Fe2O3-CaO-TiO2 体系下铁酸钙的合成过程及TiO2 和CaTiO3 的影响

为了确定高钛型钒钛磁铁矿烧结过程中铁酸钙的生成是受TiO₂还是TiO₂和CaO形成的CaTiO₃影响,首先利用Fe₂O₃和CaO的纯试剂合成了铁酸钙,并研究了TiO₂和CaTiO₃对钛铁酸钙 （FCT） 形成的影响。在Factsage 7.0软件进行热力学计算的基础上,通过在空气气氛下进行烧结,获得了在1023~1423 K温度范围内、不同烧结时间的不同样品。通过X射线衍射和扫描电镜-能谱分析等表征手段,对烧结样品的物相转变和微观结构变化进行了表征。发现FCT的形成过程主要分为2个阶段：前一阶段为1023~1223 K温度范围内Fe₂O₃与CaO之间的反应,合成产物为Ca₂Fe₂O₅,反应方程式为“Fe₂O₃(s)+ 2CaO(s)= Ca₂Fe₂O₅(s)”;后一阶段为1223~1423 K温度范围内Ca₂Fe₂O₅和Fe₂O₃的反应,主要产物为CaFe₂O₄,反应为“Ca₂Fe₂O₅(s)+ Fe₂O₃(s)= 2CaFe₂O₄(s)”,该阶段尤其是温度为1423 K时,反应速率显著加快,随温度的升高CaTiO₃显著增加。然而,Ti元素在铁酸钙中的固溶很难实现,TiO₂与铁酸钙之间的反应不是形成FCT的有效途径。随着保温时间的延长,CaTiO₃和FCT相界中Fe元素含量增加。FCT主要是通过Fe组分在CaTiO₃中固溶形成的,主要反应是“Fe₂O₃+CaTiO₃(s)=FCT(s)”。     

Cr、Mo对DO_3-Fe_3Al力学性能和电子结构影响的第一性原理计算

采用基于密度泛函理论的第一性原理方法,研究了Cr、Mo在DO_3-Fe_3Al金属间化合物中的占位以及对Fe_3Al力学性能和电子结构的影响。研究显示:Cr、Mo在Fe_3Al中优先替代Al原子;Cr、Mo的添加均提升了Fe_3Al的体模量、剪切模量、弹性模量以及塑性,其中Mo对Fe_3Al的模量以及塑性的提升效果更明显;Cr和Mo同时添加提高了Fe_3Al的体模量、剪切模量、弹性模量,然而略微降低了其塑性。电子结构和电荷密度分析表明:Cr、Mo对Fe_3Al力学性能提高的主要原因是Cr、Mo的s,p和d轨道电子参与了Fe_3Al的电子杂化,Cr、Mo增加了Fe_3Al的成键峰数量,且增加了Fe_3Al中原子间的重叠电子数。此外,Cr、Mo减弱了Fe_3Al中Fe-Fe间电子云的方向性。     

Ti3AlC2掺杂SPS法制备Ti2AlC/TiAl复合材料的研究

通过2TiC-Ti-1.2Al体系的原位热压反应制备了Ti₃AlC₂陶瓷,然后以59.2Ti-30.8Al-10Ti₃AlC₂(wt%)为反应体系,采用放电等离子烧结技术制备出Ti₂AlC/TiAl基复合材料。借助XRD、SEM分析了产物的相组成和微观结构,并测量了其室温力学性能。结果表明：原位热压烧结产物由Ti₃AlC₂和TiC相组成,Ti₃AlC₂呈典型的层状结构,TiC颗粒分布在其间。SPS法制备的Ti₂AlC/TiAl基复合材料主要由TiAl、Ti₃Al和Ti₂AlC相组成,Ti₂AlC增强相主要分布于基体晶界处,表现为晶界/晶内强化作用。力学性能测试表明：Ti₂AlC/TiAl基复合材料的密度、维氏硬度、断裂韧性和抗弯强度分别为3.85 g/cm₃、5.37 GPa、7.17 MPa?m_1/2和494.85 MPa。     

