Title: ELECTROSTATIC METHODS TO CONTROL PLACEMENT AND ORIENTATION OF SHORT GRAPHITE FIBERS. Final Report.

The oxidation behavior of a novel carbon fiber has been determined using a Thermogravimetric Analysis (TGA) technique in flowing air (52 ml/min) at temperatures ranging from 500 to 1100 C. The oxidation rates of three preparations of vapor grown carbon fiber (VGCF) are compared to PAN fiber. At 500 C, the oxidation rate of the as-grown fiber is comparable to PAN fiber, and the oxidation rate of the as-grown carbon fiber is higher than that of the PAN fiber at all temperatures above 500 C. The oxidation behavior of annealed VGCF is very much different from that of the as-grownmore » fibers. There is essentially no oxidation observed for the annealed fiber at 500 C in air. The oxidation rate of the annealed fiber at 700 - 1100 C is much lower than that of the as-grown fiber. Boronated VGCF shows even higher oxidation resistance compared to PAN fiber, as-grown VGCF, and annealed VGCF at 500 C to 700 C. Experimental results demonstrate the feasibility of VGCF-reinforced composites for operating temperatures up to 900 K.« less

This paper presents carbon fiber composites which are rendered flexible by the addition of exfoliated graphite. This new material comprises exfoliated graphite and carbon fibers disposed in separate portions of the structure, preferably in separate layers. Bonding the structure into a unitary mass is a binder, preferably thermosetting in nature, which impregnates the composite structure. 3 refs., 7 figs., 3 tabs.

The program to study the effect of accidentally released carbon fibers on electrical power equipment consisted of determining the vulnerability of system outage rates to carbon fiber contamination, and performing tests to quantitize the contamination required to cause flashover of external insulation. Part One of this final report describes an assessment of the vulnerability of power systems to accidentally released fibers from a composite burn. The assessment describes the effect of carbon fibers on individual component failure rates and discusses the effect the change in component failure rates has on the power system reliability. Part Two describes in detail testingmore » performed to determine the vulnerability of external insulation to carbon fiber contamination. Testing consisted of airborne contamination tests on distribution insulators, limited tests on suspension insulators which are commonly used for transmission class voltages, and various tests to quantify the influence of fiber length, voltage stress, etc. on flashover characteristics. The data obtained and analysis performed during this project show that the change of system reliability due to an accidental release from burned carbon fiber composite is negligible.« less

Goal was to explore the utility of coal-based pitch precursors for use in ultra high thermal conductivity carbon (graphite) fibers. From graphite electrode experience, it was established that coal-based pitches tend to form more highly crystalline graphite at lower temperatures. Since the funding was limited to year 1 effort of the 3 year program, the goal was only partially achieved. The coal-base pitches can form large domain mesophase in spite of high N and O contents. The mesophase reactivity test performed on one of the variants of coal-based pitch (DO84) showed that it was not a good candidate for carbonmore » fiber processing. Optimization of WVU`s isotropic pitch process is required to tailor the pitch for carbon fiber processing. The hetero atoms in the coal pitch need to be reduced to improve mesophase formation.« less

Titanium diboride and zirconium diboride composites containing 'Thornel' 50 graphite fibers, silicon carbide whiskers, and 'Zircar' zirconium oxide fibers were fabricated by hot-pressing. In all composites fabricated to near theoretical density, degradation of the fibrous component occurred. The degradation is a recrystallization process, rather than a chemical interaction between the fibers and the matrix components. Recrystallization took place in each of the types of fibers, including 'Thornel' 50 fibers coated with TiC and TiB/sub 2/. In diboride composites containing SiC whiskers, the recrystallization of the whiskers was greatly reduced by using large diameter (>5 micrometers) whiskers. The strength of compositesmore » containing the undegraded SiC whiskers, however, was less than that of the unreinforced diboride matrix. The strongest zirconium diboride composites were fabricated with 'Zircar' stabilized zirconia fibers. The average strength of the strongest 'Zircar'--ZrB/sub 2/ composite was 81,000 psi. The composition of the strongest composite was 64 volume percent ZrB/sub 2/ powder, 16 volume percent SiC powder, and 20 volume percent 'Zircar' ZrO/sub 2/ fibers. (auth)« less