Making YBCO superconductor

today on applied science we're going to talk about superconductors you've probably seen this cool demo of levitating a magnet above a high-temperature superconductor like this and as it turns out making superconductor is completely possible in home shop and involves quite a lot of fun stuff we've got spontaneously combusting mixtures you've got hydraulic pressing and we've got kilns with oxygen flooding but first let's check out some of the properties of the finished product that I've made here the material that we're making today is called ybco for you tree embarr um Kapoor oxide and this is a high-temperature superconductor but high-temperature is relative we still have to get it down to liquid nitrogen temperatures so very cold but not quite as cold as liquid helium which is what some superconductors require the low-temperature ones ybco is a black ceramic material and I'm making it in little disks like this the shape of it comes from the crucible in which I'm making this and it's kind of a you know it's a fairly dense thing it feels basically like a floor tile or something it's really just kind of a normal feeling ceramic and it's pretty brittle in this form too you can break this with just a pair of pliers it's really not that strong and if we break it you can see a little bit of crystalline structure inside the magnetic levitation occurs because of an effect called flux pinning and basically the crystal is not completely perfect there's little pinholes where the magnetic fields can get through the superconductor and when we drop a magnet on top the magnetic field is forced through these little pinhole defects and then can't get back out because the little pinhole is surrounded by a superconductor and there's a current that flows through there and so it's basically like a little solenoid coil holding the magnet in just that spot pretty neat effect for visual interest I thought it would be fun to put some of these colored ferrofluids on the levitating magnet you know can I have a levitating droplet of fluid with the spikes coming out and everything but as it turns out the colorant in these colored ferrofluids are just like a surface thing I put some dust or something in there so if you go into the bottle The Dropper you don't actually get the color out it's still black ferrofluid in there but nonetheless still a cool effect and then also a neat thing to do is to drop a iron filings on top of this and the momentum of the art of the falling iron filings gets caught up into the magnet and causes it to spin around and it looks pretty cool and I also got some high-speed video of this one of the best tests for a superconductor is the magnetic levitation like we've been looking at but I also wanted to measure the electrical resistance of my superconductor to see if the transition temperature agreed with the literature so I came up with a setup to do that a while ago Charles PAC sent me his great temperature lager here and because this is an open source device I was able to download the firmware and modify it for doing a superconductor transition temperature measurement so what we have here is a combination of both devices we've got the Keithley doing a 4 wire resistance measurement and the idea here is it's got a hundred milliamps flowing through the outer two probes and then it's checking the voltage between the inner two probes and figuring out the resistance that way and even at a hundred milliamps the voltage drop between these two inner probes is very small but what we're doing is instead of measuring temperature with this fourth Channel on the data logger it's basically piggybacking on the the two sense electrodes and capturing that tiny voltage and recording it and since 100 milliamps everything lines up so twenty eight millionths of real resistance corresponds to two hundred and eighty-two units in this thing's storage system it ends up being I think tens of micro volts or something and at the same time that we're recording the voltage on the sample with this channel we're also recording temperature from real type K thermocouples here so the whole setup allows us to measure temperature and then the resistance based on this sensitive setup so you can see the results of the data collection here it's actually pretty good I wouldn't worry about the absolute numbers quite so much liquid nitrogen is only negative 196 I think Celsius and you can see that my measured temperature values go lower than that which is not really possible that's because type K thermocouples aren't really the best way to measure liquid nitrogen temperatures but it is what I have on hand and it's actually surprisingly close considering everything else you can see for comparison that a regular piece of metal just gets to be a better and better conductor the colder it gets but the superconductor is special in that it's getting to be a better conductor as it gets colder and then suddenly when it hits this transition temperature it becomes a full superconductor and the resistance really does drop to zero it doesn't transition to like a another regime where it's getting better and better it really goes to out to real zero attaching the leads to the piece of superconductor was not at all easy in fact the dumbest way to do it ended up being the most effective I basically just took this you know heavy alligator clip and just bit onto it like that and that's it that actually worked really well some other things that I tried were silver based epoxy this seemed like it would have been a great way to attach you know a small wire but it doesn't work at all as soon as the thing gets cold we lose contact I'm not really sure if the epoxy is shrinking and just making poor contact with the ceramic or what but that doesn't work and then I also was clever thought I was being clever and made these four wire Kelvin probes out of pogo pins and they're nice and spring-loaded and they have like a really long travel and everything these don't make contact either I put a lot of pressure on it and between the springs freezing up from the liquid nitrogen pressure temperatures and just the small surface area there those don't make contact either so just clamp on with big alligator clips I also tried to film an experiment where I showed the magnetic flux lines being excluded from the superconductor when it becomes superconducting and this didn't work but it's actually correctly showing me what's going on so this is actually how I found out that high-temperature superconductors