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.

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.

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.

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.

Influence of TiO2 on the melting property and viscosity of Cr-containing high-Ti melting slag

A study on the melting and viscosity properties of the chromium-containing high-titanium melting slag(CaO–SiO2–MgO–Al2O3–TiO2–Cr2O3) with TiO2 contents ranging from 38.63 wt% to 42.63 wt% was conducted. The melting properties were investigated with a meltingpoint apparatus, and viscosity was measured using the rotating cylinder method. The FactSage 7.1 software and X-ray diffraction, in combination with scanning electron microscopy–energy-dispersive spectroscopy(SEM–EDS), were used to characterize the phase equilibrium and microstructure of chromium-containing high-titanium melting slags. The results indicated that an increase in the TiO2 content led to a decrease in the viscosity of the chromium-containing high-titanium melting slag. In addition, the softening temperature, hemispheric temperature, and flowing temperature decreased with increasing TiO2 content. The amount of crystallized anosovite and sphene phases gradually increased with increasing TiO2 content, whereas the amount of perovskite phase decreased. SEM observations revealed that the distribution of the anosovite phase was dominantly influenced by TiO2.

Oxidation Behaviour of Laser Remelted Cr-containing Steels

Laser surface remelting of steels with different Cr contents has been performed by using a CO_2 laser. The results of oxidation tests showed that the effects of laser remelting on the oxidation resistance of Cr-containing steels have close relation to the Cr contents and microstructures of the steels. The re- sistance to high temperature oxidation of 18-8 and HK40 at 1273 K can be obviously improved by laser remelting, whereas laser remelting showed little effect on the oxidation resistance of Fe-6Cr and Cr30 at 1173-1273 K.

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.

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.

Effects of Al and Co doping on the structural stability and high temperature cycling performance of LiNi_(0.5)Mn_(1.5)O_(4) spinel cathode materials

The poor structural stability and capacity retention of the high-voltage spinel-type LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)limits their further application.Herein,Al and Co were doped in LNMO materials for a more stable structure and capacity.The LNMO,LiNi_(0.45)Al_(0.05)Mn_(1.5)O_(4)(LNAMO)and LiNi_(0.45)Co_(0.05)Mn_(1.5)O_(4)(LNCMO)were synthesized by calcination at 900℃ for 8 h,which was called as solid-phase method and applied universally in industry.XRD,FT-IR and CV test results showed the synthesized samples have cation disordering Fd-3m space group structures.Moreover,the incorporation of Al and Co increased the cation disordering of LNMO,thereby increasing the transfer rate of Li+.The SEM results showed that the doped samples performed more regular and ortho-octahedral.The EDS elemental analysis confirmed the uniform distribution of each metal element in the samples.Moreover,the doped samples showed better electrochemical properties than undoped LNMO.The LNAMO and LNCMO samples were discharged with specific capacities of 116.3 mA·h·g^(-1)and 122.8 mA·h·g^(-1)at 1 C charge/discharge rate with good capacity retention of 95.8% and 94.8% after 200 cycles at room temperature,respectively.The capacity fading phenomenon of the doped samples at 50℃ and 1 C rate was significantly improved.Further,cations doping also enhanced the rate performance,especially for the LNCMO,the discharge specific capacity of 117.9 mA·h·g^(-1)can be obtained at a rate of 5 C.

Development of bimetallic spinel catalysts for low-temperature decomposition of ammonium dinitramide monopropellants

Ammonium dinitramide(ADN)based liquid monopropellants have been identified as environmentally benign substitutes for hydrazine monopropellant.However,new catalysts are to be developed for making ADN monopropellants cold-start capable.In the present study,performance of Co and Ba doped CuCr_2O_4 nanocatalysts prepared by hydrothermal method was evaluated on the decomposition of aqueous ADN solution and ADN liquid monopropellant(LMP103X).The catalysts were characterized by PXRD(Powder X-ray Diffraction),FTIR(Fourier Transform Infrared spectroscopy),SEM(Scanning Electron Microscopy),TEM(Transmission Electron Microscopy),EDS(Energy Dispersive X-ray Spectroscopy),and XPS(X-ray Photoelectron Spectroscopy).The nanosize was confirmed by SEM and TEM,while the nanoflake morphology was confirmed by the SEM analysis.Further,we obtained the elemental composition from the EDS analysis.We investigated the catalytic activity of the catalysts by thermogravimetric(TG)analysis and the developed catalysts lowered the decomposition temperature of ADN monopropellant by about 55℃.The XPS analysis confirmed the presence of metal ions with different chemical states.Apparently,increase in the surface area of the catalysts and the mixed active sites as well as the development of oxygen vacancy on the catalyst surface introduced by metal doping are influencing the decomposition temperature of ADN samples.

