Tuesday, July 22, 2008

Track Design

7/22

As we near the end of the RET, we have been finalizing certain aspects of the project. We had initially intended to make a track that was an oval, which the vehicle could circumnavigate. However, that was a bit impractical because the magnets are quite expensive, and funding an entire oval would cost about $1200. As it is, Ram was quite generous and we have nearly $500 worth of magnets as our track. Not being able to construct a complete track, we fashioned the magnets into the shape of California.

We kept the track with four-wide magnets, with alternating poles (N-S-N-S). At the place where San Francisco would be, we removed two of the "coastal" magnets. Since the pellets will move stably over three-wide magnets, the vehicles can navigate through the "bay" with ease. Below is a bit of the evolution of the California track. We have painted the base (magnetic stainless steel) to help show it as California. The blocks of magnets on the side are the Channel Islands, complete with polarity arrangements to allow pellets to head out to the islands and "just hang out." I think that could be a nice educational tool, because it will be easier to see how stable the pellets are, and the smaller magnetic base might be easier to explain than the entire track.

Monday, July 21, 2008

Batch Two is great!

7/21
Over the course of the past 2-3 weeks, we have been making a second batch of superconductor pellets. It is somewhat following the "more is better" philosophy that we have adopted in developing this levitating vehicle. Having more pellets allows us to make more vehicles, with possibly more pellets in each vehicle, improving their levitating power.

We made a few changes to the synthesis procedure, but one appears to be most significant. For the first preparation we used a long-cylindrical boat crucible made of alumina. The pellets leaned against the sides of the boat. We were pleased with the levitating results that we observed, but the diffraction data was a little messy. We theorized that the aberrant peaks were likely due to alumina contaminating the pellets. To avoid this, we used a more upright alumina crucible, and stacked the pellets so that they would not touch the sides.

This second batch levitates amazingly higher than our previous preparation, and the diffraction data is much cleaner, matching the reference scans with much more precision. Below are two pictures, before and after. The pictures were not taken at exactly the same angle and distance, but I think the difference in levitating ability is clear.











Another picture of the levitation with the new batch of YBCO:

Wednesday, July 16, 2008

Seeing the end

7/15

This is the second-to-last week of the RET I program, and as cliche as it sounds, it really has gone fast. As we plan our tasks, we have to take into account that next week will need to be mostly spent working on a final PowerPoint presentation, rather than furiously finishing lab work. That said, today was a great day in terms of inspiration.

We came to the conclusion that the scale of the car was not likely to change. This was a nice mental place to get to, because then we just went about refining our current cars. Trying to stay within the 0.25-0.30 g range, we carefully carved, sanded and sculpted our styrofoam blocks into a few designs that we hope will be more balanced and consistent that some earlier models. During the initial tests, they moved through the track well.

The general design is a solid body, with a channel carved into the bottom of the car. The five pellets are placed in the channel and then taped in place. The structure is then placed in a bath of liquid nitrogen until it cools below the critical temperature (takes about 30 seconds the first time, then about 10 seconds for subsequent coolings). Most surprising about this design is the strength of the tape. It withstands multiple dips into the liquid nitrogen, AND insulates well. We are getting about a minute of levitation time with the styrofoam and tape construction.


Here are some pictures of where we currently are in terms of construction.

CAR:
Videography quality poor (a little shaky)-- Watch on an empty stomach.
video

Ram had been gone for the past two weeks and had not seen our progress. Toward the end of the day, we showed him the track and movement, and he seemed to be really happy with the results. I think he is planning to order more magnets, which will be nice because the track will be longer, and more interesting. It will look pretty neat if we can get an entire oval, but that may be too many magnets. I'm excited to see how this will turn out.

Slow-Going

7/10-7/11
I have not posted in a few days, and the information of this post is actually from last week as I am writing this on the 16th.

Due to the power outages at UCSB caused by the Goleta wildfires, there has not been much lab equipment available. All furnaces were turned off, which makes since because thermal cycling (turning power on and off) is not necessarily the best way to run a solid-state reaction.

My research partner and I spent most of these days working on our PowerPoint presentations that we must produce as a part of our program.

However, the one advance that we made on these days came out of the line of thought: "If a track that is three-wide is better than two-wide, then a track that is four-wide must be better than three-wide. This turned out to be true. Our newest track design is four magnets wide. We tested the movement along both a straight and curved track. Again, the maximum curve had a distance between outer magnets of about 3-5 mm.

By Friday, we felt relatively secure that there would be no more power outages, so we set our second batch of pellets to anneal in the tube furnace (48 hr @ 940 degrees C). We made one change to the reaction conditions. Rather than using an alumina boat (long and thin) we used a crucible. This allowed us to stack the pellets and by carefully sliding the crucble into the tube, the pellets did not touch the side of the crucible, which they did in the boat. At this point we are not sure if the alumina is a source of contamination in the first batch, but that potential has made us try and avoid it with the second batch. The X-ray and Meissner effect tests will help determine whether it was a necessary change.

We also performed an X-ray diffraction of the first batch (after being annealed twice) to see what possible effect that second heating had on the crystalline structure. Initial analysis of that data shows minimal change structurally. However, the pellets are showing marked improvement in the Meissner effect since the second annealing. We are not sure why at this point, and may pursue it further but time is getting scarce and we need to finalize the project as soon as possible.

