Striking Stabilization Effect of Spinel Cobalt Oxide Oxygen Evolution Electrocatalysts in Neutral pH by Dual-Sites Iron Incorporation

Developing stable and efficient nonprecious-metal-based oxygen evolution catalysts in the neutral electrolyte is a challenging but essential goal for various electrochemical systems.Particularly,cobalt-based spinels have drawn a considerable amount of attention but most of them operate in alkali solutions.However,the frequently studied Co-Fe spinel system never exhibits appreciable stability in nonbasic conditions,not to mention attract further investigation on its key structural motif and transition states for activity loss.Herein,we report exceptional stable Co-Fe spinel oxygen evolution catalysts(~30%Fe is optimal)in a neutral electrolyte,owing to its unique metal ion arrangements in the crystal lattice.The introduced iron content enters both the octahedral and tetrahedral sites of the spinel as Fe^(2+)and Fe^(3+)(with Co ions having mixed distribution as well).Combining density functional theory calculations,we find that the introduction of Fe to Co_(3)O_(4)lowers the covalency of metal-oxygen bonds and can help suppress the oxidation of Co^(2+/3+)and 0^(2-).It implies that the Co-Fe spinel will have minor surface reconstruction and less lattice oxygen loss during the oxygen evolution reaction process in comparison with Co_(3)O_(4)and hence show much better stability.These findings suggest that there is still much chance for the spinel structures,especially using reasonable sublattices engineering via multimetal doping to develop advanced oxygen evolution catalysts.

Sr含量对Al-Si合金显微组织和热导率的影响

以纯铝、Al-20Si和Al-10Sr中间合金为原料,Sr为变质剂(含量为0.01%、0.02%、0.04%和0.06%,质量分数),制备了Al-7Si-xSr、Al-12Si-xSr和Al-20Si-xSr合金,研究了Sr含量对Al-Si合金相变储热材料显微组织及热导率的影响。利用Hot Disk热常数分析仪测量合金的热导率,通过扫描电镜观察及分析合金的显微组织。结果表明:在Al-Si合金中添加变质元素Sr会影响合金的热导率,Al-7Si-0.04Sr合金热导率较Al-7Si合金增加了73.47 W·m^(-1)·K^(-1),Al-20Si-0.04Sr合金的热导率较Al-20Si合金增加了24.09 W·m^(-1)·K^(-1),Al-12Si-0.04Sr合金的热导率较Al-12Si合金增加了17.79 W·m^(-1)·K^(-1)。铝硅合金热导率的增长主要与α(Al)、共晶硅和初晶硅的形貌有关。经过Sr变质之后,Al-7Si合金中共晶Si立体形貌均由片层状转变为珊瑚状,Al-12Si和Al-20Si合金中共晶Si立体形貌由片层状转变为枝条状;其中,Al-7Si合金中α(Al)尺寸明显减少、排列紧密,二次枝晶臂间距逐渐减小;Al-20Si合金中的初晶Si尺寸明显减小,其形貌由多角的大块状变为小块状;α(Al)形态的转变不仅能够为自由电子的传输提供快速通道,而且还会使得共晶Si的排列更加规则,减少自由电子发生散射的几率,对合金的热导率影响较大。共晶Si由片层状转变为珊瑚状或枝条状,增加电子的平均自由程,有利于电子的传输。Al-20Si合金的热导率与初晶Si的形态有着重要联系,大尺寸且形状完整的初晶Si会发生晶格振动,会提高合金的热导率。

Al-Si镀层22MnB5激光焊的熔池流动特性及元素分布

熔池流动行为对镀层元素在焊缝中的分布起决定性作用.采用建立激光焊熔池三维瞬态数值模型的方法,分析AlSi镀层22MnB5高强度钢激光焊的熔池流动行为及其对焊缝中Al元素分布的影响规律.在焊接试验中,根据能谱仪对焊接接头的扫描数据验证数值模型的可靠性.结合模拟结果与试验结果对激光焊熔池流动行为及焊缝Al元素分布规律进行研究.结果表明,根据激光焊热输入与功率密度阈值的不同,熔池形貌呈现无匙孔、未完全贯穿匙孔和完全贯穿匙孔3种特征,并存有不同的温度场、流场、流速和稳定性.无匙孔熔池由于流速分布均匀,涡流产生较少,稳定性最好.镀层Al元素在焊接接头上下焊趾区域易产生偏聚,较之上表面镀层,下表面镀层进入熔池后Al元素偏聚现象更明显.因此,上部Al元素均质化分布显著优于下部.

