多孔阳极氧化铝微孔结构的调控

多孔阳极氧化铝(AAO)是一种在酸性电解液下,通过施加电压对金属铝阳极氧化获得的多孔膜材料。AAO在当今纳米材料领域有着非常多的应用,如制备纳米阵列、进行纳米复制、制备量子点等。本文采用二次氧化法制备了AAO模板,研究了硫酸、草酸两种电解液以及氧化电压对纳米孔的影响规律。采用扫描电子显微镜(SEM)对样品的表面形貌进行分析,研究了制备工艺对孔形态的影响。通过统计不同氧化电压下AAO孔的圆度和孔径的分布,发现圆度随着电压的升高而升高。孔径随电压的升高而增大,两者呈现成指数型关系。     

两次氧化条件对阳极氧化铝孔洞的影响

采用两次阳极氧化法在草酸溶液中制备多孔氧化铝(AAO),分别研究了电压、氧化时间及草酸溶液浓度对AAO孔洞特征的影响。结果表明,在第一次氧化过程中孔间距随氧化电压的提高而增大,氧化时间和草酸溶液浓度几乎没有影响;在第二次氧化过程中时间、电压及草酸溶液浓度对孔间距基本无影响,但是随着氧化电压的增大AAO孔径明显增大,孔洞呈六方阵列排布。此外,第二次氧化电压增大时孔洞形状由圆形到长条形、再到六边形变化;第二次氧化草酸溶液浓度增大至0.4 mol/L时所制备的AAO的相邻孔洞沿特定取向发生贯穿现象,甚至溶解,而孔洞整体分布有序性几乎不受影响。     

长程有序纳米孔氧化铝模板的制备与研究

以硫酸和草酸溶液为电解液,采用二次阳极氧化法制备出高度长程有序的纳米孔氧化铝(AAO)模板,并结合扫描电子显微镜(SEM)对其微观结构及形貌进行了观察和表征.通过研究不同的氧化电压和电解液浓度对AAO模板纳米孔形貌(孔径、孔间距、面密度和长程有序性)的影响,得到了最佳的氧化电压和电解液浓度.     

阳极电压对多孔阳极氧化铝薄膜光学常数的影响

根据多孔阳极氧化铝(AAO)薄膜200～2500nm波段透射谱,计算研究了AAO薄膜的重要制备工艺参数阳极电压对其光学常数的影响.结果表明随阳极电压的升高,AAO薄膜的折射率和厚度增大,消光系数减小.这主要源于AAO薄膜中孔密度随阳极电压的升高而迅速下降,但AAO薄膜厚度的迅速增加,减弱了阳极电压对其光学常数的调制作用.     

铝箔多孔阳极氧化铝膜的低温制备及其电化学性能

以多孔阳极氧化铝(AAO)膜制备纳米材料时降低AAO膜孔径至关重要,降低电压无法达到要求,而降低氧化温度可实现这一目标。在0.4 mol/L H3PO4溶液中加入70%～80%(体积分数)1,3-丙三醇(PDO),于-10～10℃下恒压110 V阳极氧化1 h制备了多孔阳极氧化铝(AAO)膜,并在0.50 mol/L H3BO3和0.05mol/L Na2B4O7溶液中于20℃下以0.5 mA/cm2进行填孔后处理。利用SEM,EDS,XRD分析了AAO膜的表面形貌与组成,并对AAO膜填孔前后的极化曲线和交流阻抗谱进行了测试。结果表明,膜孔径随氧化温度降低而降低,80%PDO,10℃所得AAO膜的成分包括65.94%(质量分数,下同)Al,12.79%C,20.29%O和0.98%P;随氧化温度升高和PDO含量下降,AAO膜的稳定电流密度增大;随氧化温度升高,膜阻挡层厚度增大;填孔试验前AAO膜只存在一个阻挡层的相位角峰,填孔后出现两个峰,中高频段体现封闭的阻挡层特性,低频段体现的是多孔层封闭部分的特性。     

纳米氧化铝有序多孔膜制备工艺研究

为了获得大面积有序孔排列以及不同孔径的氧化铝膜,采用二次阳极氧化法可制备大面积有序铝阳极氧化多孔(AAO)膜,着重研究氧化电压、氧化时间、电解液浓度以及扩孔时间对AAO膜孔径大小、膜层厚度和形貌结构的影响,用X射线粉末衍射(XRD)仪进行物相分析,利用扫描电子显微镜(SEM)表征多孔膜的形貌.结果表明,在700 ℃以下条件下AAO膜以无定形态存在,经800 ℃退火后无定形氧化铝转化为γ-Al2O3,多孔膜随电压和电解液浓度增加而增大,经H3PO4溶液扩孔后可获得较大孔径模板,扩孔时间与孔径变化呈近似线性关系.为满足应用需求的AAO膜的制备提供了依据.     

