In this study,a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber(NR)/polybutadiene rubber(BR)composites through the construction of a ...In this study,a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber(NR)/polybutadiene rubber(BR)composites through the construction of a heterogeneous structure using pre-vulcanized powder rubber to replace traditional fillers.The matrix material is composed of a blend of NR and BR,which is widely used in tire manufacturing.By incorporating pre-vulcanized trans-1,4-poly(isoprene-co-butadiene)(TBIR)rubber powder(pVTPR)with different cross-linking densities and contents,significant improvements in the gas barrier properties and CO_(2)permselectivity of the NR/BR/pVTPR composites were observed.The results indicated that compared to NR/BR/TBIR composites prepared through direct blending of NR,BR,and TBIR,the NR/BR/pVTPR composites exhibited markedly superior gas barrier properties.Increasing the cross-linking density of pVTPR resulted in progressive enhancement of the gas barrier properties of the NR/BR/pVTPR composite.For example,the addition of 20 phr pVTPR with a cross-linking density of 346 mol/m^(3)resulted in a 79%improvement in the oxygen barrier property of NR/BR/pVTPR compared to NR/BR,achieving a value of 5.47×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1).Similarly,the nitrogen barrier property improved by 76%compared to NR/BR,reaching 2.4×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1),which is 28%higher than the conventional inner liner material brominated butyl rubber(BIIR,PN2=3.32×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1)).Owing to its low cost,exceptional gas barrier properties,superior adhesion to various tire components,and co-vulcanization capabilities,the NR/BR/pVTPR composite has emerged as a promising alternative to butyl rubber in the inner liner of tires.Furthermore,by fine-tuning the cross-linking density of pVTPR,the high-gas-barrier NR/BR/pVTPR composites also demonstrated remarkable CO_(2)permselectivity,with a CO_(2)/N2 selectivity of 61.4 and a CO_(2)/O_(2)selectivity of 26.12.This innovation provides a novel strategy for CO_(2)capture and separation,with potential applications in future environmental and industrial processes.The multifunctional NR/BR/pVTPR composite,with its superior gas barrier properties and CO_(2)permselectivity,is expected to contribute to the development of safer,greener,and more cost-effective transportation solutions.展开更多
Improving the high-temperature performance of Inconel 718(IN718)alloys manufactured via laser powder bed fusion(LPBF)has been the most concerned issue in the industry.In this study,the effects of Ti_(2)AlC inoculants ...Improving the high-temperature performance of Inconel 718(IN718)alloys manufactured via laser powder bed fusion(LPBF)has been the most concerned issue in the industry.In this study,the effects of Ti_(2)AlC inoculants on microstructures and high-temperature mechanical properties of the as-built IN718 composites were investigated.According to statistical results of relative density and unmelted particle area in as-built alloys,the optimal energy of 112 J/mm^(3)was determined.It was observed that the precipitation of the MC carbide was significantly enhanced with the addition of Ti_(2)AlC,restricting the precipitation of the Laves phase.The MC particles were uniformly distributed along the subgrain boundaries,which contributed to the dispersion strengthening.Meanwhile,the MC particles served as nucleation sites for heterogeneous nucleation during the solidification process,facilitating the refinement of columnar and cellular grains.The simulated Scheil-Gulliver curves showed that the precipitation sequence of phases did not change with Ti_(2)AlC inoculants.The as-built 1%Ti_(2)AlC/IN718 sample demonstrated an ultimate tensile strength of 998.78 MPa and an elongation of 18.04%at 650℃,revealing a markedly improved mechanical performance compared with the LPBF-manufactured IN718 alloys.The high-temperature tensile strength of 1%Ti_(2)AlC/IN718 sample increased to 1197.99 MPa by heat treatment.It was suggested that dislocation strengthening and ordered strengthening were two most important reinforcement mechanisms.展开更多
