查看更多>>摘要：Since the 1980s,mass market upholstered furniture sold in the United Kingdom has incorporated flame retardant chemicals to meet regulatory flammability requirements.However,UK fire deaths remain com-parable with similar European countries which have no such regulations.Quantitative measures of the effect that different chemical flame retardants additives have on the flammability and smoke toxicity of UK regulatory-compliant upholstered furniture remain limited.It has been shown that most fatal fires in-volve upholstered furniture;most fire deaths result from toxic gas inhalation;gas phase flame retardants increase the toxicity of smoke;and the fall in fire deaths over the last 30 years is the same in countries with and without furniture flammability regulations.Moreover,the presence of certain flame retardants in furniture is a significant obstacle to any meaningful end-of-life processing.The burning behaviour and smoke toxicity of nine upholstered furniture composites using a range of flame retardant technologies were assessed in the cone calorimeter.The total heat release(THR)varied from 46 MJ m-2 to 68 MJ m-2,the time-to-ignition(tti)from 8 s to 105 s,and peak heat release rate(pHRR)from 230 kW m-2 to 430 kW m-2.The composite filled with PET showed the longest tti while the expandable graphite fabric on the FR-foam showed the lowest pHRR.The composite with the Br-FR fabric and the FR-foam had the shortest tti,the greatest smoke,the second highest CO and the highest HCN yield.The composite with the non-FR fabric and the PET filling had the longest tti.For all the fabrics,the transition from non-FR to FR foam resulted in significant increases in the smoke,CO and HCN,except CO of Br-FR and FR-foam was slightly lower than non-FR foam.Smoke toxicity predictions show that the use of gas phase flame retardants in both the fabrics and fillings of upholstered furniture contributes to the high proportion of smoke-related fire casualties.The work shows that the smoke toxicity of upholstered furniture can be reduced by using condensed phase FRs,such as expandable graphite,or less flammable materials,such as polyester wadding.The regulatory component tests which focus on ignitability have been shown to be ineffective at assessing the fire safety of composites representative of furniture as sold.The alternative approach of assessing heat release and smoke toxicity,as described here,would improve the fire safety of furniture while reducing reliance on additive flame retardants acting in the gas phase.
查看更多>>摘要：Precipitation-strengthened medium/high-entropy alloys(MEAs/HEAs)have great potential for high-temperature applications.In this study,we designed a novel Ni45.9Fe23Cr23V4Nb3Mo1B0.1(at.％)MEA alloy,hardened by the D022(Ni,Fe,Cr)3(Nb,V)-type nanoprecipitates,with an excellent strength-ductility com-bination from room to elevated temperatures.Specifically,the tensile strengths,at 700 and 800 ℃,could be maintained as high as 845 and 589 MPa,respectively;meanwhile,elongations at all testing temper-atures exceeded 25％without any intermediate-temperature embrittlement.The temperature-dependent deformation mechanisms were unraveled using multi-scale characterizations,which involved profound slip planarities,such as stacking fault(SF)networks and deformation twins(DTs).Furthermore,the crit-ical resolved shear stress(CRSS)to initiate SFs in both face-centered cubic(FCC)and D022 phases was evaluated,and the possible reasons for the origin of anomalous DTs at 800 ℃ were discussed in de-tail.The main findings demonstrate that the shearable D022 nanoparticles can provide the FCC matrix with considerable dislocation storage capacity,reinforcing strain hardening at ambient and intermedi-ate temperatures.This work provides fundamental insights into the controllable design and deformation mechanisms of high-performance D022-strengthened MEAs/HEAs.
