共沉淀ZnO/γ-Al2O3体系EXAFS研究

用XRD和EXAFS研究了200°C,300°C,450°C,800°C焙烧的共沉淀ZnO/γ-Al₂O₃体系.通过EXAFS分析得到了Zn原子的径向分布函数,并针对第一配位层做了定量的拟合,结果是体系中第一层锌氧Zn-O保持ZnO中的四配位结构.文中还对第二层配位峰的变化趁势做了分析.     

Er3+及Er3+/Yb3+掺杂ZrO2-Al2O3的制备及发光性质

采用共沉淀法制备了纳米晶ZrO₂-Al₂O₃∶Er³⁺发光粉体.所制备的粉体室温下具有Er3+离子特征荧光发射,主发射在绿光,其中位于547 nm、560 nm的绿光最强,并得出稀土离子与基质之间有能量传递.对不同煅烧温度下的样品研究表明:因不同温度下所制得的样品晶相不同.研究了纳米晶ZrO2-Al2O3∶Er3+及ZrO₂-Al₂O₃∶Er³⁺/Yb³⁺的上转换发光,并分析了上转换的跃迁机制.发现ZrO₂-Al₂O₃∶Er³⁺的绿光为双光子过程,而ZrO₂-Al₂O₃∶Er³⁺、Yb³⁺的上转换光谱中,红光和绿光也为双光子过程,而极弱的蓝光为三光子过程.讨论了Er³⁺的浓度猝灭现象.最适宜掺杂浓度的原子分数为2%（Er³⁺/Zr⁴⁺）.     

固体颗粒的结构演化与机械力化学效应

干法、室温振动研磨制备铝超微颗粒, 分别将研磨2 h, 4 h和8 h的铝粉, 在常温下超声水解得到白色Al(OH)₃胶体, 水解产品经干燥、研磨、焙烧后制备出多孔、片状γ -Al₂O₃纳米颗粒, 粒度分布在30---50 nm之间. 借助于X射线衍射(XRD)分析方法和透射电子显微镜(TEM), 研究固体颗粒在细化过程中的能量转换, 分析颗粒的微结构演化与机械力化学反应的关系, 确定理想的研磨时间. 研究结果表明: 固体颗粒在机械力的作用下产生大量的应变和位错缺陷, 使材料处于亚稳、高能活性状态, 易于诱发机械力化学反应, 在一定条件下晶体的表面能、应变能和层错能相互转化; 研磨2 h的铝颗粒内部, 晶格畸变和位错概率最大, 材料显示出极高的化学反应活性, 在超声波激发下, 储存在材料内部的能量被充分释放, 在较短的时间内, 水解生成Al(OH)₃纳米颗粒.     

Effect of Calcination Temperature on La-Modified Al2O3 Catalysts for Vapor Phase Hydrofluorination of Acetylene to Vinyl Fluoride

利用沉积沉淀法制备出了La改性Al₂O₃催化剂,研究不同焙烧温度对La改性Al₂O₃催化剂用于乙炔气相氢氟化合成氟乙烯反应性能的影响．利用NH₃-TPD、Pyridine-FTIR、XRD和Raman等技术对不同温度焙烧的催化剂进行表征,发现焙烧过程能改变催化剂结构的同时也能调变催化剂表面的酸量．经400 °C焙烧的催化剂显示出最高的乙炔转化率(94.6%)、最高的氟乙烯选择性(83.4%)和较低的积炭选择性(0.72%)．催化剂的高活性与其表面的高酸量有关,同时积炭的选择性也与其表面的酸中心数量有关．     

压力对纳米CoFe2O4/SiO2复合材料结构的影响

 采用溶胶-凝胶工艺和高温高压实验技术,制备了纳米CoFe₂O₄/SiO₂复合材料。利用X射线衍射仪、扫描电子显微镜和振动样品磁强计,对样品的结构、微观形貌和磁性进行了研究,并对CoFe₂O₄中阳离子的占位情况进行了讨论。结果表明,随着处理压力的升高,样品的晶粒尺寸增大,晶格常数减小,比饱和磁化强度增大。通过计算结果可以推断,压力的升高导致CoFe₂O₄中的部分Fe³⁺从A位移向了B位,而部分Co²⁺则从B位移向了A位。     

双金属镍-锰/γ-Al2O3催化剂对甲烷二氧化碳重整反应的影响 (cited: 1)

