Fractal structure and optical properties of semicontinuous silver films

Semicontinuous silver films, prepared by vacuum evaporation on substrate of KBr crystals, have been made with area coverage in the range 0.3–0.8. The morphology of the films were found to change with coverage p. At small or large coverage range, homogeneous films were observed, but when the coverage approaches a critical value p_c (p_c ≈ 0.65), the film was inhomogeneous. The topologic parameters of films such as mean size of cluster S_AV, correlation length ξ and fractal dimension D_f were measured. When the area coverage was close to p_c, S_AV and ξ rapidly diverged and a knee point appeared in the curve of D_f vs. p. The transmittance of films in mid-infrared wave-band (2.5–12.5 m) was measured. For homogeneous films, as wavelength increased, transmittance increased when p < p_c but decreased when p < p_c. On the other hand, transmittance was wavelength independent for inhomogeneous films. The optical percolation phenomenon is observed at a region where the fractal dimension D_f of the film was kept approximately constant while correlation length diverges. These experimental results were compared with existing theory and we interpret the effect of deposition and coalescence on the percolation parameters by considering the growth mechanism of a nano-structured metal film.     

铬酸银纳米棒组装体的简易合成及其光学性能

在简单温和的条件下利用模板法,首次合成出了铬酸银纳米棒组装体,构成该组装体的纳米棒长度约为150～250nm,直径约70nm.当激发波长为383nm时,发射出432nm的蓝光;产物在紫外-可见光谱356nm处有明显的宽化吸收.     

Effect of microstructure morphology on mechanical properties of quenching and partitioning steel

In order to illuminate the relationship between microstructure morphology and final properties of the quenching and partitioning(Q&P) steel, the samples with different microstructure morphology (equiaxed and lamellar) and same volume fraction of each phase are obtained by controlling the initial microstructure and Q&P heat treatment. Because of the feature of microstructure morphology, a large yield ratio and total elongation are obtained in the lamellar sample though yield strength and ultimate tensile strength are relatively lower than that of equiaxed sample. Moreover, the lamellar sample produces a continuous work-hardening rate and better the fracture toughness compared to the equiaxed sample. Thus the lamellar sample is more suitable to be used as automotive structural components.     

晶粒尺寸对CVD金刚石膜电学特性的影响

通过改变生长参数,采用热丝化学气相沉积(HFCVD)法制备了从10μm到90nm四种晶粒尺寸的金刚石膜,并制作了三明治结构的光电导探测器.采用原子力显微镜和拉曼光谱仪研究了薄膜的结构和表面形貌:表面粗糙度从423nm变化到15nm;晶粒越大,金刚石膜的质量越好.I-V特性测试结果表明随着晶粒尺寸的减小,金刚石膜的电阻率从1011Ω·cm减小到106Ω·cm.在5.9 keV的55Fe X射线辐照下,随着晶粒尺寸的减小,探测器的信噪比(SNR)呈减小趋势.     

碱式硫酸镁形貌对碱式硫酸镁/聚丙烯复合材料力学性能的影响

以三种不同形貌的碱式硫酸镁(颗粒状(MOS_P)、晶须状(MOS_W)和扇形(MOS_S))为填料、月桂酸(LA)为改性剂、聚丙烯(PP)为树脂基体,通过熔融共混法制备了系列MOS/PP复合材料。SEM结果显示,改性后的MOS_P和MOS_W在基体中分散均匀,但与基体PP的相容性依然较差;MOS_S/PP样品中同时存在着尺寸较大且形貌复杂的MOS_S和部分分散的MOS_W,界面缺陷更加明显。广角X-射线衍射(WXRD)结果表明,三种MOS均能诱导β-晶型PP的产生,与月桂酸的加入无关,其中MOS_P诱导效果更明显。力学性能测试结果表明,三种形貌MOS的加入稍降低了基体的屈服强度,一方面是MOS与基体相容性差,另一方面归结于β-晶型PP生成;相比之下,MOS_W加入能较好地保持PP基体的屈服强度和拉伸断裂韧性,且明显增强基体的模量,主要归因于MOSW较大的长径比;MOS_P对基体的增韧效果更为明显,一方面是由于MOS_P诱导生成β-晶型PP的效果强于MOSW和MOS_S,另一方面则可能是由于MOS_P较大的比表面积附着了较多的脂肪酸盐,其增塑效果更强。     

