World's Lightest Solid!
发布时间 2019-05-31 16:40:50 来源
This is Aerojell, the world's lightest, that is least dense solid. This piece has a mass of just 1.22 grams. That is only a few times the mass of the same volume of air, which kind of makes sense because it is 99.8% air. In fact, some Aerojells are so light that if you removed all the air from them, they would be less dense than air.
这是Aerojell，世界上最轻、最不密实的固体。这块物品的质量只有1.22克。这仅相当于同体积空气的几倍质量，这很容易理解，因为其含气量高达99.8%。实际上，一些Aerojell非常轻，如果将其所有的空气都取出来，它们的密度将比空气还要小。
I have long been fascinated by Aerojell, so actually flew out to Aerojell Technologies in Boston to find out why was Aerojell invented? How is it made? Why is it such a good thermal insulator and what is it used for?
我一直对Aerojell着迷，所以实际上飞到波士顿的Aerojell Technologies了解一下，为什么Aerojell被发明出来？它是如何制造的？为什么它是一个好的热绝缘材料并且它被用来做什么？
Okay, we are going to try and experiment to demonstrate the insulating power of Aerojell. So over here we have two setups, one with a glass Petri dish and the other one with Aerojell on top. Both are made of silica, but with very different physical structures. We are going to see how long it takes to melt these chocolate bunnies with a bunzen burner. Now to have a look at this experiment, we have a FLIR T1020, which can see temperatures up to 2000 degrees Celsius. It is getting pretty hot.
好的，我们将进行一个实验来展示Aerojell的绝缘能力。在这里我们有两个装置，一个是玻璃蒸发皿，另一个是放置Aerojell的玻璃蒸发皿。两个都是由二氧化硅制成,但是它们具有完全不同的物理结构。我们将用火柴枪看看需要多长时间才能融化这些巧克力兔子。现在，我们使用一个FLIR T1020来观察这个实验，它可以看到高达2000摄氏度的温度。现在它变得非常热了。
Yeah, you can see that the glass is getting really hot already. And after just a minute? It started to smoke. Oh, okay. It is definitely melting and smoking. Oh yeah, here we go. I would say that that is phase change. We have got liquid chocolate situation. We have some smoking bunny. Over here the bunny is actually sort of melting over and look, it is sort of tilting to the side. Alright, I think we are going to call that a belt. What is that? Oh, on cue, on cue. I would say that that is material film. Not only did the bunny melt quickly, the Petri dish cracked under the thermal expansion.
哦，你可以看到玻璃已经变得非常热了。只过了一分钟？它开始冒烟了。哦，好的。它肯定正在融化并冒烟。哦，是的，我们来了。我会说这是相变。我们有一些液态巧克力的情况。我们有一些冒烟的兔子。在这里，兔子实际上正在融化并且它看起来有点倾斜。好的，我想我们要称其为一个失败。那是什么？哦，按时表演，按时表演。我会说这是材料薄膜。不仅兔子很快就融化了，培养皿还因热膨胀而裂开了。
So now let's try the aerogel. So how was aerogel invented? Back in 1931, a guy named Professor Samuel Kisler had a bet with his colleague Charles Lerned. Now the bet revolved around jellies, like peanut butter and jelly jellies. Now the thing about jellies is they are actually a combination of liquids and solids. I mean, they are mostly liquid, but it is embedded within this 3D solid structure. So if you think of a jell like jello has a skeleton with nanosize pores that gives it its rigidity and then that is about 1% of the jellies.
现在让我们来尝试一下气凝胶。那么气凝胶是如何发明的呢？回到1931年，一位名叫Samuel Kisler教授的人与他的同事Charles Lerned打赌。现在这个赌注与果冻有关，像花生酱果冻。现在关于果冻的事情是它们实际上是液体和固体的组合。我的意思是，它们主要是液体，但嵌入这个3D固体结构中。因此，如果你认为果冻就像果冻一样，具有纳米级孔隙的骨架，这给了它刚性，然后这只占果冻的1％左右。
So the bet was this, could you remove the liquid from the jelly without affecting the solid structure? I mean, if you just evaporate the liquid out, well then the solid structure shrinks because as you remove liquid molecules, they pull on each other and they pull on the solid structure around them, basically crumpling it from the inside. Now Samuel Kisler solved this problem in two ways. First he realized you could replace one liquid with another inside the jelly just by washing it thoroughly so you could swap out, say, water for alcohol. And then if you take the jelly and put it in a high pressure vessel called autoclave, by heating it to the high temperature and high pressure point called the critical point of the liquid.