A unique discontinuous lamellar microstructure of titanium alloys consisting of lamellar colonies at prior β-Ti grain boundaries and internal interwoven α-laths is prepared by a TiH_(2)-based powder metallurgy metho...A unique discontinuous lamellar microstructure of titanium alloys consisting of lamellar colonies at prior β-Ti grain boundaries and internal interwoven α-laths is prepared by a TiH_(2)-based powder metallurgy method.The α-variants get various crystallographic orientations and become discontinuous during vacuum annealing at 700℃.Remarkably,nanoscale phase δ-TiH compound layers are generated between α-laths and β-strips,so that dislocations are piled up at the α/δ/βinterfaces during tensile deformation.This leads to dislocation slips being confined to individual α-laths,with differentslips and particularly pyramidal<c+a>slips being activated.The efficiency of wavy slip is promoted and the work hardening rate is enhanced.Finally,the combined effect of dispersed micro-shear bands and lath distortions is considered contributive for alleviating the stress concentration at grain boundaries,resulting in a high-promising synergy of enhanced ultimate tensile strength of 1080 MPa and good elongation to fracture of 13.6%.展开更多
The rapid advancement of superalloy melting technology has increased the demands on crucible materials.Y_(2)O_(3) is a promising candidate for nickel-based superalloy melting due to its outstanding high-temperature st...The rapid advancement of superalloy melting technology has increased the demands on crucible materials.Y_(2)O_(3) is a promising candidate for nickel-based superalloy melting due to its outstanding high-temperature stability and non-wetting behavior with various alloys.However,its poor sintering performance limits its development.High-density Y_(2)O_(3) ceramics were successfully prepared via pressureless sintering at 1600℃ in a carbon-embedded atmosphere with talc powder as an additive.The resulting ceramics achieved optimal properties,including a bulk density of 4.27 g cm^(−3),apparent porosity of 1.1%,and cold compressive strength of 311.27 MPa.The talc powder introduced a liquid phase during sintering,which accelerated mass transfer and promoted grain growth and densification.During cooling,this liquid phase remained at the grain boundaries and acted as an intergranular bonding agent,strengthening grain cohesion.Nevertheless,excessive liquid phase hindered grain growth,negatively affecting sintering.Additionally,the extremely low porosity and the formation of the Mg_(2)SiO_(4) phase reduced the residual strength retention ratio of the Y_(2)O_(3) ceramic after thermal shock.展开更多
Using Ti powder as reagent, TiO 2 nanoneedle/nanoribbon spheres were prepared via hydrothermal method in NaOH solution. The samples were characterized by field emission scanning electron microscopy （FESEM）, transmis...Using Ti powder as reagent, TiO 2 nanoneedle/nanoribbon spheres were prepared via hydrothermal method in NaOH solution. The samples were characterized by field emission scanning electron microscopy （FESEM）, transmission electron microscopy （TEM） with selected area electron diffraction （SAED）, X-ray diffraction （XRD）, and UV-visible light absorption spectrum. The results indicate that the growth orientations of the crystals are influenced by the hydrothermal temperature and NaOH concentration. The diameter of the nanoneedle spheres and nanoribbon spheres （40 50 μm） are almost the same as that of Ti powders. TiO 2 nanoneedle/nanoribbon sphere powders are anatase after heat treatment at 450 °C for 1 h. Furthermore, methyl orange was used as a target molecule to estimate the photocatalytic activity of the specimens. Under the same testing conditions, the photocatalytic activities of the products decrease in the following order： TiO 2 nanoneedle sphere, TiO 2 nanoribbon sphere and P25.展开更多
α-Bi2O3 powders were prepared from nanometer Bi powders through low-temperature oxidation at less than 873.15 K. XRD, SEM, TEM and HRTEM were used to characterize the structure and morphology of Bi powders and Bi2O3 ...α-Bi2O3 powders were prepared from nanometer Bi powders through low-temperature oxidation at less than 873.15 K. XRD, SEM, TEM and HRTEM were used to characterize the structure and morphology of Bi powders and Bi2O3 particles. Kinetic studies on the bismuth oxidation at low-temperatures were carried out by TGA method. The results show that bismuth beads should be reunited and oxidized to become irregular Bi2O3 powders. The bismuth oxidation follows shrinking core model, and its controlling mechanism varies at different reaction time. Within 0-10 min, the kinetics is controlled by chemical reaction, after that it is controlled by O2 diffusion in the solid α-Bi2O3 layer. The apparent activation energy is determined as 55.19 kJ/mol in liquid-phase oxidation.展开更多
Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 （mass fraction）, which were reconstituted into micrometer-sized granu...Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 （mass fraction）, which were reconstituted into micrometer-sized granules by spray drying, subsequently sintering at different temperatures to form nanostructured feedstock for thermal spraying, and then A1203-13%TiO2 nanocoatings were deposited by plasma spraying. The evolution of morphology, microstructure, and phase transformation of the agglomerated powder and as-sprayed coatings were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that A1203 retains the same a phase as the raw material during sintering, while TiO2 changes from anatase to futile. During plasma spraying, some a-A1203 phases solidify to form metastable y-A1203, and the volume fraction of a-A1203 decreases as CPSP increases. However, peaks of the TiO2 phase are not observed from the as-sprayed coatings except for the coatings sprayed at the lower CPSP. As the CPSP increases, nanostructured TiO2 is dissolved easily in y-A1203 or z-A1203＇TiO2 phase. After heat treatment, y-A1203 in the coatings transforms to a-A1203, and rutile is precipitated.展开更多
The deformation behaviors of Al2O3/Al composites were investigated by compressive tests conducted at temperature of 300-450 °C and strain rates of 0.001-1.0 s-1 with Gleeble-1500 D thermal simulator system. The r...The deformation behaviors of Al2O3/Al composites were investigated by compressive tests conducted at temperature of 300-450 °C and strain rates of 0.001-1.0 s-1 with Gleeble-1500 D thermal simulator system. The results show that the flow stress increases with increasing strain rate and decreasing temperature. The hyperbolic sine constitutive equation can describe the flow stress behavior of Al2O3/Al composites, and the deformation activation energy and constitutive equations were calculated. The processing maps of Al2O3/Al-2 μm and Al2O3/Al-1 μm composites at strain of 0.6 were obtained and the optimum processing domains are in ranges of 300-330 °C, 0.007-0.03 s-1 and 335-360 °C, 0.015-0.06 s-1 for hot working, respectively. The instability zones of flow behavior can also be recognized by the maps.展开更多
基金supported by the National Key Research and Development Program of China (No. 2022YFB3704700(2022YFB3704702))the National Natural Science Foundation of China (No. 52473096)+1 种基金Major Scientific and Technological Innovation Project of Shandong Province (No. 2021CXGC010901)Taishan Scholar Program
文摘In this study,a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber(NR)/polybutadiene rubber(BR)composites through the construction of a heterogeneous structure using pre-vulcanized powder rubber to replace traditional fillers.The matrix material is composed of a blend of NR and BR,which is widely used in tire manufacturing.By incorporating pre-vulcanized trans-1,4-poly(isoprene-co-butadiene)(TBIR)rubber powder(pVTPR)with different cross-linking densities and contents,significant improvements in the gas barrier properties and CO_(2)permselectivity of the NR/BR/pVTPR composites were observed.The results indicated that compared to NR/BR/TBIR composites prepared through direct blending of NR,BR,and TBIR,the NR/BR/pVTPR composites exhibited markedly superior gas barrier properties.Increasing the cross-linking density of pVTPR resulted in progressive enhancement of the gas barrier properties of the NR/BR/pVTPR composite.For example,the addition of 20 phr pVTPR with a cross-linking density of 346 mol/m^(3)resulted in a 79%improvement in the oxygen barrier property of NR/BR/pVTPR compared to NR/BR,achieving a value of 5.47×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1).Similarly,the nitrogen barrier property improved by 76%compared to NR/BR,reaching 2.4×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1),which is 28%higher than the conventional inner liner material brominated butyl rubber(BIIR,PN2=3.32×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1)).Owing to its low cost,exceptional gas barrier properties,superior adhesion to various tire components,and co-vulcanization capabilities,the NR/BR/pVTPR composite has emerged as a promising alternative to butyl rubber in the inner liner of tires.Furthermore,by fine-tuning the cross-linking density of pVTPR,the high-gas-barrier NR/BR/pVTPR composites also demonstrated remarkable CO_(2)permselectivity,with a CO_(2)/N2 selectivity of 61.4 and a CO_(2)/O_(2)selectivity of 26.12.This innovation provides a novel strategy for CO_(2)capture and separation,with potential applications in future environmental and industrial processes.The multifunctional NR/BR/pVTPR composite,with its superior gas barrier properties and CO_(2)permselectivity,is expected to contribute to the development of safer,greener,and more cost-effective transportation solutions.
