All about carbon fiber

Knowing everything about carbon fiber is very important for every modern person. Understanding the technology of carbon production in Russia, density and other characteristics of carbon fiber, it will be easier to understand the scope of its application and make the right choice. In addition, you should find out everything about putty and underfloor heating with carbon fiber, about foreign manufacturers of this product and about various fields of application.

The names carbon fiber and carbon fiber, and in a number of sources also carbon fiber, are very common. But the idea of ​​the actual characteristics of these materials and the possibilities of their use is quite different for many people. From a technical point of view, this material is assembled from threads with a cross section of not less than 5 and not more than 15 microns... Almost all of the composition is made up of carbon atoms - hence the name. These atoms themselves are grouped into crisp crystals that form parallel lines.

This design provides very high tensile strength. Carbon fiber is not a completely new invention. The first samples of a similar material were received and used by Edison. Later, in the middle of the twentieth century, carbon fiber experienced a renaissance - and since then its use has steadily increased.

The most important of the characteristics of carbon fiber remains its exceptional heat resistance... Even if the substance is heated up to 1600 - 2000 degrees, then in the absence of oxygen in the environment, its parameters will not change. The density of this material, along with the usual, is also linear (measured in the so-called tex). With a linear density of 600 tex, the mass of 1 km of web will be 600 g. In many cases, the elastic modulus of the material, or, as they say, Young's modulus, is also critically important.

For high-strength fiber, this figure ranges from 200 to 250 GPa. High modulus carbon fiber based on PAN has an elastic modulus of approximately 400 GPa. For liquid crystal solutions, this parameter can vary from 400 to 700 GPa. The modulus of elasticity is calculated based on the assessment of its value when stretching individual graphite crystals. The orientation of the atomic planes is established using X-ray diffraction analysis.

The default surface tension is 0.86 N / m. When processing the material to obtain a metal-composite fiber, this figure rises to 1.0 N / m. The measurement by the capillary ascent method helps to determine the corresponding parameter. The melting point of fibers based on petroleum pitches is 200 degrees. Spinning takes place at about 250 degrees; the melting point of other types of fibers directly depends on their composition.

The maximum width of carbon cloths depends on technological requirements and nuances. For many manufacturers, it is 100 or 125 cm. As for the axial strength, it will be equal to:

• for high-strength products based on PAN from 3000 to 3500 MPa;
• for fibers with significant elongation, strictly 4500 MPa;
• for high-modulus material from 2000 to 4500 MPa.

Theoretical calculations of the stability of a crystal under a tensile force toward the atomic plane of the lattice give an estimated value of 180 GPa.The expected practical limit is 100 GPa. However, experiments have not yet confirmed the presence of a level of more than 20 GPa. The real strength of carbon fiber is limited by its mechanical defects and the nuances of the manufacturing process. The tensile strength of a section with a length of 1/10 mm established in practical studies will be from 9 to 10 GPa.

The T30 carbon fiber deserves special attention. This material is mainly used in the production of rods. This solution is distinguished by its lightness and excellent balance. The T30 index denotes a modulus of elasticity of 30 tons.

Carbon fiber can be made from a wide variety of polymer types. The processing mode determines two main types of such materials - carbonized and graphitized types. An important distinction exists between fiber derived from PAN and different pitch types. Quality carbon fibers, both high strength and high modulus, can have different levels of hardness and modulus. It is customary to refer them to different brands.

Fibers are made in filament or bundle format. They are formed from 1000 to 10000 continuous filaments. Fabrics from these fibers can also be made, like tows (in this case, the number of filaments is even greater). The starting material is not only simple fibers, but also liquid crystal pitches, as well as polyacrylonitrile. The production process involves first the production of the original fibers, and then they are heated in air at 200 - 300 degrees.

In the case of PAN, this process is called pretreatment or fire resistance enhancement. After such a procedure, pitch gets such an important property as infusibility. The fibers are partially oxidized. The mode of further heating determines whether they will belong to the carbonized or graphitized group. The end of the work implies giving the surface the necessary properties, after which it is finished or sized.

Oxidation in air increases fire resistance not only as a result of oxidation. The contribution is made not only by partial dehydrogenation, but also by intermolecular crosslinking and other processes. Additionally, the susceptibility of the material to melting and volatilization of carbon atoms is reduced. Carbonization (in the high-temperature phase) is accompanied by gasification and the escape of all foreign atoms.

Their subsequent carbonization is carried out in a nitrogen environment at 1000 - 1500 degrees. The optimal level of heating, according to a number of technologists, is 1200 - 1400 degrees. High modulus fiber will have to be heated up to about 2500 degrees. At the preliminary stage, PAN receives a ladder microstructure. Condensation at the intramolecular level, accompanied by the appearance of a polycyclic aromatic substance, is "responsible" for its occurrence.

