Influence of thermal exposure on microstructure and stress rupture properties of a new Re-containing single crystal Ni-based superalloy

In this study, the long-term thermal microstructural stability and related stress rupture lives of a new Re-containing Ni-based single-crystal superalloy, DD11, were investigated after high-temperature exposure for different lengths of time. The results show that the γ' precipitates retained a cuboidal morphology and the γ' size increased after short thermal exposure for 50 h at 1,070℃. As the thermal exposure time was prolonged to 500 h, the cuboidal γ' gradually changed into irregular raft-like morphology due to particles coalescence, and the morphology of the microstructure was almost unchanged after further thermal exposure up to 3,000 h. The stress rupture experiments at 1,070℃ and a tensile stress of 140 MPa showed that the rupture lives increased significantly after thermal exposure for 50 h and dropped dramatically with increasing exposure time up to 500 h but decreased slowly after exposure for more than 500 h. These results imply that stress rupture properties did not decrease when the γ' remained cuboidal but degraded to different extents during the γ' coarsening process. The coarsening of the γ' precipitates and change in morphology were regarded as the main factors leading to the degradation of the stress rupture lives. This study provides fundamental information on the high-temperature longterm microstructural stability and mechanical performance, which will be of great help for DD11 alloy optimization and engineering aeroengine applications.

Hierarchical CoSeS nanostructures assisted by Nb doping for enhanced hydrogen evolution reaction

Metal doping for active sites exhibits remarkable potential for improving the hydrogen evolution reaction(HER).Multi-doping and the use of a conductive substrate can further modulate catalytic performance.Herein,Nb-CoSe well dispersed in N-doped carbon nanospheres(NCs,Nb-CoSe@NC)was synthesized to serve as a conductive substrate and facilitated good dispersion of active sites for the HER.Nb doping can also change the electronic structure of CoSe,which facilitates the activity for the HER.In order to further improve the conductivity and intrinsic activity of Nb-CoSe@NC,dual,nonmetal doping was realized through gas sulfurization to prepare hierarchical Nb-CoSeS@NC.The prepared Nb-CoSeS@NC,with a core-shell structure,exhibited a low overpotential of 115 mV at 10 mA cm–2,which is smaller than that of the most doped catalysts.In addition,NCs not only improved the dispersion and conductivity of the catalyst but also prevented metal corrosion in an electrolyte,thus facilitating the long-term stability of Nb-CoSeS@NC.Moreover,the synergistic effect of the multi-doping of Nb,S,and Se was explained.This work provides a promising,multi-doping strategy for the large-scale application of transition-metal-based electrocatalysts for the HER.

Tailoring electron transfer with Ce integration in ultrathin Co(OH)_(2) nanosheets by fast microwave for oxygen evolution reaction

The intrinsic activity of Co(OH)_(2) for oxygen evolution reaction(OER)may be elaborately improved through the suitable valence adjustment.Ce modification at electronic level is proved to be an efficient strategy owing to the flexible transformation of Ce^(3+)/Ce4+.Herein,Ce0.21@Co(OH)_(2) with the optimized Ce doping have been fabricated to tailor the fast electron transfer for the enhanced activity and stability for OER.Firstly,the obtained core-shell structure composed of vertical loose Co(OH)_(2) sheets not only exposes a large number of active sites,but also provides channels for Ce doping.Secondly,the high pressure microwave with instantaneous heating can fast introduce Ce into Co(OH)_(2),obtaining Cex@Co(OH)_(2) with well dispersion and close integration.The intimated interaction between Ce and Co species may provide the"d-f electronic ladders"for accelerating electron transfer of the catalytic surface.Meanwhile,Ce promotes the formation of Co-superoxide intermediate and/or the release of oxygen,which is considered to be the rate-determining step for OER.The electrochemical measurements confirmed the low overpotential of 300 m V at 10 m A cm^(-2) and great stability of Ce0.21@Co(OH)_(2) for OER.This work demonstrates a meaningful approach to realize the tuned electronic structure through metal doping.

