Mechanical Properties of Adhesively Bonded Aluminum Structures Protected with Hydration Inhibitors.
Abstract
The use of hydration inhibitors to improve the durability of adhesively bonded aluminum structures was investigated. Pretreatment of Forest Products Laboratory (FPL) adherends in a solution of an inhibitor, such as nitrilotris methylene phosphonic acid (NTMP), increases bond durability dramatically, so that, in some cases, hydration of the adherend is no longer the limiting step in crack propagation. Pretreatment of phosphoric-acid-anodized (PAA) adherends further improves durability so that the transition to failure in the adhesive occurs at a shorter crack length. The initial strength for bonds using epoxy adhesives is not changed by such pretreatments. Adsorption of NTMP onto FPL surfaces displaces the water initially present by the formation of P-O-Al bonds. Saturation coverage is approximately one monolayer. Adsorption of NTMP onto PAA surfaces, which have little initial water, results in the occupation of residual active sites. Hydration of an inhibited FPL surface proceeds in three steps: (1) reversible physic-sorption of water, (2) slow dissolution of the inhibitor-aluminum complex followed by rapid hydration of the freshly exposed amorphous aluminum oxide to boehmite, and (3) further hydration of the boehmite to bayerite.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1985
- Accession Number
- ADA153755
Entities
People
- G. D. Davis
- J. D. Venables
- J. S. Ahearn
Organizations
- Martin Marietta