Precision LCVD System Design with Real Time Process Control

A Laser Chemical Vapor Deposition (LCVD) system was designed using a fixed 100 Watt C02 laser focused on a moveable substrate. Temperature and height measurement devices monitor the reaction at the point of deposition to provide feedback for controlling the process. The LCVD system will use rapid prototyping technology to directly fabricate fully threedimensional ceramic, metallic, and composite parts of arbitrary shape. Potential applications include high temperature structures, electronic/photonic devices, and orthopaedic implants.Mechanical Engineerin

Silicon Carbide Growth Using Laser Chemical Vapor Deposition

Silicon Carbide (SiC) has been grown from methyltrichlorosilane (MTS) and hydrogen using the Georgia Tech Laser Chemical Vapor Deposition (LCVD) system. A morphology study of LCVD-SiC fibers and lines was completed. Graphite and single crystal silicon were used as the substrates. In order to provide guidance to future growth of SiC, thermodynamic calculations for the C-H-Si-Cl system were performed using the SOLGASMIX-PV program.Mechanical Engineerin

Thermal, Fluid, and Mass Transport Modeling of a Gas-Jet Reagent Delivery System for Laser Chemical Vapor Deposition (LCVD)

A gas-jet reagent delivery system for laser chemical vapor deposition (LCVD) is modeled with respect to heat transfer, fluid flow, and mass transport. A commercial package was used to model the geometry and flow field surrounding an LCVD reaction zone. The deposition temperature was analyzed for various materials and flow conditions. The forced flow environment was compared against buoyancy-driven flow, which is more typical of a statically filled chamber. A finite difference code was also developed to analyze the effect of the gas-jet on the concentration gradients above the deposition zone.This work was supported by the National Science Foundation, the Engineering Research Program of the Office of Basic Energy Sciences at the U. S. Department of Energy and the Georgia Institute of Technology with significant input from Dr. Andrei Fedorov.Mechanical Engineerin

Fabrication of Advanced Thermionic Emitters Using Laser Chemical Vapor Deposition-Rapid Prototyping 498

Laser Chemical Vapor Deposition-Rapid Prototyping (LCVD-RP) is a relatively new manufacturing process. Its capabilities are ideally suited for the manufacturing of a type of electron emitter called an integrated-grid thermionic emitter. The integrated-grid thermionic emitter is composed of wagon wheel-like structures of alternating layers of boron nitride and molybdenum on tungsten. The goal of this paper is to determine the feasibility of using LCVDRP technology to manufacture advanced thermionic emitters.Mechanical Engineerin

Heat Transfer Analysis of a Gas-Jet Laser Chemical Vapor Deposition (LCVD) Process 461

This paper describes the development of a computer model used to characterize the heat transfer properties of a gas-jet LCVD process. A commercial software package was used to combine heat transfer finite element analysis with the capabilities of computational fluid dynamic software (CFDS). Such a model is able to account for both conduction and forced convection modes of heat transfer. The maximum substrate temperature was studied as a function of laser power and gas-jet velocity.Mechanical Engineerin

Fabrication of Multi-Layered Carbon Structures Using LCVD

Others have used Laser Chemical Vapor Deposition (LCVD) to create 3-D fibrous structures and helical springs. Current research efforts focus on the creation of more advanced three-dimensional carbon objects through the use of multi-layered deposition. Multi-layered structures require an understanding of interlayer adhesion and the propagation of geometric anomalies through multiple layers. An important aspect in minimizing these shape anomalies is the implementation of closed loop temperature control. Several laminated carbon structures are presented with discussions and observations about the fabrication process and visual characteristics of each. The major issues in using LCVD to create multi-layer carbon structures are addressed.McDonald Observator

Grade Inflation at Georgia Tech

Abstract Data showing an increase in grade point average of 0.41 over the past 30 years at the Georgia Institute of Technology were presented. The GPA increased for virtually all departments. Graduate school GPA's also increased. Several unexpected factors were shown to influence grades. For example, Summer school grades were higher than for other terms. Possible causes and consequences of increasing GPA's are reviewed as well as actions which may be warranted to permit return to a grading system that permits greater differentiation between students' performance

CVI of silicon carbide

Issued as final repor

Laminated matrix composites

Issued as Monthly progress reports [nos. 1-5], and Final report, Project E-25-A2