Nanotechnology: Carbon nanotubes. Electrophysical characteristics of modified carbon nanotubes

The invention relates to the field of manufacturing materials for hydrogen storage systems, as well as to the field of producing carbon nanotubes and can be used in the production of carbon nanotubes used as a carrier material in various hydrogen storage systems. The essence of the invention: the method of processing carbon nanotubes involves heating at a temperature of 1500-1600°C in zinc sulfide vapor for 20-30 minutes. The technical result of the invention is to increase the sorption capacity of carbon nanotubes while simultaneously reducing the temperature and duration of the treatment process. 1 table

The invention relates to the field of manufacturing materials for hydrogen storage systems, as well as to the field of producing carbon nanotubes and can be used in the production of carbon nanotubes used as a carrier material in various hydrogen storage systems.

There is a known method for treating carbon nanotubes by heating to 1700-2200°C in an argon flow for 120 minutes - prototype. The method makes it possible to increase the sorption capacity of carbon nanotubes with respect to hydrogen by 1.26-3.09 times, depending on the processing temperature. The main disadvantage of this method is the need to use high processing temperatures to significantly increase the sorption capacity of the material. Treatment at 1700°C increases the adsorption capacity only 1.26 times, while heating to 2200°C is required to increase the sorption capacity by 3.09 times. Disadvantages also include the long processing time (120 minutes).

The objective of the present invention is to increase the sorption capacity of carbon nanotubes while simultaneously reducing the temperature and duration of the treatment process.

This problem is solved in the proposed method for processing carbon nanotubes, including heating, which is carried out at a temperature of 1500-1600°C in a closed volume in zinc sulfide vapor for 20-30 minutes.

Treatment in zinc sulfide vapor makes it possible to increase the sorption capacity of carbon nanotubes in relation to hydrogen by 3.4 times, while the temperature of the process is reduced to 1500-1600°C, and the duration of treatment is reduced to 20-30 minutes.

Zinc sulfide has a melting point of 1765°C and its own vapor pressure at the melting point is over 4.5 atm. When zinc sulfide is heated in the solid phase, it sublimates; at a temperature of approximately 1550°C, the pressure of its own vapor is 1 atm. When the material is heated above 1600°C, zinc sulfide vapors intensively dissociate to form atomic zinc and molecular sulfur.

The increase in the sorption capacity of carbon nanotubes under the influence of zinc sulfide vapor is explained by an increase in the active surface area of ​​the nanotubes due to the chemical interaction of these materials.

The choice of temperature range for the treatment process is due to the fact that at temperatures below 1500°C, when the pressure of ZnS’s own vapor is less than 1 atm, zinc sulfide does not evaporate intensively enough and a significant increase in the sorption capacity of nanotubes is not achieved. At temperatures above 1600°C, zinc sulfide vapors intensively dissociate and carbon nanotubes are quickly destroyed under the influence of a strong oxidizing agent - gaseous sulfur, which is one of the dissociation products.

When the process duration is less than 20 minutes, the sorption capacity of carbon nanotubes does not reach maximum values. When the treatment duration increases beyond 30 minutes, the sorption capacity first stops increasing and then begins to decrease, which can be explained by the beginning destruction of nanotubes.

At the end of the process, excess evaporated zinc sulfide condenses on the cold walls of the treatment device and can be collected for reuse.

The processing modes are shown in the table, where, for comparison, the results of processing using the prototype method, taken from.

The table shows that only under conditions corresponding to those proposed (lines 6-8, 12-13) is the maximum increase in the sorption capacity of carbon nanotubes achieved. In this case, the temperature and duration of treatment are reduced compared to the prototype method.

A sample of carbon nanotubes weighing 1 g is placed in a container so that the nanotubes are located above a source of zinc sulfide weighing 0.5 g at a distance of 30 mm. The container is evacuated to 10 -3 mm Hg. and sealed. The container is then placed in a gradient-free oven heated to 1550°C and held for 25 minutes. Then the container is removed, cooled and opened. The evaporated zinc sulfide, condensed on the walls of the container, is collected for reuse. The treated nanotubes are saturated with hydrogen under a pressure of 100 atm and at a temperature of 25°C for 24 hours. The sorption capacity of carbon nanotubes increases by 3.4 times compared to the original sample.

