Simulation of Anodic Current and Optimization of the Fitting Equation and the Fitting Algorithm during Constant Voltage Anodization

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While porous anodic oxides have been extensively studied, there is limited research on the specific role of fluoride ions in the anodization. This study compares the morphology of titanium anodization products before and after the addition of ammonium pentaborate to the NH 4 F electrolyte. The current−time curve in anodization is analyzed to elucidate the real role of fluoride ions. The findings indicate that the real role of fluoride ions in the anodization is to form an anionic contaminated layer and cause the generation of electronic current, triggering the oxygen bubble mold effect and promoting nanotube growth. However, when pentaborate anions are introduced in the anionic contaminated layer, they hinder the production of electronic current, leading to a significant reduction in electronic current. Consequently, the growth rate of nanotubes decreases, resulting in the formation of bulb-shaped nanotube embryos. This study provides interesting evidence supporting the role of fluoride ions by combining the ionic and electronic current theory with the oxygen bubble mold effect. These pieces of evidence cast doubt on the simple chemical dissolution of fluoride ions in the traditional field-assisted dissolution theory. The experimental results significantly contribute to our understanding of the growth mechanism of porous anodic oxides.

Section: Resultsmentioning

confidence: 99%

Real Role of Fluoride Ions in the Growth of Anodic TiO₂ Nanotubes

Zhuang,

Li,

Qin

et al. 2024

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“…Here, the change of the current–time curve in Figure is explained according to the theory of ionic current and electronic current proposed by predecessors. − The ionic current and electronic current in the anodizing process can be described by the following formula J ion = A nobreak0em0.1em⁡ exp ( B E ) = A nobreak0em0.1em⁡ exp ( BU / d ) J e = J 0 nobreak0em0.1em⁡ exp ( α d ) Here, J ion represents the ionic current, J e represents the electronic current, J total represents the total anodizing current, J 0 represents the initial electronic current, A and B are temperature-dependent constants, α is the avalanche ionization constant, E represents the electric field intensity, U represents the applied voltage between barrier oxide layers, and d represents the barrier oxide layer thickness. − …”

Section: Resultsmentioning

confidence: 99%

Relationship between the Growth Rate of Nanotubes and the Current–Time Curve of the Anodizing Process

Li,

Han,

Qin

et al. 2024

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The growth mechanism of anodic TiO 2 nanotubes remains unclear. In order to investigate the factors affecting nanotube growth, the growth rate of the nanotubes is analyzed in this paper. TiO 2 nanotubes are successfully prepared in three kinds of electrolytes with equal concentrations of fluoride ions. However, the three groups of nanotubes show significant differences in growth rates (max 207.0 nm/min, min 36.6 nm/min), and the nanotube diameter does not depend solely on the same anodizing voltage, which is contradictory to the field-assisted dissolution reaction involving fluoride ions. The amount of charge accumulated during the growth of the three groups of nanotubes is positively correlated with nanotube length. The interesting results indicate that there is no field-assisted dissolution equilibrium during nanotube growth in fluoride electrolytes, while anodizing current plays a significant role in influencing nanotube growth. Article pubs.acs.org/JPCC

“…O 2– not only exists on the surface of the oxide but also can migrate inside. Under the electric field ( E ), O 2– can release electrons to form oxygen gas, 2O 2– → O 2 + 4e – or 4OH – → O 2 + H 2 O + 4e – . − This reaction leads to the generation of J e and oxygen gas evolution. Because J T is constant, part of the J ion is converted into J e and starts to decrease.…”

Section: Resultsmentioning

confidence: 99%

Effect of Chloride Ions on the Sparking Voltage of Working Electrolytes and Its Restraint Method

Wang

Zhang

et al. 2023

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As we all know, chloride ions (Cl–) are major impurities that significantly influence the lifetime and degradation of the dielectric properties of working electrolytes in aluminum electrolytic capacitors. However, the exact destructive mechanism of Cl– on the working electrolytes remains unstudied. In this work, ppm NH4Cl is added to the working electrolytes to study the formation process of dense films of anodic alumina and the sparking voltage of electrolytes. As a result, nanopores and hemispherical shapes similar to the morphologies of the porous alumina film are found in the originally dense films of anodic alumina and the sparking voltage of electrolytes also decreases. The presence of Cl– leads to the generation of electronic current (J e) and oxygen gas evolution in the anodizing process, which could decrease the sparking voltage. The oxygen bubbles inside the dense films of anodic alumina result in the generation of nanopores and hemispherical shapes within them. When 1 wt % ethylene glycol borate polyester (BPE) is added to the NH4Cl electrolytes, the morphologies of nanopores and hemispherical shapes in the dense films disappear, which proves that BPE can not only restrain the generation of J e and oxygen gas evolution but also improve the sparking voltage.