Three types of Al/Al−27%Si laminated composites,each containing 22%Si,were fabricated via hot pressing and hot rolling.The microstructures,mechanical properties and thermo-physical properties of these composites were ...Three types of Al/Al−27%Si laminated composites,each containing 22%Si,were fabricated via hot pressing and hot rolling.The microstructures,mechanical properties and thermo-physical properties of these composites were investigated.The results demonstrated that the three laminated composites exhibited similar microstructural features,characterized by well-bonded interfaces between the Al layer and the Al−27%Si alloy layer.The tensile and flexural strengths of the composites were significantly higher than those of both Al−22%Si and Al−27%Si alloys.These strengths increased gradually with decreasing the layer thickness,reaching peak values of 222.5 and 407.4 MPa,respectively.Crack deflection was observed in the cross-sections of the bending fracture surfaces,which contributed to the enhanced strength and toughness.In terms of thermo-physical properties,the thermal conductivity of the composites was lower than that of Al−22%Si and Al−27%Si alloys.The minimum reductions in thermal conductivity were 6.8%and 0.9%for the T3 laminated composite,respectively.Additionally,the coefficient of thermal expansion of the composites was improved,exhibiting varying temperature-dependent behaviors.展开更多
The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temper...The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temperature dilatometer, DSC, and laser thermal diffusivity methods were used to analyze thermal expansion coefficient （TEC）, specific heat, and thermal diffusivity. The results showed that CeO2 doped pyrochlores La2（Zr1.8Ce0.2）2O7 and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had higher TEC than La2Zr2O7 and La1.7Dy0.3Zr2O7. La2（Zr1.8Ce0.2）2O7, La1.7Dy0.3Zr2O7, and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had lower thermal conductivity than undoped La2Zr2O7. The Dy2O3, Nd2O3, and CeO2 codoped composition showed the lowest thermal conductivity and the highest TEC. Thermo-physical results also indicated that TEC of rare earth oxide doped La2Zr2O7 ceramic was slightly higher than that of conventional ZrO2-8Wt.% Y2O3 （8YSZ）, and its thermal conductivity was lower than that of 8YSZ.展开更多
(AlTa(0.76))xCoCrFeNi(2.1)(x values in molar ratio,x=0.1,0.3,0.5,0.7,1.0,and 1.5) alloys were designed to investigate the microstructure and mechanical properties of the eutectic high entropy alloys(EHEAs)consisting o...(AlTa(0.76))xCoCrFeNi(2.1)(x values in molar ratio,x=0.1,0.3,0.5,0.7,1.0,and 1.5) alloys were designed to investigate the microstructure and mechanical properties of the eutectic high entropy alloys(EHEAs)consisting of FCC,B2,and Laves phases.Depending on the compositional variatio,clear microstructural variation was observed,as follows:(1) Group 1:FCC dendrite+Laves interdendrite(x=0.1),(2) Group 2:FCC dendrite+fine-eutectic structure consisting of FCC and Laves phases(x=0.3,0.5 and 0.7),(3) Group 3:B2 dendrite+bimodal eutectic structure [FCC/B2+Laves](x=1.0),(4) Group 4:Laves dendrite+eutectic structure consisting of B2 and Laves phases(x=1.5).As the fraction of Laves or B2 phases increases,yield stress increases from 293 to 2336 MPa,while the plastic strain decreases from 50 % to 2%.Thermo-physical parameters,such as mixing entropy(△S(mix)),mixing enthalpy(△H(mix)),valence electron concentration(VEC),and atomic size difference(δr),were calculated to understand the microstructural variation.Two criteria(δr-VEC and δr-△H(mix)) were utilized to elucidate the formation of the eutectic structures in the present EHEAs,revealing the usefulness of the thermo-physical parameters in the development of EHEAs.展开更多
Rare earth oxides doped hafnia ceramics,with a formula of Hf0.76LnxY0.24-xO1.88(Ln=Gd,Yb,Gd+Yb or La+Yb),were prepared by solid state sintering at 1500℃.The effects of the rare earth oxides on the microstructures,sin...Rare earth oxides doped hafnia ceramics,with a formula of Hf0.76LnxY0.24-xO1.88(Ln=Gd,Yb,Gd+Yb or La+Yb),were prepared by solid state sintering at 1500℃.The effects of the rare earth oxides on the microstructures,sintering resistance,and thermo-physical properties of the doped hafnia ceramics were investigated.Results show that the Gd-Y,Yb-Y or Gd-Yb-Y co-doped hafnia ceramics remain the same defect fluorite(F)structure,while the La-Yb-Y co-doped hafnia revealing coexistence of pyrochlore(P)and fluorite structures.Yb-Y co-doped samples exhibited much better sintering resistance compared with Gd-Y and Gd-Yb-Y co-doped samples.The coexistence of P and F phases is beneficial to improved sintering capability.The thermal conductivities of the Gd-Y,Yb-Y and Gd-Yb-Y doped samples are relatively lower(1.4-1.7 W m^(-1)K^(-1)at 1200℃),but for the La-Yb-Y co-doped samples,the thermal conductivity increases dramatically with temperature due to increased thermal radiation at high-temperature.The average thermal expansion coefficients(TECs)of the Gd-Y,Yb-Y and Gd-Yb-Y co-doped samples are as high as10.3×10^(-6)K^(-1) in temperature range between 200-1200℃.展开更多
Al-high Si alloys were designed by the addition of Cu or Mg alloying elements to improve the mechanical properties. It is found that the addition of 1 wt.% Cu or 1 wt.% Mg as strengthening elements significantly impro...Al-high Si alloys were designed by the addition of Cu or Mg alloying elements to improve the mechanical properties. It is found that the addition of 1 wt.% Cu or 1 wt.% Mg as strengthening elements significantly improves the tensile strength by 27.2% and 24.5%, respectively. This phenomenon is attributed to the formation of uniformly dispersed fine particles(Al2Cu and Mg2Si secondary phases) in the Al matrix during hot press sintering of the rapidly solidified(gas atomization) powder. The thermal conductivity of the Al-50 Si alloys is reduced with the addition of Cu or Mg, by only 7.3% and 6.8%, respectively. Therefore, the strength of the Al-50 Si alloys is enhanced while maintaining their excellent thermo-physical properties by adding 1% Cu(Mg).展开更多
Phase stability,elastic properties,thermo-physical properties,as well as electronic properties of hexa-（Mo,Cr,W）2C carbides were investigated by first-principles calculations.The results indicated that the Mo8C4,Mo7...Phase stability,elastic properties,thermo-physical properties,as well as electronic properties of hexa-（Mo,Cr,W）2C carbides were investigated by first-principles calculations.The results indicated that the Mo8C4,Mo7Cr1C4,Mo7W1C4,Mo6W2C4,and Mo6W1Cr1C4 are stable and the stability follows the sequence：Mo6W1Cr1C4〉Mo7W1C4〉Mo7Cr1C4〉 Mo6W2C4〉 Mo8C4.Mo6W1Cr1C4 shows the highest stability,deformation resistance and hardness.G/B（shear modulus/bulk modulus）and Poisson′s ratio of the stable hexa-（Mo,Cr,W）2C are all larger than 1.75 and 0.26,respectively,which indicates that they are all brittle.The anisotropies are mainly due to the different Vogit shear modulus/Reuss shear modulus;the mechanical anisotropy of Mo7Cr1C4 is the largest,and that of Mo8C4 is the smallest.Moreover,the obtained Debye temperatureΘDand heat capacity Cpindicate that Mo6W2C4 possesses the best thermal conductivity（ΘD=497.72K）,while Mo7Cr1C4 and Mo6W2C4possess the largest heat capacity when the temperature is in the range of 0-10 Kand larger than 10 K,respectively.From the electronic property analysis,the doped Cr and W atoms can not only participate in orbitals hybridization themselves but also enhance the orbitals hybridization between Mo and C atoms,which can reinforce the interatomic interactions.展开更多