SiCp/Al-Si基复合材料界面结构调控及强化机制的研究进展

SiCp/Al-Si基复合材料具有高的比强度、比刚度、比模量,良好的导热、导电、耐磨性及尺寸稳定性等优点,作为结构功能性材料应用于空间工程、电子封装、交通运输和精密仪器等领域。其研究热点主要集中在界面结构调控、强化机制及性能调控等方面。在SiCp/Al-Si复合材料中存在着增强体与基体界面、析出相与基体界面、析出相与增强体界面,这些界面受各种因素影响,会出现多种界面反应和界面产物,界面结构和结合状态复杂而多样。基于此,本文综述了制备工艺、基体合金成分和SiCp表面改性等方面对SiCp/Al-Si基复合材料界面结构的影响及调控,并总结了影响其力学性能的因素及强化机制的研究现状,最后对复合材料未来的发展及研究方向进行了展望。

Si含量对Al-Si-Cu-Ni-Mg合金组织和性能的影响

采用搅拌铸造工艺制备不同Si含量合金,旨在揭示Si含量对Al-Si-Cu-Ni-Mg合金微观组织、力学性能和耐磨性的影响。结果表明,随着Si含量升高,合金中共晶Si长径比和平均长度先升高后降低,Si含量为16wt.%合金的长径比和平均长度最大,分别为8.8μm、24.1μm。经过520℃/6 h固溶+180℃/5 h时效处理后,共晶Si形貌由纤维状变为球状,初晶Si棱角钝化。合金中共晶Si长径比和平均长度均有明显降低,保持与铸态合金相同的变化趋势;Si含量为16wt.%合金的长径比和平均长度分别为3.5μm、12.4μm,初晶Si尺寸没有明显变化。随着Si含量的升高,铸态合金拉伸性能逐渐降低,宏观硬度逐渐上升。经过T6热处理后,合金的拉伸性能和宏观硬度有了明显提升,保持与铸态合金相同的变化趋势,随着Si含量的升高,合金磨损失重减少,耐磨性得到改善。Si含量为16wt.%的合金磨损失重最少,耐磨性最好;继续增加Si含量时,合金耐磨性降低。

固溶处理对铸造Al-Si合金相选择再结晶的影响

相选择再结晶在Al-Si合金中基于应变分配原理实现对软相进行再结晶、硬相进行回复从而球化硅相和细化铝相。相选择再结晶处理后合金呈现出高的加工硬化率和伸长率。固溶处理是实现铝合金强韧化的重要环节,与相选择再结晶互相影响。一方面,初始组织对相选择再结晶的应变分配有一定影响;另一方面铝合金固溶过程会影响析出强化作用。因此,本文探究铸造Al-7Si-0.65Mg合金固溶过程中共晶硅相的形貌对相选择再结晶的影响,结合时效析出实现合金的强韧化。结果表明,0.5 h短时间固溶处理可以保持相选择再结晶合金中清晰且不分散的共晶硅颗粒骨架状结构,同时增加基体中Si和Mg含量促进强化相Mg2Si析出,使合金屈服强度达到300 MPa,断后伸长率为9.5%,显著优于传统T6态。

Mn元素对Al-Si合金富铁相析出影响的热力学计算

本研究选取不同Mn元素含量的Al-7 wt%Si-0.2 wt%Fe铝液为研究对象,利用热力学软件定量计算了Mn元素添加量对铝液Scheil-Gulliver冷却凝固过程的析出相。结果表明:不同Mn元素含量的铝液冷却过程中相转变顺序有所不同,添加一定量的Mn元素可利于铝液凝固过程中析出Al3MnSi2相;添加Mn元素并不会大幅减少完全凝固后β-AlFeSi相的质量比,且不同Mn元素含量的铝合金中β-AlFeSi相质量比相差不超过1%,说明难以通过添加Mn元素来减少铝液完全凝固后的β-AlFeSi相质量比;铝液凝固末期,β-AlFeSi与Al3MnSi2发生共晶反应,Al3MnSi2对β-AlFeSi的形貌可能具有改性作用,是β-AlFeSi与Al3MnSi2的共晶相呈现出不规则形状的主要原因。

