Haze (known as “Mai” 霾 in Chinese) threatens the health of billions of people across the globe. To begin solving this problem without severely slowing down the economy, one has to mechanistically and geographically...Haze (known as “Mai” 霾 in Chinese) threatens the health of billions of people across the globe. To begin solving this problem without severely slowing down the economy, one has to mechanistically and geographically pinpoint the sources of these pollutants, the key of which is to thoroughly characterize and fingerprint the particulates. Here we present a broad survey and classification of thousands of individual airborne particu-lates by using the Scanning Electron Microscope (SEM) to measure their diverse mor-phologies and chemistries, which could eventually be organized into a “haze finger-print database”. For instance, one collection in Xi’an City, China during March-April 2014 yielded 494 airborne particulates that settled on silicon wafers placed outside the window of a 3<sup>rd</sup> floor office. These 494 particulates were manually imaged with high resolution (down to 2 nm), elementally mapped using Energy-dispersive X-ray Spec-troscopy (EDS), and were identified and categorized into presumed source classes such as construction activities (Ca, Al, Si-O), coal burning (sulfates), biologic (pollen, bac-teria), automotive, mining, steel making, and etc. About 20% of the particulates have mysterious origins, as it is still unclear how they were formed, and a fraction of them contained clearly hazardous elements such as lead and chromium. For future work, we propose using unmanned aerial vehicles with a special “rolling film” substrate that can autonomously collect airborne particulates, a customized SEM auto-imaging system, and machine learning software to establish an online open-access database. The end goal would be to monitor and analyze the particulate pollutants that are pumped into our atmosphere every day, and precisely track down their sources so we can better model and police the quality of the air around us.展开更多
Here,a systematic investigation was made on the interphase strengthening effects induced superior me-chanical performances of multiphase high-entropy alloys(HEAs)at micro/nano-scale,compared with sin-gle phase HEAs.A ...Here,a systematic investigation was made on the interphase strengthening effects induced superior me-chanical performances of multiphase high-entropy alloys(HEAs)at micro/nano-scale,compared with sin-gle phase HEAs.A pillar compression test under a scanning electron microscope(SEM)was performed on the individual face centered cubic(FCC),body centered cubic(BCC),and mixed-phases with different di-ameters in a Fe_(24)Co_(25)Ni_(24)Cr_(23)Al_(4)HEA using focused ion beam(FIB)milling and a nanoindenter equipped with a flat punch.The stress-strain response of pillar underneath the indenter was selected to explore the diameter/phase-dependent size effect,the periodically fluctuation of local stress,and strain hardening.It was revealed that the pillars at the interphase exhibited significantly higher strength,compared with the FCC and BCC pillars.An experiment also verified the coincident mechanical size effects independent with the type of phases.The stress responses in the mixed-phase pillars manifested as a distinct transition from the dramatic drop to the minor fluctuation during the post-yield stages with the increasing strain,indicating the propagation of Al-Ni enriched solid solution phase(BCC1)under compression.Except the BCC1 phase,numerous dislocations were observed in the post-deformed pillars,particularly serving as the major source to enhance the strain hardening of BCC pillars.展开更多
To solve the existing problems of imperfect sealing and the inaccurate measurement of gas pressure in traditional sealing,the present study builds a new model of capsule-slime sealing device based on wireless pressure...To solve the existing problems of imperfect sealing and the inaccurate measurement of gas pressure in traditional sealing,the present study builds a new model of capsule-slime sealing device based on wireless pressure gauge.The new sealing device is mainly composed of two sets of capsules,a capsule connecting piece and a slime part,measures the pressure through the wireless communication technology,and seals through chemical reaction in the capsule,which generates gas to expand the capsule and extrude the pre-stored slime.Two methods of extruding