It is well known that the use of woods as construction materials can embody carbon content of structural members,which can enhance the urban sustainability.However,due to the combustibility of wood,its current applica...It is well known that the use of woods as construction materials can embody carbon content of structural members,which can enhance the urban sustainability.However,due to the combustibility of wood,its current application is restricted.To broaden the application of wood,its thermal responses exposed to fire(high temperature)is investigated in this study.Firstly,the wood kinetic parameters are determined by coats-redfern method using thermal gravimetric(TGA)data.Secondly,the density and thermal conductivity are obtained from parallel and series models.Thirdly,the specific heat capacity formula is presented considering latent and decomposition heat,which can be directly determined by differential scanning calorimetry(DSC).Finally,the one-dimensional nonlinear heat transfer model with apparent thermo-physical properties is proposed.The four-sided heating experiment of Laminated Veneer Lumber(LVL)is carried out to investigate the temperature filed.The results show that the proposed model can predict the thermal responses of timber structures subjected to fire and high temperatures precisely.展开更多
The asymmetric thermo-physical mechanism of the resistance spot welding technique with intermediate frequency(2 kHz)and direct current(RSWIFDC)on the high strength aluminum(Al)alloy TL091 was studied here in view of t...The asymmetric thermo-physical mechanism of the resistance spot welding technique with intermediate frequency(2 kHz)and direct current(RSWIFDC)on the high strength aluminum(Al)alloy TL091 was studied here in view of the Peltier effect.On the basis of the analysis of the electrode cap surface erosion state and the shape-position of the nugget,it was concluded that asymmetric thermo-physical phenomenon occurred on both ends of the nugget,and even had an influence upon the shape-forming coefficient and the vertical position deviation of the nugget,and the erosion degree of the electrode caps.In this work,the relative thermo-physical model of the welding was established combined with the Peltier effect and the spot welding characteristics.Accordingly the relative welding phenomena,such as nugget center deviation and different erosion degree of the electrode cap surface,was explained clearly using the model related with the Peltier effect for the first time.This model provides important theoretical basis for future study and application of Al alloy spot welding,based on which,effective works may be done to promote the quality of the Al alloy welded joints and to obtain favorable control upon parameters of Al alloy welding for electrode caps.展开更多
Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) with optimum band gaps about 1.5 eV are important absorbers for solar cells. The elastic constants and the thermo-physical properties of the stannite-type CZTS and CZTSe are cal...Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) with optimum band gaps about 1.5 eV are important absorbers for solar cells. The elastic constants and the thermo-physical properties of the stannite-type CZTS and CZTSe are calculated by using density-functional theory (DFT) and the quasi-harmonic Debye model. The bonding strength along the [100] and [010] directions is the same to that along the [001] direction and the shear elastic properties of the {001} plane are anisotropic for CZTS and CZTSe. Both compounds exhibit ductile behavior due to their high ratio of bulk modulus to shear modulus (K/G). The values of thermal capacity are close to 200 J/(mol·K) at above 300 K, and the thermal expansion coefficients decrease with increasing pressure at same temperature. The entropy is variable by power-exponent, and the internal energy is almost linear with increasing temperature for CZTS and CZTSe. The Gibbs energy of CZTS is lower than that of CZTSe under same temperature and pressure. The Debye temperatures are 297 and 232 K, and Grneisen parameters are 2.36 and 2.37 for CZTS and CZTSe at 300 K, respectively.展开更多
Geothermal exploration in northern Jordan is in juvenile phase. North eastern basaltic desert is expected to host, with other rock formations, a shallow geothermal field. For efficient geothermal potential evaluation,...Geothermal exploration in northern Jordan is in juvenile phase. North eastern basaltic desert is expected to host, with other rock formations, a shallow geothermal field. For efficient geothermal potential evaluation, a complete understanding of thermo-physical properties of deep reservoir rocks is of utmost importance. Due to the complex technical thermo-physical evaluations of basalts in depth, surficial basalts extending to the west were evaluated. Accordingly, six basaltic sub-flows from Al Hashimiyya were examined into their thermo-physical and mechanical properties. The flows represent the western extinction of large olivine basalt eruption. Different properties were evaluated for oven dried samples: thermal conductivity, permeability, porosity, density and specific heat capacity. In addition, basalts mechanical properties were examined: compressional wave velocity, unconfined compressive strength, indirect tensile strength and point load tests. The results were correlated in proportional patterns. They indicated that thermal conductivity of the studied basalts is dependent on porosity and permeability in parallel with mineral composition. It’s found that mechanical properties are controlled by porosity and permeability, too. The studied basalt properties exhibit slight deviation from the continental basalts thermo-physical and mechanical properties reported in the region. Thermal conductivity ranges between 1.89 and 1.32 W·m-1·K-1, whereas the porosity and permeability averages at 10.64% and 9.75899E-15 m2, respectively. Additionally, unconfined compressive strength averages at 104.9 Mpa and it’s almost 20 times higher than indirect tensile strength which ranges from 8.73 to 2.21 Mpa. As the samples were tested under laboratory conditions, in situ conditions will not be reflected by such values. At greater depth, temperature, pressure and hydrothermal activities will certainly affect rock properties. Micro fractures, whether it will be filled or not, will affect basalts properties, too. The results of this work will be used to develop a comprehensive thermo-physico-mechanical model, and improve the ability to predict rock properties at greater depths of Jordanian basalts.展开更多
