Monday, September 20, 2010

Carbon Fibers: A Wonderful Material for the Composites Industry

Carbon fibers are a new class of high-strength performance materials for the composites industry. No doubt, carbon fibers have proven itself strong contender in the composites industry on the basis of high performance, light weight and excellent strength characteristics and high mechanical strength. The demand for carbon fibers has been steadily growing since the fiber was launched into the market about forty years ago. Even now, industries are exploring a variety of new applications made possible by the fibers.
Carbon fibers have been described as a fiber containing at least 90% carbon obtained by the controlled pyrolysis of appropriate fibers. The existence of carbon fiber came into existence in late 1879 when Edison took out a patent for the manufacture of carbon filaments suitable for use in electric lamps. However, it was only in the early 1960s when successful commercial production was started, as the requirements of the aerospace industry - especially for military aircraft – driven by the need for better and lightweight materials became of paramount importance. It was in the early 1960s when successful commercial production with carbon fiber was started as the requirements of the aerospace industry, especially for rockets and space capsules by NASA, required better and lightweight materials. The quantities were very small and price was $300 per pound. Nevertheless, as producers gained experience, the price of the material fell to the more reasonable $100-$150 a pound. And as that happened, the use of these composites slowly spread to military aircraft and then to commercial aircraft which then became an important driver of price. Over the past few years, the market has spread to sporting goods, where price was not a major issue because of perceived performance benefits. In 1980, the consumption of carbon fiber was only 4.5 million lbs. In 1995 it became more than 22 million lbs, and in 2000, more than 38 million lbs and in 2008 it was approx 60 million lbs.
Carbon fibers are generally categorized based on strength, modulus, tow size, and precursor type. In terms of modulus, they are categorized as standard modulus or intermediate modulus or high modulus fiber. There are also PAN based carbon fibers and pitch based carbon fibers. In the industry, consumption of  PAN based cabon fibers are higher compared to pitch based carbon fibers due to cost and  high cost pitch based carbon fibers are only used in places where low cost PAN based carbon fibers are being unable to meet the required properties.
Some of the categories are listed below.
  • Tensile Strength - 500 to over 900 ksi
  • Tensile Modulus - Standard (3k-24k) 33 Msi
-    Intermediate (6k-24k) 40-45 Msi
-    High (6k-24k) > 45 Msi
  • Tow Size - Small tow (1k-24k) vs. large tow (48K-320k)
  • Sizing Type - Resin compatibility
  • Application - Aerospace vs. commercial
Based on carbon fiber properties, carbon fibers can be grouped into:
  • Ultra-high-modulus, type UHM (modulus >435Gpa)
  • High-modulus, type HM ( modulus between 350-435Gpa )
  • Intermediate-modulus, type IM (modulus between 200-350Gpa)
  • Standard-modulus, (100-200Gpa)
  • 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 basically low modulus and low strength materials. 

The consumption of carbon fibers is growing day by day.Industrial and commercial aerospace applications will drive the growth of carbon fiber. Industrial applications are obviously the segment that has developed most in the past five years and these are likely to grow the most in the years to come. Such strong growth can be explained by the fact that there are a large number of highly promising projects like wind energy, pressure vessels and rollers, and industries like transportation, marine, civil engineering, offshore and more would need high performing material for competitiveness. Over recent years, the wind energy industry has become a significant user of composite materials. Significant research is being carried out for the use of carbon fiber in wind turbine applications. The two market leaders are Vestas and Gamessa, both of whom are already using carbon fibers in significant quantity for the making of large production turbine blades. The infrastructure rehabilitation industry is using carbon fiber for the construction of freeway column, parking structures, bridges, etc. This segment is also growing very fast. Filament winding and procured lamination is used for the manufacturing of the structures. The offshore oil industry uses carbon fiber for making the riser, tether, choking keel line etc.