Water induced phase segregation in hydrocarbon proton exchange membranes

Proton exchange membranes （PEMs） are a key material for proton exchange membrane fuel cells （PEM-FCs）, Non-fluorinated hydrocarbon PEMs are low-cost alternatives to Nation, but limited by the low pro-ton conductivity, because of the weak phase segregation structure and narrow ion-transport channels.Various efforts have been taken to improve the performance of hydrocarbon PEMs, but mostly with com-plex methodologies. Here we demonstrate a simple, yet very efficient method to create phase segrega-tion structure inside a typical hydrocarbon PEM, sulfonated poly（ether ether ketone） （SPEEK）. By sim-ply adding appropriate amounts of water into the DMF solvent, the resulting SPEEK membrane exhibitswidened ion-transport channels, with the phase size of 2.7 nm, as indicated by both molecular dynamic（MD） simulations and transmission electron microscope （TEM） observations, and the proton conductivityis thus improved by 200%. These findings not only further our fundamental understanding of hydrocarbonPEMs, but are also valuable to the development of low-cost and practical fuel cell technologies.

Preventing inhomogeneous elemental distribution and phase segregation in mixed Pb-Sn inorganic perovskites via incorporating PbS quantum dots

Inhomogeneous Pb/Sn elemental distribution and the resulted phase segregation in mixed Pb-Sn halide perovskites would result in energy disorder(band structure and phase distribution disorder),which greatly limits their photovoltaic performance.Here,Pb S quantum dot has been synthesized and demonstrated as seeds for modulation crystallization dynamics of the mixed Pb-Sn inorganic perovskites,allowing an enhanced film quality and significantly suppressing phase segregation.With this additive power conversion efficiency of 8%and 6%is obtained under irradiation of full sunlight in planar and mesoporous structured solar cells in combination with CsPb_(0.5) Sn_(0.5)I_(2)Br inorganic perovskite,respectively.Our finding reveals exploring the actual Pb/Sn atoms location in perovskite structure and its influence on developing efficient and stable low-bandgap perovskite solar cells.

Suppressed light-induced phase transition of CsPbBr_(2)I: Strategies, progress and applications in the photovoltaic field

The rapid rise in the power conversion efficiency(PCE)of CsPbBr_(2)I-based perovskite solar cells(PSCs),from 4.7%in 2016 to 11.08%in 2020,render it a promising material for use in photovoltaic devices.However,the phase stability and current hysteresis caused by photo-induced phase segregation in CsPbBr_(2)I represent major obstacles to further improvements in the PCE for such devices.In this review,we describe the basic structure and optical properties of CsPbBr_(2)I,and systematically elaborate on the mechanism of the phase transition.We then discuss the strategies in progress to suppress phase transition in CsPbBr_(2)I,and their potential application in the photovoltaic field.Finally,challenges and application prospects for CsPbBr2I PSCs are summarized in the final section of this article.

Moisture-Induced Non-Equilibrium Phase Segregation in Triple Cation Mixed Halide Perovskite Monitored by In Situ Characterization Techniques and Solid-State NMR

Environmental stability is a major bottleneck of perovskite solar cells.Only a handful of studies are investigating the effect of moisture on the structural degradation of the absorber.They mostly rely on ex situ experiments and on completely degraded samples,which restrict the assessment on initial and final stage.By combining in situ X-ray diffraction under controlled 85%relative humidity,and live observations of the water-induced degradation using liquid-cell transmission electron microscopy,we reveal two competitive degradation paths leading on one hand to the decomposition of state-of-theart mixed cation/anion(Cs_(0.05)(MA_(0.17)FA_(0.83))_(0.95)Pb(Br_(0.17)I_(0.83))_(3)(CsMAFA)into PbI_(2) through a dissolution/recrystallization mechanism and,on the other hand,to a non-equilibrium phase segregation leading to CsPb_(2)Br_(5) and a Cesium-poor/iodide-rich Cs_(0.05)-x(MA_(0.17)FA_(0.83))_(0.95)Pb(Br_(0.17-2y)I_(0.83)+2y)_(3) perovskite.This degradation mechanism is corroborated at atomic-scale resolution through solid-state ^(1)H and ^(133)Cs NMR analysis.Exposure to moisture leads to a film containing important heterogeneities in terms of morphology,photoluminescence intensities,and lifetimes.Our results provide new insights and consensus that complex perovskite compositions,though very performant as champion devices,are comparatively metastable,a trait that limits the chances to achieve long-term stability.

