Al-Ni掺杂改性LiMn2O4正极材料合成及电化学性能

采用固相燃烧法快速合成了单晶多面体LiAl0.08Ni0.03Mn1.89O4 (LANMO)锂离子电池正极材料,其单晶颗粒暴露面包含{111}、{110}和{100}晶面。研究结果表明,LANMO材料为单相尖晶石型结构,属于Fd3m空间群,结晶性好,颗粒尺寸200-300 nm。在1 C和5 C倍率下LANMO的初始放电比容量分别为110.6和96 mAh·g-1,循环1000次后容量保持率都达到70%以上;在高温(55 ℃)1 C条件下,LANMO材料也具有114.2 mAh·g-1初始放电比容量,表现出优良的电化学性能。动力学性能测试表明,LANMO样品有较高的Li+离子扩散系数1.58×10-11 cm2·s-1和较低的表观活化能23.89 kJ?mol-1。Al-Ni协同改性提高了单晶多面体尖晶石型LiMn2O4材料的晶体结构稳定性,有效抑制了Jahn-Teller效应及降低Mn溶解和增加Li+扩散通道,增大了Li+扩散速率和电极可逆性,提升了其倍率性能和循环寿命。     

镍基单晶高温合金性能的研究

研究在两种凝固条件下,热处理对镍基单晶高温合金性能的影响。研究表明：γ相为0．5时,镍基单晶高温合金在950～1050℃有最佳的蠕变性能;显微疏松对850℃的高周疲劳以及750℃低周疲劳有明显的影响,采用高的温度梯度下的铸造处理可以使性能得到改善;该合金的耐腐蚀性较高。     

镍基单晶高温合金沉淀相尺度效应研究

对Ni_3Al(γ')沉淀相尺寸对镍基单晶高温合金拉伸性能的影响进行了研究。对镍基单晶高温合金而言,材料的屈服来源于位错以Orowan机制绕过沉淀相,而Orowan应力与沉淀相间距有关。根据这一机理,基于晶体塑性理论,引入一个本构方程以表征沉淀相尺寸对镍基单晶高温合金屈服强度的影响。采用该本构模型,分别计算了在[001]以及[111]2个取向下,含有尺寸为0.2~2.5μm沉淀相的镍基单晶高温合金屈服强度,并与试验结果进行了对比验证。结果表明,该模型可以准确表征镍基单晶高温合金沉淀相的尺度效应。     

高电压正极材料LiMnPO4的研究进展

高电压正极材料LiMnPO4具有无毒、电压高、比容量高、循环性能和安全性能好等优点成为锂离子电池正极材料的研究热点之一,但是较低的电子导电率、本征电导率及较差的倍率性能限制了该材料的实际应用。近几年来,通过增强颗粒间电子导电性、提高颗粒内部的本征电导率和减小颗粒尺寸等,显著提升了LiMnPO4材料的电化学性能。本文介绍了LiMnPO4材料的结构和特点以及近年来国内外的合成和改性方法,包括高温固相法、溶胶-凝胶法、水热法、喷雾干燥法、表面包覆、掺杂和制备纳米尺寸材料等。揭示了目前LiMnPO4的研究现状和存在问题,并对今后的发展前景以及研究的重要方向进行了评述。     

Li2Mn0.9Ti0.1SiO4锂离子电池正极材料的合成及其性能

以Li2SiO3、Mn(CH3COO)2·4H2O和TiO2为原料,利用传统高温固相合成法成功合成出Li2Mn0.9Ti0.1Si04锂离子电池正极材料.采用XRD、FESEM等手段分析了正极材料的相组成、结构和形貌,利用电池测试仪测试了正极材料样品的电化学性能.研究结果表明,固相合成的产物主相为Li2Mn1-x,TLSiO4,同时存在少量的杂质,掺杂Ti后,材料表面形貌从近球形转变为非球形颗粒,颗粒尺寸略有增大,为200～500nm.实验结果表明,Ti掺杂以后,Li2MnSiO4正极材料的可逆容量和循环寿命都得到提高.正极材料电化学性能提高的机理在于Ti掺杂稳定了Li2MnSiO4正极材料的结构.     

