The Treatment of the BMW 801D-2 Radial Aero Engine Rescued From the Loiret River.

It has been recognised for some time that the oceans, seas and waterways of the world are repositories for objects of our aviation and maritime history that have become extinct on land. With the development of new detection and salvage methods, enthusiasts, collectors and museums are now recovering these valuable pieces of history. Thus, there is a demand to develop appropriate preservation techniques.

Unfortunately, these relics have little chance of long term survival if not treated correctly. The materials of construction have become “polluted” with salts and metal residues which promote extremely rapid corrosion on exposure to the atmosphere unless they are kept in environments of low relative humidity and oxygen level. In most cases this is quite impractical. Hence, almost all the “rescued” items are now corroding faster than if they had been left in the water.

Preservation of these objects, requires treatments that remove the “aggressive” or “initiating” species from within the object, leaving it in a “passive” state. Surface coating or inhibitor treatments will not stop the long term corrosion of the metals as all the necessary chemical species that are involved in the corrosion reaction are still present under the coating. Inhibitors may to some extent, delay the corrosion but eventually it will again take hold.

In order to halt the corrosion of aluminium based objects which have been exposed to saline environments, it is necessary to extract the salts that have pervaded the construction materials. One method for doing this was developed by Dr Ian Macleod of the Western Australian Maritime Museum.1 Although successful for its designed application, it has several drawbacks when dealing with objects of composite construction such as aircraft engine. The time necessary for a treatment is often very long, sometimes taking years.

A commonly used process for the stabilization of ferrous objects utilises an electrolytic process. Here the “contaminants” are removed from the material using electrical potentials. This method is arguably faster and more efficient than the previous “immersion” technique.

In 1990, scientists from Groupe Valectra of the Electricité de France adapted these techniques for the treatment of aluminium.2 The method involves washing the object in several chemical complexing baths and applying an electrical potential while strictly regulating both potential and pH. Thus the aggressive species are removed from the object. Having been found to be successful for the treatment of small objects, it was decided to scale up the treatment to include large technological items of “composite” construction.

1 MacLeod, LD 'Stabilization of Corroded Aluminium'. Studies in Conservation Vol 28 No. 1. Feb. 1983.
2 Degrigny, C. 'Mise Au Point D'un Traitment Cathodic De Stabilisation De Pieces En Alliages D'Aluminium Degradees Par Corrosion En Miliue Aqueux'. Theses de Doctorat L'Université Paris VI. 20 Nov. 1990.

Abstract Introduction Perspective History FW190 BMW engine
Preparation Plan Treatment Conclusions Bibliography Appendices

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