Yes! The stress visible in a polariscope is caused by compression in the outer layer of glass. Dissolving the outer layer gently relieves the stress and so it will reduce the color patterns in the remaining drop. It also makes the drop a dud. The etched surface is frosty but the change is dramatic.
@@stevestarckeI was going to say the same thing, the stress is completely contained in the outermost layer of the glass, etching it away removes the stress and makes the prd a normal glass droplet. Well that's what I think anyway.
1. It isn't any harder. It is tougher. There's a small but important difference. 2. Nothing happening there got *anywhere* near the annealing point for glass 🤣 [3] This is why you can't "experiment" on CZcams. It doesn't teach experience.
So I imagine these are like tempered glass. The second you got about 40% of the way through the glass it just explodes. It releases all the internal pressure and just gives way. Think I'll skip this one though
I suspect it would shatter like ordinary glass, because as @stevestarcke pointed out in another comment thread, the outer layer of a Prince Rupert's Drop is under compression. Based on some previous knowledge and what I can deduce from Steve's comment, this compressive force constantly pulls on the inside of the drop, leading to tensive force in response. This tug-of-war between compression and tension is what gives rise to the drop's properties. However, if that outer layer is carefully and slowly removed with HF, there is no longer a compressive outside force that leads to an inner tensive force, causing the Prince Rupert's Drop to lose its characteristic properties. However, this is only a hypothesis, and my understanding of the subject may be incomplete and/or wrong, so please take my comment with a grain of salt.
The stresses in a Prince Rupert's drop are concentrated within the surface layer, since that's where the sudden thermal shock occurs during quenching. By etching off the surface layer, the stresses were gradually relieved. That potential energy has to go somewhere however. Try etching them in total darkness. Perhaps the energy release will manifest itself as heat, light or sound.
If a compressed metal spring is dissolved in acid, while being held in compression, what happens to the potential energy that was stored in the compressed spring?
What if we drop molten glass in cold hydrofluoric acid? Would be interesting to see the stress pattern of the resulting “Prince Rupert’s drop” as the surface is being simultaneously rapidly cooled and etched!
Nice and interesting video. I think that the effect of the immersion of the tail of the Price Rupert's drops in HF inhibiting their explosion is not due to a loss of internal stress (at room temperature atoms cannot move very easily), but to surface free energy effects. What I mean is that the immersion in HF increases the surface area (and consequently the surface free energy) of the drops. The increase of surface free energy counteracts the tendency to explode of the Prince Rupert's Drops which would futher increase the surface area of the system. The surface free energy is always a positive term and hence it has a destabilising effect for condensed phase systems. Conversely, when you immerse the head, you weaken the structure of the head itself thus enabling the stress to be relieved and thus activating the explosion.
sometimes you forget how fricking dangerous the chemicals are that one random guy shows off in his basement in a way that is just stunning and frightening at the same time
A very nice experiment! The prince Rupert drop is an example of glass strengthening. The water quench puts the surface into strong compression. The cool surface is hardened while the hot center continues to contract. Glass is much stronger in compression than tension so you can hit it with a hammer. But glass is weak in tension so inducing fractures in the tail propagates through the drop causing it to explode. The tail is also under compression so breaking it off acts like a fuze (detonator). The compressive outer layer is very thin and HF eats glass very fast. By removing the compressed outer layer in the tail relieves the stress so no shock wave can propagate to the bulb. Similarly immersing the bulb or whole drop dissolves the compressive layer making the drop a dud. Exactly as theory predicts! A similar result can be obtained by immersion a sodium containing glass in molten potassium nitrate at 350C. It's called chemical strengthening or "atomic stuffing" where the larger potassium ion diffuses into the glass resulting in surface compression. Examples are Apple's gorilla glass, tempered cooking ware and glass computer memory disks. It was wonderful to see such an elegant experiment. Kudos!
So, the rapid cooling in water sets up internal stresses. Namely, tensile stress from the inner surface. Dissolving these tensile stress layers therefore removes the tensile forces. I postulate that the stress layer is very thin so when you reversed the experiment and dissolved the fat end of the drop most, but not all of the stress was removed, resulting in larger pieces. Also, the fat end of the drop will have a thicker layer under tension due to thermal retention and slower cooling. The thin tails cool much quicker and have a much thinner ‘skin’ which is dissolved very quickly.
@@Moritz___ except the forces are tensile as the outer skin solidifies and the inner core shrinks away from it setting up the tension. I’ve edited my comment after more reflection.
Very cool video I have my ideas why you received these results but I am not 100% sure. If you watch how these drops cool the glass is stressed in a pattern/direction along the surface. When the HF removes these stressed bits there is no path way for the snapping of the tail to follow to cause the explosion. If the stressed glass is all gone you cannot have the chain reaction breakage.
Great video! I never knew of HF having that kind of pink-orange color before. Does that come from dyes/impurities or is it actually intrinsic to the acid? Fluorine chemistry is understandably hard to come by on YT, but ChemicalForce never disappoints!
I love it when experiments go against my expectations fully and I'm completely wrong. It's such a good opportunity to learn and ask more questions, do more experiments!
And this is why you don't trust intuition. Factoring in Cody's video and those by Destin as well, seems thickness is a critical factor. Perhaps it's not the "drop" part that's key, but the thin tail, as it truly (or at least more readily) hardens and leads to the cascading explosion if damaged. When it's removed evenly by the acid, the remaining drop isn't under all that much stress. Granted, I'd also have to question the material the drop is cooled in too. In water, the small tail wouldn't have enough energy for the leidenfrost effect to cause issues, but the larger section likely may.