A method of processing carbon nanotubes, including heating, characterized in that the treatment is carried out at a temperature of 1500-1600°C in zinc sulfide vapor for 20-30 minutes.

Scientists from Kanagawa University (of course, this is Japan) were able to control a levitating object not only without contact, but also without changing the characteristics of the magnetic field. All this turned out to be possible thanks to a special configuration of magnets (they are placed in a checkerboard pattern) and the effect of the laser on the floating disk. The laser acts in such a way that the edge of the disk heats up, a temperature difference occurs, and the disk moves after the beam. Here's what it all looks like:

Even more interesting facts can be found on the website polezno.kg

A unique Christmas at an Antarctic polar station

Each of us celebrated Christmas differently. Some people don’t recognize this day as a holiday at all, some celebrated with friends, some went to warmer climes. But scientists from the Antarctic station decided to launch a special telescope weighing as much as 1.8 tons. This is a stratospheric telescope that performs a number of important tasks for studying the processes of star formation and planet formation. The device will hover at an altitude of about 30 kilometers, studying outer space. According to astronomers, such telescopes are cheaper than orbital telescopes, and the cost of their operation is much lower than the cost of operating orbital telescopes.

Carbon tubes are hazardous to health

Scientists from the University of Edinburgh have found that carbon nanotubes are no less (and perhaps more) harmful than asbestos. The thing is that the tube itself is very thin (the human immune system is not designed for such dimensions), but long. Thus, when a nanotube enters the lung, it infects the lung, and the immune system does not fight such a “neighbor” at all. It is not yet entirely clear whether nanotubes will accumulate in the human body in the event of long-term interaction with carbon nanotube material. But even in the short term, all this can harm human health.

If anyone is interested, you can get detailed information in English

Energy is an important industry that plays a huge role in human life. The energy situation in the country depends on the work of many scientists in this industry. Today they are searching for these purposes, they are ready to use anything, from sunlight and water to air energy. Equipment that can generate energy from the environment is highly valued.

General information

Carbon nanotubes are long, rolled graphite planes that have a cylindrical shape. As a rule, their thickness reaches several tens of nanometers, with a length of several centimeters. At the end of the nanotubes a spherical head is formed, which is one of the parts of the fullerene.

There are two types of carbon nanotubes: metallic and semiconductor. Their main difference is current conductivity. The first type can conduct current at a temperature equal to 0ºС, and the second - only at elevated temperatures.

Carbon nanotubes: properties

Most modern fields, such as applied chemistry or nanotechnology, are associated with nanotubes, which have a carbon frame structure. What is it? This structure refers to large molecules connected to each other only by carbon atoms. Carbon nanotubes, whose properties are based on a closed shell, are highly prized. In addition, these formations have a cylindrical shape. Such tubes can be obtained by rolling up a graphite sheet, or grown from a specific catalyst. Carbon nanotubes, photos of which are presented below, have an unusual structure.

They come in different shapes and sizes: single-layer and multi-layer, straight and curved. Despite the fact that nanotubes look quite fragile, they are a strong material. As a result of many studies, it was found that they have properties such as stretching and bending. Under the influence of serious mechanical loads, the elements do not tear or break, that is, they can adapt to different voltages.

Toxicity

As a result of multiple studies, it was found that carbon nanotubes can cause the same problems as asbestos fibers, that is, various malignant tumors occur, as well as lung cancer. The degree of negative impact of asbestos depends on the type and thickness of its fibers. Since carbon nanotubes are small in weight and size, they easily enter the human body along with air. Next, they enter the pleura and enter the chest, and over time cause various complications. Scientists conducted an experiment and added nanotube particles to the food of mice. Products of small diameter practically did not linger in the body, but larger ones dug into the walls of the stomach and caused various diseases.

Receipt methods

Today, there are the following methods for producing carbon nanotubes: arc charge, ablation, vapor deposition.

