Carbon Fibers

 

Carbon Fibers

Carbon fiber is a super strong material that is extremely lightweight. It is five times as strong as steel, two times as stiff, yet weighs about two-thirds less. Carbon fiber is basically very thin strands of carbon (even thinner than human hair). The strands can be twisted together, like yarn and then be woven together, like cloth. To make carbon fiber take on a permanent shape, it can be laid over a mold and coated with a stiff resin or plastic. Carbon fiber can also be defined as a fiber containing at least 92 wt % carbons.

Carbon fibers are a new breed of high-strength fiber. It came into existence in 1879 when Edison took out a patent for the manufacture of carbon filaments suitable for use in electric lamps. However, in the early 1960s, when there was a need f of the aerospace industry – especially for military aircraft – for better and lightweight materials, successful commercial production started.

In recent decades, carbon fibers have found wide usage in aeronautics, athletic performance, automobiles, building structures and, of course, musical instruments. Carbon fibers are used in composites with a lightweight matrix.

Carbon fiber composites are ideally suited for applications where strength, stiffness, lower weight, and outstanding fatigue characteristics are critical. They are used in the occasion where high temperature, chemical inertness, and high damping are important. They have been extensively used in composites in the form of woven textiles, prepregs, continuous fibers/roving, and chopped fibers. The composite parts can be produced through filament winding, tape winding, protrusion, compression molding, vacuum bagging, liquid molding, and injection molding.

There are two most important precursors in the carbon fiber industry are polyacrylonitrile (PAN) and mesophase pitch (MP). The structure and composition of the precursor affect the properties of the resultant carbon fibers significantly. Although the essential processes for carbon fiber production are similar, different precursors require different processing conditions in order to achieve improved Performance.

Examples of Application

• Aerospace – flights, rockets, satellites
• Environment and Energy-related – wind power blade, tube power tank, battery charging flywheel, fuel cell, tidal power blade, the electric cable core
• Auto-mobile – hood, roof, propeller shaft, body panel for the bus, compressed natural gas tank
• Industrial use- the body of trains, x-ray top panel, pc housing, robot hand for liquid crystal panel, bridge pier reinforcement
• Sports material – fishing rod, bicycle, hockey stick, racket, golf shaft.

Benefits of Carbon fiber

The potentially low-cost carbon fiber composites will be in a position to provide enormous advantages to a number of technologies for current and future everyday life applications, including a number of advanced technologies that are not currently commercially feasible. Lightweight components for automobiles, buses, trains, aircraft, ships, and applications including lightweight panels and load-bearing structures could result in weight savings, leading to a major saving in the nation’s and world’s energy consumption.

Low-cost carbon fiber is a national goal towards accomplishing a number of manufacturing technological breakthroughs.

Difficulties of Carbon Fiber

• Cost is the main hurdle carbon fiber will have to overcome before it can provide a viable energy solution.
• The second hurdle is waste disposal. When a typical car breaks down, its steel can be melted and used to construct another car (or building, or anything else made of steel). Carbon fiber can’t be melted down, and it’s not easy to recycle. When it is recycled, the recycled carbon fiber isn’t as strong as it was before recycling.
• Lack of high-speed composite fabrication techniques

Classification of carbon fiber

Based on modulus, strength, and final heat treatment temperature, carbon fibers can be classified into the following categories:

Based on carbon fiber properties, carbon fibers can be grouped into:

• Ultra-high-modulus, type UHM (modulus >450Gpa)
• High-modulus, type HM (modulus between 350-450Gpa)
• Intermediate-modulus, type IM (modulus between 200-350Gpa)
• Low modulus and high-tensile, type HT (modulus < 100Gpa, tensile strength > 3.0Gpa)
• Super high-tensile, type SHT (tensile strength > 4.5Gpa)

Based on precursor fiber materials, carbon fibers are classified into:

• PAN-based carbon fibers
• Pitch-based carbon fibers
• Mesophase pitch-based carbon fibers
• Isotropic pitch-based carbon fibers
• Rayon-based carbon fibers
• Gas-phase-grown carbon fibers

Based on final heat treatment temperature, carbon fibers are classified into:

• Type-I, high-heat-treatment carbon fibers (HTT), where final heat treatment temperature should be above 2000°C and can be associated with high-modulus type fiber.
• Type-II, intermediate-heat-treatment carbon fibers (IHT), where final heat treatment temperature should be around or above 1500?C and can be associated with high-strength type fiber.
• Type-III, low-heat-treatment carbon fibers, where final heat treatment temperatures not greater than 1000?C. These are low modulus and low strength materials.

Manufacturing of Carbon fibers

Carbon fiber is a super strong material that is extremely lightweight. Carbon fibers generally have excellent tensile properties, low densities, high thermal and chemical stabilities in the absence of oxidizing agents, good thermal and electrical conductivities, and excellent creep resistance. Therefore Carbon fiber is enabling advancement in aeronautics, athletic performance, automobiles, building structures and, of course, musical instruments.

Carbon fibers are manufactured by a controlled pyrolysis of stabilized precursor fibers. First Oxidization process is done wherein the stabilization of precursor fibers at about 200-400 °C in air is done. Then carbonization is done wherein these fibers which are stabilized and infusible are treated at a high temperature of about 1,000 °C in an inert atmosphere to remove hydrogen, oxygen, nitrogen, and other non-carbon elements.

Then graphitized is done on those carbonized fibers at an even higher temperature up to around 3,000 °C to achieve higher carbon content and higher Young’s modulus in the fiber direction. The properties of the resultant carbon/graphite fibers are affected by many factors such as crystallinity, crystalline distribution, molecular orientation, carbon content, and the number of defects. The resulting carbon fibers are then post-treated to improve their adhesion to composite matrices.