LiMg_(0.03)(Ni_(0.77)Co_(0.1)Mn_(0.1))O_2·B_2O_3球形高镍材料的制备与性能

采用液相共沉淀法制备球形掺镁高镍三元材料前驱体,结合高温固相法制备了氧化硼包覆高镍三元材料LiMg0.03(Ni0.77Co0.1 Mn0.1)O2·B2O3,对样品物理性能、电化学性能及安全稳定性进行分析测定,并对性能改善的机理进行分析。结果表明:通过Mg元素体相掺杂和B2O3表面包覆制备的球形高镍三元材料LiMg0.03(Ni0.77Co0.1Mn0.1)O2·B2O3具有良好的电化学性能和物理性能,对锂负极初始放电容量达到181 m A·h/g,对碳负极300次循环后,放电容量保持率达到92%,压实密度达到3.9 g/cm3。同时,LiMg0.03(Ni0.77Co0.1 Mn0.1)O2·B2O3具有良好的热稳定性和抗过充电的能力,在充电态下热分解温度比未掺杂和未包覆的样品提升12℃。     

激光熔覆Ni3Si基复合涂层相、组织及高温抗氧化性能研究

采用激光熔覆技术在镍基高温合金GH864表面制备了原位合成碳化物TiC、NbC陶瓷颗粒增强Ni3Si金属间化合物基复合涂层，采用XRD、SEM和EDAX等方法，对熔覆层相、组织进行了表征。采用循环氧化法研究了熔覆层在1100℃下的高温抗氧化性能。     

Mo和W在镍基单晶高温合金中的作用研究进展综述

镍基单晶高温合金因其优异的高温性能而广泛应用于航空发动机涡轮叶片的制备。经过几十年的发展,国外已发展至第六代镍基单晶高温合金,合金体系中的Re和Ru等贵重金属元素的含量也不断增加。贵重元素的添加导致合金的成本和密度上升,对合金的研制和批量商业化应用不利。Mo和W作为较低成本的强化元素,在镍基单晶高温合金中发挥了重要的作用。Mo 和W在镍基单晶高温合金中的作用已有较为广泛的研究,本文简单综述了Mo和W在镍基单晶高温合金中对微观结构,包括元素分布、γ/γ′相两相结构、组织稳定性等方面,以及高温持久性能、对凝固缺陷和抗氧化及抗热腐蚀性等的影响,并提出了未来潜在的研究方向。     

镍基单晶高温合金热机械疲劳本构模型研究

在晶体塑性理论的基础上,提出了一种适用于镍基单晶高温合金热机械疲劳的本构模型,并采用该模型对单晶材料不同晶体取向的热机械疲劳力学响应进行有限元模拟。结果表明,该本构模型可以较好地模拟镍基单晶合金的热机械疲劳行为。对于同相位热机械疲劳,压缩应力幅大于拉伸应力幅,循环平均应力小于零;对于反相位热机械疲劳,拉伸应力幅大于压缩应力幅,循环平均应力大于零。随着循环次数的增加,材料呈现出在高温半周为初始软化,低温半周为初始硬化的特征。晶体取向对于材料的热机械疲劳性能具有显著的影响。     

超声喷丸对不同取向单晶高温合金组织与表面性能的影响

超声喷丸作为一种有效改善疲劳性能的手段在单晶材料方面得到一定研究,但喷丸振幅对不同取向镍基单晶高温合金微观组织及表面性能的影响尚不清晰。采用生长方向为[001]的国产第三代镍基单晶高温合金为研究对象,利用显微硬度计、SEM、TEM、XRD、EBSD等研究超声喷丸振幅（22.5μm、45μm、60μm）对不同第二取向（[100]、[110]）样品组织形貌及表面性能的影响。结果表明：振幅为22.5μm喷丸处理后的样品保持单晶合金原有的γ/γ组织形貌和原始取向,并在表面局部已经形成尺寸约为10 nm的纳米晶;[100]与[110]取向样品近表层硬度相比基体硬度分别最大提高75%和68.5%。大振幅（45μm、60μm）喷丸样品的γ/γ组织发生严重畸变;随着振幅的增大,原始取向强度逐渐减弱并产生新的择优取向,样品近表层的取向偏转更加显著且沿滑移带附近产生大量小角晶界。通过分析两取向样品的近表层硬度及EBSD结果可知,在相同振幅条件下,第二取向[100]样品的近表层应变硬化效果优于[110]取向样品。研究喷丸振幅对不同第二取向单晶高温合金性能及微观组织的影响,可为生产中合理控制单晶叶片第二取向及...     

