Cation substitution induced reactivity variation on the tricalcium silicate polymorphs determined from first-principles calculations. (20th August 2019) - Wang, Qianqian
Graphical abstract: Highlights: Non bonding electrons are firstly determined and quantified in tricalcium silicates. Non bonding electrons are in both of the isolated and covalent bonded oxygen atoms. There are more non bonding electrons in M1-C3 S than that in M3-C3 S. Some substituted cations can increase the number of non-bonding electrons on O atoms. The beneficial cations substituted in alite are with weak electronegativity properties. Abstract: Alite is one of the most important phases in cement clinker. It is a solid solution of tricalcium silicate (Ca3 SiO5, C3 S for short, C = CaO, S = SiO2 ) which has seven polymorphs. M1-C3 S and M3-C3 S are the most common polymorphs in cement clinker. Much experimental research had identified that cations doping affected the polymorph of alite and the hydration properties of cement clinker. This article systemically investigated the influence of cation doping on crystal structures and electronic structures of M1-C3 S and M3-C3 S employed by first-principles calculations based on density functional theory. Non-bonding electrons dispersed on the p orbitals of Oi (the isolated oxygen atoms) and Oc (covalent bonded oxygens in nesosilicate tetrahedrons) in C3 S were determined and quantified by the integration of partial density of states at specified energy levels. Non-bonding electrons are the most probable electrons that will be transferred when the oxygen atoms suffer from electrophilic attack as minerals contact with water. The results showed that there were more non-bonding electrons in both of Oi and Oc atoms in M1-C3 S than that in M3-C3 S, which lead to M1-C3 S more reactive. The substituted cations with specific valence electrons configurations and weak electronegativity are determined, which will typically increase the amount of non-bonding electrons in the systems generally. These would help to understand how cation doping affected the hydration of alite, and furthermore, improve the quality of cement clinker.