pre-stored slime are proposed:in the first method,transverse force is generated by the expansion of the capsules at both ends,pushing the capsules toward the middle through the chute and squeezing the pre-stored slime out;in the second,high-pressure gas generated in the capsules is led into the expansion tube,which is inserted into the storage tube,squeezing it and letting the slime out to complete the sealing process.Then the research studies the effect of sealing under the condition of drilling with the structure of slime storage tube.The results indicate that the maximum standing time of slime wrapped in metal net is 2 h,instead of the expected 10 d,failing to meet the sealing requirements.When the slime viscosity is 1200–3000 m Paás in the structure of slime storage tube,the best viscosity of slime is achieved and can simulate sealing the drilling hole(5–4,4–2.36,2.36–1.18,1.18–0.15 mm in diameter),as well as the gap caused by mixed sand accumulation.展开更多
Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time...Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time, which lead to the high cost and limit the wide application of the products. Herein, nearly spherical AlN particles with the average size of 2.5 μm were successfully synthesized via an in-situ combustion synthesis method. The effect of N_(2) pressure, NH_(4)Cl content, and Al particle size on the combustion reaction procedure, phase composition, and microstructure of the products was systematically investigated. The results showed that the decreased N_(2) pressure, increased NH_(4)Cl content, and Al particle size led to the decreasing of combustion temperature and speed, which further affected the morphology of the products. As a result, low N_(2) pressure(0.2 MPa), a small amount of NH4Cl(0.5 wt%), and fine Al particles(~2.5 μm) contributed to a moderate combustion temperature and facilitated the formation of nearly spherical AlN particles. In addition, based on the gas-releasing assisted quenching experiments and thermo-kinetic analysis, a two-step growth mechanism for the nearly spherical AlN particles was rationally proposed. The present method shows the advantages of low cost and high efficiency for preparing nearly spherical AlN particles, which can be used as raw materials for electronic substrates and fillers for packaging materials.展开更多
文摘Haze (known as “Mai” 霾 in Chinese) threatens the health of billions of people across the globe. To begin solving this problem without severely slowing down the economy, one has to mechanistically and geographically pinpoint the sources of these pollutants, the key of which is to thoroughly characterize and fingerprint the particulates. Here we present a broad survey and classification of thousands of individual airborne particu-lates by using the Scanning Electron Microscope (SEM) to measure their diverse mor-phologies and chemistries, which could eventually be organized into a “haze finger-print database”. For instance, one collection in Xi’an City, China during March-April 2014 yielded 494 airborne particulates that settled on silicon wafers placed outside the window of a 3<sup>rd</sup> floor office. These 494 particulates were manually imaged with high resolution (down to 2 nm), elementally mapped using Energy-dispersive X-ray Spec-troscopy (EDS), and were identified and categorized into presumed source classes such as construction activities (Ca, Al, Si-O), coal burning (sulfates), biologic (pollen, bac-teria), automotive, mining, steel making, and etc. About 20% of the particulates have mysterious origins, as it is still unclear how they were formed, and a fraction of them contained clearly hazardous elements such as lead and chromium. For future work, we propose using unmanned aerial vehicles with a special “rolling film” substrate that can autonomously collect airborne particulates, a customized SEM auto-imaging system, and machine learning software to establish an online open-access database. The end goal would be to monitor and analyze the particulate pollutants that are pumped into our atmosphere every day, and precisely track down their sources so we can better model and police the quality of the air around us.
基金supported by the National Natu-ral Science Foundation of China(51875241)National Key R&D Program of China(2018YFF010124)+1 种基金Jilin Province Key R&D Plan Project(20190302078GX,YDZJ202101ZYTS129)Graduate In-novation Fund of Jilin University(101832020CX098).
