Dear all!
Interested in everything that has to do with the problem of FeO in clinker. In literary sources I found, that FeO causes the disintegration of C3S and in order to reduce the content of FeO in clinker, in the rotary kiln need to keep oxidizing atmosphere. I am wondering whether the mechanism is known, why FeO causes the disintegration of C3S and what is the maximum allowable concentration of FeO in clinker.
Best regards!
Dr. Michael A. Miheenkov
Dobre Den, Michael!
Yes, under high-temperature reducing conditions, Fe+2 can substitute for Ca+2 in the C3S crystal lattice. However, upon cooling to ~1180oC in an oxidising atmosphere (such as the primary cooling zone under the burner, or in the first part of the cooler), the Fe+2 in the C3S lattice is oxidised to Fe+3. This destabilises the C3S lattice and accelerates the decomposition of C3S back into C2S and free CaO.
There is no maximum allowable concentration of FeO in clinker. Normally Fe+2 in clinker is detected visibly in acidic aqueous solution using the complexing reagent 2,2'-Bipyridine (Bipyridyl). A negative test is one in which no pink colour can be detected when ~5mg of clinker is dissolved in a few drops of dilute HCl and the complexing reagent added.
I guess the practical limit for FeO in clinker is as close to zero as possible. :)
Regards,
Ted.
Dear Mr. Ted,
In white clinker manufacturing in order to maximise the clinker whiteness is by maximise the Fe content of the raw materials and fuel and to ensure that Fe is present in the ferrous (FeO) oxidation state rather than the ferric (Fe2O3) oxidation state.This can be achieved by operating the kiln in reducing atmsphere.Is the ferrous (FeO) oxidation state also disintegrate the C3S in white clinker manufacturing.
In some cemnt plant steel slag, which contain FeO, is being used as a raw mix component.Is the presence of FeO in the slag also disintegrate the C3S mineral phase?
Thanks Ted!
It makes sense. I was a little different. I thought that having in clinker FeO instead of Fe2O3 interferes with formation of CaOFe2O3 (CF) and next respectively brownmillerite C4AF. Because of these processes produce free CaO, which block up the formation of C3S. Probably both mechanism take place.