In this study,a new linear friction welding(LFW)process,embedded LFW process,was put forward,which was mainly applied to combination manufacturing of long or overlong loadcarrying titanium alloy structural components ...In this study,a new linear friction welding(LFW)process,embedded LFW process,was put forward,which was mainly applied to combination manufacturing of long or overlong loadcarrying titanium alloy structural components in aircraft.The interfacial plastic flow behavior and bonding mechanism of this process were investigated by a developed coupling EulerianLagrangian numerical model using software ABAQUS and a novel thermo-physical simulation method with designed embedded hot compression specimen.In addition,the formation mechanism and control method of welding defects caused by uneven plastic flow were discussed.The results reveal that the plastic flow along oscillating direction of this process is even and sufficient.In the direction perpendicular to oscillation,thermo-plastic metals mainly flow downward along welding interface under coupling of shear stress and interfacial pressure,resulting in the interfacial plastic zone shown as an inverted“V”shape.The upward plastic flow in this direction is relatively weak,and only a small amount of flash is extruded from top of joint.Moreover,the wedge block and welding components at top of joint are always in un-steady friction stage,leading to nonuniform temperature field distribution and un-welded defects.According to the results of numerical simulation,high oscillating frequency combined with low pressure and small amplitude is considered as appropriate parameter selection scheme to improve the upward interfacial plastic flow at top of joint and suppress the un-welded defects.The results of thermo-physical simulation illustrate that continuous dynamic recrystallization(CDRX)induces the bonding of interface,accompanying by intense dislocation movement and creation of many low-angle grain boundaries.In the interfacial bonding area,grain orientation is random with relatively low texture density(5.0 mud)owing to CDRX.展开更多
A novel in-situ reactive approach based on the reactions among TiN,aluminum and boron has been developed to synthesize TiB_(2)-based composites including TiB_(2)-h BN(TB)and TiB_(2)-h BN-AlN(TBA).Fully dense ceramics ...A novel in-situ reactive approach based on the reactions among TiN,aluminum and boron has been developed to synthesize TiB_(2)-based composites including TiB_(2)-h BN(TB)and TiB_(2)-h BN-AlN(TBA).Fully dense ceramics with fine-grained microstructure were successfully obtained via spark plasma sintering at 1850℃/60 MPa/5 min.Microstructure analysis suggests h BN flakes were homogenously distributed in the TiB_(2)matrix.For AlN,however,they were elongated into plate-like grains during sintering,in which lots of defects in terms of stacking faults and twinning structures were observed.The mechanical and thermophysical properties of as-sintered ceramics were comprehensively investigated and compared.In-corporating AlN significantly improved the flexure strength,hardness,fracture toughness and thermal conductivity of TiB_(2)-h BN ceramics.The electrical conductivity of TB(3.06×10^(6)S/m)is larger than that of TBA(2.35×10^(6)S/m)at room temperature,but the value(6×10^(5)S/m)was lower than that of TBA(6.9×10^(5)S/m)at 1173 K.Based on the measurement of electrical and thermal conductivity,electron and phonon contributions to thermal conductivities of TB and TBA were calculated and their temperature dependences were illustrated.展开更多
Laser-weldable Sip-SiCp/Al hybrid composites with high volume fraction （60%-65%） of SiC reinforcement were fabricated by compression moulding and vacuum gas pressure infiltration technology. Microscopic observation ...Laser-weldable Sip-SiCp/Al hybrid composites with high volume fraction （60%-65%） of SiC reinforcement were fabricated by compression moulding and vacuum gas pressure infiltration technology. Microscopic observation displayed that the Sip-SiCp/Al hybrid composites with bilayer structure were compact without gas pores and the intergradation between Sip/Al layer and SiCp/Al layer was homogeneous and continuous. Further investigation revealed that the Sip-SiCp/Al hybrid composites possessed low density （2.96 g/cm^3）, high gas tightness （1.0 mPa·cm^3）/s）, excellent thermal management function as a result of high thermal conductivity （194 W/（m·K） and low coefficient of thermal expansion （7.0×10^-6 K-1）. Additionally, Sip-SiCp/Al hybrid composites had outstanding laser welding adaptability, which is significantly important for electronic packaging applications. The gas tightness of components after laser welding （48 mPa·cm^3）/s） can well match the requirement of advanced electronic packaging. Several kinds of these precision components passed tests and were put into production.展开更多
It is customary to apply Newton’s cooling as the standard model investigating the temperature profile of a hot substance exposed to a cool ambient. The rate of change of temperature in Newton’s model is simplistical...It is customary to apply Newton’s cooling as the standard model investigating the temperature profile of a hot substance exposed to a cool ambient. The rate of change of temperature in Newton’s model is simplistically related to linear-temperature difference of the two e.g. [1]. In our research flavored investigation, we consider a fresh model, cooling that depends to the difference of temperature-squared conducive to similar results. Utilizing a Computer Algebra System (CAS), especially <em>Mathematica</em> [2] we show the equivalency of the two.展开更多
Supercritical fluids(e.g.,hydrocarbon fuels,water,carbon dioxide,and organic working medium,etc)have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion,and have been...Supercritical fluids(e.g.,hydrocarbon fuels,water,carbon dioxide,and organic working medium,etc)have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion,and have been used or selected as the working fluids in engineering fields such as aerospace,nuclear power,solar energy,refrigeration,geothermal energy,chemical technology,and so on.To better understand the interesting characteristic or abnormal behaviors of supercritical fluids,most valuable research works(including experimental results and numerical studies)from domestic and abroad have been documented.As such,this paper presents a comprehensive review on heat transfer behaviors of some supercritical fluids in engineering applications.This review focuses on recently available articles published mainly from 2016 up to the present time.The common problems(i.e.,heat transfer enhancement and heat transfer deterioration particularly for the supercritical hydrocarbon fuels)in the supercritical field are summarized and some perspectives on future prospects are also included.展开更多