Wednesday, July 9, 2008

Diagnostic Testing

7/8

Today, the power at UCSB was going on an off. As the wildfires reached some critical distance from the power lines in the Goleta foothills, the power for UCSB was shut off as a precaution. I allowed myself to become frustrated for a moment, then realized that being able to anneal some YBCO pellets paled in comparison to the importance of protecting those whose homes are jeopardized.

The power outtages were unannounced, so we couldn't really predict when they would happen. All furnaces and power-requiring devices were shut down. I always knew but never really thought about how dependent we are on electric power. The lab was really shut down except for the "wet chemistry" room which didn't require too much gadgetry.

To adjust our own work, we performed four diagnostic tests on our pellets and track. These tests were:
1. Finding the maximum distance between magnets on a straight track that would still allow for continuous movement
Results: 2 mm was the maximum distance. At 3 mm, the car would not move. It would move across a few magnets, then stop.
2. Finding the maximum distance between the outer magnets on a curved track.
Results: 3-4 mm allowed for continuous movement around a curve. When the curve was stretched to 4-5 mm between outer magnets (making for a sharper turn) the car would either veer off the edge of the curve or stop its motion.
3. Finding the maximum mass that 5 of our best pellets can levitate.
Results: 1.8 g

4. Average levitation height for a pellet.
Results: ~6 mm (This was tough to measure precisely, but it was in the range of 5-6 mm)

5. Average levitation time for pellets and styrofoam cars
Results:
One pellet (no insulation)
Highest Time: 17.06 s
Lowest Time: 7.31 s
Average Time: 10.52 s
Three-Pellet Car (used the three best pellets, taped to bottom of styrofoam car)
Highest Time: 45.63 s
Lowest Time: 38.61 s
Average Time: 41.07 s
Five-Pellet Car (used the best five pellets, taped to bottom of styrofoam car)
Highest Time: 63.85 s
Lowest Time: 52.68 s
Average Time 60.50 s

Without much more that we could do, we broke for the day. We seem to have found a maximum curve that we can make a car move around. Also, we have found a design that works well. We have used 84 magnets to make this track, and we may need to purchase more in order to make a complete oval track. I am not sure if that is in our budget, but it now seems that we are only making small tweaks.

Tuesday, July 8, 2008

Our Superconductors Work!!!!

7/7

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.

Quick Day

7/3

Today was cut short for several reasons. The wildfires in Goleta have left the university and the city prone to frequent power outtages. Consequently, both of our "batches" of YBCO are going to be in their respective furnaces for the rest of the day.

Our first batch is finishing up its second annealing cycle. The Meissner effect left something to be desired, so another round of oxygen was attempted to remove any remaining impurities.

Our second batch is going through its first heating cycle (48 hours at 940 degrees C). With the 4th of July holiday, we had to cut the day short and pick up next week

Wednesday, July 2, 2008

Setbacks

6/30-7/1

Well, I am coming to terms with the sinusoidal nature scientific progress. Frustration and slow progress is followed by moments of clarity and amazing results. Both Monday and Tuesday were less than stellar in terms of progress toward our ultimate goal.

The one upside of Monday's experiments was that we were able to have a pellet move along a curved track. There appears to be some critical distance beyond which the magnetic field no longer levitates the superconductor. I didn't measure that distance, but it is in the range of 3-4 mm. So, the track is ready, now we need a vehicle.
Let me back up. The current idea for our vehicle design will be a styrofoam body, with a metal bottom. The superconductors will be affixed to the underside of the metal. Inside the styrofoam body, we will pour the liquid nitrogen which will hopefully lower the temperature of the superconductors below their critical temperature. Below are some pictures of our initial design.








This was constructed from two corners of a styrofoam cooler, then glued together with styrofoam glue from Michaels craft store. It really looks, smells and feels like Elmers, but I'm a sucker for marketing and new packaging. However, this design did functions as a liquid nitrogen reservoir. There was some initial leaking, but a second layer of glue has proved to be an effective seal.

In attempting to engineer this design, these past two days were really slow-going and fraught with trials that did not work. The mass of the vehicle is going to be an issue. The sample superconductors that we have been using cannot levitate more than 2-3 grams. Consequently, my design for the vehicle underwent a series of shavings, clippings and trimmings that cut its mass from 5.0 g to 2.4 g. See below for some pictures of the evolution of the design taking mass into consideration.
The mass of this design still proved to be too much for the sample superconductors that we had.
I may not have mentioned this in all my worries about vehicle construction. On Monday, 7/1 our own samples came out of the furnace in which they were annealed in oxygen. This was to add the final oxygen atom to the unit cell of our crystal structure.
Early Monday, we tested the Meissner effect and our pellets were less than stellar. The pellet would levitate, but not evenly. It would hover at an angle, and increased in temperature much faster than the samples we had been previously working with. There may have been some impurities, or the annealing process may have been incomplete. To try and fix this, we set the pellets for another annealing in oxygen for 36 hours. Hopefully, an additional heating will improve the purity and the pellets' ability to levitate.