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
- adhesive bonding
- joint durability
Date of Defense 1998-08-26 Availability unrestricted AbstractStructural 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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