TY - JOUR
T1 - Effect of anodic aluminum oxide chemistry on adhesive bonding of epoxy
AU - Abrahami, Shoshan
AU - Hauffman, T.
AU - de Kok, JMM
AU - Mol, Arjan
AU - Terryn, Herman
PY - 2016
Y1 - 2016
N2 - The transition to Cr(VI)-free production is a great challenge in the global aerospace industry that currently still relays on it for the preparation of aluminum for bonding. Proper surface pretreatment is a prerequisite for strong and durable adhesive joint. Despite decades of experience, the nature and contribution of the different adhesion forces between the aluminum and organic adhesive remain under discussion. Herein we studied the adhesion of epoxy resin as a function of the surface chemistry of barrier-type anodic oxides prepared in sulfuric acid (SAA), phosphoric acid (PAA), and mixtures of phosphoric–sulfuric acids (PSA) and chromic acid (CAA) at different anodizing temperatures. X-ray photoelectron spectroscopy (XPS) data measured on model specimens were curve-fitted to calculate the relative amounts of O2–, OH–, PO43–, and SO42– species at the surface. The amounts of these species were then related to the mechanical performance of the joint measured by the floating roller peel test. Results show that significant initial adhesion is achieved without mechanical interlocking and independent of the type of electrolytes used for the pretreatment. Conversely, bonding stability under wet conditions is highly influenced by the surface chemistry. The wet adhesion strength increases with the hydroxyl concentration at the aluminum (oxide) surface, indicating that interfacial bonding is established through these surface hydroxyls. Phosphates and sulfates anions were not found to contribute to bonding with this type of adhesive.
AB - The transition to Cr(VI)-free production is a great challenge in the global aerospace industry that currently still relays on it for the preparation of aluminum for bonding. Proper surface pretreatment is a prerequisite for strong and durable adhesive joint. Despite decades of experience, the nature and contribution of the different adhesion forces between the aluminum and organic adhesive remain under discussion. Herein we studied the adhesion of epoxy resin as a function of the surface chemistry of barrier-type anodic oxides prepared in sulfuric acid (SAA), phosphoric acid (PAA), and mixtures of phosphoric–sulfuric acids (PSA) and chromic acid (CAA) at different anodizing temperatures. X-ray photoelectron spectroscopy (XPS) data measured on model specimens were curve-fitted to calculate the relative amounts of O2–, OH–, PO43–, and SO42– species at the surface. The amounts of these species were then related to the mechanical performance of the joint measured by the floating roller peel test. Results show that significant initial adhesion is achieved without mechanical interlocking and independent of the type of electrolytes used for the pretreatment. Conversely, bonding stability under wet conditions is highly influenced by the surface chemistry. The wet adhesion strength increases with the hydroxyl concentration at the aluminum (oxide) surface, indicating that interfacial bonding is established through these surface hydroxyls. Phosphates and sulfates anions were not found to contribute to bonding with this type of adhesive.
U2 - 10.1021/acs.jpcc.6b04957
DO - 10.1021/acs.jpcc.6b04957
M3 - Article
SN - 1932-7455
VL - 120
SP - 19670
EP - 19677
JO - The Journal of Physical Chemistry C
JF - The Journal of Physical Chemistry C
IS - 35
ER -