Effect of Al Powder and Si Powder Additions on Structure and Properties of Unburned Magnesium Aluminate Spinel Refractories

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(when Al powder addition is 4%,Si powder addition varies:1%and 2%,by mass)as additives.The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures(1000,1400,and 1600℃for 3 h)were studied.The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1000 or 1400℃,and meanwhile AlN reinforcement phase forms in the matrix,which greatly improves the hot modulus of rupture of the samples at 1400℃;however,the heat treatment at 1600℃has little influence on the strength;the addition of Al powder and Si powder results in the formation of low melting point phases,greatly reducing the hot modulus of rupture.However,the low melting point phases promote sintering,which enhances the density and the cold modulus of rupture,and decreases the volume change during heating.The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.

Gemological-Mineralogical Characteristic of Spinels from Sri Lanka

Detailed mineralogical and gemological records were conducted on 340 unheated spinels from the Horana, Eheliyagoda, Ratnapura, and Okkampatiya mining areas in Sri Lanka. The color of Sri Lankan spinel varies greatly: in addition to the mainstream pink to purple pink, green and blue can also be seen. Compared with spinel from other regions such as Myanmar, Vietnam, and Tanzania, Sri Lanka's spinel has more abundant inclusions: several mining areas generally have inclusions such as dolomite, apatite, zircon, and chondrodite. Minerals such as graphite and forsterite are also found in spinel produced in the Horana region;graphite and rutile have been found in spinel produced in the Okkamptiya region. Partially healed fissures are most common in spinel in the Okkampatiya mining area;Unlike Vietnamese spinel, dislocations and growth structures are almost absent in Sri Lankan spinel. The LA-ICP-MS analysis results showed that there were no significant differences among the mining areas. LA-ICP-MS analysis of 5 Sri Lankan cobalt blue spinels showed a variation of 11 to 120 ppm in this chromogenic element. The UV visible absorption spectrum results show that Sri Lankan spinel has a combination spectra with variable ratios of the spectral components Cr 3+ , V 3+ and Fe 2+ from pink to red, orange, purple to purple, and blue-green. The results of infrared spectroscopy and laser Raman spectroscopy analysis showed that all samples showed no indications for heat treatment.

在线净化装置对某7×××系铝合金熔体渣含量的影响

采用PoDFA法离线测渣仪对某7×××铝合金保温炉出口、在线除气装置出口、过滤装置出口熔体取样进行离线测渣,确定了夹渣物含量及夹渣物种类,并对夹渣物的来源进行了分析。结果表明:该7×××铝合金中典型夹渣物为氧化铝、氧化镁、冶金学尖晶石,夹渣物经在线除气装置处理后有所减少,经过滤装置处理后除渣效果显著。

钒基尖晶石AV_(2)O_(4)(A=Mg,Cd,Zn)拓扑平带的理论研究

基于密度泛函理论,运用Materials studio软件的CASTEP模块对3种钒基尖晶石AV_(2)O_(4)(A=Mg,Cd,Zn)进行了第一性原理计算.通过比较3种钒基尖晶石铁磁(FM)构型和反铁磁(AFM)构型的能量,得出反铁磁构型更加稳定的结论.考虑到铁磁态的3种钒基尖晶石平带结构能产生大的反常霍尔效应,分析了铁磁构型下3种钒基尖晶石的电子结构和磁学性质.3种钒基尖晶石在铁磁构型下都保持良好的半金属性,这使其在自旋电子学方面有广泛的应用.此外,分析了三者在费米能级附近的平带性质.在A^(2+)离子的位置掺杂Li~+离子,实现了稳定铁磁态的目的.