The more the temperature rises, the larger the structure of the cyclic type will be. After the end of the heat treatment according to the technology, the arrangement of molecules or aromatic fragments is such that the main axes will be parallel to the fiber axis. The tension prevents falling of the degree of orientation. The specific features of PAN decomposition during heat treatment are determined by the concentration of grafted monomers. Each type of such fibers determines the initial processing conditions.

Liquid crystal petroleum pitch needs to be kept for a long time at temperatures from 350 to 400 degrees. This mode will lead to condensation of polycyclic molecules. Their mass increases, and sticking together gradually occurs (with the formation of spherulites). If the heating does not stop, the spherulites grow, the molecular weight increases, and the result is the formation of a continuous liquid crystalline phase. Crystals are occasionally soluble in quinoline, but usually they do not dissolve both in it and in pyridine (this depends on the nuances of the technology).

Fibers obtained from liquid crystal pitch with 55 - 65% liquid crystals flow plastically. Spinning is carried out at 350 - 400 degrees. A highly oriented structure is formed by initial heating in an air atmosphere at 200 - 350 degrees and subsequent holding in an inert atmosphere. Fibers of the Thornel P-55 brand have to be heated up to 2000 degrees, the higher the modulus of elasticity, the higher the temperature should be.

Recently, scientific and engineering works are paying more and more attention to the technology using hydrogenation. The initial production of fibers is often accomplished by hydrogenating a mixture of coal tar pitch and naphthalate resin. In this case, tetrahydroquinoline should be present. The processing temperature is 380 - 500 degrees. Solids can be removed by filtration and centrifuge; then the pitches are thickened at an elevated temperature. For the production of carbon, it is necessary to use (depending on the technology) quite a variety of equipment:

• layers that distribute vacuum;
• pumps;
• sealing harnesses;
• work tables;
• traps;
• conductive mesh;
• vacuum films;
• prepregs;
• autoclaves.

The following carbon fiber manufacturers are leading in the global market:

• Thornell, Fortafil and Celion (United States);
• Grafil and Modmore (England);
• Kureha-Lone and Toreika (Japan);
• Cytec Industries;
• Hexcel;
• SGL Group;
• Toray Industries;
• Zoltek;
• Mitsubishi Rayon.

Today carbon is produced in Russia:

• Chelyabinsk plant of carbon and composite materials;
• Balakovo Carbon Production;
• NPK Khimprominzhiniring;
• Saratov enterprise "START".

Carbon fiber is used to make composite reinforcement. It is also common to use it to get:

• bi-directional fabrics;
• designer fabrics;
• biaxial and quadroaxial tissue;
• non-woven fabric;
• unidirectional tape;
• prepregs;
• external reinforcement;
• fiber;
• harnesses.

A rather serious innovation now is infrared warm floor. In this case, the material is used as a replacement for the traditional metal wire. It can generate 3 times more heat, in addition, energy consumption is reduced by about 50%. Lovers of modeling complex techniques often use carbon tubes obtained by winding. These products are also in demand by manufacturers of cars and other equipment. Carbon fiber is often used for hand brakes, for example. Also, based on this material, get:

• parts for aircraft models;
• one-piece hoods;
• bicycles;
• parts for tuning cars and motorcycles.

Carbon fabric panels are 18% stiffer than aluminum and 14% more than structural steel... Sleeves based on this material are needed to obtain pipes and tubes of variable cross-section, spiral products of various profiles. They are also used for the production and repair of golf clubs. It is also worth pointing out its use. in the production of especially durable cases for smartphones and other gadgets. Such products are usually of a premium character and have enhanced decorative qualities.

As for the dispersed graphite-type powder, it is needed:

• when receiving electrically conductive coatings;
• when releasing glue of various types;
• when reinforcing molds and some other parts.

Carbon fiber putty is better than traditional putty in a number of ways. This combination is appreciated by many experts for its plasticity and mechanical strength. The composition is suitable for covering deep defects. Carbon rods or rods are strong, lightweight and long lasting. Such material is needed for:

• aviation;
• the rocket industry;
• release of sports equipment.

By pyrolysis of carboxylic acid salts, ketones and aldehydes can be obtained.The excellent thermal properties of carbon fiber allow it to be used in heaters and heating pads. Such heaters:

• economical;
• reliable;
• are distinguished by impressive efficiency;
• do not spread hazardous radiation;
• relatively compact;
• perfectly automated;
• operated without unnecessary problems;
• do not spread extraneous noise.

Carbon-carbon composites are used in the production of:

• supports for crucibles;
• tapered parts for vacuum melting furnaces;
• tubular parts for them.

Additional areas of application include:

• homemade knives;
• use for a petal valve on engines;
• use in construction.

Modern builders have long used this material not only for external reinforcement. It is also needed to strengthen stone houses and swimming pools. The glued reinforcing layer restores the qualities of supports and beams in bridges. It is also used when creating septic tanks and framing natural, artificial reservoirs, when working with a caisson and a silo pit.

In the next video you will find more information on the production of carbon fiber.