Studies on the Influence of Sintering Temperature on Crystalline Structures of Mg-Al Spinel Synthesized by Waste Aluminum Slag

Mg-Al spinel is synthesized by using industrial waste-residue and basic magnesium carbonate in the aluminum factory as the main raw materials. The influence of sintering temperature on crystalline structure and microstructure of Mg-Al spinel has been mainly discussed. The crystalline structure of sample is characterized by using XRD, SEM and relevant analytical software. The experimental results show that compared to the conventional synthetic method, the application of waste aluminum slag as the raw material can greatly decrease the synthetic tem-perature. The content of Mg-Al spinel first increases and then decreases with the rise of sintering temperature, and its purity can reach as high as 96wt% at 1550 ℃, which is therefore determined to be the optimum synthetic temperature. SEM observations demonstrate that as the rise of sintering temperature, the grain of Mg-Al spinel grows up obviously with typical octahedral characteristic appearance.

Influence of Fe_2O_3 and V_2O_5 on Crystalline Structure of Mg-Al Spinel Synthesized by Waste Aluminum Slag

Mg-Al spinel is synthesized by using industrial waste-residue and basic magnesium carbonate in the aluminum factory as the main raw materials. The influence of V2O5 and Fe2O3 mineralizers on the structure, cell parameters and microscopic morphology of synthesized Mg-Al spinel has been discussed. The Mg-Al spinel is characterized by using XRD, SEM and relevant analytical software, such as Philips plus, Rietveld quantification and so on. The experimental results show that certain amounts of V2O5 and Fe2O3 are beneficial to the formation of Mg-Al spinel, and the optimum addition of V2O5 and Fe2O3 is respectively 2wt% and 3wt%. V2O5 has few effects on cell parameters of Mg-Al spinel; but Fe2O3 can form solid solution with Mg-Al spinel in which Mg-Fe spinel can also dissolve to form continuous solid solution. Therefore, with the increase of Fe2O3 content, the cell parameters of Mg-Al approximately present linear increase.

Influence of Cr_2O_3 on the Structure and Property of Mg-Al Spinel Synthesized by Waste Slag in Aluminum Factory

Via the solid phase reaction, Mg-Al spinel has been synthesized by using industrial waste slag from aluminum factory, basic magnesium carbonate and a little amount of clay as the main raw materials. The influences of Cr2O3 mineralizer on crystalline structure, micro-morphology and properties of synthesized Mg-Al spinel are discussed. The synthesized product was characterized by using XRD and SEM, and the relative contents of each crystalline phase are calculated by relevant analytical software such as Philips plus, Rietveld quantification and so on. The experimental results show that a certain amount of Cr2O3 is helpful to the formation of Mg-Al spinel, and when the addition of Cr2O3 is 2.0%, Mg-Al spinel in the system exists in the form of solid solution （Mg0.68A10.32）（A10.84Mg0.16）2O4 whose content is the highest reaching 91%. Then the corresponding indexes of each property are as follows： water absorption 3.0%, apparent porosity 9.8%, bulk density 3.36 g·cm^3, and flexural strength 83.32 MPa. Therefore, we can confirm that the optimum addition of Cr2O3 mineralizer is 2.0%.

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.

Mg-Al水滑石的制备及对水中氟离子的吸附效果研究

通过共沉淀法制备了Mg-Al水滑石,研究了镁铝摩尔比对Mg-Al水滑石的晶格结构、微观形貌、光谱性能的影响。以NaF溶液为模拟含氟废水,测试了Mg-Al水滑石对水中氟离子的吸附量和去除率,通过吸附模型研究了相应的吸附过程和机理。结果表明,Mg-Al水滑石外观为片层状结构,片层之间相互交叉堆积,镁铝比增大时,Mg-Al水滑石的层间距增大。水滑石对氟离子的饱和吸附量和去除率随着镁铝比的增大表现出先增大后减小的趋势,在吸附80 min时吸附量接近饱和,3Mg-Al水滑石的饱和吸附量达到最大值43.16 mg/g,去除率在120 min时达到最大值90.5%,经过5次吸附再生循环使用后,3Mg-Al水滑石对氟离子的去除率降至69.4%,保持率达到76.69%,具有良好的可重复利用性能。通过对Mg-Al水滑石吸附氟离子的数据进行拟合,发现Mg-Al水滑石吸附氟离子的过程更符合准二级动力学模型,主要以化学吸附作用为主。

