Phosphoric acid anodising

This recently developed process creates oxide films that are highly porous and ideal for 

The surface properties last for several months after treatment. These methods are used industrially with baths that have a long lifetime and are free from toxic components. 

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Boeing Process Specification, Phosphoric Acid Anodising of Aluminum for Structural Bonding, BAC 5555, revision A, 1975. 

Surface-sensitive techniques for use in the study of adhesive bonding are discussed, including X-ray photoelectron spectroscopy and auger electron spectroscopy/scanning auger microscopy. Data analysis is considered, with reference to quantification, chemical-state information, depth-distribution information and surface-behaviour diagrams. Applications to adhesive bonding are described, particularly failure analysis, hydration of phosphoric acid-anodised aluminium and adsorption of hydration inhibitors. 100 refs. 

This mechanism has been clearly identified in the case of the durability of aluminium-alloy joints. One example [10] is that of aluminium-alloy joints bonded using an aerospace epoxy-film adhesive where the aluminium-alloy substrate was subjected to a phosphoric-acid anodising (PAA) surface treatment, but where the primer (which is normally used in such an adhesive system) was omitted. Under... 

Fig, 6. Logarithmic crack growth rate per cycle, da/dN, versus logarithmic Gmax for aluminium-alloy substrates (phosphoric-acid anodised (PAA) pretreatment) bonded using an epoxy-film adhesive. Cicles are for tests conducted in a dry environment of 23°C and 55% relative humidity and dots for tests conducted in a wet environment of distilled water at 28 C. Diflerent styles of the symbols represent replicate tests [10]. 

Fig. 11. Micrograph from energy-filtered transmission electron microscopy of a cross-section of the interphase region of a phosphoric-acid anodised and primed (PAAP) pretreated joint [10].

ASTM D 3933-80 Practice for Preparation of Aluminium Surfaces for Structural Adhesives Bonding (Phosphoric Acid Anodising). 

BAC 5555 Phosphoric Acid Anodising of Aluminium Alloys for Structural Bonding. 

The Phosphoric Acid Anodisation process utilising phosphoric acid solutions. This was originally developed by the Boeing Company and is the treatment of choice for critical applications in the USA. 

Electrochemical chromic acid anodising Electrochemical phosphoric acid anodising Electrochemical sulphuric acid anodising Electrochemical hard anodising Electrochemical boric acid/sulphuric acid anodising Chemical sol-gel procedures Activated plasma... 

Anodising in chromic acid is the electrochemical pretreatment procedure favoured in Europe. European aerospace companies view this as giving a less friable oxide film than the phosphoric acid anodising process favoured in the United States and believe that it imparts much better durability to the bonded joint. This latter statement is somewhat debatable in the light of both experience in the laboratory and the actual chemical stmcture of the oxide films themselves. 

Of all the current civil engines. Rolls Royce s Trent 7(X) does have high temperature requirements. The IFS of the thrust reversers has to operate for considerable periods of time at elevated temperatures (> 140-150°C). The component manufacturers, Hurel-Hispano, believe that this is asking too much of an epoxy adhesive and hence a Cytec-Fiberite BMI film adhesive (FM-2550) is used to bond this structure. Here the BMI adhesive is reticulated onto phosphoric acid anodised aluminium honeycomb. The core is then bonded directly onto pre-cured carbon-reinforced BMI laminates to form a sandwich structure, one of the skins being perforated to produce an acoustic panel , which helps reduce engine noise. 

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