The paper reviews the development of prediction formulas for the fragmentation from bench blasting.Much attention has been paid to the Kuz-Ram model,its development and errors,and the mean vs.median misunderstanding.T...The paper reviews the development of prediction formulas for the fragmentation from bench blasting.Much attention has been paid to the Kuz-Ram model,its development and errors,and the mean vs.median misunderstanding.The work by the US Bureau of Mines(USBM)and Chung and Katsabanis are also reviewed,as well as the two Julius Kruttschnitt Mineral Research Centre(JKMRC)models,i.e.the crush zone model(CZM)and the two-component model(TCM),which were developed to cope with the underestimation of blasting fines.The change brought by the Swebrec distribution and the associated Kuznetsov-Cunningham-Ouchterlony(KCO)model is described.Studying distribution-free fragment sizes xP for an arbitrary mass passing P led to the discovery of the fragmentation-energy fan,and with the help of dimensional analysis,to the new fragmentation prediction model xP-frag,which has much lower errors than those of the Kuz-Ram and CZM models.展开更多
Fully-coupled thermo-mechanical simulations are implemented in COMSOL Multiphysics to investigate micro-scale stress-strain variability in pegmatite specimens subjected to thermal loading using microwaves. Thermally-i...Fully-coupled thermo-mechanical simulations are implemented in COMSOL Multiphysics to investigate micro-scale stress-strain variability in pegmatite specimens subjected to thermal loading using microwaves. Thermally-induced compressive and tensile stresses increase as the microwave irradiation duration increases. The dielectric constant, coefficient of expansion, and type and size of mineralogical boundary have significant impacts on the responses of the rock to microwave irradiation. The maximum principal stress of the chlorite is the smallest, indicating that the chlorite experiences the most damage under microwave irradiation, followed by the quartz. The maximum principal stress values of plagioclase and orthoclase are larger, indicating that they are likely to incur the least damage. Where quartz or chlorite is dominant, the resulting von Mises stresses are consistently higher after 120 s of microwave irradiation. The rate of generation of von Mises stresses increases most rapidly along the interface between quartz and plagioclase, and the interface between quartz and orthoclase, followed by the interface between quartz and chlorite, and finally the interface between plagioclase and orthoclase. The presented modeling approach provides a practical method to investigate stress-strain relationships within mineralogical boundaries inside a rock thin section.展开更多
Vacuum pressurizing casting technique, providing better mould filling and inter-dendritic feeding, can reduce the porosity greatly in cast aluminum alloys, and improve the fatigue properties. The rotary bending fatigu...Vacuum pressurizing casting technique, providing better mould filling and inter-dendritic feeding, can reduce the porosity greatly in cast aluminum alloys, and improve the fatigue properties. The rotary bending fatigue properties of A356-T6 alloys prepared by vacuum pressurizing casting were investigated. The S-N curve and limit strength 90 MPa under fatigue life of 107 cycles were obtained. The analyses on the fatigue fractography and microstructure of specimens showed that the fatigue fracture mainly occurs at the positions with casting defects in the subsurface, especially at porosities regions, which attributed to the crack propagation during the fatigue fracture process. Using the empirical crack propagation law of Pairs-Erdogon, the quantitative relationship among the initial crack size, fatigue life and applied stress was established. The fatigue life decreases with an increase in initial crack size. Two constants in the Pairs-Erdogon equation of aluminum alloy A356-T6 were calculated using the experimental data.展开更多
The influence of different pre-oxidation temperatures and pre-oxidation degrees on the reduction and fluidization behaviors of magnetite-based iron ore was investigated in a hydrogen-induced fluidized bed.The raw magn...The influence of different pre-oxidation temperatures and pre-oxidation degrees on the reduction and fluidization behaviors of magnetite-based iron ore was investigated in a hydrogen-induced fluidized bed.The raw magnetite-based iron ore was pre-oxidized at 800 and1000℃ for a certain time to reach a partly oxidation and deeply oxidation state.The structure and morphology of the reduced particles were analyzed via optical microscope and scanning electron microscopy(SEM).The reaction kinetic mechanism was determined based on the double-logarithm analysis.The results indicate that the materials with higher oxidation temperature and wider particle size range show better fluidization behaviors.The lower oxidation temperature is more beneficial for the reduction rate,especially in the later reduction stage.The pre-oxidation degree shows no obvious influence on the fluidization and reduction behaviors.Based on the kinetic analysis,the reduction progress can be divided into three stages.The reduction mechanism was discussed combing the surface morphology and phase structure.展开更多
