硅纳米管的理论及制备研究进展

硅纳米管在晶体管等纳米电子器件、传感器、场发射显示器件、纳米磁性器件及光电器件、储氢及电化学等领域有着广阔的应用前景.综述了近年来硅纳米管在储氢能力、热稳定性、量子限制行为及力学性能等理论方面的研究成果,以及采用水热法、模板法、电化学溶液沉积过程、化学气相沉积法、热蒸发、电弧法及激光烧蚀等方法制备单晶、多晶及非晶硅纳米管的最新研究进展,并提出了硅纳米管可能的研究方向.     

硼碳氮纳米管生长机理的研究

硼碳氮纳米管具有许多比碳纳米管更好的性质,因而成为当今世界研究的热门材料之一.用汽-液-固生长模型解释了硼碳氮纳米管的生长机理,并用化学键能分析了其C/BN相分离及结构的稳定性,指出了C和BN各自的能量及化学稳定决定B,C和N三种元素的分布情况.最后阐述了影响纳米管生长的几个主要因素.     

钛酸纳米管的AFM和STM研究

使用AFM 和STM研究了钛酸纳米管.得到了纳米管表面的精面结构.在纳米管表面观察到一个约0.8nm高的大台阶,这是由于纳米管的螺旋特性造成的.还观察到表面各处有楞边平行于管轴的小台阶.这些小台阶与钛酸片层上的相同,是Ti-O八面体的连接方式造成.这些结果与先前在TEM研究基础上提出的钛酸纳米管模型相符合.     

二氧化钛纳米管阵列的应用研究进展

二氧化钛纳米管阵列具有独特的结构、良好的化学惰性、更大的比表面积、纳米管与基底结合牢固等优点,其应用非常广泛.综述了二氧化钛纳米管阵列在太阳能电池、传感器、光解水制氢、光催化和环境分析方面的应用研究进展,并提出了二氧化钛纳米管阵列的应用发展趋势及展望.     

硅纳米管的研究进展

元素硅是sp3杂化,而不是易于形成石墨管状结构的sp2杂化,所以具有这种sp3杂化键的物质难于形成中空一维硅纳米材料,即硅纳米管.综述了硅纳米管及性能的理论研究,同时论述了采用模板法合成硅纳米管的最新实验进展情况,指出了目前硅纳米管的研究中需要解决的一些问题,并展望了发展.     

电泳沉积法制备钛酸纳米管膜层

采用水热合成法制备钛酸钠纳米管,然后依次与HNO3,正四丁基氢氧化铵水溶液(TBAOH)离子交换后,经过高速离心,将所得沉淀物分散于无水乙醇溶液中,并应用电泳沉积的方法成功地在不锈钢或导电玻璃表面构筑了钛酸纳米管薄膜.采用TEM、XRD、SEM及EDS等对纳米管薄膜的表面形貌、结构和组成等进行表征.结果表明,电泳沉积法制备钛酸纳米管薄膜致密均匀、厚度可控并与基体结合力良好;经高温烧结后,形貌基本保持不变,可望成为一种新的功能材料.文中还对纳米管薄膜的形成机理进行了讨论.     

硼碳氮纳米管制备方法的研究进展

三元化合物硼碳氮纳米管作为碳纳米管和氮化硼纳米管的衍生物,其禁带宽度主要取决于纳米管的成分,与手性和直径无关,且在0~5.5 eV范围内可调;另外,硼碳氮纳米管具有优良的电学性能、高硬度、高耐磨性及高温抗氧化等性质,使其在电子、光电子和纳米器件等领域具有广阔的应用前景。综述了硼碳氮纳米管制备方法的研究现状,并介绍了材料的生长机理、结构、性质和应用前景,简述了工艺条件对纳米管形成的影响,并对今后硼碳氮纳米管的研究方向提出了设想与展望。     

电解液组分对阳极氧化法制备TiO_2纳米管的影响

在不同电解液组分中采用阳极氧化法制备了不同结构参数的TiO2纳米管,考察了不同电解液组分对TiO2纳米管形貌和尺寸参数的影响.采用场发射扫描电子显微镜(SEM)和X射线衍射仪(XRD)对纳米管的形貌和结构进行了表征,并分析了电解液组分对纳米管生长的影响机制.结果表明,降低电解液中H+浓度以及减少电解液中H2O的含量可有效提高纳米管的长度.     

