Phases in Portland Cement Clinker
In Portland cement clinker, calcium aluminoferrite occurs as an "interstitial phase", crystallizing from the melt. Its presence in clinker is solely due to the need to obtain liquid at the peak kiln processing temperature (1400−1450 °C), facilitating the formation of the desired silicate phases. Apart from this benefit, its effects on cement properties are little more than those of a diluent. Its forms an impure solid solution that deviates markedly in composition from the simple chemical formula. The calcium aluminoferrite phase acts as a repository for many of the minor elements in the clinker. Most of the transitional elements in the cement are found in the ferrite phase, notably titanium, manganese and zinc. There is also a substantial amount of magnesium and silicon, and because of this, oxides other than CaO, Al2O3 and Fe2O3 often make up 15% of the mass of the calcium aluminoferrite. This substitution reduces the melting point to around 1350 °C.
Typical chemical compositions for various clinker bulk Fe2O3 contents are:
| Oxide | Mass % | Mass % | Mass % |
|---|---|---|---|
| Fe2O3 in Clinker | 0.29 | 2.88 | 4.87 |
| SiO2 | 4.0 | 2.6 | 6.1 |
| Al2O3 | 20.2 | 20.8 | 17.0 |
| Fe2O3 | 24.5 | 23.9 | 27.7 |
| CaO | 44.6 | 46.4 | 40.2 |
| MgO | 3.7 | 3.1 | 4.9 |
| Na2O | 0.1 | 0.1 | 0.1 |
| K2O | 0.1 | 0.1 | 0.1 |
| TiO2 | 1.9 | 2.7 | 1.7 |
| Mn2O3 | 0.1 | 0.3 | 1.5 |
| ZnO | 1.1 | 0.1 | 0.9 |
Read more about this topic: Calcium Aluminoferrite
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