Chemical dissolution resistance of anodic oxide layers formed on aluminum

Chemically resistant anodic oxide layers were formed on pure aluminum substrates in oxalic acid-sulphuric acid bath.Acid dissolution tests of the obtained anodic layers were achieved in accordance with the ASTM B 680-80 specifications：35mL/L 85% H3PO4＋20g/L CrO3 at 38℃.Influence of oxalic acid concentration,bath temperature and anodic current density on dissolution rate and coating ratio was examined,when the sulphuric acid concentration was maintained at 160g/L.It was found that chemically resistant and compact oxide layers were produced under low operational temperature （5℃） and high current densities （3A/dm^2）.A beneficial effect was observed concerning the addition of oxalic acid （18g/L）.The morphology and the composition of the anodic oxide layer were examined by scanning electron microscopy （SEM）,atomic force microscopy （AFM） and glow-discharge optical emission spectroscopy （GDOES）.

Cylindrical and Spherical Membranes of Anodic Aluminum Oxide with Highly Ordered Conical Nanohole Arrays

Nanoporous anodic aluminum oxide (AAO) with uniform and controllable pore diameters and periods over a wide range has been explored for various applications due to relatively easy fabrication processes. Moreover, one of the interesting possibilities afforded by the anodization process is that the anodization can take place on aluminum films with arbitrary shape, such as a section of cylinder or sphere, which has not yet been well studied or applied in nanofabrication. In this paper, we report that highly ordered conical nanohole arrays prepared by the anodization of cylindrical and spherical Al films have been fabricated. As can be seen by scanning electron microscopy (SEM), straight nanohole arrays have been grown along the radical directions of the cylindrical or spherical alumina membrane without bending or branching at all, the diameter of the conical nanoholes and the diameter change along individual channels can be tuned by changing the curvature of the membrane. These new types of templates may open new opportunities in optical, electronic and electrochemical applications.

Electrodeposited Ni,Fe,Co and Cu single and multilayer nanowire arrays on anodic aluminum oxide template

The Ni, Fe, Co and Cu single and multilayer nanowire arrays to make perpendicular magnetic recording media were fabricated with nanoporous anodic aluminum oxide (AAO) templates from Watt solution and additives by the DC electrodeposition. The results show that the diameters of Ni, Fe, Co and Cu single and multilayer nanowires in AAO templates are 40-80 nm and the lengths are about 30 μm with the aspect ratio of 350-750. The magnetic properties of the prepared nanowires are different under different electrodepositing conditions. The remanences (Br) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires, and coercivity (Hc) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires. These are compatible with the required conditions of high density magnetic media devices that should have the low coercivity to easily success magnetization and high remanence to keep magnetization after removal of magnetic field.

FePt nano-stripes fabricated on anodic aluminum oxide templates

A new Fe Pt nanostructure with stripe-like patterns has been prepared by direct current（DC） magnetron sputtering on anodic aluminum oxide（AAO） templates. AAO templates anodized under low voltages（7 V） demonstrate self-organized,maze-like patterns, different from the conventional porous structures obtained at high voltages. Fe Pt thin films deposited on such templates tend to replicate the morphology of the templates. Although there is no obvious spatial ordering, the dimensions of the Fe Pt nano-stripes are highly uniform, due to the constrained growth along the transverse direction of the AAO pattern. The magnetic properties are strongly influenced by this unique morphology. While continuous films demonstrate strong exchange coupling, the dominant interaction in Fe Pt nano-stripes with the same nominal thickness is magnetostatic. The morphology also dictates the magnetization reversal behaviors, with thin films dominated by domain nucleation; while nano-stripes incline to reverse their magnetization by spin rotation. Our work demonstrates that selforganized AAO templates can be used to control the morphology and magnetic behavior of Fe Pt materials.

