The mechanism of formation of anodic TiO₂ nanotubes and the cause of volume expansion are still controversial. It is well known that fluoride ions participate in the field-assisted dissolution reaction as well as in field-assisted ejection to reduce the current efficiency and the volume expansion factor. Here, the anodizing of titanium in an electrolyte with three different concentrations using four current densities is discussed in detail. We found that the total volume of the nanotube array remained about the same for a given current, being independent of the concentration of NH₄F (0.1, 0.3 and 0.5 wt%), and depending only on the anodizing current. Interestingly, regardless of the anodizing conditions, the volume expansion factor of the nanotubes was about 2.073 and the ratio of the total volume of the nanotube array to the volume of consumed titanium was about 2.285. These data are completely contrary to what would be expected on the basis of the field-assisted ejection and dissolution theories.

阳极TiO ₂纳米管的形成机理和体积膨胀的原因仍存在争议。众所周知，氟离子参与场辅助的溶解反应以及场辅助的喷射以降低电流效率和体积膨胀系数。在此，详细讨论了使用四种电流密度在三种不同浓度的电解质中对钛进行阳极氧化的方法。我们发现，在给定电流下，纳米管阵列的总体积大致保持不变，与NH ₄的浓度无关F（0.1、0.3和0.5重量％），并且仅取决于阳极氧化电流。有趣的是，不管阳极氧化条件如何，纳米管的体积膨胀系数约为2.073，并且纳米管阵列的总体积与消耗的钛的体积之比约为2.285。这些数据完全与根据现场辅助的喷射和溶出理论所期望的相反。