There are obvious differences in what is presented below and what most likely happened to WTC 1, 2, and 7 on 9/11; but thermite has been around for a while.
source: 9/11 Blogger Aug. 31, 2011
Taken from Popular Mechanics – Nov 1935 – Page 657
Skyride Tower Felled by Melting Steel Legs
Intense heat was employed by wrecking engineers in toppling the 3,000,000-pound east tower of the “Skyride,” a major attraction of Chicago’s Century of Progress. Huge “overshoes” in the form of cupolas made of steel and lined with firebrick were constructed around two legs of the tower and filled with 1,500 pounds of thermite, a mixture of aluminum and iron oxide. When fired by electricity the thermite generated a temperature of more than 5,000 degrees about the two legs, melting the ten-foot sections almost instantly, causing the tower to tip and then to crash. A microphone attached to the tip of the tower broadcast the noise of the fall by radio, and the spectacle was viewed by a crowd estimated at more than 100,000. The west tower had been wrecked several weeks earlier with dynamite. The 628-foot twin towers, the cables which supported the cars passing between them and the elevators cost more than $1,750,000 to erect.