That's a beautiful display of science right there, just when it comes to the strength of the largest mass of the drop but how it completely shatters when cutting even near the end of its tail. Great video my friend.
copper 1 oxide and any acid that forms a soluble salt will cause disproportion of the Copper 1+ to 2+ and 0. acids like HCl, HBr and HI form insoluble copper halides that can be dissolved in the form of complexes, but for example H2SO4 causes the disproportion too. This is because Cu1+ isn't stable as aquo complex.
There are few comments here about "stress(ed) layer" over a piece of tempered glass, but this is slightly more complicated than just "outer layer under compression/ tension". When you rapidly cool a very hot glass piece, the outer layer solidifies (hardens) first, and since it contracts quite a lot while doing it (regular glass has very high thermal expansion coefficient, couple of times of that of steel, if memory serves me) so it tries to compress the incompressible (obviously) inner part ("core") of this glass piece, which is still semi-liquid/ malleable at this point (glass does not have a definite melting point - technically speaking it is a "solid liquid"). So now the outer layer ("shell") is under tension (trying to compress the core), but eventually the "core" cools down too (slowly, as glass is poor conductor of heat) AND THE CORE CONTRACTS TOO. However, the "shell" is already solid and can't contract any longer, so the situation flips - now it is the core that's "pulling inward" the shell, and the shell is trying to pull apart the core. Which, in "right" situation, may lead to self-destruction of tempered glass pane, but I'm getting ahead of myself... Somehow these forces are in balance and that tension force of the "shell" is not above glass breaking point - we're talking microns perhaps of volume change in case of 4 to 6 mm (0.16 - 0.24 in) thick glass pane - but the forces are there anyway. Or, you can think of a bicycle wheel, where all the spokes are trying to pull the rim in ward and hub flanges apart (which is reversed situation), but they effectively cancel each other, putting everything (except themselves) under compression. (With the exception of radial, aka "sun ray pattern" lacing, which makes a weak wheel and is rarely used, but I digress here, and for anyone wondering I'm a chemist sorta involved in glazing industry and amateur bicycle mechanic as well, "so now you know" and NOW let us get back to the main topic, shall we? ;-) So, these forces are balancing/ cancelling themselves - that is, until a part of a tempered glass piece breaks off (or one spoke snaps) - in which case the resulting local imbalance spreads out throughout the glass piece and produces this shattering effect. QED, case closed... no, wait! "Spontaneous breakage of tempered glass panes caused by inclusions of nickel sulphide" (or something along this line) was the title of some article in rather obscure "trade periodic" ("The World of Glass") that I read years ago (well over a decade), and it addressed the problem "as stated in its title" - and the culprit, as it turned out, were "also stated" tiny inclusions of NiS. Nickel salts are not part of "regular glass" (sodium-calcium glass) composition (of which glass panes for windows and cars are made) but some parts "in the preparation section" of glass production line are made of stainless steel (which contains nickel), and sometimes a tiny bit of it breaks off or gets scrapped off, and then no sulphides are added into the mix either, but some sulphates are (again, in small amounts, as some additive/ enhancing agent, can't remember of what nature and purpose), so if the conditions are "right" some NiS particles may be created and included in a glass pane. And NiS in its crystalline form is (AFAIR) transparent, so they go undetected - and if a piece of glass with such inclusion is not tempered, nothing happens - but when it is, a tiny time bomb is created within the glass. NiS apparently has two crystal forms - one stable at high temperature (let's call it NiS-α) and the other one is stable at "normal" temperature - let's call it NiS-β. When a piece of glass undergoes tempering the inclusion is preserved as NiS-α - but then it undergoes slow transition into NiS-β - which has lower density, thus HIGHER VOLUME for the same mass. Thus that transitioning NiS crystal starts to grow, and push out surrounding glass - AND if it happen to sit in the "core", this growing crystal disrupts the existing balance - and if everything is just right ("wrong", rather...) this piece of tempered glass shatters into tiny pieces all by itself ("look, Ma - no hands!") - just like any tempered glass piece does. ...but I digress here, and probably I should just include, instead of this long-winded and kinda irrelevant story, a link to the article I just googled out, just now, _"Fully tempered glass and spontaneous fracture"_ in The Construction Specifier magazine (not the one I mentioned before, but on the same topic) - or you can just google _"butterfly pattern in tempered glass"_ phrase. So, anyway, "back to our muttons" - when one dissolves slowly *and uniformly* the part where stress concentration is the highest (the tail, I suppose...?) one of these two forces is removed from the balance - gradually and uniformly - which, apparently, does not cause the other part to explode, since now the inner part is left to release its stress by contracting to where it should be long ago, and there's nothing left that could pull it apart now. Cheers.
- The outside hardens first and then the inside hardens, which places the center in TENSION and the edge in COMPRESSION. Compression keeps micro-cracks from opening under flexing or blunt impact, which prevents breaking. - Etching off the compressed skin "should" just relieve the tension on the core, converting it into "ordinary" glass. Instead, the drop shatters, though not as violently. Dissolving an arbitrary amount of the "skin" causes a material limit to be exceeded somewhere on the drop. Uneven "skin" thickness and/or uneven rate of dissolution must be a factor. Maybe part of the core gets exposed and separates (because it is still in tension). Maybe thinning one part of the skin allows the core to shrink and locally overcompress other parts of the skin. - It is hard to predict that etching off the tail does NOT explode the drop, and that breaking the remaining tail does NOT explode the drop. It's about knowing where the stresses are. Maybe the thin tail, after a little etching, is closer to being "ordinary glass". - I think these drops are not typical because the water tank was shallow. Less of the tail was seriously quenched. (This might not matter, or it might.)
