Title page for ETD etd-110498-122417


Type of Document Dissertation
Author Nitowski, Gary Alan
Author's Email Address Gary.Nitowski@Alcoa.com
URN etd-110498-122417
Title Topographic and Surface Chemical Aspects of the Adhesion of Structural Epoxy Resins to Phosphorus Oxo Acid Treated Aluminum Adherends
Degree PhD
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Dillard, John G. Committee Co-Chair
Wefers, Karl Committee Co-Chair
Dillard, David A. Committee Member
Reynolds, William T. Jr. Committee Member
Ward, Thomas C. Committee Member
Wightman, James P. Committee Member
Keywords
  • phosphorous acid
  • aluminum surface treatment
  • vinylphosphonic acid
  • epoxy
  • adhesive bonding
  • joint durability
Date of Defense 1998-08-26
Availability unrestricted
Abstract
Structural adhesive bonding offers several advantages over other types of joining. These

include improved stress distribution and increased design flexibility. Adhesive bonding

is important in aerospace, automotive, and packaging applications. However, the full

potential of the technology has not been exploited because the understanding of the basic

mechanisms of adhesion and adhesion failure is incomplete.

This investigation elucidates the chemical and mechanical mechanisms responsible for

durable adhesion of epoxy resins to phosphorus oxo acid treated aluminum alloys. By

systematically altering the adherend surface chemistry, surface topography, and adhesive

formulation, combined with accelerated testing, the chemical and mechanical factors that

influence the properties of adhesively bonded aluminum are isolated and assessed.

It is postulated that a combination of two factors determines the strength and

environmental durability of epoxy-bonded aluminum. One is the formation of

hydrolytically stable, primary bonds between the adhesive and the adherend, and the

second is the hydrolytic stability of the surface oxide, which is always present on the

surface of aluminum and aluminum alloys.

These conditions can best be met by chemical pretreatment of the oxide surface, which

renders the oxide insoluble and creates, at the same time, functional surface sites. These

sites can form chemical bonds with reactive components of the adhesive.

Morphological and mechanical alteration of the metal surface oxide through hydroxide

formation requires liquid water. Liquid water can only form by capillary condensation in

interfacial gaps from molecularly diffusing water. A hydrolytically stable oxide will

prevent bond failure due to mechanical weakening of the substrate surface, while a high

density of hydrolytically stable surface bonding sites will minimize the occurrence of

capillary gaps at the interface, thus decreasing the formation of liquid water. It is shown

that highly chemically active, although not inherently stable, oxide surfaces can provide

environmentally stable adhesive bonds. Conversely, certain highly stable oxide surfaces

with few chemically active sites provide no environmental stability to adhesive joints,

regardless of the topography of the surface.

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