Tech Hammer

Tian Yanzhen's judgment was indeed correct. Before the afternoon, before half past ten, Ning Wei's phone rang.

"Hey, Dr. Ning, my surname is Zhang, and my name is Zhang Yancheng. I am a student of Professor Tan. Director Tan asked me to pick you up to take you to the laboratory and introduce our project to you. I am already at the entrance of your institute. Yes, are you free now?"

"Okay, Senior Brother Zhang, please wait for two minutes. I'll be out right away." After hanging up the phone, Ning Wei said hello to Lu Dongyi again and left the institute. Sure enough, a big brother wearing glasses was at the entrance of the institute. He lowered his head and studied his phone.

The reason why Ningwei thought this was Big Brother was because when he lowered his head, he could see that his face looked very mature, his eyebrows were pulled down, and he had a grimace on his face.

"Senior Brother Zhang?" Ning Wei called.

"Oops, Dr. Ning, I'm sorry, I'm looking at a set of data that was just sent to me." The old man raised his head and slipped his cell phone into his pocket, and extended his hand to Ning Wei enthusiastically.

After shaking hands with the sad-looking Senior Brother Zhang, Senior Brother Zhang immediately said: "Let's go to the laboratory quickly. I will introduce you to the project situation on the way. When we get to the laboratory later, I will explain the general situation to you. The data has been copied, you can just bring it back later. However, because this project is originally a collaborative project, all data in the laboratory must not be made public before the paper is issued."

Ning Wei nodded and said: "I understand this. The principle of confidentiality means that many of our research results cannot be leaked to the outside world before they are published. I heard that you have to upload the preprint of the paper to arXiv before publishing it. Right?"

While talking, Ning Wei discovered that Senior Brother Zhang's walking was almost like a foot race. He would not be able to keep up with the pace if he were to slow down a little.

"Yes, now that we have determined the direction of making materials, we can only study those things. If we don't pay attention, people can restore the results and produce a complete laboratory report from beginning to end. Who can explain this? And Dr. Ning You don’t know, it’s hard to produce materials, but we are pretty good, and most of the projects the boss gets are relatively high-end projects.”

"You don't know, the people next door to us are researching new energy batteries and making catalysts. They have to wash bottles for several hours every day. The battery components are not visible at all. They deal with various chemicals every day. Tell me about this kind of achievement. If you are really plagiarized by your peers, do you want to die? You are better off studying mathematics! I just don’t have the brains, otherwise I would definitely go to the Mathematics Institute!"

Senior Brother Zhang sighed with emotion.

Well, all walks of life have their own hardships. Ning Wei actually wanted to talk to this senior brother Zhang about the hardships of learning mathematics, but thinking that he seemed to have no position to say this, he gave up and simply brought the topic to the right track: "Brother Zhang, Professor Tan This project is a collaboration between your laboratory and the National Laboratory of Condensed Matter Physics? What does it do specifically? What do you need me to do? Let me tell you first so that I can prepare."

Zhang Yancheng replied: "Well, our project uses carbon nanotubes as hotspot materials. Specifically, it uses oriented nanotubes to produce a macroscopically braidable fiber. We hope to use it to create a textile thermoelectric generator. Specific situation That’s right, a previous experiment in the physics laboratory unexpectedly found that the high power factor of a single nanotube can still be maintained after macroscopic assembly of carbon nanotubes.”

"Before this, it was generally believed that it was difficult to achieve this, mainly due to the poor morphology of the carbon nanotube sample itself and the lack of appropriate Fermi energy tuning. But after that experiment, the physics laboratory believed that carbon nanotube fibers could Having ultra-high electrical and thermal conductivity allows it to have a very high ZT value and become a nearly perfect thermoelectric active cooling material. After all, compared with traditional materials such as bismuth telluride, lead telluride, and silicon germanium alloys, carbon Nanotubes are more environmentally friendly and have abundant reserves, so our boss went over to talk and the two parties hit it off and started the project."

"oh!"

Ning Wei nodded, and then asked: "But I really wanted to read an article last time, saying that if a material like carbon nanotubes wants to maintain the performance at the nanoscale to the macroscale, judging from the current situation, it is not possible. It’s very difficult. The preparation method in the laboratory cannot be used for industrial mass production, so even if you really prepare this material, it seems that it can’t be used now, right?”