用浸渍法制备γ-Al₂O₃负载的Ni-Mn双金属催化剂．在500～700 oC按照17:17:2的CO₂/CH₄/N₂比例,以36 mL/min的载气流速进行甲烷二氧化碳重整反应, 利用甲烷二氧化碳的转化率、生成的合成气H₂/CO比例以及长期稳定性等指标评价了催化剂的催化性能． 实验表明, 添加Mn提高催化性能并使双金属催化剂的稳定性更高, 比单金属催化剂更好地抑制焦炭生成,Mn最合适的添加量0.5wt％ ．通过BET、CO2-TPD、TGA、XRD、SEM、EDX和FTIR各种技术对催化剂进行了表征．     

掺入Ni2+和V3+对α-Al2O3晶体光谱精细结构、晶体局域结构和零场分裂参量的影响

应用晶体场理论和不可约张量算符方法构造了3d2/3d8态离子在C3v对称晶场中包含自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用四种微观磁效应的45阶可完全对角化的能量哈密顿矩阵.利用该矩阵,计算了V³⁺∶α-Al₂O₃和Ni²⁺∶α-Al₂O₃晶体的光谱精细结构、晶体局域结构和零场分裂参量,研究了掺入两种互补态离子Ni²⁺和V³⁺对同种晶体的光谱精细结构、晶体局域结构和零场分裂参量的影响,理论计算值和实验值相符.研究发现：掺杂没有改变晶体的光谱精细结构和能级分裂条数,但改变了能级间距|掺杂也没有改变晶体的对称性,但使晶体局域结构发生了一定程度的畸变| Ni²⁺∶α-Al₂O₃晶体局域结构的伸长畸变量大于V³⁺∶α-Al₂O₃晶体,键角的变化量小于V³⁺∶α-Al₂O₃晶体.     

焙烧温度对SiO2负载的Co3O4纳米粒子表面氧缺陷浓度和CO氧化催化性能的影响

以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co₃O₄/SiO₂催化剂．通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构．在所有的催化剂中,XRD和Raman光谱都只检测到了Co₃O₄晶相的存在．与Co₃O₄体相相比,XPS结果表明在200 oC焙烧的(Co₃O₄(200)/SiO₂)催化剂中Co₃O₄表面上存在着过量的Co²⁺．与XPS的结果一致,TPR结果表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄表面上存在氧缺陷, 并且XAFS结果也表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄具有更多的Co²⁺．提高焙烧温度使得过量的Co²⁺进一步氧化为Co³⁺,同时降低了表面氧缺陷浓度,从而得到计量比的Co₃O₄4/SiO₂催化剂．在所有的负载催化剂中Co₃O₄(200)/SiO₂催化剂表现出了最好的CO氧化催化性能,表明过量Co²⁺和表面氧缺陷的存在能够促进Co₃O₄催化CO氧化反应的活性.     

SiO2内保护层对LiB3O5晶体倍频增透膜损伤阈值的影响

 利用离子辅助电子束沉积方法在LiB₃O₅基底上镀制了不加SiO₂内保护层和加SiO₂内保护层的倍频增透膜，测量了两类薄膜在波长1 064 nm多脉冲辐照下的激光损伤阈值，获得了两种不同的损伤形貌，并对损伤原因作了初步探讨。实验结果表明：保护层的加入把由基底膜层界面缺陷吸收所决定的阈值改变到由HfO₂膜层内缺陷吸收所决定的阈值，显著提高了倍频增透膜的抗激光损伤能力。     

块状Ta2O5-TiO2复合气凝胶的制备与表征

 以乙醇钽、钛酸丁酯为原料,以乙醇为溶剂,通过溶胶-凝胶法及超临界干燥成功制备了Ta₂O₅-TiO₂复合气凝胶。用场发射扫描电镜（SEM）、透射电镜（TEM）、扫描电镜模式下的电子能谱仪（EDS）以及比表面积吸附仪（BET）对其进行表征。结果表明:该气凝胶是由粒径在nm量级的Ti和Ta的羟基氧化物胶体颗粒堆积而成的低密度、高比表积的多孔网络结构材料,孔径分布主要集中在5~15 nm,比表面积为492.9 m²/g,密度为90 mg/cm³左右。     

Low-temperature deposition of α-Al2O3 films by laser chemical vapor deposition using a diode laser

