Dr. James Millette
MVA Scientific Consultants
American Academy of Forensic Science
2012 Annual Meeting
The composition of the four samples of dust chosen for study were consistent with WTC dust previously published 2,3 (Appendix A).
Red/gray chips that had the same morphology and appearance as those reported by Harrit et al.1, and fitting the criteria of being attracted by a magnet and having the SEM-EDS x-ray elemental spectra described in their paper (Gray: Fe, Red: C,O, Al, Si, Fe) were found in the WTC dust from all four locations examined. The red layers were in the range of 15 to 30 micrometers thick. The gray layers were in the range of 10 to
50 micrometers thick (Appendix B).
The FTIR spectra of the red layer were consistent with reference spectra of an epoxy resin and kaolin clay (Figure 8) (Appendix C).
The SEM-EDS and backscattered electron (BE) analysis of the cross-sections of the gray layer in the red/gray chip showed it to be primarily iron consistent with a carbon steel. The cross-sections of the red layer showed the presence of equant-shaped particles of iron consistent with iron oxide pigment and plates of aluminum/silicon consistent with reference samples of kaolin. The thinnest kaolin plates were on the order of 6 nm with many sets of plates less than 1 micrometer thick. Small x-ray peaks of other elements were sometimes present. The particles were in a carbon-based matrix (Figures 9 through 14) (Appendix D).
TEM-SAED-EDS analysis of the residue after low temperature ashing showed equant-shaped particles of iron consistent with iron oxide pigment and plates of kaolin clay. Small numbers of titanium oxide particles consistent with titanium dioxide pigment were also found (Figure 15) (Appendix E).
PLM analysis of the residue from red/gray chips after muffle furnace ashing at 400oC for 1 hour showed very fine red particles consistent with synthetic hematite (iron oxide) pigment particles (Figure 16). PLM also found possible clay present based on a micro-chemical clay-stain test. TEM-SAED-EDS analysis of another portion of the same muffle furnace residue showed equant-shaped particles of iron consistent with iron oxide pigment, plates of kaolin clay and some aciniform aggregates of carbon soot consistent with incomplete ashing of a carbon-based binder (Figure 17). The SAED pattern of the kaolin particles (Figure 18) matched the kaolin pattern shown in the McCrone Particle Atlas8 (Appendix E). The values for the d-spacings determined for the diffraction patterns matched those produced by reference kaolin samples.
TEM-SAED-EDS analysis of a thin section of the red layer showed equant-shaped particles of iron consistent with iron oxide pigments and plates of kaolin clay (Figures 19 and 20). The matrix material of the red coating layer was carbon-based. Small numbers of titanium oxide particles consistent with titanium dioxide pigment and some calcium particles were also found (Appendix F).
The solvents had no effect on the gray iron/steel layer. Although the solvents softened the red layers on the chips, none of the solvents tested dissolved the epoxy resin and released the particles within. SEM-EDS phase mapping (using multivariate statistical analysis) of the red layer after exposure to MEK for 55 hours did not show evidence of individual aluminum particles (Appendix G).
In summary, red/gray chips with the same morphological characteristics, elemental spectra and magnetic attraction as those shown in Harrit et al.1 were found in WTC dust samples from four different locations than those examined by Harrit, et al.1 The gray side is consistent with carbon steel. The red side contains the elements: C, O, Al, Si, and Fe with small amounts of other elements such as Ti and Ca. Based on the infrared absorption (FTIR) data, the C/O matrix material is an epoxy resin. Based on the optical and electron microscopy data, the Fe/O particles are an iron oxide pigment consisting of crystalline grains in the 100-200 nm range and the Al/Si particles are kaolin clay plates that are less than a micrometer thick. There is no evidence of individual elemental aluminum particles detected by PLM, SEM-EDS, or TEM-SAED-EDS, during the analyses of the red layers in their original form or after sample preparation by ashing, thin sectioning or following MEK treatment.