Influence of platform position on stray grain nucleation in Ni-based single-crystal dummy blade clusters

Stray grains are the most severe of the solidification defects that occur in the industrial single-crystal blade preparation process.In this study,a single-crystal dummy blade cluster with different crystal orientations controlled by the seeding method was prepared,and the influence of the position of the circular platform(relative to the sample and furnace body)on stray grain nucleation was investigated.Results show that the microstructure of the circular platforms could be divided into the center,expansion,and stray grain regions.The inside of the circular platform facing the center of the cluster is more prone to stray grain formation than the outside of the circular platform facing the furnace body.With an increase in the distance between the circular platform and the bottom of the dummy blade cluster,the stray grain region expands,whereas the expansion region narrows.The stray grain is slightly aggravated with increase of the misorientation.Finally,the mechanism underlying the influence of platform position on the formation of stray grains in single-crystal dummy blade clusters is discussed based on the temperature evolution during directional solidification.

Early Triassic Legoupil Formation in Schmidt Peninsula,Antarctic Peninsula:Provenance and Depositional Settings

Geochemical compositions can be used to determine the tectonic setting of sedimentary basins,while where the link of source to sink is no longer preserved,detrital zircon age patterns can aid in resolving the original basin setting.The metasedimentary Legoupil Formation,located at Cape Legoupil and the Schmidt Peninsula,could give a hint for the tectonic evolution of Antarctic Peninsula.In this contribution,we constrain the sedimentary provenance of the Legoupil Formation through geochemistry and detrital zircon U-Pb geochronology.The petrography and geochemical features indicate that the provenance of the Legoupil Formation could be felsic rocks.Detrital zircon grains record a steady supply of Permian and Ordovician material into the Legoupil Formation.The youngest concordant zircon ages of 262 Ma suggest that the depositional time of Legoupil Formation is no older than Late Permian.The detrital zircon age spectrum of Legoupil Formation suggests that the Legoupil Formation sediments should be derived from regional sources endemic to western Gondwana prior to its breakup.Together with the previous studies,geochemistry and detrital zircons reflect an active continental margin tectonic setting and the detrital zircon spectra of Legoupil Formation are similar to the ones deposited in forearc tectonic setting.

Creep property and microstructural evolution of DD11 alloy under high temperature and low stress

In this paper,the interrupted and ruptured creep tests were carried out in a novel second generation single crystal superalloy named DD11 at 1100℃/130 MPa.The alloy exhibited typical creep curve including primary,steady,and tertiary three creep stages.The microstructural evolution at different stages of the creep were analyzed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that theγ′phases transform into rafted structure at the early stage of the steady creep and keep stable during the steady creep stage.As the creep goes on,the rafted structure further coarsens and the topological inversion occurs.In addition,at the primary creep,the dislocations mainly move in theγmatrix and pile up in theγ/γ′interface since the matrix channels widen slightly.The formation of the regular interfacial dislocation networks occurs at the early stage of the steady creep.Under the low stress,the dominated deformation mechanism during steady creep stage is the climbing of the〈010〉type edge dislocation.Furthermore,the effect of the deformation mechanism on creep property was discussed in detail.

Self-supported Fe_(x)Ni_(1-x)MoO_(4) with synergistic morphology and composition for efficient overall water splitting at large current density

Developing the high activity,low cost and robust large-current-density-based electrocatalysts is of great significance for the industrial electrolytic water splitting.However,the current range of most reported materials is small,which makes it difficult for them to play their roles in practical applications.Here,a self-supported amorphous FexNi1-xMo O4/IF treated with ammonium fluoride (AF_(0.1)-FNMO/IF) is synthesized by one-step hydrothermal method.With the help of NH4F,AF_(0.1)-FNMO/IF exhibits a vertically cross-linked nanosheet with spherical structure.Electrochemical measurement shows that AF_(0.1)-FNMO/IF affords a large current density ordeal and only need low overpotentials of 289 and 345 m V to reach a current response of 500 m A/cm ^(2)for oxygen evolution reaction and hydrogen evolution reaction,respectively,together with long-time stability (both at 500,1000 and 2000 m A/cm ^(2)) in 1.0 mol/L KOH solution.Using it as bifunctional catalyst for overall water splitting,the current densities of 100,500,1000 and1500 m A/cm ^(2)are achieved at a cell voltage of 1.71,1.88,1.94 and 1.97 V with excellent durability,which is much better than that of most published electrodes.The work provides valuable insight for designing higher activity nickel iron-based molybdate catalysts with large current density.