PHASE INTERFACE SEGREGATION OF Mg IN A Ni-BASE SUPERALLOY IN100

The segregation of Mg to phase interfaces in a nickel base superalloy IN 100 has been investi- gated using EPT(Electron Microprobe Technique).AES(Auger Electron Spectroscopy) and EDS analyses on thin TEM film.The results show that Mg segregates to the phase inter- faces of MC/γ and γ′/γ.The segregation concentration and layer thickness of Mg on MC/γ phase interface are larger than that on γ′/γ phase interface.Mg is not only a grain boundary segregation element,but also a phase interface segregation one.

A-site phase segregation in mixed cation perovskite

Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability.However,adverse impact also accompanies the mixed cation system simultaneously.It brings the compositional instability,wherein the homogeneous film is likely to segregate into multi-phases during the fabrication and ageing process,thus resulting in the efficiency reduction of perovskite solar cells(PSCs)devices.This review focuses on the cation induced phase segregation,and elucidates the segregation mechanisms from the perspectives of film formation and ageing process,respectively.Furthermore,the influence of cation segregation on device performance and operational stability are discussed.And based on these understandings,viable strategies are proposed for the design of phase-stable mixed composition halide perovskites and for suppressing segregation to benefit its development towards commercial applications.

Phase Behaviors in Bi-phase Simulation of Powder Segregation in Metal Injection Molding

Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. Wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.

Effect of phosphorus segregation on as-cast microstructure and homogenization treatment of IN706 alloy

The distribution of phosphorus in IN706 alloy was studied,with particular emphasis on the as-cast microstructure and homogenization treatment.It is found that phosphorus is segregated in Laves phase and markedly influences the as-cast microstructure of IN706 alloy.Phosphorus retards the formation of Laves phase with the eutectic form,but promotes the Laves formation with the blocky form.Phosphorus refines the dendritic structure and noticeably enlarges the interdendritic area.The reason for phosphorus influencing the as-cast microstructure is attributed to its extremely low solubility in γ matrix and great retarding effect on γ matrix solidification.In addition,phosphorus slightly decreases the melting temperature of Laves phase,and retards the dissolution of Laves phase and the element diffusion between dendrite core and interdendritic area during the homogenization treatment.And it is thought that phosphorus delays the homogenization process by inhibiting the element diffusion.

Investigation on the homogenization treatment and element segregation on the microstructure of a γ/γ′-cobalt-based superalloy

The aim of the present study was to investigate the effect of element segregation on the microstructure and γ′ phase in a γ/γ′ cobalt-based superalloy. Several samples were prepared from a cast alloy and homogenized at 1300°C for different times, with a maximum of 24 h. A microstructural study of the cast alloy using wavelength-dispersive spectroscopic analysis revealed that elements such as Al, Ti, and Ni segregated mostly within interdendritic regions, whereas W atoms were segregated within dendrite cores. With an increase in homogenization time, segregation decreased and the initial dendritic structure was eliminated. Field-emission scanning electron microscopy micrographs showed that the γ′ phases in the cores and interdendritic regions of the as-cast alloy were 392 and 124 nm, respectively. The size difference of γ′ was found to be due to the different segregation behaviors of constituent elements during solidification. After homogenization, particularly after 16 h, segregation decreased; thus, the size, chemical composition, and hardness of the precipitated γ′ phase was mostly uniform throughout the samples.

Relieving segregation in twin-roll cast Mg-8Al-2Sn-1Zn alloys via controlled rolling

Twin-roll casting(TRC)of Mg alloys with high Al content has unique advantages and broad development prospects.However,the severe segregation of high-alloyed Mg caused by TRC technology is difficult to solve at present,which restricts its practical application.In this work,the homogenization of coarse segregated phases in a twin-roll cast Mg-8Al-2Sn-1Zn(ATZ821)alloy was successfully achieved by a method combining solid-solution heat treatment and controlled rolling,which is suitable for industrial-scale production.In addition,the evolution of the microstructure was studied in detail.It was found that phases dynamically precipitated and dissolved repeatedly during the hot rolling process,and the evolution of entire second phases can be classified into three stages,i.e.,the net dissolution,balancing and net precipitation stages.During the process,the large-size chain-like eutectic phases evolved into a fine and nearly spherical(∼0.4μm)morphology that was uniformly dispersed in the Mg-matrix due to the thermodynamic coupling and the Ostwald ripening effect.Moreover,a fine grain microstructure(∼4μm)was obtained.The formidable segregation problem of twin-roll cast Mg alloys with high Al content was solved,which is an important finding for the industrial application of high-alloyed twin-roll cast sheets.©2020 Published by Elsevier B.V.on behalf of Chongqing University.

