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The Heat is On
May 31, 2012   
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Łukasz Ciupiński, Ph.D., of the Warsaw University of Technology Research Center, manager of the TERMET project, which aims to develop new structural materials with increased thermal conductivity, talks to Karolina Olszewska.

Why is research into developing materials with increased thermal conductivity important and for whom?

Materials of this type are very important for the electronics industry and for manufacturers of various components that are produced with the use of cutting machines or machine tools. These materials are also intended for the automotive industry, especially manufacturers of motorcycles. When computer parts, machine tools or brakes are at work, they generate large amounts of heat. This heat cannot be put to use, unlike in the case of radiators, for example. It’s an undesirable side effect that reduces the efficiency of the systems, increases the risk of failure, and leads to production losses. For this reason, it should be dissipated as soon as possible. And this is exactly the role that is played by materials with very high thermal conductivity. The materials currently in use fail to meet the challenges of miniaturization when it comes to equipment and its increasing efficiency. Equipment heats up more and more these days and we are reaching a limit beyond which new materials will become indispensable.

What kind of materials can solve this problem?

We call them composites. They are created by combining, in the laboratory, materials that could not normally create chemical connections in nature. For example, a combination of diamond and copper. Such a composite could be used for cooling electronic devices, for example processors in computers.

The combination of a highly conductive metal with the highly conductive ceramic material that diamond is, is not our original idea. There have been publications on this topic in the literature for 10 years. The whole project is based on developing the technology for manufacturing these materials. This technology is so complicated that these materials are not commonly used.

What is the technology developed under the TERMET project all about?

Today, mainly copper components are used for cooling computers. The thermal conductivity of synthetic diamond is at least twice as high as that of copper. By combining these two we have a chance to bring about intermediate conductivity, which significantly improves the heat dissipation capacity of the new material.

The problem is that copper does not bind with diamond. If you pour liquid metal over diamond, the resulting combination will not ensure a satisfactory transfer of heat between the components. The connection will not be chemical in nature. This explains why this technology still requires a lot of research and an appropriate modification of components in the new material. We have already managed to do that on a laboratory scale. However, the transition from the sample to the actual production process requires a lot of work. Certainly, we should be helped by a new device that we have purchased as part of the project; the device makes it possible to increase the temperature of the synthesis of our composites.

Our technology is based on the sintering of powders under the influence of electricity, and that’s why we needed a battery of capacitors capable of generating a large electrical impulse. The device has been upgraded so increasingly larger samples will be possible.

Will the use of such an expensive material as diamond prove to be worthwhile for producers of electronic devices?

Many people think of diamond in terms of jewelry, which of course is very expensive. We use synthetic diamond. In terms of physical properties, it is no different from natural diamond, but is obtained on an industrial scale and is cheaper. We use grains of diamond sand whose size is comparable to the thickness of a human hair. Such dust is not that expensive; after all, it is used in polishing discs or diamond saws. We can afford to put such an item into the laptop.

Mobile phones are another likely application for our materials. The market demands products of increasingly smaller dimensions, phones equipped with features that even computers did not have until just a few years ago. So producers will find it worthwhile to use our composite materials.

Your technology is also appealing to machine tool manufacturers. Why’s that?

Machine tools will work more efficiently if they heat up more slowly. Even though liquid cooling systems are used in such equipment, if the tool itself is able to give off the heat to the coolant quickly, then the cooling mechanism will be more efficient.

That new technologies are needed is shown by the market pressure we feel. We have been approached by a company that specializes in the heat treatment of components and which is having a serious problem with heat dissipation using copper. Some of the components break during this procedure. The rate at which heat is dissipated is too slow and there is too much temperature difference, which leads to a situation in which the size of the machined parts is variable. Improving the process will significantly reduce the number of faults. But this is where the financial aspect of the deal begins—whether we should continue doing business the old way and end up with a larger number of defective products that will have to be either thrown away or reworked or whether we should switch to the new technology. If we test out the new material and the number of defects turns out to be significantly smaller, then even buying new, more expensive equipment may turn out to be worthwhile.

Why is thermal expansion an important problem?
In the case of both machine tools and electronic parts, it is important to make sure that the materials used expand—or, in other words, increase their volume under the influence of heat—as little as possible. In electronics, heat must be dissipated from the semiconductor on which the integrated circuits are built. The material has its specific coefficient of thermal expansion. If we combine it with our heat-dissipating material, then we must make sure that both materials have similar coefficients of thermal expansion. If their coefficients are very different, stress will appear in the system that may lead to the destruction of the item. In the case of diamond, this coefficient is even smaller than in commonly used semiconductors.