Wear of a zirconia graphite slagband material by mold slag during casting of a TRIP steel grade was investigated on worn specimens with respect to corrosion and erosion. Corrosion dissolution of both the stabilizer ox...Wear of a zirconia graphite slagband material by mold slag during casting of a TRIP steel grade was investigated on worn specimens with respect to corrosion and erosion. Corrosion dissolution of both the stabilizer oxide and the zirconia is decisive. Oxidation is dominating graphite wear whereas a possible dissolution in the liquid steel was not observed to play an important role here. The ratio of oxide corrosion to graphite oxidation decreases with decreasing vertical distance of the hot face to the steel bath. Unfortunately and contrary to other applications of carbon bonded refractories in steel industry graphite exhibits to be wetted by mold slag in the special case investigated here: it still acts as a refractive component but only partly as an infiltration inhibitor. Infiltration is followed by zirconia corrosion thus reducing erosion resistance, but nevertheless also gas phase transport of slag components may cause exsolution of the stabilizer oxide in un-infiltrated regions.展开更多
The performance of CdZnTe X/γ-ray detectors is strongly affected by the electric field distribution in terms of charge transport and charge collection. Factors which determine the electric field distribution are not ...The performance of CdZnTe X/γ-ray detectors is strongly affected by the electric field distribution in terms of charge transport and charge collection. Factors which determine the electric field distribution are not only electric contact, but also intrinsic defects, especially grown-in twin boundaries. Here, the electric field distribution around twin boundaries is investigated in a CdZnTe bicrystal detector with a {111}–{111} twin plane using the Pockels electro-optic effect. The results of laser beam induced current pulses are also obtained by the transient current technique, and we discuss the influence of the twin boundary on the electric field evolution. These studies reveal a significant distortion of the electric field, which is attributed to the buildup of space charges at twin boundaries. Also, the position of these space charge regions depends on the polarity of the detector bias. An energy band model based on the formation of an n–n+–n junction across the twin boundary has been established to explain the observed results.展开更多
A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of f...A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of fragmentation in the formation of as-cast structure. Test simulations are made for the solidification of a model alloy(Sn-10wt.%Pb) with two different geometries. The first one is a 2D rectangular domain(50 × 60 mm^2) as cooled from the top boundary. Solidification starts unidirectionally as columnar structure from the top. The solute(Pb) enriched interdendritic melt is heavier than the bulk melt, and sinks downwards, hence leads to solutal convection. Fragmentation phenomenon occurs near the columnar tip front. The fragments are transported out of the columnar region, and they continue to grow and sink, and finally settle down and pile up at the bottom. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally lead to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition(CET). The second geometry is a 3D plate, 100 × 60 ×10 mm^3, as cooled laterally from one side. It was cast experimentally and analyzed for the as-cast structure. The equiaxed fragments are produced in the solidification front and transported into the bulk melt, leading to a special pattern of as-cast structure: columnar structure in the cool wall side and equiaxed structure in the upper left corner near the hot wall side, extending downwards to the middle bottom region. Numerically calculated as-cast structures agree with the experiment results.展开更多
Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test r...Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test results have been used for material characterization especially with respect to brittleness.Furthermore a microscopic fractographic test procedure was developed and applied on fractured test specimens.In order to explain brittleness dependence on structure properties correlation of fractographic and fracture mechanical results has been evaluated.Frequently brittleness reduction is achieved by a lower amount of transgranular crack propagation associated with a strength decrease while maintaining specific fracture energy unchanged.Deviations from pure linear fracture mechanics increase with decreasing brittleness and contribute to specific fracture energy.Shear specimens may show two generations of cracks,a first one initiated by tensile loads (stable propagation) and a second one by shear loads (unstable propagation).展开更多
