Influence of magnesite burning modes on structure and properties of magnesia stone

V. N. Derevianko, A. Biegun, H. Hryshko, A. A. Maksimenko

Abstract


 

In Ukraine there is an unreasonably high use of Portland cement, it is even used in the cases, when one can use the binding materials, manufactured at lower temperatures with less energy consumption. Manufacture of magnesium binding materials requires low–grade heat, as the base component MgO is burnt at temperatures lower than 1000° С. Energy required for production of the magnesium binding material is 30…40 % of the one required for Portland cement production, and the natural resources of magnesium minerals are abundant and make up at least 8 % of the Earth’s crust. Therefore low energy consumption allows for extensive use of magnesium binding materials in air–dry operating conditions, and studies on influence of magnesite burning modes on a structure and properties of a magnesia stone are up–to date.

Adding of a fine–dispersed silica MgO–Н2O in the system will result in generation of magnesium silicate hydrates, which harden the magnesia stone, similarly to the behavior of calcium silicates at their hydration, while micro silica (silica fume) provides binding of free MgO to a complex oxychloride compound and increases the softening coefficient of hardened materials.

The purpose of our studies was determining the influence of the burning temperature and the burning period on the properties and the mineralogical composition of the caustic magnesite.

Moreover, we defined the methods for improving the properties of the caustic magnesite: waterproofing, reduced corrosivity, and thermal expansion coefficient.

The article presents the results of chemical mechanical studies on the magnesium binding material, burnt at temperatures of 800, 970 and 1150° С. 

Burning of the magnesite at t = 800° С within 3 hours resulted in formation of a structure without oversintering (i.e. ballast) with crystals sized 34.4 nm, which is susceptible to cracking, with the bulk density of the powder ρон = 960 kg/m3, which implies a poorly crystalline structure and unsuitability for construction purposes.

It was established, that binding properties are exhibited by the caustic magnesite produced at temperature of t = 970° С, the structure of which is formed by crystals sized from 38 to 43 nm. Increase of the burning temperature to 1150° С results in formation of a structure with oversintering of MgO grains from 7 % to 10,5 %. In this case, the sizes of the crystals were 47,9 to 48,1 nm.

In the micrographs, hydrated at 25°С, there is displayed gel–like sodium hydroxide, which films unreacted MgO crystals. The scanning microscope study showed that the mass of the hydration product is much aggregated. These aggregates are clearly visible at low magnifications.

The analysis of the electron microscopic studies on hydration of fine–dispersed periclase shows that the periclase crystals with no mechanical damages can reduce their sizes in aqueous environment within some period and not show evidence of surface hydration. This allows for creating a fast hardening solid structure of the magnesia stone due to simultaneous hydration of the burnt magnesite and interaction of magnesium hydroxide with fine ground quartz.

Adding of a fine–dispersed silica MgO–Н2O in the system results in generation of magnesium silicate hydrates, which harden the magnesia stone.


Keywords


magnesium binding material; caustic magnesite; burning temperature; silica; mineralogical composition; magnesium silicate hydrates; softening coefficient; electron–microscopic studies

References


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