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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hi all.
I have come up with a possible method of increasing the useable fraction by utilising heat assisted electromigration to "force" the lattice into the desired formula combined with a novel way of laying out the initial compounds alternating with the barium and calcium oxides. In theory it could work, in much the same way as molten glass conducts electricity.
I hope to have something working shortly, this all depends on how long it takes me to build the sintering jig using fire bricks and tungsten welding rod as the electrodes, and hydrogen peroxide + MnO2 as the oxygen source.
As for testing it, a relatively simple approach is to stack three peltier junctions then water cool the "base" to reduce the thermal gradient allowing the stack to reach -40 Celsius in principle. Obviously it will not superconduct at this temperature but I can observe the drop in resistance
(maybe there is a use for one of those car aircon pumps..)
EDIT:- I found a reference to using induction heating in order to alter the microstructure of a superconducting disc to change the formula very slightly, in a similar way that it is used to anneal metal alloys. if this works with the high temp. materials then I might be able to synthesize higher useable fractions without messing around with the oxygen content.
"After that, the disk was put back in the furnace at 600C, and the upper surface was quickly heated to 1200C using a planar high frequency inductor as shown in Figure 1. During this last heating, the gap between the disk and the inductor was chosen precisely so that heating would occur only in the top 2 mm-thick layer of the disk, although the material's high heat conductivity caused some heating below this region"
For those looking into making these materials, be aware that even microscopic quantities of some contaminants such as iron and nickel can quench superconductivity entirely even at LN2 temperatures. I'd avoid low purity "ceramics grade" chemicals even though they are cheaper, unless you have a way to test them for contamination and purify them.
Depending on exactly what the contaminant is it may be possible to chemically separate them, iron oxide being somewhat insoluble could be extracted in this way and crystallising barium carbonate then regrinding to a uniform particle size would get rid of some (thanks for the tip Weston!)
as for induction heating,
EDIT:- I have emailed NASA re. a similar idea, am waiting for a response. Making HTSCs cheaper would be one way to get my name in the history books, if low grade materials could then be used for direct radiation shielding by tweaking the formula..
-A
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Homemade superconductors?