This paper summarizes experimental approaches and simulation results in order to establish a general proposition regarding SEN wear mechanisms.Marangoni convection is considered to be a major contribution to continuou...This paper summarizes experimental approaches and simulation results in order to establish a general proposition regarding SEN wear mechanisms.Marangoni convection is considered to be a major contribution to continuous SEN wear,usually causing characteristic corrosion grooves.It is governed by the interface tension gradient in the vicinity of the three phase boundary slag/refractory/steel.This interface tension gradient is caused by a lower activity of the oxygen dissolved in the steel close to the refractory/steel interface.This is due to the reducing action of the solid carbon,which is a component of the refractory.By a simulation model using the Effective Equilibrium Reaction Zone technique a calculation of the interface tension differenceΔσwas performed.While for an LC steel and the related slag a valueΔσ=150mN/m was received,this quantity is negligible in the case of a TRIP steel.Accordingly,also the wear is much less for the TRIP steel.Marangoni convection is decisive for the mass transfer at the refractory/slag interface.Here dissolution of zirconia,but also oxidation of carbon takes place.For the latter one,the above mentioned simulation showed that reduction of silica in the mold slag takes place at the three phase boundary slag/refractory/steel by solid carbon,as the activity of silicon is reduced by dissolution in the liquid steel.This is the main source of oxygen for carbon oxidation at the three phase boundary.Therefore the three phase boundary is the focus of SEN wear:It unites intense bath movement due to Marangoni convection,oxidation of carbon by SiO_2reduction and zirconia erosion and dissolution into the melt.Within the refractory itself,a thin layer of several millimetres shows reactions with slag components.This causes especially destabilisation of stabilised zirconia and prepares later erosive wear.Steel does not penetrate into the SEN microstructure,carbon dissolution is only possible at the steel/refractory interface.The results quoted here enable justified expectations about the SEN wear in dependence on the steel/slag grade.Further simulation offers the possibility to quantify the effect of parameter variations on SEN wear.展开更多
Glass manufacturing is an energy-intensive process with high demands on product quality. The wide usage of glass products results in a high end-product diversity. In the past, many models have been developed...Glass manufacturing is an energy-intensive process with high demands on product quality. The wide usage of glass products results in a high end-product diversity. In the past, many models have been developed to optimize specific process steps, such as glass melting or glass forming. This approach presents a tool for the modeling of the entire glass manufacturing process for container glass, flat glass, and glass fibers. The tool considers detailed bottom-up energy and material balance in each step of the processing route with the corresponding costs and CO<sub>2</sub> emissions. Subsequently, it provides the possibility to quantify optimization scenarios in the entire glass manufacturing process in terms of energy, material and cost flow efficiency.展开更多
Methods for the characterization of mould slag crystallization with special emphasis on the single/double hot thermocouple technique(SHTT/DHTT)are reviewed.In the continuous casting process of steels,horizontal heat t...Methods for the characterization of mould slag crystallization with special emphasis on the single/double hot thermocouple technique(SHTT/DHTT)are reviewed.In the continuous casting process of steels,horizontal heat transfer is mainly influenced by the crystallization behaviour of the mould flux film.Here,both precipitation of crystals out of a liquid phase and devitrification of the glassy film in contact with the mould are of main interest.Therefore,various investigation methods are implemented to characterize different slag properties related to crystallization:a viscometer for determining the break temperature,differential thermal analysis(DTA),confocal scanning laser microscopy,and the water-cooled copper finger test.For near-service conditions,DHTT reveals the most detailed information,including not only the crystallization or devitrification temperature but also the morphology as well as the crystallization velocity.Due to improvements in the device and the representation of the results,a comparison of different samples is possible.Nevertheless,the application field of SHTT/DHTT is restricted to slag systems with low contents of evaporating components.Furthermore,the time required for data analysis is significantly longer than that required for other methods,e.g.DTA.Therefore,the application of DHTT is mainly advisable for mould slag research and development,whereas DTA can also be used for incoming inspections.展开更多
A laboratory fluidized bed reactor was used to investigate the fluidization behavior and reducibility of various iron ore fines.Hydrogen was chosen as a reducing agent across a temperature range of 873-1073 K.The magn...A laboratory fluidized bed reactor was used to investigate the fluidization behavior and reducibility of various iron ore fines.Hydrogen was chosen as a reducing agent across a temperature range of 873-1073 K.The magnetite ore used exhibited strong sticking behavior after the initiation of metallic iron formation.All other tested ores fluidized sufficiently well when subjected to the same high reduction temperatures.Parallel kinetic analysis was conducted using a previously developed model to include three rate-limiting step types.The trend of apparent activation energy was correlated with the degree of reduction.Additionally,the influence of varying the specific gas rate was investigated.The results show the variation in reducibility as a result of different interactions,which influence the rate-limiting mechanisms of nucleation and the undertaken chemical reactions,which vary as a function of temperature and degree of conversion.The apparent activation energies,determined from the reduction of wtistite to metallic iron,were in the range of 15-60 kJ/mol,depending on the iron ore used and the degree of conversion.The change in apparent activation energy deriving from the increased specific gas rate can be explained by an increasing nucleation effect,especially at lower reduction temperatures.展开更多