This question obviously made Senior Brother Zhang next to him look a little embarrassed. He subconsciously raised his hand and touched his nose and explained: "Ahem, how do you say this? How about cutting-edge materials research, although it is definitely not useful for the time being. But it is kept there as a technical reserve. When the industrial base develops in the future and it is possible to produce oriented carbon nanotube materials that maintain properties at a macro scale, it can be used immediately."

Well, Ning Wei decided not to care about the application problem anymore and continued to ask: "What's the problem now? Do you need my help?"

"Well, in order to find this material, we have screened out four samples that represent the density of states of carbon nanotubes, including inner-wall semiconductor carbon nanotubes, inner-wall metallic carbon nanotubes, outer-wall semiconductor carbon nanotubes and outer-wall metal Carbon nanotubes. First we need to do optical spectroscopy measurements, but compared to the fiber state, the size and absorption of carbon nanotubes are more suitable for optical measurements."

"So we used a simple blade coating technique to produce oriented carbon nanotube films for optical measurements. Here's the problem. We used solution spinning to start by dissolving the carbon nanotubes in CSA and then generate the film. This The process uses the same nanotube raw materials and ensures that the chemical treatment is exactly the same as the fiber treatment, including CSA concentration, doping and annealing conditions, etc."

"But when we calculated and obtained the results based on the spectral measurement and absorption data brought into the previous laboratory, they were all very different from the theoretical model we had previously determined. The same experiment has been carried out seven times, and the results obtained The deviation of the results from the theoretical model has always been unacceptable. So we need a mathematician to integrate the existing data and help us find out where the problem lies. This will facilitate us to adjust and improve the direction of the experiment."

Senior Brother Zhang briefly introduced the situation.

Ning Wei nodded and calmly experienced the experience of his brain acting as a translator. Specifically, he translated the professional terms in Zhang Yancheng's mouth that should be separated by lines one by one into various methods in the laboratory.

Although it can't be said that Ning was able to figure out the entire laboratory process, at least he didn't know anything about what he was doing in the laboratory.

"Oh, what is the annealing temperature?" Ning Wei asked casually.

In fact, these data are not related to his work yet, but talking about nothing while walking on the road seems a bit monotonous. Moreover, Senior Brother Zhang obviously had no intention of appreciating the surrounding scenery.

This question made Zhang Yancheng look at Ning Wei in surprise. After all, the mathematics PhD students who had been borrowed in the past were full of all kinds of mathematical formulas and were not very familiar with some engineering terms and were not familiar with their experimental processes. interested.

"The annealing temperature is based on the data provided by the laboratory there, which is divided into two batches of 500°C and 350°C." Zhang Yancheng replied.

Ning Wei thought for a while and asked: "I remember that this type of thermoelectric material needs to increase the ZT value. If I remember correctly, the formula should be ZT=S^2Tσ/k, right? In essence, what do you think? This combination of carbon nanotubes should have a higher Sebel coefficient, higher electrical conductivity and lower thermal conductivity, right? So what exactly is it that does not conform to your pre-established theoretical model?"

"Have you ever studied thermoelectric materials?" Zhang Yancheng blinked and subconsciously slowed down.

After all, Ning Wei's achievements in mathematics and computer algorithms are too great. Even if he is not majoring in these majors, even if he spends time in the laboratory every day, he can't help but hear the legendary stories of the young man in front of him every day.

In less than one year of my senior year, I published six top-notch papers. This efficiency will definitely make any academic person feel incredible. Moreover, one of the papers made a generation of mathematics celebrities hate the hospital, one paper found a new way to solve the world's problems, and the other three papers directly involved an algorithm that can change the world. Nowadays, it is easier to book air tickets for laboratory business trips than before. It seems that All thanks to the young man in front of me.

And now he can still talk to him about materials science. Is this a monster?

"Haha, this Senior Brother Zhang, to be honest with you, I only have a brief understanding of it. I have read a few articles casually, but I don't dare to say that I have studied it." Ning Wei replied quickly.

"Oh, I understand a little bit."

Zhang Yancheng nodded suddenly, and then explained: "Okay, actually the problem is here. Theoretically, you are right. Many previous studies on traditional thermoelectric materials have been to increase the ZT value by reducing thermal conductivity. , but we believe that improving the power factor is more important. This is also the innovative point of our project. We define the power factor as PF=S^2σ, then the larger the power factor, the better when dealing with extremely large heat sources, such as solar energy. Or when industrial waste heat is used, the output power density can be maximized."