Influence of adipic acid on anodic film formation and corrosion resistance of 2024 aluminum alloy

The influence of adipic acid on the formation and corrosion resistance of anodic oxide film fabricated on 2024 aluminum alloy was investigated. The morphology was investigated by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）, respectively. The corrosion resistance was evaluated by electrochemical impedance spectroscopy （EIS）. The results showed that the adipic acid was absorbed at the electrolyte/anodic layer interface during anodizing. The corrosion rate of anodic film decreased and the film thickness increased. The film was uniform and compact especially at the film/substrate interface. After sealing procedure, anodic film formed with the addition of adipic acid exhibited improved dielectric property and corrosion resistance in aggressive environment.

Influence of oxidation heat on hard anodic film of aluminum alloy

The special experimental device and sulfuric acid electrolyte were adopted to study the influence of anodic oxidation heat on hard anodic film for 2024 aluminum alloy. Compared with the oxidation heat transferred to the electrolyte through anodic film, the heat transferred to the coolant through aluminum substrate is more beneficial to the growth of anodic film. The film forming speed, film thickness, density and hardness are significantly increased as the degree of undercooling of the coolant increases. The degree of undercooling of the coolant, which is necessary for the growth of anodic film, is related to the degree of undercooling of the electrolyte, thickness of aluminum substrate, thickness of anodic film, natural parameters of bubble covering and current density. The microstructure and performance of the oxidation film could be controlled by the temperature of the coolant.

电解液中铈盐对LDH/AAO复合膜层耐蚀性影响

普通阳极氧化膜难以对铝合金形成有效的防护作用,须进行封孔处理以改善膜层耐蚀性差问题。采用原位生长法制备的层状双金属氢氧化物(LDH)膜对阳极氧化(AAO)膜进行封闭,得到LDH/AAO复合膜层,研究阳极氧化电解液中三价铈盐浓度对AAO膜层及LDH/AAO复合膜层耐蚀性影响。利用扫描电子显微镜(SEM)、能谱仪(EDS)、辉光放电发射光谱仪(GDOES)分别表征膜层的微观形貌和元素组成,通过电化学交流阻抗(EIS)、动电位极化曲线和酸性盐雾试验检测膜层的耐蚀性。结果表明,在阳极氧化电解液中添加铈盐能够提高AAO膜层的致密性和耐蚀性,并改善后续LDH膜层在AAO膜表面的生长。LDH可以在AAO孔洞和缺陷中生长,并完全覆盖AAO层,耐蚀性明显优于铈盐封闭,铈盐浓度为0.03 mol/L时AAO膜层与LDH/AAO复合膜层耐蚀性更好。通过对LDH层负载钒酸根缓蚀剂,进一步优化了复合膜层的耐蚀性能。复合膜层的耐蚀作用主要归因于电解液中添加铈盐提高了AAO内层的物理阻隔性能,负载钒酸根的LDH外层对腐蚀性离子的捕获及对层间缓蚀剂的释放双重作用为基体铝合金提供了长效保护。提出层状双金属氢氧化物/阳极氧化复合膜层,并采用“纳米容器”负载缓蚀剂策略进一步提升复合膜层耐蚀性能。

AAO模板制备中高纯Al电解抛光工艺的研究

阳极氧化铝模板以其低成本、高通量、柔性和结构可控性等特点已被用于制备纳米结构材料和光子器件等模板。为促进规则多孔的形成和控制所需的性能,高纯Al片表面的预处理是必需的。为此本文研究了高纯Al片的抛光条件,将面积相近的阳极Al片与阴极碳板以相互平行的方式垂直放置于高氯酸与乙醇的体积比为1∶7抛光液中。在电解抛光过程中,当外加电压增至9 V以上时,Al片表面开始形成阳极膜,Al片面积越大该阳极膜所受重力势能作用越显著,致使在完成形成均匀阳极膜拐点处对应的电流密度值随Al片面积的增加而增加,且同一Al片面积具有较佳拐点值,以获得理想的表面光洁度。

Effect of the microstructure of Al 7050-T7451 on anodic oxide formation in sulfuric acid

