Formation mechanism of nanopores in dense films of anodic alumina

致密型阳极氧化铝薄膜中纳米孔洞的形成机理

Constant-current anodization of pure aluminum was carried out in non-corrosive capacitor working electrolytes to study the formation mechanism of nanopores in the anodic oxide films.Through comparative experiments,nanopores are found in the anodic films formed in the electrolytes after high-temperature storage(HTS)at 130°C for 240 h.A comparison of the voltage-time curves suggests that the formation of nanopores results from the decrease in formation efficiency of anodic oxide films rather than the corrosion of the electrolytes.FT-IR and UV spectra analysis shows that carboxylate and ethylene glycol in electrolytes can easily react by esterification at high temperatures.Combining the electronic current theory and oxygen bubble mold effect,the change in electrolyte composition could increase the electronic current in the anodizing process.The electronic current decreases the formation efficiency of anodic oxide films,and oxygen bubbles accompanying electronic current lead to the formation of nanopores in the dense films.The continuous electronic current and oxygen bubbles are the prerequisites for the formation of porous anodic oxides rather than the traditional field-assisted dissolution model.

为了探讨阳极氧化膜中纳米孔洞的形成机理,在无腐蚀性的电容器工作电解液中进行纯铝的恒流阳极氧化实验。对比实验发现,在130℃高温储存240 h后的电解液中形成的阳极氧化膜中发现了纳米孔洞。由电压-时间曲线可知,纳米孔洞的形成是由于氧化膜形成效率的降低而不是电解液的腐蚀。傅里叶红外和紫外光谱分析结果表明,电解液中的羧酸盐和乙二醇在高温条件下很容易发生酯化反应。结合电子电流和氧气泡模具效应,电解液成分的改变会增大阳极氧化过程中的电子电流。电子电流会降低阳极氧化膜的形成效率,而伴随其产生的氧气泡会导致纳米孔洞的产生,即电子电流和氧气泡才是多孔氧化铝形成的先决条件,而非传统的场致助溶模型。