We prepared Al₂O₃ films by laser chemical vapor deposition (LCVD) using a diode laser and aluminum acetylacetonate (Al(acac)₃) precursors and investigated the effects of laser power (P_L), deposition temperature (T_dep), and total pressure (P_tot) in a reaction chamber on the crystal phase, microstructure, and deposition rate (R_dep). An amorphous phase was obtained at P_L = 50 W, whereas an α-phase was obtained at P_L > 100 W. At P_L = 150 and 200 W (1 0 4)- and (0 1 2)-oriented α-Al₂O₃ films were obtained, respectively. The R_dep of α-Al₂O₃ films increases with decreasing P_L and P_tot. Single-phase α-Al₂O₃ film was obtained at T_dep = 928 K, which is about 350 K lower than that obtained by conventional thermal CVD using Al(acac)₃ precursor.     

Er3+掺杂SiO2复合的Al2O3粉末结构及光致发光特性

采用溶胶-凝胶(sol-gel)工艺制备0.1 mol% Er³⁺掺杂Al₂O₃体系和SiO₂-Al₂O₃复合体系粉末. 实验结果表明：5 mol%的SiO₂复合加入Al₂O₃抑制γ→θ和θ→α相转变. 掺0.1 mol%Er³⁺:Al₂O₃体系粉末，900℃烧结，在1.47—1.63μm波段内光致发光(PL)谱为中心波长1.53 μm、半高宽56 nm的单一宽峰，1000—1200℃烧结，劈裂为多峰PL谱. 掺0.1 mol%Er³⁺:SiO₂-Al₂O₃复合体系粉末，在高达1200℃烧结，仍保持中心波长1.53 μm的单一宽峰PL谱，由于—OH更完全的脱除，PL强度较900℃烧结Al₂O₃体系，SiO₂-Al₂O₃复合体系均提高1个数量级. 关键词： 2-Al₂O₃复合体系')" href="#">SiO₂-Al₂O₃复合体系 掺铒 溶胶-凝胶工艺 光致发光     

Influence of postdeposition annealing on structural properties and electrical characteristics of thin Tm2O3 and Tm2Ti2O7 dielectrics

We describe the structural properties and electrical characteristics of thin thulium oxide (Tm₂O₃) and thulium titanium oxide (Tm₂Ti₂O₇) as gate dielectrics deposited on silicon substrates through reactive sputtering. The structural and morphological features of these films were explored by X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy, measurements. It is found that the Tm₂Ti₂O₇ film annealed at 800 °C exhibited a thinner capacitance equivalent thickness of 19.8 Å, a lower interface trap density of 8.37 × 10¹¹ eV⁻¹ cm⁻², and a smaller hysteresis voltage of ∼4 mV than the other conditions. We attribute this behavior to the Ti incorporated into the Tm₂O₃ film improving the interfacial layer and the surface roughness. This film also shows negligible degrees of charge trapping at high electric field stress.     

Constituted oxides/nitrides on nitriding 304, 430 and 17-4 PH stainless steel in salt baths over the temperature range 723 to 923 K

The progressively developed oxides and nitrides that form on nitriding 304, 430 and 17-4 PH stainless steel are analysed by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) in this study. The experimental results show that the Cr contents and matrix structures (ferrite, austenite and martensite) play an important role in forming FeCr₂O₄, Cr₂O₃ and Fe₂O₃ oxides as well as nitrides. After a short immersion time, oxides of Cr₂O₃ and FeCr₂O₄ form in nitride films on 304 stainless steel samples. Fe₂O₃ oxide will subsequently form following an increasing immersion time. For the 430 stainless steel, Cr₂O₃ predominately forms after a short dipping time which hinders the growth of the nitride layer. As a result, this sample had the thinnest nitride film of the three for a given immersion time. After the formation of oxides, both CrN and Cr₂N were detected near the surface of the nitride films of three samples while Cr₂N phases formed in the deeper zone. The greatest amount of Fe₂O₃ oxide among the three samples was obtained on the nitriding 17-4 PH stainless steel which also had a high intensity count of N 1s.     