Electric arc discharge. Obtaining (carbon nanotubes are described in this article) an electric charge in the plasma, which burns using helium. This process can be carried out using special technical equipment for producing fullerenes. But this method uses other arc burning modes. For example, it is reduced, and cathodes of enormous thickness are also used. To create an atmosphere of helium, it is necessary to increase the pressure of this chemical element. Carbon nanotubes are produced by sputtering. In order for their number to increase, it is necessary to introduce a catalyst into the graphite rod. Most often it is a mixture of different metal groups. Next, there is a change in pressure and spray method. Thus, a cathode deposit is obtained, where carbon nanotubes are formed. The finished products grow perpendicular to the cathode and are collected into bundles. They are 40 microns long.

Ablation. This method was invented by Richard Smalley. Its essence is to evaporate different graphite surfaces in a reactor operating at high temperatures. Carbon nanotubes are formed by the evaporation of graphite at the bottom of the reactor.

They are cooled and collected using a cooling surface. If in the first case, the number of elements was equal to 60%, then with this method the figure increased by 10%. The cost of the laser absolation method is more expensive than all others. As a rule, single-walled nanotubes are obtained by changing the reaction temperature.

Vapor deposition. The carbon vapor deposition method was invented in the late 50s. But no one even imagined that it could be used to produce carbon nanotubes. So, first you need to prepare the surface with the catalyst. It can be small particles of various metals, for example, cobalt, nickel and many others. Nanotubes begin to emerge from the catalyst layer. Their thickness directly depends on the size of the catalytic metal. The surface is heated to high temperatures, and then a gas containing carbon is supplied. Among them are methane, acetylene, ethanol, etc. Ammonia serves as an additional technical gas. This method of producing nanotubes is the most common. The process itself takes place at various industrial enterprises, due to which less financial resources are spent on producing a large number of tubes. Another advantage of this method is that vertical elements can be obtained from any metal particles that serve as a catalyst. The production (carbon nanotubes are described from all sides) was made possible thanks to the research of Suomi Iijima, who observed their appearance under a microscope as a result of carbon synthesis.

Main types

Carbon elements are classified by the number of layers. The simplest type is single-walled carbon nanotubes. Each of them is approximately 1 nm thick, and their length can be much greater. If we consider the structure, the product looks like wrapping graphite using a hexagonal mesh. At its vertices are carbon atoms. Thus, the tube has the shape of a cylinder, which has no seams. The upper part of the devices is closed with lids consisting of fullerene molecules.

The next type is multi-walled carbon nanotubes. They consist of several layers of graphite, which are folded into a cylinder shape. A distance of 0.34 nm is maintained between them. This type of structure is described in two ways. According to the first, multilayer tubes are several single-layer tubes nested inside each other, which looks like a nesting doll. According to the second, multiwalled nanotubes are a sheet of graphite that wraps around itself several times, similar to a folded newspaper.

Carbon nanotubes: application

The elements are an absolutely new representative of the class of nanomaterials.

As mentioned earlier, they have a frame structure, which differs in properties from graphite or diamond. That is why they are used much more often than other materials.

Due to characteristics such as strength, bending, conductivity, they are used in many fields:

• as additives to polymers;
• catalyst for lighting devices, as well as flat panel displays and tubes in telecommunication networks;
• as an absorber of electromagnetic waves;
• for energy conversion;
• production of anodes in various types of batteries;
• hydrogen storage;
• manufacturing of sensors and capacitors;
• production of composites and strengthening their structure and properties.

For many years, carbon nanotubes, whose applications are not limited to one specific industry, have been used in scientific research. This material has a weak position in the market, as there are problems with large-scale production. Another important point is the high cost of carbon nanotubes, which is approximately $120 per gram of such a substance.

They are used as a basic element in the production of many composites, which are used to make many sporting goods. Another industry is the automotive industry. The functionalization of carbon nanotubes in this area comes down to imparting conductive properties to polymers.

The thermal conductivity coefficient of nanotubes is quite high, so they can be used as a cooling device for various massive equipment. They are also used to make tips that are attached to probe tubes.

