Dielectric properties of KDP filled porous alumina nanocomposite thin films

A new concept of a composite dielectric thin film fabrication is presented. The fabrication process consists of two stages. The first stage is anodizing a thin aluminum film to produce a porous alumina film that contains an array of nanometer sized parallel pores. The second stage is filling the pores with a saturated KDP (KH2PO4) liquid solution due to capillary forces. After drying KDP nanocrystals are formed inside the pores. This process results in a formation of a composite dielectric thin film composed of the alumina pores walls as one dielectric material and the KDP nanocrystals inside the pores as another dielectric material. The dielectric permittivity of this composite film is higher than that of the porous alumina film at all applied frequencies. The dielectric enhancement is more pronounced at low frequencies due to an interface polarization mechanism. This fabrication process enables controlling the size, composition, and microstructure of the composite dielectric film constituents and thus changing its dielectric properties over a wide range of values.     

Optical properties of porous anodic alumina membrane uniformly decorated with ultra-thin porous gold nanoparticles arrays

In this paper, we directly develop a facile method to decorate a modified porous anodic alumina membrane (PAA) with an ultrathin porous film of gold nanoparticles with sub-gaps less than 25 nm and particle size less than 40 nm on the top surface and Au nanoparticles uniformly attached to the pore walls as well as the bottom of the pores, utilizing radio-frequency magnetron sputtering. The size as well as the interparticle distance of the gold nanostructures is adjusted by changing the structural properties of PAA membrane and the sputtering time. According to the measured reflection spectra, the saturation of interference color is significantly enhanced. As a result, the Au-coated PAA membrane exhibits a brilliant and tunable color. Field enhancement can be achieved in these structures through the excitation and constructive interference of surface plasmon waves. In addition, the role of localized surface plasmon and propagating surface plasmon was discussed. A four-layered model is presented to describe the reflectance data that show excellent agreement with the experimental data. The brilliant Au-coated PAA membrane is useful for decorative purposes and holds promise as an effective surface enhanced Raman scattering (SERS) substrate.     

多孔氧化铝陶瓷的凝胶注模成型

选用石墨粉作为造孔剂,加入已分散良好的氧化铝浆料中,球磨均匀后注模成型。成型后的坯体在1520℃保温烧结2h,获得了分布均匀,孔径为15－30μm的多孔氧化铝陶瓷。     

Self-assembly of diverse alumina architectures and their morphology-dependent wettability

This work reports the fabrication of diverse nanostructured alumina films under high-field anodization in oxalic-acid electrolytes. Different surface morphologies of these alumina films can be obtained by adjusting reaction parameters, which was ascribed to the anisotropic chemical etching induced by the reaction heat and the concentration gradient of the oxalic-acid solution along the nanopore channels during the high-field anodization process. These alumina surfaces without coating low energy materials show remarkable morphology-dependent wettability. Specially, the alumina surface consisting of porous underlayer and nanowire pyramids with no chemical modification reveals excellent super water-repellent behavior for the first time. This study could provide a new approach for designing functional surfaces with tunable wettability.     

Thermal shock behaviour of a coarse grain porous alumina

An apparatus of thermal shock by air cooling in which experiments can be precisely modelled is presented. The different physical parameters have been measured as a function of the temperature. The heat transfer coefficient has also been determined by two methods, on a copper specimen and directly on the alumina thermal shock specimen. A precise knowledge of the transient temperature field is therefore available.     

氧化铝多孔支撑体的研究

用挤出成型的方法制备高性能陶瓷膜用Ａｌ２Ｏ３〉９９％支撑体，制备中受初闰度、烧成温度、粘结等因素的影响，因此可以调节一个或几个因素来控制支撑体的性能。用硬脂酸铝为造孔剂，调节支撑体的孔径和气孔率时发现造孔剂质量分数〈５％和〉５％在坯体中的分布不同，成孔的作用也不一样，造孔剂用量〈５％时，对成孔作用不大，〉５％时成孔明显，但造孔剂的添加量不宜超过１５％。     

Fabrication of bimodal porous alumina ceramics

An alumina foam with two kinds of pores was prepared by combining the sponge method and the pore-former method. The large pores were provided by the sponge method, and their sizes were in the range of 1-2 mm. The small pores were produced by the pore-former method with size in the micrometer range. The large pores offered a high porosity while the small pores offered a large surface area. The strength of samples sintered at different temperatures was measured, and the effect of sintering temperature on foam strength was analyzed by discussing porosity and grain bonding area. The sample sintered at 1550 °C has a compressive strength of 1.3 MPa and a porosity of 86%.     

Low-temperature properties of porous silicon-indium nanocomposite

A new nanocomposite material with stable properties has been obtained representing a metal (indium) incorporated into a semiconducting porous silicon (por-Si) matrix. Electrical properties of the por-Si-In nanocomposite have been studied for the first time. At low temperatures (T = 1.4?C4.2 K), the por-Si-In samples exhibit a positive magnetoresistance [??R/R(H = 0) ?? 600%], which is related to breakage of the superconducting state of In particles in the por-Si matrix.     

多孔阳极氧化铝模板的影响因素

近年来,随着纳米技术的发展,研究制备具有纳米孔结构的氧化铝多孔膜越来越受到人们的关注.多孔阳极氧化铝(porous anodic alumina,PAA)薄膜具有易于制备,工艺简单,且价格便宜等诸多优点而被广泛地应用于各个领域.为了制备出性能更加优越的PAA模板,各国学者都对其进行了一些研究.但目前的研究大都不系统,针对这一问题,作者进行了大量的实验,通过实验总结出了PAA模板的主要影响因素,并分别讨论了这些影响因素对模板的有序度、孔密度和模板厚度的影响.     