纳米银-聚合物薄膜的制备及力电性能测试

聚合物基底上纳米银颗粒薄膜的制备工艺相对简单,成本较低,且该薄膜具有成为高敏感性压阻应力/应变传感材料的潜力。本文采用银镜制备法在聚酰亚胺(PI)和聚乙烯(PE)上合成了纳米银颗粒薄膜,系统研究了该薄膜制备工艺、结构特性、材料性能之间的关系。实验考察了材料“浸泡”时间及聚合物材料前处理等因素对材料表面吸附纳米颗粒含量的影响,研究了 “浸泡”时间对纳米银颗粒粒径大小、颗粒含量及分布的影响,并探讨了不同聚合物基体的颗粒特性对薄膜二维导电渗滤,压阻特性及拉伸性能的影响。研究表明,增加“浸泡”时间能够增加纳米银颗粒粒径大小,提高银颗粒的含量及分布均匀性；在相同的制备条件下,PI基底较PE基底对纳米银颗粒具有更加优异的吸附效果；在PI 和PE基底上的纳米银颗粒薄膜均表现出显著的压阻性能,且电阻对应变的敏感性随应变的增大及银颗粒含量的减少而显著提高。     

EVA/纳米TiO2复合体系的制备工艺对力学性能及分散状态的影响

详细研究了乙烯-醋酸乙烯酯共聚物(EVA)和纳米氧化钛(nano-TiO2)复合体系的制备工艺对力学性能、分散状态的影响.研究表明,如果把乙烯基三乙氧基硅烷(硅烷偶联剂)作为一个组分,直接与基体EVA及分散相纳米TiO2进行混合,更有利于纳米粒子在基体中的分散.在该复合体系中,纳米TiO2与乙烯基三乙氧基硅烷达到了协同增韧EVA的目的,同时,纳米TiO2具有补强作用,当复合体系的组成为EVA/纳米TiO2=95:5时,对EVA的改性效果最佳.     

Electronic properties of semiconducting silicides: fundamentals and recent predictions

This review emphasizes progress in theoretical simulation and experiments that have been performed in the past years for semiconducting silicides. New fundamental electronic and optical properties of Ca₂Si and BaSi₂, recently found RuSi₂ phase, ternaries in Fe-Os-Si and Ru-Os-Si systems, β-FeSi₂, Mg₂Si and CrSi₂ with stretched and compressed lattices as well as transport properties of β-FeSi₂, ReSi_1.75, Ru₂Si₃ are presented. Prospects for practical applications of semiconducting silicides are discussed.     

无机盐离子对多孔VO_2薄膜微观形貌及热致相变性能的影响

以云母(001)为衬底,采用无机溶胶-凝胶法,通过添加表面活性剂十二烷三甲基溴化铵(CTAB),以及加入同一元素族、不同粒径的无机盐离子Li+、Na+、K+和同一周期、不同价态的Na+、Mg2+、Al3+制备多孔VO2薄膜。采用SEM、FT-IR等手段分析薄膜的微观形貌特征和热致相变性能。结果表明,不同化合价、不同粒径的无机盐离子对多孔VO2薄膜的颗粒尺寸分布、微观形貌以及热致相变性能产生影响。     