Kinetics and formation mechanism of amorphous Fe52Nb48 alloy powder fabricated by mechanical alloying

A single phase amorphous Fe₅₂Nb₄₈ alloy has been synthesized through a solid state interdiffusion of pure polycrystalline Fe and Nb powders at room temperature, using a high-energy ball-milling technique. The mechanisms of metallic glass formation and competing crystallization processes in the mechanically deformed composite powders have been investigated by means of X-ray diffraction, Mössbauer spectroscopy, differential thermal analysis, scanning electron microscopy and transmission electron microscopy. The numerous intimate layered composite particles of the diffusion couples that formed during the first and intermediate stages of milling time (0–56 ks), are intermixed to form amorphous phase(s) upon heating to about 625 K by so-called thermally assisted solid state amorphization, TASSA. The amorphization heat of formation for binary system via the TASSA, ΔH_a, was measured directly as a function of the milling time. Comparable with the TASSA, homogeneous amorphous alloys were fabricated directly without heating the composite multilayered particles upon milling these particles for longer milling time (86 ks–144 ks). The amorphization reaction here is attributed to the mechanical driven solid state amorphization. This single amorphous phase transforms into an order phase (μ phase) upon heating at 1088 K (crystallization temperature, T_x) with enthalpy change of crystallization, ΔH_x, of −8.3 kJ mol⁻¹.     

Microwave ECR plasma CVD of cubic Y2O3 coatings and their characterization

Yttrium oxide (Y₂O₃) thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process at a substrate temperature of 350 °C using indigenously developed metal organic precursors (2,2,6,6-tetra methyl-3,5-heptane dionate) yttrium, commonly known as Y(thd)₃ synthesized by ultrasound method. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, EDS and infrared spectroscopy. The characterization results indicate that it is possible to deposit non-porous coatings with excellent uniformity of a single phase cubic Y₂O₃ on various substrates by this process at reasonably low substrate temperature that is desirable in various manufacturing processes.     

Hydrothermal synthesis of hexagonal and orthorhombic MoO3 nanoparticles

Molybdenum oxide (MoO₃) with two different crystal structures (hexagonal and orthorhombic) was successfully synthesized by an effective and environmental friendly hydrothermal method. The phase confirmation and structural properties of the sample was elucidated by X-ray diffraction (XRD) method. The reaction temperature has great impact on the crystal structure, size, shape and chemical composition of the samples. Vibration behavior of chemical bonds was characterized by Fourier transform infrared spectroscopy (FT-IR) and the observed peaks confirm the formation of MoO₃. Scanning electron microscopy (SEM) observation shows that an increase in reaction temperature, the shape was drastically changed from one dimensional (1D) to two dimensional (2D) layered structures. Energy dispersive X-ray analysis (EDX) reveals that the as-prepared samples are in non-stoichiometric composition and their composition varies with reaction temperature. The thermal study was acquired by thermo gravimetric analysis and it demonstrates the process of dehydration and deammonization, observed below 260 °C and phase transformation from hexagonal to highly stable orthorhombic phase at 400-450 °C. Additionally, the optical absorption properties were measured using diffuse reflectance spectroscopy (DRS) and the band gap energy, estimated from Kubelka-Munk function (K-M) was found to be in the range of 3.01-3.24 eV.     

碱钨青铜粉体的溶胶-凝胶法合成与表征

采用溶胶-凝胶法合成了碱钨青铜(M_xWO_3,M=Cs,Rb中的1种或2种)粉体,探究了铯、铷分别单掺杂和铯、铷共掺杂对钨青铜粉体晶相、形貌的影响。利用X射线衍射仪(XRD)、X射线能谱仪(EDS)、扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)、紫外可见近红外光谱(UV-Vis-NIR)、隔热膜温度测试仪对所合成碱钨青铜粉体的物相、形貌、光学性能和隔热性能进行了表征。结果表明:溶胶-凝胶法所合成的碱钨青铜粉体结晶性较好、粒径较小;Cs、Rb共掺杂的透明绝热指数K=157.34比Rb单掺杂提高了23.92,改善了Cs单掺杂在1076 nm处透过率突变的情况;Cs、Rb共掺杂的温差(与起始温度相比)为4.9℃,比Rb单掺杂的温差下降了5.7℃。     

均匀自支撑的二氧化钒纳米线的水热合成及相变特性研究

二氧化钒(VO₂)在接近室温时发生由半导体态向金属态的Mott相变,在智能窗和红外自适应伪装技术领域具有一定的应用前景。本文采用一种新颖的水热法制备均匀自支撑的VO₂纳米线。合成的纳米线的直径为150±30 nm,长度达到几十微米。通过X射线衍射、X射线光电子能谱、高分辨透射电镜和选取电子衍射等手段验证了高纯单斜相VO₂纳米线的成功制备。而且,VO₂纳米线的可逆相变性能采用差示量热扫描、变温XRD和变温Raman光谱进行了探究。结果表明：VO₂纳米线升温相变点为65.2 °C,磁滞回线宽度窄至6.5 °C,具有良好的可逆相变性。这些为VO₂纳米线的金属-半导体相变研究提供基础。     

Oxidation behaviour of Nimonic 263 in high-temperature supercritical water

The oxidation tests of the Nimonic 263 alloy exposed to deaerated supercritical water at 600–700°C under 25?MPa were carried out for up to 1000?h. Oxidation rate increased with an increase in temperature. The microstructure and phase composition of oxide scale were analysed by scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. It can be seen that a complex oxide structure formed on the surface of Nimonic 263 including an outer layer of Ni–Fe/Ni–Cr spinel oxide, Ni/Co hydroxide and TiO₂ and an inner layer of a mixture of NiCr₂O₄ and Cr₂O₃ while the innermost layer is made up of Cr₂O₃. The MoO₃ can be observed at 600°C but disappeared with the increasing temperature. The growth mechanism of oxide scale was discussed.     