The Encyclopedia of Explosives9 describes thermite as essentially a mixture of powdered ferric oxide and powdered or granular aluminum. There are two sets of ingredients listed for thermite in Crippen’s book on explosives identification.10 The first is iron oxide and aluminum powder and the second is magnesium powder, ferric oxide, and aluminum powder. Nano-thermite (thermatic nanocomposite energetic material) has been studied in the Lawrence Livermore National Laboratory in California. A TEM image of a thin section of that material was published by R. Simpson11 in 2000 and
shows material that is made up of approximately 2 nanometer iron oxide particles and approximately 30 nanometer aluminum metal spheres (Figure 21).
According to the Federation of Societies for Coatings Technology, kaolin (also known as aluminum silicate or china clay) is a platy or lamellar pigment that is used extensively as a pigment in many segments of the paint industry.12 It is a natural mineral (kaolinite) which is found in vast beds in many parts of the world.13 Iron oxide pigments are also used extensively in paints and coatings.13,14 Both kaolin and iron oxide pigments have been used in paints and coatings for many years.13,14 Epoxy resins were introduced into coatings in approximately 194715 and are found in a number of specially designed protective coatings on metal substrates.
In forensic studies, paints and coatings often must be broken down so that the components of the entire coating product can be studied individually. Epoxy resins are formed from the reaction of two different chemicals which produces a polymer that is heavily cross-linked. Epoxy resins can be especially difficult to dissolve. Organic solvents, including those sold commercially for epoxy paint/coating stripping, were found to soften the red layer of the red/gray chips but did not dissolve the epoxy resin sufficiently so particles within the coating could be dispersed for direct examination. In this study no organic solvent was found to release particles from within the epoxy resin and it was necessary to use low temperature ashing to eliminate the epoxy resin matrix and extract the component parts of the coating. The other procedures generally used to examine component particles within a coating without extraction (cross-sections and thin sections) were also applied in this study.
The red/gray chips found in the WTC dust at four sites in New York City are consistent with a carbon steel coated with an epoxy resin that contains primarily iron oxide and kaolin clay pigments.
There is no evidence of individual elemental aluminum particles of any size in the red/gray chips, therefore the red layer of the red/gray chips is not thermite or nano-thermite.
Notes on the Source of the Red/Gray Chips
At the time of this progress report, the identity of the product from which the red/gray chips were generated has not been determined. The composition of the red/gray chips found in this study (epoxy resin with iron oxide and kaolin pigments) does not match the formula for the primer paint used on iron column members in the World Trade Center towers (Table 1).16 Although both the red/gray chips and the primer paint contain iron oxide pigment particles, the primer is an alkyd-based resin with zinc yellow (zinc chromate) and diatomaceous silica along with some other proprietary (Tnemec ) pigments. No diatoms were found during the analysis of the red/gray chips. Some
small EDS peaks of zinc and chromium were detected in some samples but the amount detected was inconsistent with the 20% level of zinc chromate in the primer formula.
Material Safety Data Sheets (MSDS) contain some information about product materials. According to the MSDS currently listed on the Tnemec website,17 55 out of the 177 different Tnemec coating products contain one or two of the three major components in the red layer: epoxy resin, iron oxide and/or kaolin (aluminum silicate) pigments. However, none of the 177 different coatings are a match for the red layer coating found in this study.
1. Harrit, N.H., Farrer, J., Jones, S.E., Ryan, K.R., Legge, F.M., Farnsworth, D., Roberts, G., Gourle, J.R., and Larsen, B.R., "Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe", The Open Chemical Physics Journal, 2009, 2, 7-31.
2. Lioy, P.J, Weisel, C.P., Millette, J.R., Eisenreich, S., Vallero, D., Offenberg, J., Buckley, B., Turpin, B., Zhong, M., Cohen, M.D., Prophete, C., Yang, I., Stiles, R., Chee, G., Johnson, W., Porcja, R., Alimokhtari, S., Hale, R.C., Weschler, C., and Chen, L.C., "Characterization of the Dust/Smoke Aerosol that Settled East of the World Trade Center (WTC) in Lower Manhattan after the Collapse of the WTC 11 September 2001", Environmental Health Perspectives, Vol. 110, No. 7, 703-714, July 2002.
