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Introduction
Anodisation is described as the creation of a coat of oxygen on a certain material, usually to prevent corrosion and wear. Anodised materials are used widely in fields such as aerospace and medicine. In these fields specifically, anodised Titanium (Ti) is very popular for its strength, lightness, biocompatibility, and especially its colourful appearance.
Process and Colouration
Anodisation takes place when electrolysis occurs. The power supply creates a current, which in turn creates a potential difference that splits the electrolyte. The split causes oxide ions to be free, which then bind with the Ti foil, creating Titanium Dioxide (TiO2). Figure 1 depicts the setup for the anodisation in a lab.
Figure 1: Apparatus and setup for anodisation of titanium
While accurate, it is important to note that the lab diagrams shown are not necessarily replicative of mass-producing industrial electrolytic systems. However, this provides a general idea. If further interested in the mass production process, refer to the video link below.
Titanium Anodizing Large Quantities Of Medical Parts:
The colour of the material itself is induced by the thickness of the oxide coat, which is dependent on the power supply. This is measured in voltage, as depicted in Figure 2.
Figure 2 (adapted): Colour scale of anodising titanium, accompanied by their corresponding voltages
Real World Applications
Including aesthetic purposes, the anodisation achieves properties which add versatility.
Aerospace
Since the 1920s, the aerospace industry has utilised anodised titanium to prevent corrosion, wear and ageing. Different grades of coatings are used for different purposes. Anodised Titanium prevents galling (the abrasive process which creates friction and potentially causes component failure) since its surface provides reduced friction, and additionally provides compatibility between materials. The anodising process causes the newly formed Titanium Oxide to be non-toxic and compatible with other materials. Additionally, the lightweight structure of Titanium Dioxide makes it favourable over alternatives, when used for the airframe.
Figure 3- Aeroplane, where anodised titanium is used in the airframe/Photo by Gary Lopater on Unsplash
Medical
The alloy’s biocompatibility and lack of reactivity allow it to be optimal for biomedical engineers, specifically when designing medical implants. Firstly, implants constructed using anodised titanium are equipped with greater corrosion resistance. Therefore, no corrosion occurs between bodily fluids and the implant. Secondly, the ability to control the colour of the alloy allows simpler colour coordination between implant sizes. Finally, the use of anodised titanium outweighs other alternatives due to its lightweight structure, as the lighter material creates less stress on bones. For example, although heavier than titanium implants and utilized less often, Ceramic is a common alternative. Figure 4 shows a dental implant utilising anodised titanium.
Figure 4- Anodised titanium in a dental implant / Photo by Bogdan condr on Unsplash
Conclusion
In conclusion, anodised titanium should be considered for applications that either require compatibility in many environments, a strength and lightweight structure, aesthetic decoration or a combination of these properties.
Bibliography:
Ayal, A.K., Ismail, S.S.B., Zain, Z.M. and Chin, L.Y. (2018). EFFECT OF GOLD SOLUTION CONCENTRATION ON THE FORMATION AND PHOTOELECTROCHEMICAL PROPERTIES OF GOLD DEPOSITED TITANIUM DIOXIDE NANOTUBES. Malaysian Journal of Analytical Science, 22(5). doi:https://doi.org/10.17576/mjas-2018-2205-02 Photo used for figure 1.
Barjaktarević, D.R., Cvijović‐Alagić, I.Lj., Dimić, I.D., Đokić, V.R. and Rakin, M.P. (2016). Anodization of Ti-based materials for biomedical applications: A review. Metallurgical and Materials Engineering, 22(3), pp.129–144. doi:https://doi.org/10.30544/209.
EDC Specialities (2021). Titanium Anodization (See Color Chart) - EDC Specialties | Every Day Carry Essentials. [online] EDC Specialties | Every Day Carry Essentials. Available at: https://edcspecialties.com/product/titanium-anodization/ [Accessed 4 Jan. 2025]. Photo used for figure 2.
Jasonxue (2024). Exploring the Diverse Coloration of Titanium: From Anodizing Colors to Natural Hues. [online] ETCN. Available at: https://etcnmachining.com/blog/exploring-the-diverse-coloration-of-titanium/ [Accessed 4 Jan. 2025].
Sims, J. (2023). An Overview Of Titanium Anodizing And Its Applications In Aerospace. [online] Valence Surface Technologies. Available at: https://www.valencesurfacetech.com/the-news/titanium-anodizing/.
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