X-ray absorption studies of phase formation in a Ti/TiN coating on cubic boron nitride

We report on the use of X-ray absorption spectroscopy as a tool for the identification of the phases formed in the technological process of composite preparation. A composite is a mixture of several compounds and, in many cases, the use of traditional X-ray diffraction to determine the phases can be difficult because of the small amount of phases present. X-ray absorption studies (XANES and EXAFS) of the c-BN Ti/TiN layered system are presented. These materials are models of the powdered composites used in industry for tool production. XANES and EXAFS analyses showed that, after annealing up to 1300 °C, a TiB₂ phase is formed, but the chemical bonding of the Ti atoms differs slightly from that of standard TiB₂ powder, showing the presence of defects in site occupancy. Assuming that the X-ray absorption spectral shape is a linear combination of the spectra of all the components, we estimated the kind and limits of other phase inclusions.     

Synthesis, structure and optical properties of CoAl2O4 spinel nanocrystals

CoAl₂O₄ nanocrystals were synthesized by sol-gel method using citric acid as a chelating agent at low temperature. The as-synthesized samples were characterized by thermal analysis, X-ray powder diffraction, infrared spectroscopy and transmission electron microscopy. The results show that CoAl₂O₄ spinel is the only crystalline phase with a size of 10-30 nm in the temperature range 500-1000 °C. The temperature dependence of the distribution of Al³⁺ and Co²⁺ ions in the octahedral and tetrahedral sites in nanocrystals was investigated by X-ray photoelectron spectroscopy (XPS). It is observed that the inversion parameter decreases with increasing annealing temperature. Analysis of the absorption properties indicates that Co²⁺ ions are located in the tetrahedral sites as well as in the octahedral sites in the CoAl₂O₄ nanocrystals. The origin of the green color (300-500 nm absorption band) should be due to the octahedrally coordinated Co²⁺ ions.     

Effect of Mn addition on the thermal stability and magnetic properties of rapidly-quenched L10 FePt alloys

Nano-composite magnets with L1₀ structure derived from binary FePt alloys and prepared as melt-spun ribbons are of current interest due to their higher operating temperature and the ability to be cast as a two-phase magnet with exchange spring magnetic properties, as both soft and hard magnetic phase may emerge from the same metastable precursor, i.e. the disordered cubic A1 phase. The present paper studies the effect of Mn addition on the thermal stability and phase structure, on the abundance of the hard magnetic phase and relative proportion of the soft ones, on the microstructure of the alloy as a function of temperature and on the overall magnetic properties. The interplay of the various magnetic sublattices in the ordering of the L1₀ phases as a consequence of introducing antiferromagnetically coupled Mn atoms in the alloy composition is discussed and interpreted in terms of microstructural changes induced by this addition as revealed by high resolution transmission electron microscopy and X-ray diffraction. The temperature evolution of the phase composition and structural parameters is monitored using synchrotron radiation powder diffraction, while the compositional aspects are investigated using proton-induced X-ray emission and energy dispersive X-ray spectroscopy. Magnetic measurements reveal the magnetic parameters of interest (coercivity, remanence, Curie temperature, saturation magnetization), as well as the exchange-coupled two-phase nature of these magnets and provide information that hints at possible spin reorientation transitions in the Mn-containing planes of the L1₀ superlattice.     

A simple thermal decomposition-nitridation route to nanocrystalline boron nitride (BN) from a single N and B source precursor

Nanocrystalline boron nitride (BN) was synthesized via a simple thermal decomposition-nitridation route by the reaction of hydrated ammonium tetraborate (NH₄HB₄O₇·3H₂O) and metallic magnesium powders in an autoclave at 650 °C. The crystal phase, morphology, grain size, and chemical composition of the as-prepared products were characterized in detail by X-ray powder diffraction (XRD), energy dispersion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The products were also studied by FT-IR and the thermogravimetric analysis (TGA). Results revealed that the as-synthesized nanocrystalline were h-BN, and they had diameters within 100 nm. They had good thermal stability and oxidation resistance in high temperature.