基金supported by the National Natural Science Foundation of China(Nos.52374396 and 52122409).
文摘Improving the high-temperature performance of Inconel 718(IN718)alloys manufactured via laser powder bed fusion(LPBF)has been the most concerned issue in the industry.In this study,the effects of Ti_(2)AlC inoculants on microstructures and high-temperature mechanical properties of the as-built IN718 composites were investigated.According to statistical results of relative density and unmelted particle area in as-built alloys,the optimal energy of 112 J/mm^(3)was determined.It was observed that the precipitation of the MC carbide was significantly enhanced with the addition of Ti_(2)AlC,restricting the precipitation of the Laves phase.The MC particles were uniformly distributed along the subgrain boundaries,which contributed to the dispersion strengthening.Meanwhile,the MC particles served as nucleation sites for heterogeneous nucleation during the solidification process,facilitating the refinement of columnar and cellular grains.The simulated Scheil-Gulliver curves showed that the precipitation sequence of phases did not change with Ti_(2)AlC inoculants.The as-built 1%Ti_(2)AlC/IN718 sample demonstrated an ultimate tensile strength of 998.78 MPa and an elongation of 18.04%at 650℃,revealing a markedly improved mechanical performance compared with the LPBF-manufactured IN718 alloys.The high-temperature tensile strength of 1%Ti_(2)AlC/IN718 sample increased to 1197.99 MPa by heat treatment.It was suggested that dislocation strengthening and ordered strengthening were two most important reinforcement mechanisms.
基金financially supported by the National Natural Science Foundation of China(Nos.52301145,52275329)the Applied Basic Research Program of Liaoning Province,China(No.2023JH2/101300158)+1 种基金the Fundamental Research Fund for the Central Universities,China(No.N2202010)the Key Research Programs of High Education Institutions in Henan Province,China(No.24A430017).
文摘A unique discontinuous lamellar microstructure of titanium alloys consisting of lamellar colonies at prior β-Ti grain boundaries and internal interwoven α-laths is prepared by a TiH_(2)-based powder metallurgy method.The α-variants get various crystallographic orientations and become discontinuous during vacuum annealing at 700℃.Remarkably,nanoscale phase δ-TiH compound layers are generated between α-laths and β-strips,so that dislocations are piled up at the α/δ/βinterfaces during tensile deformation.This leads to dislocation slips being confined to individual α-laths,with differentslips and particularly pyramidal<c+a>slips being activated.The efficiency of wavy slip is promoted and the work hardening rate is enhanced.Finally,the combined effect of dispersed micro-shear bands and lath distortions is considered contributive for alleviating the stress concentration at grain boundaries,resulting in a high-promising synergy of enhanced ultimate tensile strength of 1080 MPa and good elongation to fracture of 13.6%.
基金financially supported by the National Natural Science Foundation of China(No.U21A2057).
文摘The rapid advancement of superalloy melting technology has increased the demands on crucible materials.Y_(2)O_(3) is a promising candidate for nickel-based superalloy melting due to its outstanding high-temperature stability and non-wetting behavior with various alloys.However,its poor sintering performance limits its development.High-density Y_(2)O_(3) ceramics were successfully prepared via pressureless sintering at 1600℃ in a carbon-embedded atmosphere with talc powder as an additive.The resulting ceramics achieved optimal properties,including a bulk density of 4.27 g cm^(−3),apparent porosity of 1.1%,and cold compressive strength of 311.27 MPa.The talc powder introduced a liquid phase during sintering,which accelerated mass transfer and promoted grain growth and densification.During cooling,this liquid phase remained at the grain boundaries and acted as an intergranular bonding agent,strengthening grain cohesion.Nevertheless,excessive liquid phase hindered grain growth,negatively affecting sintering.Additionally,the extremely low porosity and the formation of the Mg_(2)SiO_(4) phase reduced the residual strength retention ratio of the Y_(2)O_(3) ceramic after thermal shock.
