(Dr. Jack Lackey, advisor)
"Fabrication and Analysis of Prosthetic Heart Valves Using Liquid Reagent CVD"
A chemical vapor deposition (CVD) furnace using a liquid reagent was designed and operated. Pyrolytic carbon coatings were successfully deposited on graphite and molybdenum substrates from benzene and cyclohexane precursors. The goal was to demonstrate the feasibility of using the liquid reagent CVD process to deposit pure pyrolytic carbon that possesses the microstructures and properties required for mechanical heart valves. Such valves are currently fabricated using a time consuming, conventional, gaseous reagent CVD process.
The correlations between deposition conditions, microstructure, and properties of the pyrolytic carbon were investigated. The crystallite size of the pyrolytic carbon was about 20-30 Å for a deposition temperature range of 950-1150°C. TEM micrographs revealed that the deposit was of the desired turbostratic nodular structure with low texture. Suitable densities were achieved. Reduced modulus and nanohardness were strongly dependent on the microstructure of the deposits. It is believed that both the high deposition rate and the unique fluid flow mode of the liquid reagent CVD process provide the possibility of forming small crystallite size and nearly isotropic pyrolytic carbon. Kinetics analyses were performed, and the apparent activation energy and pre-exponential constant were calculated for both benzene and cyclohexane. It was demonstrated that the hydrogen inhibition effect can be neglected for liquid reagent CVD process.