钛盐纳米管的制备及光电性能研究

采用水热法制备了钛盐纳米管,并用TEM、XRD对其进行了表征.结果表明,纳米管是在洗涤过程中形成的,管径在5～30nm之间,管长约为0.1～1μm.纳米管具有不同于锐钛矿型的钛盐的结构;将其在450℃下热处理2h后,纳米管转变为锐钛矿型TiO2粒子.将钛盐纳米管制备成纳米管结构电极,并进行了光电化学研究.钛盐纳米管产生阳极光电流,为n型半导体.     

氧化钒纳米管的自组装合成机理

以V₂O₅和十六胺为原料在水热条件下合成了氧化钒纳米管, 采用XRD、SEM、TEM、FTIR、ESR等手段分析研究了氧化钒纳米管的形成机理. 结果表明, 氧化钒纳米管的形成主要基于“卷曲机理”, 其形成过程包括: 表面活性剂分子嵌入到钒氧化物层间, 形成新层状化合物前驱体; 水热驱动下层状化合物边缘松动, 并开始卷曲, 降低体系能量; 合适的水热反应时间下最终形成钒氧化物纳米管. 模板剂嵌入到钒氧化物层间形成一定大小的层间距以及V⁴⁺的存在对从层状化合物卷曲成纳米管起到了积极的作用.     

Direct Evidence for Structural Transition Promoting Shear Thinning in Cylindrical Colloid Assemblies

In this paper, we describe stimuli‐responsive hydrogels prepared from a rigid rod‐like polyelectrolyte ‘imogolite’ and a dicarboxylic acid. The hydrogel exhibited thixotropy in response to mechanical shock within the order of seconds or sub‐seconds. Here, using the latest structural/rheological characterisation techniques, the relationship between the structural transition processes and the shear thinning was estimated. The evidence obtained by the experiments revealed for the first time the direct relationship between the microscopic structural change and the macroscopic thixotropic behavior that have been extensively discussed. The thixotropic hydrogel has the hierarchical architecture in the combination of imogolite and dicarboxylic acid, i.e., sheathed nanotubes/hydroclusters of cross‐bridged nanotubes/frameworks. The formation and disintegration of the network structure upon resting and agitating, respectively, were the origin of gel/sol transition (thixotropy), although the hydroclusters of cross‐bridged nanotubes were maintained throughout the transition.     

螺旋形手征碳纤维的微波介电特性

研究了线圈状和麻花状两种典型螺旋形手征碳纤维以及直线形碳纳米管在8.2-12.4GHz的微波介电特性.螺旋形手征碳纤维通过催化化学气相沉积法制备,直线形碳纳米管用催化裂解浮游法以苯为碳源制备.螺旋形手征碳纤维与石蜡复合体的介电常数的实部(ε′)和虚部(ε″)比直线形碳纳米管与石蜡复合体的小,但线圈状螺旋形碳纤维的介电损耗角正切(tgδ=ε″/ε′)却明显偏大,线圈状和麻花状螺旋形碳纤维的tgδ分别为0.77—0.80和0.47—0.53,直线形碳纳米管的tgδ为0.45-0.77.螺旋形碳纤维与微波作用时的手征特性是导致其tgδ增大的主要原因,螺旋形手征碳纤维对微波的吸收与其自身的形状和尺寸密切相关,所以线圈状螺旋形碳纤维的tgδ比麻花状的大得多,探讨了螺旋形手征碳纤维与微波的作用机理,螺旋形手征碳纤维是一种非常有发展前景的微波吸收材料.     

CFRP层间碳纳米管定向喷涂工艺及断裂韧性研究

为了提高碳纤维增强树脂基复合材料(CFRP)层间性能,采用共沉淀法在碳纳米管上接枝磁性Fe₃O₄粒子,通过定向喷涂工艺使磁性碳纳米管(Fe₃O₄-MWCNTs)在碳纤维表面取向一致,并喷涂树脂加以固定,形成碳纤维-定向碳纳米管-树脂界面,采用真空辅助树脂渗透成形(Vacuum assisted resin infusion, VARI)工艺制备层间性能优异的Fe₃O₄-MWCNTs层间定向增强CFRP。试验结果表明,喷涂树脂可改善和巩固定向喷涂工艺。与未加磁场喷涂工艺相比,当Fe₃O₄-MWCNTs的质量分数为0.3wt%时,采用定向喷涂工艺试件的I型层间断裂韧性(G_IC)提升幅度最大,G_IC提高了37.7%。断面形貌分析表明其增强机制以树脂的塑性变形、Fe₃O₄-MWCNTs棒状聚集体的拔出及树脂塑性孔洞的生长为主。该研究为具有可控定向行为的磁性碳纳米管改性CFRP层间力学性能提供了新思路与方法。      

