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# Molten Glass Dropped In Liquid Nitrogen Is Not A Prince Rupert's Drop

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When you drop molten glass in water, you end up with a glass structure that is extremely hard at the bulbous base but can be fractured easily at its tail.  This is known as a Prince Rupert's drop.

However, this youtube video seems to demonstrate that dripping molten glass into liquid nitrogen produces a drop that can withstand the tail end being clipped off.  I know of no situation where a Prince Rupert's drop wouldn't shatter if the tail was clipped, so dropping molten glass into liquid nitrogen does not produce a Prince Rupert's drop.  Why not?  If the temperature is a factor, then what is the temperature differentiation that determines whether or not a Prince Rupert's drop is produced?  If one dropped molten glass into a liquid that was just 50 degrees C less than the glass, then would you end up with a Prince Rupert's drop?  I'm assuming that relative temperature is the determining factor here, but I don't know.  Is there something else that I'm missing?  If it's a Leidenfrost effect then why doesn't it apply to both water and liquid nitrogen?

Can anyone give a reasonable explanation?

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When you drop molten glass in water, you end up with a glass structure that is extremely hard at the bulbous base but can be fractured easily at its tail.  This is known as a Prince Rupert's drop.

However, this youtube video seems to demonstrate that dripping molten glass into liquid nitrogen produces a drop that can withstand the tail end being clipped off.  I know of no situation where a Prince Rupert's drop wouldn't shatter if the tail was clipped, so dropping molten glass into liquid nitrogen does not produce a Prince Rupert's drop.  Why not?  If the temperature is a factor, then what is the temperature differentiation that determines whether or not a Prince Rupert's drop is produced?  If one dropped molten glass into a liquid that was just 50 degrees C less than the glass, then would you end up with a Prince Rupert's drop?  I'm assuming that relative temperature is the determining factor here, but I don't know.  Is there something else that I'm missing?  If it's a Leidenfrost effect then why doesn't it apply to both water and liquid nitrogen?

Can anyone give a reasonable explanation?

I had to look up Prince Rupert's Drops: https://en.wikipedia.org/wiki/Prince_Rupert%27s_Drop  so I've already learnt something. :)

My guess is that the drops from liquid N2 may not be under the same compressive stress as those from water quenching, since they do not disintegrate when the tail is broken.

If that is so, then one explanation could be that the rate of cooling in liquid N2 may be less than that in water.

Water has a famously high latent heat of vaporisation and specific heat, whereas those of liquid N2 are far lower. My guess is you are also on the right track with the Leidenfrost effect, in that the gas production when liquid nitrogen is used will be far greater (due to the low latent heat) than the steam given off by water, and the insulating effect on the drop could thus be greater.

So as a result of all this, perhaps counterintuitively, it may cool a lot more slowly in liquid N2, allowing the stresses to dissipate within the drop as it cools, rather than being frozen in.

Edited by exchemist
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Water may either cause steam bubbles in the glass or at least distort it's surface

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I used to quench swords in oil instead of water, because the turbulence in water is so extreme, and oil produces a better quench when it comes to stresses. I bet there's data somewhere on these effects in metallurgy.

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I used to quench swords in oil instead of water, because the turbulence in water is so extreme, and oil produces a better quench when it comes to stresses. I bet there's data somewhere on these effects in metallurgy.

Perhaps this is significant, but I'm not sure.  I presume that the temperature of the oil was relatively the same as the temperature of the unused water in quenching products of blacksmithing.  I further presume that the latent heat of the quenching oil is the reason why you found it superior to water.  These presumptions may be incorrect based on my complete ignorance of blacksmithing.

What I found remarkable, though, is that in this video, a Prince Rupert's drop was not created when molten glass was dropped into liquid Nitrogen.  The best explanation I can find for this is that the production of gaseous Nitrogen around the molten glass insulated the drop so that it was able to cool more slowly than had the molten glass been dropped in water.  I do not know this to be the case, though, and I would like to know whether or not this conclusion is valid.  If it is, then there might also be a quenching liquid that is close enough to the temperature of molten glass that would prevent the formation of Prince Rupert's drops because the quenching liquid is of too high a temperature.  I know of no such studies that identify what this temperature may be.

In case you are unfamiliar with Prince Rupert's drops, you may find the following youtube video interesting.  They are exceedingly strong on one end, almost bullet-proof, while any disturbance on their tail end will drive a catastrophic fracturing along stress lines.

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There's significantly different bubbling properties between different quenching mediums. Some fluids seem to make contact with the metal better because they don't produce voids around contact sites like water does as it turns to steam. Oil would flame up at the surface, but deep down in the container it was too anaerobic to allow combustion. People use quite an odd variety of quenching fluids. I am not sure how much science is available on the matter though. It would be interesting to know. I suspect the water bubbles may create inconsistent localized cooling on the surface, probably creating millions of micro-cracks or radically changes the crystalline structure, but that is just speculation.

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• 3 years later...

It's not temperature but the viscosity of the fluid that changes the structure a less viscous fluid means less air trapped inside and a more solid structure but I don't know about nitrogen but metals are cooled in oil for this reason and to control the rate of heat loss

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• 1 year later...

Okay. There is something I would like to clear up here.

as a glass artist of ten years and an engineer by degree I can say with confidence that- yes. A “prince rupert’s drop” is created with LN2. Let me explain.

So, is it still strong? Does it withstand the crazy forces that it’s subjected to? Yes and yes. So something is indeed going on with it’s stresses that are set into it by rapid cooling in the LN2. Just because the tail breaking doesn’t shatter it doesn’t mean that it isn’t a prince Rupert’s drop.

Also, I’ll clear up another misconception I saw here. What is going on is not micro-cracks- if it was then it would have shattered during formation because glass fractures concoidally in the path of least resistance. Therefore, if there are ANY surface cracks, micro or not, the glass will break along those cracks of least resistance. Also glass by definition is an amorphous solid and does not crystallize. Except in the unfortunate case of devitrification. In which case it ceases to become a glass. So, no. Glass doesn’t “crystallize”. If it did it’s not glass any more.

Okay. So my work is done here.

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