Relations between Hydration Reactivity and Crystal Structures of Alpha'_L-,Beta-and Gamma-Dicalcium Silicate in Cement Clinker:First Principles Study

【Author】

Qianqian Wang;Feng Li;Xiaodong Shen;Xuerun Li;

【Abstract】

<正>First principles simulations based on density functional theory have been performed to investigate the electronic structure properties ofα'L-dicalcium silicate(α'L-C_2S),β-dicalcium silicate(β-C_2S) andγ-dicalcium silicate(γ-C_2S).The aim is to elucidate the effect of the crystal structures on reactive sites and further reveal the relationship between polymorphs and hydration reactivity.The results illuminate that the local density of sates(LDOS) of valence band maximum(VBM) and conduction band minimum(CBM) accumulated around O and Ca atoms,which are the reactive sites. Furthermore,the LDOS of VBM mainly accumulate around some special kinds of O atoms(defined as Oa) forα'L-C_2S andβ-C_2S resulting in Oa exhibiting a trend more easily to lose electrons,which makes them susceptible to undergo electrophilic attack Moreover,the partial density of state(PDOS) around Fermi level is mainly dominated by O-p and Ca-d orbitals,which is consistent with the LDOS result Meanwhile,the exclusive occupation of O 2p orbitals at VBM for a'L-C_2S andβ-C_2S reveal that these orbitals are actually in the non-bonding state(or in a dangling bond state).The cohesive energy suggests thatγ-C_2S is the most stable phase.This paper proposes a new method to determine reactive sites using combination of LDOS of VBM and CBM and the PDOS. This may provide new insights into explaining the fact thatα'L-C_2S andβ-C_2S can react with water at room temperatures whileγ-C_2S scarcely reacts. Originality First principles simulations are used to derive the influence of the crystal structures for polymorphism ofα'L-C_2S,β-C_2S andγ-C_2S on reactivity.The electronic structure properties are characterted by VBM,CBM and PDOS.This paper proposes a new method to characterize reactive sites intuitively using LDOS of VBM and CBM and the PDOS is another way to describe active sites qualitatively.From the calculation results, we find the reactive sites and these results are agreement with the PDOS analysis.Inα'L-C_2S andβ-C_2S,the LDOS of VBM mainly accumulate around Oa atoms.The O 2p orbitals at VBM are exclusive occupation and are actually in the non-bonding states(or in a dangling bond state).However,we don't find these Oa atoms inγ-C_2S.These calculation results give us some opinions to interpretation the experimental results thatα'L-C_2S andβ-C_2S can react with water at room temperatures whileγ-C_2S is stable against with water at the nano-level.The cohesive energy is calculated and suggests thatγ-C_2S is the most stable phase in the polymorphisms of C_2S

【Keywords】

dicalcium silicate;;reactivity;;crystal structure;;electronic properties;;first principles simulations

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