Synthesis, Structure, and Thermal Stability of Magnesium Oxychloride 5Mg(OH)2∙MgCl2∙8H2O

Anna-Marie Lauermannová,Michal Lojka,Filip Antončík,Martina Záleská,Zbyšek Pavlík,Ondřej Jankovský,Adéla Jiříčková,David Sedmidubský,Milena Pavlíková

doi:10.3390/app10051683

Abstract

Today, low-energy and low-carbon footprint alternatives to Portland cement are searched because of huge CO2 emissions coming from Portland clinker calcination. Because of some superior properties of magnesium oxychloride cement (MOC) and the lower carbon footprint of its production, MOC became an intensively studied material with high application potential for the design and development of construction products. In this contribution, magnesium oxychloride with stoichiometry 5Mg(OH)2∙MgCl2∙8H2O (Phase 5) was prepared and characterized. The kinetics of formation and the phase composition of the material were determined using X-ray diffraction and consequent Rietveld analysis. The morphology was studied by scanning electron microscopy, and the chemical composition was determined by both energy-dispersive spectroscopy and X-ray fluorescence. Moreover, the simultaneous thermal analysis in combination with mass spectroscopy and Fourier-transform infrared spectroscopy was employed to study the thermal stability. Using mass spectroscopy, we were able to clarify the mechanism of water and hydrochloric acid release, which was not previously reported. The observed structural and chemical changes induced by exposure of studied samples to elevated temperatures were linked with the measured residual macro and micro parameters, such as bulk density, specific density, porosity, water absorption, compressive strength, and pore size distribution. The Phase 5 revealed a needle-like crystalline morphology which formed rapidly and was almost completed after 96 h, resulting in relatively high material strength. The four-day compressive strength of magnesium oxychloride cement was similar to the 28-day compressive strength of Portland cement. The thermal stability of Phase 5 was low as the observed disruptive thermal processes were completed at temperatures lower than 470 °C.

Highlights

Magnesium oxychloride cement, known as magnesium oxychloride cement (MOC) or Sorel cement, was discovered in 1867 by Stanislas Sorel [1] shortly after the discovery of the well-known Portland cement (PC)
The suspension was divided into two parts, where one was applied to the X-ray powder diffraction (XRD) holder for the analysis of kinetics of formation, and the other one was poured into a plastic beaker for other analyses
The first measurement showed that only MgO (ICDD 01-075-0447) was present in the sample because of its insolubility in water, whereas magnesium chloride was completely dissolved

Summary

Introduction

Known as MOC or Sorel cement, was discovered in 1867 by Stanislas Sorel [1] shortly after the discovery of the well-known Portland cement (PC). The specific density is significantly lower giving the material higher compressive and flexural strengths It has elevated fire resistance [2], good resistance to abrasions [3], and low thermal conductivity, and it does not get affected by oils, grease, and paints. A wide variety of applications for magnesium oxychloride cements were found, primarily as a flooring material for its elastic and acoustic properties, resistance to a charge accumulation, and decorative ivory-like appearance [10]. It was successfully used in fire protective systems [11], grinding wheels [12], decorative elements [13], wall insulation [14], ship decks, underground armament factories, and bunkers [15]

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Results

Conclusion