聚丁烯及聚丁烯合金的溶液等温结晶行为研究

研究了聚丁烯-1(PB-1)及聚丁烯合金(PBA)中PB-1的溶液等温结晶行为.测定了PB-1在正庚烷溶剂中的溶解度曲线,采用膨胀计法研究了PB-1和PBA中PB-1组分的溶液等温结晶动力学.研究发现,等温结晶温度的升高会降低PB-1的结晶速率,但不影响PB-1在溶液中的结晶成核方式;PBA中PB-1组分的溶液等温结晶速率更快,聚丙烯(PP)组分的存在改变了PB-1的结晶成核方式.示差扫描量热仪(DSC)和广角X射线衍射仪(WAXD)测试表明PB-1的溶液等温结晶形成I′和III晶型,结晶温度的提高与PP组分的存在都会促进PB-1晶型III的产生.

Differential Polymorphic Transformation Behavior of Polybutene-1 with Multiple Isotactic Sequences

For the solid-solid transformation from form Ⅱ to form Ⅰ of isotactic polybutene-1(iPB),the temperature dependence of form Ⅰ nucleation and growth was deemed to control the transformation process.However,the relationship between formⅠ formation and form Ⅱ disappearance in the transformation process is not clear.In this work,the spontaneous crystal transformation from form Ⅱ to Ⅰ of iPB with 81 mol%mmmm sequence concentration is studied firstly by tracking the two processes,the decay of form Ⅱ and the yielding of form Ⅰ in a wide range of temperature spanning from 0℃ to 50℃ and in a long transformation time ranging from 5 min to 65 days with in situ FTIR and WAXD.Unlike the literature reports,the decay rate of form Ⅱ is firstly found to be lower than the yielding rate of form Ⅰ at all studied temperatures,especially at low transition temperature.This is attributed to the amorphous chains which locate near crystal lamella participating into the nucleation of form Ⅱ.The regular chain folding and growth of i PB form Ⅰ from amorphous chains containing short isotactic sequences also lead to an increase in crystallinity of form Ⅰ compared with that of initial form Ⅱ crystallized at 60℃.An increase in the annealing temperature results in decrease in crystallinity and increase in lamellae thickness of i PB formⅠ.

Triazine COF-supported single-atom catalyst (Pd/trzn-COF) for CO oxidation

Single-atom catalysts(SACs) with well-defined and specific single-atom dispersion on supports offer great potential for achieving both high catalytic activity and selectivity. Covalent organic frameworks(COFs) with tailormade crystalline structures and designable atomic composition is a class of promising supports for SACs. Herein, we have studied the binding sites and stability of Pd single atoms(SAs)dispersed on triazine COF(Pd1/trzn-COF) and the reaction mechanism of CO oxidation using the density functional theory(DFT). By evaluating different adsorption sites, including the nucleophilic sp2C atoms, heteroatoms and the conjugated π-electrons of aromatic ring and triazine, it is found that Pd SAs can stably combine with trzn-COF with a binding energy around-5.0 eV, and there are two co-existing dynamic Pd1/trzn-COFs due to the adjacent binding sites on trzn-COF. The reaction activities of CO oxidation on Pd1/trzn-COF can be regulated by the anion–π interaction between a +δ phenyl center and the related-δ moieties as well as the electron-withdrawing feature of imine in the specific complexes. The Pd1/trzn-COF catalyst is found to have a high catalytic activity for CO oxidation via a plausible tri-molecular Eley-Rideal(TER) reaction mechanism. This work provides insights into the d–π interaction between Pd SAs and trznCOF, and helps to better understand and design new SACs supported on COF nanomaterials.

In-situ electrochemical activation designed hybrid electrocatalysts for water electrolysis

Developing transition metal-based electrocatalysts with rich active sites for water electrolysis plays important roles in renewable energy fields. So far, some strategies including designing nanostructures, incorporating conductive support or foreign elements have been adopted to develop efficient electrocat- alysts. Herein, we summarize recent progresses and propose in-situ electrochemical activation as a new pretreating technique for enhanced catalytic performances. The activation techniques mainly comprise facile electrochemical processes such as anodic oxidation, cathodic reduction, etching, lithium-assisted tuning and counter electrode electro-dissolution. During these electrochemicaI treatments, the catalyst surfaces are modified from bulk phase, which can tune local electronic structures, create more active spe- cies. enlarge surface area and thus improve the catalytic performances. Meanwhile, this technique can couple the atomic, electronic structures with electrocatalysis mechanisms for water splitting. Compared to traditional chemical treatment, the in-situ electrochemical activation techniques have superior advantages such as facile operation, mild environment, variable control, high efficiency and flex- ibility. This review may provide guidance for improving water electrolysis efficiencies and hold promis- ing for application in many other energy-conversion fields such as supercapacitors, fuel cells and batteries.