这个赌注的问题是，你能否在不影响固体结构的情况下将果冻中的液体去除？我的意思是，如果你只是把液体蒸发出来，那么固体结构会缩小，因为随着你移除液体分子，他们会相互牵扯，并拉拽周围的固体结构，从而使其从内部皱缩。现在萨缪尔·基斯勒用两种方法解决了这个问题。首先，他意识到你可以通过彻底清洗果冻来用另一种液体替换里面的一种液体，比如说用酒精代替水。然后，如果你将果冻放到一个高压容器中，称为压力釜，在达到液体的高温高压临界点时，就可以使果冻达到高温高压状态。
The liquid transformed into a semi-liquid semi-gas called a supercritical fluid. At this point there is no longer a distinction between liquid and gas. Those molecules are no longer pulling on each other. So once you've depressurized the vessel, that solid skeleton that 1% of the mass of the jell is left behind intact except for where there was liquid in the pores before is now gas. And that solid skeleton, that nanopore solid is what we call aerogel. Kisler published his findings in nature in 1931.
这种液体会转化为一种半液态半气态的物质，称为超临界流体。此时液体和气体之间已经没有区别了。这些分子不再相互牵引。所以，一旦你将容器减压，那个占这种凝胶1%质量的固体骨架就留了下来，除了原来存在液态的孔隙中的部分，此时已经变成了气态。这个固体骨架，也就是纳米孔固体就是我们所说的气凝胶。 Kisler 在 1931 年在自然杂志上发表了他的发现。
It is getting pretty hot as you can see through the thermal camera. But coming up on three minutes, there's still no sign of melted chocolate. So we're going to pull out a thermocouple and just check the temperature underneath the bunny, like underneath the aerogel and see what the flame temperature is. You can kind of see that the parts of the bunny are getting hot, but it's not the bottom of the bunny. It's all around the bunny. Exactly, that convective heat is moving up and around the aerogel. So you can see the thing is getting red hot. And by four minutes the bunny is looking a little soft. Pretty good though. Considering how easy this to melt chocolate.
从热像仪中可以看出，温度正在升高。但已经过去了三分钟，还没有发现巧克力融化的迹象。因此，我们将拿出热电偶，只检查兔子底部，就像检查气凝胶底部一样，看一下火焰温度是多少。你可以看到兔子的某些部分变得很热，但不是兔子底部。它是在兔子周围。确切地说，对流热正在上下运动并绕过气凝胶。因此，您可以看到物体变得非常红热。到了四分钟，兔子看起来有点松软，但还非常好。考虑到巧克力有多容易融化，这还不错。
Can I put my finger here? Be careful. It's not that it's hot. It's that it's real. Right. But yeah, totally cool to touch, right? It is just warm to the touch. He made aerogels out of all sorts of things. He made them out of eggs. He made them out of rubber out of nitro cellulose. And included in there was silica. Actually right here on the table I have some examples of some silica gels. This is a wet silica gel. It's kind of rubbery, so I can just carve out a piece. It is 97% alcohol in type of its pores. And then the remaining 3% solid is amorphous silica. Can I touch it? Absolutely. It's kind of rubbery. Not that strong. So was I cracking it there or was it a really kind of crack? No, it's very easy to break, very crumbly.
我能摸这里吗？小心一点。不是因为它很烫，而是因为它是真实的。好的。但是，它是完全可以触摸的，对吗？它只是手触感温暖而已。他用各种材料制造气凝胶。他用鸡蛋制造，用硝化纤维胶制造，其中包括二氧化硅。实际上，我桌子上就放着一些二氧化硅凝胶样本。这是一种湿的二氧化硅凝胶。它有点橡胶质地，所以我可以切下一块。它的孔隙度为97%酒精，其余3%固体为无定形二氧化硅。我可以摸它吗？当然可以。它有些橡胶质地，不是很坚固。所以我是在折断它还是它本来就很脆？不，它很容易碎裂，非常易碎。
The next step is to replace the alcohol in the gel with liquid carbon dioxide. We're about to see liquid CO2. Liquid CO2 has the advantage of being non-flammable. Plus it's got a low critical temperature.
下一步是用液态二氧化碳替换凝胶中的酒精。我们即将见到液态二氧化碳。液态二氧化碳的优点是不易燃。此外，它具有低临界温度。
Open up. Let's see it flooding in there. Yeah, it's flooding in. There it goes. Just another solvent. You can clearly see it's just so much cooler on top. What temperature is it on the bottom? We're at 600 right now. 600 degrees Celsius. That's 1200 meltdown. That's 50 fair meltdown right now.
