Effect of Calcination Temperature on Mechanical Properties of Magnesium Oxychloride Cement.

Jing Wen,Chenggong Chang,Lingyun An,Rui Lin,Xueying Xiao,Weixin Zheng,Jinmei Dong,Fengyun Yan

doi:10.3390/ma15020607

Abstract

In order to make full use of magnesium chloride resources, the development and utilisation of magnesium oxychloride cement have become an ecological and economic goal. Thus far, however, investigations into the effects on these cements of high temperatures are lacking. Herein, magnesium oxychloride cement was calcinated at various temperatures and the effects of calcination temperature on microstructure, phase composition, flexural strength, and compressive strength were studied by scanning electron microscopy, X-ray diffraction, and compression testing. The mechanical properties varied strongly with calcination temperature. Before calcination, magnesium oxychloride cement has a needle-like micromorphology and includes Mg(OH)2 gel and a trace amount of gel water as well as 5 Mg(OH)2·MgCl2·8H2O, which together provide its mechanical properties (flexural strength, 18.4 MPa; compressive strength, and 113.3 MPa). After calcination at 100 °C, the gel water is volatilised and the flexural strength is decreased by 57.07% but there is no significant change in the compressive strength. Calcination at 400 °C results in the magnesium oxychloride cement becoming fibrous and mainly consisting of Mg(OH)2 gel, which helps to maintain its high compressive strength (65.7 MPa). When the calcination temperature is 450 °C, the microstructure becomes powdery, the cement is mainly composed of MgO, and the flexural and compressive strengths are completely lost.

Highlights

The Qaidam Basin in Qinghai Province, China is extremely rich in magnesium chloride resources; the existence of 4.82 billion tons of this mineral have been verified in this area
After calcination at different temperatures, the colour of the magnesium oxychloride cement changes significantly, and the surface colour appears to be different for each temperature (Figure 1b–g)
While the flexural strength is almost completely lost, the compressive strength drops to 65.7 MPa; this is still 57.99% of the value measured for the room-temperature sample

Summary

Introduction

The Qaidam Basin in Qinghai Province, China is extremely rich in magnesium chloride resources; the existence of 4.82 billion tons of this mineral have been verified in this area. After years of potassium extraction, Qinghai has accumulated a large amount of bischofite, the main component of which is MgCl2·6H2O These magnesium chlorides have not been fully exploited and they have accumulated for a long time. Magnesium oxychloride cement (MOC), known as magnesium cement, is a slurry prepared by combining a specific mass ratio of light burned magnesia powder and magnesium chloride solution. After solidification, it has superior mechanical properties [3,4], and it is a ternary system, MgO–MgCl2–H2O, at room temperature. The chemical compositions of these two raw materials are listed in Tables 1 and 2

Preparation

Characterisation

Results and Discussion

Conclusions