Processing and characterization of porous alumina scaffolds

Bioceramic materials are used for the reconstruction or replacement of the damaged parts of the human body. In this study an improved procedure is described for producing ceramic scaffolds with controlled porosity. Bioinert alumina ceramic was used to make porous scaffolds by using indirect fused deposition modeling (FDM), a commercially available rapid prototyping (RP) technique. Porous alumina samples were coated with hydroxyapatite (HAp) to increase the biocompatibility of the scaffolds. Initial biological responses of the porous alumina scaffolds were assessed in vitro using rat pituitary tumor cells (PR1). Both porous alumina and HAp coated alumina ceramics provided favorable sites for cell attachments in a physiological solution at 37 °C, which suggests that these materials would promote good bonding while used as bone implants in vivo. Based on these preliminary studies, similar tests were performed with human osteosarcoma cells. Cell proliferation studies show that both the ceramic materials can potentially provide a non-toxic surface for bone bonding when implanted in vivo.     

Constrained densification in boehmite–alumina mixtures for the fabrication of porous alumina ceramics

It is demonstrated that inherent constrained densification characteristics of the bimodal size distributed powders can be utilized to fabricate porous alpha alumina. Seeded boehmite was mixed with coarse alpha alumina particles to produce various compositions of bimodal mixtures. The densification behaviour of the mixtures was correlated with shrinkage and microstructural evolution. The mixtures sintered at 1200 °C contained more than 30% porosity and the mechanical strength of the mixtures was increased by 2–4 fold relative to the coarse particles alone with similar porosity (<5 MPa). © 1998 Chapman & Hall     

从壁垒型氧化膜生长过程研究PAA的生长机制

为研究PAA的生长机理,设计了铝在3种电解液中的阳极氧化,通过SEM和阳极氧化曲线详细分析了规则圆柱形孔道和表面不规则孔洞产生的原因.电解液中阴离子使氧化膜变成了壁垒层和污染层两层.雪崩电子电流导致了在壁垒层/污染层界面上O2的析出.PAA中圆柱形孔道的形成是氧气析出的结果,传统的"酸性场致溶解"只在表面形成不规则的孔洞.当电解液中磷酸含量减少后,氧气析出持续的时间降低,O2析出停止后,多孔孔道被新生成的氧化铝封堵,最后PAA膜转变成BAA膜.     

A dielectric anomaly in electrolyte-saturated porous alumina ceramics

In order to understand the relation between the conductivity and the dielectric properties of porous materials and their pore fluid content, we report and discuss dielectric constant measurements of brine-saturated porous alumina ceramics which exhibit a gigantic increase of the low frequency dielectric constantwhile the sample remains conducting. Generalizing a model derived to study the properties of porous sedimentary rocks, where such an effect has been known for more than two decades, we discuss the effect of the pore geometry on the frequency, salinity and porosity variation of the ceramic dielectric constant and conductivity. This can provide a partial explanation of the reported measurements. Such a study provides a new and interesting method to investigate the microgeometry of composite materials and in particular the pore geometry of ceramics.     

Fabrication of high-aspect-ratio Prussian blue nanotubes using a porous alumina template

Prussian blue nanotubes were fabricated by using a sequential deposition technique inside the 60-nm well-ordered pores of anodic alumina. By varying the deposition parameters and the dimensions of the template, we could tailor the length and the outer as well as the inner diameter of the tubes. The nanotubes were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD).     

多孔阳极氧化铝膜的结构修饰研究

以5%草酸为电解液,温度控制在5℃左右,采用两步阳极氧化工艺制备出多孔氧化铝膜,在1 μm范围内获得了孔径为10～60nm的多孔结构.通过原子力显微技术分析氧化时间及热处理条件对多孔氧化铝膜结构的影响,阳极氧化3h后,在0.3μm2范围内获得了有序的纳米孔阵列,当氧化时间延长至24h,有序孔阵列范围增加至～1μm2.将在聚乙烯中经过超声振荡过的样品在600～700℃中热处理3h.研究结构表明,经过适当的热处理能有效改善多孔氧化铝膜的结构特性,X射线衍射分析结果证实经过结构修饰后的样品呈非晶态结构.     

Synthesis of tailored porous alumina with a bimodal pore size distribution

Hierarchical channel or well-connected small and large pore networks show multiple advantages for application in catalysis or adsorbent in aqueous condition. Micro- and mesopores provide size or shape selectivity for a guest molecule, while additional macropores reduce transport limitations. In this study, we proposed a novel method to prepare bimodal porous aluminas, which have meso- and macropores with narrow pore size distribution and well defined pore channels. The framework of the porous alumina is prepared via a chemical templating method using alkyl carboxylates. Polystyrene (PS) beads are employed as a physical template for macropores. We examined polydiallyldimethylammonium chloride (PDDA)-treated aluminas as organic adsorbent in aqueous solution. Above 90% of the anionic dye (acid red 44) is removed within 10 min, and the adsorption rate of PDDA/P4 (supported on the bimodal porous alumina) is faster than that of PDDA/P2 (supported on the unimodal porous alumina) because macropore of P4 have reduced transport limitation and enhanced the accessibility to the active site of cationic charge.