The atomic structure and roughness on the surface of a carbon fiber have a great effect on the degree of bonding of that fiber in a carbon fiber composite. Although there have been many studies on the bulk structure of these fibers, this is the first study dealing with the atomic surface structure of several carbon fibers. With the advent of the scanning tunneling microscope (STM), it is now possible to study both the roughness and structure of these fibers on the atomic scale. Type II PAN based fibers were found to have a rougher surface than type II pitch-based fibers. Similar to what has been observed in the interior of pitch fibers, the percentage of graphitic structure on the surface increased with the degree of heat treatment and with the modulus of the fiber.
The vibrational excitation of H F and DF and the energy transfer efficiencies for various collision partners were investigated over the temperature and pressure ranges of 1400°K to 4100°K and 0.1 to 0.3 atm, respectively. The extent of excitation was determined as a function of time by continuously monitoring the infrared emission intensity at the center of the 1-0 vibration-rotation band of the molecule. Collisional efficiencies of HF, NB, 02, F, C1, and DF in relaxing H F and of DF, HF, and Nf in relaxing DF are reported. A comparison with relaxation data for pure H F taken at lower temperature suggests that long-range attractive forces are mechanistically of major importance in the relaxation process. The relatively high efficiency of atomic chlorine in relaxing HF, i.e., (TP)HF-HF/ ( T P ) H F -c~ 2 5 at 3000°K is discussed in terms of our previous result for atomic fluorine, i.e., (TP)HF-HF/(TP)HF-F = 18.
The catalytic efficiencies of H20, D20, NO, and HCI in the vibrational relaxation of HF and of NO in the vibrational relaxation of DF were investigated over the temperature and total pressure ranges of 1000 to 4100 0 K and 0.1 to 0.3 atm, respectively. Measurements were made in an Ar diluent behind incident shock waves. The extent of vibrational excitation in HF was determined as a function of time by continuously monitoring the infrared emission intensity at 4150±200 em-I. Water appears to relax HF principally by means of a direct transfer of vibrational energy (V-V) between the collision partners. Furthermore, its collisional efficiency was found to be in fair agreement with the results reported by others for the analogous process of HCI relaxation by H20. Nitric oxide was found to be at least an order-ofmagnitude more efficient as a collision partner in the vibrational relaxation of HF than is known for either of the molecules N2 or O2. A small amount of data regarding the effect of HCI upon the vibrational relaxation of HF was collected. Within the temperature range considered, its catalytic efficiency was found to be comparable to that of HF itself.
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