A comparative study of the influence of trivalent and tetravalent nano-sized oxides on the performance and microstructure of dolomite refractories
Abstract Contrary to the many benefits of dolomite refractories, their usage has been limited due to poor hydration resistance. For this reason, the aim of this research work is a comparative study of the influence of trivalent and tetravalent nano-sized oxides [iron (Fe 2 O 3 ), alumina (Al 2 O 3 ), zirconia (ZrO 2 ), and titania (TiO 2 )] on the performance and microstructure of dolomite refractories with an affirmation their hydration resistance improvement. After preparation and firing the specimen's, physical properties such as bulk density, apparent porosity, and hydration resistance tests were examined. Furthermore, XRD and SEM/EDX analysis were used to evaluate the ceramic phases and their microstructure, respectively. Results revealed that specimens with trivalent and tetravalent nano-sized oxides have improved densification and hydration resistance of the specimens through the liquid phase mechanism and solid state firing mechanism, respectively. Also, the specimens with tetravalent nano-sized oxides have higher hydration resistance than the specimens with trivalent nano-sized oxides. Generally, the hydration resistance improvement trend of specimens with various nano-sized oxides presence is Al 2 O 3 2 O 3 2 2 .
IMPROVING HYDRATION RESISTANCE OF MAGNESIA-DOLOMA REFRACTORIES BYIRON OXIDE ADDITION
There have been lots of studies to control the poor hydration resistance of dolomite refractories; one of the most effective solutions has been the addition of magnesia to doloma. Using a co-clinker of magnesia-doloma as a starting material would provide more homogeneity in the properties of the product and has been published recently. On the other hand, addition of iron oxide to doloma has been found to increase the hydration resistance. In this paper, the effect of iron oxide addition on hydration phase analysis and microstructure of two different magnesia- doloma samples, one with CaO content of 25 wt% and the other one with that of 35 wt% has been investigated. Ten samples were prepared by pressing followed by firing at 1750 oC for 3hrs. Results showed that the hydration resistance of the samples improved by decreasing the CaO content, because CaO is much more prone to hydration comparing to MgO. Besides, iron oxide addition lead to the formation of iron-containing phases which increased the hydration resistance of the samples both by capsulating the CaO and MgO grains and by promoting the liquid phase sintering.
Effect of Zircon on Sintering, Composition and Microstructure of Magnesia Powders
The effects of zircon on sintering, composition and microstructure of fused magnesia powders were studied by XRD, SEM and EDAX. With the increase of zircon content up to 6 wt%, the strength of sintered samples increased but the apparent porosity decreased. 6 wt% is an appropriate content of zircon to possess better properties of samples, and in this case the samples have a dense microstructure and lower content of glass phase. The presence of a liquid phase resulting from zircon addition is the main reason to improve sintering of magnesia powders.