Integral PVA-PES Composite Membranes by Surface Segregation Method for Pervaporation Dehydration of Ethanol

A facile surface segregation method was utilized to fabricate poly（vinyl alcohol）-polyethersulfone （PVA-PES） composite membranes. PVA and PES were first dissolved in dimethyl sulfoxide （DMSO）, then casted on a glass plate and immersed in a coagulation bath. During the phase inversion process in coagulation bath, PVA spontaneously segregated to the polymer solution/coagulation bath interface. The enriched PVA on the surface was further crosslinked by glutaraldehyde. Scanning electron microscopy （SEM）, X-ray photoelectron spectroscopy （XPS） and energy dispersive spectrometer （EDS） confirmed the integral and asymmetric membrane structure with a dense PVA-enriched surface and a porous PES-enriched support, as well as the surface enrichment of PVA. The coverage fraction of the membrane surtace by PVA reacned up to 86.8% when me PVA content m me membrane recipe was 16.7% （by mass）. The water contact angle decreased with the increase of PVA content. The effect of coagulation bath type on membrane structure was analyzed. The membrane pervaporation performance was evaluated by varying the PVA content, the annealing temperature, feed concentration and operation temperature. The membrane exhibited a fairly good ethanol dehydration capacity and long-term operational stability.

Effect of magnetic field on segregation behavior of α-Fe particles in Cu-Fe thin film prepared by magnetron sputtering

The segregation behavior of α-Fe particles in Cu-Fe film prepared by magnetron sputtering was studied by X-ray scattering and X-ray diffraction. The results show that the roughness of the film surface increases with the sputtering time increasing. The as-sputtered films are super saturation solid solution of Cu-Fe. After annealing at 500℃, α-Fe particle can be segregated from the Cu matrix. The orientations α-Fe particles in the annealed film without magnetic field are random. But the clear texture of α-Fe particles in the annealed film with magnetic field is formed, and the 〈001〉 direction of α-Fe particles tends to be parallel to the magnetic field direction.

Premature failure induced by non-equilibrium grain-boundary tantalum segregation in air-plasma sprayed ZrO_(2)-YO_(1.5)-TaO_(2.5)thermal barrier coatings

ZrO_(2)-YO_(1.5)-TaO_(2.5)(ZYTO)is a promising top-coat material for thermal barrier coatings(TBCs).The bulk properties of ZYTO have been reported by several studies,but its performances as TBCs are less-well understood.In this work,ZYTO TBCs were prepared by air plasma spraying(APS)and their thermal cycling performances were investigated at 1150℃.Despite of the good bulk properties,APS ZYTO TBCs present an extremely short thermal fatigue life.This is attributed to the non-equilibrium grain-boundary segregation of TaO_(2.5) induced by limited solubility and rapid quenching during APS process,resulting in a tetragonal(t)to cubic(c)and metastable-tetragonal(tm)phase transformation in ZYTO TBCs.The volume shrinkage(~0.74vol%)of phase transformation leads to many cracks at the c/tm phase boundaries after deposition.On the other hand,the formation of cubic phase with massive grain-boundary Ta segregation induces a large intergranular embrittlement and a weak bonding strength(~5.3 MPa),resulting in the premature failure of the ZYTO TBCs.

A Quantitative Analysis of Mn Segregation at Partitioned Ferrite/Austenite Interface in a Fe-C-Mn-Si Alloy

Mn segregation at austenite/ferrite interface is studied in a Fe-C-Mn-Si alloy held at 656℃. Mn is partitioned during the growth of ferrite and as a result, a Mn pile-up exists in front of interface on the matrix side. An approach to evaluate Mn segregation quantitatively is developed by combining STEM raster window scanning and simulation of the interaction of the electron beam with the sample to subtract the contribution of Mn pile-up and obtain pure Mn segregation value. The evaluated maximum Mn interfacial segregation is in the order of a half-monolayer.

