Date of Award

Fall 2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Yuri Lvov

Abstract

In this study we have explored the applications of halloysite clay nanotubes as a nanocontainer. Halloysite nanotubes are used as a storage unit for anticorrosion agents, flame retardants, and a dopant to extend the curing time for geopolymer composites. Halloysite is a naturally occurring clay mineral with a chemical formula of Al2Si2O 5(OH)4 · 2 H2O and is identical to kaolinite with the exception that it holds an additional water monolayer in its interlayered spaces. Upon heating at higher temperatures, halloysite loses the additional water monolayer, and this variant known colloquially as "meta-halloysite" has a chemical formula of Al2Si2O5(OH) 4 [1][3].

This study has been divided into five sections. The first section explores the implementation of acid etching for interlayered alumina to increase the loading efficiency of the halloysite. Halloysite is mixed with the sulfuric acid at 0.5 M, I M and 2 M concentrations at varying temperature. It is observed that the alumina that composes the halloysite is degraded faster at temperatures above room temperature and at higher concentrations of sulfuric acid.

The second section addresses the application of halloysite as a nanocontainer for the anticorrosion agents for the protection of ASTM A366 steel plates. Halloysite nanotubes are loaded with different types of anticorrosion agents, and are then admixed with an acrylic paint. Samples are exposed to a saline environment for one month. Compared to the controlled samples, halloysite loaded with corrosion inhibitors are found to enhance self-healing. This makes halloysite nanotubes a strong candidate for self-healing composites.

In the third section, controlled release of dodecylamine from halloysite nanotubes is used in the implementation of metal-organic and polymeric stoppers. Different types of metal stoppers and polymeric stoppers are analyzed and release studies for dodecylamine are performed in water and paint thinner.

In the fourth section, halloysite is explored as a flame retardant. Halloysite nanotubes are mixed with latex paint in concentrations of 5 wt% and 7 wt%, and the samples are tested for flame retardancy by exposing them to a flame torch following the ASTM E84 standard. Simultaneously, paint is mixed with a commercial flame retardant additive and the results are compared pre and post-flame exposure for both samples, with and without halloysite mixed paint.

In the final section, halloysite nanotubes used to extend the curing time of geopolymer samples can be achieved for the fly ash samples with a higher calcium content. High calcium content fly ash samples set faster than normal fly ashes. Halloysite coating increases the curing time, therefore giving ample time for the cement sample to flow and set in any desired shape. Utilizing the Layer-by-Layer (LbL) technique, fly ash particles are coated with halloysite, and the curing time is analyzed using Theological testing at room temperature and at 100° C. The coating of halloysite on the fly ash particles is characterized with SEM and Zeta-potential resulting in an optimized shell coating on the fly ash. An extension of curing time from 2 to 8 hrs is reached which is patented (pending) as an important technological development in this new constructional material.

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