The most important application area is computer technology. Thanks to nanotubes, particularly flat displays are created. Using them, you can significantly reduce the overall dimensions of the computer itself, as well as increase its technical performance. The finished equipment will be several times superior to current technologies. Based on these studies, high-voltage picture tubes can be created.

Over time, the tubes will be used not only in electronics, but also in the medical and energy fields.

Production

Carbon tubes, the production of which is divided between two types, are unevenly distributed.

That is, MWNTs are produced much more than SWNTs. The second type is done in case of urgent need. Various companies are constantly producing carbon nanotubes. But they are practically not in demand, since their cost is too high.

Production leaders

Today, the leading place in the production of carbon nanotubes is occupied by Asian countries, which are 3 times higher than in other countries of Europe and America. In particular, Japan is engaged in the production of MWNTs. But other countries, such as Korea and China, are in no way inferior in this indicator.

Production in Russia

Domestic production of carbon nanotubes lags significantly behind other countries. In fact, it all depends on the quality of the research being conducted in this area. There are not enough financial resources allocated here for the creation of scientific and technological centers in the country. Many people are not accepting of developments in nanotechnology because they do not know how it can be used in industry. Therefore, the transition of the economy to a new path is quite difficult.

Therefore, the President of Russia issued a decree indicating the development paths for various areas of nanotechnology, including carbon elements. For these purposes, a special development and technology program was created.

To ensure that all points of the order were carried out, the Rusnanotech company was created. A significant amount from the state budget was allocated for its operation. It is she who should control the process of development, production and industrial implementation of carbon nanotubes. The allocated amount will be spent on the creation of various research institutes and laboratories, and will also strengthen the existing work of domestic scientists. These funds will also be used to purchase high-quality equipment for the production of carbon nanotubes. It is also worth taking care of those devices that will protect human health, since this material causes many diseases.

As mentioned earlier, the whole problem is raising funds. Most investors do not want to invest in scientific developments, especially for a long time. All businessmen want to see profits, but nanodevelopment can take years. This is what repels representatives of small and medium-sized businesses. In addition, without government investment it will not be possible to fully launch the production of nanomaterials.

Another problem is the lack of a legal framework, since there is no intermediate link between different levels of business. Therefore, carbon nanotubes, the production of which is not in demand in Russia, require not only financial, but also mental investments. So far, the Russian Federation is far from the Asian countries that are leading in the development of nanotechnologies.

Today, developments in this industry are carried out at the chemical faculties of various universities in Moscow, Tambov, St. Petersburg, Novosibirsk and Kazan. The leading producers of carbon nanotubes are the Granat company and the Tambov plant Komsomolets.

Positive and negative sides

Among the advantages are the special properties of carbon nanotubes. They are a durable material that does not collapse under mechanical stress. In addition, they work well in bending and stretching. This was made possible thanks to the closed frame structure. Their use is not limited to one industry. The tubes have found application in the automotive industry, electronics, medicine and energy.

A huge disadvantage is the negative impact on human health.

Particles of nanotubes entering the human body lead to the occurrence of malignant tumors and cancer.

An essential aspect is the financing of this industry. Many people do not want to invest in science because it takes a lot of time to make a profit. And without the functioning of research laboratories, the development of nanotechnology is impossible.

Conclusion

Carbon nanotubes play an important role in innovative technologies. Many experts predict the growth of this industry in the coming years. There will be a significant increase in production capabilities, which will lead to a decrease in the cost of goods. With decreasing prices, tubes will be in great demand and will become an indispensable material for many devices and equipment.

So, we found out what these products are.

Carbon nanotubes are known for their unique mechanical, electrical and thermal properties, suitable for a wide range of polymer applications. Young's modulus of 1000 GPa and tensile strength of 60 GPa were measured on the individual structure. These indicators are several orders of magnitude higher than those of conventional engineering plastics. High electrical and thermal conductivity were also established experimentally, with their values ​​approaching or exceeding those of metals. This combination of properties and product form, compatible with modern polymer processing technologies, ensures the creation of new structural materials.

