isotope dynamics and its role in the biogeochemical cycle within the TP region.
文摘Twenty kinds of adsorptions of HCN on the Fe（100）, Fe（111） and Fe（110） surfaces at the 1/4 monolayer coverage are found using the density functional theory. For Fe（100）, the adsorption energy of the most stable configuration where the HCN locates at the fourfold site with the C-N bonded to four Fe atoms is 1.928 eV. The most favored adsorption structure for HCN on Fe（111） is f-η3（N）-h-η3（C）, in which the C-N bond is almost parallel to the surface, and the adsorption energy is 1.347 eV. On Fe（110）, the adsorption energy in the most stable configuration in which HCN locates at the two long-bridge sites is 1.777 eV. The adsorption energy of the parallel orientation for HCN is larger than that of the perpendicular configuration. The binding mechanism of HCN on the Fe（100）, Fe（111） and Fe（110） surfaces is also analyzed by Mulliken charge population and the density of states in HCN. The result indicates that the configurations in which the adsorbed HCN becomes the non-linear are beneficial to the formation of the addition reaction for hydrogen. The nature that the introduction of Fe into the catalyst could increase the catalytic activity of the bimetallic catalyst in the addition reaction of hydrogen for nitriles is revealed.
基金supported by the National Natural Science Foundation of China (No 90922022)the NCETFJ Program (No. HX2006-103)+1 种基金the Science and Technology Foundation of Fujian Education Bureau (No. JA08019)the Foundation of State Key Laboratory of Coal Combustion (No. FSKLCC0814)
文摘First-principles calculations based on density functional theory （DFT） and the generalized gradient approximation （GGA） have been used to study the adsorption of CO molecule on the perfect and defective FeS 2 （100） surfaces. The defective Fe 2 S（100） surfaces are caused by sulfur deficiencies. Slab geometry and periodic boundary conditions are employed with partial relaxations of atom positions in calculations. Two molecular orientations, Cand O-down, at various distinct sites have been considered. Total energy calculations indicated that no matter on perfect or deficient surfaces, the Fe position is relatively more favored than the S site with the predicted binding energies of 120.8 kJ/mol and 140.8 kJ/mol, respectively. Moreover, CO was found to be bound to Fe atom in vertical configuration. The analysis of density of states and vibrational frequencies before and after adsorption showed clear changes of the C–O bond.
基金This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil(CAPES)—Finance Code 001The authors are grateful too to the FAPEMIG and the Post Graduate Program of Mechanical Engineering of UFU for financial support.Authors are also grateful to Villares Metals(Brazil)+1 种基金Saint Gobain Abrasives for supporting this work with workpiece material and wheel.One of authors thanks CNPq(PQ 2013 Project No.308067/2013)for the research scholarship and FAPEMIG project process No.PPM-00265-13 for financial supportThe authors are also thankful to ABCM for transferring the copyright of the article.
文摘Grinding operation is a finishing process often employed when high precision and narrow geometric tolerances are required.These requirements can be achieved only if cutting conditions are properly selected,especially the cooling-lubrication technique.In general,grinding is performed in presence of cutting fluid,however,due to the environmental impacts and costs of the conventional coolant delivery technique(flow rates from 4 L/min to 300 L/min),alternative cooling-lubrication techniques have been developed on restriction of the coolants use.Among the several techniques,MQL(minimum quantity of lubricant)technique has received special attention from machining users because of its advantages in terms of surface quality of workpiece and drastic reduction in use of coolant.In this context,this paper evaluated the performance of the MQL technique as compared to the flood coolant in peripheral surface grinding of AISI P100(VP100)steel with conventional aluminum oxide grinding wheel in relation to the surface roughness(Ra and Rz).Input parameters tested were equivalent chip thickness(0.09μm,0.18μm and 0.27μm)and flow rate of the cutting fluid(60 mL/h,150 mL/h and 240 mL/h)of the MQL system.Results showed that the grinding with MQL technique provided lower surface roughness values compared to conventional flood cooling,especially when machining under the intermediary cutting conditions.Also,with exception of heq of 0.09 m,the MQL technique resulted in lower values of Rz parameter as compared to the conventional coolant technique,regardless of the flow rate tested.
