From Molten Calcium Aluminates through Phase Transitions to Cement Phases.

Hao Liu,Gregory A Chass,Louis Hennet,Wenlin Chen,Yuanzheng Yue,G Neville Greaves,James W E Drewitt,Ruikun Pan,Zhitao Shan,Sandro Jahn,David P Langstaff,Haizheng Tao,Ang Qiao

doi:10.1002/advs.201902209

Abstract

Crystalline calcium aluminates are a critical setting agent in cement. To date, few have explored the microscopic and dynamic mechanism of the transitions from molten aluminate liquids, through the supercooled state to glassy and crystalline phases, during cement clinker production. Herein, the first in situ measurements of viscosity and density are reported across all the principal molten phases, relevant to their eventual crystalline structures. Bulk atomistic computer simulations confirm that thermophysical properties scale with the evolution of network substructures interpenetrating melts on the nanoscale. It is demonstrated that the glass transition temperature (T g) follows the eutectic profile of the liquidus temperature (T m), coinciding with the melting zone in cement production. The viscosity has been uniquely charted over 14 decades for each calcium‐aluminate phase, projecting and justifying the different temperature zones used in cement manufacture. The fragile–strong phase transitions are revealed across all supercooled phases coinciding with heterogeneous nucleation close to 1.2T g, where sintering and quenching occur in industrial‐scale cement processing.

Highlights

Crystalline calcium-aluminate phases are the critical setting agents in cement technology.[1,2,3] The melts from which they crystallize comprise a remarkable glass-forming system whose compositions, structures and thermophysical properties have not yet been correlated with real-world cement processing
The viscosity has been uniquely charted over 14 decades for each calciumaluminate phase, projecting and justifying the different temperature zones used in cement manufacture
As local structures of the network modifier (CaO) and network former (Al2O3) in calcium-aluminate melts differ greatly (Figure 2C), we have explored whether clustering of these component features in long range order and the degree to which clusters are interconnected, with respect to crystalline structures

Summary

Introduction

Crystalline calcium-aluminate phases are the critical setting agents in cement technology.[1,2,3] The melts from which they crystallize comprise a remarkable glass-forming system whose compositions, structures and thermophysical properties have not yet been correlated with real-world cement processing. The viscosities η and densities ρ of these important cement phases, are mostly unknown, yet the relationship between thermophysical and structural properties of supercooled liquids lies at the heart of nucleation and vitrification processes This relation is well studied for the following two extreme scenarios: one in respect to the liquids with exceptional lability-like elemental metals,[13] the other concerning glass-forming liquids such as silicates[12,14] where crystallization is inhibited by high η(Tm) values. But is distinct from less well-packed oxide polyamorphic networks, where dT/dP is negative.[26,27]

Discussion

Conclusions

Experimental Section

Conflict of Interest