Publication Date

2007

Document Type

Thesis

Committee Members

Sharmila Mukhopadhyay (Advisor)

Degree Name

Master of Science in Engineering (MSEgr)

Abstract

Carbon foam has many applications in the fields of thermal management, net-shape composites and electronic cooling due to its porous structure, low density, electrical and thermal conductivities. However it is prone to oxidation at high temperatures in air. Whereas some previous studies have reported oxidation protective coatings on other carbon structures such as graphite parts and fibers, there is very limited work on foam. Moreover, earlier methods have used vapor phase techniques such as Plasma Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD). There is no known study involving such coatings using simple scalable liquid phase method. This thesis reports our results on such coatings obtained on carbon foam. Boron Nitride was chosen as the coating material. Several solvents and processes were investigated. Finally a two step process using PVP binder in alcohol-based solution is found to be most effective. Unlike other available methods this technique does not involve toxic precursors or by-products. This method is simple and can be obtained at atmospheric pressure. Different coating combinations using various particle sizes were applied and their surface morphologies were studied using SEM (Scanning Electron Microscopy) and FESEM (Field Emission Scanning Electron Spectroscopy). It was observed that coating formed using 1μ BN followed by 0.7μ size BN particles has the best performance so far. The surface chemistry of this coating was studied using X-ray Photo Spectroscopy (XPS) and found to be that of pure BN after heat treatment. This coating was tested on several grades of aerospace foams having different porosities and cell sizes. The testing shows that this layer enhances the oxidation resistance of all foams to a certain extent. However it is most effective on the foams that have ridged ligaments compared to those having smooth ligaments. On carbon foams having high surface roughness this layer could suppress oxidation even at 800 C and enhance the survivability by 333%. This coating approach therefore shows promise as a scalable, environmentally friendly way of inhibiting oxidation in porous carbon structures.

Page Count

109

Department or Program

Department of Mechanical and Materials Engineering

Year Degree Awarded

2007

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