There are still a few individuals who claim the three World Trade Center towers were destroyed by controlled demolitions and that airplanes flying into the buildings couldn't have toppled them. One problem with this theory is that demolitions of this sort would have produced a lot of explosive noise, which no people on the scene report hearing. So conspiracy theorists have been forced to come up with another method that would support their wild claims.
What they came up with is thermite which can get hot enough to melt iron and steel. They claim that red-gray chips and iron-rich microspheres found in WTC dust are residue from thermite fires that support their idea about thermite.
But this claim took a hit this spring when the microscopy consulting firm MVA Scientific Consultants in Duluth, Ga. released a study of these chips collected from WTC dust. They used a stereomicroscope and polarized light microscopy, among other things, to analyze the samples. MVA says the analytical procedures used to characterize the red/gray chips were based on recommended guidelines for forensic identification of explosives and the ASTM standard guide for forensic paint analysis and comparison. Scientists there ran additional tests an the samples that included Fourier transform infrared spectroscopy (FTIR); SEM-EDS of cross-sections; low temperature ashing and residue analysis by transmission electron microscopy (TEM) with selected area electron diffraction (SAED) and EDS; and several other more involved methods.
Their conclusion: There is no evidence of individual elemental aluminum particles that you would expect to see from a thermite burn. They say 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. And there is no evidence of individual elemental aluminum particles of any size in the red/gray chips, so the red layer of the red/gray chips is not thermite or nano-thermite.
And WTC conspiracy theorists' claim that microscopic spheres of iron found in WTC dust could only have been formed with thermite was recently debunked by a group called New Mexicans for Science and Reason who pointed out that very small metal particles have a much lower melting point than bulk material. Wires and filaments from electronics in the WTC are the likely source of the microspheres. The NMSR group even produced a YouTube video showing how to create your own microspheres by burning steel wool: http://www.youtube.com/watch?v=jZ9wSD4Hcys&list=UUb1Lcha1B51ChVrbBi548OA&index=2&feature=plcp
You can read the MVA report here: http://dl.dropbox.com/u/64959841/9119ProgressReport022912_rev1_030112webHiRes.pdf
Finally, with regard to the the structural integrity of the WTC towers, I am reminded of a conversation I once had with CAD/CAM Hall of Fame member Michael Bussler, who created the first FEA system for personal computers and pioneered many computer-aided engineering software innovations. Mike recalled visiting the WTC on vacation in the 1990s. He said he began to get curious about its construction and started wandering around the WTC and noticed its support structure. At some point, it dawned on him that load-bearing steel columns around the perimeter were the main structural elements. "I then decided I didn't want to be in there," he said.
Of course, that sort of insight is a lot less sinister than a conspiracy theory.