查看更多>>摘要：The nucleation and transition sequences of topologically close-packed(TCP)phases in a Re-containing Ni-based single crystal superalloy were systematically investigated using in-situ transmission electron microscopy(TEM)and three-dimensional atom probe technology(3D-APT).During the initial stage of heat-exposure at 1100 ℃,the TCP phase forming elements(Re,Co,Cr,etc.)segregated at the γ/γ'in-terface near the y matrix side to provide the concentration undulations for the nucleation sites of TCP phases,following which the σ and P phase coherently nucleated along the(1(11))γ and(022)γ planes from the γ/γ'interface near the γ matrix side,respectively.With prolonged heat-exposure time,transitions from σ phase to P phase,σ phase to μ phase,and P phase to µ phase occurred.Besides,the orientation relationships of TCP phase intergrowth structures indicated that the P phase grew along the(101)σ plane of the σ phase by co-lattice precipitation,meanwhile,the μ phase grew with smaller lattice misfits along the(040)σ plane of the σ phase and the(400)p plane of the P phase.Additionally,the result by first-principles calculation evidenced that the μ phase had the lowest system energy to make the transition of σ phase and P phase to μ phases inevitable,therefore,the TCP phase ultimately existed as the most stable μ phase.Finally,the transition sequences of TCP phase during heat-exposure could be summarized into three types:γ matrix→σ→μ,γ matrix→ P→µ,and γ matrix→ σ→P→μ.
查看更多>>摘要：It is hard to simultaneously realize the high dielectric tunability and low loss for the single Ba0.6Sr0.4TiO3(BST)dielectric film made through chemical method.Garnet structured Y2.80Pr0.20Fe5O12(YPrIG)ex-hibits the merits of high saturation magnetization and a much high resistivity,which are helpful for realizing magnetoelectric double tuning and suppressing the dielectric loss of BST film.In this work,Y2.80Pr0.20Fe5O12/Ba0.6Sr0.4TiO3(YPrIG/BST)composite films were fabricated by sol-gel method.The com-posite films exhibited a low dielectric loss(0.0087),and got a magnetic tunability of 11.73％at 10 kOe and 1.44 MHz.Compared with BST film,the tunability of YPrIG/BST film was enhanced from 56.25％to 73.24％under the bias electric field of 800 kV/cm.Additionally,YPrIG/BST films exhibited an electromag-netic double adjustability.The electromagnetic tunability of YPrIG/BST composite films was as high as 80.40％at 1.44 MHz,under the DC bias electric field of 800 kV/cm and magnetic field of 10 kOe.This phenomenon can be explained in terms of the superposition effect of electric field and magnetic field.
查看更多>>摘要：Incorporating one-dimensional(1D)nanofillers into carbon/carbon composites(C/Cs)can increase their mechanical strength.However,this method is ineffective in improving the fracture toughness of C/Cs be-cause cracks can easily pass over the 1D nanofillers,resulting in a flat fracture surface.Herein,we propose a new technique to significantly improve both the strength and toughness of C/Cs by incorporating 2D ribbon-shaped nanofillers.Silicon nitride nanoribbons(SiNNRs)are assembled into a film-like structure and inserted into each layer of a carbon fiber laminate,which is then densified with a pyrocarbon matrix.Due to the large interfacial contact area between the nanoribbon and matrix,ribbon-shaped SiNNRs can efficiently arrest and deflect cracks in both two and three dimensions,exhibiting a higher reinforcement efficiency than that of slender silicon nitride nanowires(SiNNWs).Mechanical tests show that the per-centage increases in fracture toughness,flexural strength,and compressive strength of C/Cs produced by SiNNRs are approximately 9.8,1.8,and 1.25 times higher than those produced by SiNNWs at the same volume fraction of nanofillers,respectively.This study suggests that 2D ribbon-shaped nanofillers are more effective than 1D fibrous nanofillers in enhancing the strength and toughness of C/Cs.
查看更多>>摘要：Lithium borohydride(LiBH4)is regarded as a potential hydrogen storage material due to its high gravi-metric and volumetric capacity,but its practical application suffers from high operating temperature and poor reversibility.Herein,porous hollow carbon microspheres composed of carbon-coated Ni nanoparti-cles with high content(denoted as Ni/C)are rationally designed as functional support,which not only induces effective nanoconfinement of LiBH4 but also promotes efficiently homogeneous destabilization reaction between LiBH4 and Ni nanoparticles.The introduction of Ni nanoparticles leads to the decrease of the Gibbs free energy change for H2 desorption of LiBH4 based on the formation of Ni2B down to-0.95 eV while this value reaches 1.19 eV for bulk LiBH4,validating the effective role of Ni in thermo-dynamically destabilizing H2 desorption.Impressively,the average B-H bond length of LiBH4 on Ni2B reaches 1.291 Å and thus the corresponding dissociation energy of removing one H atom from LiBH4 is lowered to 1.00 eV,much lower than bulk LiBH4(4.22 eV)and even LiBH4 on Ni(1.27 eV),which verifies superior role of Ni2B than Ni in catalytically enhancing H2 desorption.Therefore,a capacity of 8.86 wt.％is obtained for LiBH4 confined into Ni/C at 320 ℃ after 10 cycles.