AAO模板快速制备方法探究

为了快速制备出高度有序且孔径可调控的AAO(阳极氧化铝)模板应用于工业生产,通过改进传统的两步阳极氧化法,采用逐步提高电解液浓度的硬氧氧化法制备了AAO模板,并确定了最佳制备工艺为初始电解液浓度0.15mol/L,添加电解液浓度0.40mol/L,温度保持在5℃左右,无水乙醇添加比例为1:1,从而使铝片的击穿电压从40V上升到130V左右(模板面积1.5cm×4.5cm),采用DimensionEdge型号的原子力显微镜(AFM)对多孔氧化铝模板进行了表征。结果表明:未经退火处理的铝片,也可以制备出高度有序的AAO模板,但其粗糙度略有增加,并与在高压条件下二次氧化、三次氧化、四次氧化制备AAO模板进行了比较,发现二次氧化制备的AAO模板有序度、孔径、孔间距均优于三次、四次氧化法。     

降低二次氧化温度制备高度有序阳极氧化铝模板

传统的两步阳极氧化方法在制备多孔阳极氧化铝(AAO)模板时需要两次反应都在低温条件(0~5℃)下进行以保证膜的稳定生长,然而该制备工艺在温度控制方面通常比较复杂。尝试对制备工艺进行改进,在一次高温(20℃)二次低温(5℃)条件下成功制备出了高度有序的AAO模板。随着第二次反应温度的降低,孔的排列趋于整齐,其孔径、孔隙率和孔的深度都有较显著的变小趋势,而孔间距无明显变化。此外,实验中还发现在高温下容易出现套孔现象,这可能是反应时释放出的焦耳热消散不充分所致,当第二次反应温度降到5℃时被完全消除。     

结构调制型氧化铝模板的制备及表征

采用两种不同方法制备了结构调制的多孔氧化铝(AAO)模板,一种是磷酸扩孔法,另一种是非对称阳极氧化法。磷酸扩孔法是根据传统有序氧化条件,在模板二次阳极氧化后,用磷酸对已形成的孔道进行扩孔,然后再进行第三次阳极氧化;非对称阳极氧化法是在第一次氧化后形成的有序凹痕上,在始终保持氧化电压与第一次氧化时相同,同时确保相邻两次氧化在不同类型电解液中进行的条件下,制备出孔间距相同、孔径不同的有序结构调制的AAO模板。这些方法扩展了在给定电解液中制备AAO模板的孔径,从而实现了AAO模板的结构调制。     

碳纳米管管径的可控性研究

为了合理有效控制碳纳米管(CNTs)的管径,比较研究了化学气相沉积(CVD)-模板法与CVD-中毒法.通过透射电镜(TEM)观察碳纳米管形貌及其管径尺寸,分析了不同条件下,碳纳米管的形貌差异,讨论了制备阳极氧化铝(AAO)膜的氧化电压对碳纳米管的管径、管的有序度的影响和碳酸钠毒物对碳纳米管的管径、管形、产率的影响,并且分析了两种制备方法的生长机理.结果表明,在CVD-模板法中,在一定范围内,电压升高可以使AAO膜孔增大,从而控制碳纳米管的外径;在CVD-中毒法中,微量的碳酸钠粉末能增大碳纳米管的内径.     

Humidity control porous ceramics prepared from waste and porous materials

This study investigated the feasibility of generating humidity control porous ceramics by sintering a mixture of volcanic ash, weathered volcanic ash, and waste glass. The sintering conditions, including sintering time, sintering temperature, and various mixed portions of glass amendment, were tested. The final ceramics were analyzed for their pore distribution, pore volume, adsorption and desorption characteristics, and bending strength. The results indicate that the pore size of the volcanic ash ceramics tends to distribute in the range from 70 to 100 nm, whereas that of the weathered volcanic ash ceramics is in the range of 7-9 nm. The humidity controlling conditions of the ceramics take advantage of the inherent porosity of the natural materials. The bending strengths in both cases were all satisfying with the fractural intensity specification of ceramics (> 6 Mpa).     

Light-emitting porous silicon

Although porous silicon has been known for more than 35 years, only in 1990 was it recognized that porous silicon shows an increased bandgap and efficient room-temperature photoluminescence in the visible. This paper will give an overview of porous silicon research, with special emphasis on the formation mechanism of microporous silicon in terms of a depletion of holes in the porous region due to quantum confinement and the understanding of the origin of the visible luminescence. The status of research on electroluminescent and other devices based on porous silicon will be discussed, as well as results for other luminescent forms of nanocrystalline silicon.     

