- 2000 JUl 19 -


00-07-19          0700    Morning routine.  Worked on notes and admin, doing up a memo for the recent report from CANMET entitled “Oxidation of Molten Aluminium Alloys in Different Atmospheres”.  John GARSTANG has a copy and I was able to peruse it to go over the contents with him.  The following memo was given to Insp. LATHEM for forwarding to Vic GERDEN.

            Generally, the test failed what it was intended to show.  It was hoped that the aluminium that melted in rich nitrogen would show a different oxidation level than that melted in rich oxygen.  But aluminium oxidizes so rapidly that under the conditions in the test or in the aircraft, it was and would be impossible to tell the difference.  Even in seawater, there is sufficient oxygen to oxidize the freshly exposed layers.  If I remember my elementary chemistry correctly, aluminium tends to oxidize very rapidly to a thin layer of aluminium oxide.  The difference between it and iron is that the aluminium layer remains intact and retains roughly the same properties as the non-oxide aluminium.  It protects the underlying layers, forming a barrier to further oxidation.  What we are used to seeing on aluminium foil, etc., is actually aluminium oxide.  Iron works differently in that we call the oxide layer rust, and it falls off without protecting the underlying layer of iron.  It certainly was worth the effort to do the test, but one cannot always be successful in these endeavours. 

           However, a by-product of the tests was that AES was used for some of the analysis and very high levels of magnesium were found in the environmental layer of the molten aluminium drops.  This matter was discussed on 00-05-25 in a meeting with TSB, and my notes for that date apply.  It was determined at that time (having been suggested by Larry VANCE) that the cause of the high levels was the contaminated fin plate on which they were dropped.  What was not known at that time and has never been mentioned, but what tends to confirm the theory is that relatively high levels of carbon were also found in the AES readings.  But there was no carbon present to burn, as these were aluminium alloy coupons from Boeing without paint or anything else containing carbon.  So I certainly feel confident that the high magnesium readings were from the contamination on the fin plate that had been selected from the crash debris.






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