Nanofluids(NFs) are nanotechnology-based colloidal suspensions fabricated by suspending nanoparticles(NPs) in a base liquid. These fluids have shown potential to improve the heat transfer properties of conventional he...Nanofluids(NFs) are nanotechnology-based colloidal suspensions fabricated by suspending nanoparticles(NPs) in a base liquid. These fluids have shown potential to improve the heat transfer properties of conventional heat transfer fluids. In this study we report in detail on fabrication, characterization and thermo-physical property evaluation of SiC NFs, prepared using SiC NPs with different crystal structures,for heat transfer applications. For this purpose, a series of SiC NFs containing SiC NPs with different crystal structure(α-SiC and β-SiC) were fabricated in a water(W)/ethylene glycol(EG) mixture(50/50 wt%ratio). Physicochemical properties of NPs/NFs were characterized by using various techniques, such as powder X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM),Fouriertransform infrared spectroscopy(FTIR), dynamic light scattering(DLS) and Zeta potential analysis.Thermo-physical properties including thermal conductivity(TC) and viscosity for NFs containing SiC particles(α- and β- phase) weremeasured. The results show among all suspensions NFs fabricated with α-SiC particles have more favorable thermo-physical properties compared to the NFs fabricated with β-SiC.The observed difference is attributed to combination of several factors, including crystal structure(β- vs. α-), sample purity,and residual chemicals exhibited on SiC NFs. A TC enhancement of ～20% while 14% increased viscosity were obtained for NFs containing 9 wt% of particular type of α-SiC NPs indicating promising capability of this kind of NFs for further heat transfer characteristics investigation.展开更多
The heat transfer equation is used to determine the heat flow by conduction through a composite material along the real axis.An analytical dimensionless analysis is implemented in the framework of a separation of vari...The heat transfer equation is used to determine the heat flow by conduction through a composite material along the real axis.An analytical dimensionless analysis is implemented in the framework of a separation of variables method(SVM).This approach leads to an Eigenvalues problem that is solved by the Newton’s method.Two types of dynamics are found:An unsteady condition(in the form of jumps or drops in temperatures depending on the considered case),and a permanent equilibrium(tending to the ambient temperature).The validity and effectiveness of the proposed approach for any number of adjacent layers is also discussed.It is shown that,as expected,the diffusion of the temperature is linked to the ratio of the thermo-physical properties of the considered layers and their number.展开更多
In this paper,a fully bio-based vinyl oligomer with high functionalities was successfully prepared from rapeseed oil by three modification steps:epoxidation of rapeseed oil,solvent-free and catalyst-free ring opening ...In this paper,a fully bio-based vinyl oligomer with high functionalities was successfully prepared from rapeseed oil by three modification steps:epoxidation of rapeseed oil,solvent-free and catalyst-free ring opening by 10-undecylenic acid followed by esterification with 10-undecenoyl chloride.Then,the renewable polymers were prepared by photo-polymerization of these modified vegetable oils with typical thiol monomers:pentaerythritol tetrakis(3-mercaptopropionate),pentaerythritol tris(3-mercaptopropionate)and 1,2-ethanedithiol.The synthesis of the vinyl oligomer was monitored by nuclear magnetic resonance and Fourier-transform infrared spectroscopy.The average number of the carbon-carbon double bonds of the resulting vinyl oligomer is high to be 7.2.The kinetic of thiol-ene photo-polymerization of vegetable oil-based vinyl oligomer was studied by FTIR-ATR analyses.In addition,the thermo-physical properties,thermal stability and solvent resistance of these UV cured films were characterized.The polymers from 1,2-ethanedithiol exhibit higher gel content,storage modulus and glass transition temperature than those from other thiol monomers due to the high crosslinking densities of the resulting polymers.All polymers show excellent thermal stability up to 290oC.The resulting polymers exhibit thermo-physical properties,excellent water resistance and thermals stability,which is promising to find application in coatings and adhesives.展开更多
In order to prepare heatresistant inner layer of hot-forging die, plasma spraying, plasma re- melting and plasma spray welding were adopted. Cr3C2 coatings of Ni-Based were prepared respectively with 10%, 20% and 30% ...In order to prepare heatresistant inner layer of hot-forging die, plasma spraying, plasma re- melting and plasma spray welding were adopted. Cr3C2 coatings of Ni-Based were prepared respectively with 10%, 20% and 30% Cr3C2 powder and W6Mo5Cr4V2 substrate. The coating microstructure analysis, the micro-hardness test, and the measurement of thermal parameters of coating were conducted. The experimental results show that the coating has the better thermo-physical property by using plasma spray welding method with the powder ratio of 90% Ni60 and 10% Cr3C2, and by this way the micro-hardness of coating can achieve 1100 HV.展开更多
Standard treatments of thermodynamic equilibrium are incomplete. They do not take account of all factors determining equilibrium, cannot explain why many systems do not reach equilibrium and do not discuss the questio...Standard treatments of thermodynamic equilibrium are incomplete. They do not take account of all factors determining equilibrium, cannot explain why many systems do not reach equilibrium and do not discuss the questions of reaching and maintaining equilibrium. The arguments presented here provide a single physical definition of thermodynamic equilibrium that accounts for all factors determining thermodynamic equilibrium for mixtures of combustible gases and air. Based on the standard delrmition of thermodynamic equilibrium, the MBD （Maxwell Boltzmann distribution） and a simple molecular model lead to three possible types of equilibrium. The regions of temperature pressure and composition for each type of equilibrium are defined by the measured values of ignition temperatures and the explosive and flammability limits. How this definition of thermodynamic equilibrium can be extended to all molecular systems is discussed in the following papers.展开更多
基金supported by the National Natural Science Foundation of China(No.52274369)the National Key Laboratory of Science and Technology on High-strength Structural Materials,China(No.623020034).
