A big debate started in the graduate student office, which spread around our building like wildfire. The simple question was: could we take a glass soda bottle and cool it down to drinking temperature quickly using liquid nitrogen? As this is one of my first posts though, perhaps a bit of background would be beneficial.
I am a PhD student researching high temperature ceramics for jet engines. That is just a fancy way of saying I work with ceramic materials that get heated to insanely high temperatures (often hotter than lava) in jet engines. We use these specifically to protect metal parts in the engines, which would melt without these ceramics protecting them. The lab that I work in is full of experts of ceramic and metallic materials—we all work on high temperature research and we should know a thing or two about how materials fail.
So, back to the question at hand. One of our senior graduate students, Stefan (who has since graduated, earning his PhD), was complaining that he bought a bottle of soda the night before, but couldn’t drink it because “Drinking it at room temperature would be a crime.” This launched an innocent question of whether or not we could quickly cool this bottle of soda using liquid nitrogen. Sure, he could have put the bottle of soda in the refrigerator for a few hours, but we are impatient people...who also happen to have a liquid nitrogen hose in our lab. The real question here is whether or not the glass bottle would survive being submerged into liquid nitrogen. I’ll come to why this turns out to be an interesting question soon, but first we need to make some heroes and villains.
The main debate started with Stefan and myself. Stefan was very confident the bottle would break; I thought that the bottle might just survive. And now, before you go thinking I am writing this story just because I was right, know that there are few things more exciting to a scientist than being wrong! We talked over the materials science behind the problem, leveraging our some 15 years of experience combined. However, neither of us were able to sway the other (maybe because we are both just stubborn). Later in the day, we involved our other office mates into the debate; they too thought it was an interesting question but disagreed. We were no closer to an answer based on knowledge alone. There was one thing left to do: we had to do the experiment.
Stefan and I (politely) burst into the office of the engineer in charge of our lab. We said, “Deryck, we have a virtual bet that we need to settle. We want to drop a glass soda bottle into liquid nitrogen to see if it breaks or survives.” Deryck was in. We setup a time to run the experiment a few days later so we could get some soda bottles. In the mean time the word spread among the other staff scientists on campus; they too were joining the debate. I’d estimate there was now well over 100 years of combined materials expertise between all of us now debating this problem—including people who have the job of breaking things!
Everything was set. We had approval to run the experiment, we had a time, a place, and the interest.
I haven’t actually told you yet why this is an interesting question. Well, as many of us will have some intuition for, glass is fragile. We know this from the drinking glasses we have in our house; glass shatters if we drop it on the floor, leaving us to carefully vacuum the remains ever concerned a small unseen piece will sneak its way into our foot later. Well, these glass soda bottles are made from the same materials! We know that if we drop the soda bottle, it will explode and spill soda all over the place, creating a sticky unfortunate mess. But the main question here is whether or not a glass bottle survives being submerged in liquid nitrogen. This is a question of thermal shock.
If you talk to somebody that cooks, they will probably tell you to not take a glass baking pan out of the hot oven and immediately run water over it. Doing so can shatter your glass pan. This is such a big deal, it has received national attention by Consumer Reports and CBS news1. In this case, it isn’t rapid heating that does any damage (you can put your room temperature glass pan into the hot oven without concern), but rapid cooling causes the glass to shatter.
This is exactly what we are doing with our glass soda bottle—except, rather than going from hot to cool, we are going from cool to really really cold. What made this such an interesting problem to us was that it turns out the change in temperature between the hot oven and running water is very similar to that of going from room temperature to liquid nitrogen temperatures (-196°C or -321°F). If this temperature change is enough to thermally shock glass cooking pans to failure, would it also be enough for our glass soda bottles?