发泡废纸板纤维/LDPE复合材料的加工流变性及泡孔形态

以废弃瓦楞纸板纤维和低密度聚乙烯(LDPE)为基体辅以相应的相容剂、 润滑剂和发泡剂, 利用挤出发泡法制备了发泡废纸板纤维/LDPE木塑复合材料。通过熔融指数仪研究了废纸板纤维含量、 相容剂马来酸酐接枝聚乙烯(MAH-g-PE)的用量、 润滑剂的种类与用量以及发泡剂偶氮二甲酰胺(AC)的用量对该复合材料加工流变特性的影响; 并利用SEM观察不同熔融指数的复合材料对泡孔形态的影响。结果表明: 随着废纸板纤维含量的增加, 复合材料的熔融指数(MFI)迅速下降; MAH-g-PE增加了纤维填料与树脂基体之间的相互作用, 复合材料的熔融指数随着相容剂用量的增加先降低后升高, 其含量的转变点为15%; PE蜡对复合材料的综合润滑作用最明显, 复合材料的熔融指数随着PE蜡的含量呈近线性变化; AC发泡剂的加入降低了复合材料的熔融指数, AC发泡剂的含量超过5%将使复合材料产生明显的壁滑移; 随着熔融指数的增加, 复合发泡材料的泡孔逐渐变大, 当熔融指数为1.5时, 泡孔大小适中且分布均匀。     

Electronic mechanism of sintering: Some case studies on real systems

The paper reviews the role of electronic configuration model of condensed state in explaining the sintering behaviour of various alloys. The systems are copper base alloys, ferrous alloys containing phosphorus, tungsten based heavy alloys, Al-refractory carbide composites, 6061 Al-alloy composites, high speed steel composites and tungsten carbide based cemented carbides. These studies cover the research activities of the Powder Metallurgy Laboratory at IIT, Kanpur.     

Effect of eggshell powder as nucleating agent on the structure,morphology and functional properties of normal corn starch foams

Corn starch and eggshell powder (with particle sizes of 4–5µm and 8–10µm) composite foams were prepared by extrusion. Effects of eggshell on the structure, morphology, physical properties (unit density and expansion ratio), mechanical properties (spring index and compressibility) and thermal behaviour (thermal transition and stability) of the foams were investigated. Foam cell size decreased and cell population increased with addition of eggshell into starch matrix. The foam unit density, expansion ratio and compressibility decreased significantly (p < 0.05), while the spring index increased significantly (p < 0.05) as the eggshell content increased from 0 to 6wt%. Further increasing eggshell content to 10wt% increased the unit density and compressibility and decreased the expansion ratio and spring index. The thermal transition and stability increased with the addition of eggshell. The optimum eggshell content was 6wt% and the smaller‐sized eggshell powder had a favourable effect on the functional properties of the foams. Copyright © 2006 John Wiley & Sons, Ltd.     

有机改性蒙脱土的制备及其对聚乙烯-聚苯乙烯相态和力学性能的影响

利用Gemini表面活性剂对蒙脱土进行插层改性制备得到有机改性蒙脱土（OMMT）,采用溶液混合法制备了OMMT/聚苯乙烯（PS）母料,将OMMT/PS母料与聚乙烯（PE）熔融共混制备得到OMMT/PS-PE复合材料。研究了蒙脱土的插层改性对OMMT/PS-PE复合材料相形态和力学性能的影响。对OMMT进行FTIR、XRD、TG表征,结果表明Gemini表面活性剂成功插层进入蒙脱土层间。通过SEM和电子万能试验机研究了OMMT/PS-PE复合材料相结构、分散相粒径的及相态与力学性能之间的关系。结果表明,随着OMMT含量的增加,PS分散相的粒径逐渐减小;当OMMT含量为2.5wt%时,OMMT/PS-PE复合材料的相形态由“海-岛”转变为双连续结构。与未添加OMMT的PE-PS树脂相比,OMMT/PS-PE复合材料弯曲模量和断裂伸长率显著提高,分别提高了约18%和近50倍。      

利用第一性原理研究Ge:Si电子结构与光学性质

采用基于密度泛函理论的平面渡超软赝势方法和广义梯度近似,计算了掺杂Ge前后单晶Si中Si-Ge键的布居值、键长以及能带结构和态密度.计算结果表明,Ge掺杂后体系晶格常数发生变化,Ge-Si键变长,布居值及带隙宽度减小.还进一步研究了掺杂Ge后的光学性质,掺杂后静态介电常数值与纯Si相比有所增大,且吸收带宽变窄、吸收带边明显红移,并对这些掺杂诱导的材料物性变化进行了解释.     