文摘Three types of Al/Al−27%Si laminated composites,each containing 22%Si,were fabricated via hot pressing and hot rolling.The microstructures,mechanical properties and thermo-physical properties of these composites were investigated.The results demonstrated that the three laminated composites exhibited similar microstructural features,characterized by well-bonded interfaces between the Al layer and the Al−27%Si alloy layer.The tensile and flexural strengths of the composites were significantly higher than those of both Al−22%Si and Al−27%Si alloys.These strengths increased gradually with decreasing the layer thickness,reaching peak values of 222.5 and 407.4 MPa,respectively.Crack deflection was observed in the cross-sections of the bending fracture surfaces,which contributed to the enhanced strength and toughness.In terms of thermo-physical properties,the thermal conductivity of the composites was lower than that of Al−22%Si and Al−27%Si alloys.The minimum reductions in thermal conductivity were 6.8%and 0.9%for the T3 laminated composite,respectively.Additionally,the coefficient of thermal expansion of the composites was improved,exhibiting varying temperature-dependent behaviors.
基金supported by the Postdoctoral Foundation of China (20060400261)the Special Finance Scheme of Post Doctoral Foundation of China (200801350)
文摘The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temperature dilatometer, DSC, and laser thermal diffusivity methods were used to analyze thermal expansion coefficient （TEC）, specific heat, and thermal diffusivity. The results showed that CeO2 doped pyrochlores La2（Zr1.8Ce0.2）2O7 and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had higher TEC than La2Zr2O7 and La1.7Dy0.3Zr2O7. La2（Zr1.8Ce0.2）2O7, La1.7Dy0.3Zr2O7, and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had lower thermal conductivity than undoped La2Zr2O7. The Dy2O3, Nd2O3, and CeO2 codoped composition showed the lowest thermal conductivity and the highest TEC. Thermo-physical results also indicated that TEC of rare earth oxide doped La2Zr2O7 ceramic was slightly higher than that of conventional ZrO2-8Wt.% Y2O3 （8YSZ）, and its thermal conductivity was lower than that of 8YSZ.
基金financially supported by the Basic Research Laboratory Program through the Ministry of Education of the Republic of Korea (No. 2019R1A4A1026125)the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government Ministry of Trade, industry & Energy (No. 20164030201340)。
文摘(AlTa(0.76))xCoCrFeNi(2.1)(x values in molar ratio,x=0.1,0.3,0.5,0.7,1.0,and 1.5) alloys were designed to investigate the microstructure and mechanical properties of the eutectic high entropy alloys(EHEAs)consisting of FCC,B2,and Laves phases.Depending on the compositional variatio,clear microstructural variation was observed,as follows:(1) Group 1:FCC dendrite+Laves interdendrite(x=0.1),(2) Group 2:FCC dendrite+fine-eutectic structure consisting of FCC and Laves phases(x=0.3,0.5 and 0.7),(3) Group 3:B2 dendrite+bimodal eutectic structure [FCC/B2+Laves](x=1.0),(4) Group 4:Laves dendrite+eutectic structure consisting of B2 and Laves phases(x=1.5).As the fraction of Laves or B2 phases increases,yield stress increases from 293 to 2336 MPa,while the plastic strain decreases from 50 % to 2%.Thermo-physical parameters,such as mixing entropy(△S(mix)),mixing enthalpy(△H(mix)),valence electron concentration(VEC),and atomic size difference(δr),were calculated to understand the microstructural variation.Two criteria(δr-VEC and δr-△H(mix)) were utilized to elucidate the formation of the eutectic structures in the present EHEAs,revealing the usefulness of the thermo-physical parameters in the development of EHEAs.
基金supported financially by the National Natural Science Foundation of China(Nos.U1537212,51971013,51590894and 51425102)the National Key Research and Development Program of China(No.2016YFB0300901)。
文摘Rare earth oxides doped hafnia ceramics,with a formula of Hf0.76LnxY0.24-xO1.88(Ln=Gd,Yb,Gd+Yb or La+Yb),were prepared by solid state sintering at 1500℃.The effects of the rare earth oxides on the microstructures,sintering resistance,and thermo-physical properties of the doped hafnia ceramics were investigated.Results show that the Gd-Y,Yb-Y or Gd-Yb-Y co-doped hafnia ceramics remain the same defect fluorite(F)structure,while the La-Yb-Y co-doped hafnia revealing coexistence of pyrochlore(P)and fluorite structures.Yb-Y co-doped samples exhibited much better sintering resistance compared with Gd-Y and Gd-Yb-Y co-doped samples.The coexistence of P and F phases is beneficial to improved sintering capability.The thermal conductivities of the Gd-Y,Yb-Y and Gd-Yb-Y doped samples are relatively lower(1.4-1.7 W m^(-1)K^(-1)at 1200℃),but for the La-Yb-Y co-doped samples,the thermal conductivity increases dramatically with temperature due to increased thermal radiation at high-temperature.The average thermal expansion coefficients(TECs)of the Gd-Y,Yb-Y and Gd-Yb-Y co-doped samples are as high as10.3×10^(-6)K^(-1) in temperature range between 200-1200℃.