Phase-stable wide-bandgap perovskites enabled by suppressed ion migration

Wide-bandgap(>1.7 eV)perovskites suffer from severe light-induced phase segregation due to high bromine content,causing irreversible damage to devices stability.However,the strategies of suppressing photoinduced phase segregation and related mechanisms have not been fully disclosed.Here,we report a new passivation agent 4-aminotetrahydrothiopyran hydrochloride(4-ATpHCl)with multifunctional groups for the interface treatment of a 1.77-eV wide-bandgap perovskite film.4-ATpH^(+)impeded halogen ion migration by anchoring on the perovskite surface,leading to the inhibition of phase segregation and thus the passivation of defects,which is ascribed to the interaction of 4-ATpH^(+)with perovskite and the formation of low-dimensional perovskites.Finally,the champion device achieved an efficiency of 19.32%with an open-circuit voltage(V_(OC))of 1.314 V and a fill factor of 83.32%.Moreover,4-ATpHCl modified device exhibited significant improved stability as compared with control one.The target device maintained 80%of its initial efficiency after 519 h of maximum power output(MPP)tracking under 1 sun illumination,however,the control device showed a rapid decrease in efficiency after 267 h.Finally,an efficiency of 27.38%of the champion 4-terminal all-perovskite tandem solar cell was achieved by mechanically stacking this wide-bandgap top subcell with a 1.25-eV low-bandgap perovskite bottom subcell.

Photoinduced phase segregation in wide-bandgap mixed-halide perovskite solar cells

Wide-bandgap(WB)mixed-halide perovskite solar cells(PSCs)play a crucial role in perovskite-based tandem solar cells(TSCs),enabling them to exceed the Shockley-Queisser limits of single-junction solar cells.Nonetheless,the lack of stability in WB perovskite films due to photoinduced phase segregation undermines the stability of WB PSCs and their TSCs,thus impeding the commercialization of perovskite-based TSCs.Many efforts have been made to suppress photoinduced phase segregation in WB perovskite films and significant progresses have been obtained.In this review,we elaborate the mechanisms behind photoinduced phase segregation and its impact on the photovoltaic performance and stability of devices.The importance role of advanced characterization techniques in confirming the photoinduced phase segregation are comprehensively summarized.Beyond that,the effective strategies to alleviate photoinduced phase segregation in WB mixed halide PSCs are systematically assessed.Finally,the prospects for developing highly efficient and stable WB PSCs in tandem application are also presented.

Phase transformation and liquid density redistribution during solidification of Ni-based superalloy Inconel 718

The influences of chemical segregation and phase transformation on liquid density variation during solidification of Ni-based supperalloy Inconel 718 were investigated using SEM and EDS. It was found that significant segregation in liquid prompts high Nb phase to precipitate directly from liquid, which results in the redistribution of alloy elements and liquid density in their vicinity. The term "inter-precipitate liquid density" is therefore proposed and this concept should be applied to determine the solidification behavior of superalloy Inconel 718.

Microscopic phase-field simulation of ordered domain interfaces formed between DO_(22) phases along [100] direction

Ordered domain interfaces formed between DO22 (Ni3V) phases along [100] direction during the precipitation process of Ni75AlxV25-x alloys were simulated by using the microscopic phase-field model. The atomic structure, migration process, and compositions of interfaces were investigated. It is found that there are four kinds of stable ordered domain interfaces formed between DO22 phases along [100] direction and all of them can migrate. During the migration of interfaces, the jump of atoms shows site selectivity behaviors and each stable interface forms a distinctive transition interface. The atom jump selects the optimist way to induce the migration of interface, and the atomic structures of interfaces retain the same before and after the migration. The alloy elements have different preferences of segregation or depletion at different interfaces. At all the four kinds of interfaces, Ni and Al segregate but V depletes. The degrees of segregation and depletion are also different at different interfaces.

THE MINIMUM SQUARED EUCLIDEAN DISTANCE OF MULTI-h PHASE CODES

The minimum squared Euclidean distance(MSED) of binary multi-h phase codes is presented. The signal segregation degree(SSD) has been put forward to determine MSED of multi-h phase codes. In order to maximize MSED, SSD should be as large as possible. The necessary and sufficient conditions of maximizing SSD are derived. Finally, SSD and the exact formulae for MSED of binary 2-h phase codes are also presented.

阳极氧化后某2A12铝合金零件表面缺陷的成因

阳极氧化后某2A12铝合金零件膜层异常发亮、存在表面缺陷。采用光学显微镜、扫描电子显微镜、能谱仪、X射线衍射仪等分析技术,研究了阳极氧化后零件膜层颜色异常,显现出线条状缺陷的原因。结果表明:该铝合金基体存在富铜偏析相和夹杂相,在阳极氧化过程中,基体中的偏析相优先溶解,杂质相不被氧化,导致阳极氧化膜不均匀,膜层局部区域出现孔洞和夹杂物。