"In addition, during active cooling mode, high thermal conductivity can utilize the Peltier effect to increase the heat flow rate from the hot side to the environment, which is very promising in electronic thermal management applications. In this active cooling mode, heat can Pumped from the cold side to the hot side via the Peltier effect, the maximum hot side heat flow in active cooling is proportional to the effective thermal conductivity κ eff, which we define as κ eff = κ + PFT2H2ΔT, where TH is the hot side temperature , ΔT is the temperature difference between the two sides, so you understand, right? This shows that active cooling requires large κ and large PF, not high ZT!”

"Actually, the research on traditional materials has almost reached the ceiling. For example, Bi2Te3 and its alloys have shown extremely high performance. But firstly, they are poisonous, secondly, the raw materials are relatively scarce, and thirdly, they require It is very difficult to improve stiffness; organic materials are also a direction, but we have also studied organic materials, and they are difficult to increase their PF value. Therefore, if our project can succeed, we will wait until the industrial foundation is improved to industrialize carbon nanotubes that maintain microscopic properties. Once mass production technology appears, it will be widely used immediately.”

Well, with the extremely detailed explanation, Ning Wei has roughly understood the significance of this project and the material theory model mentioned by Senior Brother Zhang. It is nothing more than improving the power factor and thermal conductivity at the same time. While not simply pursuing a high ZT value, it can also achieve a certain advantage in the ZT value to meet the needs of the future thermoelectric material market.

The only thing that remained unexplained was probably what the problem was. Fortunately, before Ning Wei could ask further questions, the laboratory building had already arrived.

The majestic cylindrical laboratory building is right next to the teaching building of the School of New Materials. Ning Wei discovered that after arriving at Yanbei University, he had not really taken a tour of the school. For example, he had never been to the School of New Materials. Pass.

Following Senior Brother Zhang into the laboratory allowed Ning Wei to see the true heritage of the top universities in the country. Under the introduction of Senior Brother Zhang, Ning Wei looked at the high-precision laboratory equipment displayed in various laboratories like Grandma Liu entering the Grand View Garden, such as differential scanning thermal analyzers, X-ray photoelectron spectrometers, and X-ray diffractometers. , Atomic force microscope, specific surface area and porosity analyzer, micro-Raman spectroscopy measurement system, multi-channel electrochemical workstation, high-resolution field emission scanning electron microscope (SEM), high vacuum coating instrument, cutting and grinding integrated machine...

Through Senior Brother Zhang's introduction, he probably understood the reason why Professor Tan often asked Tian Yanzhen for help. It was most likely because each project required the use of the above instruments. Not only did they need to make reservations and apply in advance, but the project team also charged for using them. It didn't sound like much. too cheap.

For example, the cutting and grinding all-in-one machine charges 500 per hour internally in the school, and 600 per hour if it is used externally; another example is the use of a micro-Raman spectroscopy measurement system, which charges 300 per hour internally, and 400 externally. If charged per piece, each sample does not charge internally. Below 50, the outside is not below 100.

And it was different from Ning Wei’s imagination. The entire project team was not busy in one laboratory, but was working together in multiple laboratories. Senior Brother Zhang was mainly responsible for coordinating the operation of the entire project team.

Think about it this way, for the seven previous experiments, four samples had to be prepared for various treatments. This time and money were simply spent like water...

Although the money earned by the laboratory will definitely be used for equipment maintenance and maintaining the laboratory's competitiveness, and purchasing new high-end equipment according to the application, but for the project team, it is actually settled with money. If you want to look at it, it really hurts.

After taking Ning Wei to learn about the various large-scale equipment in the laboratory testing center, Zhang Yancheng brought Ning Wei to the door of a laboratory: "We usually mainly work here, and various data are also stored here. in the computer."

"By the way, Senior Brother Zhang, don't you need me to come to the laboratory to report every day? Professor Tan also said that I can take the data to the institute for analysis." Ning Wei said.

"Oh, it's okay. I brought you here mainly to show you our complete testing process, and then you can do the calculations wherever you want. It's just that we are pressed for time, so it would be best if we can do it as quickly as possible." Zhang Yancheng replied .