Commercial Application
The use of carbon nanotubes to impart antistatic and conductive properties to polymers is now a commercial practice and is expanding into industries such as electronics and the automotive industry. Figure 1 shows a typical image of the conductivity of an engineering thermoplastic. The filling to achieve electrical transmission in the case of multi-walled carbon nanotubes can be 5-10 times lower than for conductive carbon black. Similar comparisons are made in thermosetting resins such as epoxy, but at significantly lower filling. This phenomenon can be explained by percolation theory: a path for electron flow is created when particles are very close to each other or have reached the percolation threshold. Fiber structures with a high ratio (length/diameter) increase the number of electrical contacts and provide a more uniform path. The geometric ratio of hydrocarbon nanotubes in the final product (such as injection molded parts) is typically greater than 100 compared to short carbon fibers (<30) и техническим углеродом (>1). This explains the lower dosage required for a given resistivity. Percolation behavior can vary depending on the resin type, viscosity, and polymer processing method.

Rice. 1. Dependence of electrical conductivity on the content of carbon fillers: carbon nanotubes, highly conductive carbon black, standard carbon black.

Reduced filler content can provide several benefits such as improved processability, surface appearance, reduced sagging, and increased ability to retain the mechanical properties of the original polymer. These advantages have enabled the introduction of multi-walled carbon nanotubes into conductive polymer applications, Table 1. In these applications, they can compete with additives such as highly conductive carbon black and carbon fibers on a cost/performance basis or on the basis of unique characteristics that are not possible achieve or match to product specifications.

Table 1. Commercial applications of conductive polymers with multi-walled carbon nanotubes.

The incorporation of multi-walled carbon nanotubes into plastics or elastomers relies on relatively standard devices used in rubber compounds and thermoplastics, such as fine screw extruders and closed rubber mixers. Nanocyl's multi-walled carbon nanotubes can be supplied in powder form (Nanocyl® 7000) or thermoplastic concentrates (PlastiCyl™).

Application of composite materials for structural purposes
The exceptional strength of carbon nanotubes has beneficial applications in the creation of various types of sporting goods based on carbon fiber and epoxy resin composite materials. To facilitate incorporation and improve bonding with the binder phase (such as epoxy or polyurethane), carbon nanotubes are typically chemically modified at the surface. Typical improvement measured on fiber reinforced composite material is 10 to 50% in strength and live load. This level of reinforcement can be significant for a given composite material, usually limited by the properties of the resin.

New developments
The network of exceptionally thin conductive structures, such as carbon nanotubes, also provides new opportunities in thin film technology, including antistatic clear and conductive coatings with permanent conductivity, improved mechanical properties and enhanced chemical resistance. Highly conductive transparent film technologies are currently being developed that will in the near future compete with metal oxide technologies, such as indium tin oxide sputtering technology, used today to make transparent electrodes in flat panel displays and more limited designs such as flexible displays.
A modern paper production technology using multi-walled carbon nanotubes has been developed. Such paper is used to create a more flexible thermal barrier coating to protect car mirrors from icing, underfloor heating and other heating devices.
Research is being conducted into new properties obtained by minor additions of multi-walled carbon nanotubes to polymers, such as fire resistance and anti-rot resistance, which could lead to the development of new products that are more compliant with modern environmental requirements and have improved performance compared to existing materials, subject to cost savings.

Reinforced elastomers
Carbon black and other powder fillers are widely used to reinforce rubber in tires and other industrial rubbers. The composition may contain a high loading of fillers to increase strength and stiffness to the required level (more than 50% by weight), but may lack elasticity in some applications. Replacing 5-10% infill with multi-walled carbon nanotubes such as Nanocyl® 7000 can provide high-performance elastomers with similar levels of strength and stiffness with improved elasticity, presenting a new balance of mechanical properties unmatched by traditional materials.

The use of carbon nanotubes for commercial purposes is now a reality and is attracting increasing attention. This means that they are accepted by industry as a value-added component that competes with other options that are regulated by industry standards. Research is currently underway into new beneficial and unpredictable properties of carbon nanotubes that will expand their penetration into the polymer industry.