On March 18 of the year 1958, Roger Bacon filed a patent application entitled "Filamentary Graphite and Method for Producing the Same", which would issue in 1960 as U.S. Patent No.: 2,957,756. Bacon had discovered how to make high performance carbon fiber, the strongest material known to mankind (on a per weight basis). This discovery (sometimes referred to as "Bacon's Breakthrough") transformed material science and ushered in the modern era of carbon fiber. The discovery also earned Bacon a place in the Inventor's Hall of Fame and the Benjamin Franklin Medal for Mechanical Engineering.
At the time he made his discovery, Bacon was working for the Union Carbide Corporation in their Parma, Ohio research facility, just outside of Cleveland. Bacon was a native of the Cleveland area and had recently received his PhD in physics from the Case Institute of Technology, which would later merge with the Western Reserve University to form Case Western Reserve University.
At the Parma facility, Bacon was tasked with measuring the triple point of carbon, which is the temperature and pressure where solid, liquid and gas are in thermodynamic equilibrium. The equipment he used was similar to the carbon arc streetlamps that were popular in the late 1800s, but utilized much higher temperatures and pressures. Inside a closed pressure vessel filled with Argon gas, a positive upper electrode composed of graphite was struck against a lower carbon block to generate an arc in-between. DC current was fed to the electrode to maintain the arc and to achieve a temperature in a range of 3500 to 4000 degrees Kelvin.
Bacon found that if he kept the vessel pressure in a particular range below 1470 psi (the triple point), graphite would vaporize from the tip of the upper electrode and directly condense to a solid on the carbon block. This pressure range was between 1150 psi and 1400 psi. The graphite that was deposited on the carbon block was generally cylindrical and had a diameter slightly larger than the upper electrode. The deposit, which Bacon called a "boule", grew like a stalagmite at the rate of about one-half inch per minute until it reached a length of five or six inches.
When Bacon broke the boule into two pieces, he found hundreds of "whiskers" extending from the exposed surfaces of the broken halves. In each half of the boule, portions of the whiskers remained embedded in the boule, while other portions of the whiskers had pulled out of the other half of the boule so as to protrude from the exposed surface. Some of these whiskers protruded up to 3 cm from the exposed surfaces, while the diameter of the whiskers ranged from a fraction of a micron to five microns. However, what was really amazing about the whiskers was their strength. In the '756 patent, Bacon noted that the tensile strength of the filaments was "about three million pounds per square inch with strains of approximately 0.4 percent", which converts to 20.68 GPa.
Bacon stated that "[a]fter studying the heck out of these things, I finally published a paper in the Journal of Applied Physics in 1960". This paper, entitled "Growth, Structure, and Properties of Graphite Whiskers" provided further information on the strength of the whiskers, noting that the whiskers had a tensile strength of 2000 kg mm-2 (19.61 GPa) and a minimum Young's modulus of 7X 1012 dynes cm-2 (700 GPa). Tensile strength measures the amount of force with which a material can be pulled before it breaks, while Young’s modulus is a measure of a material’s ability to resist elongation under load. By comparison, typical steel has a tensile strength of 1-2 GPa and a Young’s modulus of 200 GPa.
One of the most intriguing aspects of Bacon's paper was its discussion of the morphology of the whiskers. Based on images from an electron microscope, Bacon described the whiskers as being composed of concentric "tubes" and hypothesized that the structure of the whiskers was actually that of a "scroll" in which "a graphite sheet (presumably consisting of several monolayers) overlaps itself and continues to wind around the whisker axis many times". From the standpoint of growth mechanism, Bacon was more comfortable with this hypothesis than one in which the graphite sheet had "joining opposite edges after a single turn to form a perfect cylinder". This disclosure in the Bacon paper suggests that Bacon may have been the first to produce carbon nanotubes, but did not recognize it due to the limitations of the electron microscope he was using. Bacon acknowledged this possibility, stating "I may have made nanotubes, but I didn't discover them." It wasn't until 1991 that the existence of carbon nanotubes was definitively established by the Japanese researcher, Sumio Iijima.
After his initial breakthrough, Bacon continued to work on carbon fibers. In 1964, Bacon, together with co-worker Wesley Schalamon, invented a method by which carbon fiber could be commercially produced for the first time. Pursuant to this method, rayon fiber was stretched at high temperatures (more than 2800 ºC), thereby orienting the graphite layers to lie nearly parallel with the fiber axis. A series of high-modulus carbon fibers produced by Bacon's hot-stretching process were sold by Union Carbide under the "Thornel" trademark. One of the first uses of the Thornel carbon fiber was in a resin used to form the leading edges of the wing tips of the F-5 jet fighter. Other military uses of the carbon fiber followed.
Bacon worked with carbon fiber until his retirement in 1998. In 2003, the American Chemical Society recognized the development of carbon fibers as a National Historic Chemical Landmark, and in 2016, Bacon was inducted into the National Inventors Hall of Fame.