XPS Study on the Stability and Transformation of Hydrate and Carbonate Phases within MgO Systems.

Vanessa Rheinheimer,Shaoqin Ruan,Jiawei Liu,Cise Unluer,Jisheng Pan,Paulo Monteiro

doi:10.3390/ma10010075

Abstract

MgO cements have great potential for carbon sequestration as they have the ability to carbonate and gain strength over time. The hydration of reactive MgO occurs at a similar rate as ordinary Portland cement (PC) and forms brucite (Mg(OH)2, magnesium hydroxide), which reacts with CO2 to form a range of hydrated magnesium carbonates (HMCs). However, the formation of HMCs within the MgO–CO2–H2O system depends on many factors, such as the temperature and CO2 concentration, among others, which play an important role in determining the rate and degree of carbonation, the type and stability of the produced HMCs and the associated strength development. It is critical to understand the stability and transformation pathway of HMCs, which are assessed here through the use of X-ray photoelectron spectroscopy (XPS). The effects of the CO2 concentration (in air or 10% CO2), exposure to high temperatures (up to 300 °C) and curing period (one or seven days) are reported. Observed changes in the binding energy (BE) indicate the formation of different components and the transformation of the hydrated carbonates from one form to another, which will influence the final performance of the carbonated blends.

Highlights

The high energy requirement and CO2 emissions associated with the production of Portland cement (PC), amounting to at least 5% of global anthropogenic emissions [1], has led to the development of alternative cementitious binding materials with lower environmental impact
magnesium oxide (MgO) can be produced from readily available minerals and waste brine obtained from desalination plants
Reactive MgO cements offer several advantages in terms of their technical and sustainable features when compared to traditional PC: in addition to the lower temperatures (i.e., 700 ◦ C vs. 1450 ◦ C for PC) required for their manufacturing, they have the ability to sequester significant quantities of CO2, resulting in carbon-neutral cements

Summary

Introduction

The high energy requirement and CO2 emissions associated with the production of Portland cement (PC), amounting to at least 5% of global anthropogenic emissions [1], has led to the development of alternative cementitious binding materials with lower environmental impact. One class of alternatives involves reactive magnesium oxide (MgO)-based binders, which have attracted significant attention in recent years [2]. Reactive MgO cements offer several advantages in terms of their technical and sustainable features when compared to traditional PC: in addition to the lower temperatures (i.e., 700 ◦ C vs 1450 ◦ C for PC) required for their manufacturing, they have the ability to sequester significant quantities of CO2 , resulting in carbon-neutral cements. The resulting construction materials can have high strengths, and they can be recycled, as their carbonation leads to the formation of carbonates from which MgO is predominantly obtained.

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