mackey said-
There is no possible way you can have "liquid iron, elemental sulfur, and oxygen" in a mixture without some kind of reaction. Therefore, that is NOT what he is talking about. The very idea is positively absurd. He very, very specifically refers to a slag composed of those elements. That means a compound. That means the iron is not pure, and that obviates any need for temperatures hot enough to melt iron.
i thought it sounded strange too!!! that is why i asked. next time im on campus, ill check it out. ive read greening, yours, godisenergy, prof jones.
im ready for someone to take it to the next stage, that is test their hypothesis. jones can recreate his red chip thermite and test it on some a36 steel. sisson can create a burning debris pile with his "slag" attacking a36 steel.....thats what im waiting for!!!
It's quite difficult for someone who has not been taught phase diagrams, especially with respect to steel and the way in which the structure of a steel can be changed via different heat treatments and therefore it's properties changed let alone mechanisms of corrosion to understand exactly what is happening. If they have a chemistry/physics/engineering background then it's easier to explain. It can also be explained to a layman if the language is chosen carefully but that is difficult - e.g. try explaining what a solid solution is! So I applaud you in looking for yourself and trying to understand a complex, albeit, tiny subject.
One thing that I have noticed when some people talk about molten iron (and they often quote 1540°C ish) is that they do not understand the basic notion (which is taught around 11 years old in my experience) that an impurity will lower the melting point of a pure element. Hence, Carbon in Iron lowers the melting point of the material.
One of the other things that is noticeable is that people do not understand the mechanism of how Sulphur and Oxygen "enter" the steel and then cause the chemical attack seen. This mechanism is called diffusion. It's this diffusion of one "species" into another that changes the characteristics of the resulting material. At room temperature oxidation (rust) occurs, but we also have to realise that water is present in air and therefore there are other complex mechanisms at work.
http://www.staff.tugraz.at/robert.schennach/Theory_of_Metal_Oxidation.pdf
In the WTC case and other scenarios, what is happening is that a solid is absorbing elements of a gas, yet the solid is remaining as a solid even though it now contains elements of that gas. There is a gradient of concentration between the very solid, material surface, that is exposed to the gas and the interior of the solid that is not. Elements such as Sulphur and Oxygen can penetrate the surface and travel towards the interior of the exposed material - in this case Steel (Fe alloyed with C and other elements). The extent to which an element can penetrate depends upon a number of parameters - temperature, partial pressure (of the gas) and species (the element that is being "absorbed") concentration are the "primary driving forces", but there are others.
Metallurgists use this knowledge to produce techniques such as carburising and nitriding in steels (or a mixture carbo-nitriding). That is heating a steel component upto a temperature and then exposing it to a gas; for example methane (carburising). This makes the Carbon in the gas diffuse into the surface of the steel. We can control the concentration and the depth of this added carbon by adjusting; time, temperature, gas concentration etc so that we can produce a component that has all of the general properties we want in the bulk of the component, yet has a very hard surface due to a very high level of Carbon. (If we had this very high carbon level throughout the component then we would have very different properties and some of these properties would be detrimental eg: Brittleness)
Diffusion of Sulphur and Oxygen in to the steel will occur at greater rates as temperature increases. So it's happening at 100, 200, 300, 400, 500, 600, 700 800, 900°C whilst the steel and resulting eutectic is
solid - that is to say
the composition that is liquid at 940°C is solid below that temperature and that the steel can reach that composition via diffusion whilst solid. It is only when the resulting material (the FeS-Fe0 eutectic) reaches 940°C will it liquefy or melt - yet the remaining bulk or parent steel remains solid. The steel is coming under a combination of attack, from oxidation, sulphidation, the production of which causes a "slag" that attacks the steel resulting in grain boundary attack, subsequent grain boundary melting (liquation) and spallation (bits falling off). Sulphidation and it's resulting corrosion rates have been seen to increase with additional Carbon in the gas atmosphere. Don't forget that there would have been a whole constituent of species that would have been caused by not only burning jet fue,l but also a huge amount of other building materials.
Corrosion is on the surface (no pun intended) is a relatively straight forward thing, we know what causes it, we know how to combat it quite effectively, yet the underlying mechanisms (and by that I mean the actually interaction between elements and their electrons on the sub-atomic level) are vastly complex and therefore our models are not complete (see paper above). When it comes to one-off scenarios such as the WTC attacks we have a very good understanding of how such erosion of steel occurs.
If thermite had been used then it would have left far more than microscopic traces, it would have left behind hundreds of apparatus designed to apply that material as well as material such as detonation cord etc. Where's the "det-cord" in the rubble?
