This article is from WeChat public account: span> CC Forum (ID: ccjt2014) span> , author: Fei Wei (Department of chemical Engineering, Tsinghua University professor and doctoral tutor, the Ministry of Education,” Cheung Kong scholar “Professor), drawing from the title: game” halo “ span> p>
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The pursuit of the ultimate performance of materials has always been one of the important driving forces for the development of human society. The mechanical strength of a material is one of the most important properties of a material. p>
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Professor Wei Fei led the team to carry out a lot of research on ultra-long carbon nanotube growth mechanism, structure controllability, performance characterization and application exploration, and made a series of important breakthroughs. The team has produced a single carbon nanotube with a length of more than half a meter, and has a perfect structure and excellent performance, setting a world record. strong> p>
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In addition, for the first time, the team discovered the superlubrication phenomenon strong> between macro-length carbon nanotube layers, and realized optical visualization and controllable manipulation at the macro-scale of a single carbon nanotube. p>
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Carbon nanotubes have many amazing mechanical, electrical, and chemical properties, especially its tensile strength strong> is one hundred times that of steel, and its density is one sixth of that. This allows people to Build an extra-long ladder to erect a ladder to space. p>
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Good afternoon everyone, the topic I share with you is Building a ladder to space strong>. Everyone knows that carbon is a very common and very common material. SP2 carbon has diamond, which is something everyone likes. But I want to tell you that the graphite carbon in pencils that people usually use is more solid than diamond. Many people may not believe it, but in fact, in the past 30 years, with the deepening of nanotechnology research, from the beginning of carbon 60 to carbon nanotubes to graphene, there have been two carbon 60 and graphite The ene research has won the Nobel Prize, and you can imagine the emphasis on carbon in the nanometer field strong>. p>
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I am going to talk about carbon nanotubes today. Actually, it is a single layer of graphene rolled material. strong> There are several rolls in this roll. Comes metallic and semiconducting. p>
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Over ten years ago, the Clinton administration in the United States proposed a Nano Innovation Program strong>. In the preface, you can imagine that we can use ordinary carbon as a material. The strength is one hundred times that of steel, and the density is one-sixth that of steel. When this material can be mass-produced, what is the national security, scientific and technological progress, and humanity of the United States? p>
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In fact, everyone is dreaming about building a ladder to space with this thing. Other materials cannot do it, as long as a rope made of other materials is 140,000 long. Kilometers, its own weight will break it, only carbon nanotubes can. So I am sharing with you what our dream is and whether we can achieve it. p>
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For this reason, in the past two decades, the research of carbon nanotubes, whether in terms of papers, patents, and production, has basically grown according to Moore’s Law, and has grown very, very rapidly. More than 10,000 articles per year. In fact, it’s not just the tech industry. You take a closer look at the world’s famous Damascus army knife. The reason why this knife is very sharp is that it has a wide range of applications in sports equipment, tires, and super materials. p>
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There is also a more widely used smartphone recently. Everyone knows that smartphones now use touch screens. Academician Fan Shoushan of Tsinghua University has arranged carbon nanotubes neatly through ten years of work, and then Pulled into a film, this film is made into a mobile phone touch screen, and has an annual output of 20 million in our country. This is the first time that carbon nanotubes have a large scale in general electronic products.Application. strong> p>
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Recently (United States) span> NASA is preparing to make a carbon nanotube rocket. It is expected to launch next year, replacing carbon fiber, which can affect the world. Another very interesting thing is that NASA has mentioned it for six or seven years. Just talking about one thing, you make a material with a hair diameter of 20cm, which is enough. You just need to make the material stronger than the existing one. The best material, that is, double the carbon fiber, (reward) span> 2 million US dollars, no one has got it so far, we Is it possible to accomplish this, in theory it should be possible. p>
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In the past many years, we have always been doing some work, starting from the self-assembly of the atom to make it very precise, then controlling its aggregates, controlling the core process of its reaction, controlling the entire production, Finally, it serves the society. In this environment, not only should it take advantage of its benefits, but also its disadvantages. This is a core idea. strong> p>
