Physicochemical Study of the Self-Disintegration of Calcium Orthosilicate (β→γ) in the Presence of the C12A7 Aluminate Phase.

Michał Pyzalski,Anna Adamczyk,Tomasz Brylewski,Jarosław Dąbek

doi:10.3390/ma14216459

Abstract

The β-γ polymorphic transition of calcium orthosilicate (C2S) is a key phenomenon in cement chemistry. During this transition, the compound expands due to structural changes and a significant reduction in its density is observed, leading to its disintegration into a powder with a very high specific surface area. Owing to this tendency of the C2S material to “self-disintegrate”, its production is energy-efficient and thus environmentally friendly. A physicochemical study of the self-disintegration process was conducted with the aim of determining how the amount of dodecacalcium hepta-aluminate (C12A7) in calcium orthosilicate (C2S) affects the temperature at which the polymorphic transi-tions from α’L-C2S to β-C2S and from β-C2S to γ-C2S undergo stabilization. The applied techniques included differential thermal analysis (DTA), calorimetry and X-ray diffraction (XRD), and they made it possible to determine what C2S/C12A7 phase ratio in the samples and what cooling rate constitute the optimal conditions of the self-disintegration process. The optimal cooling rate for C2S materials with a C12A7 content of up to 60 wt% was determined to be 5 K·min−1. The optimal mass ratio of C2S/C12A7 was found to be 70/30, which ensures both efficient self-disintegration and desirable grain size distribution.

Highlights

Academic Editor: Jeong Gook JangReceived: 10 August 2021Accepted: 19 October 2021Published: 28 October 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Calcium orthosilicate with the formula Ca2[SiO4] (2CaO·SiO2) and——as a solid solution known as belite and referred to as C2S, is one of the four main constituent phases of the currently manufactured Portland cements
The results presented in [23,26,27] focused on the stabilization of the polymorphic C2 S
Based on the results presented in [16] it can be stated that cooling the sinters at a slow rate promotes the transition from β-C2 S to γ-C2 S

Summary

Introduction

Calcium orthosilicate with the formula Ca2[SiO4] (2CaO·SiO2) and——as a solid solution known as belite and referred to as C2S, is one of the four main constituent phases of the currently manufactured Portland cements. It is found in alkali-activated blast furnace slag [1], steel slag [2], or hydraulic lime [3], in which it serves the role of the main component that gives the material its hydraulic properties. The fifth phase, namely β, is the most important with regard to hydraulic properties, and it is thermodynamically stable only under high pressure.

Methods

Results

Conclusion