Ph.D. Thesis Defense by Daniel Jean

(Dr. Jack Lackey, advisor)

"Design and Operation of an Advanced Laser Chemical Vapor Deposition System with On-Line Control"

Abstract

Solid freeform fabrication (SFF) from the gas phase holds great promise as an extremely flexible fabrication technique applicable to high precision small parts containing multiple materials. One of these fabrication techniques is pyrolytic Laser Chemical Vapor Deposition (LCVD) which combines gaseous reactants with the heat from a laser to selectively deposit solid material.

Although the potential for this technology is great, the LCVD process is inherently unpredictable. Deposit nucleation and growth is heavily dependent on the substrate temperature, which can vary by more than an order of magnitude over the width of the laser spot. Changes in conductivity, reflectivity, and convection all affect the spot temperature leading to an unstable process.

This research was focused on the design and operation of an LCVD system with an emphasis on process control. A thermal imaging camera was used in conjunction with customized Labview software to control the temperatures in the LCVD process. The LCVD reaction was successfully controlled to produce carbon fibers and carbon walls from methane and propylene precursors. The growth kinetics of the carbon fibers were further explored to determine the activation energy of pyrolytic carbon growth from methane and propylene. The successfully grown carbon walls and fibers serve as the building blocks for complex structures with intricate geometries and multiple matierials.