The effect of the microstructure of an Al 7050-T7451 substrate on the anodic oxide formation in sulfuric acid was studied in this article. The microstructure of the substrate was assessed by optical microscope （OM） and transmission electron microscope （TEM）. The surface and cross-section morphologies of the oxide films were examined by scanning electron microscope （SEM）. The chemical composition of intermetallic particles in the alloys and films was investigated using energy dispersive spectroscope （EDS）. The roles of intermetallic phases and grain or subgrain boundaries on the oxide film formation were researched using the potentiodynamic and potentiostatic polarization technique in sulfuric acid solution. The results show that the transition of coarse intermetallic particles or grain （subgrain） boundaries at the surface of Al alloys can be characterized by potentiodynamic polarization curves. The surface and cross-section micrographs of the anodic layer seem to preserve the microstructure of the substrate. Large cavities in the anodic films are caused by the preferential dissolution of coarse AItCuMg particles and the entrance of Cu-rich remnants into the electrolyte during anodizing. The Al7Cu2Fe particles tend to be occluded in the oxide layer or lose from the oxide surface because of peripheral trenching. Small pores in the films are induced by the dissolution of precipitates in grain or subgrain boundaries. The film surface of recrystallized grain bodies is smooth and homogeneous.

Effect of intermetallic phases on the anodic oxidation and corrosion of 5A06 aluminum alloy

Intermetallic phases were found to influence the anodic oxidation and corrosion behavior of 5A06 aluminum alloy. Scattered in- termetallic particles were examined by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） after pretreatment. The anodic film was investigated by transmission electron microscopy （TEM）, and its corrosion resistance was analyzed by electrochemical impedance spectroscopy （EIS） and Tafel polarization in NaC1 solution. The results show that the size of A1-Fe-Mg-Mn particles gradually decreases with the iron content. During anodizing, these intermetallic particles are gradually dissolved, leading to the complex porosity in the anodic film beneath the particles. After anodizing, the residual particles are mainly silicon-containing phases, which are embedded in the an- odic film. Electrochemical measurements indicate that the porous anodic film layer is easily penetrated, and the barrier plays a dominant role in the overall protection. Meanwhile, self-healing behavior is observed during the long immersion time.

Evaluation of nanometer-sized zirconium oxide incorporated Al-Mg-Ga-Sn alloy as anode for alkaline aluminum batteries

Zirconium oxide nanoparticles with 0.4 wt.%and 0.8 wt.%are incorporated into the Al-0.65 Mg-0.05 Ga-0.15 Sn(wt.%)alloy anode(base alloy)in order to improve the performance of the resulting anodes.Electrochemical characterization of the reinforced alloys was done by potentiodynamic polarization,electrochemical impedance spectroscopy and galvanostatic discharge and corrosion behavior was evaluated using self-corrosion rate and hydrogen evolution in 4 mol/L KOH solution.The surface morphology of the alloys was also studied using field emission scanning electron microscope(FESEM).The obtained results indicate that the base alloy shows high corrosion rate in 4 mol/L KOH solution by releasing 0.47 m L/(min·cm^2)hydrogen gas,whereas the alloy containing 0.8 wt.%Zr O2 provides the lowest hydrogen evolution rate by releasing 0.32 m L/(min·cm^2)hydrogen gas.Furthermore,by increasing zirconium oxide nanoparticles,the corrosion current density of the aluminum anodes is decreased and their corrosion resistance increases significantly compared to the base alloy in alkaline solution.In addition,nanometer-sized zirconium oxide incorporated anodes exhibit the improved galvanic discharge efficiencies,so that 0.8 wt.%nano-zirconium oxide incorporated base alloy displays the highest power density and anodic utilization compared with the others in 4 mol/L KOH solution.

Electrochemical Fabrication of Pd-Ag Alloy Nanowire Arrays in Anodic Alumina Oxide Template

The synthesis of Pd-Ag alloy nanowires in nanopores of porous anodic aluminum oxide （AAO） template by electrochemical deposition technique was reported. Pd-Ag alloy nanowires with 16%-25% Ag content are expected to serve as candidates of useful nanomaterials for the hydrogen sensors. Scanning electron microscopy （SEM） and energy dispersed X-ray spectroscopy （EDX） were employed to characterize the morphologies and compositions of the Pd-Ag nanowires. X-ray diffraction （XRD） was used to characterize the phase properties of the Pd-Ag nanowires. Pd-Ag alloy nanowire arrays with 17.28%-23.76% Ag content have been successfully fabricated by applying potentials ranging from -0.8 to -1.0 V （vs SCE）. The sizes of the alloy nanowires are in agreement with the diameter of AAO nanopores. The underpotential deposition of Ag＋ on Pd and Au plays an important role in producing an exceptionally high Ag content in the alloy. Alloy compositions can still be controlled by adjusting the ion concentration ratio of Pd^2＋ and Ag＋ and the electrodeposition processes. XRD shows that nanowires obtained are in the form of alloy of Pd and Ag.