Fe3O4/SiO2/Bi2WO6磁性复合光催化剂的制备及其光催化性能

钨酸铋(Bi₂WO₆),结构最简单的Aurivillius相化合物,是近期受到研究者关注的新型光催化材料。然而,光催化剂粉末在反应介质中难被回收,工业化应用成本较高。本文用三步方法合成了可回收的Fe₃O₄/SiO₂/Bi₂WO₆磁性复合光催化剂,通过溶剂热法合成具有磁性的Fe₃O₄,用溶胶凝胶法在Fe₃O₄表面覆盖SiO₂层,后将磁性颗粒与Bi₂WO₆纳米片相结合。光催化剂的形貌结构及性能通过XRD、SEM、PL、UV-vis进行表征测试。结果表明,直径约500 nm的Fe₃O₄微球附着在边长约500 nm的Bi₂WO₆纳米片的表面,SiO₂在两者之间起到了粘连作用。光催化剂Fe₃O₄/SiO₂/Bi₂WO₆对于罗丹明B的光降解活性较好,且有一定磁性,可以通过外加磁场将其从溶液中分离,有较大的应用潜力。     

Al0.7Sb2Te3三元靶材的结构性能表征

以原子比Al:Sb:Te=0.7:2:3的混和粉为原料,采用真空合成法与烧结-热等静压制备Al_0.7Sb₂Te₃三元靶材,通过XRD、FESEM、EDS、XPS等手段表征其性能,且重点采用XPS研究Al在Al_0.7Sb₂Te₃三元靶材的存在状态。结果表明：Al掺杂后,靶材主相Sb₂Te₃的晶格常数减小,且单质Al弥散相与Al_0.1Sb₂Te₃基体相共存,表明掺杂对靶材的组织结构确有影响;刻蚀深度从0增加至405.9nm,Al价态从以Al₂O₃的化合态为主逐渐过渡至以单质态为主,且Al以Al₂O₃形态为主的区域深度约90nm;刻蚀深度为405.9nm时,来自非氧化物的Al价态与来自AlSb的Sb价态联合表明：Al_0.1Sb₂Te₃中的Al通过有效化合形成AlSb影响着靶材的组织结构。     

L12型Al3Sc基金属间化合物有序化行为和力学性能的第一性原理计算

本文采用亚晶格模型,辅助以第一性原理总能计算,研究了L1₂型Al₃Sc基金属间化合物中元素的占位有序化行为和力学性能。结果表明：Al₃Sc合金呈现完全有序化,其中Al占据3c亚晶格位置,Sc占据1a亚晶格位置；L1₂-Al₃(Sc_0.75M_0.25)金属间化合物(M=Y、Ti、Zr和Hf)也呈现完全有序化,第三组元M均只占据1a亚晶格位置,这些元素的占位行为均不受温度的影响。L1₂-Al₃(Sc_0.75M_0.25)金属间化合物均满足力学稳定性条件。M为Y时,L1₂-Al₃(Sc_0.75M_0.25)金属间化合物的剪切模量、体弹模量和杨氏模量和硬度下降；M为Ti、Zr或Hf时,随着原子半径增大,剪切模量、体弹模量、杨氏模量和硬度逐渐降低,其中Ti的加入可使L1₂-Al₃(Sc_0.75M_0.25)金属间化合物的塑性和韧性达到最好。     

La2O3含量对搅拌摩擦加工制备Ni /Al复合材料组织和性能的影响

采用搅拌摩擦加工方法在Al基体中添加不同La₂O₃含量的混合粉末(Ni+La₂O₃),制备 (Ni+La₂O₃)/Al复合材料。采用SEM、EDS、 EPMA及XRD对复合区微观结构及相组成进行分析,采用室温拉伸试验对 (Ni+La₂O₃)/Al复合材料力学性能进行了测试。结果表明,随着La₂O₃含量的增加,(Ni+La₂O₃)/Al复合材料的组织和性能先变好后变差。当La₂O₃添加量达到5%时,复合材料中Al₃Ni增强颗粒分布均匀、颗粒数量最多,块状的Ni粉团聚减少,其抗拉强度达到最大值215MPa,相比Ni/Al复合材料(抗拉强度176MPa),其抗拉强度提高了22%;当La₂O₃的添加量为7%时,复合材料中Al₃Ni增强颗粒含量减少,块状Ni粉团聚重新出现,抗拉强度下降至201MPa。     

