Tuesday, July 8, 2008

Our Superconductors Work!!!!


This title was the first lab entry in my book today. After removing the first set of pellets from its second annealing cycle in the tube furnace, we poured some liquid nitrogen and tested their levitation over our magnetic track. And it worked! There was a certain trepidation as we placed the first pellet over the track, because if they did not work we had three weeks of work mostly wasted. Fortunately, we did not have to go through those emotions.

Once we realized that the YBCO would sufficiently demonstrate the Meissner effect, we set out to test the individual pellets. Some of the pellets still showed signs of incomplete levitation, so we used a stopwatch to test each pellet's levitating duration. Over an average of 3 trials, the longest duration time was 15 seconds. The shortest average levitation time was 8 seconds. One possible explanation for the difference is that some of the pellets were touching the alumina boat as they sat in the furnace. At 930 degrees, the alumina may have some interaction with the pellet. Evidence for this is that the weaker pellets levitate unevenly, tilted to one side.

Once we found the three best pellets, we taped them the bottom of a small (0.25 g) styrofoam car. There was a channel carved into the bottom of the car which held the pellets, which were then taped in place. Three pellets taped to the bottom of the the car levitated over the track for an average of 50 seconds.

To determine the effect of more pellets, we took the next two best levitating pellets and added them to the bottom. The five pellets, when taped to the bottom of a styrofoam car levitated for an average of one minute.

By the end of the day, we had a good starting point to continue with the engineering aspect of this project. We have 9 working pellets, and a design that can produce levitation for a sufficient time. From here, we will improve the design and performance.

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