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In the past fourteen to five years, we have done a lot of work, mainly to find ways to apply this material on a large scale. In fact, we now use our technology to build the largest carbon in the world. Nano tube production plants, 80% of the lithium-ion batteries produced in our country use our materials. p>
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I do n’t talk about it today, but today we still talk about our dream. What is this dream? p>
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That is, Can we control the growth accuracy of such a carbon nanotube to the sub-nanometer level through nanotechnology? strong> In terms of length, think of a way to achieve meter-level length and complete atom arrangement. It is perfect, and it is likely that it will have some unique properties under such conditions. p>
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It is actually quite simple when growing this way. The first one is its catalyst strong>. In fact, it is our common iron. You make it into nanometer grade. The bigger the catalyst, the longer it grows. Thick, we go according to one or two nanometers, which is one ten thousandth of the level of hair. We try to use a carbon source, which is actually natural gas. strong> Then grow at 1000 ° C. There are two basic growth modes, one is top growth and the other is bottom growth. There is no difference in length, but it is not the same when it grows. What is it? Is it different? When it is long, there are airflow and various forces in it. When this is done, all the forces of carbon nanotubes are concentrated at this point, so it will always be defective. p>
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So people in the world who have worked for twenty years will find that I can grow quite long, but without strength and performance. Is there a long skill and good performance? This is what I care about. Only after we perform well, can we make a ladder to space. This ladder is really strong. strong> p>
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We have done a lot of work in the past ten years or so, how do we think of a long way, we first found that in fact, it can grow very fast with a little water, about 80um per second, which means that The distance of a person’s hair is not small. If you compare it with the growth speed of your hair, it will look 10,000 times higher. Compared with some things that grow in industry, it can be higher. Out a million times. p>
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This is a fairly fast speed, and it can also be very stable, but we will find that if you want to be long, always shorter, longer, and less, then you are thinking of some ability to control this A closer study will reveal that some time is long and some time is short. strong> p>
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What is in control? p>
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Actually, if you think about it, it is that the iron particles are in this place, and the carbon is an atom that goes up one by one. There are only two states on the base. Dead, not long. p>
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If we consider these two states to be constant throughout the growth process, then there is only one factor controlling it, which is carbon growth factor strong>, the higher the growth factor The better the activity, we will find that this line is the growth factor line strong>. If your growth factor is high, you can grow very long immediately, how long can it grow? We take a closer look at the growth factor controlled by many things, mainly temperature, concentration, flow rate and other factors will affect it. If you can control it at the best point, we use such a moving furnace, which is at 1000 ℃ The lower length, as long as the temperature does not exceed the error of 1 ℃ in the growth process. The other indicators are well controlled, and you will find that it can grow very long, at least half a meter long. We can now grow to 700mm. p>
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A long timeAll conform to such a distribution relationship. What is the concept of growing to such a length? If you want to grow 30 billion carbon atoms, you can only have one carbon atom in trouble, and you can grow so long. This is a very difficult process of control. Fortunately, we have excellent students who work very hard and see this law under atomic conditions. p>
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Then you will find that it is not only super long, but also free of defects. strong> As you will notice from the measurement results, in fact, its strength can be theoretically strong, because all our ordinary steels It is difficult to reach 1 GPA, and we can reach 100 GPA. p>
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People around the world have done this measurement many times before, and they have found that it can reach 30 GPA at the micron level. The tube we grow can achieve 100 GPA. Not only that, is it structurally perfect? Our students did another very careful job. A 100 cm long carbon nanotube was grown, and it was broken into pieces. Let’s see what this carbon nanotube looks like. You can see that this carbon nanotube is three-walled. It can be determined by electron diffraction Its structure. After we made 50mm, we took out another piece to see it. We diffracted it several times. What is the concept of 50mm? It is about 5 billion carbon atoms. We found that it is very The perfect carbon nanotube structure has a constant helix angle. This is a six-membered ring without any defects. strong> p>
