The microstructure and mechanical properties of titanium dioxide nanotubes synthesized in the fluoride-based electrolyte

Titanium is one of the biomaterials commonly used for prosthetic devices due to its bio-inert properties. The discovery of titanium dioxide nanotubes (TDNTs) has created a great interest in medical applications such as dental and orthopedic implants. The synthesizing of TDNTs can produce different morphology, sizes and mechanical properties of the nanotubes – depending on the applied method. In this study, an electrochemical anodization method was used for synthesizing the TDNTs. A 100 ml mixture of 99% of ethylene glycol (EG), 1% of deionized water and 1 wt.% of ammonium fluoride (NH4F) was used as the electrolyte of the electrochemical cell. Parameters such as anodization time and the voltage applied were used to alter the morphology of the TDNTs formed. The produced nanotubes were analyzed and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness tester. The SEM results showed that the formed diameter of nanotubes was mainly affected by the anodizing voltage. The wall thickness was found to be irrelevant to the parameters conducted in this study. The diameter of nanotubes formed with an anodizing voltage of 30, 45 and 60 V have the diameters ranging from 46 nm to 71 nm. All of the TDNTs samples formed have a wall thickness between 11 nm and 13 nm. With the use of EG and NH4F as an electrolyte, the array of TDNTs with honeycomb structure was formed. In general, hardness test showed that the hardness of the nanotubes was inversely proportional with the anodizing time. The anodizing voltage only has little effect on the hardness of the nanotubes. The nanotubes formed by 60 V have about 3 to 5% lower hardness compared to those formed by 30 V for different anodizing times.