@@quaztron Thank you for your input on the matter - I think your explanation makes more sense than what I wrote, and I have to admit the last time I read about this (i.e. "changing/ swapping of compression and tension forces" during glass tempering process) was well over a decade ago - in the same article about spontaneous breakage" I mentioned earlier. That "compression vs tension" was only an introduction to the issue, to which I paid less attention (and it wasn't explained very clearly anyway), so I might got it wrong or it just got mixed up in my head over the years. And at any rate I was more interested in the second part - since (digression alert! ;-) just around (prior to) this time there was some discussion, or an argument on Subaru Forum (a web forum, of which I was back then an active member), exactly about this problem - namely, someone bought new Legacy (if memory serves me) from local dealership, and these beauties aren't exactly cheap - then few months latter the rear glass in this car shattered in broad daylight all by itself, while the car was parked on a secured parking right next to the office this guy worked in, the guard/ security guy was there, overlooking the parking and there was no-one else around - yet the dealership refused to replace the glass under the warranty, and since "original Subaru parts" would cost you an arm and a leg here (and it HAD to be replaced by the original one, unless he'd be willing to wave the entire remaining warranty period, and YES, the only channel to obtain this part was through the same dealership), so this guy was quite pissed and brought up the issue on aforementioned forum, and this is how I learned about it, and few months latter that article came up (it was relatively new phenomenon back then, or at lest it was only then when someone started to look closely at this issue), but then I digress here again, just as I warned you before ;-) Cheers!
I think the gradual uniform erosion of Prince Rupert's Drop by the Hydrofluoric acid also causes the gradual relief of stress in the structure of the drop. I believe the reason the drop instantly explodes when the tail is cut is due to stress between the inner and outer parts of the drop. When the acid erodes the surface it relieves the stress to a degree, leaving the stressed inner core of the drop which is not as catastrophically affected as when the surface and interior are intact.
I wonder if the energy of the relaxation of the compressive strain of the drop during HF immersion is measurable… the energy has to go somewhere, after all…. Perhaps with a very accurate temperature probe could show this. Of course, you would need a baseline with non stressed glass to compare with, and equivalent acid volume or mass, as the reaction with glass will itself produce some heat (or so I assume that it is exothermic) but that’s not too difficult to establish :)
I read somewhere that upto 10% distance from surface glass is under high compressive stress and you must reach beyond this to trigger the explosion so even the acid failed as it never reached that stress boundary
slow reaction eases internal stress gradually, explosions are a rapid release of force. The breaking of the tail triggers it, unless the stress is already relieved.
One question remains: The last of the blue drops, the one with etched tail but intact body, that didn't explode upon cutting the tail...did remain as hard as usual?? I mean: - Sure, the etched body explodes - Sure, the whole drop gets stress relieved and behaves like regular glass But what about an unetched body? Would break if hit between hammer and anvil??
who'd have guessed, dissolving the surface of an object that has high stress levels in its surface due to surface tension and thermal shock, renders it less unstable!
Prince Rupert Drops have high compressive stress on the outer skin with high tensile stress in the core. If you etch the outer surface uniformly, it is possible to reduce the internal tensile stress without causing failure. But the etching must mirror the shock cooling which formed the drop. Likewise, tempered safety glass cannot be cut, drilled or otherwise modified. Cody's Lab tried etching holes in it using NaOH, resulting in failure. Guess he now needs to try uniform etching..
This is fun, because somehow this is one of the things I always wondered about Prince Rupert's Drops. What if their surface doesn't get mechanically, but chemically attacked? Awesome, can't wait to see the results!!!
makes me wonder if much of the stress is held in the outer layer of glass, and once it's etched off, the drop becomes more stable. I assume, when the tail is out of the acid, it shatters because the thinnest part near the surface becomes narrower than the portion out of the acid. It would then break from the tail outside the acid, down towards the head. That's my theory at least.
super dangerous experiment. but i wonder what would happen if you dissolved away the tail entirely. would the bead retain its almost indestructible temper?
Would this apply to just Prince Rupert's drops, which are cooled rapidly and have stress particularly concentrated near the surface, or will it work with any untempered glass? Like, if you make a blob of homemade glass, it might stay solid while cooling in air, but will usually explode within a day or two.
I have a feeling that microscopic etching relieved the stress after the tail was removed but when immersed first the head explodes due to the more rapid etching over a larger area. Would be curious to see tail first v head first etching compared using a polariscope?
Hydrofluoric acid one of the scariest acids, binds to calcium in your bones and can lead to a heart attack, also HF doesn't burn like other acids, you can have contact of it on your skin and not even notice until its too late because it destroys the nerves.
The inner tensions make the drop resistant to hammering. So I imagine the drops competently immersed in acid are no longer resistant to being hammered too.
Great video! Any idea why it still explodes with the tail out? I assumed removing the surface would remove the surface strain and thus prevent the submersed part from exploding after a while (surface layer completely removed, thus no strain left), but this is obviously not the case.
I would love for you to do this again, only use a polarizer to look at the drop change as the acid does its thing. You can see the massive amount of stress through a polarizer, so would be interesting to see if that dissipates visibly.
Perhaps you PR drops where not as "explosive" as they should be because the head of the drop was not glowing hot when quenched in water. Still interesting results.
glass objects can be viewed through polarized light filters to observe the stress pattern. i wonder if the stress patterns change after acid etching??? -hydroxides can also etch glass.