打开它，让它涌进去。是的，它正在涌进去。它就像另一种溶剂。你可以清楚地看到它的表面要凉快得多。底部的温度是多少？我们现在是在600度。600摄氏度。那就是1200度的熔毁。现在是50度的安全熔毁。
Notice where the bunny is melting. It's melting right on that edge where the heat's like the flame is kind of crawling up and over. So again, that's the. Oh, bunny down. Well, not a bad result. Not a bad result at all. I'm interested in tasting some of this chocolate here. It's hot. It's warm. It's delicious. Like fondue. Mm-hmm. That was great.
注意兔子正在溶化的地方。它正在那个边缘溶化，那里的热度就像火焰一样爬上来。所以再次强调，这就是......哦，兔子倒了。呃，结果还不错。结果还不错。我很想尝一些这里的巧克力。它很热，很温暖，很美味，就像火锅一样。嗯。太棒了。
Once the liquid CO2 has filled all the pores of the gel, it's time to take it super critical. It was. I would say kind of a spiritual experience the first time that I saw a super critical fluid will get to be there. I love how much you're into these autoclades. I love aerogels. I like to make a super critical fluid. We can heat this with a hair dryer, actually.
一旦液态二氧化碳充满了凝胶的所有孔隙，就需要对其进行超临界处理。第一次看到超临界流体时，我会说这是一种类似于灵性的体验。我喜欢你对这些高压釜的热情。我喜欢气凝胶。我喜欢制造超临界流体。我们实际上可以用吹风机加热它。
As we approach the critical point, the surface of the liquid becomes kind of blurry. Weird, huh? That is like weird waves in there. Yeah. I'll speed it up so you can watch the surface disappear altogether. You're now looking at the super critical fluid of CO2. In this state, the CO2 can be vented without affecting the solid structure and what you're left with is aerogel.
当我们接近临界点时，液体表面会变得有点模糊。很奇怪，对吧？就像里面有奇怪的波浪一样。是的，我会加速它，这样你就可以看到表面完全消失。现在你看到的是CO2的超临界流体。在这种状态下，CO2可以排出而不影响固体结构，留下的是气凝胶。
If you look at aerogel on a light background, it's almost impossible to see because it is pretty transparent. But if you look at it on a darker background, then you can see that it has a slight bluish color. And it's bluish for the same reason that the sky is blue. Because all those tiny little nanoscale structures, they scatter the light according to Rayleigh scattering.
如果你在浅色背景下看气凝胶，几乎无法看到它，因为它相当透明。但如果你在深色背景下看它，那么你会发现它有轻微的蓝色。它之所以呈现蓝色，是因为和天空呈现蓝色的原因相同。因为所有那些微小的纳米级结构，它们会根据瑞利散射效应，散射光线。
And the intensity of light scattered is proportional to 1 over wavelength to the power of 4, which means that scatters shorter wavelengths like blue much more than it scatters yellow or red. And for that reason, aerogel looks opaque in the ultraviolet and transparent in the infrared.
光散射强度与波长的倒数的4次方成比例，这意味着它比散射黄色或红色更容易散射蓝色等短波长的光线。因此，气凝胶在紫外线下看起来不透明，在红外线下透明。
Now, what do you think this would look like if I held it up to the blue sky? What do you think we would see? Would it look ultra blue? No, it looks yellow. And that's because the aerogel is actually scattering out that blue light. And so what passes through and makes it to our eyes is the longer wavelengths like the yellows and oranges. It's basically the same effect as looking at a sunset.
现在，你认为如果我把它举起来放在蓝天下，会是什么样子？你认为我们会看到什么？它会显得极蓝吗？并不是，它是黄色的。这是因为气凝胶实际上是将蓝光散出去了。因此，穿过去并到达我们眼睛的是像黄色和橙色这样的较长波长。这基本上就是看日落时的效应。
When you see the yellows and oranges of a sunset, it's because the blue light has already been scattered out by the atmosphere the light had to pass through before it reached your eyes. So effectively looking at aerogel against blue sky is like looking at a portable sunset.
当你看到日落的黄色和橙色时，那是因为光线在到达你的眼睛之前必须穿过大气层，蓝色的光已经被散射出去了。因此，把气凝胶放在蓝天下看起来就像是看一个便携式的日落。
The nanoscale pores of the aerogel are also what makes it such a good thermal insulator. That's awesome. Does that look hot? It's definitely hot. You might think that because aerogel is largely comprised of air, like 99% air, that has the same thermal properties as air, but that is not correct.
