Lam H.PhamNgoc Thuy NguyenDang Mao NguyenTuan An Nguyen...
1-13页
查看更多>>摘要：This study focuses on the improvement of the thermal stability and flame-retardant performance of polyurethane(PU)foam by using effective flame-retardant additives and nano silica(nSiO2)particles from rice husk.The addition of non-halogen flame retardants(FRs)including aluminum trihydroxide(ATH),triphenyl phosphate(TPP),and diammonium phosphate(DAP)leads to markedly enhanced thermal sta-bility and fire resistance of the PU/nSiO2/FRs nanocomposites,resulting in achieving UL-94 HB standard.In particular,the nanocomposites met the UL-94 V-0 criteria thanks to the inclusion of DAP at 25 phr.The LOI value of the nanocomposites reached 26％which is much higher than that of PU/nSiO2 nanocompos-ite,about 20％.In order to further understand the fire-proof mechanism,the residue char layer remaining of the PU/nSiO2/FRs nanocomposites after being burned was also investigated by scanning electron mi-croscopy(SEM)and Fourier transform infrared(FTIR).In addition,the microstructure,thermal stability,thermal conductivity,and mechanical properties of nanocomposites were also evaluated in this study.
查看更多>>摘要：Al7075 sheets are widely used in aerospace industry and their higher strength-plasticity collaborative improvement requirement is urgent.In this study,the microstructure inheriting the evolution and me-chanical properties of Al7075 sheets during multidirectional rotary forging(MRF)and T6 heat treatment are analyzed.The results show that the average grain size exhibits near-parabolic evolution with increas-ing MRF deformation amount.MRF20％+T6(20％MRF deformation amount+T6)condition possesses the largest grain size of 72.6 μm,and its abnormal grain growth mechanism is that the medium deformation energy and high deformation heterogeneity in MRF20％deformed grains could cause asynchronous re-crystallization behavior during T6 heat treatment,and the grains with comparatively higher deformation energy get recrystallized firstly and devour adjacent grains along preferred<011>or(223>misorientation axis.MRF70％+T6 condition possesses the finest grain size of 14.2 μm,and its fine grain inheriting mech-anism is that the uniformly high deformation energy in MRF70％deformed grains causes uniformly rapid recrystallization,and rapidly recrystallized grains effectively suppress grain boundary motion from adja-cent grains.With increasing MRF deformation amount,tensile strength and elongation values both exhibit near-antiparabolic evolution.MRF70％+T6 condition possesses the largest tensile strength(563 MPa)and elongation(17.73％),which increases by 8.27％and 80.55％compared to as-annealed+T6(MRF0％+T6)condition(tensile strength is 520 MPa and elongation is 9.82％),respectively.The strength-plasticity col-laborative improvement is mainly because the combination of effectively inherited fine grains,refined inclusion particles,and uniformly distributed fine η'particles after T6 heat treatment could promote smooth dislocation movement and coordinated slip behavior in most matrix grains,which contributes to the delay of stress localization and strength-plasticity collaborative improvement.
查看更多>>摘要：The study provided a systematic investigation into the creep behavior of a γ'-strengthened Co-based single crystal superalloy Co-7Al-8W-1Ta-4Ti(at.％)under compressive creep conditions at 1000 ℃ and 137 MPa.Simultaneously,the microstructural changes during thermal exposure at 1000 ℃ were thor-oughly examined.The microstructure analysis of the creep samples revealed the presence of y/y'rafts,twins,stacking faults,and dislocation networks.Statistical analyses were conducted to assess the dimen-sions and volume fractions of γ',alongside Vickers hardness tests and nanoindentation experiments.Re-sults show that γ'dissolution in the creep samples with substantially higher dissolution rates compared to thermal exposure.Localized Co depletion and Ti enrichment in twin is observed in creep sample,po-tentially initiating localized phase transformations.Concurrently,lattice rotation occurred during creep,resulting in a progressive deviation of crystal orientation away from the[001]direction.Stacking faults transitioned from network-like structures to parallel configurations,and twins played a significant role in creep deformation,particularly in samples subjected to 382 h creep.The study also explored the evo-lution of Vickers hardness and the elastic modulus,introducing a systematic linear model to describe Vickers hardness changes during both thermal exposure and creep conditions.
查看更多>>摘要：A metastable ω single-phase nanograined(NG)Ti-Fe alloy was synthesized using laser inert-gas conden-sation(IGC).Upon being annealed at 360 ℃,the NG Ti-Fe alloy exhibited a remarkable ultra-hardening,increasing the hardness from 4.7 to 8.6 GPa.Subsequent findings revealed an unexpected hardness en-hancement,rising from 6.6 GPa at 420 ℃ to 7.6 GPa at 460 ℃,despite the occurrence of grain growth.In-depth investigations into the strengthening mechanisms of the NG Ti-Fe alloy were conducted using in-situ synchrotron high-energy X-ray diffraction(XRD)and transmission electron microscopy(TEM).The comprehensive analysis unveiled that the diffusion-controlled structure evolution during annealing played a pivotal role in enhancing the alloy's mechanical properties.This study not only presents the synthesis of a novel metastable alloy but also provides valuable insights into the intricate relationship between diffusion-controlled structure evolution and the resulting superior mechanical properties.