文摘Here,a systematic investigation was made on the interphase strengthening effects induced superior me-chanical performances of multiphase high-entropy alloys(HEAs)at micro/nano-scale,compared with sin-gle phase HEAs.A pillar compression test under a scanning electron microscope(SEM)was performed on the individual face centered cubic(FCC),body centered cubic(BCC),and mixed-phases with different di-ameters in a Fe_(24)Co_(25)Ni_(24)Cr_(23)Al_(4)HEA using focused ion beam(FIB)milling and a nanoindenter equipped with a flat punch.The stress-strain response of pillar underneath the indenter was selected to explore the diameter/phase-dependent size effect,the periodically fluctuation of local stress,and strain hardening.It was revealed that the pillars at the interphase exhibited significantly higher strength,compared with the FCC and BCC pillars.An experiment also verified the coincident mechanical size effects independent with the type of phases.The stress responses in the mixed-phase pillars manifested as a distinct transition from the dramatic drop to the minor fluctuation during the post-yield stages with the increasing strain,indicating the propagation of Al-Ni enriched solid solution phase(BCC1)under compression.Except the BCC1 phase,numerous dislocations were observed in the post-deformed pillars,particularly serving as the major source to enhance the strain hardening of BCC pillars.
基金the support from the National Key Research and Development Program of China (No. 2017YFC0805201)the Fundamental Research Funds for the Central Universities of China (No. 2017CXNL02)+1 种基金the program for Innovative Research Team in University of Ministry of Education of China (No. IRT13098)the Priority Academic Program Development of Jiangsu Higher Education Institutions of China (PAPD)
文摘To solve the existing problems of imperfect sealing and the inaccurate measurement of gas pressure in traditional sealing,the present study builds a new model of capsule-slime sealing device based on wireless pressure gauge.The new sealing device is mainly composed of two sets of capsules,a capsule connecting piece and a slime part,measures the pressure through the wireless communication technology,and seals through chemical reaction in the capsule,which generates gas to expand the capsule and extrude the pre-stored slime.Two methods of extruding pre-stored slime are proposed:in the first method,transverse force is generated by the expansion of the capsules at both ends,pushing the capsules toward the middle through the chute and squeezing the pre-stored slime out;in the second,high-pressure gas generated in the capsules is led into the expansion tube,which is inserted into the storage tube,squeezing it and letting the slime out to complete the sealing process.Then the research studies the effect of sealing under the condition of drilling with the structure of slime storage tube.The results indicate that the maximum standing time of slime wrapped in metal net is 2 h,instead of the expected 10 d,failing to meet the sealing requirements.When the slime viscosity is 1200–3000 m Paás in the structure of slime storage tube,the best viscosity of slime is achieved and can simulate sealing the drilling hole(5–4,4–2.36,2.36–1.18,1.18–0.15 mm in diameter),as well as the gap caused by mixed sand accumulation.
基金supported by the National Natural Science Foundation of China (Nos. 51872222 and 51002115)the Shaanxi Innovation Capacity Support Program (2018TD-031)the State Key Laboratory for Mechanical Behavior of Materials (20202208)。
文摘Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time, which lead to the high cost and limit the wide application of the products. Herein, nearly spherical AlN particles with the average size of 2.5 μm were successfully synthesized via an in-situ combustion synthesis method. The effect of N_(2) pressure, NH_(4)Cl content, and Al particle size on the combustion reaction procedure, phase composition, and microstructure of the products was systematically investigated. The results showed that the decreased N_(2) pressure, increased NH_(4)Cl content, and Al particle size led to the decreasing of combustion temperature and speed, which further affected the morphology of the products. As a result, low N_(2) pressure(0.2 MPa), a small amount of NH4Cl(0.5 wt%), and fine Al particles(~2.5 μm) contributed to a moderate combustion temperature and facilitated the formation of nearly spherical AlN particles. In addition, based on the gas-releasing assisted quenching experiments and thermo-kinetic analysis, a two-step growth mechanism for the nearly spherical AlN particles was rationally proposed. The present method shows the advantages of low cost and high efficiency for preparing nearly spherical AlN particles, which can be used as raw materials for electronic substrates and fillers for packaging materials.