文摘Al-high Si alloys were designed by the addition of Cu or Mg alloying elements to improve the mechanical properties. It is found that the addition of 1 wt.% Cu or 1 wt.% Mg as strengthening elements significantly improves the tensile strength by 27.2% and 24.5%, respectively. This phenomenon is attributed to the formation of uniformly dispersed fine particles(Al2Cu and Mg2Si secondary phases) in the Al matrix during hot press sintering of the rapidly solidified(gas atomization) powder. The thermal conductivity of the Al-50 Si alloys is reduced with the addition of Cu or Mg, by only 7.3% and 6.8%, respectively. Therefore, the strength of the Al-50 Si alloys is enhanced while maintaining their excellent thermo-physical properties by adding 1% Cu(Mg).
文摘Phase stability,elastic properties,thermo-physical properties,as well as electronic properties of hexa-（Mo,Cr,W）2C carbides were investigated by first-principles calculations.The results indicated that the Mo8C4,Mo7Cr1C4,Mo7W1C4,Mo6W2C4,and Mo6W1Cr1C4 are stable and the stability follows the sequence：Mo6W1Cr1C4〉Mo7W1C4〉Mo7Cr1C4〉 Mo6W2C4〉 Mo8C4.Mo6W1Cr1C4 shows the highest stability,deformation resistance and hardness.G/B（shear modulus/bulk modulus）and Poisson′s ratio of the stable hexa-（Mo,Cr,W）2C are all larger than 1.75 and 0.26,respectively,which indicates that they are all brittle.The anisotropies are mainly due to the different Vogit shear modulus/Reuss shear modulus;the mechanical anisotropy of Mo7Cr1C4 is the largest,and that of Mo8C4 is the smallest.Moreover,the obtained Debye temperatureΘDand heat capacity Cpindicate that Mo6W2C4 possesses the best thermal conductivity（ΘD=497.72K）,while Mo7Cr1C4 and Mo6W2C4possess the largest heat capacity when the temperature is in the range of 0-10 Kand larger than 10 K,respectively.From the electronic property analysis,the doped Cr and W atoms can not only participate in orbitals hybridization themselves but also enhance the orbitals hybridization between Mo and C atoms,which can reinforce the interatomic interactions.
基金by the National key research and development program of China(Grant No.2017YFC0703001)National Natural Science Foundation of China(Grant No.51678297).
文摘It is well known that the use of woods as construction materials can embody carbon content of structural members,which can enhance the urban sustainability.However,due to the combustibility of wood,its current application is restricted.To broaden the application of wood,its thermal responses exposed to fire(high temperature)is investigated in this study.Firstly,the wood kinetic parameters are determined by coats-redfern method using thermal gravimetric(TGA)data.Secondly,the density and thermal conductivity are obtained from parallel and series models.Thirdly,the specific heat capacity formula is presented considering latent and decomposition heat,which can be directly determined by differential scanning calorimetry(DSC).Finally,the one-dimensional nonlinear heat transfer model with apparent thermo-physical properties is proposed.The four-sided heating experiment of Laminated Veneer Lumber(LVL)is carried out to investigate the temperature filed.The results show that the proposed model can predict the thermal responses of timber structures subjected to fire and high temperatures precisely.
文摘The asymmetric thermo-physical mechanism of the resistance spot welding technique with intermediate frequency(2 kHz)and direct current(RSWIFDC)on the high strength aluminum(Al)alloy TL091 was studied here in view of the Peltier effect.On the basis of the analysis of the electrode cap surface erosion state and the shape-position of the nugget,it was concluded that asymmetric thermo-physical phenomenon occurred on both ends of the nugget,and even had an influence upon the shape-forming coefficient and the vertical position deviation of the nugget,and the erosion degree of the electrode caps.In this work,the relative thermo-physical model of the welding was established combined with the Peltier effect and the spot welding characteristics.Accordingly the relative welding phenomena,such as nugget center deviation and different erosion degree of the electrode cap surface,was explained clearly using the model related with the Peltier effect for the first time.This model provides important theoretical basis for future study and application of Al alloy spot welding,based on which,effective works may be done to promote the quality of the Al alloy welded joints and to obtain favorable control upon parameters of Al alloy welding for electrode caps.
基金supported by the National Natural Science Foundation of China (No. 51075197)
文摘Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) with optimum band gaps about 1.5 eV are important absorbers for solar cells. The elastic constants and the thermo-physical properties of the stannite-type CZTS and CZTSe are calculated by using density-functional theory (DFT) and the quasi-harmonic Debye model. The bonding strength along the [100] and [010] directions is the same to that along the [001] direction and the shear elastic properties of the {001} plane are anisotropic for CZTS and CZTSe. Both compounds exhibit ductile behavior due to their high ratio of bulk modulus to shear modulus (K/G). The values of thermal capacity are close to 200 J/(mol·K) at above 300 K, and the thermal expansion coefficients decrease with increasing pressure at same temperature. The entropy is variable by power-exponent, and the internal energy is almost linear with increasing temperature for CZTS and CZTSe. The Gibbs energy of CZTS is lower than that of CZTSe under same temperature and pressure. The Debye temperatures are 297 and 232 K, and Grneisen parameters are 2.36 and 2.37 for CZTS and CZTSe at 300 K, respectively.