这种超小型孔道的气凝胶也是它成为极好的隔热材料的原因。太赞了！看上去很热吗？它确实很热。你可能会认为，因为气凝胶主要由空气组成，像99%是空气，所以它具有与空气相同的导热性质，但实际并非如此。
That's because the width of the pores is smaller than the distance air molecules travel on average before colliding with something. They're so called mean free path. Hence it's really difficult for the hot fast moving air molecules below the aerogel to diffuse through it and transfer heat to the top of the aerogel. This is called the Knutson effect.
这是因为气孔的宽度比空气分子在平均碰撞前行驶的距离更小。这就是所谓的平均自由程。因此，对于在气凝胶下方热而快速运动的空气分子来说，它们很难扩散穿过气凝胶，把热量传递到气凝胶的顶部。这被称为Knutson效应。
It is so weird because you don't expect something that's transparent to block the heat that well, but this really does. And that's why NASA used aerogel insulation on the Sojourner rover, Spirit and Opportunity, the Curiosity rover, and they plan to use it on future missions to Mars.
这很奇怪，因为人们不会想到透明物质可以如此有效地隔热，但事实上它能够实现。这也是为什么NASA在Sojourner漫游车、精神号和机遇号探测器、好奇号探测器上使用气凝胶隔热材料，而且他们计划在未来的火星任务中继续使用气凝胶。
Why does it need insulation? The electronics because they don't want the electronics to get cold during the cold nights on Mars. NASA has also put aerogel to more exotic uses, notably to catch dust from a comet as part of the star dust mission.
为什么需要隔热层？因为电子设备不希望在火星的寒冷夜晚受到寒冷的影响。此外， NASA 还将气凝胶用于更多的外星探索，尤其是作为"星尘任务"中捕捉彗星尘埃的一部分。
So the particles were traveling about 6 kilometers per second relative to the aerogel. So when they hit the aerogel, because the aerogel is a very low density material, very, very porous material, the particles actually enter the aerogel and as they travel through the aerogel, they basically break apart the network that makes up the aerogel and they lose energy in the process and eventually come to a stop.
这些粒子相对于气凝胶的速度约为每秒6公里。当它们碰撞到气凝胶时，由于气凝胶是一种非常低密度、非常多孔的材料，这些粒子实际上会进入气凝胶，并穿过气凝胶时破坏了构成气凝胶的网络，同时它们在这个过程中失去了能量并最终停止了。
This is good for capturing particles because if a particle like that were to hit a solid surface, then it just stops immediately and vaporizes. So should we expect to see aerogel in our everyday lives anytime soon? One of my running jokes is when they build skyscrapers in Antarctica, they'll use aerogel as thermal insulation.
这对于捕捉微粒很有用，因为如果这样的微粒碰到了坚实的表面，它就会立即停止并蒸发。那么我们应该期望在不久的将来在日常生活中看到气凝胶吗？我的一个俏皮话是，当他们在南极洲建造摩天大楼时，他们将使用气凝胶作为隔热材料。
Why do you say that? Well, because then they'll really care about just how thermal efficient is because it would be so cold there. So instead of having 10 feet of fiberglass insulation, you could have 6 inches or something of aerogel.
你为什么这么说呢？因为在那种情况下，他们会非常关注保温效率，因为那里很冷。因此，你可以用6英寸或其他厚度的气凝胶代替10英尺厚的玻璃纤维绝缘材料。
Scientists are currently working on reducing costs and increasing durability. And that's true. They do have some elasticity. There we go. It is not hard to break. They've already made a lot of progress.
科学家目前正在努力降低成本并提高耐久性。这是真的。他们确实具有一定的弹性。它不难被打破。他们已经取得了很多进展。
For example, original silica aerogel is hydrophilic. There we go. Now this is a hydrophilic aerogel. So once we've done this, is that piece of aerogel ruined now? Pretty much. But there are ways to make it waterproof.
例如，原始的二氧化硅气凝胶是亲水性的。现在这是一个亲水性气凝胶。那么，一旦我们这样做了，这块气凝胶就毁了吗？基本上是的。但有方法可以使其防水。
So if you want to see that and all the other next generation aerogels, then subscribe to the channel and this may be the start of an aerogel trilogy.
如果你想看到这个以及其他下一代气凝胶的内容，那么订阅这个频道吧，这可能是一个气凝胶三部曲的开始。