Transport phenomena including the electromagnetic,concentration of ions,flow,and thermal fields in the electroslag remelting(ESR)process made of slag,electrode,air,mold,and melt pool are computed considering tertiary ...Transport phenomena including the electromagnetic,concentration of ions,flow,and thermal fields in the electroslag remelting(ESR)process made of slag,electrode,air,mold,and melt pool are computed considering tertiary current distribution.Nernst-Planck equations are solved in the bulk of slag,and faradaic reactions are regarded at the metal-slag interface.Aiming at exploring electrochemical effects on the behavior of the ESR process,the calculated field structures are compared with those obtained using the classical ohmic approach,namely,primary current distribution whereby variations in concentrations of ions and faradaic reactions are ignored.Also,the influence of the earth magnetic field on magnetohydrodynamics in the melt pool and slag is considered.The impact of the polarity of electrode,whether positive,also known as direct current reverse polarity(DCRP),or negative,as known as direct current straight polarity(DCSP),on the transport of oxygen to the ingot of ESR is investigated.The obtained modeling results enabled us to explain the experimental observation of higher oxygen content in DCSP than that of DCRP operated ESR process.展开更多
In this work, a model based on the optical rectification effect and the photocurrent surge effect is proposed to describe the terahertz emission mechanism of the layered GaTe crystal. As a centrosymmetric crystal, the...In this work, a model based on the optical rectification effect and the photocurrent surge effect is proposed to describe the terahertz emission mechanism of the layered GaTe crystal. As a centrosymmetric crystal, the optical rectification effect arises from the breaking of the inversion symmetry due to lattice reorganization of the crystal’s surface layer. In addition, the photocurrent surge originating from the unidirectional charge carrier diffusion-due to the noncubic mobility anisotropy within the layers-produces terahertz radiation. This is confirmed by both terahertz emission spectroscopy and electric property characterization. The current surge perpendicular to the layers also makes an important contribution to the terahertz radiation, which is consistent with its incident angle dependence. Based on our results, we infer that the contribution of optical rectification changes from 90%under normal incidence to 23% under a 40° incidence angle. The results not only demonstrate the terahertz radiation properties of layered GaTe bulk crystals, but also promise the potential application of terahertz emission spectroscopy for characterizing the surface properties of layered materials.展开更多
The aging-hardening kinetics of powder metallurgy processed 2014Al alloy and its composite have been studied. The existence of n-SiC particulates leads to the increase of peak hardness. Interestingly, the aginghardeni...The aging-hardening kinetics of powder metallurgy processed 2014Al alloy and its composite have been studied. The existence of n-SiC particulates leads to the increase of peak hardness. Interestingly, the aginghardening peak of the composite takes place at earlier time than that of the unreinforced alloy. Transmission electron microscopy(TEM) studies indicated that the major precipitation phases are Al_5Cu_2Mn_3 and θ′(Al_2Cu). Besides, Ω phase appeared in both specimens at peak hardening condition, which has been rarely observed previously in aluminum metal matrix composites without Ag. Accelerated aging kinetics and increased peak hardness may be attributed to the higher dislocation density resulted from the mismatch of coefficients of thermal expansion between n-SiC and 2014Al matrix. The results are beneficial to fabricating high performance composites for the application in automobile field such as pistons, driveshaft tubes, brake rotors, bicycle frames, railroad brakes.展开更多
基金provided by MULUniversidad Politecnica de Madrid
文摘The paper reviews the development of prediction formulas for the fragmentation from bench blasting.Much attention has been paid to the Kuz-Ram model,its development and errors,and the mean vs.median misunderstanding.The work by the US Bureau of Mines(USBM)and Chung and Katsabanis are also reviewed,as well as the two Julius Kruttschnitt Mineral Research Centre(JKMRC)models,i.e.the crush zone model(CZM)and the two-component model(TCM),which were developed to cope with the underestimation of blasting fines.The change brought by the Swebrec distribution and the associated Kuznetsov-Cunningham-Ouchterlony(KCO)model is described.Studying distribution-free fragment sizes xP for an arbitrary mass passing P led to the discovery of the fragmentation-energy fan,and with the help of dimensional analysis,to the new fragmentation prediction model xP-frag,which has much lower errors than those of the Kuz-Ram and CZM models.