I'm also less stressed following prolonged immersion in HF. I reckon that HF can insinuate itself into the glass and react with the strained silicate bonds. Is the head still tough to break? If so we need an explanation for both the acid and how a Rupert's drop works.
The drop is that special, because it was cooled down very fast (on the surface-layer of the glass, whilest the inner structure is cooled much slower).... that lead to a special glass crystal-structure (and gradial differences between the srface-layer and the inner glass structure) and that lead to the totaly splittering of glass if the surface-tension is broke up by cutting through.. The acid then seems to stabilize the surface-structure or it leads to a relaxing of surface-tension... however it can do it. But those drops are formed (and cooled down) in special condition, the inner structure and the surface-structure of the glass is under diferent tension, and if you cut a weakness in the surface-structure, the glass will instantly relaxe all the (difrent) tensions in the different strucutres and... that leads to the complete splittering of the hole glass-form. Because thesurface of the glass is cooled way faster, as the inner sturctures, i think, that the surface-sturcture is under tension, because it itself got shrinked whilest faster cooling, whilest the inner structure is cooled down slower and not shrinked as much. The surface-structure can only hold its form and coherence, because its connected to the inner structre and stabilzed by that in a high-tension-state, that is only able to hold its form, as long the hole structure is untouched/undamaged (espacialy the surface-layer). The acid may seems to lead to a after hardening-change in that tension in the surface-structre, so that its not anymore in such a strong tension state. How acid can do that, i do not know. Espacialy, because glass should be resistant to acidic and other substances. But as it seems, its not completely resistant. I mean, in chemical laboratory,. the glas-jars are produced in special way to not get damaged by chemical agressive substances. Or even because glass is a priori the most robust material for handling in chemical laboratory. But that drops may aren´t that robust...espacialy not, because its surface-structure is not as perfect, as usual special glass produced for chemical laboratory use... and so, the acid can manipulate the glass structure, so that it changes its reaction to physical influence (as it is done with the metal-knipper).
You should observe it in crosspolarized light. It's only the surface where the stress is lost. I'm sure stress remains inside, but it's much more difficult to "unlock".
You should do your next video documenting pure anhydrous hydrogen fluoride, as there is so little footage I can find about it and you've done a video of a scarier derivative of it
Knew a kid who picked up 2 of these while we were making them in science class and put them up to his eyes to pretend they were tears when they suddenly exploded. His eyeballs got infected and went to his brain and he died RIP my homie Bart Simpson
Is it possible to use polarized light and/or bi-refringence to visualize the stress inside the Prince Rupert's Drop? If yes, then I would like to see the stress dissipate while being etched.
Would be interesting to see the drop under polarised light initially to see the internal stresses then treat with HF and check again under polarised light to see the effect on the stress lines......
Hydrofluoric acid and explosion are not words I want to see in the same sentence...
Then you are in the wrong channel!
Madness as usual on this channel
Typed blindfolded. ;)
@@user255 It's okay. so long as it's all going on waaaaay over there!
Don't be a princess, be a prince
I wonder if the stress patterns look different under a polariscope before and after etching away the surface
My first thoughts too
same for me ^^
Yes! The stress visible in a polariscope is caused by compression in the outer layer of glass. Dissolving the outer layer gently relieves the stress and so it will reduce the color patterns in the remaining drop. It also makes the drop a dud. The etched surface is frosty but the change is dramatic.
I bet it does look different! Great question
@@stevestarckeI was going to say the same thing, the stress is completely contained in the outermost layer of the glass, etching it away removes the stress and makes the prd a normal glass droplet. Well that's what I think anyway.
1. Test the hardness after dissolving tail.
2. Try to keep the acid in a cold bath to avoid annealing the glass.
Annealing was my thought... but I have no idea how hot this stuff gets.
No annealing will occur at these temperatures. The highly stressed outer layer is removed by the acid.
1. It isn't any harder. It is tougher. There's a small but important difference.
2. Nothing happening there got *anywhere* near the annealing point for glass 🤣
[3] This is why you can't "experiment" on CZcams. It doesn't teach experience.
I wonder if the head of the drops is still as stable, or if it just shatters now if hit by a hammer
Yea this is the only thing missing in this experiment, time for part 2
First thing I thought as well.
So I imagine these are like tempered glass. The second you got about 40% of the way through the glass it just explodes. It releases all the internal pressure and just gives way. Think I'll skip this one though
I suspect it would shatter like ordinary glass, because as @stevestarcke pointed out in another comment thread, the outer layer of a Prince Rupert's Drop is under compression. Based on some previous knowledge and what I can deduce from Steve's comment, this compressive force constantly pulls on the inside of the drop, leading to tensive force in response. This tug-of-war between compression and tension is what gives rise to the drop's properties. However, if that outer layer is carefully and slowly removed with HF, there is no longer a compressive outside force that leads to an inner tensive force, causing the Prince Rupert's Drop to lose its characteristic properties.
However, this is only a hypothesis, and my understanding of the subject may be incomplete and/or wrong, so please take my comment with a grain of salt.
The stresses in a Prince Rupert's drop are concentrated within the surface layer, since that's where the sudden thermal shock occurs during quenching. By etching off the surface layer, the stresses were gradually relieved. That potential energy has to go somewhere however. Try etching them in total darkness. Perhaps the energy release will manifest itself as heat, light or sound.
Or just manifest as a quicker dissolve, try ordinary glass with the same mass and see which dissolves first :)
@@pon1 not just mass, but try to get the surface area as close as possible as well, for most comparable dissolution
@@aweshad9 True.