Effects of RE2O3 (RE = Tm, Sc, Yb) addition on the superconducting properties of ErBa2Cu3Oy

We investigated the effects of added Tm₂O₃, Sc₂O₃, and Yb₂O₃ on the superconducting properties of sintered Er123 samples. Tm₂O₃ addition caused the least T_c degradation, exhibiting a T_c above 90 K even for 17 vol% addition. Samples with added Sc₂O₃ maintained a T_c at above 90 K up to an addition of 7.2 vol%, while Yb₂O₃-containing samples showed a monotonic decrease in T_c with increased vol% of added Yb₂O₃. Tm₂O₃-containing samples exhibited a slight increase in J_c(0.1 T)/J_c(0) and had constant J_c values even for 17 vol% addition. XRD and SEM results indicate that the Tm₂O₃ is very stable in the superconducting matrix.     

Multi-scale theoretical study of support effect on sintering dynamics of Pt

The capability of theoretical durability studies to offer an efficient alternative methodology for predicting the potential performance of catalysts has improved in recent years. In this regard, multi-scale theoretical methods for predicting sintering behavior of Pt on various catalyst supports are being developed. Various types of Pt diffusions depending on support were confirmed by the micro-scale ultra accelerated quantum chemical molecular dynamics (UA-QCMD) method. Moreover, macro-scale sintering behavior of Pt/γ-Al₂O₃, Pt/ZrO₂ and Pt/CeO₂ catalysts were studied using a developed 3D sintering simulator. Experimental results were well reproduced. While Pt on γ-Al₂O₃ sintered significantly, Pt on ZrO₂ sintered slightly and Pt on CeO₂ demonstrated the highest stability against sintering.     

Preparation, characterization and dye adsorption properties of γ-Fe2O3/SiO2/chitosan composite

A γ-Fe₂O₃/SiO₂/chitosan composite was prepared by water-in-oil emulsification, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Effects of various factors, including adsorbent dosage, initial dye concentration, solution pH, and competing anions, on the adsorption of methyl orange from aqueous solutions by the resulting composite were studied by batch adsorption experiments. The adsorption kinetics was found to follow the pseudo-second-order kinetic model, and intraparticle diffusion was related to the adsorption, but not as a sole rate-controlling step. The equilibrium adsorption data were well described by the Freundlich isotherm model. Evaluation of the thermodynamic parameters ΔG°, ΔH°, and ΔS° revealed that the adsorption process was naturally feasible, spontaneous, and exothermic. The composite was proven to be efficient, suitable and promising for the removal of methyl orange from aqueous solutions since it has a relatively higher adsorption capacity than other low-cost adsorbents.     

The electrical properties of dielectric stacks of SiO2 and Al2O3 prepared by atomic layer deposition method

We produced dielectric stacks composed of ALD SiO₂ and ALD Al₂O₃, such as SiO₂/Al₂O₃, Al₂O₃/SiO₂, and SiO₂/Al₂O₃/SiO₂, and measured the leakage currents through the stacks in comparison with those of the single oxide layers. SiO₂/Al₂O₃ shows lowest leakage current for negative bias region below 6.4 V, and Al₂O₃/SiO₂ showed highest current under negative biases below 4.5 V. Two distinct electron conduction regimes are observed for Al₂O₃ and SiO₂/Al₂O₃. Poole-Frenkel emission is dominant at the high-voltage regime for both dielectrics, whereas the direct tunneling through the dielectric is dominant at the low-voltage regime. The calculated transition voltage between two regimes for SiO₂ (6.5 nm)/Al₂O₃ (12.6 nm) is −6.4 V, which agrees well with the experimental observation (−6.1 V). For the same EOT of entire dielectric stack, the transition voltage between two regimes decreases with thinner SiO₂ layer.     

Point defects related to 260 K thermostimulated luminescence in α-Al2O3

Abstract

Thermo- and photostimulated processes are studied in reduced hydrogen containing α-Al₂O₃ excited by UV light. It is found that UV excitation in F absorption band at 90 K results in a ionization of the F-centers and capture of released electrons at defects thus producing an anisotropy absorption band at 4.2 eV and the dominant thermoluminescence (TL) peak at 260 K. The 260 K TSL peak is accompanied by complete bleaching of the 4.2 eV absorption band and vice versa—by light stimulation in the region of the 4.2 eV band the 260 K TSL peak disappear and released electrons recombine with F⁺-centers. Both the effect of the preliminary high-temperature thermal treatment of samples on formation of 4.2 eV-centers and the observed dichroism characteristics allows to conclude that corresponding complex defect contains hydrogen and can involve vacancy pair.