Electrical,rheological and morphological studies in co-continuous blends of polyamide 6 and acrylonitrile–butadiene–styrene with multiwall carbon nanotubes prepared by melt blending

Multiwall carbon nanotubes (MWNT) were incorporated in melt-mixed co-continuous blends of polyamide 6 (PA6) and acrylonitrile–butadiene–styrene (ABS) using a conical twin-screw microcompounder. The state of dispersion of MWNT in the blends was assessed through AC electrical conductivity measurements and melt-rheological investigations. The electrical and rheological percolation threshold in PA6/ABS blends was ～3–4 and ～1–2 wt% MWNT, respectively. A unique reactive modifier (sodium salt of 6-amino hexanoic acid, Na–AHA) was employed to facilitate ‘network-like’ structure of MWNT and to confine them in a specific phase. This was achieved by establishing specific interactions with the delocalized ‘π-electron’ clouds of MWNT and melt-interfacial reaction during melt-mixing. The electrical percolation threshold was significantly reduced in the blends (～0.25 wt%) in the presence of Na–AHA modified MWNT and even coincided with the rheological percolation threshold. Significant refinement in the co-continuous structure was also observed in the presence of Na–AHA modified MWNT.     

Fabrication of yttria stabilized zirconia coatings by a novel slurry method

By adopting a ‘bricks and mortar’ approach, yttria stabilized zirconia (YSZ) coatings were produced on Fecralloy substrates by a novel slurry method. The slurry contained large preformed particles of 10–60 μm, as the ‘bricks’, and concentrated nano-particle slurry, as the ‘mortar’. Green coatings were prepared by spreading the slurry on substrates. Then sintering at 1200 °C was carried out to produce coatings with grain size up to 200 nm. The presence of larger preformed particles hindered the shrinkage of the coatings during drying and sintering. It was observed that the ‘mortar’ could form inter-preformed particle ‘bridging’, an underlying mechanism for the formation of ‘cemented’ preformed particle network. By using different preformed particles, different micro-architectures were obtained and reduced thermal diffusivities were achieved. The microstructure and density of the coatings can also be modified by infiltration of the nano-slurry.     

Intellectual contribution of Indian periodontists to world literature: a bibliometric evaluation of Pubmed database till 1st March, 2012

Scientifically liberated and developed countries produce huge amounts of cutting-edge publications in peer-reviewed impact-creating journals. These publications may become basis for various policies/other blueprints. There is no reported study regarding the publication trends of Periodontists from India. The aim of this study was to assess the trends of Indian Periodontist’s publications in Pubmed database till 1st March, 2012 by taking quantitative bibliometric approach. Studies were identified by running select search phrases on Pubmed search engine. Search inputs included, ‘dental’, ‘oral’, ‘periodontal’, ‘gingiva’, ‘gingival’, ‘periodontology’, ‘periodontics’, ‘periodontia’, ‘periodontitis’, ‘gingivitis’, and ‘dental implant’. A parallel search with above phrases along with ‘India’ also done to assess India-specific publications. All publications with or without available abstracts were analyzed for selected parameters. Analysis was performed to determine name of the journal, number of authors, year of publication, type of institute, statewide distribution, type of study etc. The approximate contribution of Indian Dental/Periodontal literature to Pubmed database is 1.45 % till 1st March 2012. The number of articles published by Indian Periodontists is 764 across 107 journals and starting from 1960. The number of original articles published were 510 (66.75 %) as opposed to 127 (16.62 %) each for review articles and case reports/case series. The average contribution of an Indian Periodontist to Pubmed database is 0.53 articles. The contribution of Indian Periodontists to world literature through Pubmed database is not voluminous but, the publications are multiplying every passing year almost in an exponential way. There is also an increasing trend towards original articles to be published.     