In fact, one of the main points brought up during the debate is that it might even be worse for the soda bottles. Critically important for thermal shock is the temperature change across the material. Our soda bottle will be filled with soda, which will keep the temperature on the inside of the bottle above freezing. Remember the goal is to cool the liquid only down to drinking temperature; we don’t want to freeze the soda! This will make sure that the temperature change across the glass bottle is always about 200°C (about 400°F); over only a few millimeters!
To put this crazy large temperature gradient into perspective, we can imagine your body having this same temperature gradient. In this case, your head would be comfortable at about 20°C (68°F). Your feet, however, would be at about 114,000°C (205,000°F)! To get that hot, you’d have to go towards the center of our sun. You too would be very unhappy under such an extreme temperature change.
We were all in agreement the glass bottle will experience a very large thermal shock. The question was whether or not this would break the bottle. Stefan was very confident it would—he even bet 10,000 virtual dollars (the only thing a graduate student can bet) the bottle would break. By intuition alone, I thought the bottle might survive.
The answer would effectively come down to the exact type of glass used to make the bottles (as this will change the properties of the material) and how well the bottle was made. If the bottle was damaged during production or just poorly made, it might have flaws in the glass that amplify stresses and make failure more likely. I was putting more faith into the bottle being well produced than anything else.
This is why this question was so fascinating to us. We agreed that the bottle would have a massive thermal shock, but would the glass be able to withstand it? Was the glass made well enough? Let's find out!
Obviously with any experiment, safety is paramount. Do not try to repeat this at home without the proper safety gear!
We had setup a styrofoam cooler with liquid nitrogen on the floor. The plan was to attach a string to the soda bottle and lower it from the ceiling of the lab so that we didn’t need to be close (in case the bottle broke). Remember that we are also dealing with a bottle under pressure and extremely cold liquid nitrogen. We agreed that the goal was to submerge the soda bottle as quickly as possible; we wanted to give the bottle the best chance possible to fail. We also didn’t want the soda to freeze inside, which certainly would have broken the bottle due to the expansion of ice. Taking a guess, we thought 30 seconds would be enough time for the soda to cool to a perfect temperature. The bottle would stay in for 30 seconds, if it survived, but no longer.
Both Stefan and I were gowned up in lab coats, face shields, full pants, closed-toe shoes, and special cold gloves. All of the spectators were standing safely back.
Stefan lowered the bottle close to the cooler. I aligned it. We let it fall gently into the liquid nitrogen.
And...
The bottle survived!
Thirty seconds later, Stefan pulled the soda bottle out of the cooler. It turned out that our time guess was spot on! Ice had just started to form along the inside of the bottle. We opened the bottle and Stefan got to taste defeat. I tasted victory—it was delicious.
Now lets enter speculation land! Why didn’t the bottle break? Glass pans are made of similar materials and they can break from a similar temperature change, why did our bottle survive? There are two possible reasons that I can think of.
First, the outside of the bottle may have cooled slower than expected due to the Leidenfrost effect. In this case, the pocket of nitrogen gas around the bottle probably will have slowed down the cooling. In fact, if the Leidenfrost effect stayed active the entire time the bottle was submerged, it would likely keep the bottle from cooling all the way to liquid nitrogen temperatures! In either case, the Leidenfrost effect was likely a friend. But, this effect can also be observed with a water droplet on a hot pan, so what else could be responsible?
My second possible reason for the bottle surviving is that bottles are used only once, unlike our glass cooking pans. As mentioned earlier, the material of glass is really sensitive to flaws in the glass. Over the years of using glass cookware, it may develop flaws; maybe it was dinged on the counter or previously cooled quickly, but not fast enough to shatter the glass. The accumulation of these flaws in glass would eventually give a flaw large enough to make it shatter! Perhaps the soda bottle would fail too if we beat it up a bit beforehand.
In any case, this was a really fun experiment for us to go through. Although we are all doing science for our jobs, these adventures are a blast and are really refreshing! It piqued the interest of everyone in the lab (and even people outside the lab) and was a great talking point for weeks afterwards.