文摘Geothermal exploration in northern Jordan is in juvenile phase. North eastern basaltic desert is expected to host, with other rock formations, a shallow geothermal field. For efficient geothermal potential evaluation, a complete understanding of thermo-physical properties of deep reservoir rocks is of utmost importance. Due to the complex technical thermo-physical evaluations of basalts in depth, surficial basalts extending to the west were evaluated. Accordingly, six basaltic sub-flows from Al Hashimiyya were examined into their thermo-physical and mechanical properties. The flows represent the western extinction of large olivine basalt eruption. Different properties were evaluated for oven dried samples: thermal conductivity, permeability, porosity, density and specific heat capacity. In addition, basalts mechanical properties were examined: compressional wave velocity, unconfined compressive strength, indirect tensile strength and point load tests. The results were correlated in proportional patterns. They indicated that thermal conductivity of the studied basalts is dependent on porosity and permeability in parallel with mineral composition. It’s found that mechanical properties are controlled by porosity and permeability, too. The studied basalt properties exhibit slight deviation from the continental basalts thermo-physical and mechanical properties reported in the region. Thermal conductivity ranges between 1.89 and 1.32 W·m-1·K-1, whereas the porosity and permeability averages at 10.64% and 9.75899E-15 m2, respectively. Additionally, unconfined compressive strength averages at 104.9 Mpa and it’s almost 20 times higher than indirect tensile strength which ranges from 8.73 to 2.21 Mpa. As the samples were tested under laboratory conditions, in situ conditions will not be reflected by such values. At greater depth, temperature, pressure and hydrothermal activities will certainly affect rock properties. Micro fractures, whether it will be filled or not, will affect basalts properties, too. The results of this work will be used to develop a comprehensive thermo-physico-mechanical model, and improve the ability to predict rock properties at greater depths of Jordanian basalts.
基金co-supported by the National Natural Science Foundation of China(Nos.52105411,52105400and 52305420)the China Postdoctoral Science Foundation(No.2023M742830)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2023008).
文摘In this study,a new linear friction welding(LFW)process,embedded LFW process,was put forward,which was mainly applied to combination manufacturing of long or overlong loadcarrying titanium alloy structural components in aircraft.The interfacial plastic flow behavior and bonding mechanism of this process were investigated by a developed coupling EulerianLagrangian numerical model using software ABAQUS and a novel thermo-physical simulation method with designed embedded hot compression specimen.In addition,the formation mechanism and control method of welding defects caused by uneven plastic flow were discussed.The results reveal that the plastic flow along oscillating direction of this process is even and sufficient.In the direction perpendicular to oscillation,thermo-plastic metals mainly flow downward along welding interface under coupling of shear stress and interfacial pressure,resulting in the interfacial plastic zone shown as an inverted“V”shape.The upward plastic flow in this direction is relatively weak,and only a small amount of flash is extruded from top of joint.Moreover,the wedge block and welding components at top of joint are always in un-steady friction stage,leading to nonuniform temperature field distribution and un-welded defects.According to the results of numerical simulation,high oscillating frequency combined with low pressure and small amplitude is considered as appropriate parameter selection scheme to improve the upward interfacial plastic flow at top of joint and suppress the un-welded defects.The results of thermo-physical simulation illustrate that continuous dynamic recrystallization(CDRX)induces the bonding of interface,accompanying by intense dislocation movement and creation of many low-angle grain boundaries.In the interfacial bonding area,grain orientation is random with relatively low texture density(5.0 mud)owing to CDRX.
基金This work was financially supported by the National Nat-ural Science Foundation of China(Nos.52022072,51972243,92060202 and 52102029)the National Key R&D Programs(No.2021YFB3701400)+1 种基金Hubei Provincial Natural Science Foundation of China(Distinguished Young Scholars 2022CFA042)Independent Innovation Projects of the Hubei Longzhong Laboratory(2022ZZ-10)were also acknowledged.
文摘A novel in-situ reactive approach based on the reactions among TiN,aluminum and boron has been developed to synthesize TiB_(2)-based composites including TiB_(2)-h BN(TB)and TiB_(2)-h BN-AlN(TBA).Fully dense ceramics with fine-grained microstructure were successfully obtained via spark plasma sintering at 1850℃/60 MPa/5 min.Microstructure analysis suggests h BN flakes were homogenously distributed in the TiB_(2)matrix.For AlN,however,they were elongated into plate-like grains during sintering,in which lots of defects in terms of stacking faults and twinning structures were observed.The mechanical and thermophysical properties of as-sintered ceramics were comprehensively investigated and compared.In-corporating AlN significantly improved the flexure strength,hardness,fracture toughness and thermal conductivity of TiB_(2)-h BN ceramics.The electrical conductivity of TB(3.06×10^(6)S/m)is larger than that of TBA(2.35×10^(6)S/m)at room temperature,but the value(6×10^(5)S/m)was lower than that of TBA(6.9×10^(5)S/m)at 1173 K.Based on the measurement of electrical and thermal conductivity,electron and phonon contributions to thermal conductivities of TB and TBA were calculated and their temperature dependences were illustrated.
文摘Laser-weldable Sip-SiCp/Al hybrid composites with high volume fraction （60%-65%） of SiC reinforcement were fabricated by compression moulding and vacuum gas pressure infiltration technology. Microscopic observation displayed that the Sip-SiCp/Al hybrid composites with bilayer structure were compact without gas pores and the intergradation between Sip/Al layer and SiCp/Al layer was homogeneous and continuous. Further investigation revealed that the Sip-SiCp/Al hybrid composites possessed low density （2.96 g/cm^3）, high gas tightness （1.0 mPa·cm^3）/s）, excellent thermal management function as a result of high thermal conductivity （194 W/（m·K） and low coefficient of thermal expansion （7.0×10^-6 K-1）. Additionally, Sip-SiCp/Al hybrid composites had outstanding laser welding adaptability, which is significantly important for electronic packaging applications. The gas tightness of components after laser welding （48 mPa·cm^3）/s） can well match the requirement of advanced electronic packaging. Several kinds of these precision components passed tests and were put into production.
文摘It is customary to apply Newton’s cooling as the standard model investigating the temperature profile of a hot substance exposed to a cool ambient. The rate of change of temperature in Newton’s model is simplistically related to linear-temperature difference of the two e.g. [1]. In our research flavored investigation, we consider a fresh model, cooling that depends to the difference of temperature-squared conducive to similar results. Utilizing a Computer Algebra System (CAS), especially <em>Mathematica</em> [2] we show the equivalency of the two.
基金sponsored by the National Natural Science Foundation of China(Nos.51676163,51976161,U1867218)the National 111 Project,China(No.B18041)+1 种基金the Fundamental Research Funds of Shenzhen City,China(No.JCYJ20170306155153048)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX202029).
