Identifier

etd-11122009-141820

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

Syntactic foams are composite materials in which the matrix phase is reinforced with hollow particles called microballoons. They possess properties such as low moisture absorption, low thermal conductivity and high damage tolerance because of their compositions. Traditionally, syntactic foams are used for many high strength applications and as insulating materials. But for applications demanding better heat dissipation from syntactic foam, conductive filler materials need to be added while maintaining its property of low density. Carbon nanotubes although extremely conductive, have issues of agglomeration in the matrix. In this research, a new approach to the problem of dispersion of nanotubes was attempted by growing the nanotubes on the surface of glass microballoons. S22 glass microballoons with low density were used in this work. Chemical vapor deposition was used for growing nanotubes on the microballoons using nickel as a catalyst. Nickel coating on microballoons was obtained via an electroless plating process. Observations were made on the nickel coating and nanotube growth processes with the help of a Scanning Electron Microscope (SEM). Thickness of the catalyst layer, growth temperature, gas flow rates and the quality of palladium activation were found to be the determining steps for nanotube growth. Transmission Electron Microscopy (TEM) was used to characterize the growth of nanostructures. Multi-walled carbon nanotubes of 6 – 20 nm were grown in this research. The thermal conductivity of nanotube-grown syntactic foam was tested on a Flashline thermal analyzer utilizing a flash method. For comparison purposes, plain and nanotube-mixed syntactic foams were fabricated and tested for conductivity. The effect of amount of nanotube and microballoon on the conductivity of the material was studied. The conductivity increments were low due to thermal boundary resistance occurring at the interface of nanotubes and resin. Nanotube-grown foams increase the thermal conductivity of plain syntactic foam by 86%, as opposed to nanotube-mixed ones which showed lower conductivity values than plain syntactic foam. TEM images showed that the mixing method had nanotubes being highly agglomerated whereas the growing method was successful in creating a well dispersed network of nanotubes.

Date

2009

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Woldesenbet, Eyassu

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