基金supported by the US National Science Foundation (CMMI award 1550307)the China Scholarship Council for financial support as a visiting scholar at the Colorado School of Mines (Grant No. 201706375077)
文摘Fully-coupled thermo-mechanical simulations are implemented in COMSOL Multiphysics to investigate micro-scale stress-strain variability in pegmatite specimens subjected to thermal loading using microwaves. Thermally-induced compressive and tensile stresses increase as the microwave irradiation duration increases. The dielectric constant, coefficient of expansion, and type and size of mineralogical boundary have significant impacts on the responses of the rock to microwave irradiation. The maximum principal stress of the chlorite is the smallest, indicating that the chlorite experiences the most damage under microwave irradiation, followed by the quartz. The maximum principal stress values of plagioclase and orthoclase are larger, indicating that they are likely to incur the least damage. Where quartz or chlorite is dominant, the resulting von Mises stresses are consistently higher after 120 s of microwave irradiation. The rate of generation of von Mises stresses increases most rapidly along the interface between quartz and plagioclase, and the interface between quartz and orthoclase, followed by the interface between quartz and chlorite, and finally the interface between plagioclase and orthoclase. The presented modeling approach provides a practical method to investigate stress-strain relationships within mineralogical boundaries inside a rock thin section.
基金financially supported by the National Basic Research"973"Program of China(2011CB610406)the National Natural Science Foundation for the Major International(Regional)Joint Research Project(51420105005)
文摘Vacuum pressurizing casting technique, providing better mould filling and inter-dendritic feeding, can reduce the porosity greatly in cast aluminum alloys, and improve the fatigue properties. The rotary bending fatigue properties of A356-T6 alloys prepared by vacuum pressurizing casting were investigated. The S-N curve and limit strength 90 MPa under fatigue life of 107 cycles were obtained. The analyses on the fatigue fractography and microstructure of specimens showed that the fatigue fracture mainly occurs at the positions with casting defects in the subsurface, especially at porosities regions, which attributed to the crack propagation during the fatigue fracture process. Using the empirical crack propagation law of Pairs-Erdogon, the quantitative relationship among the initial crack size, fatigue life and applied stress was established. The fatigue life decreases with an increase in initial crack size. Two constants in the Pairs-Erdogon equation of aluminum alloy A356-T6 were calculated using the experimental data.
基金the funding support of K1-MET GmbH,metallurgical competence centerthe financial support from the program of China Scholarship Council(No.201908420284)。
文摘The influence of different pre-oxidation temperatures and pre-oxidation degrees on the reduction and fluidization behaviors of magnetite-based iron ore was investigated in a hydrogen-induced fluidized bed.The raw magnetite-based iron ore was pre-oxidized at 800 and1000℃ for a certain time to reach a partly oxidation and deeply oxidation state.The structure and morphology of the reduced particles were analyzed via optical microscope and scanning electron microscopy(SEM).The reaction kinetic mechanism was determined based on the double-logarithm analysis.The results indicate that the materials with higher oxidation temperature and wider particle size range show better fluidization behaviors.The lower oxidation temperature is more beneficial for the reduction rate,especially in the later reduction stage.The pre-oxidation degree shows no obvious influence on the fluidization and reduction behaviors.Based on the kinetic analysis,the reduction progress can be divided into three stages.The reduction mechanism was discussed combing the surface morphology and phase structure.