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Everyone jokingly said that if you want to do this, at least 1.3 billion people don’t have a bad person, and this can be achieved. p>
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What about it? p>
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If we draw a seam on this tube, this seam is a millimeter length, and we will find a way to smoke some carbon dioxide on the seam. You can see that this carbon dioxide is a micron. This is our white color. This is This carbon nanotube, so that it can be seen with the naked eye, is actually very strong. p>
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In this way, we can put a variety of carbon nanotubes. Nano-level gadgets can be seen with the naked eye. Not only that, this carbon nanotube can dance with music, not only can dance, We found that it can actually vibrate 200 million times continuously under the condition of moving, it can be like a super spring with great amplitude, and it will not break. Strong> Actually, the weight of this carbon dioxide is this carbon nanotube. It looks like 20,000 times, it doesn’t bend at all, it will move only when you blow. p>
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In this way, we can measure the strength of carbon nanotubes in the millimeter length. We found that it is still 100 GPA and 17% elongation at break. Generally speaking, 3% of steel will be completely broken. We can 17%. This is a super rubber band. To what extent is this rubber band used for mechanical energy storage, it can achieve this level. Everyone I have no impression of this level, but everyone knows that lithium-ion batteries have 5 times the energy of stored mechanical energy than lithium-ion batteries. strong> p>
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What is this concept? p>
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You use a thick carbon nanotube rope with your finger to pull a two-kilometre-long high-speed rail at a speed of 350 kilometers per hour, absorb all its energy, and then release it when it is released. It has such great capabilities. You can notice that the reason for this ability is due to the perfect super-long structure. strong> p>
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In this case, we have this material, and when we use this material to make the ladder, it is better than the Americans think. What I want to do is a 1m wide and 0.1mm thick tape. In this case, it will weigh 20 tons and cost 10 billion US dollars. He hopes to make it quickly. It is not easy now. In fact, we found that we have 120 GPA strengths, which can reach half a meter, so that 3-6 tons will do. In this case we have taken another step forward in this dream. p>
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Actually, that’s not all. Recently, you will find even greater discoveries with such materials for experiments. p>
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Everyone knows that a perpetual motion does not exist at a macro scale, but it does exist at a micro level, such as our gas molecule motion. If it moves permanently, you do n’t need to add energy to it, it will not dissipate. Off. p>
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Is there a way to make our perpetual motion macro feasible? p>
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This seems unimaginable. In fact, this matter has made rapid progress in the past few years. One of them is that you can notice that on two solid surfaces, such as graphite, it has Two basic modes: strong> One is that if the materials are arranged in the same way and they slide, there is a common relationship. At this time, the resistance will be particularly large. This is also the case that our bearings can never use the same type. Material is used to make the bearing pad and the shaft are generally separated, but if you make a wrong angle, it is notThe common state is mainly the interaction between atoms. p>
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In 1990, a Japanese person proposed that if it is an incommensurate solid surface, it may have low friction, but it is too small for everyone to count. p>
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Let ’s do an experiment. Is it possible to let the carbon nanotubes slide inside? If you can ensure that the helix angles of the two tubes are different, they are perfectly structured tubes, it has May vibrate forever. strong> We found that when we do experiments, they sometimes appear. In this case, our millimeter-length tube will pop up when we slam. We carefully measured and found that it can be pulled out for a long time. There is no force on it, how small is it? A centimeter-long length is pulled out, and one billion carbon atoms are pulled out, and there is only one nano cow, that is, the power of a covalent bond exceeds this. It just overcomes the force on the graphite surface. The friction we measured is four orders of magnitude smaller than all the existing reports. Everyone thinks if I did it in the centimeter length. Only the force to overcome the surface, although this is never the same Perpetual motion is okay, but from this perspective, it brings hope to everyone. In the future, we may be able to make what we dreamed of before. p>
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In general, you will notice that if we pursue excellence, perfection, and extreme materials, we can realize our dreams. p>
This article is from WeChat public account: span> CC pulpit (ID: ccjt2014) span> , author: Wei Fei (Professor, Department of Chemical Engineering, Tsinghua University, Doctoral Supervisor, Distinguished Professor of the Yangtze River Scholars, Ministry of Education) span>
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