Thermodynamic solubility and solvation behavior of ferulic acid in different (PEG-400 + water) binary solvent mixtures

This work was carried out to determine solubility, solution thermodynamics, solvation behavior, and molecular interactions of a natural compound ferulic acid (FLA) in different ‘[polyethylene glycol-400 (PEG-400) + water]’ binary solvent mixtures at ‘T?=?298.2 K to 318.2?K’ and ‘p?=?0.1?MPa.’ The mole fraction solubilities (x_e) of FLA were determined by liquid chromatographic technique using a static equilibrium technique. The obtained solubility data of FLA were regressed using ‘Van’t Hoff, Apelblat, Yalkowsky-Roseman and Jouyban-Acree models.’ The solubility of FLA (expressed in mole fraction) was enhanced with elevation in absolute temperature in each ‘PEG-400?+?water’ binary solvent mixture evaluated. The maximum x_e values of FLA were recorded in neat PEG-400 (1.94?×?10^?1) at ‘T?=?318.2 K.’ While, the minimum one was obtained in neat water (4.90?×?10^?5) at ‘T?=?298.2 K.’ The molecular interactions between FLA-PEG-400 and FLA-water were obtained by determination of activity coefficients of FLA in different ‘PEG-400?+?water’ binary solvent mixtures. The physical data of activity coefficients recorded in this work suggested strong molecular interactions in FLA-PEG-400 in comparison with FLA-water. ‘Apparent thermodynamic analysis’ suggested an ‘endothermic and entropy-driven dissolution’ of FLA in each ‘PEG-400?+?water’ binary solvent mixture investigated.     

石英基底上定向单壁碳纳米管阵列可控生长

以铜为催化剂,甲烷为碳源,采用化学气相沉积法在石英单晶基底上生长定向单壁碳纳米管阵列,分别用扫描电子显微镜、原子力显微镜对其结构进行表征,研究了使用聚合物聚乙烯丙烯酸甲脂（PMMA）分散催化剂对碳纳米管密度和定向性的影响,利用PMMA分散催化剂能提高催化剂的活性,增加定向碳纳米管的密度,使催化剂形成规则的条状,能进一步提高其密度和定向性。采用微加工工艺做成器件,并利用半导体参数测试仪对器件进行了电学测试。     

多壁碳纳米管/天然橡胶复合材料压阻传感特性实验分析及理论预测

为实现对隔震支座工作性能的有效监测,采用开炼法制备了多壁碳纳米管(MWCNT)/天然橡胶(NR)复合材料,研究了该复合材料在恒应变和间歇加载下的电阻-应变响应行为。结果表明：MWCNT/NR复合材料电阻-应变响应稳定性、重复性、单调性、对称性及“肩峰”效应依赖恒应变载荷;随着间歇时间的增加电阻变化幅值趋于稳定,所建立的理论模型能有效预测该幅值变化。不同脱层形式下MWCNT/NR复合材料表现出不同的压阻行为,采用Digimat和Workbench解释了其响应机制。基于MWCNT导电网络和橡胶材料黏弹性,一个能够完整表征和预测循环电阻-应变响应的数学模型被提出和验证,模型拟合结果与实验结果高度吻合,为实现MWCNT/NR复合材料的工业应用奠定理论基础。     

Optimization of the liquid–liquid interfacial precipitation method for the synthesis of $$\hbox {C}_{60}$$ nanotubes

Tubular fullerene nanowhiskers called ‘fullerene nanotubes’ are composed of \(\hbox {C}_{60}\) fullerene molecules (\(\hbox {C}_{60}\) NTs) are synthesized at room temperature using the liquid–liquid interfacial precipitation method in the pyridine and isopropyl alcohol (IPA) system. The growth control of fullerene nanotubes is important for their chemical and physical properties as well as for their future applications. In the present study, we investigated the effect of light, water, solvent ratio and temperature on the synthesis of \(\hbox {C}_{60}\) nanotubes. A marked development in the yield of \(\hbox {C}_{60}\) NTs was achieved using dehydrated solvents, a solution with a volume ratio of 1:9 for pyridine: IPA, a growth temperature equal to \(5{^{\circ }}\hbox {C}\) and by illuminating the \(\hbox {C}_{60}\)-pyridine solution with ultraviolet light (wavelength 302 nm) for 102 h. The synthesized fullerene nanotubes were characterized by different analytical techniques including Raman and Fourier transform infrared spectroscopy, optical microscopy, focussed ion beam scanning electron microscopy and transmission electron microscopy.