I have been noticing an incredibly thin shiny "foil" that forms on very thin leaked areas of the casting. My assumption is those areas freeze very quickly and probably chill. I suppose that is related to the formation of the foil. The foil is thin enough that small bits of it float in the air. Can anyone explain what I am seeing here? For some reason the "Embed Media" link did not want to accept the YouTube address. So, I am just pasting the link address here. https://www.youtube.com/shorts/8XyIfaPZvuY Denis
I had a look at the video and was thinking if you were using a mold coating it what was left over after burning?
No mold coating. The core is sodium silicate/coal/sand. This is metal. It must be iron. Next time I’ll touch a magnet to it. Denis
Could it be a film of lustrous carbon? https://www.giessereilexikon.com/en...-3796/?cHash=050c6583c9c614927660569e861151bf Tim
Now, that sounds like a very likely explanation! I did not know "Lustrous Carbon" was a thing. The fact that these flakes are so seemingly light that they can be carried around by gentle air currents seemed surprising were they iron. Next time I will test the flakes with a magnet. I could also flame test them to see if they seem to ignite. Denis
Denis, I wonder if it's a combination of the coal dust and the graphite which increases the carbon content above normal conditions?
Yes, I do put 6% sea coal in the core and I guess (who really knows after so many uses) a similar amount in the molding sand. I guess and add back some coal to the molding sand each time I remull it. I think the idea that this could form metallic carbon is very cool. Denis
It's at this point Denis discovers it's not actually attracted to magnets but floats above them, due to the Meissner effect and the material being a room temperature superconductor.....
I went out to the foundry and mulled some sand this afternoon. And I looked over my molding table hoping to find some shiny flakes even though I had "cleaned off" the table. Not being particularly meticulous in cleaning it previously, I did find a number of 1/4 to 1/8" flakes of that very light shiny material previously noted. So, I put a flake on a small steel spatula and applied a MAPP gas flame to the undersurface of the spatula being careful not to blow the flake off the spatula. I heated the spatula until it was a fairly bright cherry red but the flake was completely unaffected. It remained very shiny, did not show any inclination to flame, and did not change shape. After I removed the flame the spatula, being steel discolored to a dark grey as expected. But the flake was as shiny as ever. I also tested a flake's magnetic properties. A strong magnetic field had no effect. So, this is extremely interesting. I am guessing this is indeed lustrous carbon film. Good call, Tim. I made a 15 min effort to discover what physical characteristics lustrous carbon should demonstrate, but found no information. I'd be interested if anyone could provide info predicting its flame susceptibility, electrical conductivity (almost certain I would think), or any other features that might help confirm or deny its identity. I do find it fascinating to see it "floating" in the air glinting in the light as it turns this way and that. Denis
This article mentions that it's pyrolytic graphite sheet. https://www.google.com/url?sa=t&sou...YQFnoECBAQAQ&usg=AOvVaw3vhXrtLGHiIVEGlLPinAv8 If so, physical properties can be found here https://www.americanelements.com/pyrolytic-graphite-7782-42-5
Very interesting information in Mach’s article. It makes sense as I have in one way or another noticed the shiny surface of cold shuts and also noted increased luster of castings (not a bad thing in itself) when I increased coal content of my cores. Right now the cores contain around 6 to 7 percent coal. They produce a surface that is slightly lustrous and easily shaken out. The luster is gone after stress relief at 1150F. But I actually like the clean surface produce. No build up of film has been seen. I will see if I can float the film over a neodymium magnet. Thanks for the information contributed above. Denis
I found some flakes of shiny foil (presumably lustrous carbon) and tested them for magnetic properties with a powerful 1/2” x 1/4” round neodymium magnet. The best way to do this seemed to be to allow a flake to “float” on the gentle air currents at my indoor molding bench. As they fluttered randomly I approached them with the magnet. When I got within an inch or so they zipped to the surface and oriented their long axes parallel to the presumed magnetic lines of flux! So, this foil does not seem to be diamagnetic. What does that mean? If they are lustrous carbon, I thought they should show diamagnetism. Or, given how much carbon can “shape shift” can the there be magnetic and diamagnetic forms of foil. Is my method faulty? Denis
