Like every Friday, the weekly "Physics Bite" column is back — number 21.
This week: electrochemical coating with titanium, oxidation-reduction reactions, and the surprising connection between color and the interference of light waves.
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Titanium metal coating is widely used across many industries, including medicine, aerospace, and even jewelry.
In the video, the mesh is connected to a positive power source and serves as the anode.
The screws are connected to a negative voltage source and become the cathode.
The liquid in the vessel is called the electrolyte, and it acts as an electrical conductor that completes the circuit.
The electric current causes oxygen ions from the electrolyte to combine with the electrons in the screws, forming a layer of titanium dioxide.
At the same time, the molecules in the mesh break down through electrolysis into hydrogen, oxygen, and electrons.
The hydrogen and oxygen remain in the electrolyte, continuing to feed the titanium layer formation process, while the electrons flow through the electrical circuit to the screws.
The reaction is called oxidation-reduction (redox): oxidation occurs at the anode, which breaks down and loses electrons, while reduction occurs at the cathode, which gains electrons through the electrical circuit.
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The color variation depends on the thickness of the titanium layer on the surface of the screws.
The higher the voltage, the faster the coating process and the thicker the resulting layer.
Surprisingly, the color changes are not due to differences in material composition. The material is titanium dioxide at every thickness.
The color changes arise from interference, in which light waves reflected from the bottom and top surfaces of the coating travel different paths and combine to produce light of a specific color.
The thicker the layer, the more the wavelengths of the reflected light shift — which is why we see such a wide range of colors.
Shabbat Shalom 🌹
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