莫来石-刚玉-镁铝尖晶石复相材料的抗碱侵蚀性能研究

为了提高莫来石-刚玉质匣钵的抗碱侵蚀性能,以煤矸石、工业氧化铝和工业氧化镁为原料,采用二步煅烧法制备了莫来石-刚玉-镁铝尖晶石复相材料,研究了工业氧化镁加入量(加入质量分数分别为1%、2%、3%、4%和5%)对试样物相组成、显微结构及物理性能的影响,并探究了试样抗钠离子电池正极材料的侵蚀机制。结果表明:1)氧化镁可促进莫来石晶体生长和试样烧结致密化,且由于莫来石晶体直接结合及微晶镁铝尖晶石颗粒增韧,所有试样均具有高的常温耐压强度,≥248 MPa;2)以不同形态分布于试样中的镁铝尖晶石可形成物理屏障,阻止Na^(+)渗透,阻隔其与莫来石和刚玉反应,提高试样的抗碱侵蚀性能;3)综合试样的物理性能和抗碱侵蚀性能,工业氧化镁的最佳加入量为4%(w)。

基于层状锌铝复合氢氧化物前驱体优化制备Cu/ZnO/Al_(2)O_(3)气相醛加氢催化剂

以偏铝酸钠作为铝源通过一步法、两步法和混合法引入Cu制备基于ZnAl-LDH前驱体的3种不同的Cu/ZnO/Al_(2)O_(3)催化剂,对催化剂及其前驱体结构性质进行表征,结合辛烯醛(2-乙基-2-己烯醛,EPA)加氢反应评价结果,探究不同制备方法、不同铝的引入方式对ZnAl_(2)O_(4)尖晶石形成的影响,考察不同条件下所得催化剂的结构与反应性能之间的构效关系。结果表明:与工业催化剂相比,在辛烯醛气相加氢反应中混合法制得的催化剂与工业催化剂活性相当,产物选择性在空速1.5 h^(-1)时高于工业剂1.9%,在空速4.0 h^(-1)时高于工业剂2.5%;以偏铝酸钠作为铝源制备的ZnAl-LDH前驱物大大提高锌铝结合效率,减少非结合Al_(2)O_(3)的产生,提高产物选择性,同时实现380℃低温焙烧条件下ZnAl-LDH向ZnAl_(2)O_(4)尖晶石的转变,避免传统的高温焙烧过程中CuO的烧结。

不同碱度渣对刚玉-尖晶石浇注料的侵蚀行为研究

浇注料的抗渣侵蚀性能与钢渣的碱度密切相关。以烧结刚玉、缺陷尖晶石微粉、活性α-Al_(2)O_(3)微粉、电熔镁砂细粉和铝酸钙水泥(Secar71)为主要原料,制备了刚玉-尖晶石浇注料,采用静态坩埚法于1600℃保温3 h进行抗渣试验,并用热力学模拟计算了液相量和液相组成,研究了刚玉-尖晶石浇注料对3种不同碱度渣(1.6、2.3和7.6)的抗渣侵蚀性能。结果表明:刚玉-尖晶石浇注料在高碱度渣中溶解能力有限,在熔渣-耐火材料界面极易形成尖晶石固溶体和六铝酸钙等高熔点物相,形成致密层阻挡熔渣渗透和侵蚀。而其在低碱度渣中溶解度较高,在浇注料-熔渣达到较高反应程度时,才开始形成尖晶石固溶体和六铝酸钙等高温相,无法形成有效的致密层阻止熔渣对浇注料的侵蚀和渗透。因此,刚玉-尖晶石浇注料对高碱度渣抗渣侵蚀能力较强,对低碱度渣抗渣侵蚀能力较弱。

不同形貌Co_(3)O_(4)的控制合成及其催化氧化甲苯性能

采用溶剂热方法控制合成了一系列具有球状、蝴蝶结状和块状的Co_(3)O_(4)催化剂,并评价其催化氧化消除甲苯的性能。通过X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(Scanning electron microscopy,SEM)、H2程序升温还原(H2-temperature programmed reduction,H2-TPR)和X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)等方法表征了这些催化剂的结构和表面性质,探讨其形貌结构与活性的关系。研究结果表明,在质量体积空速为40000 mL·g^(-1)·h^(-1)的条件下,所制备的具有不同形貌的三种催化剂中,球状Co_(3)O_(4)催化剂活性最佳,可以在246℃时使甲苯达到90%的转化(T_(90)),而蝴蝶结状和块状催化剂催化甲苯转化的T_(90)分别为250和263℃。而且球状Co_(3)O_(4)催化剂在250℃时,甲苯转化率可以在12 h内保持稳定。表征结果表明,在三种同为尖晶石相的Co_(3)O_(4)催化剂中,球状样品表面的Co3+和晶格氧含量最高,且其氧化能力最强,这可能是该样品具有优异催化氧化甲苯活性的原因。