Fractionated and Confined Crystallization of Polybutene-1 in Immiscible Polypropylene/Polybutene-1 Blends

In this work, the crystallization of immiscible polypropylene （PP）/polybutene-1 （PB） blends, in particular the effect of crystal morphology of PP （HTC, high Tm component） on the subsequent crystallization behavior of PB （LTC, low Tm component） was studied. Herein, we firstly indicated that PP/PB blends were not completely compatible but characterized as the LCST-like phase diagram above the melting temperature of PP. Crystallization of PP at different crystallization temperatures brought about different PP crystal morphologies and PB was segregated and confined at different locations. Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature. As temperature continued to fall below Tm of PB, the fractionated and confined crystallization of PB occurred in the framework of PP spherulites, reflected by the decreased crystallization temperature （To） of PB and the formation of form I＇ beside form II. Notably, if PP previously crystallized at high Tc, fractionated crystallization of PB became predominant and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.

Polymerization Kinetics of Propylene with the MgCl_(2)-Supported Ziegler-Natta Catalysts——Active Centers with Different Tacticity and Fragmentation of the Catalyst

The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_(4)/MgCl_(2) Ziegler-Natta(Z-N) catalysts are determined by the structure and nature of active centers, which are mysterious and fairly controversial. In this work, the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers [C*] with different tacticity. SEM was applied to characterize the catalyst morphologies and growing polypropylene(PP) particles. The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS. The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method. The catalytic activity, active centers with different tacticity and propagation rate constant kp, fragmentation of the catalyst, crystalline structure of PP are correlated with temperature and time for propylene polymerizations. The polymerization temperature and time show complex influences on the propylene polymerization. The higher polymerization temperature(60 ℃) resulted higher activity, kp and lower [C*], and the isotactic active centers Ci* as the majority ones producing the highest isotactic polypropylene(iPP) components showed much higher kp when compared with the active centers with lower stereoselectivity. Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation. This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles, and provide the solutions to the improvement of catalyst activity and isotacticity of PP.

Structure and Properties of Isotactic Polypropylene/Polybutene-1 In-reactor Alloys

The composition and structure of polymer largely determine the properties of its final products.As a novel polymer material,the composition,structure,and properties of the isotactic polypropylene/polybutene-1 in-reactor alloy(PPIPB alloy)synthesized by sequential two-stage polymerization with Ziegler-Natta catalyst were correlated for the first time in this work.The iPP/PB alloy was fractionated by temperature rising elution fractionation(TREF)in a broad temperature ranged from-30℃ to 140℃,and the chain microstructures and sequence distributions of isolated fractions were analyzed by DSC,GPC,13C-NMR,and FTIR.The iPP/IPB alloy was composed of five components,namely high isotactic PB(PB,85.8 wt96),medium isotactic PB(mPB,5.1 wt%),polyl(butene-1)-block propylene copolymers(PB-6 PP,4.1 wt%6)which contained PB and PP blocks with dfferent lengths according to the isolation temperature,isotactic PP(iPP,2.7 wt%6),and atactic PB(aPB,2.3 wt96).Compared to other commercial pipe materials,the P/iPB alloy presented outstanding thermal creep resistance and gas permeability resistance,high strength and low deformation at high temperature,and appropriate flexural strength.The roles of PP and PB-b-PP components in the alloy were interpreted.This work is expected to elucidate the potential application of PPIPB aloy as pipe materials and provide solutions for the design and synthesis of high performance pipe materials.

Fabrication of Trans-1,4-polyisoprene Nanofibers by Electrospinning and Its Crystallization Behavior and Mechanism

Trans-1,4-polyisoprene（TPI） nanofibers have been fabricated successfully through electrospinning technology.Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly of β phase were produced. Morphology and diameter of TPI nanofibers can be controlled by adjusting the electrospinning conditions. The in situ observations of FTIR spectra revealed that the crystallinity of the TPI fibers decreased with aging. While for TPI nanofibers aging at 45 °C for 24 h, a decrease in crystallinity as well as β to a transformation was observed with aging and these changings happened in the first 50 h during aging. The mechanism for β-TPI formation during electrospinning process and the reduced crystallinity with aging were proposed.