Fe2+、Fe3+对CaO-Al2O3-SiO2-MgO系微晶玻璃析晶性能的影响规律

为了利用大量的含铁铝硅酸盐固体废弃物制备具有高附加值的微晶玻璃,采用DTA、XRD、SEM、EDS等手段研究了Fe2+、Fe3+对CASM系微晶玻璃析晶性能的影响.结果表明,Fe2+在微晶玻璃中与Mg2+的作用相同,取代以网络外体形式存在的Al3+,使得微晶玻璃的析晶温度逐渐下降,而对析晶能力几乎没有影响,并当Fe2+掺入量为2%时,主晶相由铝黄长石转变为镁黄长石,在7.5%时,进一步转变为透辉石.Fe3+掺量小于7.5%时,起到补充Si4+不足的作用,当大于7.5%时,部分Fe3+起到与Fe2+、Mg2+相同的作用,使得析晶温度呈先升后降的变化,在掺量为7.5%时,铝黄长石主晶相才开始转变为镁黄长石,在10%时,转变为透辉石,且析晶能力得到大幅提升.随着Fe2+和Fe3+含量增加,虽然微晶玻璃中主晶相的变化顺序相同,但Fe2+具有降低微晶玻璃析晶温度的作用,而一定量的Fe3+可作为晶核剂提高微晶玻璃的析晶能力.     

超临界流体干燥法制备TiO2/ Fe2O3 和TiO2/ Fe2O3/ SiO2 复合纳米粒子及光催化性能

以TiCl₄ 、Fe (NO₃ )₃·9H₂O 和Na₂SiO₃19H₂O 为原料, 采用溶胶凝胶法结合超临界流体干燥法(SCFD)制备了纳米级TiO₂/ Fe₂O₃ 和TiO₂/ Fe₂O₃/ SiO₂ 复合光催化剂。以光催化降解苯酚对所得催化剂的催化活性进行了评价。结果表明, 纳米TiO₂/ Fe₂O₃ 复合粒子与单组分TiO₂ 比较, 复合粒子光催化活性高于单组分的TiO₂, 6h 苯酚降解率高达95.9 %。SiO₂ 的加入可以抑制纳米粒子粒径的长大和晶相的转变, 增强TiO₂ 纳米粒子的热稳定性。复合光催化剂中Fe₂O₃ 最佳掺入量为0.06 %, SiO₂ 最佳掺入量为10 %(摩尔分数) 。并用XRD、TEM 和FTIR 等手段进行了表征。TiO₂ 以锐钛矿型形式存在, SiO₂ 以无定性形式存在。比较了不同制备方法制得的TiO₂/ Fe₂O₃ 复合光催化剂, 得出超临界干燥法制备的光催化剂具有粒径小、比表面积大、分散性好、光催化活性高等特点。采用超临界流体干燥可直接得锐钛型纳米复合光催化剂。     

纳米-Al2O3/SiO2加入量对MgO-Al2O3-SiO2复相陶瓷烧结机理的影响

为了探究纳米-Al₂O₃/SiO₂加入量对MgO-Al₂O₃-SiO₂复相陶瓷烧结行为的作用机理。以微米级MgO、纳米级Al₂O₃和SiO₂为主要原料制备陶瓷基复合材料。通过XRD和 SEM等检测手段对烧后试样的物相组成和微观结构进行测试与表征,重点研究Al₂O₃/SiO₂的加入对复相陶瓷物相组成、微观结构及烧结性能的影响。结果表明:随着Al₂O₃/SiO₂加入量的增大,试样烧后相对密度和烧后线变化率呈先增大后减小再增大的趋势,加入15%Al₂O₃/SiO₂(质量分数)的试样经1 500 ℃烧结后,其相对密度可以达到94%。引入的Al₂O₃/SiO₂与基体中的MgO生成镁铝尖晶石与镁橄榄石相,原位反应伴随的体积膨胀,抵消部分烧结过程中的体积收缩。Al₂O₃/SiO₂加入量为75%(质量分数)的试样经1 400 ℃烧结后,基体中有大量堇青石相生成,随着煅烧温度提高到1 500 ℃,堇青石分解所产生的高温液相促进了试样的烧结收缩。     