有机蒙脱土对ABS-PA6共混物形态结构与力学性能的影响

熔融挤出制备了不同有机蒙脱土(OMMT) 含量的OMMT/丙烯腈-丁二烯-苯乙烯(ABS) -尼龙6 (PA6) (30/70,质量比) 复合材料,用透射电子显微镜(TEM),扫描电子显微镜(SEM) 等研究了OMMT在ABS-PA6共混物中的分布及其对ABS-PA6共混物形态结构与力学性能的影响。结果表明:在OMMT/ABS-PA6复合材料中,OMMT主要以剥离形态分布在PA6基体相中,少量分布在PA6与ABS两相界面处,具有明显的选择分布性;随着 OMMT含量增加,ABS分散相尺寸逐渐减小且分布均匀OMMT/ABS-PA6 复合材料的强度、模量逐渐提高,当OMMT含量为7 wt%时 , 弯曲强度和模量分别由未加OMMT时的66. 7 MPa、2. 308 GPa上升至94. 1 MPa、3. 184 GPa,缺口冲击强度在OMMT含量为3 wt%时出现极大值3. 7 kJ / m,但总体变化不大。      

晶粒生长的控制及对铅钙铁铌陶瓷体系微波介质性能影响的研究

研究了晶粒生长的固有机制,并针对铅钙铁铌陶瓷体系的掺杂改性设计一组实验,实验结果表明工艺因素特别是烧结温度及保温时间对晶粒形貌有显著影响,随烧结温度及保温时间的增加晶粒尺寸不断增加,但超过一定值后,不断减小的气孔率又会增加。本文提出一种晶粒生长模型,将烧结分成烧结前期、烧结中后期以及临界点后烧结期3个阶段,并证明每种材料由于组成不同和基本晶粒的不同会有最佳的烧结临界点,把握该临界点是控制材料性能的关键。     

Geometries, electronic and magnetic properties of hafnium clusters: A density functional calculation

The geometries, electronic and magnetic properties of Hf_n (n = 2-13,14,18) clusters are studied by using density functional methods. Particularly, the studies focus on the averaged atomic binding energies, equilibrium geometries, detachment energies, and magnetic characteristics of Hf_n clusters. Relative stabilities of Hf_n clusters in terms of the calculated detachment energies are discussed, exhibiting that the magic numbers of stabilities are n = 4, 7, 9, and 12, and that the nonmagnetic Hf₁₂ geometry is the most stable isomer and ground state. Furthermore, the calculated highest occupied orbital and lowest unoccupied orbital gap of Hf_n (n = 6-13) displays a small odd-even oscillation feature. The calculated ground state magnetic moments for Hf_n are respectively 4.0 μ_B (n = 4,11), 2.0 μ_B (n = 2,5,7-9,13), and 0.0 μ_B (n = 3,6,10,12,14,18); the averaged atomic magnetic moment of Hf_n is generally decreased as the number of n being increased. Comparison of our calculated results with available experimental data is made.     

Electronic properties of WC nano-compound: Compton spectroscopy and band structure calculations

We present the electronic properties of tungsten carbide (WC) nano-compound using the Compton scattering technique. We have measured the Compton profile (CP) of nano-powder using our ¹³⁷Cs Compton spectrometer. To determine the theoretical CPs of WC nano-compound, we have employed linear combination of atomic orbitals (LCAO) with Hartree-Fock and density functional theory. Although all the LCAO-based calculations show similar agreement with the experiment, the second-order generalised gradient approximation gives a marginally better agreement with the measured CP data. Layered structures and slight over-lapping in energy bands show a small role of exchange and correlation potentials in case of WC nano-compound, which is in contrast to bulk WC.     

Effects of ultrasonic treatment on microstructure and mechanical properties of 6016 aluminium alloy

Ultrasonic treatment was applied during solidification forming of 6016 aluminium alloys. The effects of ultrasonic vibration on the microstructure and mechanical properties of the 6016 aluminium alloy ingot were studied. Compared with conventional casting, the ingot prepared with ultrasound applied to the molten metal had a fully refined microstructure and greater material homogeneity. Ultrasonic treatment reduced the amount of porosity developed by embedded gas and also resulted in an obvious decrease in solidification defects, like shrinkage. In addition, component segregation was minimised and the mechanical properties were enhanced.