If a compressed metal spring is dissolved in acid, while being held in compression, what happens to the potential energy that was stored in the compressed spring?
@@juliavixen176 I think the energy is released into the process of dissolving it, so it dissolves faster.
What if we drop molten glass in cold hydrofluoric acid? Would be interesting to see the stress pattern of the resulting “Prince Rupert’s drop” as the surface is being simultaneously rapidly cooled and etched!
Hot glass in hydrofluoric acid sounds like my personal nightmare 😂
Might be good to do it in much more dilute HF to ensure the surface is not completely dissolved.
This was a really surprising result, before I watched this I was sure it would explode! The polariscope idea would def be interesting
Nice and interesting video. I think that the effect of the immersion of the tail of the Price Rupert's drops in HF inhibiting their explosion is not due to a loss of internal stress (at room temperature atoms cannot move very easily), but to surface free energy effects. What I mean is that the immersion in HF increases the surface area (and consequently the surface free energy) of the drops. The increase of surface free energy counteracts the tendency to explode of the Prince Rupert's Drops which would futher increase the surface area of the system. The surface free energy is always a positive term and hence it has a destabilising effect for condensed phase systems. Conversely, when you immerse the head, you weaken the structure of the head itself thus enabling the stress to be relieved and thus activating the explosion.
sometimes you forget how fricking dangerous the chemicals are that one random guy shows off in his basement in a way that is just stunning and frightening at the same time
I'd be curious to see whether the head retains its incredible hardness and impact resistance after the tail has been dissolved.
I was really hoping it would explode. But my curiosity was satisfied.
I want a 2 headed Prince Rupert Drop.
They’d look like Prince Ruperts testicles 😂
A very nice experiment! The prince Rupert drop is an example of glass strengthening. The water quench puts the surface into strong compression. The cool surface is hardened while the hot center continues to contract. Glass is much stronger in compression than tension so you can hit it with a hammer. But glass is weak in tension so inducing fractures in the tail propagates through the drop causing it to explode. The tail is also under compression so breaking it off acts like a fuze (detonator).
The compressive outer layer is very thin and HF eats glass very fast. By removing the compressed outer layer in the tail relieves the stress so no shock wave can propagate to the bulb. Similarly immersing the bulb or whole drop dissolves the compressive layer making the drop a dud.
Exactly as theory predicts! A similar result can be obtained by immersion a sodium containing glass in molten potassium nitrate at 350C. It's called chemical strengthening or "atomic stuffing" where the larger potassium ion diffuses into the glass resulting in surface compression. Examples are Apple's gorilla glass, tempered cooking ware and glass computer memory disks.
It was wonderful to see such an elegant experiment. Kudos!
Thanks chatgpt.
It's very surprising it exploded in one orientation but not the other. Very interesting results!
So, the rapid cooling in water sets up internal stresses. Namely, tensile stress from the inner surface. Dissolving these tensile stress layers therefore removes the tensile forces. I postulate that the stress layer is very thin so when you reversed the experiment and dissolved the fat end of the drop most, but not all of the stress was removed, resulting in larger pieces. Also, the fat end of the drop will have a thicker layer under tension due to thermal retention and slower cooling. The thin tails cool much quicker and have a much thinner ‘skin’ which is dissolved very quickly.
very possible
@@Moritz___ except the forces are tensile as the outer skin solidifies and the inner core shrinks away from it setting up the tension. I’ve edited my comment after more reflection.
This is so-called chemical annealing. Stressed portions of a solid will usually etch a bit faster than the rest of the bulk.
Very cool video I have my ideas why you received these results but I am not 100% sure. If you watch how these drops cool the glass is stressed in a pattern/direction along the surface. When the HF removes these stressed bits there is no path way for the snapping of the tail to follow to cause the explosion. If the stressed glass is all gone you cannot have the chain reaction breakage.
I said it in my comment on the community page... it needs the shock wave to travel through the stressed zone.
A beautiful "Everyone was correct" situation!
Great video! I never knew of HF having that kind of pink-orange color before. Does that come from dyes/impurities or is it actually intrinsic to the acid? Fluorine chemistry is understandably hard to come by on YT, but ChemicalForce never disappoints!
Nice, so now we know is surface stress
I love it when experiments go against my expectations fully and I'm completely wrong. It's such a good opportunity to learn and ask more questions, do more experiments!
And this is why you don't trust intuition. Factoring in Cody's video and those by Destin as well, seems thickness is a critical factor. Perhaps it's not the "drop" part that's key, but the thin tail, as it truly (or at least more readily) hardens and leads to the cascading explosion if damaged. When it's removed evenly by the acid, the remaining drop isn't under all that much stress. Granted, I'd also have to question the material the drop is cooled in too. In water, the small tail wouldn't have enough energy for the leidenfrost effect to cause issues, but the larger section likely may.
Please film a clear drop in acid through a polarizing filter as it dissolves!!!
04:56 the answer
That's a beautiful display of science right there, just when it comes to the strength of the largest mass of the drop but how it completely shatters when cutting even near the end of its tail. Great video my friend.
copper 1 oxide and any acid that forms a soluble salt will cause disproportion of the Copper 1+ to 2+ and 0.
acids like HCl, HBr and HI form insoluble copper halides that can be dissolved in the form of complexes, but for example H2SO4 causes the disproportion too.
This is because Cu1+ isn't stable as aquo complex.
