Direct observation and characterisation of the oxide nanostructured interface resulting from organosilane pre-treatment
- PDF / 1,375,708 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 192 Views
B1.8.1
Direct observation and characterisation of the oxide nanostructured interface resulting from organosilane pre-treatment of aluminium Mark J. Whiting, Vlad Stolojan, Ann Rattana and John F. Watts Centre for Advanced Surface, Particle and Interface Analysis, School of Engineering, University of Surrey, Guildford, Surrey, UK ABSTRACT The pre-treatment of aluminium surfaces prior to adhesive bonding and coating processes is of major technological significance. However, the two major commercial pre-treatments, chromic acid and phosphoric acid anodising, both make use of Cr(VI) containing solutions with the attendant problems of waste disposal. The disposal of this harmful solution poses severe environmental problems. Therefore, other environmentally friendly alternatives are being investigated, one of the most popular candidates is the use of one-step pretreatment processes based on organosilane adhesion promoters.
This study examines a model system made from polished aluminium sheet treated with an organosilane; γ-glcidoxypropyltrimethoxysilane (GPS). The interface was characterised by TEM carried out on microtomed sections. The information gained from imaging and Electron Energy Loss Spectroscopy (EELS) analysis revealed a layer of oxide, approximately 70 nm thick. Silicon was found to have been incorporated within this oxide layer. Thus it is suggested that during the curing of the GPS, at elevated temperature, growth of aluminium oxide takes place which gives rise to an Al/O/Si phase.
INTRODUCTION
Traditional methods for the chemical pretreatment of aerospace aluminum alloys prior to adhesive bonding pose serious environmental problems (see for example [1]). Harmful chromium (VI) compounds are produced by these anodizing pretreatments. Chromium (VI) compounds result directly from chromium acid anodising and during the initial etching stages of phosphoric acid anodising. This has necessitated the development of other pretreatments that enable the production of strong joints with good durability without such environmentally harmful byproducts.
B1.8.2
One of the most promising alternatives is a procedure involving the application of a 1% aqueous solution of γ-glycidoxypropyltrimethoxysilane (GPS) adhesion promoter. The trials of this system have indicated that it has durability of the level required for aerospace systems and test repairs have been flying since the mid 1990s. The excellent prognosis for the future of this process led to a detailed investigation to the role of process parameters on durability and interfacial chemistry [1]. The nature of the GPS/aluminium interface resulting from this treatment has previously been studied extensively by secondary ion mass spectrometry [2,3]. In particular Si-O-Al primary bonds have been suggested as the basis for the strong GPS/substrate adhesion and good durability [2].
However, no direct work has been done on characterising the oxide layer that evolves during the curing process integral to the silane pre-treatment. One of the difficulties in studying this
Data Loading...