文摘Supercritical fluids(e.g.,hydrocarbon fuels,water,carbon dioxide,and organic working medium,etc)have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion,and have been used or selected as the working fluids in engineering fields such as aerospace,nuclear power,solar energy,refrigeration,geothermal energy,chemical technology,and so on.To better understand the interesting characteristic or abnormal behaviors of supercritical fluids,most valuable research works(including experimental results and numerical studies)from domestic and abroad have been documented.As such,this paper presents a comprehensive review on heat transfer behaviors of some supercritical fluids in engineering applications.This review focuses on recently available articles published mainly from 2016 up to the present time.The common problems(i.e.,heat transfer enhancement and heat transfer deterioration particularly for the supercritical hydrocarbon fuels)in the supercritical field are summarized and some perspectives on future prospects are also included.
基金financial support from the EU (Project Reference: 228882)Swedish Research Council (VR) for the project NanoHex (Enhanced Nano-fluid Heat Exchange)
文摘Nanofluids(NFs) are nanotechnology-based colloidal suspensions fabricated by suspending nanoparticles(NPs) in a base liquid. These fluids have shown potential to improve the heat transfer properties of conventional heat transfer fluids. In this study we report in detail on fabrication, characterization and thermo-physical property evaluation of SiC NFs, prepared using SiC NPs with different crystal structures,for heat transfer applications. For this purpose, a series of SiC NFs containing SiC NPs with different crystal structure(α-SiC and β-SiC) were fabricated in a water(W)/ethylene glycol(EG) mixture(50/50 wt%ratio). Physicochemical properties of NPs/NFs were characterized by using various techniques, such as powder X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM),Fouriertransform infrared spectroscopy(FTIR), dynamic light scattering(DLS) and Zeta potential analysis.Thermo-physical properties including thermal conductivity(TC) and viscosity for NFs containing SiC particles(α- and β- phase) weremeasured. The results show among all suspensions NFs fabricated with α-SiC particles have more favorable thermo-physical properties compared to the NFs fabricated with β-SiC.The observed difference is attributed to combination of several factors, including crystal structure(β- vs. α-), sample purity,and residual chemicals exhibited on SiC NFs. A TC enhancement of ～20% while 14% increased viscosity were obtained for NFs containing 9 wt% of particular type of α-SiC NPs indicating promising capability of this kind of NFs for further heat transfer characteristics investigation.
文摘The heat transfer equation is used to determine the heat flow by conduction through a composite material along the real axis.An analytical dimensionless analysis is implemented in the framework of a separation of variables method(SVM).This approach leads to an Eigenvalues problem that is solved by the Newton’s method.Two types of dynamics are found:An unsteady condition(in the form of jumps or drops in temperatures depending on the considered case),and a permanent equilibrium(tending to the ambient temperature).The validity and effectiveness of the proposed approach for any number of adjacent layers is also discussed.It is shown that,as expected,the diffusion of the temperature is linked to the ratio of the thermo-physical properties of the considered layers and their number.
基金sponsored by the National Natural Science Foundation of China(51563011)the Natural Science Foundation of Jiangxi Province(2016BAB203094)+1 种基金the Young Talents Project of Jiangxi Science and Technology Normal University(2016QNBJRC007)the Postgraduate Innovation Fund Project of Jiangxi Science and Technology Normal University(YC2019-X31).
文摘In this paper,a fully bio-based vinyl oligomer with high functionalities was successfully prepared from rapeseed oil by three modification steps:epoxidation of rapeseed oil,solvent-free and catalyst-free ring opening by 10-undecylenic acid followed by esterification with 10-undecenoyl chloride.Then,the renewable polymers were prepared by photo-polymerization of these modified vegetable oils with typical thiol monomers:pentaerythritol tetrakis(3-mercaptopropionate),pentaerythritol tris(3-mercaptopropionate)and 1,2-ethanedithiol.The synthesis of the vinyl oligomer was monitored by nuclear magnetic resonance and Fourier-transform infrared spectroscopy.The average number of the carbon-carbon double bonds of the resulting vinyl oligomer is high to be 7.2.The kinetic of thiol-ene photo-polymerization of vegetable oil-based vinyl oligomer was studied by FTIR-ATR analyses.In addition,the thermo-physical properties,thermal stability and solvent resistance of these UV cured films were characterized.The polymers from 1,2-ethanedithiol exhibit higher gel content,storage modulus and glass transition temperature than those from other thiol monomers due to the high crosslinking densities of the resulting polymers.All polymers show excellent thermal stability up to 290oC.The resulting polymers exhibit thermo-physical properties,excellent water resistance and thermals stability,which is promising to find application in coatings and adhesives.
文摘In order to prepare heatresistant inner layer of hot-forging die, plasma spraying, plasma re- melting and plasma spray welding were adopted. Cr3C2 coatings of Ni-Based were prepared respectively with 10%, 20% and 30% Cr3C2 powder and W6Mo5Cr4V2 substrate. The coating microstructure analysis, the micro-hardness test, and the measurement of thermal parameters of coating were conducted. The experimental results show that the coating has the better thermo-physical property by using plasma spray welding method with the powder ratio of 90% Ni60 and 10% Cr3C2, and by this way the micro-hardness of coating can achieve 1100 HV.
文摘Standard treatments of thermodynamic equilibrium are incomplete. They do not take account of all factors determining equilibrium, cannot explain why many systems do not reach equilibrium and do not discuss the questions of reaching and maintaining equilibrium. The arguments presented here provide a single physical definition of thermodynamic equilibrium that accounts for all factors determining thermodynamic equilibrium for mixtures of combustible gases and air. Based on the standard delrmition of thermodynamic equilibrium, the MBD （Maxwell Boltzmann distribution） and a simple molecular model lead to three possible types of equilibrium. The regions of temperature pressure and composition for each type of equilibrium are defined by the measured values of ignition temperatures and the explosive and flammability limits. How this definition of thermodynamic equilibrium can be extended to all molecular systems is discussed in the following papers.