Al9Fe0.7Ni1.3相对喷射沉积Al-Zn-Mg-Cu-Ni合金组织和性能的影响

本文利用喷射沉积技术合成含Ni的Al-Zn-Mg-Cu合金,合金中的Ni元素以亚微米球状Al₉Fe_0.7Ni_1.3化合物的形式存在。利用扫描电镜和电子背散射衍射、透射电镜以及拉伸测试研究了Al₉Fe_0.7Ni_1.3颗粒对合金固溶处理后组织和性能的影响。结果发现：Al₉Fe_0.7Ni_1.3颗粒主要在晶界附近分布,说明该颗粒在固溶过程中具有有力的抑制再结晶作用。固溶处理后,合金的拉伸强度为603 MPa,断裂延伸率为11.79%,主要断裂方式为穿晶延性断裂。实验结果表明亚微米球状Al₉Fe_0.7Ni_1.3化合物对合金性能有重要影响,可以产生细晶强化和Orowan强化,是合金发生穿晶延性断裂的主要原因。     

γ-TiAl合金表面Al2O3/Al复合涂层的抗高温熔盐腐蚀性能研究

采用磁控溅射技术于γ-TiAl合金表面制备Al₂O₃/Al复合涂层。在850 °C下、 100 wt.% Na₂SO₄熔盐中观测Al₂O₃/Al复合涂层的高温腐蚀行为。结果表明,Al₂O₃/Al复合涂层具备由Al₂O₃表层、富Al中间层以及互扩散层组成的梯度结构,因而有效地提高了基体γ-TiAl合金的抗高温腐蚀性能。在腐蚀实验后,涂层试样表面相结构为Al₂O₃,TiO₂和TiAl₃。致密的Al₂O₃/Al复合涂层有效地抑制了O_2-,S_-和Na₊对基体γ-TiAl合金的侵蚀。并且,Al₂O₃/Al复合涂层的梯度结构亦使其表现出了优异的抗开裂和抗剥落性能。     

功率对激光熔覆(Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)86B14涂层组织均质性及磨损性能的影响*

目前激光熔覆缺少对涂层组织、相结构纵向均质性与性能关联的研究。采用激光熔覆技术,选取不同的激光功率,制备(Fe_0.25Co_0.25Ni_0.25Cr_0.125Mo_0.125)₈₆B₁₄ 高熵合金涂层;借助电子探针(EPMA)、扫描电子显微镜(SEM)、能谱仪(EDS)和 X 射线衍射仪(XRD)等观察涂层微观组织与物相纵向分布,利用显微硬度计和摩擦磨损试验机测试涂层不同深度部位显微硬度及磨损性能,分析激光功率对熔覆(Fe_0.25Co_0.25Ni_0.25Cr_0.125Mo_0.125)₈₆B₁₄ 涂层纵向组织、物相分布影响规律及磨损性能。结果表明：三种功率下,涂层均由 BCC+FCC 相、硬质相 Mo₂B 组成,Mo₂B 在枝晶间富集。随着功率的增加,涂层中底部显微组织由细枝晶向粗大的柱状晶转变。三种涂层硬度均由表及里先增加后降低,摩擦因数先降低后增加;但是当激光功率为 1.6 kW 时,涂层呈现以 BCC 相为主的 FCC+BCC 双相结构,且由表及里 BCC 相含量不断增加、Mo₂B 含量逐渐减少,涂层组织均质化最高,摩擦因数变化梯度最小,耐磨损性能最佳。激光功率会影响熔覆高熵合金耐磨涂层均质性,进而影响摩擦性能的稳定性。     

Effect of adding carbon nanotubes on stress of Fe3A1 intermetallics

Analyses on the stress in the carbon nanotube/Fe₃Al composites were performed. The biphase interface valence electron structure was established on the basis of Pauling's nature of the chemical bond. The stress occurs by the huge interface electron density difference, which will block the Fe₃Al grain agglomeration and growth. With the X-ray diffractions, the calculated magnitude of compressive stress existing in the CNT/Fe₃Al interface is 0.38 GPa. The experimental result verifies that the stress has a positive effect on the enhancement of mechanical properties of composite.     

Influence of Cr on the Oxidation of Fe3Al and Ni3Al at 500°C

The influence of chromium on the mechanical properties of the aluminides Fe₃Al and Ni₃Al has been studied extensively. In order to evaluate the role of Cr during the early stages of oxidation, Fe₃Al and Ni₃Al containing 2 and 4 at.% Cr were oxidized in dry air at 500°C for 6, 50, and 100 hr. The oxide scale on Fe₃Al consists of a layer of Fe₂O₃ mixed with FeAl₂O₄ on top of a continuous layer of (Al, Cr)₂O₃. Ni₃Al is covered with a mixed layer of (Al, Cr)₂O₃ and NiO/NiAl₂O₄ underneath a layer of NiO/NiAl₂O₄. Moreover, Cr induces the nucleation and growth of Fe₂O₃ and NiO particles at the oxide surface of Fe₃Al and Ni₃Al, respectively. This is due to enhanced cationic diffusion through the Cr-modified oxides. As a conclusion, additions of Cr up to 4 at.% are detrimental to the oxidation behavior of both aluminides at 500°C.     