Is the excellent thermal conductivity of new-generation materials a cure for all ills?

Thermal conductivity is not the only factor. Materials giving off heat must have additional properties, as evidenced by aluminum-silicon carbide composite.

They should be durable and have low thermal expansion so that, after a change in temperature, their size does not change substantially. They cannot be very heavy, either. We are working on a technology for injecting aluminum into silicon carbide. The main selling point of this material is that it is lightweight, and so it has little inertia, which, in the case of the quickly revolving machine tools, can improve the precision with which the cutting tool moves.

In high-precision machine tools, each part that is in motion is subject to the phenomenon of inertia. We know this phenomenon from everyday life. When an object with a large mass, such as a car, enters a turn at high speed, it will probably spin out of the turn. It is precisely this phenomenon. When we reduce the mass, and for example take the same turn in a motorcycle at the same speed, it is more likely that the maneuver will be successful. By reducing the weight of parts that must move in machine tools, we can make the equipment more precise and perhaps faster, and therefore more effective.

Since you’ve mentioned fast motorbikes, how can the new materials improve the way in which brake discs work?

Indeed, a lot of heat is produced in the process of braking. The hotter the brakes become, the longer they take to stop the vehicle, and the worse their performance is. That’s why it is important to dissipate heat from the braking system. At the same time, the coefficient of friction is important. The material from which the brake disc is made must have a high coefficient of friction in combination with the brake pad to make sure that braking is effective. In our project, we focus on working together with the motorcycle industry because it uses systems that work briefly and very intensively. Due to the high speeds achieved by technologically advanced motorcycles, their brake systems are more demanding. Another use is braking systems in aircraft, in which the maximum braking effect needs to be produced at the time of landing.

Where else is heat management important?
The composite materials we develop will find application in modern industries such as electronics and photonics as well as in the energy sector, precision engineering and transportation. But this list can go on, as exemplified by a sensor for use in medicine that makes it possible to determine the content of carbon dioxide or oxygen in a patient’s blood without the need to break the skin to take a blood sample. This sensor is being developed at the Warsaw University of Technology as part of another project. To ensure the desired functions for the device, the researchers at the Department of Mechatronics were looking for a material with good heat conductivity, but one that would not conduct electricity. It turned out that our partners from the AGH University of Science and Technology in Cracow are experts on ceramic materials that are electrical insulators. The engineers from Warsaw were looking for precisely such a material. The researchers from Cracow obtained a variety of sintered aluminum nitride whose characteristics in terms of thermal conductivity are better than those of other materials currently available on the market. We are currently at the stage of fine-tuning the details and specifying the shape of the material intended for the tip of the sensor probe.

Who will deal with the testing and implementation of the new technology?

The project is being carried out by a group of institutions comprising the AGH University of Science and Technology in Cracow, and three organizational units of the Warsaw University of Technology: the Research Center for Functional Materials as the main beneficiary; the Faculty of Materials Engineering; and the Institute of Heat Engineering, part of the Faculty of Power and Aeronautical Engineering. This research project involves research intended for practical application. We are trying to establish cooperation with companies that could potentially be interested in using the materials we’ve developed in their solutions and products. We talked with several companies from Polish industry, and we also have working contacts with a global company.

We are thinking of working with manufacturers of cutting tools and machine tools, because we can offer an attractive product in this area. If we develop original technological solutions we will patent them. Universities will not be offering finished products; for this purpose a firm would have to be set up to manufacture them. Maybe one of the entrepreneurial-minded doctoral students cooperating with us will start such a firm.

You have received zl.24 million in funds from the Innovative Economy Operational Program through the National Center for Research and Development. How did you spend the money?

First of all, we bought the three most important devices. The largest of them, the X-ray microtomography system, allows us to conduct non-invasive observation of the inner structure of our material and check the quality of components and their spatial distribution. It cost more than zl.2.5 million. This piece of equipment will remain at the university, and because it has a wider range of applications, it will certainly be used for many other studies after the project ends. Another piece of equipment we bought is a device for about zl.1 million that is installed at the Institute of Thermal Technology. It enables the measurement of thermal diffusivity, or the property on the basis of which it is possible to calculate the coefficient of thermal conductivity, which is of the greatest interest to us. The third device is a furnace for about zl.650,000 which our colleagues at the AGH University of Science and Technology needed to produce ceramics. We have spent some of the money on materials needed for experiments. We are also using the funds we have obtained to finance the work of a 35-person team. The project covers four years and will run until the end of 2013.
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