基金The research program of the competence center Advanced Metallurgical and Environmental Process Development(KlMET) is supported within the Austrian program for competence centers COMET (Competence Center for Excellent Technologies) with funds of the Federal Ministry for TransportInnovation and Technology.the Federal Ministry of Economy,the province of Upper Austria and Styria,the Styrian Business Promotion Agency,of the Tyrol and the Tyrolian Future Foundation
文摘Wear of a zirconia graphite slagband material by mold slag during casting of a TRIP steel grade was investigated on worn specimens with respect to corrosion and erosion. Corrosion dissolution of both the stabilizer oxide and the zirconia is decisive. Oxidation is dominating graphite wear whereas a possible dissolution in the liquid steel was not observed to play an important role here. The ratio of oxide corrosion to graphite oxidation decreases with decreasing vertical distance of the hot face to the steel bath. Unfortunately and contrary to other applications of carbon bonded refractories in steel industry graphite exhibits to be wetted by mold slag in the special case investigated here: it still acts as a refractive component but only partly as an infiltration inhibitor. Infiltration is followed by zirconia corrosion thus reducing erosion resistance, but nevertheless also gas phase transport of slag components may cause exsolution of the stabilizer oxide in un-infiltrated regions.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1631116 and 51702271)the National Key Research and Development Program of China(Grant No.2016YFE0115200)+3 种基金the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2017KW-029)Austrian Academic Exchange Service(D-WTZ)through project CN 02/2016the Fundamental Research Funds for the Central Universities of China(Grant Nos.3102017zy057 and 3102018jcc036)the Young and Middle-aged Teachers Education and Scientific Research Foundation of Fujian Province,China(Grant No.JAT170407)
文摘The performance of CdZnTe X/γ-ray detectors is strongly affected by the electric field distribution in terms of charge transport and charge collection. Factors which determine the electric field distribution are not only electric contact, but also intrinsic defects, especially grown-in twin boundaries. Here, the electric field distribution around twin boundaries is investigated in a CdZnTe bicrystal detector with a {111}–{111} twin plane using the Pockels electro-optic effect. The results of laser beam induced current pulses are also obtained by the transient current technique, and we discuss the influence of the twin boundary on the electric field evolution. These studies reveal a significant distortion of the electric field, which is attributed to the buildup of space charges at twin boundaries. Also, the position of these space charge regions depends on the polarity of the detector bias. An energy band model based on the formation of an n–n+–n junction across the twin boundary has been established to explain the observed results.
基金supported by the Austrian Research Promotion Agency(FFG)through the project of Bridge Early Stage(No.842441)technically supported by the industrial partner Primetals(former Siemens VAI)
文摘A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of fragmentation in the formation of as-cast structure. Test simulations are made for the solidification of a model alloy(Sn-10wt.%Pb) with two different geometries. The first one is a 2D rectangular domain(50 × 60 mm^2) as cooled from the top boundary. Solidification starts unidirectionally as columnar structure from the top. The solute(Pb) enriched interdendritic melt is heavier than the bulk melt, and sinks downwards, hence leads to solutal convection. Fragmentation phenomenon occurs near the columnar tip front. The fragments are transported out of the columnar region, and they continue to grow and sink, and finally settle down and pile up at the bottom. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally lead to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition(CET). The second geometry is a 3D plate, 100 × 60 ×10 mm^3, as cooled laterally from one side. It was cast experimentally and analyzed for the as-cast structure. The equiaxed fragments are produced in the solidification front and transported into the bulk melt, leading to a special pattern of as-cast structure: columnar structure in the cool wall side and equiaxed structure in the upper left corner near the hot wall side, extending downwards to the middle bottom region. Numerically calculated as-cast structures agree with the experiment results.
文摘Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test results have been used for material characterization especially with respect to brittleness.Furthermore a microscopic fractographic test procedure was developed and applied on fractured test specimens.In order to explain brittleness dependence on structure properties correlation of fractographic and fracture mechanical results has been evaluated.Frequently brittleness reduction is achieved by a lower amount of transgranular crack propagation associated with a strength decrease while maintaining specific fracture energy unchanged.Deviations from pure linear fracture mechanics increase with decreasing brittleness and contribute to specific fracture energy.Shear specimens may show two generations of cracks,a first one initiated by tensile loads (stable propagation) and a second one by shear loads (unstable propagation).