TiO2-SiO2复合材料的结构调变对其催化应用的影响

TiO₂-SiO₂复合材料(TSCM)的催化应用性能受到其所含TiO₂物种的晶相和SiO₂骨架的孔道结构的显著影响。本文归纳总结了TSCM中TiO₂物种晶相、SiO₂骨架的孔道结构、形貌等特性的调变规律及其对TSCM催化性能的影响,并展望了TSCM材料的结构特性演变趋势以及在制备方法上的取舍。TSCM直接作为催化剂时,其活性位普遍被认为是TiO₂-SiO₂界面上的Ti—O—Si键位和酸性位点。而作为载体材料时,TSCM中的TiO₂物种可以与负载的金属活性中心表现出显著的载体-金属相互作用(SMSI),TiO₂物种的晶相可以对形成的金属活性中心的性能产生显著影响。在TSCM材料的合成研究中,合成含有单一锐钛矿相(Anatase)TiO₂物种的Anatase-SiO₂或单一金红石晶相(Rutile)的Rutile-SiO₂类型TSCM材料,以及同时含有这两个晶相TiO₂,但晶相比例可调的A/R-SiO₂类型TSCM材料仍充满挑战。TSCM的SiO₂骨架特性调控也同样具有挑战,如何在得到特定晶相和粒子尺寸的TiO₂物种的同时获得特定孔道特性和形貌特征的SiO₂骨架,仍是研究的难点和热点。两步法无需同时控制TiO₂和SiO₂物种的制备参数,重现性好,多用于特殊形貌的TSCM的制备,但通常其中TiO₂物种的分散度不佳。而一步法制备过程简短,更容易得到多孔-大比表面积材料,有利于实现TiO₂粒子的尺寸控制及其在SiO₂骨架中的均匀分布,从而得到更丰富的Ti—O—Si界面活性物种,但需要在同一合成体系中同时控制相互影响的TiO₂和SiO₂物种的制备参数,调控难度极大,与两步法相比,重现性较差。     

纳米Al2O3颗粒增强新型铜基自润滑复合材料

以Cu-Ni-Y₂O₃-MoS₂-Graphite混合粉为基体,加入质量分数分别为0%、1%、2%、3%、4%的纳米Al₂O₃增强相,采用粉末冶金方法制备纳米Al₂O₃增强新型铜基自润滑复合材料。结果表明：随着铜合金粉末中纳米Al₂O₃颗粒含量的增加 , 所制备自润滑复合材料样品的密度下降,但硬度和压溃强度先上升后下降,在Al₂O₃含量为2%时硬度从HV 23.7增加到HV 35.1,压溃强度从189 MPa提高到276 MPa。由石墨和MoS₂组成的混合固体自润滑材料的摩擦系数小且稳定,约0.12。Al₂O₃质量分数为2%的样品磨损量最小,是未加Al₂O₃试样磨损量的1/7～1/8。铜基体经过镍、纳米Al₂O₃等弥散颗粒强化和固体润滑相石墨和MoS₂的加入,所制备的材料已具有一定的自润滑性能。     

Fe3O4/Ni复合纳米颗粒的制备及其微波吸收特性

采用电爆炸技术,合成了粒径约为70nm 的Ni纳米颗粒,以3-巯基丙基三甲氧基硅烷偶联剂(MPTS)对Ni颗粒进行表面改性,利用共沉淀法对改性Ni颗粒进行包覆得到核-壳结构的复合纳米颗粒。将获得的复合纳米颗粒作为微波吸收剂, 并以不同比例分散到热固性酚醛树脂中,涂刷在200mm×200mm的金属板上,用RAM反射率远场RCS测量法研究了微波吸收特性。研究表明,核-壳结构Fe₃O₄/Ni复合颗粒作为微波吸收剂,在相同质量比条件下,其微波吸收性能明显优于纯Ni纳米颗粒或Fe₃O₄纳米颗粒的情况,并且在Fe₃O₄/Ni核-壳结构复合纳米颗粒中随着镍含量的提高,微波吸收增强,而随着Fe₃O₄含量的增加,微波吸收频段向高频段移动。     