基金Project (NS2010153) supported by Nanjing University of Aeronautics and Astronautics Research Funding, ChinaProject (BE2009130) supported by Jiangsu Key Technology R&D Program, China
文摘Using Ti powder as reagent, TiO 2 nanoneedle/nanoribbon spheres were prepared via hydrothermal method in NaOH solution. The samples were characterized by field emission scanning electron microscopy （FESEM）, transmission electron microscopy （TEM） with selected area electron diffraction （SAED）, X-ray diffraction （XRD）, and UV-visible light absorption spectrum. The results indicate that the growth orientations of the crystals are influenced by the hydrothermal temperature and NaOH concentration. The diameter of the nanoneedle spheres and nanoribbon spheres （40 50 μm） are almost the same as that of Ti powders. TiO 2 nanoneedle/nanoribbon sphere powders are anatase after heat treatment at 450 °C for 1 h. Furthermore, methyl orange was used as a target molecule to estimate the photocatalytic activity of the specimens. Under the same testing conditions, the photocatalytic activities of the products decrease in the following order： TiO 2 nanoneedle sphere, TiO 2 nanoribbon sphere and P25.
基金Project (2006BAB02B05-04- 01/02) supported by the National Key Technologies R&D Program of China
文摘α-Bi2O3 powders were prepared from nanometer Bi powders through low-temperature oxidation at less than 873.15 K. XRD, SEM, TEM and HRTEM were used to characterize the structure and morphology of Bi powders and Bi2O3 particles. Kinetic studies on the bismuth oxidation at low-temperatures were carried out by TGA method. The results show that bismuth beads should be reunited and oxidized to become irregular Bi2O3 powders. The bismuth oxidation follows shrinking core model, and its controlling mechanism varies at different reaction time. Within 0-10 min, the kinetics is controlled by chemical reaction, after that it is controlled by O2 diffusion in the solid α-Bi2O3 layer. The apparent activation energy is determined as 55.19 kJ/mol in liquid-phase oxidation.
基金Projects(51072045,51102074)supported by the National Natural Science Foundation of China
文摘Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of A1203-13%TiO2 （mass fraction）, which were reconstituted into micrometer-sized granules by spray drying, subsequently sintering at different temperatures to form nanostructured feedstock for thermal spraying, and then A1203-13%TiO2 nanocoatings were deposited by plasma spraying. The evolution of morphology, microstructure, and phase transformation of the agglomerated powder and as-sprayed coatings were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that A1203 retains the same a phase as the raw material during sintering, while TiO2 changes from anatase to futile. During plasma spraying, some a-A1203 phases solidify to form metastable y-A1203, and the volume fraction of a-A1203 decreases as CPSP increases. However, peaks of the TiO2 phase are not observed from the as-sprayed coatings except for the coatings sprayed at the lower CPSP. As the CPSP increases, nanostructured TiO2 is dissolved easily in y-A1203 or z-A1203＇TiO2 phase. After heat treatment, y-A1203 in the coatings transforms to a-A1203, and rutile is precipitated.
基金Project(2012AA030311)supported by the National High-tech Research and Development Program of ChinaProject(2010BB4074)supported by the Natural Science Foundation of Chongqing Municipality,ChinaProject(2010ZD-02)supported by the State Key Laboratory for Advanced Metals and Materials,China
文摘The deformation behaviors of Al2O3/Al composites were investigated by compressive tests conducted at temperature of 300-450 °C and strain rates of 0.001-1.0 s-1 with Gleeble-1500 D thermal simulator system. The results show that the flow stress increases with increasing strain rate and decreasing temperature. The hyperbolic sine constitutive equation can describe the flow stress behavior of Al2O3/Al composites, and the deformation activation energy and constitutive equations were calculated. The processing maps of Al2O3/Al-2 μm and Al2O3/Al-1 μm composites at strain of 0.6 were obtained and the optimum processing domains are in ranges of 300-330 °C, 0.007-0.03 s-1 and 335-360 °C, 0.015-0.06 s-1 for hot working, respectively. The instability zones of flow behavior can also be recognized by the maps.
