Carbon fiber, a material for the 21st century
Carbon Fiber (CF) is a material formed by fibers of 50-10 microns in diameter, composed mainly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the longitudinal axis of the fiber. The crystal alignment gives the fiber of high resistance depending on the volume (it makes it strong for its size). Several thousand carbon fibers are braided to form a thread, which can be used by itself or woven into a fabric.
The properties of carbon fibers, such as high flexibility, high strength, low weight, tolerance to high temperatures and low thermal expansion, make them very popular in the aerospace industry, civil engineering, military applications, motor sports along with many Another sports. It is marketed in the form of fabrics or felts. Its main characteristics are its resistance, its elegant appearance and its light weight. This polymer is obtained from another polymer called polyacrylonitrile, which consists of very thin strands of carbon (as thin as human hair) that are braided, which are twisted and grouped continuously for the formation of a strand of several strands , it is placed on a mold and on top of it a resin or plastic is poured to glue these woven threads and shape their diverse applications.
A little history:
Although carbon fiber is synonymous with the avant-garde, the origin of this material created by man goes back to the end of the 19th century. It is believed that it was Thomas Edison, inventor of the incandescent bulb, who created the first commercialized carbon fiber. In 1879, before the invention of the tungsten bulb, Edison manufactured the filaments of his bulbs with cotton threads or bamboo sheets, cut to obtain the necessary shape, and heated to the oven at very high temperatures. Cotton and bamboo are mainly made up of cellulose, a natural polymer rich in carbon, so the filaments were carbonized and left an exact copy with the original proportions of the initial material. Obviously, the quality of the carbon fiber that resulted from this rudimentary process is not close to that of modern carbon fiber composites.
In 1960 in Akio Shindo, Japan. A carbon fiber was produced from polyacrylonitrile (PAN) containing 55% carbon, which began to be used in the year 63 in the United Kingdom for the manufacture of aircraft. The company Roll-Roys applied it in the development of engines for airplanes, but it had disastrous results due to its high cost and variable quality, so finally the company Courtaulds finished as the only manufacturer of the product and it was improving only for the use in the aerospace and sports equipment area.
In 1970 the manufacture of carbon fibers from petroleum pitch is experimented, which results in a resistant fiber with 85% carbon. However, fibers from coal, oil and phenol resins have lower mechanical properties, although they are currently used for industrial fibers.
1985 Cleveland, Ohio. Roger Bacon creates high-performance carbon fibers by carbonizing rayon filaments from cellulose. This process gave very bad results.
Carbon fiber is used in the design and industry of:
Automobiles, boats, aircraft parts and spaceships, racing racing, bicycle rings, fishing rods, automobile springs, boat mast, blades for windmills in wind energy, laptop cases.
Almost all steel components are used in car construction, while using carbon fiber, the weight would be reduced by almost half since the chassis would be lighter, in addition smaller engines could be used or the use of electric motors.
Carbon fiber is used to reinforce materials such as reinforced plastics, it is also used in high temperature gas filtration, as a large surface electrode and impeccable resistance to corrosion and as an anti-static component.
This new material is composed mainly of carbon atoms. It is made up of carbon atoms joined together in crystals aligned with the longitudinal axis of the fiber, which gives it high strength as a function of volume.
It is five times stronger than steel, but with its same strength and lighter than aluminum; it has a unique microscopic crystal structure, since it is composed mainly of carbon atoms that are bound together in microscopic crystals aligned and parallel to the long axis of the fibers.
When carbon fiber is produced, thousands of thin strands of carbon are twisted together to form a thread, this thread is then woven into a flexible fabric that can be molded into many different shapes.
To examine carbon fiber is to study carbon
It is undoubtedly the most versatile of the elements known to man, as we can see by the fact that it is the basis of life on the planet. Carbon is part of all organic chemistry and 20 million known molecules, of which 79 percent classify them as organic. The carbon atom has 6 electrons, with the particularity that it can form 4 covalent bonds with other atoms, with which it acquires a tetrahedron geometry, which reminds us of the diamond.
Carbon can be combined with many elements such as N, S, O, Cl, Br and P that are thermodynamic ally stable, and with other carbon atoms with very strong bonds (the diamond) and can form long carbon chains.
Carbonization
To obtain a high strength fiber, the carbonization heat treatment is used: the PAN is heated to 2500-2000ºC in an oxygen-free atmosphere, the polymer chains are aligned to form graphene sheets, very thin, two-dimensional ribbons, and a tensile strength of 5,650 N / mm2.
Structure and properties of Carbon Fiber
Each strand of carbon filament is a set of many thousands of carbon filaments. One of these filaments is a thin tube with a diameter of 5.8 micrometers and is composed almost exclusively of carbon. The first generation of carbon fibers had a diameter of 7.8 micrometers. Later, fibers with diameters that are approximately 5 microns were reached.
The atomic structure of carbon fiber is similar to that of graphite, which consists of sheets of carbon atoms (sheets of graphene) arranged in a regular hexagonal pattern. The difference lies in the way in which the sheets are linked. Graphite is a crystalline material in which the sheets are stacked parallel to each other in a regular manner. The intermolecular forces between the sheets are relatively weak (Van der Waals forces), giving the graphite its soft and brittle characteristics.
Depending on the precursor to make the fiber, the carbon fiber may be turbostratic or graphitic, or have a hybrid structure with the parts present in both graphitic and turbostratic. In turbostratic carbon fiber sheets of carbon atoms are stacked randomly or irregularly. Carbon fibers derived from polyacrylonitrile (PAN) are turbostratic, while carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures above 2,200 ° C. Turbostratic carbon fibers tend to have high tensile strength, while a heat treatment in mesophase pitch derived from carbon fibers with a high Young's modulus (ie, low elasticity) and high thermal conductivity.
The miraculous fiber
The Japanese Association of manufacturers of CF call it: "Light in weight, strong and durable". Undoubtedly it has a great industrial future, even outside the aeronautical-space area. It is the technological material of the 21st century, precursor of nano materials. High price, but with a tendency to go down. Low density, exquisite mechanical properties, electrically conductive, high modulus elastic and tensile, resistant to heat, low thermal expansion, chemical stability, thermally conductive and also permeable to X-rays, an important property in medical equipment. The transport industry, especially aerospace has been looking for composite materials (C / C) for decades to replace metal. The objective is to reduce the vehicle weight and increase efficiency. The industry of satellites and military aircraft is ahead; the high price of the C / C is not an inconvenience.