【作者】 马迪；

【导师】 梁成浩； 李淑英；

【作者基本信息】 大连理工大学 ， 化学工程， 2010， 博士

【摘要】 多孔阳极氧化铝(AAO)膜以高密度孔排列、可控孔径和优良的形态结构等特点在纳米科学和技术领域引起广泛的关注。因此,研究预处理的电化学抛光行为和AAO膜的生长动力学,对提高膜的性能具有重要意义。本文采用电化学方法研究高纯铝在高氯酸和无水乙醇混合溶液中的电化学抛光行为,并对抛光表面的形态和组成进行了表征。结果表明,高纯铝最佳电抛光条件是高氯酸和乙醇体积比为1：8,温度范围为10-30℃。抛光机理遵循溶解产物限制传递机理,高纯铝表面形成难溶的固体盐膜,其组成为无定形氧化铝。电抛光过程中引入超声波后,搅拌作用和空化效应使具有屏蔽作用的极性有机分子CH3CH2OH在高纯铝表面微观突起处分散更均匀,吸附间距缩短,导致自组织条纹宽度由212 nm减至54 nm,且均方根粗糙度RMS从23.5 nm降至17.4 nm。恒电流条件下0.3mol/L H2C2O4溶液中AAO膜生长动力学研究表明,膜形成的稳定阶段,随电流密度升高,膜迅速增厚使离子穿过膜的阻力增加,离子传导性能下降而引起电压升高。温度的升高导致膜溶解,膜阻力减小,离子传导性能提高,从而降低了膜生长稳定阶段的电压。AAO膜厚随氧化时间的延长逐渐增厚,当出现特征时间tc时,膜厚达到了最大值。之后,随时间继续延长,膜厚保持一定或略微下降。电流密度从10mA/cm2增至20 mA/cm2时,特征时间tc从110 min降至80 min,膜极限厚度从15.6 u m增至23μm。AAO膜动力学方程为δp =k′·it(t≤tc),其中k′是与温度和电流密度无关的常数,拟合值为1.45×10-6 cm3/(mA·min)。本文将1,2-丙二醇(PROH)加入0.4mol/L H3PO4溶液和0.3mol/L H2C2O4溶液中,开发了在-15～0℃条件下制备AAO膜的方法。-15℃时,0.4mol/L H3PO4溶液中得到的膜平均孔径最小可达56.29 nm,是20℃制备膜平均孔径(218.51 nm)的1／4,这是由于降低温度导致离子传递速率减缓,阻滞了AAO膜氧化和溶解速度。随着温度的降低,孔密度减小,孔隙率降低,据此可推断,温度降低导致高纯铝表面初始氧化中心的生成速率降低,单位面积形成的晶胞数量减少。电解液中PROH含量从25%增至75%时,溶液黏度的增加和双电层内OH-的累积,使得AAO膜孔径和孔隙率减小,孔密度降低。填孔实验前后AAO膜的交流阻抗测试结果表明,填孔后中高频区的相位角峰和低频区的相位角峰分别表征阻挡层和多孔层。计算出阻挡层厚度δb在1-18 nm。随PROH含量从25%增至75%,阻挡层电容CPEb下降,电阻Rb增加,阻挡层厚度δb增大。填孔实验后膜表面的不均匀度有所改善,因此CPEp下降,计算的多孔层厚度δp增大。更多还原

【Abstract】 Anodic aluminum oxide (AAO) film have attracted great attention in the areas of nanoscience and engineering due to their highly ordered pore arrangement, controllable pore diameter and well-characterized morphology. Therefore the study of electropolishing behaveiour of high-purity aluminum and growth kinetics of AAO film to further improve the performance of AAO film is of great significance.The electropolishing behavior of high-purity aluminum in perchloric acid ethanol electrolytes is studied by the electrochemical methods. The morphologies and composition of electropolished surface are examined. The results shows that the high-purity aluminum can be electrochemically polished in the mixed solution with volume ratios of 1:8 in the temperature range of 10-30℃. The electropolishing of high-purity aluminum follows dissolution product limited transport mechanism, a salt film precipitated on the electropolishing surface, consists of amorphous alumina. In addition, the effect of fierce stiring agitation and cavitation of ultrasonic agitation is to make ethanol molecule which is a polar molecule with a repulsive shield dispersion homogeneously dispersed, to shorten adsorption spacing on surface microscopic concave. The root-mean-square (RMS) surface roughness of the aluminum electropolished surface decreases from 23.5 nm to 17.4 nm and the self-organized nanostripes decreases from 212 nm to 54 nm after using the ultrasonic agitation.The growth kinetics of AAO films formed in 0.3 mol/L H2C2O4 under galvanstatic conditions shows that the film thickness increases with an increase in the current density in steady-state stage of AAO film formation, the film resistance and the ionic conductivity are also increased, which lead to voltage increases. It has been found that the film thickenss increases with the anodizing time and achives the limiting thickenss when the time is characteristic time, and then with the increase of the anodizing time, the film thickensss maintains certain or appreciably decreases. The chatacteristic time dencreases form 110 min to 80min and the limiting thickenss increases from 15.6μm to 23μm, increasing current density from 10 mA/cm2 to 20 mA/cm2. The film Growth can be expressed by the equationδp= k" it (t≤tc) and k" is a constant independent of the current density and the anodization temperature with a average value of 1.45×10-6 cm3/(mA·min).A method of fabrication of AAO film in in 0.3 mol/L H2C2O4 and 0.4 mol/L H3PO4 by adding 1,2-propanediol(PROH) and at sub-zero temperature has been proposed. The smallest pore diameter of AAO film is 56.29 nm, which is one quarter of those anodized in 20℃0.4 mol/L H3PO4. Sub-zero andization decrease the pore diameter possibly by retarding the ionic transport in the oxide and thus decreasing the rate of oxidation and dissolution. A uniform pore-size distribution with ordered pore arrangement of AAO films is observed in the SEM images. Moreover, the pore density and the porosity of AAO films were found to decrease with decreasing anodizing temperature hereby referred that the lower is the rate of formation of defect sites in the first place and less unit cells are developed around these centers for a given area with decreasing temperature. An increase of the volume percentage of PROH in electrolyte from 25% to 75% results in a corresponding increase in electrolyte viscosity and an accumulation of OH- in double layer causes the pore diameter, pore density and porosity of AAO film decreased.The electrochemical characteristics of the barrier and porous layers of AAO films before and after pore-filling are examined using electrochemical impedance spectroscopy (EIS). It is shown that the high and medium frequency range corresponds to the barrier layer properties and the low frequency ranges reflect the sealed porous layer properties. Calculated thickenss of the barrier layer is in the range of 1-18 nm. The resistance (Rb) and the thickness (8b) of the barrier layer increase and the capacitance of the barrier layer (CPEb) decreases with the volume percentage of PROH increasing from in electrolyte from 25% to 75%. The surface non-homogeneity of AAO film goes better by pore-filling, leads to decrease in the capacitance of porous layer (CPEp) and increase in the porous layer thickness.更多还原