Dear All,

Which liquid phase is beneficial? Al2O3 rich or Fe2O3 rich? What is the state of affairs in case of white cement production(Negligible Fe2O3) or what would have been in entirely reverse case i.e. negligible Al2O3.

Regards,

 Gulam Dastgir

Hello Dastgir,

Fe2O3 is only present to lower the temperature of formation of the liquid phase which is essential for rapid conversion of C2S and Free lime to C3S. Its presence makes cement manufacture more economical. C4AF has negligible (if any) contribution to concrete strength.

White cement clinker reacts at a higher temperature and is therefore more expensive to manufacture.

Although Fe2O3 is not strictly necessary to produce cement, Al2O3 is required to produce the mineral C3A, which governs cement setting time and early strength.

Therefore a cement with 'negligible' Al2O3 is not really feasible.

In addition, the ratio of Al2O3 to Fe2O3 determines the viscosity of the liquid phase and therefore to some extent the granulometry of the clinker and the behavior of the coating. Depending on the type of cement, an alumina ratio of between 1.3 and 2.5 is usual.

So, neither an Fe2O3-rich nor an Al2O3-rich liquid phase is necessarily beneficial on their own. You need to balance many factors, taking into account the requirements of your market, the raw materials available and the performance of your kiln.

Hope this helps...

Regards,

Ted.

Dear Ted,

I have also came across some articles which claim that viscosity and surface tension of liquid phase is more important than its amount. Is it true?

Moreover, how these two properties affect burning and overall properties of clinker?

Kind Regards,

Gulam Dastgir

Gulam,

Such a statement can't make any sense.
Obviously this would mean that very small quantities with the right viscosity or surface tension would do the job. This makes obviously no sense.

However, it is also clear that above a certain quantity, the liquid phase will not be useful anymore. This is already obvious since 100% liquid phase is useless. The ideal quantity is -theoretically- related to the contact surface which will determine the rate of interaction of the solids with the liquid. It could be also determined by the volume of liquid since -probably- a certain concentration of CaO and c2s needs to be reached to produce c3s with a sufficient rate. It might also depend on many other chemical and mineralogical parameters like at least the fineness of the various components, or the process. The temperature itself has an effect on the quantity of liquid as well as on the kinetics of the reactions.

Scientifically complicated, but can be determined empirically,

lal