Marc Ewenz Rocher, tells us about an exciting collaboration between the University of Oxford, Imperial College London and the University of Stuttgart.
In this experiment, a porous ZrB2 sample was sealed into a copper dome and placed inside a plasma wind tunnel as shown in Figure 1. The wind tunnel generates a very hot flow, which heats up the sample to 2000 °C. You can see a picture of this in Figure 2.
The sample discolours to white, because its surface undergoes oxidation as shown in Figure 3. Essentially what happens is that Oxygen damages the material at temperatures higher than 700°C and you see this in the form of discolouration.
The team repeated the experiment, but this time they fed a gas through the porous sample – a method called transpiration cooling. The results show that oxidation of the sample is prevented with this exciting new approach to cooling (Figure 4).
Figure 3 Uncooled Sample with Oxidised Surface
Figure 4 Transpiration Cooled Sample with Undamaged Surface
Marc tells us that the experiment was a great success. By avoiding oxidation, the team are able to heat the ZrB2 ceramic right upto its melting point of 3200 °C (a whopping 2500 °C higher than before!).
Transpiration cooling is a key technology for the design of extremely fast planes that could fly from London to Sydney in less than four hours.