I am always amazed when something that I think I understand completely turns out to be far more complicated than I first thought. The anodizing process was one of these things as, back in the day, I had investigated anodizing some of my PC components as a way of avoiding having to go through the laborious process of painting them. Of course I stopped short after finding out the investments I’d need to make in order to do it properly (something my student budget could not afford) but the amount of time I poured into researching it left me with a good working knowledge of how it worked. What I didn’t know was what it could achieve when titanium was used for anodizing as it’s able to produce an entire rainbow’s worth of colours.
The wave of colours you see the metal rapidly transition through aren’t some kind of trick it’s one of the interesting properties of how the thickness of a deposited titanium layer interferes with light passing through it. As the thickness of the layer increases the interference increases, starting off with a kind of blue colour and then shifting through many different wavelengths before finally settling on the regular metallic colour that we’re all familiar with. This process can be accurately controlled by varying the voltages applied during the anodizing process as that determines the resulting thickness of the layer that’s deposited onto the host material. In the above example they’re going for a full coating, hence why the bar rapidly flashes through different colours before settling down.
These kinds of reactions always fascinate me as it shows how things can behave in extraordinarily different ways if we just vary a small few parameters in one way or the other. It’s one of those principles that drove us to discover things like graphene which, at its heart, is just another arrangement of carbon but the properties it has are wildly different to the carbon that most of us are familiar with. It just goes to show that when you think you know science is always ready to throw you another curveball and that’s why I find things like this so exciting.
Kinematics was my least favourite part of physics, mostly because I always had a rough time wrapping my head around the various rules and principles that govern the way things move in our world. However one lesson always stuck with me in my head, the one relating to friction and it’s various forms. Whilst I’m sure the teacher delighted in tricking us all by asking us what kind of friction a rolling tire has (hint: it’s either static or kinetic and it’s not the one you’d first think it is) that example rooted the principle firmly in my head. Understanding that made further concepts a lot easier to grasp although I’d never really considered friction a powerful force until I saw this:
What you’re seeing happen here is a process called Friction Welding although in technical terms it’s actually not welding at all. Instead it’s actually a type of forging as in traditional welding two pieces of metal are joined via melting whereas in friction welding no such melt occurs. This process has a lot of advantages most notably allowing 2 dissimilar metals, say high grade aluminium and steel (a common pair in space fairing missions), to be joined together. Doing this process via other means is extremely difficult due to the different melting points of each material and would likely lead to a much weaker bond. Friction welding by comparison always creates a full strength bond without the additional weight introduced via other methods.
Interestingly enough this process can also be used with materials other than metals, specifically thermoplastics which are a type of plastic that becomes pliable under heat. Friction welding can then also be used to join said plastics onto metal surfaces, enabling cross material bonds that are far stronger than those that could be achieved via other methods.
Pretty fascinating, isn’t it?