- 2000 NOV 06 -


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00-11-06          0700    Morning routine.  ..

            The following email was received this morning from Dr. BROWN in response to my request to him last week:

From: Brown, Jim []     Sent: Friday, November 03, 2000 6:30 PM

To: ''

Subject: RE: Potential Leaching of Magnesium in Aluminium Alloys

Afternoon Tom

Was rushed yesterday so response had to be very brief.     Details follow to your questions.

1 & 3.  Skin and frame Al alloys were not examined by AES.  No fresh (unpainted) aircraft Al alloy provided me. I did get to analyze a piece of recovered sheet Al from the crash that was painted; 2 layers present, an inner green (likely primer) and an outer white layer.  Neither paint layer contains Mg.  Determining the Mg level at the paint-alloy interface (a layer of interest only 100 or so angstroms thick could not be done with the precision needed.  Pieces of factory fresh alloys would be required.

2.         My comment about Mg segregation in Al alloys is a general observation from many specimens of Al foils and rolled Al sheets from Alcan, Alcoa etc.  Typically, the outermost 50-100 angstroms of an Al foil/sheet is oxidized (passive layer) and enriched in Mg (5-10 at%) compared to bulk Mg levels of <1 to 3 at% generally. Under a typical manufacturing environment (+ stamping pressures and heat) the passive (Mg & Al -rich) oxide layer is further altered along with the alloy's grains (crystals) and casting contaminants (inclusions); more Mg can migrate/segregate during such processing.

 4.        The drop melt test performed at MTL last May was done on fresh pieces of 6061 alloy for reference purposes.  I examined the surface skin of several 6061 melt puddles. All had very high Mg (>30 at%) and Al present as oxides.  This Mg-Al-O layer is only 40-60 angstroms thick however. AES detection limit for Mg was about 2 at%; none was detected deeper.    

            Mg is of special interest to me as well.  The seawater-arc bead study was performed to determine how much, if any, of the Mg, Ca, Al, Si, etc. measured by AES in the exhibit arc melts could have come from post crash inorganic precipitation and/or microbiological activity while submerged in seawater and surrounded by crash materials (or even after the wiring had been retrieved, dried and stored on land).

            The FIB/TEM work in progress is to determine the porosity (cracks, pores, voids) etc. in the outermost few microns of flagged arc melts to determine if Mg and other elements of interest detected to considerable depth in the melts by AES could be seawater artifacts.

          Many other materials have also been examined (various wiring polymer insulations, kapton inner wrap film, fresh Ni- and Sn-plated Cu wire strands, Al-mylar, fiberglass, as well as various natural precipitates, corrosion deposits and particles found on seawater exposed arc melts and wire strands. 

           Unfortunately, the fresh Al metal foil sandwiched between mylar (Aluminized mylar) and glued to onboard thermal/sound insulation was to be provided for surface analysis but to date has not been provided.   This is also true of skin and frame Al alloys.

            Interestingly, Mg was found on Cu wiring kapton after seawater exposure, but it was not present on factory fresh wiring kapton.  But, obviously the kapton onboard (wiring of interest) had been burned prior to seawater so a Kapton-Mg fire association is not an issue. 

            Mg (and low Al) was also found in Sn/Cu-plated wire strands (far from arc) from triple-twist 12-gauge wires on pallet #2 (seawater tests) indicating an affinity of Mg to sorb/migrate into this Sn/Cu plating layer.  No Mg was measured in Sn plated strands not exposed to seawater.  Regardless the exhibit wiring and their arc melts had all Sn-plating removed by heat long before wire exposure to seawater; so again, Mg presence in exhibit melts due to other reasons.

            Mg and Ca (as Mg-Ca oxy-hydroxl-carbonates) is present in visible whitish and greenish colored precipitates/deposits on some arc melts (exhibits and seawater trials) so a Mg and Ca presence on seawater submerged arc melts can/does occur. However, some of our exhibits show the presence of Mg in a solid Cu arc melt region (no visible porosity and well into the solid Cu) where no seawater precipitate deposit could have formed (unless micro-cracks or pore openings to surface exist).   Wire strands and arc melts recovered from the pallet #2 (Mg metal foot pedal) were partially coated in large fragile, white particles (powder) readily visible to the eye. Powder is Mg oxy-carbonate. However, Mg is not detected into/below the Cu arc melt surface only on it.  Again, not explaining the exhibits Mg observations.

            Bottom Line:  I have not been able to determine a natural source of Mg to explain the amount of Mg found in many of the exhibit arc melts given the materials examined to date.  Seawater exposure is a nasty complexity to the problem, but I am convinced another source is responsible.  I hate to speculate what that source is; it may be Al foil from aluminized mylar, it may be Al alloy (plane skin and frame) or something more sinister. An added problem is that one would expect an Al - Mg correlation and high Al/Mg ratio in Cu arc melts if aluminized mylar or Al-alloys were the source of Mg. In many arcs with a high Mg level at depth there is no Al present however.   My report will provide the AES results and my observations to date.  This will include my interest in better understanding the source of Mg, its levels, its associations and its distribution.

            You mentioned the FBI were conducting some arc melt AES work on another case.  Have you heard anything since?  If so, do you think I (we) could/should contact them to compare/discuss the protocol and suspicious findings.  I'd like to know if their AES people have similar, complexing concerns. 

regards,  Jim Brown, MTL

            In reply, the following was sent:

To: James R. Brown

Subject: Potential Leaching of Magnesium in Aluminium Alloys


            Thank you very much for your latest message. 

            Regarding materials to be further tested.  I will check with John GARSTANG and Larry FOGG to make a very serious effort to get you some suitable test strips of skin and frame pieces, and samples of the Metallized Mylar and Tedlar.

            Regarding the FBI AES examinations.  What I had mentioned to you was in regard to flight TWA 800.  However, it seems that neither the FBI nor the NTSB performed AES examinations of the arc melts in the tank.  We were given incorrect information during our initial meeting with New York members of the FBI, and no such testing had been done.  A comment had been made during the meeting that they had run into the very same problems, but it appears that there was a misunderstanding about the testing method, and what exactly the problems were that were being discussed.  So, this avenue is of no help to us.

            It will be next week before I have any contact with John GARSTANG as he is away in Zurich this week, and Larry FOGG is somewhere on the Orient Express on holidays.  But it is a priority to get this material supplied.

            Thank you again for your prompt reply to my questions.

Tom Juby     RCMP 


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