Preparation of tungsten carbide porous sphere core wrapped by porous multiwall

Tungsten carbide porous sphere core wrapped by porous multiwall was prepared by spray drying sphere miniaturation—gas–solid reaction, used ammonium metatungstate as precursors, hydrogen and methane as reduction and carbonization atmosphere. The sample was characterized by SEM, XRD and BET, respectively. The SEM results show that the sample is constituted by two parts, a core with porosity and porous multiwall, and the wall is made up of a lot of nanoscale particles. The XRD results show that the crystal phase of the sample is tungsten carbide (WC) only, and the average size of the WC crystal estimated according to XRD data is around 14 nm. The BET specific area of the sample is 10.2834 m²/g.     

Effects of porous boundaries on peristaltic transport through a porous medium

Summary Peristaltic pumping by a sinusoidal traveling wave in the porous walls of a twodimensional channel filled with a viscous incompressible fluid through a porous medium is investigated theoretically and graphically. It has been considered that the fluid is entering the flow region through one plate at the same rate as it is leaving through the other plate. A perturbation solution is obtained, which satisfies the momentum equation for the case in which the amplitude ratio is small. It has been noticed that the mean axial velocity and the reversal flow increase by increasing the permeability parameterW. The mean axial velocity and the reversal flow decrease by increasingV until at the upper quarter of the channel it increases by increasingW. Also, the fluid motion is nonsymmetric. Numerical results are reported for various values of the physical parameters of interest.     

Vapor phase manufacture of porous TiN deposits on/in porous supports

Particle Precipitation aided Chemical Vapor Deposition (PP-CVD) is a modification of the conventional CVD process. In PP-CVD an aerosol is formed in the gas phase at an elevated temperature, and particles are deposited on a substrate surface. The synthesis of titanium nitride (TiN) using titanium tetrachloride vapor, nitrogen, ammonia, and hydrogen is studied. TiN is formed by a heterogeneous reaction involving a titanium containing species and nitrogen, whereas simultaneously a TiN aerosol is formed by a reaction involving ammonia. Dense columnar microstructures are formed in the absence of a temperature gradient. At low temperature differences between substrate and gas phase only dense microstructures with virtually equiaxed grains are observed. Porous coherent layers are found in experiments, where larger temperature differences are applied. The observed interconnection of the particles originates from a heterogeneous reaction. A further increase in temperature difference between the susceptor and the gas phase only leads to loose powder deposits.     

Magneto-transport in porous silicon

Magnetoresistance (MR) measurements have been performed in the temperature range 100–300 K on macroporous porous silicon (P.S.) samples. P.S. layers have been prepared by the anodic dissolution of Si in HF acid. The MR has been found to be positive in P.S. for the temperature range 100–300 K and for the entire range of magnetic field (0–5 kG). However the magnitude of the positive MR is found to be much less than expected on the basis of free electron conduction. Also the value of n in the relation Δρ/ρ_o∞Bⁿ for the temperature range 100–300 K is found to be < 2, implying that there is a contribution of some phenomenon other than the free electron conduction to MR. The measured data suggest that it is the contribution of localized state conduction near the Fermi level and in the localized states near the band edges.     

Tortuosity of porous particles

Tortuosity is often used as an adjustable parameter in models of transfer properties through porous media. This parameter, not reducible to classical measured microstructural parameters like specific surface area, porosity, or pore size distribution, reflects the efficiency of percolation paths, which is linked to the topology of the material. The measurement of the effective conductivity of a bed of particles saturated with an electrolyte is a simple way to evaluate tortuosity. Nevertheless, it received only little attention because of the real difficulties in both getting reliable results and interpreting data. Notably, the discrimination between the contribution of interparticle and intraparticle porosities to the tortuosity is not resolved. To our knowledge, there is no model able to fit the experimental data of the tortuosity of a suspension, and a fortiori of a particle bed, in the whole porosity range. Only empirical expressions have been proposed, but they do not allow deriving intratortuosity of a porous particle. For a dilute system, Maxwell's equation predicts the effective conductivity of suspensions of spherical particles as a function of the bulk electrolyte conductivity and of particle conductivity. The intraparticle tortuosity can be derived from the particle conductivity obtained from the Maxwell equation applied to data at infinite dilution of particles. Then, by assuming that the Maxwell equation is a first-order approximation of the conductivity as a function of porosity, we propose an explicit relation of the tortuosity tau of a suspension of porous particles, obtained by conductivity measurement, as tau = tau(epsilon, epsilon(p), tau(p)), where epsilon is the total porosity of the suspension, tau(p) is the intraparticle tortuosity, and epsilon(p) is the particle porosity. This relationship fits the experimental data in the whole porosity range and can be used to determine tau(p) from an experiment at only one porosity. Finally, the obtained values of tau(p) for a set of porous particles used in chromatography are discussed and compared to the data available in the literature.     

Efficiency of porous cooling

The authors present results of a numerical analysis of the efficiency of porous cooling of a cylindrical tube with one-sided heating, accounting for the thermophysical properties being temperature dependent.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 3, pp. 468–474, September, 1980.