Healing the structural defects of spinel MnFe_(2)O_(4) to enhance the electrocatalytic activity for oxygen reduction reaction

Spinel metal oxides containing Mn,Co,or Fe(AB_(2)O_(4),A/B=Mn/Fe/Co)are one of the most promising nonPt electrocatalysts for oxygen reduction reaction(ORR)in alkaline conditions.However,the low conductivity of metal oxides and the poor intrinsic activities of transition metal sites lead to unsatisfactory ORR performance.In this study,eutectic molten salt(EMS)treatment is employed to reconstruct the atomic arrangement of MnFe_(2)O_(4)electrocatalyst as a prototype for enhancing ORR performance.Comprehensive analyses by using XAFS,soft XAS,XPS,and electrochemical methods reveal that the EMS treatment reduces the oxygen vacancies and spinel inverse in MnFe_(2)O_(4)effectively,which improves the electric conductivity and increases the population of more catalytically active Mn^(2+)sites with tetrahedral coordination.Moreover,the enhanced Mn-O interaction after EMS treatment is conducive to the adsorption and activation of O_(2),which promotes the first electron transfer step(generally considered as the ratedetermining step)of the ORR process.As a result,the EMS treated MnFe_(2)O_(4)catalyst delivers a positive shift of 40 mV in the ORR half-wave potential and a two-fold enhanced mass/specific activity.This work provides a convenient approach to manipulate the atomic architecture and local electronic structure of spinel oxides as ORR electrocatalysts and a comprehensive understanding of the structureperformance relationship from the molecular/atomic scale.

Effects of iron oxide on crystallization behavior and spatial distribution of spinel in stainless steel slag

Chromium plays a vital role in stainless steel due to its ability to improve the corrosion resistance of the latter.However,the re-lease of chromium from stainless steel slag(SSS)during SSS stockpiling causes detrimental environmental issues.To prevent chromium pollution,the effects of iron oxide on crystallization behavior and spatial distribution of spinel were investigated in this work.The results revealed that FeO was more conducive to the growth of spinels compared with Fe2O3 and Fe3O4.Spinels were found to be mainly distrib-uted at the top and bottom of slag.The amount of spinel phase at the bottom decreased with the increasing FeO content,while that at the top increased.The average particle size of spinel in the slag with 18wt%FeO content was 12.8μm.Meanwhile,no notable structural changes were observed with a further increase in FeO content.In other words,the spatial distribution of spinel changed when the content of iron oxide varied in the range of 8wt%to 18wt%.Finally,less spinel was found at the bottom of slag with a FeO content of 23wt%.

Microwave-assisted exploration of the electron configuration-dependent electrocatalytic urea oxidation activity of 2D porous NiCo_(2)O_(4) spinel

Urea holds promise as an alternative water-oxidation substrate in electrolytic cells.High-valence nickelbased spinel,especially after heteroatom doping,excels in urea oxidation reactions(UOR).However,traditional spinel synthesis methods with prolonged high-temperature reactions lack kinetic precision,hindering the balance between controlled doping and highly active two-dimensional(2D)porous structures design.This significantly impedes the identification of electron configuration-dependent active sites in doped 2D nickel-based spinels.Herein,we present a microwave shock method for the preparation of 2D porous NiCo_(2)O_(4)spinel.Utilizing the transient on-off property of microwave pulses for precise heteroatom doping and 2D porous structural design,non-metal doping(boron,phosphorus,and sulfur)with distinct extranuclear electron disparities serves as straightforward examples for investigation.Precise tuning of lattice parameter reveals the impact of covalent bond strength on NiCo_(2)O_(4)structural stability.The introduced defect levels induce unpaired d-electrons in transition metals,enhancing the adsorption of electron-donating amino groups in urea molecules.Simultaneously,Bode plots confirm the impact mechanism of rapid electron migration caused by reduced band gaps on UOR activity.The prepared phosphorus-doped 2D porous NiCo_(2)O_(4),with optimal electron configuration control,outperforms most reported spinels.This controlled modification strategy advances understanding theoretical structure-activity mechanisms of high-performance 2D spinels in UOR.

