Ted Krapkat
Hello Maw,
Alumina is always more than iron in kiln feed because the Alumina Modulus (Al2O3/Fe2O3) controls the ratio of C3A to C4AF in the clinker. If iron was more than alumina the alumina modulus would be less than 1. If the Alumina Modulus reaches 0.64 then theoretically, at that point, no C3A would form at all (instead, C2F and C4AF would form).
Very low or zero C3A content would result in a lack of control over cement setting times as well a causing low early strengths. Some recent research also suggests that C3A influences the rate of hydration of the calcium silicates in a positive way. So a large reduction in C3A content would have a detrimental effect on later strengths as well as early strengths (See http://www.sciencedirect.com/science/article/pii/000888467690096X)
The Alumina Modulus also controls liquid phase viscosity and clinker nodulisation. If the Alumina Modulus falls below about 1.2 the liquid phase becomes very fluid and could attack the bricks as well as promote snowman formation. Also, as the Alumina Modulus is reduced, the resulting clinker tends to be fine-grained and dusty, causing problems with burning zone temperature and increasing the chance of snowmen and rings.
For all these reasons, the Alumina Modulus should lie between 1.3 and 2.3 for normal grey OPC clinker.
Regards,
Ted.
maw
thanks mr Ted , in addition to that you mentioned i read one paper tell that the volume of AL is more than Fe due to AL density is more less ( lower Mwt) .so volume of liquid phase promote wetting more than amount .
Ted Krapkat
Hello Maw,
Yes, it's true that weight for weight, the volume occupied by C4AF is approximately 25% less than that occupied by C3A (since C4AF has a specific gravity of 3.77g/cm3 while C3A has an s.g. of 3.04g/cm3).
However, this difference in volume only really becomes noticeable at Alumina Moduli above about 1.6, which is the point where C3A and C4AF theoretically occupy roughly equal volumes in the liquid phase.
Below an Alumina Modulus of 1.6, there is always more C4AF by both %volume and %weight in the liquid phase, and the closer the Alumina Modulus is reduced towards 0.64, the closer the C4AF approaches 100% while the C3A moves towards 0% .
Regards,
Ted.