Identification of the spinel (Cr,Al)3S4 in the internal sulfidation zone of Al-diffusion coatings

The thiospinel (Cr, Al)₃S₄ has been identified in the internal sulfidation zone of Al-diffusion coatings by electron diffraction in a transmission electron microscope. The Al/Cr ratio of this phase can vary over a rather broad range, obviously dependent on the Al/Cr ratio in the surrounding metallic matrix. The spinel can dissolve significant amounts of Ni and Mo, some Co but only traces of Ti. Increasing Al-content extents its stability to higher temperatures.     

Interface electron structure of Fe3Al/TiC composites

1 Introduction Recently a few studies[1?3] have been carried out to utilize carbides or borides as reinforcements in iron aluminides, thus improving their mechanical properties. Additionally, an intermetallic matrix reinforced with ceramic phase might mak…     

Preparation, microstructure and properties of molybdenum alloys reinforced by in-situ Al2O3 particles

The conventional molybdenum alloys, lacking of hard particles enhancing wear property, have relative poor wear resistance though they are widely used in wear parts. To resolve the above question, Mo alloys reinforced by in-situ Al₂O₃ particles are developed using powder metallurgy method. The in-situ α-Al₂O₃ particles in molybdenum matrix are obtained by the decomposition of aluminum nitrate after liquid-solid incorporation of MoO₂ and Al(NO₃)₃ aqueous solution. The α-Al₂O₃ particles well bonded with molybdenum distribute evenly in matrix of Mo alloys, which refine grains of alloys and increase hardness of alloys. The absolute density of alloy increases firstly and then decreases with the increase of Al₂O₃ content, while the relative density rises continuously. The friction coefficient of alloy, fluctuating around 0.5, is slightly influenced by Al₂O₃. However, the wear resistance of alloy obviously affected by the Al₂O₃ particles rises remarkably with the increasing of Al₂O₃ content. The Al₂O₃ particles can efficiently resist micro-cutting to protect molybdenum matrix, and therefore enhances the wear resistance of Mo alloy.     

First-principles study of pressure-induced magnetic transition in siderite FeCO3

The crystal structure, electronic configuration, spin state and electronic structure of siderite FeCO₃ under pressure have been studied by first-principles calculations in the framework of density functional theory (DFT). The real antiferromagnetic (AFM) spin ordering state has been considered and the hydrostatic pressure condition is simulated. The calculated geometric structural data (unit-cell volume V, lattice constant a, cell angle α and atomic internal coordinate u) of FeCO₃ at ambient condition in good agreement with available data from the literature. FeCO₃ transforms from high spin (HS) AFM state to low spin (LS) nonmagnetic (NM) state between 40 and 50 GPa, concomitant with a volume collapse of 11%. The unit cell volume V₀, bulk moduli B₀, and its pressure derivative B′₀ of the HS and LS state are fit with a 3rd-order Birch-Murnaghan equation of state, which consist well with available experimental results. The insulating nature of FeCO₃ is remained after the magnetic transition. The 3d electrons of Fe²⁺ ions for the LS NM state are more localized than those of the HS AFM state, which leading to the magnetic transition.     

Low temperature synthesis of Fe3O4 micro-spheres and its application in lithium ion battery

Fe₃O₄ micro-spheres with nanoparticles close-packed architectures were synthesized via a simple chemical method using (NH₄)₂Fe(SO₄)₂·6H₂O, hexamethylenetetramine, and NaF as reaction materials. This chemical synthesis took place in a vitreous jar under low temperature (90 °C) and atmospheric pressure. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ micro-spheres as anode electrode of lithium ion batteries were studied by conventional charge/discharge tests, which exhibit steady charge/discharge platforms at different current densities. The as-prepared Fe₃O₄ electrode shows high initial discharge capacity of 1166 and 1082 mAh g⁻¹ at current density of 0.05 and 0.1 mA cm⁻², respectively.