查看更多>>摘要：Solid-state hydrogen storage tanks are key equipment for fuel cell vehicles and hydrogen storage.How-ever,the low heat transfer properties of hydrogen storage tanks result in the inability to meet the hy-drogen supply requirements of fuel cells.In this study,different thermal management approaches were explored through the design of LaNi5-based solid-state hydrogen storage tanks.We experimentally stud-ied the effects of different internal heat transfer methods,that is,expanded natural graphite(ENG),cop-per foam,and copper fins on the hydrogen absorption and desorption performance.We also studied the effects of external cooling methods with natural convection,air cooling,and water cooling,respectively.Under the same external cooling method of natural convection,a solid hydrogen storage tank filled with 5 wt.％ENG has similar performance to a tank filled with copper foam.Compared to natural convection,air and water cooling can significantly improve the heating performance of metal hydride(MH)beds by increasing the external heat transfer coefficient.The effect of water cooling is better than that of air cool-ing,and in these two enhanced performance conditions,the tank filled with copper foam performs better than with ENG.In the case of water cooling,by adding copper fins to a hydrogen storage tank filled with 5 wt.％ENG,the tank was saturated with hydrogen absorption in only 29.4 min,which is 55.6％shorter than the hydrogen uptake time in a hydrogen storage reactor without copper fins.And its stable hydrogen desorption(1 NL/min)has reached 98.1％of the total hydrogen released.The results show that the effec-tive thermal conductivity and heat transfer area of metal hydride bed play key roles in improving heat transfer and reaction rate.In addition,heat transfer is more important than mass transfer to improve the performance of the hydrogen storage tank.
查看更多>>摘要：Wire arc-directed energy deposition(WADED)has shown great advantages and potential in fabricating large-scale aluminum(Al)alloy components.However,WADED Al alloys typically exhibit low strength and reliability due to pore defects and lack of work hardening or precipitation strengthening.This study utilized a combination of laser shock peening(LSP)and annealing to regulate the microstructure of WADED Al-Mg4.5Mn alloy and enhance mechanical properties.The effects of LSP and annealing on phase composition,pore distribution,and microstructures at multiple scales were systematically investigated to reveal the mechanical property improving mechanism.The results demonstrated that LSP-induced plastic deformation formed a defect-free zone by closing near-surface pore defects.LSP created the hardened layer with gradient mechanical properties by inducing gradient changes in grain size,the number of low-angle grain boundaries(LAGBs),and dislocation density along the depth direction.The annealing process promoted grain coarsening and reduced excessive dislocations and LAGBs,weakening the work harden-ing effect caused by LSP.Furthermore,the high-density dislocations and high stored energy generated by LSP accelerated the recrystallization,facilitating growth of near-surface grains.The defect-free zone,dislocation strengthening,and LAGBs strengthening were responsible for the increase in strength,while the synergistic deformation between hardened layers and soft core facilitated maintaining excellent elon-gation.The strength and elongation of WADED Al alloy can be synergistically improved by balancing the effects of LSP and heat treatment.
查看更多>>摘要：Corrosion engineering is an effective way to improve the oxygen evolution reaction(OER)activity of al-loys.However,the impact of grain boundary corrosion on the structure and electrochemical performance of alloy is still unknown.Herein,the vacuum arc-melted CrCoNiFe alloys with interlaced network struc-tures via grain boundary corrosion methods were fabricated.The grain boundaries that existed as de-fects were severely corroded and an interlaced network structure was formed,promoting the exposure of the active site and the release of gas bubbles.Besides,the(oxy)hydroxides layer(25 nm)on the sur-face could act as the true active center and improve the surface wettability.Benefiting from the unique structure and constructed surface,the CrCoNiFe-12 affords a high urea oxidation reaction(UOR)perfor-mance with the lowest overpotential of 250 mV at 10 mA/cm2 in 1 M KOH adding 0.33 M urea.The CrCoNiFe-12‖Pt only required a cell voltage of 1.485 V to afford 10 mA/cm2 for UOR and long-term sta-bility of 100 h at 10 mA/cm2(27.6 mV decrease).These findings offer a facile strategy for designing bulk multiple-principal-element alloy electrodes for energy conversion.
查看更多>>摘要：The development of efficient hydrazine oxidation reaction(HzOR)catalysts is important for the construc-tion of remarkable energy storage and conversion systems.However,after a period of electrochemical reaction,the active site of the catalyst will be irreversibly reduced or inactivated,and how to recover the active site is a major challenge.Here,we report 2D Co(OH)2/Ti3C2(OH)x MXene composites with rapid re-construction and self-healing behaviors as efficient and stable electrocatalysts during HzOR process.Both experimental and theoretical results indicate that the introduction of Ti3C2(OH)x MXene can effectively reduce the dehydrogenation barrier of Co(OH)2,from 0.584 eV to 0.481 eV to form the real catalytic active center Co(OH)O.Subsequently,Co(OH)O/Ti3C2(OH)x MXene composites with metal-like conductiv-ity not only present spontaneous adsorption capacity of N2H4,but also can modulated rate-determining step of dehydrogenation of*N2H4 to*N2H3(0.54 eV)compared with Co(OH)O.Finally,the electrophilic oxygen of Co(OH)O/Ti3C2(OH)x can spontaneously obtain electrons and protons from N2H4,achieving the oxidation of N2H4 while reducing Co(OH)O to Co(OH)2,thus completing the self-healing of the efficient catalyst.
查看更多>>摘要：Oxygen evolution reaction(OER)is one of the most important issues for hydrogen production from water splitting.During the OER process,electrochemical reconstruction is widely observed for the majority of electrocatalysts,which is strongly related to the formation and evolution of real active species.Herein,bimetal metal-organic framework(MOF)with an equal ratio of Co and Fe sites is screened to exhibit the superior OER property.An obvious reconstruction is observed to transform single MOF phase into the heterostructure composed of active CoOOH and FeOOH.Meanwhile,the generation of Co3+species is more reliant on the blessing of electricity and electrolyte than that of Fe3+species.As a result,the optimal electrocatalyst shows the overpotential of 267 mV at 10 mA/cm2 and ultra-low Tafel slope of 24.7 mV/dec with a stable OER performance.
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