La2O3-TiC/W复合材料组织结构与力学性能

采用真空热压烧结法制备La₂O₃-TiC/W复合材料,并对其组织结构和力学性能进行了研究。结果表明：在一定成分范围内,La₂O₃和TiC的加入提高了复合材料的力学性能,La₂O₃和TiC共同作用时的强化效果强于La₂O₃和TiC单独作用的强化效果,但La₂O₃-TiC/W复合材料的密度和相对密度随TiC含量的增加而下降,并进而影响硬度和弹性模量的提高, 适量的La₂O₃有益于相对密度的提高;抗弯强度在1%La2O3 5%TiC/W成分含量时出现最大值901MPa,而断裂韧性在成分含量为0.5%La₂O₃-10%TiC/W时出现最大值10.07MPa·m1/2。本研究中,1%La₂O₃-5%TiC/W成分配比时具有较好的综合力学性能。La₂O₃-TiC/W复合材料的强化机制为细晶强化和载荷传递,韧化机制为细晶韧化、裂纹偏转和桥接。     

热处理对Bi2O3-B2O3-SiO2凝胶玻璃粉体结构与性能的影响

采用溶胶-凝胶法制备了一种Bi₂O₃-B₂O₃-SiO₂系玻璃粉体,在200 ℃、400 ℃、600 ℃和800 ℃温度下分别对凝胶玻璃粉体进行热处理,借助SEM、TEM、XRD、FT-IR、Raman、XPS、DSC、热膨胀仪及“纽扣”烧结实验分别测定了经不同温度热处理后玻璃粉体的结构与性能,分析了其结构变化对玻璃粉体转变温度T_g和烧结特性的影响。结果显示,在实验温度范围内,随热处理温度升高,Bi³⁺逐渐进入玻璃网络中,[BiO₆]八面体和[BiO₃]三角体、[BO₄]四面体和[BO₃]三角体分别与[SiO₄]四面体以顶角相连的方式构建玻璃网络结构。O1s和Bi4f的电子结合能逐渐增大,B1s的电子结合能减小,玻璃网络结构稳定性增强,导致玻璃转变温度T_g及玻璃膨胀软化点温度T_d升高、 润湿性降低且热膨胀系数略有降低。经600 ℃热处理后,玻璃粉体具有较优的烧结性能,T_g、T_d分别约为485 ℃及542 ℃,热膨胀系数α约为7.067×10-6/℃。     

Y2O3添加量对Al2O3/ZrO2共晶陶瓷显微组织及力学性能的影响

为探索第三组元Y₂O₃添加对Al₂O₃/ZrO₂共晶陶瓷显微组织与机械性能的影响,本文利用低温度梯度的高温熔凝法制备了直径为20 mm的Al₂O₃/ZrO₂(Y₂O₃)共晶陶瓷块体,采用SEM、EDS及XRD技术对共晶陶瓷进行微结构分析,并利用维氏压痕法对其硬度和断裂韧性进行测试。SEM结果表明,凝固组织由群集的共晶团结构组成,随着Y₂O₃添加量的增加,共晶团形态由胞状转变为枝晶状,内部相间距在1~2 μm范围内变化。力学测试表明,Y₂O₃摩尔分数小于1.1%时,由于组织内部存在低硬度m-ZrO₂及微裂纹缺陷,故陶瓷硬度较低,约为(9.53±0.22 )GPa;当Y₂O₃摩尔分数为1.1%时,陶瓷硬度最大,约为(18.05±0.27)GPa;当Y₂O₃的摩尔分数大于1.1%时,由于共晶团边界区内气孔缺陷及粗大组织增多,引起陶瓷硬度值略有下降。低Y₂O₃摩尔分数添加时,陶瓷断裂韧性相对较高,约为(6.30±0.16)MPa·m^1/2,这与其内部存在大量微裂纹缺陷有关;随着Y₂O₃添加量的增加,陶瓷的微裂纹数量减少、边界区内缺陷增多,断裂韧性降低。     

