Publication Date

2009

Document Type

Honors Thesis

Department

Engineering

Abstract

The effect of changing different parameters involved in the chemical vapor deposition (CVD) process for the synthesis of novel carbons was studied. The parameters that were varied during this process were: the deposition substrate, the reaction time and gas concentrations. In addition, the presence of an Fe catalyst in the form of ferrocene was observed. The substrates used were type P silicon wafers and quartz slides. The time of the reaction was varied between 15 minutes and 3.5 hours. During this study, CH4 (0.8 - 20 sccm) was used as a carbon source, Ar (188 - 200 sccm) was used as an inert carrier gas and H2 (100 - 1000 sccm) was used to preserve the tetrahedral structure of CH4. To accurately measure and control the mass flow rate of gasses, three MKS mass flow controllers were installed and calibrated. Three type M100B mass flow controllers were used to control the CH4:H2 ratio to the levels of 0.002%, 0.004%, 0.01% and 0.1%. The reactions were run at a temperature of 850º C and a total pressure of 97kPa. Thermodynamical calculations were undertaken to predict the products of formation via FACT Sage 5.3.1. The thermodynamic equilibrium calculations were modeled for the C-H-Fe system, at temperatures between 0 and 1600º C and a total pressure of 97 kPa. The predictions show that graphite is the only phase of carbon that is thermodynamically stable, and the addition of hydrogen at ratio of 100:1 H2:CH4 to the reaction stabilizes the methane promoting the formation of C(s) only at temperature in excess of 1000º C. The presence of the ferrocene as a catalyst accelerates the reaction and yields Fe3C as a product of formation. The deposit's microstructure and crystal structure were analyzed using scanning electron microscopy, optical microscopy and X-ray diffraction. The deposits produced iii vary in dimensions and geometries, from spherical, hexagonal, and irregular to acicular. X-ray powder diffraction was used in this work to analyze the crystal structure of the CVD deposits. Powder diffraction patterns of graphite and diamond were collected as reference.

Language

English

Comments

ix, 95 p. : ill. (some col.) Honors Project-Smith College, Northampton, Mass., 2009. Includes bibliographical references (p. 91-95)

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