Shows you how thin the tempering layer is
There are few comments here about "stress(ed) layer" over a piece of tempered glass, but this is slightly more complicated than just "outer layer under compression/ tension".
When you rapidly cool a very hot glass piece, the outer layer solidifies (hardens) first, and since it contracts quite a lot while doing it (regular glass has very high thermal expansion coefficient, couple of times of that of steel, if memory serves me) so it tries to compress the incompressible (obviously) inner part ("core") of this glass piece, which is still semi-liquid/ malleable at this point (glass does not have a definite melting point - technically speaking it is a "solid liquid").
So now the outer layer ("shell") is under tension (trying to compress the core), but eventually the "core" cools down too (slowly, as glass is poor conductor of heat) AND THE CORE CONTRACTS TOO. However, the "shell" is already solid and can't contract any longer, so the situation flips - now it is the core that's "pulling inward" the shell, and the shell is trying to pull apart the core. Which, in "right" situation, may lead to self-destruction of tempered glass pane, but I'm getting ahead of myself...
Somehow these forces are in balance and that tension force of the "shell" is not above glass breaking point - we're talking microns perhaps of volume change in case of 4 to 6 mm (0.16 - 0.24 in) thick glass pane - but the forces are there anyway.
Or, you can think of a bicycle wheel, where all the spokes are trying to pull the rim in ward and hub flanges apart (which is reversed situation), but they effectively cancel each other, putting everything (except themselves) under compression. (With the exception of radial, aka "sun ray pattern" lacing, which makes a weak wheel and is rarely used, but I digress here, and for anyone wondering I'm a chemist sorta involved in glazing industry and amateur bicycle mechanic as well, "so now you know" and NOW let us get back to the main topic, shall we? ;-)
So, these forces are balancing/ cancelling themselves - that is, until a part of a tempered glass piece breaks off (or one spoke snaps) - in which case the resulting local imbalance spreads out throughout the glass piece and produces this shattering effect. QED, case closed... no, wait!
"Spontaneous breakage of tempered glass panes caused by inclusions of nickel sulphide" (or something along this line) was the title of some article in rather obscure "trade periodic" ("The World of Glass") that I read years ago (well over a decade), and it addressed the problem "as stated in its title" - and the culprit, as it turned out, were "also stated" tiny inclusions of NiS.
Nickel salts are not part of "regular glass" (sodium-calcium glass) composition (of which glass panes for windows and cars are made) but some parts "in the preparation section" of glass production line are made of stainless steel (which contains nickel), and sometimes a tiny bit of it breaks off or gets scrapped off, and then no sulphides are added into the mix either, but some sulphates are (again, in small amounts, as some additive/ enhancing agent, can't remember of what nature and purpose), so if the conditions are "right" some NiS particles may be created and included in a glass pane.
And NiS in its crystalline form is (AFAIR) transparent, so they go undetected - and if a piece of glass with such inclusion is not tempered, nothing happens - but when it is, a tiny time bomb is created within the glass.
NiS apparently has two crystal forms - one stable at high temperature (let's call it NiS-α) and the other one is stable at "normal" temperature - let's call it NiS-β.
When a piece of glass undergoes tempering the inclusion is preserved as NiS-α - but then it undergoes slow transition into NiS-β - which has lower density, thus HIGHER VOLUME for the same mass. Thus that transitioning NiS crystal starts to grow, and push out surrounding glass - AND if it happen to sit in the "core", this growing crystal disrupts the existing balance - and if everything is just right ("wrong", rather...) this piece of tempered glass shatters into tiny pieces all by itself ("look, Ma - no hands!") - just like any tempered glass piece does.
...but I digress here, and probably I should just include, instead of this long-winded and kinda irrelevant story, a link to the article I just googled out, just now, _"Fully tempered glass and spontaneous fracture"_ in The Construction Specifier magazine (not the one I mentioned before, but on the same topic) - or you can just google _"butterfly pattern in tempered glass"_ phrase.
So, anyway, "back to our muttons" - when one dissolves slowly *and uniformly* the part where stress concentration is the highest (the tail, I suppose...?) one of these two forces is removed from the balance - gradually and uniformly - which, apparently, does not cause the other part to explode, since now the inner part is left to release its stress by contracting to where it should be long ago, and there's nothing left that could pull it apart now.
Cheers.
- The outside hardens first and then the inside hardens, which places the center in TENSION and the edge in COMPRESSION. Compression keeps micro-cracks from opening under flexing or blunt impact, which prevents breaking.
- Etching off the compressed skin "should" just relieve the tension on the core, converting it into "ordinary" glass. Instead, the drop shatters, though not as violently. Dissolving an arbitrary amount of the "skin" causes a material limit to be exceeded somewhere on the drop. Uneven "skin" thickness and/or uneven rate of dissolution must be a factor. Maybe part of the core gets exposed and separates (because it is still in tension). Maybe thinning one part of the skin allows the core to shrink and locally overcompress other parts of the skin.
- It is hard to predict that etching off the tail does NOT explode the drop, and that breaking the remaining tail does NOT explode the drop. It's about knowing where the stresses are. Maybe the thin tail, after a little etching, is closer to being "ordinary glass".
- I think these drops are not typical because the water tank was shallow. Less of the tail was seriously quenched. (This might not matter, or it might.)
@@quaztron Thank you for your input on the matter - I think your explanation makes more sense than what I wrote, and I have to admit the last time I read about this (i.e. "changing/ swapping of compression and tension forces" during glass tempering process) was well over a decade ago - in the same article about spontaneous breakage" I mentioned earlier.