ZrO2在β"─Al2O3复合陶瓷中的作用

本文研究了四方和立方ZrO₂在与Na-β"-Al₂O₃的复合陶瓷中作为第二相所起的各种作用。结果说明ZrO₂对复合陶瓷具有细化晶粒、改善显微结构、提高强度和断裂韧性的作用,与此同时也在一定程度上降低离子电导率。在提高力学性能方面,四方ZrO₂除了具有与立方ZrO₂相同的弥散颗粒的作用外,相变所起的作用也是很显着的。ZrO₂-Na-β"-Al₂O₃复合陶瓷是一种有应用价值的固体电解质材料。     

Structural and morphological properties of Fe2O3/TiO2 nanocrystals in silica matrix

We report on structural, morphological and ordering properties of Fe₂O₃/TiO₂ nanoparticles embedded in SiO₂-based multilayers. We investigated the structure of these systems by X-ray diffraction and grazing incidence small angle X-ray scattering after post-growth annealing. We found that the presence of TiO₂ promotes the growth and crystallization of the nanocrystals of Fe₂O₃. In multilayers containing both Fe₂O₃ and TiO₂, crystalline nanoparticles create partially ordered three-dimensional arrays.     

Effect of Y3+ codoping on luminescence decays of the 4I13/2 level in Er3+-doped Al2O3 powders prepared by a sol-gel method

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er³⁺- and 0–20 mol.% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er³⁺-doped Al₂O₃ by Y³⁺ codoping. For the 0.1 mol.% Er³⁺-Y³⁺-codoped Al₂O₃ powders, the measured lifetime of Er³⁺ gradually increases with increasing Y³⁺ concentration. Consequently, codoping with 20 mol.% Y³⁺ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er³⁺ concentrations in the Al₂O₃ powders, the radiative lifetime of both the Er³⁺-doped and the Er³⁺-Y³⁺-codoped Al₂O₃ powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y³⁺ codoping does not change the-OH content in the Er³⁺-Y³⁺-codoped Al₂O₃ powders. The prolonged luminescence lifetime of the ⁴I_13/2 level of Er³⁺ in Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping is ascribed to the decrease in the energy transfer rate between the Er³⁺ ions and the Er³⁺ and -OH, respectively, due to the suppressed interaction between Er³⁺ ions.     

Epitaxial growth of Fe3Si/CaF2/Fe3Si magnetic tunnel junction structures on CaF2/Si(111) by molecular beam epitaxy

The Fe₃Si(24 nm)/CaF₂(2 nm)/Fe₃Si(12 nm) magnetic tunnel junction (MTJ) structures were grown epitaxially on CaF₂/Si(111) by molecular beam epitaxy (MBE). The 12-nm-thick Fe₃Si underlayer was grown epitaxially on CaF_2/Si(111) at approximately 400 °C; however, the surface of the Fe₃Si film was very rough, and thus a lot of pinholes are considered to exist in the 2-nm-thick CaF₂ barrier layer. The average roughness (Ra) of the CaF₂ barrier layer was 7.8 nm. This problem was overcome by low-temperature deposition of Fe and Si at 80 °C on CaF₂/Si(111), followed by annealing at 250 °C for 30 min to form the Fe₃Si layer. The Ra roughness was significantly reduced down to approximately 0.26 nm. A hysteresis loop with coercive field H_c of approximately 25 Oe was obtained in the magnetic field dependence of Kerr rotation at room temperature (RT).     