Unveiling the geometric site dependent activity of spinel Co_(3)O_(4)for electrocatalytic chlorine evolution reaction

Spinel cobalt oxide(Co_(3)O_(4)),consisting of tetrahedral Co^(2+)(CoTd)and octahedral Co^(3+)(CoOh),is considered as promising earth-abundant electrocatalyst for chlorine evolution reaction(CER).Identifying the catalytic contribution of geometric Co site in the electrocatalytic CER plays a pivotal role to precisely modulate electronic configuration of active Co sites to boost CER.Herein,combining density functional theory calculations and experiment results assisted with operando analysis,we found that the Co_(Oh) site acts as the main active site for CER in spinel Co_(3)O_(4),which shows better Cl^(-)adsorption and more moderate intermediate adsorption toward CER than CoTd site,and does not undergo redox transition under CER condition at applied potentials.Guided by above findings,the oxygen vacancies were further introduced into the Co_(3)O_(4) to precisely manipulate the electronic configuration of Co_(Oh) to boost Cl^(-)adsorption and optimize the reaction path of CER and thus to enhance the intrinsic CER activity significantly.Our work figures out the importance of geometric configuration dependent CER activity,shedding light on the rational design of advanced electrocatalysts from geometric configuration optimization at the atomic level.

Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

The Spectral Characterization of Blue Spinel and Other Blue Gemstones with the Alexandrite Effect

In gemmology,the term“Alexandrite effect”is used to describe colour change phenomenon when a gemstone is observed under different light sources,usually between daylight and incandescent light.The definition of the Alexandrite effect is constantly being broadened with new discovery of gem resource.The traditional definition of the Alexandrite effect attributing the colour change phenomenon to the presence of two maximum transmission regions and a maximum absorption region in the absorption spectra.In this study,7 blue spinels and 5 blue gemstones(including tanzanite,kyanite,fluorite,and 2 sapphires)showing the Alexandrite effect were investigated.The goal is to explain the cause of blue-to-violet Alexandrite effect and the spectral features causing such colour change.In the UV-Vis spectra,all samples showed a maximum absorption peak in the range of 534-610 nm,within the green region to orange region.The traditional explanation of green to red Alexandrite effect required a transmission window in the red region;however,some of our samples did not show this transmission window and the blue-to-violet Alexandrite effect was still visible.Therefore,it is incomplete to explain the mechanism of the Alexandrite effect according to their characteristic absorption spectra,a systematic study based on modern colour science and colour perception in human vision is required to elucidate the blue-to-violet Alexandrite effect.

Al-Si合金大型薄壁铸件抗变形工艺研究

使用Novacast软件模拟了铸件充型和凝固过程,采用3DP砂型打印机生产砂芯,在差压设备炉中进行熔炼浇注。由于舱体内部无凸台及环筋,在铸造及热处理过程中容易发生热变形,针对该问题修改工艺方案,在舱体外表面增加防变形环,防止铸件整体发生扭曲,对铸件增加防变形环状态进行模拟仿真,确保铸件内部质量符合要求,增加防变形工装后,内腔尺寸变形量控制在±0.5 mm,铸件尺寸得到保证,解决了该大型薄壁铝硅合金铸件铸造及热处理变形问题。

拉伸变形Al-Si合金中Si颗粒相对于晶粒旋转的原位证据

为确定Si颗粒在拉伸变形过程中是否相对于基体晶粒发生旋转,采用原位拉伸扫描电子显微镜(SEM)和离位背散射电子衍射(EBSD)相结合的方法,研究Al-Si合金在拉伸变形过程中Si颗粒旋转与晶粒旋转之间的关系。通过对比晶粒的EBSD三维取向的平面投影信息与Si颗粒的原位SEM信息,发现Si颗粒在样品表面的平面上具有明显的相对旋转。此外,根据EBSD数据的中心点平均取向差(KAM)分析,发现Si颗粒的较大相对旋转会引入更高密度的几何必需位错(GND),这会在颗粒附近的基体中产生较强的加工硬化效应。总之,Si颗粒的相对旋转度越大,加工硬化效果越强。

新型薄Al-Si镀层热成形高强钢的性能研究

为了突破传统Al-Si镀层热成形钢的专利限制,开发一种新型薄Al-Si镀层热成形钢,通过严格限定镀层厚度上下限来保证钢板的各项性能。采用拉力实验机验证新材料热成形前、后机械性能;采用金相显微镜验证热成形前、后的组织演变和镀层演变;采用盐雾试验来验证热冲压后的钢板耐腐蚀性能;采用现有生产线所使用的焊装胶来验证钢板的粘胶匹配性能;采用现生产涂装工艺来验证钢板的前处理兼容性和电泳漆性能。各项验证结果显示新型薄Al-Si镀层热成形钢满足机械性能、防氧化、耐腐蚀要求,同时与常规的焊装工艺和涂装工艺具备良好的兼容性。