新型Al-C晶粒细化剂的制备及对Mg-Al合金显微组织的影响研究

采用原位反应烧结法制备了新型Al-5C中间合金,利用光学显微镜(OM)、X射线衍射(XRD)和扫描电子显微镜(SEM)等研究了制备工艺对Al-5C中间合金组织以及该中间合金对Mg-Al合金晶粒细化的影响。结果表明,原位反应烧结法改善了Al与C的润湿性,Al-C的反应程度与球磨时间、烧结温度、烧结时间和压块方式有关;延长球磨时间、提高烧结温度或适当延长烧结时间均能促进Al-C反应,生成细小的Al4C3颗粒;Al-5C中间合金能有效地细化Mg-3Al合金的组织,添加量(质量分数)为2%时晶粒细化效果最佳。

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.

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.

反相微乳液法对Mg-Al LDHs材料结构及近红外光谱的性能研究

采用反相微乳液法制备出了具有介孔结构的Mg-Al LDHs粉体,采用XRD、SEM、BET、DSC/TG、傅立叶红外光谱仪、可见光-近红外分光光度计对样品的结构、成分、形貌、近红外光学性能进行了测试分析,系统研究了反相微乳液反应环境对Mg-Al LDHs粉体介孔结构、水负载量、近红外反射光谱的影响规律,进而探索了一种通过调控Mg-Al LDHs材料形貌结构以模拟天然植物近红外光谱特性的高光谱伪装颜料设计方法。当反相微乳液油-水体系中的水含量达到24%时,成功制备出了一种具有多孔结构的Mg-Al LDHs粉体,通过增大材料内部的孔隙率可以明显提高其在近红外波段的“水吸收峰”强度,并获得与天然植物高度相似的可见光-近红外光谱曲线,余弦相似度高达95.13%。多孔材料的内部孔隙一方面可有效提升材料对水分的负载能力,增强Mg-Al LDHs粉体在近红外波段的水吸收峰强度;另一方面,还能使入射光在材料内部发生多次折射,增大了材料对入射光吸收的几率,从而降低了光谱的整体反射率。在上述效应的综合作用下,最终实现了对天然绿色植物近红外反射光谱的精细化模拟。

微量Y_(2)O_(3)对多孔Mg-Al合金组织和性能的影响

镁基多孔材料在生物医用领域具有广阔的应用前景,为提高多孔Mg-Al合金在人体体液中的耐腐蚀性,采用粉末冶金法制备多孔Mg-Al合金,添加不同含量(0,0.2%,0.4%,0.6%)的Y_(2)O_(3)对Mg-Al合金进行改性。采用金相显微镜、XRD、SEM、万能试验机和电化学工作站探究了Y_(2)O_(3)含量对多孔Mg-Al合金的孔隙率和孔隙形貌、显微组织、抗压强度及其在Hank’s仿生溶液中耐蚀性的影响。结果表明:采用粉末冶金法制备的多孔Mg-Al合金的孔隙率为39%左右,粉末冶金法可较为准确地控制多孔Mg-Al合金的孔隙形貌和大小。多孔Mg-Al合金主要由Mg和第二相Al12Mg17组成,Y_(2)O_(3)的添加可使多孔Mg-Al合金晶粒得到细化、晶粒尺寸均匀化,第二相分布更加均匀,并提高多孔Mg-Al合金的抗压强度及其在Hank’s仿生溶液中的耐蚀性。当Y_(2)O_(3)含量为0.4%时,多孔Mg-Al合金的抗压强度为46.4 MPa,在Hank’s仿生溶液中的腐蚀速率为0.88744 mm/a。

变质细化在Mg-Al系合金中的应用及研究进展

介绍了Mg-Al系合金的特点。综述了C、Sr、Ti、RE元素对Mg-Al系合金变质细化的影响和作用机理。从AZ、AM、AS、AE合金体系出发,对比了不同变质处理下的差异,指出了变质剂使用的最佳用量、加入温度、保温时间,归纳了变质剂对合金晶粒尺寸、组织演变、力学性能的影响,为Mg-Al系合金变质细化提供参考,最后总结了几类合金中变质剂的作用特点,为制备高性能低成本的镁合金提供系统思路。

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.

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.

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.

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.