That "compression vs tension" was only an introduction to the issue, to which I paid less attention (and it wasn't explained very clearly anyway), so I might got it wrong or it just got mixed up in my head over the years.
And at any rate I was more interested in the second part - since (digression alert! ;-) just around (prior to) this time there was some discussion, or an argument on Subaru Forum (a web forum, of which I was back then an active member), exactly about this problem - namely, someone bought new Legacy (if memory serves me) from local dealership, and these beauties aren't exactly cheap - then few months latter the rear glass in this car shattered in broad daylight all by itself, while the car was parked on a secured parking right next to the office this guy worked in, the guard/ security guy was there, overlooking the parking and there was no-one else around - yet the dealership refused to replace the glass under the warranty, and since "original Subaru parts" would cost you an arm and a leg here (and it HAD to be replaced by the original one, unless he'd be willing to wave the entire remaining warranty period, and YES, the only channel to obtain this part was through the same dealership), so this guy was quite pissed and brought up the issue on aforementioned forum, and this is how I learned about it, and few months latter that article came up (it was relatively new phenomenon back then, or at lest it was only then when someone started to look closely at this issue), but then I digress here again, just as I warned you before ;-)
Cheers!
I think the gradual uniform erosion of Prince Rupert's Drop by the Hydrofluoric acid also causes the gradual relief of stress in the structure of the drop. I believe the reason the drop instantly explodes when the tail is cut is due to stress between the inner and outer parts of the drop. When the acid erodes the surface it relieves the stress to a degree, leaving the stressed inner core of the drop which is not as catastrophically affected as when the surface and interior are intact.
I wonder if the energy of the relaxation of the compressive strain of the drop during HF immersion is measurable… the energy has to go somewhere, after all….
Perhaps with a very accurate temperature probe could show this. Of course, you would need a baseline with non stressed glass to compare with, and equivalent acid volume or mass, as the reaction with glass will itself produce some heat (or so I assume that it is exothermic) but that’s not too difficult to establish :)
I appreciate that you used colored glass, very nice.
I read somewhere that upto 10% distance from surface glass is under high compressive stress and you must reach beyond this to trigger the explosion so even the acid failed as it never reached that stress boundary
slow reaction eases internal stress gradually, explosions are a rapid release of force. The breaking of the tail triggers it, unless the stress is already relieved.
Uuuh 70% HF, he better wear his gasmask 😊Edit: And his gloves, too
One question remains:
The last of the blue drops, the one with etched tail but intact body, that didn't explode upon cutting the tail...did remain as hard as usual??
I mean:
- Sure, the etched body explodes
- Sure, the whole drop gets stress relieved and behaves like regular glass
But what about an unetched body? Would break if hit between hammer and anvil??
Hmm... the HF Acid must have relieved the internal stresses... brb gonna go open my own spa
who'd have guessed, dissolving the surface of an object that has high stress levels in its surface due to surface tension and thermal shock, renders it less unstable!
What would really be interesting is watching the reaction going on through the view of a polariscope!
Prince Rupert Drops have high compressive stress on the outer skin with high tensile stress in the core. If you etch the outer surface uniformly, it is possible to reduce the internal tensile stress without causing failure. But the etching must mirror the shock cooling which formed the drop.
Likewise, tempered safety glass cannot be cut, drilled or otherwise modified. Cody's Lab tried etching holes in it using NaOH, resulting in failure. Guess he now needs to try uniform etching..
I'd love so see what these experiments look like when filmed through a polarization filter
This is fun, because somehow this is one of the things I always wondered about Prince Rupert's Drops. What if their surface doesn't get mechanically, but chemically attacked? Awesome, can't wait to see the results!!!
In chemistry poker, if my opponent bets “HF” and “Explosion”, I don’t call, I fold (and run for my life).
Willingly going near HF and hot glass, what a legend.
🤑 Thanks a lot! 🤑 Considering the number of views of my latest videos this is a significant contribution! :D
makes me wonder if much of the stress is held in the outer layer of glass, and once it's etched off, the drop becomes more stable. I assume, when the tail is out of the acid, it shatters because the thinnest part near the surface becomes narrower than the portion out of the acid. It would then break from the tail outside the acid, down towards the head. That's my theory at least.
super dangerous experiment. but i wonder what would happen if you dissolved away the tail entirely. would the bead retain its almost indestructible temper?
Very surprising result. Terrific experiment!
Would this apply to just Prince Rupert's drops, which are cooled rapidly and have stress particularly concentrated near the surface, or will it work with any untempered glass? Like, if you make a blob of homemade glass, it might stay solid while cooling in air, but will usually explode within a day or two.
Would be curious if it still maintained its extreme hardness. Hammer test!
I have a feeling that microscopic etching relieved the stress after the tail was removed but when immersed first the head explodes due to the more rapid etching over a larger area. Would be curious to see tail first v head first etching compared using a polariscope?
That was a BIG surprise!
Hydrofluoric acid one of the scariest acids, binds to calcium in your bones and can lead to a heart attack, also HF doesn't burn like other acids, you can have contact of it on your skin and not even notice until its too late because it destroys the nerves.
I would have said no at one point in my life, but honestly I've seen people melt the Tails off leaving just the nearly indestructible head.
The inner tensions make the drop resistant to hammering. So I imagine the drops competently immersed in acid are no longer resistant to being hammered too.
Now you've got to soak them in a very strong base and check the effects
This needs to be filmed through a polariscope.
Glad to be watching this through a sceeen! Was the soundtrack of this video purposefully sped up and slowed down? (I know Nurdrage does this)
Great video!