3. Millette, J.R., Boltin, R., Few, P. and Turner, Jr., W., "Microscopical Studies of World Trade Center Disaster Dust Particles", Microscope, 50(1): 29-35, 2002.
4. Turner, W.L., J.R. Millette, W.R. Boltin, and T.J. Hopen, A Standard Approach to the Characterization of Common Indoor Dust Constituents. Microscope 53(4):169-177. 2005.
5. TWGFEX Laboratory Explosion Group, Recommended Guidelines for Forensic Identification of Intact Explosives and Recommended Guidelines for Forensic Identification of Post-Blast Explosive Residues (Rev. 8 - 2009), Technical Working Group for Fire and Explosions, National Institute of Justice - Office of Justice Programs, U.S. Department of Justice.http://www.ncfs.org/twgfex/docs.
6. ASTM E1610-02, Standard Guide for Forensic Paint Analysis and Comparison. ASTM –International, West Conshohocken, PA. Reapproved 2008.
7. COMPASS multivariate statistical analysis software program for Noran System Six x-ray system. Minoru Suzuki, Thermo Fisher Scientific, Yokohama, Japan; Pat Camus, Ph.D., Thermo Fisher Scientific, Madison, WI, USA. Application Note: 51220. 2008.
8. McCrone, W.C. and Delly, J.G. The Particle Atlas, 2nd Ed. Ann Arbor Press. Vol. 3, p. 584. 1973.
9. Kaye, S.M. “Thermite”, Encyclopedia of Explosives and Related Items, Vol. 9, PATR 2700, US Army Armament Research and Development Command, Dover, New Jersey, 1980, (available from NTIS, US Department of Commerce, Springfield, Virginia 22161), page T189.
9119ProgressReport022912s Page 8 of 21
10. Crippen, J.B. Explosives and Chemical Weapons Identification. CRC Taylor &
Francis, Boca Raton, FL, 2006, p.149.
11. Simpson, R., Nanoscale Chemistry Yields Better Explosives, Science and Technology Review. Lawrence Livermore National Laboratory October, 2000.
12. Smith, A. “Inorganic Primer Pigments”, Federation Series on Coating
Technology, Federation of Societies for Coatings Technology, Philadelphia, PA. 1988.
13. Gettens, R.J. and Stout, G. L., “Painting Materials”, Dover Publications, 1966.
14. Petraco, N. and Kubic, T., Color Atlas and Manual of Microscopy for Criminalists, Chemists, and Conservators. CRC Press, Baca Raton, 2004.
15. Prane, J.A., “Introduction to Polymers and Resins”, Federation Series on
Coating Technology, Federation of Societies for Coatings Technology,
Philadelphia, PA. 1986.
16. Sramek, T.F.: Correspondence between Pittsburgh-Des Moines Steel Co. and
R. M. Monti, Port of New York Authority, giving clarification and attaching a
product sheet for Tnemec 69 and 99 column paints, Nov 22, 1967. As cited in:
Banovic, S.W. and Foecke, T., Assessment of Structural Steel from the World Trade Center Towers, Part IV: Experimental Techniques to Assess Possible Exposure to High –Temperature Excursions. Journal of Failure Analysis and Prevention. 6(5):103-120. Oct 2006.
17. www.tnemec.com [ last accessed on Feb. 26, 2012].
Table 1. Composition of Primer Paint on the World Trade Center Towers according to T. F. Sramek16
Pigment Iron Oxide 35.9%
Zinc Yellow (Zinc Chromate13) 20.3%
Tnemec pigment (proprietary composition) 33.7%
Diatomaceous silica 10.1%
Vehicle Soya alkyd resin solids 16.5%
Hard Resin 2.8%
Raw Linseed Oil 35.1%
Bodied Linseed Oil 6.4%
Suspension agents 2.2%
Driers and antiskin 4.8%