When particles are embedded in the ice near its bulk melting temperature,a premelted film forms between the particles and ice in a process known as"interfacial premelting".Under the influence of a temperatur...When particles are embedded in the ice near its bulk melting temperature,a premelted film forms between the particles and ice in a process known as"interfacial premelting".Under the influence of a temperature gradient,the premelted film varies in thickness,modulating the strength of ice-particle interactions and producing a net pressure that drives the particles to migrate towards higher temperatures in a phenomenon known as"thermal regelation".The phenomenon of thermal regelation is related to frost heave of soil,cryopreservation of organisms and methods of ice core paleoclimatology.In order to further investigate the principles of thermodynamics and dynamics in thermal regelation,we built a temperature gradient control platform and a single layer visual polydimethylsiloxane(PDMS)chip for thermal regelation experiments of individual silica particles.In the experiment,we measured the migration velocity of individual particles at different locations in the ice,and found that the thermal regelation of particles can be divided into high speed and low speed stages.As the particles approach the ice-water interface,the migration velocity increases dramatically.By combining the experimental data with the premelting theory,we found that the observed behavior is phenomenologically consistent with expectations for van der Waals force with radii of 12.5μm and 10μm.However,when the particle size was reduced to 7.5μm,the observed behavior was phenomenologically consistent with expectations for undelayed van der Waals force.In addition,under different temperature gradients and particle sizes,the thickness of the premelted film was maintained in the range of 20 nm-60 nm close to 273.15 K.However,under the same supercooling degree,the thickness of the premelted film increases with the increased of temperature gradient.Among the extracted parameters,the parameterλ,which was related to the van der Waals force,was linearly related to the temperature gradient.These experimental results not only provided important quantitative information for further understanding of thermal regelation but also provided a theoretical basis for optimizing related applications.展开更多
The fundamental equations of thermodynamics of a film have been used for describing a fundamental property of solid crystalline materials i.e. the first-order phase transition on the grain boundaries by the formation ...The fundamental equations of thermodynamics of a film have been used for describing a fundamental property of solid crystalline materials i.e. the first-order phase transition on the grain boundaries by the formation of two-dimensional liquid. The generalized equation that is obtained is used for calculating the premelting temperature of any metal, which has a value in the range of 0.55-0.86 of the melting point. The experimental diffusion coefficient of nitrogen in steel at premelting temperature is the same as in the liquid phase. The described phenomenon of phase transition on the grain boundaries decreases in case of radical modification of the existing process engineering of handling metals. It also provides a precise physical explanation to the super plasticity of fine-structure metal alloys.展开更多
The pick-up of hydrogen during electroslag remelting process for several slags consisting of CaF2-Al2O3-CaO-SiO2-MgO had been investigated.The laboratory-scale remelting experiments had been carried out in open air an...The pick-up of hydrogen during electroslag remelting process for several slags consisting of CaF2-Al2O3-CaO-SiO2-MgO had been investigated.The laboratory-scale remelting experiments had been carried out in open air and water-free argon atmosphere,and then the influencing factors were analyzed.It had been found that the hydrogen content in steel varied with different slag compositions.The compositions and state of slag had significant effect on the hydrogen level in steel.Partial return slag and premelted slag could avoid the hydrogen pick-up especially in the early stages of the process.However,premelted slag was the optimum state to control the hydrogen pick-up in steel.Experimental results indicated that water-free argon atmosphere was very favorable to the control of hydrogen in steel in the normal remelting period.展开更多
Ice premelting,the formation of a quasi-liquid layer on ice surfaces below the bulk melting point,plays a crucial role in various processes,ranging from glacier dynamics to ice friction and surface chemistry.Despite i...Ice premelting,the formation of a quasi-liquid layer on ice surfaces below the bulk melting point,plays a crucial role in various processes,ranging from glacier dynamics to ice friction and surface chemistry.Despite intensive research,the microscopic structure of the premelting layer and underlying molecular mechanisms remain poorly understood.In this work,we studied the temperature-and pressure-dependent structural disordering of crystalline Ih(0001)surface near the onset of premelting on the atomic scale by qPlus-based cryogenic atomic force microscopy.The linear correlation between the density of planar local structure(PLS)and the fraction of disordered surface region showed that the PLS mediated early-stage premelting by serving as a metastable seeding state.Notably,the associated surface disordering is cooperative,extending over an area of roughly~2 nm^(2) around a PLS.We further found a striking structural similarity between the kinetic-trapped regime below the surface crystallization temperature(T_(c))and the premelting-dominated regime above T_(c).As the deposition pressure increased,the characteristic temperature dependence was preserved,with only T_(c) shifting to higher values due to kinetic effects.Finally,we proposed a surface phase diagram for ice Ih(0001)based on our experimental observations.展开更多
We study the friction when a rectangular tire tread rubber block is sliding on an ice surface at different temperatures ranging from−38 to−2℃,and sliding speeds ranging from 3μm/s to 1 cm/s.At low temperatures and l...We study the friction when a rectangular tire tread rubber block is sliding on an ice surface at different temperatures ranging from−38 to−2℃,and sliding speeds ranging from 3μm/s to 1 cm/s.At low temperatures and low sliding speeds we propose that an important contribution to the friction force is due to slip between the ice surface and ice fragments attached to the rubber surface.At temperatures above−10℃ or for high enough sliding speeds,a thin premelted water film occurs on the ice surface and the contribution to the friction from shearing the area of real contact is small.In this case the dominant contribution to the friction force comes from viscoelastic deformations of the rubber by the ice asperities.We comment on the role of waxing on the friction between skis and snow(ice particles).展开更多