Any idea why it still explodes with the tail out?
I assumed removing the surface would remove the surface strain and thus prevent the submersed part from exploding after a while (surface layer completely removed, thus no strain left), but this is obviously not the case.
I was thinking the same. Somehow the breaking continues to the rest of the glass... even to completely normal glass..?
I would love for you to do this again, only use a polarizer to look at the drop change as the acid does its thing. You can see the massive amount of stress through a polarizer, so would be interesting to see if that dissipates visibly.
Those were very interesting experiments! I think you are the 1st to dump Prince Rupert drops into HF on YT (surely the 1st I've ever seen).
Jesse, we need to dissolve the Rupert's Drop in Hydrofluoric Acid..
Perhaps you PR drops where not as "explosive" as they should be because the head of the drop was not glowing hot when quenched in water. Still interesting results.
try dilute HF, like just a few percent over a few hours
Perhaps the surface is fluorinated which keeps it together better?
glass objects can be viewed through polarized light filters to observe the stress pattern. i wonder if the stress patterns change after acid etching??? -hydroxides can also etch glass.
The inherent stress in the drop is released gently when the tail is dissolved.
I'm also less stressed following prolonged immersion in HF.
I reckon that HF can insinuate itself into the glass and react with the strained silicate bonds. Is the head still tough to break? If so we need an explanation for both the acid and how a Rupert's drop works.
this experiment really is interesting.
so what would happen if you drop some molten glass into HF acid?
That "explode in HF acid" turned out to be clickbait, and honestly I'm not even sure if I hate it or prefer it this way.
Cool experiment.
We need more testing please this is to interesting
The drop is that special, because it was cooled down very fast (on the surface-layer of the glass, whilest the inner structure is cooled much slower).... that lead to a special glass crystal-structure (and gradial differences between the srface-layer and the inner glass structure) and that lead to the totaly splittering of glass if the surface-tension is broke up by cutting through.. The acid then seems to stabilize the surface-structure or it leads to a relaxing of surface-tension... however it can do it. But those drops are formed (and cooled down) in special condition, the inner structure and the surface-structure of the glass is under diferent tension, and if you cut a weakness in the surface-structure, the glass will instantly relaxe all the (difrent) tensions in the different strucutres and... that leads to the complete splittering of the hole glass-form. Because thesurface of the glass is cooled way faster, as the inner sturctures, i think, that the surface-sturcture is under tension, because it itself got shrinked whilest faster cooling, whilest the inner structure is cooled down slower and not shrinked as much. The surface-structure can only hold its form and coherence, because its connected to the inner structre and stabilzed by that in a high-tension-state, that is only able to hold its form, as long the hole structure is untouched/undamaged (espacialy the surface-layer). The acid may seems to lead to a after hardening-change in that tension in the surface-structre, so that its not anymore in such a strong tension state.
How acid can do that, i do not know. Espacialy, because glass should be resistant to acidic and other substances. But as it seems, its not completely resistant. I mean, in chemical laboratory,. the glas-jars are produced in special way to not get damaged by chemical agressive substances. Or even because glass is a priori the most robust material for handling in chemical laboratory. But that drops may aren´t that robust...espacialy not, because its surface-structure is not as perfect, as usual special glass produced for chemical laboratory use... and so, the acid can manipulate the glass structure, so that it changes its reaction to physical influence (as it is done with the metal-knipper).
Nice experiment! Once you have deactivated the tail, is the drop still as hard?
Fantastic. Very interesting and surprising result. Tempering the drop like that.
Do the heads still retain their strength? If so it could an interesting process for making hardened glass.
It looks like a great demonstration of hoe fluoride strengthens teeth. 😉
You should observe it in crosspolarized light. It's only the surface where the stress is lost. I'm sure stress remains inside, but it's much more difficult to "unlock".
I've been waiting for this video
On the fully submerged drops that lose the tension, are they still as durable? I would love to see a hammer test on a drop that has been fully etched!
Jee, I love that song.. Marten Moses - The Mill :)
You just annealed the glass) Instead of HF (which heated during tge process), you could have used a regular furnace for the same effect
The long tail of Prince Rupert's Drop used to be very clumsy, and this chemical etching process can trim it down to desired and useful shape. 💎
You should do your next video documenting pure anhydrous hydrogen fluoride, as there is so little footage I can find about it and you've done a video of a scarier derivative of it
Great experiment, thank you!
Glad you’re safe. HF is so dangerous
Knew a kid who picked up 2 of these while we were making them in science class and put them up to his eyes to pretend they were tears when they suddenly exploded. His eyeballs got infected and went to his brain and he died RIP my homie Bart Simpson
Is it possible to use polarized light and/or bi-refringence to visualize the stress inside the Prince Rupert's Drop? If yes, then I would like to see the stress dissipate while being etched.
Does the drop that has had the pressure removed and tail dissolved retain its durability?
well that was cool! thank you mr force
I wanted to see a drop with a dissolved tail hammered!
Would be interesting to see the drop under polarised light initially to see the internal stresses then treat with HF and check again under polarised light to see the effect on the stress lines......
This seems to tell us that most of the tension in the glass is at the surface.
You should write a paper on this!
Its restructuring the crystals and relieving the stress into the acid?
I think you should start making youtube shorts to further your reach.
I have more questions now than I had before.
dude fascinating!
The joys of surface tension.
1:16 lol "high speed"... not. even. close.
How exactly does the volume of the glass change? Does it change differently in low stress glass pieces?
This is a very interesting episode!!!! You may have a valuable video here (scientifically speaking).