Ferrimagnetic and semiconducting CaCu3Fe2Sb2O12 by first principles

CaCu₃Fe₂Sb₂O₁₂ is mechanically stable, thermodynamically stable at pressures above 18 GPa. Both GGA and GGA + U methods predict that it is a ferrimagnetic semiconductor with Fe³⁺ in high spin state (S = 5/2). The coupling of Fe–Cu is antiferromagnetic, while that of Cu–Cu is ferromagnetic. The calculated total spin moment is 6.17 μ_B.     

Self-controlled growth of Fe3BO6 crystallites in shape of nanorods from iron-borate glass of small templates

Fe₃BO₆ can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe₃BO₆ growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B₂O₃ − xFe₂O₃, x = 40–50 mol%. B₂O₃ as a strong glass former co-bridges the Fe³⁺ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe³⁺ species in form of a compound Fe₃BO₆, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B₂O₃ layer (15–25 nm thickness) has grown on the Fe₃BO₆ of the nanorods in situ in a specific structure. XPS bands in the Fe³⁺, B³⁺ and O²⁻ species confer this model structure. A local BO₃ → BO₄ conversion has incurred in the boroxol (B₃O_4.5)_n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm⁻¹.     

Synthesis of nanostructured M/Fe3O4 (M = Ag,Cu) composites using hexamethylentetramine and their electrocatalytic properties

Nanoscaled Ag/Fe₃O₄ hybrids with different Ag contents and Cu/Fe₃O₄ nanoshpere and microsphere were successfully synthesized with assistance of sodium citrate and (CH₂)₆N₄ via a hydrothermal process. The as-prepared samples were identified and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS), respectively. All samples were used as electrocatalysts modified on a glassy carbon electrode for p-nitrophenol reduction in a basic solution. The catalytic activity of Ag/Fe₃O₄ samples increased first and then decreased by increasing Ag content from 0% to 8%, and the one with 6% Ag displayed the highest catalytic activity. All the Cu/Fe₃O₄ samples exhibited enhanced catalytic activity by comparison with a glassy carbon electrode, and the one prepared with the molar ratio of Cu²⁺, Fe³⁺, citrate anion, and (CH₂)₆N₄ with 1:1:3:5 exhibited the highest catalytic activity.     

UV-visible spectra of perovskite iron-doped Ba0.72Sr0.28TiO3

The ultraviolet-visible spectra of the pure barium strontium titanate (Ba_0.72Sr_0.28TiO₃) and the Fe³⁺-doped Ba_0.72Sr_0.28TiO₃ were measured. The pure barium strontium titanate exhibited an ultraviolet (UV) absorption effect. The addition of Fe₂O₃ resulted in an increase of absorption wavelength. This red-shift effect was very strong even though the amount of Fe³⁺ was very small. The similar phenomenon was also observed in pure BaTiO₃ and Fe³⁺-doped BaTiO₃. The UV-absorption behavior was discussed in terms of Fe³⁺ replacing Ti⁴⁺ in the titanate with perovskite structure.     

Influence of Ga2O3 addition on transparent conductive oxide films of In2O3-ZnO

Influence of incorporation of Ga in amorphous In-Zn-O transparent conductive oxide films was investigated as a function of Zn/(Zn + In). For In-Zn-O films with no Ga₂O₃, the range of Zn/(Zn + In) ratio where the amorphous phase appears became narrow at a substrate temperature of 250 °C. With increasing Ga₂O₃ quantity, amorphous films were obtained even at a high substrate temperature of 250 °C in a wider range of Zn/(Zn + In) than that of In-Zn-O films with no Ga₂O₃. This means that the trend of crystallization at higher substrate temperature was disturbed with additional Ga incorporation. For the film deposited from ZnO:Ga (Ga₂O₃: 4.5-7.5 wt%) and In₂O₃ targets, we obtained a resistivity of 2.8 × 10⁻⁴ Ω cm, nearly the same value as that for an In-Zn-O film with no Ga₂O₃. The addition of more than 7.5 wt% Ga₂O₃ induced a widening of the optical band gap.