are type 2 superconductors like ybco actually let a lot of magnetic flow through them it's just through this flux pinning that all these weird magnetic levitation effects happen type 1 superconductors at really low temperatures like pure mercury for example as a type 1 superconductor those actually exclude magnetic flux lines and this experiment I'm gonna try to do this if I ever get access to liquid helium the iron filings should move away from the superconductor showing that the flux lines are going around it rather than through it but type 2 superconductors the flux lines do go through they just get concentrated into these defects if you search the internet for recipes to make ybco superconductor you'll find that the most common method is called the shake and bake method and it's called this because you basically just put the three ingredients together get REME oxide barium carbonate and copper oxide together in a mortar pestle you shake it up you grind it up and then you put it in a kiln and you heat it up to about 950 degrees C the baked part of the shake and bake then you take it out and you grind it up and you shake it again and then you put it back in the kiln and you take it out and then you grind it up and shake it and put it back in the kiln and you do this three or four times the problem is that when it's in the kiln it spends about a day at 950 degrees C and then another whole day to cool down so this whole process can take about a week and if it doesn't work at the end like is what happened to me it's very difficult to debug the process because changing it requires another a few days or a week to even find out if the change you made works or not in any case the main problem with the shake-and-bake method is that we really want these three ingredients to be in like atomic contact with each other I mean we want to make crystals that have atrium barium and copper in them and so to make that crystal structure the atoms really kind of need to be almost touching the problem is that even if these are super finely ground powders and we put them in a mortar and pestle and grind them I mean that the chunks of material have got to be like you know millions or billions of atoms big right so you're only going to form ybco at the place where these chunks are touching each other and so the point of regrinding it and firing and regrinding it and firing it is that you keep the chunks open and letting more and more surface area together so I actually never got this to work I'm sure it can if with enough grinding like they talked about sitting there with a mortar and pestle for like 30 minutes of straight grinding and I admit I never got to that level but anyway I found a much more fun and effective method of doing this the pyrophoric process involves finding compounds of yttrium copper and barium that are soluble in water and then we boil the thing down to make this sludge that ignites and since the three chemicals are all soluble they were all in you know intimate contact with each other because they were in solution so we don't have this problem of big chunks of of powder like not getting together close enough in this case it's easy to find barium nitrate which is soluble in water and copper nitrate which is soluble in water if we could find it really nice rate that would be great but typically it's it's hard to find so what we do instead is add a little bit of nitric acid to the water and then add the yttrium oxide and that will dissolve it into the water the reason that we use nitrates one is because it's soluble and also because there are oxidizers and so since we want this process to generate its own heat we're going to use these as oxidizers and the fuel is actually going to be citric acid also soluble in water so we put all these things together and then as we cook it we boil off the water and end up with a very thick sludge I should point out that this releases some really nasty fumes and so I have sort of a makeshift fume hood it's actually a very efficient fume extractor and it blows the exhaust out the roof of the garage here after maybe an hour or two of slow boiling the sludge is getting hotter and hotter because the water content is going down and the heat input is about the same so as the water goes away that you know the temperature starts going up and eventually it gets to the ignition temperature and self ignite it's a really cool-looking process it doesn't explode it's just a very quick burning sort of like burning black powder out in air in fact black powder is very similar we've got a nitrate and a fuel and we're burning it in an open container so it doesn't explode it just burns very quickly and I got some high-speed footage of this too this was actually an interesting shot because the amount of infrared light coming off of the combustion was so high it was overpowering the camera and so I had to add an extra little infrared filter in front of it but then also I had to have the fume extractor going because it was blowing you know nitric acid fumes and ash and everything out of there too so I had the the tube setup and the camera aiming in there and it was it was kind of an interesting shot after the combustion is done we're left with this really loose sort of brown ash it's very lightweight in fact it's so lightweight that some of it just sort of floats out from the hot gases being released during the combustion I tested some of this in liquid nitrogen to see if it was superconducting and of course it isn't we'll talk about why in a minute but at least all the ingredients have been mixed together perfectly because they were all in solution and then in the heat of that fireball all of them got forged together into ybco but unfortunately it's not quite enough just to have all the ingredients in the right place at the right time we also have to get more oxygen injected into this thing and then also cool it down very slowly so that it forms nice big crystals I later found out that you don't have to hydraulically press these if you want to make a pellet just putting them loosely into a crucible or a dish in aluminum oxide dish and putting that in the furnace and heating it up to about 950 is good enough you'll actually get a perfectly fine hard disc out of it that way that's that's mechanically fine however if you do want a really nice puck shape without any cracks or anything in it you might need to hydraulically press it and I tried this a little bit and had some success not a whole lot the pressing die is the geometry that I have is