液锻压力对亚共晶Al-Si合金吊架的组织与性能影响

研究了液态模锻工艺下,亚共晶Al-Si合金吊架在不同液锻压力下的成形质量、力学性能及不同位置处的微观组织。结果表明,随着压力的增加,铸件的成形质量逐渐提高,液锻压力为128 MPa时,抗拉强度为250.7 MPa,断后伸长率为9.7%,力学性能最好,较0 MPa下的抗拉强化及断后伸长率分别增加了14.5%和547%,之后再增加压力,对吊架的力学性能无明显强化效果。此外,随着压力的增加,晶粒得到细化,Si相逐渐球化,且高压力下团聚现象明显,二次枝晶臂间距(SDAS)先减小后基本保持不变,在154 MPa时取得最小值16.3μm,SDAS仅为0 MPa时的54.2%,比50 MPa液锻压力下SDAS减少24.5%,共晶团尺寸则是先减小再增大,共晶团尺寸为308μm时对基体产生割裂作用,从而影响力学性能。

Enabling structural and interfacial stability of 5 V spinel LiNi0.5Mn1.5O4 cathode by a coherent interface

Spinel LiNi_(0.5)Mn_(1.5)O_(4)(LNMO),a 5 V class high voltage cathode,has been regarded as an attractive candidate to further improve the energy density of lithium-ion battery.The issue simultaneously enabling side stability and maintaining high interfacial kinetics,however,has not yet been resolved.Herein,we design a coherent Li_(1.3)A_(l0.3)Ti_(1.7)(PO)_(4)(LATP)layer that is crystally connected to the spinel LNMO host lattices,which offers fast lithium ions transportation as well as enhances the mechanical stability that prevents the particle fracture.Furthermore,the inactive Li_(3)BO_(3)(LBO)coating layer inhibits the corrosion of transition metals and continuous side reactions.Consequently,the coherent-engineered LNMO-LATPLBO cathode material exhibits superior electrochemical cycling stability in a window of 3.0–5.0 V,for example a high-capacity retention that is 89.7%after 500 cycles at 200 m A g-1obtained and enhanced rate performance(85.1 m A h g^(-1)at 800 m A g^(-1))when tested with a LiPF6-based carbonate electrolyte.Our work presents a new approach of engineering 5 V class spinel oxide cathode that combines interfacial coherent crystal lattice design and surface coating.

电子封装用Al-Si功能梯度材料的显微组织和性能

通过喷雾沉积法制备用于电子封装的双层和三层Al-Si功能梯度材料。结果表明,梯度材料具有致密的显微组织和良好的层间结合。三层梯度材料的抗弯强度高于双层梯度材料,以高Si含量层为承载面的H-L方向的抗弯强度高于以低Si含量层为承载面的L-H方向。所有梯度材料的导热系数均超过140W/(m·K),且其热膨胀系数没有明显的差异。经热冲击处理后,双层梯度材料出现的裂纹比三层梯度材料更多更大,这是由于界面上的高热应力和大尺寸Si颗粒因应力集中而趋于破裂。

Effects of ZnO,FeO and Fe_(2)O_(3)on the spinel formation,microstructure and physicochemical properties of augite-based glass ceramics

Augite-based glass ceramics were synthesised using ZnO,FeO,and Fe_(2)O_(3)as additives,and the spinel formation,matrix structure,crystallisation thermodynamics,and physicochemical properties were investigated.The results showed that oxides resulted in numerous preliminary spinels in the glass matrix.FeO,ZnO,and Fe_(2)O_(3)influenced the formation of spinel,while FeO simplified the glass network.FeO and ZnO promoted bulk crystallisation of the parent glass.After adding oxides,the grains of augite phase were refined,and the relative quantities of augite crystal planes were also influenced.All samples displayed good mechanical properties and chemical stability.The 2wt%ZnO-doping sample displayed the maximum flexural strength(170.3 MPa).Chromium leaching amount values of all the samples were less than the national standard(1.5 mg/L),confirming the safety of the materials.In conclusion,an appropriate amount of zinc-containing raw material is beneficial for the preparation of augite-based glass ceramics.