Formation of unidirectional nanoporous structures in thickly anodized aluminum oxide layer

A series of anodic aluminum oxide(AAO) was grown on the commercially pure 1050 aluminum sheet by controlling electrolyte temperature(2-15 ℃) and anodizing time(0.5-6 h),using a fixed applied current density of 3 A/dm2 in diluted sulfuric acid electrolyte.A crack-free thick AAO with the thickness of 105-120 μm and containing unidirectional nano sized pores(average pore diameter of 5-7 nm) is successfully achieved in the specimens anodized for 2 h,irrespective of electrolyte temperature.When anodizing time reaches 6 h,very thick AAO with the thickness of 230-284 μm is grown,and average diameter of unidirectional pores is in the range of 6-24 nm.The higher values in both the AAO thickness and pore diameter are attained for the specimens anodized at higher temperatures of 10-15 ℃.A crack is observed to exist in the AAO after anodizing up to 4 h and more.A higher fraction(more than 9%) of the crack is shown in the specimens anodized at higher temperatures of 10-15 ℃ for 6 h and a considerable amount of giant cracks are contained.

Evolution of insoluble eutectic Si particles in anodic oxidation films during adipic–sulfuric acid anodizing processes of ZL114A aluminum alloys

The effects of insoluble eutectic Si particles on the growth of anodic oxide films on ZL114A aluminum alloy substrates were in- vestigated by optical microscopy （OM） and scanning electron microscopy （SEM）. The anodic oxidation was performed at 25℃ and a con- stant voltage of 15 V in a solution containing 50 g/L sulfuric acid and 10 g/L adipic acid. The thickness of the formed anodic oxidation film was approximately 7.13 μm. The interpore distance and the diameters of the major pores in the porous layer of the film were within the ap- proximate ranges of 10~20 nm and 5-10 nm, respectively. Insoluble eutectic Si particles strongly influenced the morphology of the anodic oxidation films. The anodic oxidation films exhibited minimal defects and a uniform thickness on the ZL114A substrates; in contrast, when the front of the oxide oxidation films encountered eutectic Si particles, defects such as pits and non-uniform thickness were observed, and pits were observed in the films.

Anodic Coating Characteristics of Different Aluminum Alloys for Spacecraft Materials Applications

Anodic oxide coatings on aluminum alloys are used for space environment applications. These provide specific thermo-optical properties to spacecraft surface. Fragments of these coatings lead to generate the contamination in satellites and affect the mission lifetime. The current work concerns studying of the anodic processes applied on aluminum and different groups of aluminum alloys as Al7075, Al2024 and Al6061. Experimental procedures are performed using sulfuric acid at different values of current density (1 - 2 A/dm2). The influence of the parameters of anodic film formation on the coating characteristics and layer thickness of aluminum alloys has been investigated. Reflectance and optical properties of the anodized aluminum alloy coatings are determined and found to be dependent on the alloying elements. Changes in anodic coating weight and film thickness of aluminium alloys with the process parameters as current density, temperature, time duration, acid concentration, and sealing system have been studied. Moreover, morphology and surface structure of the considered samples are carried out in attempt to understand the physical characteristics. The obtained results are compared and briefly outlined.