not very good and so the diode is Jama but anyway I did make a few pellets this way and they were kind of ok so after we're left with the pellet of this pressed brown powder or just sort of loosely tapped down into a crucible the kiln serves two jobs here one of them is to get the crystal structure as uniform as possible just by cooling it slowly and the other job is to get more oxygen injected into the ybco crystals despite all the literature on the internet about ybco it's actually difficult to figure out the exact temperature ranges and times needed to do this you would think it would be pretty well-established by now but there's actually a fair bit of disagreement on the internet about what's going on with all this stuff so I can report what worked for me basically heating up to 960 degrees C and then decreasing the temperate holding for about maybe one or two hours and then decreasing at 1 degree C per minute over the over the down to room temperature with oxygen flowing in it's what ended up working for me at first I had just a thin stainless steel tube that was allowing the oxygen into the kiln and I was using a pretty high rate kind of about 50s CCM standard cubic centimeters a minute and then I realized that could be a whole lot more efficient with the oxygen and also have a better chance of getting the oxygen into the crystal by making like a little container within the kiln so I drilled a hole in the bottom of a crucible and then put it used it as a lid basically and put it on top of the crucible that was going into the kiln holding the powder so that way the oxygen would sort of be forced to hang out with the powder that I was trying to oxygenate in there and I ended up using a flow rate of about 10 SEC M another major problem that I had was that my kilns thermometer was not quite accurate enough to get the proper temperature for doing this process so most of the literature says you need to be around 940 to 960 even as high as a thousand degrees C to get ybco crystals into the annealed state and then start cooling down slowly from there and so originally I was setting my kiln to 940 and none of my samples were working I did this probably you know 5 10 times and none of them were any good and eventually I realized that a temperature that the kilns reported temperature was not quite right so you can see inside this kiln the stock temperature sensor is up there and near the roof and I'm mostly interested in the temperature inside this little crucible within the kiln thing so I added another thermometer or another type K thermocouple and had that set up with my data logger and that's how I got the profile to see what the actual temperature was inside there but I didn't realize I had this problem and then after I did realize it I used these pyro metric cones to figure out if the temperature at the base of the kiln here is really what it says they are these cones are designed to calibrate the temperature of your kiln are tested and they are made from a specific material that begins to soften at a very specific temperature range so this one is set to go at just under a thousand degrees C and it's kind of a it's kind of a hard material it's actually very brittle I'll just break this one just so you can see it just snaps right off it's it feels kind of like a ceramic but it's a little bit lighter weight it's kind of like a choco most or something like that and the idea is that you put one in your kiln and then start raising the temperature and keep checking on it looking in there and checking on the state of this thing and when it's folded over then you know you've reached the right temperature so a very good way to calibrate your thermometers so basically as it turned out when I was setting my kiln to 940 it was really only about 9:10 at the floor of the kiln and none of those samples came out working so it definitely needs to be hotter than that I think 950 or 960 is fine and then in the reading I've done since then I think maybe the best temperature profile is to go from 960 down to maybe 500 and then you hold there for another 8 hours and then from 500 down to room temperature and you generally want to go pretty slow like a degree per minute fortunately but you need a temperature controller that can adjust the temperature slowly enough basically and that that's not so easy 1 degree C is actually the minimum rate of travel for my temperature controller the point of stopping it 500 like this is to get as much oxygen in there as possible so the like you say there's these two stages where there's setting of the crystals and there's like this maximum oxygenation which happened at different temperatures the liquid nitrogen that I used in this experiment is indeed homemade I used my DIY liquid nitrogen generator kind of an Express mode so instead of having the original power supply with the digital control I've got this big very act that my dad gave me and I've connected it directly up to the cryocooler and then I have a clamp meter here to monitor the current going into the cooler and a power meter to monitor the you know a number of watts going into the system totally and then I also have this kind of makeshift air dryer here which is just a bunch of silica gel and the the intake hose goes to the bottom of this column of silica gel while reading some of these papers about making ybco a lot of times you'll see something like use a flow of 2 ml per minute of oxygen but that doesn't mean just get a big kiln and then stick a tube in aside and get 2 ml per minute of oxygen going in there it almost certainly means use a vacuum tube furnace like this where there's a quartz tube that goes all the way through the middle and it gets hot of course in the middle but you can connect process gas or even a vacuum pump to the outside and I've kind of wanted one of these for a while because there's a lot of other experiments you can do with it that are pretty cool and I didn't end up needing this since I got the ybco working in my small tabletop furnace but this is a indication of what's to come on the channel I'm going to use this to make all kinds of cool stuff and it's it's not built yet so maybe that'll even be its own video is putting this together ok see you next time bye

Channel: Applied Science

Views: 622,592

Keywords: Applied Science, ben krasnow, YBCO, superconductor, pyrophoric, create, liquid nitrogen, science, DIY, hts, superconductivity, magnet levitation, flux pinning

Id: sLFaa6RPJIU

Length: 19min 37sec (1177 seconds)

Published: Mon Feb 26 2018