基金the funding support of K1-MET GmbH,metallurgical competence centerthe competence center K1-MET is supported by COMET (Competence Center for Excellent Technologies) ,the Austrian program for competence centers
文摘This paper summarizes experimental approaches and simulation results in order to establish a general proposition regarding SEN wear mechanisms.Marangoni convection is considered to be a major contribution to continuous SEN wear,usually causing characteristic corrosion grooves.It is governed by the interface tension gradient in the vicinity of the three phase boundary slag/refractory/steel.This interface tension gradient is caused by a lower activity of the oxygen dissolved in the steel close to the refractory/steel interface.This is due to the reducing action of the solid carbon,which is a component of the refractory.By a simulation model using the Effective Equilibrium Reaction Zone technique a calculation of the interface tension differenceΔσwas performed.While for an LC steel and the related slag a valueΔσ=150mN/m was received,this quantity is negligible in the case of a TRIP steel.Accordingly,also the wear is much less for the TRIP steel.Marangoni convection is decisive for the mass transfer at the refractory/slag interface.Here dissolution of zirconia,but also oxidation of carbon takes place.For the latter one,the above mentioned simulation showed that reduction of silica in the mold slag takes place at the three phase boundary slag/refractory/steel by solid carbon,as the activity of silicon is reduced by dissolution in the liquid steel.This is the main source of oxygen for carbon oxidation at the three phase boundary.Therefore the three phase boundary is the focus of SEN wear:It unites intense bath movement due to Marangoni convection,oxidation of carbon by SiO_2reduction and zirconia erosion and dissolution into the melt.Within the refractory itself,a thin layer of several millimetres shows reactions with slag components.This causes especially destabilisation of stabilised zirconia and prepares later erosive wear.Steel does not penetrate into the SEN microstructure,carbon dissolution is only possible at the steel/refractory interface.The results quoted here enable justified expectations about the SEN wear in dependence on the steel/slag grade.Further simulation offers the possibility to quantify the effect of parameter variations on SEN wear.
文摘Glass manufacturing is an energy-intensive process with high demands on product quality. The wide usage of glass products results in a high end-product diversity. In the past, many models have been developed to optimize specific process steps, such as glass melting or glass forming. This approach presents a tool for the modeling of the entire glass manufacturing process for container glass, flat glass, and glass fibers. The tool considers detailed bottom-up energy and material balance in each step of the processing route with the corresponding costs and CO<sub>2</sub> emissions. Subsequently, it provides the possibility to quantify optimization scenarios in the entire glass manufacturing process in terms of energy, material and cost flow efficiency.
文摘Methods for the characterization of mould slag crystallization with special emphasis on the single/double hot thermocouple technique(SHTT/DHTT)are reviewed.In the continuous casting process of steels,horizontal heat transfer is mainly influenced by the crystallization behaviour of the mould flux film.Here,both precipitation of crystals out of a liquid phase and devitrification of the glassy film in contact with the mould are of main interest.Therefore,various investigation methods are implemented to characterize different slag properties related to crystallization:a viscometer for determining the break temperature,differential thermal analysis(DTA),confocal scanning laser microscopy,and the water-cooled copper finger test.For near-service conditions,DHTT reveals the most detailed information,including not only the crystallization or devitrification temperature but also the morphology as well as the crystallization velocity.Due to improvements in the device and the representation of the results,a comparison of different samples is possible.Nevertheless,the application field of SHTT/DHTT is restricted to slag systems with low contents of evaporating components.Furthermore,the time required for data analysis is significantly longer than that required for other methods,e.g.DTA.Therefore,the application of DHTT is mainly advisable for mould slag research and development,whereas DTA can also be used for incoming inspections.
基金the financial support from the project E3-SteP(Enhanced Energy Efficient Steel Production),which is funded by the Austrian Research Promotion Agency(FFG).