基金supported by The National Science Foundation for Distinguished Young Scholars of China(No.12102418)Zhejiang Provincial Natural Science Foundation of China(No.LQ21A020007)Youth Science and Technology Innovation Personnel Training Project(Category B)(No.2021YW48)。
文摘When particles are embedded in the ice near its bulk melting temperature,a premelted film forms between the particles and ice in a process known as"interfacial premelting".Under the influence of a temperature gradient,the premelted film varies in thickness,modulating the strength of ice-particle interactions and producing a net pressure that drives the particles to migrate towards higher temperatures in a phenomenon known as"thermal regelation".The phenomenon of thermal regelation is related to frost heave of soil,cryopreservation of organisms and methods of ice core paleoclimatology.In order to further investigate the principles of thermodynamics and dynamics in thermal regelation,we built a temperature gradient control platform and a single layer visual polydimethylsiloxane(PDMS)chip for thermal regelation experiments of individual silica particles.In the experiment,we measured the migration velocity of individual particles at different locations in the ice,and found that the thermal regelation of particles can be divided into high speed and low speed stages.As the particles approach the ice-water interface,the migration velocity increases dramatically.By combining the experimental data with the premelting theory,we found that the observed behavior is phenomenologically consistent with expectations for van der Waals force with radii of 12.5μm and 10μm.However,when the particle size was reduced to 7.5μm,the observed behavior was phenomenologically consistent with expectations for undelayed van der Waals force.In addition,under different temperature gradients and particle sizes,the thickness of the premelted film was maintained in the range of 20 nm-60 nm close to 273.15 K.However,under the same supercooling degree,the thickness of the premelted film increases with the increased of temperature gradient.Among the extracted parameters,the parameterλ,which was related to the van der Waals force,was linearly related to the temperature gradient.These experimental results not only provided important quantitative information for further understanding of thermal regelation but also provided a theoretical basis for optimizing related applications.
文摘The fundamental equations of thermodynamics of a film have been used for describing a fundamental property of solid crystalline materials i.e. the first-order phase transition on the grain boundaries by the formation of two-dimensional liquid. The generalized equation that is obtained is used for calculating the premelting temperature of any metal, which has a value in the range of 0.55-0.86 of the melting point. The experimental diffusion coefficient of nitrogen in steel at premelting temperature is the same as in the liquid phase. The described phenomenon of phase transition on the grain boundaries decreases in case of radical modification of the existing process engineering of handling metals. It also provides a precise physical explanation to the super plasticity of fine-structure metal alloys.
文摘The pick-up of hydrogen during electroslag remelting process for several slags consisting of CaF2-Al2O3-CaO-SiO2-MgO had been investigated.The laboratory-scale remelting experiments had been carried out in open air and water-free argon atmosphere,and then the influencing factors were analyzed.It had been found that the hydrogen content in steel varied with different slag compositions.The compositions and state of slag had significant effect on the hydrogen level in steel.Partial return slag and premelted slag could avoid the hydrogen pick-up especially in the early stages of the process.However,premelted slag was the optimum state to control the hydrogen pick-up in steel.Experimental results indicated that water-free argon atmosphere was very favorable to the control of hydrogen in steel in the normal remelting period.
基金Project supported by the National Key R&D Program of China(Grant Nos.2021YFA1400500 and 2025YFF1502400)the National Natural Science Foundation of China(Grant Nos.92361302,12250001,12535001,and U22A20260)+3 种基金the China Postdoctoral Science Foundation(Grant Nos.BX20230021,2023T160011,and 2024M760068)support from the National Program for Support of Top-notch Young professionalssupport from Beijing Outstanding Young Scientist Program(Grant No.JWZQ20240101002)the New Cornerstone Science Foundation through the New Cornerstone Investigator Program and the XPLORER PRIZE。
文摘Ice premelting,the formation of a quasi-liquid layer on ice surfaces below the bulk melting point,plays a crucial role in various processes,ranging from glacier dynamics to ice friction and surface chemistry.Despite intensive research,the microscopic structure of the premelting layer and underlying molecular mechanisms remain poorly understood.In this work,we studied the temperature-and pressure-dependent structural disordering of crystalline Ih(0001)surface near the onset of premelting on the atomic scale by qPlus-based cryogenic atomic force microscopy.The linear correlation between the density of planar local structure(PLS)and the fraction of disordered surface region showed that the PLS mediated early-stage premelting by serving as a metastable seeding state.Notably,the associated surface disordering is cooperative,extending over an area of roughly~2 nm^(2) around a PLS.We further found a striking structural similarity between the kinetic-trapped regime below the surface crystallization temperature(T_(c))and the premelting-dominated regime above T_(c).As the deposition pressure increased,the characteristic temperature dependence was preserved,with only T_(c) shifting to higher values due to kinetic effects.Finally,we proposed a surface phase diagram for ice Ih(0001)based on our experimental observations.
文摘We study the friction when a rectangular tire tread rubber block is sliding on an ice surface at different temperatures ranging from−38 to−2℃,and sliding speeds ranging from 3μm/s to 1 cm/s.At low temperatures and low sliding speeds we propose that an important contribution to the friction force is due to slip between the ice surface and ice fragments attached to the rubber surface.At temperatures above−10℃ or for high enough sliding speeds,a thin premelted water film occurs on the ice surface and the contribution to the friction from shearing the area of real contact is small.In this case the dominant contribution to the friction force comes from viscoelastic deformations of the rubber by the ice asperities.We comment on the role of waxing on the friction between skis and snow(ice particles).