Fabrication of anodized aluminum oxide membrane with nanometer pores

The pure aluminum and Al Mg Mn alloy were anodized in 4%, 10% and 18.5% phosphoric acid solution, respectively. As for pure Al, the maximum thickness of anodized aluminum oxide (AAO) membrane, 216 nm, is obtained by being anodized in 4% solution. Its average pore diameter is around 70 nm, and pore density exceeds 10 10 /cm 2. Under the same technology condition, the membrane thickness decreases with increment of electrolyte content. TEM images show that element Mg or Mn added into aluminum alloy can damage the integration of AAO membrane. During anodizing of aluminum, the formed oxide layer is amorphous. After being annealed at 600 ℃ for 24 h, it is still amorphous. However, when membrane is annealed at 930 ℃, the amorphous oxide begins to transform to γ Al 2O 3 .

激光除漆对铝合金基材表面质量的影响

目的研究激光除漆后对铝合金基材表面阳极氧化膜的损伤情况。方法采用纳秒脉冲激光器对涂覆复合漆层的2A12铝合金表面进行激光清洗试验。采用超景深显微镜对清洗后表面形貌与横截面进行观察,利用扫描电子显微镜与能谱仪观察清洗后的微观形貌,并利用维氏硬度计对表面显微硬度进行检测。结果选择合适的激光参数能够完全除去复合漆层,当激光功率过高或激光扫描速度较低时,会发生过度清洗现象,清洗后表面的阳极氧化膜层发生损伤,甚至被去除的情况。在激光功率为450、400 W,扫描速度为4.5 mm/s时,清洗后表面的阳极氧化膜层发生破损;在激光功率为450、400 W,扫描速度为4 mm/s时,清洗后表面的阳极氧化膜层已经被去除。在激光功率为500 W,扫描速度为5.5 mm/s,与激光功率为450 W,扫描速度为5 mm/s时,完全去除复合漆层后的阳极氧化膜层表面的平均维氏硬度分别约为211HV与242HV,在工艺参数为450 W、4.5 mm/s时,表面平均维氏硬度约为168HV。结论在激光除漆的过程中,采用合适的激光工艺参数彻底去除漆层后,铝合金表面阳极氧化膜层的显微硬度并未受到影响。在发生过度清洗时,铝合金表面的阳极氧化膜层会发生烧蚀损伤以及弹性振动剥离。

Co/AAO纳米有序阵列复合结构的光致发光和光吸收特性

以草酸电解液制备的高度有序的纳米级多孔阳极氧化铝(AAO)为模板,采用交流电化学沉积工艺合成了Co/AAO纳米有序阵列复合结构。分别研究了AAO模板和Co/AAO结构的光致发光和光吸收特性。结果表明,AAO模板在350～550nm范围内存在较强的光致发光带,其峰位在395nm处;Co/AAO纳米有序阵列复合结构的光致发射峰位亦在395nm处,且发光峰强度随Co沉积量的增加而迅速减弱。实验发现,Co/AAO纳米有序阵列复合结构的光吸收边从近紫外至近红外的波段范围内发生大幅度红移,最大红移量甚至超过380nm。文章定性分析并解释了Co/AAO纳米有序阵列复合结构吸收边大幅度红移及其光发射峰位不变、而峰强减弱的主要原因。

AAO模板外表面自组织纳米孔洞的差异性研究

以草酸为电解液,分别用一次阳极氧化法和二次阳极氧化法制备了阳极氧化铝(AAO,anodic alu-minum oxide)模板,在较大范围内得到了纳米孔分布均匀、孔洞大小均一、尺寸可控、排列有序的双通模板.采用扫描电镜(SEM)对其形貌进行表征,发现一次阳极氧化法制得的AAO模板的反面孔洞排列较为规则,而正面的孔洞排列规则性明显不如反面;二次阳极氧化法制备得到的模板正、反面孔洞的排列都比较规则.比较了模板正、反面纳米孔洞的差异,并结合阳极氧化过程中电流的变化,探讨了自组织孔洞的形成机理.目前尚未发现关于纳米孔洞差异性及原因分析的文献报道.

AAO模板的制备及其应用

阳极氧化铝模板由于其价廉,制备工艺简单,以及特殊的结构和多样的组装方法得到了广泛的研究和应用。主要阐述了AAO模板的制备、影响因素,及其在纳米组装体系中的应用,包括量子点、纳米线、纳米管和"同轴电缆式"层状纳米材料等,介绍了AAO组装体系的应用,最后提出了AAO模板的潜在发展。