文摘A laboratory fluidized bed reactor was used to investigate the fluidization behavior and reducibility of various iron ore fines.Hydrogen was chosen as a reducing agent across a temperature range of 873-1073 K.The magnetite ore used exhibited strong sticking behavior after the initiation of metallic iron formation.All other tested ores fluidized sufficiently well when subjected to the same high reduction temperatures.Parallel kinetic analysis was conducted using a previously developed model to include three rate-limiting step types.The trend of apparent activation energy was correlated with the degree of reduction.Additionally,the influence of varying the specific gas rate was investigated.The results show the variation in reducibility as a result of different interactions,which influence the rate-limiting mechanisms of nucleation and the undertaken chemical reactions,which vary as a function of temperature and degree of conversion.The apparent activation energies,determined from the reduction of wtistite to metallic iron,were in the range of 15-60 kJ/mol,depending on the iron ore used and the degree of conversion.The change in apparent activation energy deriving from the increased specific gas rate can be explained by an increasing nucleation effect,especially at lower reduction temperatures.
文摘Transport phenomena including the electromagnetic,concentration of ions,flow,and thermal fields in the electroslag remelting(ESR)process made of slag,electrode,air,mold,and melt pool are computed considering tertiary current distribution.Nernst-Planck equations are solved in the bulk of slag,and faradaic reactions are regarded at the metal-slag interface.Aiming at exploring electrochemical effects on the behavior of the ESR process,the calculated field structures are compared with those obtained using the classical ohmic approach,namely,primary current distribution whereby variations in concentrations of ions and faradaic reactions are ignored.Also,the influence of the earth magnetic field on magnetohydrodynamics in the melt pool and slag is considered.The impact of the polarity of electrode,whether positive,also known as direct current reverse polarity(DCRP),or negative,as known as direct current straight polarity(DCSP),on the transport of oxygen to the ingot of ESR is investigated.The obtained modeling results enabled us to explain the experimental observation of higher oxygen content in DCSP than that of DCRP operated ESR process.
基金National Key Research and Development Program of China(2016YFE0115200)Ministry of Industry and Information Technology of the People’s Republic of China(MIIT)(MJ-2017-F-05)+2 种基金Fundamental Research Funds for the Central Universities(3102017zy057,3102018jcc036)Austrian Academic Exchange Service(OAD-WTZ)(CN 02/2016)National Natural Science Foundation of China(NSFC)(51872228)
文摘In this work, a model based on the optical rectification effect and the photocurrent surge effect is proposed to describe the terahertz emission mechanism of the layered GaTe crystal. As a centrosymmetric crystal, the optical rectification effect arises from the breaking of the inversion symmetry due to lattice reorganization of the crystal’s surface layer. In addition, the photocurrent surge originating from the unidirectional charge carrier diffusion-due to the noncubic mobility anisotropy within the layers-produces terahertz radiation. This is confirmed by both terahertz emission spectroscopy and electric property characterization. The current surge perpendicular to the layers also makes an important contribution to the terahertz radiation, which is consistent with its incident angle dependence. Based on our results, we infer that the contribution of optical rectification changes from 90%under normal incidence to 23% under a 40° incidence angle. The results not only demonstrate the terahertz radiation properties of layered GaTe bulk crystals, but also promise the potential application of terahertz emission spectroscopy for characterizing the surface properties of layered materials.
基金Financial support by the National Basic Research Program of China(“973”Program,No.2012CB619600)the National Natural Science Foundation of China(No.51474111)+2 种基金the Science and Technology Development Project of Jilin Province(No.20160519002JH)support came from the Fundamental Research Funds for the Central Universities(JCKY-QKJC02)the Chang Bai Mountain Scholars Program(2013014)
文摘The aging-hardening kinetics of powder metallurgy processed 2014Al alloy and its composite have been studied. The existence of n-SiC particulates leads to the increase of peak hardness. Interestingly, the aginghardening peak of the composite takes place at earlier time than that of the unreinforced alloy. Transmission electron microscopy(TEM) studies indicated that the major precipitation phases are Al_5Cu_2Mn_3 and θ′(Al_2Cu). Besides, Ω phase appeared in both specimens at peak hardening condition, which has been rarely observed previously in aluminum metal matrix composites without Ag. Accelerated aging kinetics and increased peak hardness may be attributed to the higher dislocation density resulted from the mismatch of coefficients of thermal expansion between n-SiC and 2014Al matrix. The results are beneficial to fabricating high performance composites for the application in automobile field such as pistons, driveshaft tubes, brake rotors, bicycle frames, railroad brakes.