查看更多>>摘要：The global energy crisis and environmental problems have become two unprecedented challenges.Semi-conductor photocatalysis offers a promising strategy to solve them,while its practical application requires advanced photocatalytic materials.In recent years,one-dimensional(1D)alkali-metal hexatitanate(AHT)photocatalysts have attracted considerable attention in energy and environmental fields due to their high chemical stability,excellent photoactivity,unique ion-exchange,environment-friendly,and cost-effective properties.In this review,we firstly introduce the basic properties of AHT including crystal and electronic band structure,photoactivity,and structure-property-performance relationship.Secondly,the recent ad-vances in synthesis and modification strategies of 1D AHT photocatalysts are summarized thoughtfully,followed by a comprehensive discussion on their various environmental and energy applications,includ-ing pollutant degradation,H2 generation,and CO2 reduction.Finally,the key challenges and prospects are also highlighted for the development of high-performance 1D AHT-based photocatalysts for practi-cal applications.We hope that this review will shed some light on the rational design of 1D Ti-O-based nanomaterials for efficient environmental remediation and solar fuel production.
查看更多>>摘要：The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on the microstructural and mechanical characteristics(tensile properties and Charpy V-notched impact energy)of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated.Rectangular samples were prepared using long raster and short raster scanning strate-gies for changing heat buildup,and the mechanical tests were conducted depending on build direction.The time-temperature profile measured at a fixed point in the long raster sample showed a lower max-imum temperature and a higher cooling rate,indicating lower heat accumulation compared to that of the short raster sample.In each build direction,the yield strength of the long raster sample was 45.8％-60.5％higher and its ductile-brittle transition temperature was 76.8-103.8 ℃ lower than that of the short raster sample.Additionally,compared to conventionally made samples and without requiring heat treat-ment,the long raster sample exhibited over a 45％increase in yield strength and a 22.7 ℃ reduction in the ductile-brittle transition temperature.The superior combination in long raster samples is induced by smaller effective grain size,smaller cementite,and a higher pre-existing dislocation density.The re-sults emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.
查看更多>>摘要：The common problem of low strength-ductility matching prevails in near-α high-temperature titanium matrix composites(TMCs).In this work,the design strategy of ultrafine grains and dispersed(Ti,Zr)6Si3 nanoprecipitates in the microstructure of TiBw/near α-Ti composites via low-temperature isothermal mul-tidirectional forging(IMDF),is expected to break the trade-off dilemma between strength and ductility.The results show that with the decrease in the temperature of IMDF,the grain scale decreased from 0.98 to 0.59 μm,and the location of silicide precipitation shifted from phase boundaries and grain boundaries to α-grain boundaries and intracrystalline regions.The experiments confirm that the local segregation of Si and the temperature of thermomechanical deformation are the key factors affecting the precipitation behavior of silicides.With the decrease of the deformation temperature,the precipitation mechanism of silicides changes from a single diffusion-controlled precipitation to the coupling of two mechanisms,namely,elemental diffusion and dislocation-assisted nucleation,which facilitates the successive precip-itation of nanometer-sized silicides at the grain boundaries and in the inner regions.The ultimate ten-sile strength(UTS)and elongation of the composites were substantially increased after IMDF at 950 and 800 ℃,especially the excellent performance at 800 ℃,where the strength reached 1320.3 MPa and the elongation was 5.8％.The room and high-temperature strengthening and failure mechanisms of the com-posites are analyzed and discussed,and the yield strength(YS)increments provided by various strength-ening mechanisms at room temperature are quantified,aiming to provide a potential preparation strategy for the synergistic strengthening of near-α TMCs with ultrafine grains and nanoparticles.
NETL
NSTL
万方数据